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Mekong River Commission

MRC Secretariat’s Initial Assessment Report

On the Don Sahong Hydropower Project

January 2014

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Table of Contents  

Hydrology .......................................................................................................................................... 1 

 Sediment Transport and Morphology................................................................................................. 4 

 Water Quality and Aquatic Ecosystem Health .................................................................................... 6 

Dam Design and Operation ................................................................................................................ 6 

 Navigation ......................................................................................................................................... 6 

Social Issues ....................................................................................................................................... 6 

Table of Contents

Hydrology ........................................................................................................................ 1

Sediment Transport and Morpholgy................................................................................. 8

Fisheries ......................................................................................................................... 14

Water Quality and Aquatic Ecosystem Health ................................................................ 22

Dam Design and Operation ............................................................................................ 28

Navigation ...................................................................................................................... 48

Social Issues .................................................................................................................. 50

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Hydrology

Scope of the reviewThe reference for this section is the Don Sahong Hydropower Project (DSHPP) - Engineering Status Report (September 2011), and Environmental Impact Assessment Report (January

2013). The objectives of the review presented in this chapter are: ‐  Hydrological data collection and bathymetric surveys; ‐  Methodology in Hydrology and Hydraulics; ‐  Engineering approach in design of the Don Sahong Hydropower Project with

respect to hydrology; ‐  Flow duration and distribution in the various channels within the project area;‐  Flood analysis and future hydrology of the project area;‐  Likely changes in local flow regime.

Description of hydrological data collection and bathymetric surveyEngineering Status Report (ESR) and Environmental Impact Assessment Report (EIA) of the proposed Don Sahong Hydropower Project contain field and secondary hydrological data, design concept, methodology, analysis results in format of photos, maps, tables and figures. They are briefly mentioned, but not always fully described in detail.

Flow records of the Mekong at Pakse, about 150 km upstream of the project site, were collected and intensively used in the provided documents, however, the source of this secondary hydrological data was not clearly referenced. Some analysis regarding the quality of flow records at Pakse for the period of 1925-2009 was performed in the Feasibility Study Review and it was recognised that the records for the period of 1982-2009 was appropriate for analysis and modelling. Hence, this most recent 28-year series was adopted to represent current baseline conditions.

Three automatic water level recorders (15-min intervals) and three staff gauges (daily reading) were installed in the project area in 2010. Flows in the project area were measured at 16 locations during dry and wet season conditions between 2008 and 2011, using a boat-mounted Acoustic Doppler Current Profiler (Teledyne RDI 600kHz Rio Grande) for high flow and Price AA current meter for low and medium flows.

Bathymetric surveys in parts of the project area were conducted. Total Station combined with Depth Sounding were used to measure cross sections of the Hou Sahong channel (100 m spacing in the upper reach and 50 m spacing in the lower reach), Hou Sahong, northern channel, eastern channel, Hou Sadam, Hou Xang Peuk and Hou En. These data together with topographic data of the area were merged into a single Digital Elevation Model (DEM) which was used as a basis for computational modelling.

Methodology in Hydrology and HydraulicsExpected future hydrology for the flow of the Mekong at Pakse was developed based on results of the MRC Definite Future Scenario. A Flow Duration Curve (FDC) of the Mekong at Pakse was prepared for the period 1982-2009 (baseline conditions) and the expected future hydrology was derived from the FDC, using steady-state flow conditions and historical occurrence probabilities, which were not clearly presented. In addition, extreme flood peak flows at the project site were

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estimated by an extreme value analysis of observed annual flow peaks at Pakse over the period of 1925-2009. Annual maximum flow at Pakse were fitted with several statistical distributions, namely the Generalised Extreme Value (GEV), three parameter log-normal (LN3), log-Pearson Type III (LP3) and Extreme Value Type I (EV1 or Gumbel) distributions.

In preparation for the Feasibility Study Report (2009), two separate one-dimensional (1D) hydraulic models were built, calibrated and subsequently used to estimate water surface elevation, velocities and depths for a range of river flows under existing conditions and under various development scenarios. The two one-dimensional computational hydraulic models were: (1) headwater model including the northern channel, the inlet and the Hou Sahong channel; and (2) tailwater model including the downstream end of the Hou Sahong channel and the channel below the confluence of Hou Sahong and Hou Xang Peuk. In the ESR, two-dimensional (2D) hydraulic models are described and used to perform accurate prediction of the flow split at Hou Sahong inlet. The two 2D hydraulic models (Mike21) were: (1) the Hou Sahong headwater model including the inlet of Hou Sahong and headpond, together with the main channel upstream and downstream of the inlet, the Hou Xang Peuk inlet and the Hou Sadam inlet; and (2) the Hou Sahong – Hou Xang Peuk tailrace model including the outlet of Hou Sahong and the confluence of Hou Sahong and Hou Xang Peuk.

Findings of the MRC technical review

Flow duration and distributionStatistics of historical flow of the Mekong at Pakse for 1982-2009 were estimated as 9,663 m3/s for mean flow; 4,734 m3/s for median flow (corresponding to 50% of the time); 1,934 m3/s for mean flow in March-April; 25,809 m3/s for mean flow in August-September. It was reported that six water level observation stations were installed in the project area since 2010, but this data were not presented in the reports. The site visits for flow and water level measurements at some selected sites were sparsely conducted during the pre-feasibility (2006-2007) and feasibility studies (2008-2011). Therefore the flow distribution in the project area may not be well represented.

To understand the range of flow distribution at the project area, correlations were developed between the flows of the Mekong at Pakse and limited spatio-temporal measured flows at the project area. As Pakse is about 150 km from Hou Sahong, the time lag between the sites were investigated by incorporating rising and falling flows at different flow ranges at Pakse. Estimates of the time lag were analytically achieved using a kinematic wave model, however, these results were not presented. Alternatively, the time lag was presented by comparison between rising flow at Pakse and water level at Hou Sahong, ranged from 15 hours for low to 3.5 days for high flow conditions. This comparison has to be considered rather vague from a hydrology point of view.

The flow at Pakse with the above time lag was correlated with multiple flow measurements in various sites in the project area. Thus, the flow range, flow distribution and flow duration (1982-2009) for various sites were derived by regression analysis between the flow at Pakse and the interest sites. It was noted that the correlation between the flows at Pakse and site “CS02”, and between Pakse and “Thakho” were not very strong as the points were scattered around the proposed regression curves. This would lead to under- or over-estimate the flow at these two respective sites and error could propagate to estimation of flow distribution of other sites in the project area.

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Flood analysisExtreme peak flows at the project sites were estimated by an extreme value analysis of annual peak flows of the Mekong at Pakse for the period of 1925-2009. Annual maximum flow at Pakse were fitted with several statistical distributions, namely the Generalised Extreme Value (GEV), three parameter Log-normal (LN3), Log-Pearson Type III (LP3) and Extreme Value Type I (EV1 or Gumbel) distributions. Statistics of the peak flows at Pakse were presented: 37,378 m3/s as mean;

24,600 m3/s for the minimum; 57,800 m3/s for the maximum, and 5,674 m3/s as standard deviation. It was observed that the maximum annual peak flow (57,800 m3/s) was significantly higher than any other observed value. The EV1 distribution closely fitted this point, but overestimated more frequent peak flows. Moreover, the LN3 and LP3 distributions closely matched smaller peak flows, but predicted that the observed peak flow of 57,800 m³/s has 1000-year period. The fitted GEV was upper-bounded, closely matched most observed peak flows, but underestimated the observed peak flow of 57,000 m³/s. The EV1 distribution was adopted in the design of the DSHPP as it was closely match the flood estimate published in Annual Mekong Flood Report of MRC in 2006, and its values were conservative for the peak flow of 57,800 m³/s.

Future hydrologyAn expected future scenario of flows of the Mekong at Pakse was developed based on the reported results of MRC’s modelling of the Definite Future. The MRC’s Definite Future scenario included the effects of developments that are expected to occur by 2015, i.e. are existing, under construction or already committed. It includes the regulating effects of 25 hydropower projects in the tributaries of the Lower Mekong Basin, and six dams on the Lancang River (Upper Mekong), which are expected to be completed by 2015. Hence, development of the future hydrology of the project area was achieved by scaling (by time-of-year) the flow duration of the Mekong at Pakse for the period of 1982-2009.

Environmental flowsA minimum environmental flow of 800 m³/s over the Phapheng Falls was suggested for the DSHPPscheme. This flow was considered to be rather low as the minimum flow estimated in the ESR for1982-2009 was 1,224 m³/s. This would certainly put pressure on the ecosystem and biodiversity of the Phapheng Falls and it’s vicinity. In addition, the Si Phan Don area is a regional tourism attraction especially the beautiful Phapheng Falls, but there was not clear assessment on the impact of the DSHPP on this area.

Headwater model and tailrace modelThe inlet of Hou Sahong and the headpond, together with the main channel upstream and downstream of the inlet, the Hou Xang Peuk inlet, and the Hou Sadam inlet were modeled using a two-dimensional (2D) hydraulic model (Mike21). Mike21, which solves the depth-averaged dynamic wave equations using a finite difference numerical method and computes velocity and momentum in two-dimension plan, was required to accurately predict the flow split at the Hou Sahong inlet, a complex area where two channels (either side of Don Puay) converge immediately before the Hou Sahong branches off from the right bank. Tailrace model included the outlet of Hou Sahong and the combined Hou Sahong and Hou Xang Peuk channels.

Initial model runs were made with existing river bathymetry (i.e., without any excavation) to allow the model to be calibrated with site observations of water level and to reproduce natural conditions of the modelled sites. Bed roughness was the main parameter to calibrate the model. A single roughness value for all channels in the models was used, with the exception of the shallow Hou Sahong and Hou Xang Peuk inlets, where the flow was significantly shallower and the vegetation presented more of an obstruction to flow.

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Methodology of headwater and tailrace models were considered appropriate for the stated purposes. The results from the model were not extensively presented at various sites in the area.

Likely changes in local flow regimeThe ESR states that the DSHPP is a run-of-river scheme, including essentially no active storage of water, meaning there would not be significant change in total Mekong flow as a result of the scheme.

With the DSHPP in operation, local water levels around the Hou Sahong inlet will be drawn down, due to the increased flow in the Hou Sahong, and corresponding reduced flow in the Hou Xang Peuk and Hou Sadam. excavation works was proposed at these two channels, to ensure that flows in these channels remained similar to natural flows, and to improve conditions for fish passage. Favouritable conditions for fish passage should be considered, not only the amount of flow, but also water velocity, water temperature, pools, incremental steps, and natural condition of the river profile.

An engineering solution was introduced in the project site to benefit hydropower operation, by removing flow obstacle and deepening conveying channels. Water surface profile and velocity were modelled to evaluate optimal removal of the tip of Don Puay and excavation of Hou Sahong channel, and confluence of Hou Sahong and Hou Xang Peuk. Detailed results from the model was not accessible for further evaluation. These excavations may introduce change in flow velocity and direction, thus, intensify erosion and deposition, which leads to river morphology change. This engineering approach would require significant underwater blasting, which put very likely high risk to the surrounding environment during the construction.

To increase headwater levels at the inlet of the Hou Sahong, a possibility of an engineering option of submerged rock weir on the eastern channel (just downstream) of the inlet was explored. The submerged weir had a small effect in increasing water level. The degree of flow constriction and thus the upstream water level increase could be increased if the weir were constructed higher, though this would also increase flood levels upstream and the resultant higher velocities over the weir would increasingly disrupt surface navigation.

Upstream and downstream transient condition for full flow rejection (no flow though generating units), sluicing mode (rapidly reduced from 1,600 m3/s to 1,100 m3/s),controlled shut-down (from full discharge of 1,600 m3/s to 0) and controlled start-up (from 0 to full discharge of 1,600 m3/s) were modelled. Full flow rejection would cause a rapid rise in water level, for median flow of 4,734 m3/s (corresponding to 50% of the time) at headwater at Ban Thankho: no rise in first 30 min, rise to 0.6 m after 30 min to 1 hour, rise from 0.6 m to 1.0 m from 1 hour to 2 hours after flow rejection. This rapid rise could be reduced in sluicing mode: no rise in first 30 min, rise to 0.2 m after 30 min to 1 hour, rise from 0.2 m to 0.3 m from 1 hour to 2 hours. While there would be a relatively sudden water level drop of 0.35 m in the tailrace at downstream power station for sluicing mode. For the controlled shut-down and start-up events, the largest change in water level was modelled to be approximately 1.25 m as station discharge changes from 1,600 to 0 m³/s or vice versa. The rate of water level rise (on start-up) or water level fall (on shut-down) would depend upon ramp rates at which turbine discharge is altered. The actual turbine ramp rates should be studied and an appropriate warning system would also be implemented in the events of a flow rejection, controlled shut-down and start-up.

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The water level in the Hou Sahong channel turned headpond varied between 70 masl and 74 masl in an average year depending on the total flow in the Mekong River and the discharge through the turbines. The maximum daily water level rise remained similar to current conditions and may reach a maximum of up to 1.2 m/day during the onset of the wet season.

There was a significant change in discharge through the Hou Sahong. Currently, less than 2 % of the time, flow of 1,600 m3/s passed as natural flow, whereas in future almost 60 % of the time, this discharge passed through the channel. In the event of an extreme flood, starting at a 100 years flood, more than 1,600 m3/s was discharged through the channel reaching a maximum of 2,400 m3/s at a 1000-year flood.

Due to the concentration of discharge in the Hou Sahong channel, the other two eastern branches Hou Sadam and Phapheng Falls received decreased flows. The natural flows in the Hou Sadam ranged from less than 10 m³/s in the dry season to approximately 300 m³/s in the wet season. The flow in this channel would not change much in the future. On other hands, natural flows in the Phapheng Falls ranged from 1,224 m³/s to 5,550 m³/s. In future, these flows would be reduced essentially all year round and quasi fixed to a minimum flow (environmental flow) of 800 m³/s over about 40 % of the time (i.e. about 150 days per year). This leads to a large drawdown at Thakho ranging from 0.2m to 1.2m.

Large variation of drawdown was clearly observed and ranged from 0.3 m to 2.1 m at immediately upstream of Hou Sahong inlet, and from 0.0 m to 1.3 m at immediately downstream of Hou Sahong inlet, as the tip of Don Puay was excavated.

The daily water level changed due to the operation of the DSHPP were evaluated at 3 representative locations: upstream of Hou Sahong inlet, downstream of Hou Sahong inlet near Ban Hou Sadam, and eastern channel near Ban Thakho. The changes can be described as almost parallel shifts and a slight magnification of the amplitude. Currently the maximum daily water level changes were in the range of 0.35, 0.39 and 0.34 m and will be in future 0.40, 0.66 and 0.55 m, respectively, at these three selected characteristic sites.

The effect of increased flow just downstream of the DSHPP leaded to an increase of water level, which may reach up to 0.70 m during the dry season because of a proportionally higher flow component through the Hou Sahong. However, it was stated that further downstream the water level in the wide mainstream Mekong River would not be significantly affected.

Key review findings - Hydrology‐  Field measurements such as water level, flow records at the DSHPP site and its

vicinity and the used equipment appeared reasonable for the stated purposes. However, the number of taken measurements was considered limited. The source of the secondary flow records of the Mekong at Pakse used was not clearly referenced. Limited field records can lead to under or overestimate of the flow distribution in the project area.

‐  Method for selection of the period of baseline condition and expected future scenario were considered appropriate.

‐  Expected future hydrology at Pakse was developed based on MRC’s Denifite

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Future Scenario.‐  Methodology for hydrology and hydraulics were mentioned, but not clearly

presented. The results from the models were not extensively illustrated. ‐  The planned DSHPP is a run-of-river plant with minimal active storage, meaning

there would not be a significant change in total Mekong flow.

Gaps and uncertaintiesThe main gap within the analysis of the submitted documents is the issue that the flow regime for environmental analysis needs to consider more than just the flow rate. It is important to consider other changes such as water velocity and channel morphology.

The developer has surveyed a number of cross-sections and collected water level and flow data at the project sites. It would be useful to have access to such data for any future studies or detailed project assessment. The water level drawdown in the upstream section of the Hou Sahong inlet are based on modeling results as well as the evaluations of the rate of daily water level changes. The used hydraulic model would need to be explained in more detail (e.g. detailed modeling report and remarks on reliability and accuracy).

Flood analysis during construction was considered, but its management strategy was not proposed including the likelihood of cofferdams being overtopped and washed away creating potential impacts and pollution incident downstream.

The reasoning to choose an environmental flow of 800 m3/s was not clear and should be better explained.

Hydrological monitoring programmes during construction and operation in the project area is currently missing in the submitted documents and a respective revision is needed.

The actual turbine ramp rates should be studied and an appropriate warning system would also be implemented in the events of a flow rejection, controlled shut-down and start-up to minimise water level fluctuation.

Conclusions and recommendationsThe planned DSHPP is a run-of-river plant with minimal active storage. The maximum daily water level rise is given with a value of up to 1.2 m during the onset of the wet season. In the report it should be clearly stated that this fluctuation will not be used to practice hydro-peaking and hence the total instantaneous inflow to the system will always equal the total outflow.

The presented flow duration curve for Hou Sahong and Khone Phapheng are put in perspective to the overall discharge of the Mekong but should also address the local changes in the flow durations of the other channels.

From the reports it is not clear how the flow characteristic of the Hou Sadam and Hou Xang Peuk channels will change. This needs to be more detailed since these channels will be developed as a new alternative fish passage.

The hydrological monitoring program should be considered during the project construction and operation. Furthermore, the location of the network and observation method should be reviewed, revised and improved.

Due to the change of flow and sediment regime a proposal for a separate hydrologic and sediment monitoring scheme should be included for the downstream section of the Hou Xang

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Peuk and Hou Sahong (downstream of the DSHPP) which indicates the extent, the type and frequency of observations and the reporting periods.

Data on cross-section, local surveys and water level monitoring and flow observation before and during project construction, and during operation should be shared with MRCS for consolidation.

MRCS in collaboration with Lao PDR and its Line Agencies should develop a hydraulic model to investigate possible negative impact of DSHPP on the transboundary Mekong mainstream.

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Sediment Transport and MorphologyIn the Environmental Impact Assessment (EIA) Final Report (January 2013) possible problems related to sediment transport due to the Dong Sahong Hydro Power Plant (DSHPP) are addressed circumstantially with respect to water quality issues (3.1.6 and 3.1.7) and the extraction of construction materials (3.1.4). In Annex A of the EIA the MRC comments on the EIA report 2007 have been addressed and some answers can be found there (e.g. underwater blasting and increase of turbidity / suspended sediments). The report would be more readable if all these comments would have been incorporated in the current EIA. Within the Cumulative Impact Assessment (CIA) report the aspects of sediment transport and sedimentation of the reservoir are summarized as insignificant with respect to the Mekong River.

In the Environmental Management and Monitoring Plan (EMMP) sediments are treated as tertiary aspect and are not explicitly addressed. The Impact matrix (Table 1) refers only to the development of best management practices e.g. for soil erosion and sedimentation and refers to more detail in the appendices. However, the described measures in Appendix B also only state “Develop best management practice” without detailing the actually planned or foreseen measures and hence the statements are not really satisfactory.

The various topics related to sediments are only addressed in the Engineering Status Report (ESR) from September 2011.

Assessment of relevant issues with respect to sediment transport

The below assessment follows in principle the content of the ESR (Volume1) and discusses the topics under chapter 4.8 - Sediment Studies and 4.9 - Sediment Management. Missing aspect or aspects which need further clarification will be outlined below.

Mekong Sediment Data:

The used sediment data are in principle all from MRC and limited to suspended sediments only. The closest Mekong monitoring site is Pakse which is approximately 150 km upstream of the planned HPP. Suspended sediment data for 1985 to 2009 (with some gaps in the time series) were used and evaluated (Fig. 4-30). On the average 123 Mt/yr (with a range of fluctuation) of suspended sediment are transported in the Mekong River and it is assumed that this quantity will reduce with the further development of upstream hydropower on the mainstream and its tributaries.

Since no bed load data were available at any nearby monitoring site a literature search was conducted. An engineering approach was chosen to come up with reasonable bed load estimates. It had been derived that bed load assumes 15 % of the total transported sediments. A sensitivity analysis is presented with amounts from 5 % to 20 %.

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To determine the grain size distribution of the suspended sediments 3 samples from sandbars were taken and analyzed (Fig. 4-31). It is recognized in the ESR that these values will represent most likely the coarser fractions of the suspended sediments. Based on experiences on other rivers a range (envelope) of the expected suspended sediments grain size distribution was developed (Fig. 4-32). Apparently the sand samples were also petrographically analyzed.

MRCS Comments: The calculation of the suspended sediment load on the Mekong River follows established approaches and is based on the available literature. The derived values and time series fits the current knowledge but could be extended with more recent data (e.g. up to 2012)

It is difficult to fathom that for such a large project no actual suspended sediment samples were taken. Hence the estimation on the grain size distribution is based on estimates and most likely not representative samples from sand bars. More recent data with respect to the grain size distribution of the suspended sediments for Pakse are now available through the MRCS (e.g. up to 2012)

The bed load estimates follow a reasonable engineering approach, however as said above actual measurements should have been taken during the planning period to support the provided values.

It is not understandable why the petrographic analysis of the sand samples are not included in the report. It would be of great interest to notice the composition of the (settled) sediments. It is assumed that the quartz content may be rather high which will affect the turbines and other machinery parts. This information should be included in the report.

Sediment Load of Hou Sahong:

The estimated sediment loads for the time series 1982 to 2009 are based on derived sediment rating curves which were applied to the discharge time series at Pakse (Fig. 4-33). The resulting values were then correlated with the proper proportion of flow for the Hou Sahong branch to determine the amount of diverted sediment loads.

Based on the flow duration for the HPP on the average about 8 % of the suspended sediments carried in the Mekong River will pass through the Hou Sahong, which is approximately 9.3 Mt/yr with a variation form 5.6 to 13.1 Mt/yr (Fig. 4-34). Due to the increased flow into the Hou Sahong to ensure optimal hydro power production more suspended sediments are drawn into the branch and the reservoir. To account for this effect aduration curve for diverted sediment was derived to determine the increase of suspended sediment flux (Fig. 4-36). Since sediments are mostly transported during the 4 months of the wet season it is estimated that about 85 % of the diverted suspended sediment load will pass through the Hou Sahong during that time. Monthly values were also derived and show clearly the concentration during July to October (Fig. 4-38).

MRCS Comments: To estimate sediment loads by means of sediment rating curves is consistent with current practice and the results are conclusive.

The estimated sediment loads which are drawn into the Hou Sahong channel seem to be in the order of magnitude and are not underestimated. This is also valid for the estimated increase of the daily and monthly diverted sediment flux into the Hou Sahong.

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Headpond Sediment Deposition:

It is expected that due to the increase of the channel cross-section that suspended sediments will be deposited in the created headpond reservoir. On the average 9.3 Mt/yr will need to pass through this channel/reservoir but due to the reduction of the flow velocity some amounts will settle out. According to the design and calculations, sediments will be deposited in particular in a 1200 m long section immediately upstream of the HPP, where the flow velocity will drop below 0.5 m/s for most of the year.

It is assumed that the headpond will have a trapping efficiency slightly below 20 % and hence the annual average sediment load deposited is estimated to amount to 1.8 Mt/yr. Values for deposited materials were calculated for the time series 1982 to 2009 which vary significantly between 1.1 Mt/yr to 2.6 Mt/yr. It is assumed that of the amount of diverted sediments into the headpond a significant proportion will be sluiced naturally through the turbines and the balance will be deposited (Fig. 4-40). A sensitivity analysis was undertaken to test the range of possible annual sedimentation rates for the headpond (Table 4-30).

At the entrance to the Hou Sahong channel a raised sill will be constructed to divert heavier bedload material to avoid that these coarser fractions enter the headpond. Currently the sill height is given with 65 masl without any other detail why this is optimal.

With respect to the density of the expected deposited sediment in the headpond literature values were taken. It is assumed that the bulk density of the deposits is on the average 0.96 t/m3 which equates to an average annually deposited volume of about 1.9 Mm3.

Using these values and the reservoir storage curve (Fig. 4-42) it can be seen that the reservoir would be filled to the level of the intake sill (65 masl) in approximately 2 ½ years and to a level of 69 masl in over 10 years. Since the filling of the reservoir will result in a headloss for power generation a value beyond the 65 masl is not a good economical option. Hence it is concluded that sediment management is needed to operate the HPP efficiently

MRCS Comments: The results with respect to sediment deposition in the headpond are based on a detailed hydraulic model and are consistent and can be considered conservative. However, as said above the deposition depends on the actual grain size distribution of the suspended sediments.

The construction of a submerged sill at the entrance of the headrace to divert bed load material is common practice. However, since no samples of bed load were taken it is difficult to judge if this is also true for the proposed design. Also the river morphology of the mainstream at the point diversion (channel inlet) may have an effect on the transport and distribution of bed load material.

No details are presented on the calculation of headloss due to the increase in reservoir sedimentation. Although the principle is well understood the results should be included in the report.

Effects of Don Sahong HPP on Mekong Sediment Budget:

As described above it is assumed that approximately 85 % of the diverted suspended sediments are discharged through the turbines and that about 15 % will settle out in the headpond. For economical reasons a sediment deposit level of up to about 65 masl seems acceptable, beyond that level sediment flushing or dredging is required on an annual basis. The hydraulic residence time in the headpond is very short and given with only 2 to 4 hours during the wet season.

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Due to the increase of flow through the Hou Sahong (essentially a constant flow of 1600 m3/s throughout the year) immediately downstream of the HPP more sediments are introduced (see Table 4-31). Form the project it can be seen that the tailrace will be excavated over a significant length to minimize headloss.

MRCS Comments: It is not clear how the sediment management of the tailrace will be handled. Since a higher sediment load will pass through the Hou Sahong the river morphology in the downstream area will change. There is no mentioning of effects or possible measures with respect to the outlet and rejoining the Mekong branch.

Sediment management – Sediment Routing:

To reduce or even completely avoid the introduction of bed load into the headpond the construction of a submerged skimming wall as well as the lowering of a rock outcrop in the upstream vicinity of the Hou Sahong intake is proposed (Fig. 4-44). According to the current design a height of 65 masl is considered, however an elevation of up to 67 masl is also positively mentioned (Fig. 4-45). A natural rock levee (rock bar) currently exists at the inlet to Hou Sahong. This circumstance is attributed to the existence of finer sandbars in the Hou Sahong channel.

MRCS Comments: No details are presented on the calculation of the optimal submerged skimming wall height. The principle of skimming walls is well understood but the results of the calculations/models should be included in the report. Also a comparison with the existing natural rock levee (height, length) should be considered.

The lowering of the rock outcrop in the upstream vicinity of the Hou Sahong intake, the construction of a submerged skimming wall as well as the changed flow regime (1600 m3/s throughout the year) will have some effect on the river morphology of the main branch leading to the Khone Phapheng. An evaluation of the possible effects should be included in the report.

Sediment management – Sediment Flushing:

The idea of sediment flushing is to mobilize by re-suspending settled sediments due to increase in flow velocity. At the DSHPP it is proposed to increase the flow through the turbines above the normal operation (1600 m3/s). It is suggested that increasing the combined turbine discharge by 100 to 300 m3/s is sufficient to draw down the water level in the headpond and thereby increasing the velocity to levels where settled sediments will be flushed out through the turbines (Fig. 4-46 and 4-47).

It is argued that flushing during the wet season is straightforward and can be achieved by simply increasing the turbine capacity to approximately 110 %. During the dry period periodic flushing is also suggested and may be restricted to night times. Flushing will temporarily reduce the flow to the Khone Phapheng Falls and hence may adversely affect tourism.

Monitoring of the success of the flushing operations are mentioned by means of regular bathymetric survey and headloss measurements, but no values or intervals are mentioned what is an acceptable range of removal or headloss.

If sediment flushing is found not to be effective a mechanical dredging solution is thought.

Another common flushing technique is the provision of low level outlets which will be opened regularly to increase the flow velocity for a short time period. According the report this solution is not feasible due to the additional requirements for length (width) for the outlets. The powerhouse is already relatively narrow and the space requirement for the bulb turbines

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is considerable. Since the turbines will need already for normal operation erosion protection to accommodate the continuous transport of suspended sediment the additional cost for low level outlets is considered uneconomical.

Since the turbines constitute the lowest point along the flow path from upstream to downstream it is considered not necessary to include low level outlets for dewatering the reservoir or in case of any emergency.

MRCS Comments: It is not clear from the description how the additional discharge of up to300 m3/s will be possible through the turbines.

It is mentioned that during flushing operations the downstream suspended sediment concentration should be monitored but no design of the monitoring programme as well as limits on concentration is found.

No criteria on the effectiveness of flushing are mentioned and under what conditions mechanical dredging will be considered.

The elimination of any emergency or low level outlet should be argued more clearly and conclusive.

Sediment management – Sediment Dredging:

As stated above, if sediment management by flushing through the turbines is not successful the proposed alternative methods are either “siphon dredging” (Fig. 4-48) or “pumped dredging”. The consideration for mechanical dredging is not very detailed and without any clear choice for any dredging system. To provide for O&M for the coming years mechanical dredging is included in the economic evaluation.

MRCS Comments: Since mechanical dredging is considered a feasible solution, it would be worth to evaluate the available systems in more detail and chose the most effective.

Other aspects not explicitly addressed in the report:

Monitoring:

In the Environmental Management and Monitoring Plan (EMMP) sediments are not really included. We are aware that the HPP operator will monitor the sedimentation rate of the reservoir to maximize power production. However, a detailed plan on monitoring the movement of sediment through the system, in particular during flushing operation is expected (map of observation points, frequency of sampling, frequency of bathymetric surveys, setting of benchmarks, etc.). Also it is expected that the results of these monitoring efforts will be documented and made available to the downstream neighbors on an annual basis.

Floating Wood and Debris:

Particularly during the onset of the annual flood large amounts of floating wood and other debris is carried down the river. In the report no explicit mentioning of the expected quantities was found or how the debris will be used or deposited. Due to the permanently increased flow into the Hou Sahong it can be expected that also a significant amount of floating debris will be drawn into the channel during the wet season.

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The amount of debris will most likely reduce with the development of other major HPP upstream and on the tributaries.

Decommissioning and use of Reservoir Sediments:

During decommissioning large amounts of sediments, gravel, rock debris and construction materials (concrete) will need to be excavated and deposited. The deposition or use of the reservoir sediments at the stage of decommissioning needs to be addressed.

Recommendations for the next steps

As outlined above the main points which need clarification at this point are:

a) Detailed estimation of sediment transport (suspended and bed load) based on measured data;

b) Evaluation of the suspended sediment grain size distribution based on actually measured data;

c) Detailed planning of extraction of material from the river (from sediment extraction to excavation of bed rock) and evaluation of the environmental impact;

d) Selection and detailing of the chosen reservoir sediment flushing approach;

e) Development of sediment flushing operation rules;

f) Evaluation of the impacts of the chosen flushing approach;

g) Predictions of the river morphological changes at the inlet (widening of the inflow channel) and the dredged tailrace downstream of the HPP;

h) Concept for monitoring sediment transport (suspended and bed load), reservoir sedimentation and the change in river morphology;

i) Measures to extract floating wood and debris with a concept of disposal;

j) The deposition or use of the reservoir sediments at the stage of decommissioning needs to be addressed.

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Fisheries

1.     INTRODUCTION  

This document presents an initial review of the Fisheries Annexes C and D to the Environmental Impact Assessment of the Don Sahong Hydropower Project 2013 (EIA). The EIA aims at providing more detailed information regarding the project’s likely impacts on the fisheries of the Mekong River, and what actions the project would take to mitigate those impacts. To this end, the EIA provides a Fisheries Monitoring and Action Plan (FishMAP) that proposes a package of mitigation measures. The results of FishMAP generated during 2010- 2012 and presented in the EIA are considered a “living document” aimed at “improving the models and mitigation efforts as understanding of how the system works evolves”.

Hou Sahong channel is critically important for basin-wide fish migration and, thus, the long- term sustainability of migratory fish species in the Lower Mekong Basin. There is a direct interdependency between fish productivity in the Great Lake Tonle Sap and 3-S Rivers of Cambodia and fish migration through Khone Falls area, most prominently through Hou Sahong channel. Also some commercially important aquatic species (including Pa Suay Hang Leung Pangasius kremfi, the anadromous species like Salmon) migrate from the Vietnamese Delta through the Khone Falls area up into Lao PDR. While the Khone Falls has a series of water channels that allow for fish migrations at certain periods of the year, depending mainly on the water level, it is only the Hou Sahong channel, which allows for year-round migration and is large enough to support migration of big groups of large fish, including the Mekong giant catfish Pangasianodon gigas, and small fish, including the mud carps Cirrhinus spp., all year round.

Considering the large number of assumptions and lack of resolution in data and analysis presented in the EIA report, the EIA is still at a preliminary stage as high risks remain due to the impact mitigation measures suggested in the EIA are unproven and untested in a fisheries environment such as the Mekong. They might work, and they might not, but the stakes are very high, and if they don't work, everyone in the basin will pay.

2. ISSUES that REQUIRE FURTHER CONSIDERATION2.1 Monitoring Methods Fisheries monitoring methods are not clearly described and explained – rather

folkloristic and not scientifically robust. It seems that the monitoring focused on traps (which are highly selective gear) albeit the fact that gillnet was mentioned to have widely been used. No dimensions of gears are reported; no detailed analysis of fish species composition is conducted and reported except for aggregated data on some selected fishers’ daily catch.

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The household fish catch monitoring methods does not consider any household- specific characteristics such as gender composition, age structure, decision-making processes, income generating and livelihoods portfolios, fishing dependency etc. and, thus, data are little representative and of little use as baselines - “household catches” is too imprecise.

The monitoring is only conducted at a limited number of local sites; not put into perspective of trans-boundary context.

Though monitoring drift of fish larvae and juveniles is mentioned, neither the methods used nor the results are reported.

o For larvae monitoring, MRC FP has been supporting long-term fish larvae monitoring only in Cambodia and Viet Nam. Regional Ichthyoplankton Study (RIS pilot study) was implemented in 2009 in the four member countries with limited sample sizes taken in each country as it aimed for the regional coverage.

Standard methods for monitoring capture fisheries in the Mekong basin are required to generate reliable baselines and strengthen robustness of scientific insights.

2.2 Impact Analysis and Mitigation Measures

DSHPP EIA : EIA responds to the recommendations by MRC on the 2008 initial impact analysis and

mitigation measures (EIA 2013 Annex C: 10-11).

MRCS Comments: Annex C offers little concrete action, at best; it lacks sufficient detail with adequate

resolution and proper explanations – most of the proposed mitigation measures are unproven and not tested in fisheries environments similar to the Mekong and, thus, their effectiveness is only assumed.

The proposed mitigation measures remain highly experimental and risk-prone.

2.3 Fish migration

DSHPP EIA: Fish migration and implications for fisheries are described in general terms in the

immediate vicinity, i.e. the Hou Sahong channel, of the project site. Threats such as alteration of natural flow regime, altered sediment loads, and loss of

critical habitat to migratory fishes are acknowledged, however, it is stated that the project will not increase these threats and, thus, no mitigation or management action is required.

MRCS Comments: Trans-boundary fisheries impacts up-stream in Lao PDR and down-stream in

Cambodia and Viet Nam are not assessed (the same applies for social impacts and economic impacts);

Impacts from altered flow regime on fish migration during and after dam construction need to be assessed; this need to include impacts on river dolphin population in the Lao-Cambodia border area that may be impacted by blasting and dredging during the construction phase as well as 17-fold higher discharge of water during the operation phase in the dry season (Figure 8 in EIA Annex C).

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2.4 Flow regime and fish migration

DSHPP EIA: Threats such as alteration of natural flow regime, altered sediment loads, and loss of

critical habitats to migratory fishes are acknowledged but it is stated that the project will not increase these threats and, thus, no mitigation or management action is required.

Hou Sadam and Hou Xangpueak channels can absorb fish migrations disabled by the dam at Hou Sahong.

MRCS Comments: Hou Sahong is a one of the most prominent migration corridors in the Mekong Basin

as it is the only channel that allows for fish migration throughout the whole year and as such it is a key habitat to maintain connectivity between important lifecycle habitats of many migratory fish species;

EIA report does not provide information on average monthly water flows of pre-dam and post-dam situation of Hou Sadam and Hou Xang Pueak and other channels that are supposed to absorb all the fish migration movements including those disabled by Hou Sahong dam.

Reduction of fish up-stream migration would adversely affect brood stock populations downstream. The severity of the impacts will not be known until after DSHPP is built, unless exhaustive research, testing of mitigation measures and adequate (well calibrated) modelling is conducted.

Hydrological changes downstream of DSHPP most likely have impacts on “hydrological triggers” that affect fish migrations and may cause interruption of lifecycle completion of certain fish; this aspect remains unaddressed in the EIA;

It is an unproven and untested assumption that Hou Sadam and Hou Xangpueak can absorb all fish migrations from Hou Sahong; the different physiographic conditions of these channels and strongly altered water flow conditions, after dam construction, in these two channels are not put into context of migratory requirements of the actual migration guilds, let alone of single fish species. According to the PDG (2009), “… of particular importance are size at time of migration; swimming capabilities (prolonged and burst swimming speeds); depth and horizontal positioning in the river channel downstream or the impoundment upstream of the dam wall; diurnal movements; and cover, substrate and light preferences…..”;

Hou Sadam and Hou Xangpueak channels will experience a much reduced dry season water flow, which will contrast to the extremely increased water flow (6 to 17 higher) in dry season through the Hou Sahong dam – with potentially high impact on the attraction flow that could trigger fish migration through the proposed alternative migration routes. Fish will be attracted to the flow from the turbines and will approach the flow from surface, mid-water, along the river bottom, and along the thalweg; hence, fishway entrances need to accommodate these behaviours. No attempt has been made to prove the acceptance of other channels for alternative fish migration once migration through Hou Sahong would be disabled;

Adequate flows must be directed through the fishways to ensure they function effectively in both the high and low flow seasons, and at all times are sufficient to ensure optimal effectiveness for fish passage targets (PDG,

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2009). “To provide sufficient attraction for migrating fish, effective upstream fish passage on the mainstream Mekong River would need to pass 10% (100 m3/s) of low flows and 1% (230 m3/s) of the maximum design flow” (Xayaburi Prior Consultation Review Report, MRC 2011).

Von Raben blade strike model (of the fish-friendly turbine solution proposed) has never been proved in Mekong River. Calculations are based on experience outside Mekong with much less biodiversity.

Numeric and physical models of the dam and adjacent river are necessary to accurately predict flow patterns, and hence dam and fish passage design (PDG, 2009).

“Fishways should be fully operational from minimum low season flow of up to the 1:20 year flood level” (PDG, 2009).

Table 1: Type of fish migrations and alteration of Mekong flow through Hou Sahong

Season / Month

Dec

em

Janu

ar

Febr

ua

Mar

ch

Apr

il

May

June

July

Aug

ust

Sep

tem

Oct

obe

Nov

em

Dec

em

Janu

ar

% of normal pre- construction Mekong flow through Hou Sahong channel

6 4 4 3 3 5 6 5 5 5 5 6 6 6

% of Mekong mainstream flow diverted through Hou Sahong dam

37

45

49

50

49

40

21

11 7 7 1

223

37

45

Type of fish migration Medium-sized cyprinid carps

Small cyprinid fish (minnows)

Large carps, nearly exclusively through Hou Sahong

Catfishes (Pangasiusmacronema fromCambodia to Laos through Hou Sahong)

Catfishes (Pangasius krempfi from Vietnamese Delta up into Laos through Hou Sahong) P. krempfirepresents 5% of lee trap fishery. P. conchophilus represents 40% of lee trap catch

Large fish (MGC)Endangered Probarbusjullieni

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Sources: EIA DSHPP 2013, Annex C; Baird 2011

Table 1 shows that 37% to 50% of the Mekong water flow passes through Hou Sahong channel after potential dam construction during the six month dry season, representing a 6 to 17-fold increase of water discharge as compared to normal (without dam) situation. As a consequence, the water discharge through Hou Phapeng, Hou Sadam and Hou Xangpueak and other minor channels is significantly reduced during dry season. These hydrological changes potentially severely impair and impact on the capacity of fish to migrate up-stream, especially medium-sized cyprinid carps and small cyprinid fishes (minnows) representing important trans-boundary fisheries resources may be impacted.

2.5 Up-stream fish migrationDSHPP EIA: Fish caught in Cambodia first, Tonle Sap is blocked all the time now … (Page8- Table

1 of the Annex C) It is proposed to reduce fishing efforts immediately below dam as well as further

downstream. Xang Phueak and Sadam channels will “imitate the conditions the same as previously

existed in the Hou Sahong Channel” to allow up-stream migration. Channel modification in Hou Wai and Xang Phueak channels to improve fish migration

pathways has been trialled

MRCS Comments: This statement (on page 8-Table 1) is a misleading as the migration route to and from

Tonle Sap is open all year round; Dai fishery operates between late Oct and Feb or early March – these fishing

operations do not completely block off the river but are limited to specified anchoring positions; sufficient space is always available for navigation during this period. More than 100 fish species are, including small mud carps up to Mekong giant catfish, recorded to migrate upstream to access vital dry season and spawning habitats in the Mekong River of Kratie and Stung Treng provinces in Cambodia and Champasack province in Lao PDR to sustain fisheries production;

All fishing lots in Cambodia including in Tonle Sap flood plain lots have been cancelled;

Fish breeders are believed to freely migrate upstream the Mekong. In recent years evidence suggests that increased downstream drift of fish larvae and juveniles have been observed (MRC FP larvae drift monitoring programmes).

Up-stream migration will be blocked by dam. Increased concentration of migrating fish is expected downstream, including in the border area with Cambodia. How this will be managed remains unaddressed.

The attraction flow from Hou Sahong will be multi-fold higher (up to 17 times) in dry season than under natural conditions (before construction) – how can fish migrate through alternative channels given that their water flow are significantly reduced as compared to national flow conditions and will have a much inferior attraction flow as a consequence of the potential Hou Sahong dam.

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Channel modification in Hou Wai and Xang Phueak channels to improve fish migration pathways have been trialled. However, preliminary results based on anecdotal records of fishers do not give evidence that the modifications in fact can absorb those fish migrations blocked by the Hou Sahong dam, especially those in the dry season. This requires further detailed study proving the effectiveness of the modified channels for year round fish migration prior to dam construction.

2.6 Downstream migrationDSHPP EIA: Threat is acknowledged; “Trap- and transport systems, alternative fishways and turbine bypass screening and

fish-friendly turbines” are proposed including further studies on their functionality and efficiency;

Further studies proposed “which can then be imputed into the process for determining further development of water infrastructure related project in the wider basin”;

Downstream mortality (Page12 in Annex C): DSHPP proposes a testing programme to be undertaken by the turbine supplier to provide more definitive information about expected fish survival through actual turbine type to be installed.

MRCS Comments: No proven solution are provided; the proposed mitigation measures do not have any

previous track record of success in the Mekong, the solutions are not further detailed and, thus, remain highly experimental and extremely risk-prone as.

All the measures suggested in the EIA are unproven and untested. They might work, and they might not, but the stakes are very high, and if they don't work, everyone in the basin will pay;

Impacts from river blasting, dredging and other earth movements and construction activities on river dolphin population in the immediate vicinity of the project site are not addressed; neither is the impact of increased discharge from dam operation.

It would be better to do these studies at a dam with less impact on fish migration (e.g. upstream from Xayaburi).

Recommendation: this testing programme should be conducted prior to dam construction to prove that the turbine is practically effective as theoretically stated.

2.7 Fish production and valueDSHPP EIA: Method to measure fish production is “household fish catch”; “Anecdotal evidence of household fish catch yield” and trends is provided; An average of 2,871 USD/household is recorded for 2009;

MRCS Comments: The overall economic value of fish migrating through the three main channels Hou

Sahong, Hou Sadam and Hou Xang Pheuak needs to be assessed with particular emphasis on trans-boundary species (see Table 1);

o giant freshwater shrimp (Macrobrachium resenbergi), Pangasius krempfi andothers migrate up-river from Mekong Delta into Laos;

o Small minnow or mud carps represents more than 21% of whole inland fisheries catch in Cambodia; this species depends on long distance migrations

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from Tonle Sap in Cambodia and would potentially be highly affected by Hou Sahong dam.

o Labeo erythropterus, Bangana behri and others migrating to and from the 3-S rivers basin;

o The endangered Mekong giant catfish and Probarbus jullieni, Pangasius concophilus and others migrating from Tonle Sap.

Impacts for Tonle Sap fisheries in terms of fish species, yield and value needs to be assessed and subsequent economic and social impacts including on food security and nutrition security; this also applies for impacts along the Mekong river and its tributaries in Lao PDR;

Not enough is known about the migratory requirements of the various fish species to predict the results of mitigation measures – knowledge gap to be filled;

Fish loss up-stream of DSHPP in Lao PDR is not assessed; Accumulative and synergistic impacts in aquatic communities, e.g. in biodiversity not

addressed. o Cumulative and synergistic impacts on food web not assessed; including

focus on how perturbations at lower trophic levels ripple up through the food web to affect valuable prey and predator fish dynamics;

o Loss of migratory species would lead to negative changes in all aquatic communities, both up-stream and down-stream. However, cumulative and synergistic impacts will not be known until the dam is built – unless comprehensive monitoring, modelling and calibration of models precede and informs about effective mitigation measures of the project;

Footprint on food security and nutrition is not assessed; Trans-boundary impacts including Lao PDR up-stream of DSHPP, Cambodia and Viet

Nam not assessed – in terms of income generation, livelihoods, food security and nutrition security as well as replacement costs from loss of fisheries;

Value of income from eco-tourism and dependence of eco-tourism on landscape panorama and existence of river dolphins not assessed.

2.8 Excavation and water quality:

DSHPP EIA: There was concern on the various forms of excavation including underwater blasting.

DSHPP responded that ‘no underwater blasting at the downstream end will be permitted (Page10 of Annex C)’.

MRCS Comment: This is inconsistent with EIA report 2013, points out that ‘To improve flow through the

Hou Sahong the river bed will be excavated to an average of 3 m and 1.5 m at the upstream and downstream ends of the channel, respectively’ (PageVIII in EIA report).

Impacts of blasting and dredging during construction on river dolphin population in immediate vicinity of project site in cross-border area with Cambodia;

3. SUMMARY of CONCLUSIONS and RECOMMENDATIONS3.1 The EIA report makes an attempt to assess the negative impacts of the Don

Sahong hydropower construction and proposes a series of mitigation measures to respond to identified threats; some of the issues identified and mitigation measures proposed do point into the right direction

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proposing additional studies to increase the knowledge base. At this stage, the present EIA would not allow for scientifically sound decision-making about the design of the dam construction as the data/information and analysis provided is still incomplete. To improve the proposed mitigation measures clear identification and scientifically sound assessment of the local, trans-boundary and cumulative impacts are required.

3.2 Scientifically robust methods for capture fisheries monitoring are required;

3.3 Comprehensive trans-boundary fish and fisheries impact assessment, including fish species diversity, fish production and their economic, ecological and welfare values, food security and nutrition security, and ecological impacts in terms of food web alterations;

3.4 Mitigation measures need to be proven;

3.5 Information gaps as identified in the above Sections need to be filled allowing for well-calibrated modelling and scientifically sound decision making including concerning project design, operation and impact monitoring.

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Water Quality and Aquatic Ecosystem Health

Criteria for review: Completeness, consistency and adequacy of information provided. In particular, potential transboundary impacts are considered. Adherence to MRC PDG, where relevant.

Scoping of potential impacts

The scoping of potential environmental impacts (EIA report, Figure 2-8) seems questionable, e.g. impacts on species and populations due to presence of the dam are assessed as “potential minor negative impact”, although one of the important impacts listed in the Executive Summary (p. viii) is on fish, and p. 5-18 says “The potential impacts of the proposed DSHPP on the fisheries are by far the most important aspects of the Project”. Furthermore, there is no methodology (impact criteria) described for the scoping process.

Environmental issues of potential relevance for this review

It is assessed that some of the relevant issues related to environment for the review of the EIA of the DSHPP would be the following:

1. Impacts on environmental flows? 2. Water quality during construction? 3. Water quality in the head pond/impoundment? 4. Water quality during flushing? 5. Water quality during decommission? 6. Impacts on sediment balance? 7. Impacts on nutrient balance? 8. Impacts on fish migration, both upstream and downstream passage? 9. Impacts on habitat continuity (fragmentation)? 10. Impacts on wildlife? 11. Impacts on tourism? 12. Impacts on health and livelihoods?

1 A general comment to the EIA report: In Annex A it seems that all MRC comments to the 2007 EIA report have been addressed. However, it is very difficult to check because there are no references to the relevant sections in the updated EIA report. 

 

Water Quality and Aquatic Ecosystem Health

Criteria for review: Completeness, consistency and adequacy of information provided. In particular, potential transboundary impacts are considered. Adherence to MRC PDG, where relevant.

Scoping of potential impacts

The scoping of potential environmental impacts (EIA report, Figure 2-8) seems questionable, e.g. impacts on species and populations due to presence of the dam are assessed as “potential minor negative impact”, although one of the important impacts listed in the Executive Summary (p. viii) is on fish, and p. 5-18 says “The potential impacts of the proposed DSHPP on the fisheries are by far the most important aspects of the Project”. Furthermore, there is no methodology (impact criteria) described for the scoping process.

Environmental issues of potential relevance for this review

It is assessed that some of the relevant issues related to environment for the review of the EIA of the DSHPP would be the following:

1. Impacts on environmental flows? 2. Water quality during construction? 3. Water quality in the head pond/impoundment? 4. Water quality during flushing? 5. Water quality during decommission? 6. Impacts on sediment balance? 7. Impacts on nutrient balance? 8. Impacts on fish migration, both upstream and downstream passage? 9. Impacts on habitat continuity (fragmentation)? 10. Impacts on wildlife? 11. Impacts on tourism? 12. Impacts on health and livelihoods?

1 A general comment to the EIA report: In Annex A it seems that all MRC comments to the 2007 EIA report have been addressed. However, it is very difficult to check because there are no references to the relevant sections in the updated EIA report. 

23

 

1. Impacts on environmental flows (EIA report p. 5-28 – 5-33)Environmental flows (EF) over Khone Phapheng is chosen as 800 m3/s – the lowest flow recorded in the extreme dry season of 2010. This will not be an exceptional situation with the project but rather the norm: In at least 40% of the time the flow over Khone Phapheng will be confined to 800 m3/s (Table 5-8). What will this mean for tourism at Khone Falls? Perhaps a higher EF should be considered? For example, the natural 99% exceedance flow at Khone Phapheng is 1,410 m3/s (Tab. 5-7). It would be prudent to analyse the impact on the project economy of selecting this (or another) flow as the minimum (ref. comment #58 in MRC’s EIA review of 2007). There is no analysis of this and no photos of less than 1,450 m3/s (p. 3-7) – however, this level visually seems OK for tourism purposes. It would also have been interesting to see an assessment of the impact of climate change on the EF over Khone Falls.

No EF impacts of the DSHPP are anticipated elsewhere than the Khone Phapheng branch as the HP flow is diverted solely at the expense of this branch (Table 5-8).

2. Water quality during constructionWater quality impacts during construction are addressed and mitigation plans anticipated for collection of waste and waste water. However, potential impacts on water quality from excavation of bedrock for channel modification purposes are not analysed in detail. The EIA report (p. 5-11) refers to approx. 1 million cubic meter of sediment/rock that needs to be disposed of. Impacts from loss of sediments during excavation or from deposition have not been addressed (other than measures for protection of dolphins from sediments, see below) and deposit site has not yet been decided. Therefore, the conclusion that “impacts from cofferdam construction will not be significant” seems premature. Just for comparison, the 1 million cubic meter of excavated sediment/rock corresponds to the amount of sediment transported during 3 days by the Mekong mainstream at Pakse (assuming 123 Mt/yr (ESR p. 96) and bulk density of 1 t/m3 (ESR p. 106)).

3. Water quality in the head pond/impoundment (EIA report 5.4.4)Water quality impacts during operation are not addressed in the EIA. Given the short water residence time (max. 4 hrs, EIA report p. 5-22), it seems reasonable to expect no significant water quality impacts from the impoundment. Sedimentation of coarse material may occur in a zone of approx. 1 km in front of the impoundment (ESR Fig. 4-39). The impact of this reduction has not been addressed but is expected to be minimal.

4. Water quality during flushing (ESR p. 111-5)The EIA report only briefly mentions flushing (p. 5-23) but the ESR (p. 111-5) mentions two options for sediment management: periodic flushing and mechanical removal. Flushing would have the greatest impact on water quality and the ESR suggests to apply this methodology and monitor the results. Impacts are not addressed further by the EIA. However, it is appropriate and in line with the MRC Preliminary Design Guidance that the EIA report suggests flushing sediment during high flow periods in order to mimic the natural sediment dynamics. Approx. 2 million cu m of sediment needs to be removed from the head

24

 

pond every year (ESR p. 114), corresponding to less than 2% of the annual total sediment transport in the Mekong mainstream at Pakse. Potential short-term water quality impacts, e.g. on dolphins or other aquatic organisms living immediately downstream of the dam, could potentially be expected during flushing periods. The EIA report (p. 5-23) argues without further documentation that the hydraulic conditions of the area are such that the discharge from the DSHPP will bypass the deep pool dolphin habitat, especially at low water levels. This should preferably be investigated using 2-D or 3-D hydraulic models of the near- field area. Also other aquatic organisms could potentially be impacted by short-term high concentrations of sediment during flushing which has not been analysed in the EIA report.

5. Water quality during decommissionTo the extent blasting to remove dam and concrete infrastructures will take place during the decommissioning phase (p. 5-17), it may affect dolphins and other aquatic animals. The details of blasting (if and how) are not highlighted in the EIA report. Neither are the consequences for the water quality (short-term increases in sediment concentrations) from blasting the concrete structures. Given the size of the structures and the magnitude of the natural sediment transport in the Mekong the impact may be small – but it has not been assessed.

6. Impacts on sediment balance (Engineering Status Report p. 95-115)This issue seems not to be addressed by the EIA. However, the ESR addresses it in Section 4.8-4.9. According to this, long term impacts on sediment balance are not possible. Without any sediment management, up to 3 Mt/yr in the first years and up to 10 Mt in total could theoretically be retained in the head pond (ESR p. 107-108). Natural sediment load in the Mekong is estimated at 123 Mt/yr. With sediment management scheme implemented (for which there is a strong economic incentive) there will be no accumulation of sediment in the head pond other than an initial approx. 2 Mt. [It is expected that IKMP will provide a more in-depth analysis of the sediment transport issue]

7. Impact on nutrient balanceThis issue has not been addressed – but could easily have been. Nutrients are transported either as soluble (with the water) or as suspended (with the sediment). Since the issue is not a local but a regional one (nutrient transport from upstream reaches to downstream Ton Le Sap and delta areas), and given the fact that no regional-scale flow or sediment changes occur with the DSHPP it is to be expected that no impacts on the nutrient balance will occur from the project.

8. Impacts on fish migration (upstream and downstream)Fish migration appears to be by far the most important environmental issue related to the DSHPP. The EIA report (p. 3-15) argues that household catch data from the project shows that upstream fish migration also occurs in other channels than Hou Sahong. Irrespective of this, it is widely agreed that Hou Sahong is by far the most important channel for fish migrating up the Mekong river. Therefore, the introduction of an insurmountable barrier like the proposed dam is a potentially serious environmental impact. Although the suggested

25

 

mitigation (deepening of the Hou Xang Pheuak) appears conceptually sound there is still no certainty that the proposed modifications to the channel will actually work in terms of providing a full substitution for the lost fish passage. It has not been tested before; it is a large-scale experiment and this seems to be a key risk of the project. The deepening of alternative channels should be tested before implementation of the project.

If the suggested channel excavations are implemented, we assume underwater rock blasting will be necessary. How does this comply with the assurance that such practices will not be allowed (EIA report p. 5-22)?

Downstream fish passage is less critical as there are more available channels than Hou Sahong for downstream migration. However, the suggested mitigation measures (monitoring of mortality, use of ‘fish-friendly’ turbines, screen and bypass structure at Hou Sahong inlet, EIA p. 5-21) seem relevant and appropriate – although the effect of ‘fish-friendly’ turbines may not be fully documented yet. [It is expected that Fisheries Programme will provide a more in-depth analysis of the fish passage issue]

9. Impacts on habitat continuityBecause the DSHPP is a project that spans only one channel and not the entire Mekong mainstream, the risk of destroying habitat continuity is less than for other mainstream dams. Except, maybe, for fish (as described above) the dam does not create any insurmountable barrier for movement of species between habitats. It is therefore not expected that this issue will be of great importance – and it is not addressed in the EIA.

10. Impacts on wildlifeOther than the Irrawaddy dolphins there is no information about other wildlife species, including terrestrial species, of regional importance depending on the resources altered by the DSHPP. The EIA report (p. 3-13) describes the project area as being of poor status as a wildlife habitat. However, the EIA also notes that this assessment may hinge on the efforts put into the survey. Also, the survey found that 5 out of 48 bird species reported are classified as endangered species. This suggests that wildlife assets in the project area may not be properly inventoried and assessed. The project does not seem to have used the data suggested by MRCS in the 2007 review (comment #48).

There is a small population of the rare and critically endangered Irrawaddy dolphin living immediately downstream of the project area, using the Chiteal deep pool as habitat. Particularly the changed sediment patterns, but also the changed flow regimes, in the vicinity of the project area might alter the conditions of the dolphins’ most important habitat. The dolphins might also potentially be impacted by noise and high sediment concentrations during construction and decommission, and by high sediment concentrations during operation of the dam (especially during flushing).

The EIA mentions that underwater rock blasting will not be permitted as an excavation method. Furthermore, the EIA refers to two important aspects for the dolphins, the reliance

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on i) the deep water pool during the dry season and ii) the annual migration of fish as feeding stock. The EIA report argues that since both aspects are insignificantly affected by the project, the dolphins are not threatened by the project. The EIA report (p. 5-23) argues without further documentation that the hydraulic conditions of the area are such that the discharge from the DSHPP will bypass the deep pool dolphin habitat, especially at low water levels. This should preferably be investigated using 2-D or 3-D hydraulic models of the near- field area.

11. Impacts on tourismTourism in the Si Phan Don area is of regional importance due to the proximity and accessibility of tourists particularly from Cambodia as and Thailand. A great deal of the tourism centers on the Khone Falls and the dolphin population. The EIA seems to have a quite superficial assessment of the potential impacts from the DSHPP. It assumes with little argument (p. 5-16) that no or little negative will occur. However, the visual impacts and the impacts on tourism of flows over Khone Falls of max. 800 m3/s for 50 % of the time has not been assessed. Neither has the scenario where Dolphins are no longer present in the area due to the DSHPP. Both would be relevant to analyse.Information on tourist arrivals is generally outdated in the EIA report with typical figures from2005-06 (p.3-23)

12. Impacts on health and livelihoodsThe issue at stake for this review is not the local impacts on livelihoods – that may also be an important issue but it is a national one. The issue is whether there are transboundary impacts of the project on livelihoods for people living in other Member Countries. Consultations have been conducted with some communities in Cambodia (in Ton Le Sap and the area between Phnom Penh and Stung Treng).

The fish passage issue has a clear potential to impact livelihoods for people depending on fish catches upstream as well as downstream of the DSHPP. According to the Social Impact Assessment Report, sale of fish is one of the major sources of income (ranked first among income-generating activities) by households (SIA report, Table 14 & 15, p. 30-31). If the migration of fish should be impeded by the DSHPP and the amount of fish decline, contrary to the assessments of the EIA, then there is a risk of deterioration of the livelihoods of many people, also in other Member Countries. Also the nutrition and health of the population at large might be impacted if the source of protein and nutrition that fish from the Mekong constitute would be reduced. These aspects have not been analysed and assessed by the EIA report because it is assumed that with the proper mitigation measures these risks are not relevant. The consequence is that currently we have no assessment and mitigation plans for a “worst case scenario”, i.e. if the fish migration gets blocked. It would be relevant with a mitigation plan for handling such a scenario.

Due to the limited size of the project (no change in flow, sediment transport and water quality except in a limited near-field area) it is not anticipated that the project will have other regional impacts than on fish catch.

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Alternative optionsThere is some mentioning of the Thakho project (an alternative that diverts water from just above the Khone Falls to just below the falls) in the EIA report (sections 4.3.1 and 4.3.6). However, the information and discussion of this alternative seem to be based on a report from 2004 (p. 4-4) and not the much newer ESIA report from 2010. What is the reason for this? It would be interesting to have a more detailed comparison of the two alternative projects.

Summary of conclusions and recommendations#1: Assess the impacts on the project economy of selecting a minimum flow over Khone

Phapheng higher than 800 m3/s and assess the impact of climate change on the flow over Khone Phapheng.

#2: Assess impacts on water quality from loss of sediments during excavation and deposition.

#3: It seems justified not to anticipate any water quality deterioration in the head pond. #4: Investigate potential impacts from sediment flushing on the dolphin deep pool

immediately downstream of the dam using 2-D or 3-D hydraulic models of the near-field area.

#5: Assess short-term consequences of increased sediment concentrations if blasting of structures during decommission take place.

#6: Due to the physical characteristics of the head pond, long-term impacts on the regional sediment balance are not possible.

#7: It is unlikely that impacts on the nutrient balance (although not addressed by the EIA) will occur.

#8a: Fish migration over the Great Fault Line (particularly in the upstream direction) is by far the most important environmental issue of the DSHPP. Although the suggested mitigation measures proposed for provision of alternative upstream migration routes seem reasonable and sound, they remain to be tested and this issue seems to be a key risk of the project. The deepening of alternative channels should be tested before implementation of the project.

#8b: Describe how deepening of channels will take place without underwater rock blasting in order to protect the dolphins and other aquatic animals.

#9: Due to the physical characteristics of the project it is not expected that discontinuity of habitats will be an issue (other than fish migration as already mentioned)

#10: Assess the data suggested by the 2007 MRC Review regarding status of wildlife. #11: Assess impacts on visual appearance and tourism of flow over Khone Phapheng of 800

m3/s. Up-to-date data on tourist arrivals should be used. #12: Assess the impacts of reduced fisheries on nutrition and livelihoods under the

assumption that the fish migration mitigation measures fail. #13: Compare the DSHPP project with the Thakho project alternative, using up-to-date

information for the Thakho project.

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Dam Design and Operation 1. DON SAHONG HYDROPOWER DAM DESIGN AND OPERATION

1.1 Basic information on project layout, design and construction sequence(i) General LayoutMFCB engaged AECOM to extend and finalize the feasibility studies to incorporate additional hydraulic and geotechnical investigations and corresponding reporting, and to develop a concept design and a preferred concept arrangement. This Final Feasibility Study (FFS) was completed in November 2009 and the corresponding report issued and dated 27 November 2009. Since then, additional hydraulic model studies and geotechnical investigations have been carried out as well as updating of the project costs and economics and completion of the reference design for construction, allowing a substantially more precise evaluation of the Project and justifying an update of the Final Feasibility Study of November 2009.

The main findings and outcome of those studies are reported in the “Engineering Status Report”. The investigations undertaken in 2008/2009 involved field data collection from the project site including: hydrologic survey and river gauging, geotechnical investigations, and topographic survey. These data were used to develop and finalize the technical feasibility studies. In 2010 and 2011 the project was further developed with a reference design in preparation for the “Engineer, Procure and Construct (EPC)” construction contract documents.

The Don Sahong Hydropower Project presents the Developer's conceptualization and optimization of the project. The scheme comprises a power station in the form of a reinforced concrete barrage structure at the downstream end of the Hou Sahong channel, with embankment sections returning along the islands of Don Sadam and Don Sahong that border the Hou Sahong, all of which will form a small reservoir or headpond bounded within the embankments on these two islands. The scheme utilizes a natural fall of about 20m in the Mekong River formed by a feature known as the ‘Great Fault’. The gross head on the scheme varies from about 13m – 21m depending on the seasonal variation in flow and relative variations in the depth of flow upstream and downstream of the falls. The powerhouse barrage spans the approximately 100m wide Hou Sahong with a maximum height of about 30m above the natural channel bed.

The reference design for the generating plant comprises four low-head Bulb turbo/generating units. Other configurations may be implemented depending on EPC tenders received. The impounding embankments are approximately 7 km long in total, with height varying from a maximum of 25m above natural ground adjacent to the powerhouse, to 1m at the upstream end. Only about 800m of the Embankment Dams are higher than 10m above natural ground level. To ensure that water level rise is limited in extreme flood events, the design concept includes a 700m long emergency spillway section at the right bank of Hou Sahong, close to the Powerhouse. The spillway crest is set at a level that will have a 1% probability of being exceeded in any given year. This lowered section of embankment will act as a broad-crested weir free overflow.

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The storage available in the headpond is relatively small with no significant capability to store water to accommodate variable energy demand. The absence of storage capability means that any water available that is not used for generation is spilled. The power station dispatch must therefore closely follow the natural river patterns to maximize utilization. These are typical characteristics of run-of-river hydroelectric schemes. The headpond will, however, act as buffer storage and will mitigate the effects of the surge resulting from discharge change due to start up and shut down ramp rates and load rejection at the station.

Figure 1 Overall layout of Don Sahong dam project (Engineering Status Report, 2011).

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Figure 2 Layout of Don Sahong dam project with Project components (EngineeringStatus Report, 2011).

Table 1:Summary of Main Project Features

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......

Mean flow

m Is 47,600 47,600

-

inlirii

wtN

m

Basin andMain River Characteristics

Unit Data (240 MWnlled-··

Data (260MWrllted_

: !:1!9 (::::::::::::::::::::::::::Expected futureMekflO'NS at Pakse

::::::::::::::::::::::.::::@::::::::::::::::::::::::Q: ::::::::::::.!9!£1:lm.?.L9m...1....•••••••..••••••••••••••••••::::::::: [ :fu? i:: %: Jrj J:::: ::: ::::........ .r:ry - -x-.· ··-·······-·······-........Min -?...'li!!Y.-................ .... ..

·····m..,iS····-., ····--····-g:s·7a---·····-···· ·-··········g:57a········· ··-::::: ::::::::::::::::::: :?:···::::::::::: :::::::: :::::;:?:M:::::::::::::::::::.n: ::::::::::::::: :::1:?:::::: :::::::: :::::::::::::::1:;::::::::: :::::

- .1?£! -!!! ?!f...... ............. ......... ............ ·····-·······-·····-······ ··-······ ··-·····-·····-····················-·····-···Maxim1.mimpounanent area within ha 220 220.e...m.....b..a...n...k...m....e...n...t..s.................................. ............. ..... ... .........-..c....... ·······--····-'-' ····--····-······ ··--···· ··-·····-····· ········· ·················Headwaterlevel atinlet: masl:::::::(:::::: ::::::::::::::::::::::::::: ::::::: ··············7tf7··························=·;o.7··············

····------·--·7···-0--7-···· ··-·····-····· ···· ············7-0·.·-7··-'-···········-·9-5··%···e··x-c··e··e·d··e-·d······························- ········ ····-m··a··s·l··-·71-a. ····-···- ····......................=;al ·····--······-........ .... ..... ..... .............. ......... ...........................··-·.···-·-....•.····-·····--·····-· ···..--····.-···-........ ........ ...···-..........H5%eadeWxo3eier.leedver.:·:so·%·i\Er·iiOOd·(ri......

mas1 · 74.1 · 74.1····m···a·s·l···· -······--·····-······-··········· ···················--·····-·······

....... .. ).·-···.........····-·...... -............ ................. ... .····-·............ -- : .............···-··· ··_Headwaterlevel -0.1%AEPllood mas1

.........ttJ,- !1.......................... ........ ...........······-·······-·...............:-.--······· ·······........... .....:..... ............- 2-- !9}' .-----------------·---------.------·--.D---is--o·.h.-a-f'i . ·---·........ -----···---·-··---·.........----·..·- .....m1iS-··--

:. :..... .......... -

-------- 9------------------------·-- ------..,------- : !L: : :: :: ! L::::········ Y...l. ----·····················-

.....'.!!...... ............J.L¥.............................11............Average station cischarge-v.ettest year

------·-{_- )_ ·---------------------------------·----·-·--Average stationdscharge -driest year

....... ..ttt....···-·-...... ..... ...-..... ...... ..... ........ .··-

.N...e.t..H.Re3aid€d'h'e.ad'""'..................................···-·

....................... ................................................................ ...........

ml/s

m

1,518 1.560

1,340 1,383

····--·········r.o··--··········..............i.ro······--···---···············;·r.7····-·····--··-·--··· ··--··17.7..............

.------Y.-.-. .-----·-----·-----·-.----·-.------.·-- .......-m.........-.. --··-··---···9.!f"''"'"""'""'' --··-··---·-·;·-gjf""----···---·-----··MainxiimumtiheeaCadi···----··-·-·-··----·------··-----···--p();.er----.·-----------------------------------------------·--

m ·---··-----·--;·4·_7..............----·--··-····-i4:_·r·-··········-

...................................................... _............

........................................................-------- !?.1- <:!!Y -------·-------·-.........Y.. f!. '!:····-·......-................•..•...·-····-····P<oYw.e.r:-eexxceeeddee(dis9s0%%·0o1f·.t;h;e·ttiiimlieee_ ···-········

........... _.._............_.. -·--------·-··-i4ii·-········· -···- ---·----·--·--·:260·---.··---···-·-----W.·MfNil----- ------------ i2 -------·----···--------235 --------·-.............. _. ·············---;99··· ···· ···-·-···.................,95........ ..... ...····-.tWvmNIJ····· -----··· ·-····--;so·.............--······ ---··-···;ss·--··--······-

.......................... .,........ ... ,..····-·............ .... .......... ............... ....i.iJV..•.. • .................. .... . ... ...,. ....,•• •••-oe•••--•••••--••••••••••-•••

·····--· Y.. - - .f.' .{l-------......... x-- ?: j xL......J-...9.!J .P.9.i.........................··-.-----·.!'!---·····-·-·.---·-·.------..----·..·-

..........._.._ .............-.. ----.-·---·----i2-3i §8------------.- ---------··· ----2m4_8-----.·----·---

· ··G·W·ii·__·· ········· ····:·c980···· --··-·-···....... .......2:044··········· ····

........ ...Y.t ..·····-·.... ...... .... ...... .... ......... .··-Driest year

.P.! - !':!.-.····-········..................•......··-

Ernban'krnent:R:::::::: ::::::::::

::::::::::::::::::::::: ::::::::::::Crest elevation

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m

····GVVii··-·

...···--······-······-kams·l···-

::):::::::::::::

1,895 1.953

····-········Rcc....... ........···········-··R<:SC········ ········........ ......76.90"'"'''""''''--·····---···-76.9-0"''""""'''":9:! 6::::::::::::::::::::::: :::::: :::: :::::::: :::::::::::: ..........._.._..............._.. ::: ::::::r:...::::::::::::::::= :::: :::: !. "&::::: ::::::::

--r:ry- l --l ---··········- m

.!!'- !.' §P.i Y:····-·......-........................·-25 25

.-----·..·--··· .-----·.-----.···----------. ·---·...----·..-- "'"masi"'" ::::::!:: ( :::::::::::::::::::!:::::::::····-····· ···--7775o.o4··5····· ·····--· ·-·--····-···?7o5c.4r.5.····· ··-···

....... ..:§m.. :!!l.C?..':.'•...····-·.... ...-..... ...... .... ......... .··--·····-.t.' ---·........--·--·-.--···.·-··-..·---....

-···--m···· ···-·

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(ii) Head and Flow Characteristics:A feature of Don Sahong, and typically of run of river hydroelectric projects, is that as flows increase into the wet season, the headwater level rise is much less than the tailwater level rise thus reducing the head across the turbines. Conversely, when flows decrease during the dry season the tailwater level drops much more than the headwater level, thus increasing the head across the turbines which will contribute to Don Sahong good dry season generation characteristic, and relatively consistent generation from month to month.

(iii) Optimum installed capacity:The installed capacity optimization essentially involved trialing different scenarios to find the one that produces the most amount of energy or revenue for the least cost. For each scenario trialled it was therefore necessary to estimate the amount of energy that could be generated and the capital cost. The energy was determined by the flow that is available and can be diverted into the Hou Sahong at the corresponding head. Therefore the variable that most significantly influenced the installed capacity was the excavation required to increase the hydraulic capacity (flow) of the inlet and reduce channel head losses. Excavation at the outlet also influences the installed capacity as this has the effect of lowering the water level for a given discharge which increases the available head and therefore the energy that can be generated.

The FS Review (2009) indicated that an installed capacity of 200 MW is likely if only minimum works are undertaken in the main river upstream of the Hou Sahong and that this could be increased to 250 MW with the construction of a submerged diversion sill in the main stream just downstream from the Hou Sahong inlet.

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For the recent review the range of installed capacities trialled was 160 MW, 200 MW, 240 MW and 280 MW. For each installed capacity trialled, environmental flows of 1000, 800 and 600 m³/s were considered along with a range of inlet and outlet excavation levels. Finally the environmental flow option of 800 m3/s for an installed capacity of either 240 MW or 260 MW was adopted with an inlet excavation level of 65 masl and an outlet excavation level of 46 masl.

The final decision on the capacity will be made after scrutiny of the tenders for electrical and mechanical equipment supply and construction.

(iv) Powerhouse:The design of the Powerhouse is constituted with standard components and equipped with standard equipment. The station design total flow is 1,600 m3/s. This assumes a combined turbine/generator unit efficiency at rated head and design flow of 92%. It is also noted that the peak combined efficiency would be expected to be slightly higher than this and in the order of 93.5% (95% for turbine, 98.5% for generator), as the peak efficiency is typically set at an intermediate value of turbine flow, depending on the operating characteristics. This is particularly the case for a run-of-river plant where generation normally occurs across a wider range of flows, and a good efficiency characteristic is normally desirable across as much of the range as possible. The power plant is proposed to have a nominal installed capacity of 240 MW or 260 MW, developed by discharging the design flow of 1,600 m3/s operating at the rated head of 17.0m.

(v) Overview of the Dam operation plan and Power Output:The DSHPP will cause water to back up in Hou Sahong, creating a small headpond, the level of which will vary with the level of the Mekong upstream. The top of the dam is set at RL 76.9m, which is above the maximum level that the Mekong will achieve at the upstream entrance to the Hou Sahong. Based on daily water levels recorded at Thakho since 1995, the average level of the reservoir is expected to vary about 3.2 meters, with its highest level in August-September and its lowest level in late April-early May, each year. The projected water surface elevations upstream and downstream of the dam are shown on Figure 3 The variation in the inundated area within the embankments during normal operations of the DSHPP is illustrated in Figure 4, indicating the relatively small difference between low water and high water conditions.

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Figure 3: Monthly Variation of Water Surface Elevations Upstream (HWL) andDownstream (TWL) of the DSHPP Dam

Figure 4: Inundated Areas during DSHPP Normal Operations(Low Water at left and High Water at right)

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Power output will vary with the seasonal flow variation, as in general terms a particular headwater/tailwater condition will correspond to a particular river flow, thus a particular power output. An emergency power supply will be provided by a diesel generator set to supply essential station loads and start-up power for one turbine generator unit when AC power is not available via the unit auxiliary transformers. The essential loads will consist of battery charging, emergency motors, control room lighting and various other loads which are still required, when the normal AC source is not available.

The energy figures given in Figure 5 represent the total modelled generation output for a 240 MW station, as would be measured at the power station metering point. Comparative results for a 260 MW station are given in Figure 6.

Energy estimates are subject to the following assumptions:

- No differentiation between power supplied to either EGAT or EDL,

- The Delivery Point is taken to be at the station switchyard boundary just downstream of the transformer terminals. Any transmission losses required to be adopted will be subject to review following finalization of transmission requirements with either EGAT or EDL.

- No deduction for maintenance outages or other unplanned (forced) outages. It is suggested that an allowance for unplanned outages of 1.0% of total energy be made for planning purposes. The effect of maintenance outages on energy output is described in the section below.

Figure 5 shows that most of the variation occurs in the dry season. However the variation in annual energy of the driest and wettest of the 28 year hydrologic series studied is relatively low, at 95% and 103% of the average year respectively. The low variation is largely a result of the relatively even and predictable energy generated during the wet season, which does not vary significantly from year to year.

Annual maintenance will be scheduled in the dry season, where available flow is lowest and thus not all units may be required in service. Because of the high plant factor however, in many years the available dry season generation flows are above 1,200 m³/s (see Figure 5 and Figure 6), meaning all four units are required to fully utilize the available flow. In many years, annual maintenance will result in a reduction in energy output from the maximum output figures provided in Figure 5 and Figure 6. Assuming that each unit requires 10 days offline annually for maintenance, scheduled in the driest period of February through April, the average annual output is reduced for a 240 MW station to 1,980 GWh and for a 260 MW station to 2,044 GWh. Assuming that a periodic major overhaul of each unit would require 50 days offline, and that 2 units would be overhauled sequentially in one dry season, the average annual output for an ‘overhaul year’ is estimated to be 1,912 GWh for a 240 MW station and 1,996 GWh for a 260 MW station. A major overhaul would be required every 15-20 years.

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Figure 5: Variation of Monthly Station Energy Output for 240 MW Station.

Figure 6: Variation of Monthly Station Energy Output for 260 MW Station.

(vi) Local Effect on Flow Distribution during dam operation:The scheme is designed to operate to take as much flow as possible up to its design flow of 1,600 m³/s while always leaving a minimum of 800 m³/s in the Eastern Channel to discharge over Phapheng Falls.

Scheme operation will alter the flow distribution in the channels in the local area, including the Hou Sahong and the Eastern Channel. Excavation works are proposed at the inlets of the Hou Xang Peuk and Hou Sadam channels such that they will maintain natural flow rates, despite altered water levels resulting from scheme operation. The modelling demonstrates that construction and operation of the scheme will not affect water levels or flows upstream of the Hou Xang Peuk inlet. There will be no change to river conditions as a result of this scheme in

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the Don Det – Somphamit Falls area. Flow changes as a result of DSHPP as shown schematically in the following figure.

Figure 7: Schematic of flow changes as a result of DSHPP construction and operation

The effect of the DSHPP is represented by a simplified conceptual diagram of the channels in Figure 8. The relevant branches of the River are represented by numbers as

follows: (1) Flow coming in to the Si Phan Don region (1a) Northern-most branch upstream of Ban Thakho passing Ban Nakasang (1b) Main branch passing between Don Tan and Don Det (1c) Western and Southern-most branches including Lippi falls (2) Hou Sahong (3) Branch downstream of Sahong inlet and north of Don Sadam (4) Main branch over the Khone Phapheng falls including Hou Sadam which represents less than one percent of this total (5) Main branches entering Cambodia

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Figure 8: Seasonal changes in flows in the Channels.

Table 2 and Table 3 provide flow data (in m3/s) on the changes that will occur in the various branches represented in Figure 5-7 without (before) and with DSHPP, for a range of flows from the 1% exceeded to the 99% exceeded values. Measured flows were used during the modeling deliberately to avoid the influences of future upstream storage schemes.

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Table 2: Natural Flow Durations - without DSHPP

Table 3: Estimated Flow Durations with DSHPP

The following observations are made from the results: 1. Flow in to the region (1) is always equal to flow entering Cambodia (5) without or with

DSHPP. 2. The post construction effects on the river system are localized with only flows in

branch2, 3 and 4 and the short reach between the Sahong outlet (2) and the Phapheng outlet (4) experiencing change.

3. The changes in the short reach between the Sahong and Phapheng outlets are not tabulated, but can be taken as the difference between the without and with flows in columns 2 and 4.

4. The flow change associated with branch 4 can be attributed to the extra flow that is diverted into the Hou Sahong (2) for generation.

5. From Figure 8 above (also Figure 8 of the EIA Annex C), it can be seen that, during the 7 dry season months the flows in the Hou Sahong increase from 3% to 5% of the total

river flow to 30% to 50% of dry season flow. 6. Minimum flow passing through branch 4 (Khone Phapeng) is in accordance with

required minimum environmental flow of 800m3/s. From Figure 8 above this indicates a

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reduction in the Khone Phapeng flows of some 30% to 50%. 7. Maximum diverted flow into the Hou Sahong is 1750 m3/s which represents the

maximum overall turbine discharge. 8. The annual average flow in the Sahong channel will increase by approximately 1000

m3/s, and the annual average flow over the falls reduces by a corresponding amount.

In summary, the DSHPP is only expected to have an effect on flows on the Hou Sahong, Hou Sadam, and Hou Phapheng. The Project claims not to affect downstream flows including the Tonle Sap and the Mekong delta.

(vii) Bypass Requirements and Flow ManagementA station full flow rejection may cause an unacceptable rate of rise (surge) in water level at the upstream end of the headpond, continuing to the Hou Sahong inlet and dispersing on the Mekong branches immediately adjacent. Full flow rejection might be caused by a load rejection due to the abrupt loss of the transmission line capacity, for example. During flow rejection, the rate of water level rise on the Mekong branches immediately adjacent to the Hou Sahong inlet can be reduced by providing an emergency discharge capability from the headpond as follows:

- via the turbine units operating in sluicing mode, - via the ungated emergency spillway provided on the Hou Sahong right bank, or - via a gated bypass spillway.

The DSHPP has used the principle of increasing the turbine sluicing capacity as to reduce the capacity and cost of the gated spillway facility required to accommodate the surge limits requirement. The turbine sluicing operating condition must be suitable for extended operation for periods of up to several days, because it may also be used to route a fraction of the flood discharge, and therefore must be stable without excessive vibration or cavitation. The Engineering Status Report describes the various modelling simulations to mimic the station load rejections as to foresee the likely impacts. The various simulations result reveal small surge wave (300 mm -400 mm height) .

(viii) Sediment and Strategies for removal:The sediment management strategy is based on the conclusion that the volumes of sediment potentially deposited within the headpond are insignificant in terms of the overall Mekong sediment budget. It is estimated that 80%-90% of the total suspended load diverted to the Hou Sahong will pass directly through the station turbines as a natural function of operation. Accordingly the sediment management strategy does not aim to re-suspend and pass all trapped sediment, but rather aims to manage deposited sediment volumes to generally not exceed about 2 Mt in the headpond so as to mitigate adverse effects of sedimentation (mainly loss of power generation). Consequently, to remove accumulated sediments from the headpond is very much necessary as to avoid the build-up of sediment in the headpond which will important adverse effects on station operation. There are two methods are considered for sediment removal. These are: Sediment flushing, and Mechanical removal by dredging.

2. DAM SAFETY AND THE PROPOSED DON SAHONG HYDROPOWER DAM

As noted in the Prior Consultation (PC) Scoping Assessment, steps to ensure the safe design, construction and operation of the proposed DSHPP dam project are in the interest of all MRC countries. All MRC stakeholders expect that appropriate steps would be taken to ensure the protection of life, property and the environment, as well as the protection of economic assets. This review considered, firstly, the extent to which the proposed design and construction, operation and maintenance regimes for the Project follow existing Lao PDR technical standards

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and safety rules. Secondly, the review considers how the measures that the developer propose conform to regional and international good practice, as viewed through the lens of the MRC Preliminary Design Guidance (PDG) agreed by MRC Countries at the Joint Committee level.

2.1 Basic information related to Dam safety1. Safety Consideration in Dam Design

The overarching dam safety objective is to protect people, property and the environment from the harmful effects of mis-operation or failure of the dam. As set out in ICOLD Bulletin 130, the level of safety provided is by necessity an economic balance based on the consequences of dam failure.

Consequences of Dam Failure

In terms of the downstream flooding hazard, dams are typically (e.g. ANCOLD 2000, USBR 1988) classified according to the potential impact of failure of the dam on people, property and the environment. An initial assessment into dam failure consequence has been made following the ANCOLD (2000) guidelines. The village of Ban Hang Sadam is considered a population at risk in the event of dam break. Owing to the close proximity to the mainstream Mekong, and the relatively small impounded height and volume of the Don Sahong headpond, there are no other populations identified to be at direct risk. The next sizable population centre downstream, Stoeng Treng at the confluence with the Se Kong River, is about 50 km away. At that distance,it can reasonably be concluded that the surge resulting from a dam failure would be sufficiently dampened to be barely perceptible. Based on this assessment, the Don Sahong embankments and powerhouse are provisionally considered to fit the ‘Significant’ hazard classification according to the Lao Electric Power Technical Standards.

To confirm this classification, the EPC Contractor is required under the tender documents to develop a risk analysis in compliance with ICOLD bulletin 130-2005, Risk Assessment in Dam Safety, to assess the probability and evaluate consequences of dam failure.

Design Flood Assessment

Lao Electric Power Technical Standards define the inflow design flood (IDF) that should be considered in design of a hydropower dam. The relevant table (Table 17-1) from the standard is reproduced below as Table 9-8:

Accordingly the powerhouse barrage and embankment should be designed for at least a 1 in 1,000 AEP flood event. The powerhouse upstream wall level and the embankment crest level are set to provide a 1/1,000 AEP standard of protection, being higher than the design flood level for a 1/1,000 AEP flood plus a freeboard allowance.

Freeboard allows for physical processes that affect the flood level that have not been allowed for in the design flood level (e.g. wind waves, settlement, etc.) and adverse uncertainty in the prediction of design flood level. Lao Electric Power Technical Standards define a minimum required freeboard of 1.0m for a cementitious (overtoppable) dam type.

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The concept of a ‘check’ flood, being a flood level higher than the IDF, was used to check the appropriateness of the freeboard provision. In this case the 1/10,000 AEP flood was modelled, and found to have a level of El. 76.3 masl. This remains lower than the crest level of El. 76.90 masl, which validates the selected freeboard provision.

The derivation of design flood levels for various flood events is discussed in Section 4.7.9.of which report?

Provision of Emergency Overflow Spillway

To ensure that water level rise at Don Sahong is limited in extreme flood events, the design concept includes a 700m-long emergency overflow spillway section in the western headpond embankment. The spillway crest is set at a level that will have a 1% probability of being exceeded in any given year (1/100 AEP). From the free-overflow crest, flow energy is dissipated over a stepped spillway, and is conveyed overland approximately 250m, down existing gullies into a branch of the adjacent Hou XangPeuk.

Derivation of the spillway crest level is provided in Section 4.7.9.

(ii) Construction and Commissioning

The contractor is responsible for ensuring that appropriate measures are taken and sufficient resources provided for the safety of the dam during construction. The tender documents require the contractor to provide rigorous Emergency Contingency Plans and a Quality Assurance Plan that will be implemented by the contractor. Reviews and audits of these plans are regularly set up during construction and commissioning. These plans are required to be designed on the basis of effective coordination and open communication between the contractor and the developer. A detailed plan for construction supervision will be prepared and implemented by the developer.

(iii) Operation Phase

The tender documents specify a comprehensive Operation, Maintenance and Monitoring Training Plan to ensure the Operator’s Counterpart Personnel are proficient in operating, maintaining and monitoring of every part of the facility.

The Operation, Maintenance and Monitoring Training Plan syllabus will be developed by the contractor in liaison with the developer. With regards to dam safety, the plan will emphasis instrumentation readings, analysis and related risk evaluation and decision streams, and surveillance programs including inspection of the embankments at regular intervals, immediately after large floods, and routine inspection of equipment necessary for safe operation of the facility.

Instrumentation of the embankment and the structures, as well as measurement of hydrometric and climate data at several locations throughout the facility is specified in the tender documents. Details are to be developed by the EPC contractor’s embankment designer.

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The tender documents require that instrumentation programs, periodic inspection, and evaluation of the structures comply with the U.S. Army Corps of Engineers Engineer Regulation 1110-2-100, Periodic Inspection and Continuing Evaluation of Completed Civil Works Structures.

(iv) Emergency Preparedness Plan

An Emergency Preparedness Plan will be prepared in the interests of public safety in the event of an emergency. It will be developed as construction progresses since several of the specific details required for such a plan are site and construction specific. An inventory of failure mechanisms at each related part of the works will be developed to evaluate and classify potentially serious situations.

The Emergency Preparedness Plan will comply with the requirements of the Environmental Management and Monitoring Plan (EMMP) and of the Social Management and Monitoring Plan (SMMP).

The general purpose of the plan is to:

Provide a plan that facilitates public safety by notifying all appropriate authorities; Provide information to all stakeholders to allow for an informed evaluation to be made

during emergency events; Provide plans of action for foreseeable flood emergencies affecting safety of the facility

and affected property downstream; Provide for a plan of action to carry out repairs and reduce the impact of any such event where possible.

(v) Dam Safety Management System

The Emergency Contingency Plans, Operation, Maintenance and Monitoring Plan, and Emergency Preparedness Plan will form the basis of the Dam Safety Management System that will be developed by the facility owner and d implemented by the Station Operator. The Dam Safety Management System defines dam safety requirements, how they are implemented, reviewed, and updated during the lifespan of the facility. The Dam Safety Management System and its plans will reflect current best practice and prompt checks for updates to relevant guidelines (e.g. ICOLD bulletins), Ongoing dialogue with the local community is expected to be required to ensure understanding and appreciation of the Emergency Preparedness Plan in particular, and to gather feedback on the social effects of the facility operation

(vi) Seismic hazard

Reference to the United Stated Geological Survey (USGS) database shows the central and southern regions of Lao PDR to be seismically quiet. The seismic hazard map indicates peak ground accelerations are likely to be in the region of 0.2 to 0.4 m/s2 (0.02g to 0.04g).

3. SUMMARY OF COMMENTS:

LNMC has provided, as part of the notification for Don Sahong HPP, a set of detailed documents including the Engineering Status Report, the EIA, SIA, SMMP, RAP and various Fisheries Annexes. This level of openness and transparency about the project details is very

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welcome and allows a far more informed debate about the project impacts and planned mitigation options.

Information displayed above was collected from the DSHPP Engineering Status Report 2011. Nevertheless, the MRCS will confirm the completeness of this information in the design report based on instruction from the JC on the PNPCA process.

The content of the DSHPP Engineering Status Report 2011 has given a best estimate of impacts resulting from the construction and operation of the power plant and the mitigation measures. However, in some places the description of mitigation measures is still limited and requires further elaboration to ensure smooth coordination and that shared responsibilities are well understood by all stakeholders to maximise safety and reduce impacts to the environment.

Overall impression is that the transboundary impacts need to be more clearly assessed and mitigation measures more clearly laid out including the adaptive management approach.

The link between the operational social and environmental impacts is clear for this project. More evidence is needed to confirm that the affected people will have sustainable and improved livelihoods established as envisioned by the SIA.

Comments related to Design, Construction and Operation of DSHPP:

1. Project Siting and Options Economic Analysis: For sustainable hydropower design, it is important for this project to be seen in the context of the other power options available to the purchasers of the power and alternative siting options. As this report is clearly undertaken

by the developer under the existing PDA, it would not be expected to discuss these points. However, from the MRCS perspective (basin planning), and as per common practice in the PDP process, it would be important for the economic assessment of these alternatives to be fully assessed to ensure the best outcomes for the Lao PDR, the power purchaser, and other MRC member countries. This economic analysis should show the relative benefits of the DSHPP over other fuel options and other HPP locations (e.g. Takho).

2. Project Scale and Location: The above review could also be supplemented by further explanation of the project scale relative to the demand in the southern region of Laos PDR. This would include the assessment of how the DSHPP production would feed into the Southern Grid and ensure that this project will work in coordinated operation with other power stations to maximise system production and minimise effects on environment and affected parties. Aspects of the connection to the grid and related operations are yet to be resolved. This needs to include network modelling to ensure production is maximised and outages minimised.

3. During construction: the estimated quantities of materials to be excavated in many areas particularly in the channel area are huge but disposal areas are not final and still subject to detailed negotiation with local village officials. It is important that the plan contain an adequate erosion and sediment control plan to prevent environmental degradation of lands and streams during construction. The erosion and sediment control plan is required and the approved plan should include a Quality Control Inspection Plan to ensure that adequate inspection and reporting is in place to minimize pollution to the Mekong River. The plan should address the protection of existing vegetation, grading of slopes, control of surface drainage, sediment containment measures, temporary topsoil stockpiling, storage and disposal of excess excavation and debris, construction and upgrading of access roads, and clearing and construction of the transmission line rights-of-way. Approved disposal sites should be indicated.

4. Effects of unexpected and possibly rapid changes in water surface level and flow rates downstream due to DSHPP operation: These effects have been addressed in the content of

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the DSHPP Engineering Status Report in connection mainly to station flow and surge effects which may cause serious impacts to people. Result from simulations appear to give small raise in water level for different scenarios .Therefore, for preventive measures the selected equipment suppliers must manufacture, supply and install their turbines with similar or better sluicing flow rate capability results as shown in the DSHPP Engineering Status Report.

5. Operation requires a pro-active approach to risk management, in part due to the run-of-river operation concept and relatively limited storage in relation to the high river flows that DSHPP must accommodate. Rates of change of water surface elevations in the reservoirs would sometimes be fast. Reaction times of dam operation staff in emergencies will equally need to be rapid and fail-safe. Mechanical and electrical control equipment must be well conceived and designed, and thoroughly backed-up to ensure the operation flexibility can be maintained during emergency situations, where different failure modes can arise with critical equipment, such as controls for spillway gates or stop logs. Therefore, to prevent accidents and hazards resulting from rapid rises in water surface level, DSHPP must implement adequate risk mitigation measures including public safety information and operational guidelines. .

Comments related to Dam Safety for DSHPP:

The reports make a detailed assessment of the project against the PDG in both the Engineering Status Report and the EIA. This is a good feature of the report and will need more detailed review at some point. Proposals for improvement will be in the detail.

1. The report calls out the ICOLD and Lao regulations on dam safety risks. Given the location of the project, the use of an expert panel would be most important to reviewseismic, flood risk management and the detailed design parameter selection. These will be further considered during any agreed PNPCA process.

2. Beyond clarity on the institutional arrangements, it is also important to confirm that the five main sub-plans prescribed in the PDG would be prepared and implemented. These plans include (i) a construction supervision plan (ii) a quality assurance plan (iii) an instrumentation plan (iv) an operation and maintenance (O&M) plan, and (v) an emergency preparedness plan (EPP).

3. In the Mekong transboundary context, this means mechanisms to ensure the four MRC countries have information access throughout the project development stages, in the manner that may be agreed, including monitoring and compliance activities.

4. All four Member countries have a stake in the safe design and operation of mainstream dams due to potential transboundary impacts of dam failure and the need to assure the public that mainstream dams are well managed. As a consequence, all MRC countries need to be appropriately involved in various safety aspects from the design stage to monitoring and review processes.

5. The Mekong is also projected to see a significant increase in the frequency of extremeflood peaks over the longer-term, due to climate change. Given the permanent nature of dam structures, an assessment of integrity of hydraulic structures against the range of projected flood extremes that MRC had developed is important to satisfy concerns and perceptions of hydrological risk.

6. The PDG notes that broadly, a consistent approach to the safe passage of extreme floods is required for critical structures during construction and operation of the mainstream dams, also taking into account the potential development of other dams in the mainstream cascade proposed in northern Lao PDR.

7. The PDG states (paragraph 182) that “Developers and owner / operators will need to demonstrate how they will apply the entire OP/BP 4.37 (which is embodied in the PDG).Consideration should also be given to ensuring that relevant dam safety measures provided

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in this guidance is appropriately reflected in Concession Agreements

Comments on the other Aspects of the reports:

Environmental flows and incentives:

The incentives for the developer to maintain environmental flows across Khone Phapeng falls and into the fish passage channels in Hou Xieng Peuk and Hou Sadam needs to be considered. Approximate trade -off is shown in the optimisation section of the report.

E-Flow Generation Lost revenue (%)

1000m3/s 1676 GWh -5%

800m3/s 1757 GWh Selected case

600m3/s 1774 GWh +1%

.

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Navigation

1. Summary of negative impacts on navigation and measures considered by theDeveloper

According to the report there would be no impacts on upstream or downstream navigation operations. This will however need to be investigated as there may be changes to the accessibility for shipping in the estuaries and delta navigation. The impacts of any dam development scenario/ knock-on effects on morphological and geomorphological, hydraulic and hydrological changes that effect critical water levels and flows are to be studied. The changes in hydrological processes in the LMB should be evaluated, and it should be assessed how these changes may impact shipping in the Delta and floodplains in Viet Nam and Cambodia.

Most of this will be carried out by the Navigation Impact Assessment under the Study of the Impact of Mainstream Hydropower on the Mekong River (Mekong Delta Study - MDS). The MDS will study what will be the effect on the important shipping in the Lower Mekong Delta. Whatthe MDS will do:

- Mathematical models will be applied to simulated river morphological changes dueto dam operation. At the same time consultations will be conducted with experts and stakeholders. Specifically these approaches can be described as flows.

- Determination of key activities that may have direct or indirect impacts on navigation, of transportation demands at macro level related to impacts of mainstream hydropower impact on navigation

- Mathematical modeling will provide quantitative assessment of the expected impacts which include flow regimes, sedimentation transport and river morphological changes. Water level fluctuations, bank erosion and obstructions appearances will be simulated and scenarios be analysed.

- Consultations with publics and institutions in Vietnam, Lao and Cambodia to have consensus on the impact assessment findings.

2. Potential for navigation developments to be consideredThree zones of commercial river trade are currently active, from Yunnan Province in PR China to northern Thailand, between Cambodia and Viet Nam, and maritime links between Cambodia, Viet Nam and overseas ports. River cruise tourism is also active in northern and southern Lao PDR, but more in the Delta. The potential for increasing river trade and tourism is significant and a regional development approach is very much needed. Navigation between Cambodia and the Lao PDR, which would actually connect the Lower and Upper reaches of the Mekong River has always been considered but has never been fully investigated. Now that the discussion on dam development in the area between Cambodia and the Lao PDR has started,it would be unwise not to study the possibility of longitudinal navigation accessibility between the two regions.

A common interest in increasing international trade was the reason that the MRC signatories opted for a separate article in the 1995 Agreement on Freedom of Navigation (Article 9). So when hydropower schemes are planned for the Mekong mainstream, improved conditions for long-haul waterway transport should be considered. The Lao PDR has a wealth of mining

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products and natural resources, and because of its size and location the country offers a vast potential for increased agricultural production. Unfortunately it is a landlocked country so all modes of transportation and accessibility should be carefully looked at. Moreover, it is a known fact that such voluminous goods are best exported by large inland barges.

It can however also be acknowledged that the upstream and downstream river stretches are quite shallow and not very navigable. But the prospects of “passing or bypassing the Khone Falls for navigation” have always been on the agenda of authorities and shipping companies who wish to see the Lancang-Mekong utilised as a transport artery. Of course its economic viability depends on the needs and prospects of changing that transport corridor into a trade corridor. Developing the hydropower scheme without navigation facilities may lower any prospects of materializing a transport corridor in the future.

The Developer has not considered the potential for navigation development and improved longitudinal connectivity for navigation accessibility in case of increased water levels through hydropower development. This is indeed a transboundary component that is of a different nature than topics such as fisheries, water quality or environmental flows, and is referring more to an economic and transport infrastructure development dimension. But it’s a potential that should be studied and considered.

Output 1.1 of the Navigation Programme 2013-2015 will see the Formulation of a Regional Master Plan for Waterborne Transportation with Multimodal Transport Links and will look into the financial and technical viability of “passing or bypassing the Khone Falls”. If it would indeed be viable then the incorporation of a shiplock would be something worth looking at.

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Social Issues 1. GENERAL OUTLINE

The following preliminary review of the social issues1 related to the project is based on the following project preparation documents provided by Lao PDR:

Social Impact Assessment (SIA); Cumulative Impact Assessment (CIA); Resettlement Action Plan (RAP); and Social Management and Monitoring Plan (SMMP).

These documents have been prepared in according with laws and regulations from the Lao government, including guidelines and standards from ministries such as MONRE and MEM. In general, the guidelines and standards used by the project developer to prepare the above documents are similar to the ones used by international organizations, such as the World Bank.

It is BDP’s assessment that – in general - the SIA, CIA, RAP and SMMP are fit-for- purpose, i.e. they are mostly complete, consistent and provide the required information with adequate quality. However, some of the proposed mitigating measures need to be further prepared and planned together with the affected population, such as the livelihood development measures to maximize employment opportunities.

In BDP’s evaluation, the main challenge has to do with (independent) oversight and compliance assurance of the implementation of the proposed mitigation measures and with adaptive management based on good monitoring of a range of parameters.

There is scope for further improvement of the above assessments and plans (SIA, CIA, RAP and SMMP). BDP’s specific recommendations are provided below.

2. RECOMMENDATIONS FOR IMPROVEMENT OF THE SOCIALASSESSMENTS AND PLANS

In order to place our recommendations for improvement of the social assessments and plans in context, first a short summary is provided of the social impacts assessed and the mitigating measures proposed by the project developer. This information and our recommendations is presented are the structured according to the project scale, the local to sub-regional scale, and the transboundary scale.

1 This review is part of a broader review prepared by the BDP in December 2013 after reviewing the project preparation report and participating in a study visit to the project area.

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2.1 The project scale

The project scale refers to the built up area of the project infrastructure, such as the dam and the reservoir. The people living in this area have to be resettled. The RAP demonstrates that resettlement issues are relatively small (11 households of Ban Hang Sadam). The main reason for this is that the project will be a run-of-river scheme with only ‘buffer’ storage in the head pond (volume less than 0.1 km, surface area less than 2 km2).

However there are a few issues that need further consideration in the RAP. These are summarized below:

The RAP implementation schedule is planned for 24 months which may be too short to really ensure successful resettlement (RAP, page 18 on Figure 7).

Resettlement location: From the map on page 12 showing the original hamlet and the resettlement site which is deep inside the island away from the river bank while Conceptual Layout of Hang Sahong Resettlement Village on page C 15 of Appendix C of RAP showing the resettlement will be near Hou Xang Phuek so which is the actual resettlement site?

The RAP states that DSHPP will provide adequate clean water for HH consumption but it is not clear about the water for farming in which the original location is closer to water source at the Hou Sahong, the construction site of the Hydropower dam.

The report of 2007 survey did not take into account the amount of increased in-migration workers and some may bring families with them to stay on Don Sahong for the construction period of the dam. This large amount of workers may lead to high demand for shelters, food, water, etc., and a need for proper waste disposal (garbage, human waste) that should include the island communities.

2.2 The local to sub-regional scale

The local to sub-regional scale refers to the wider project area where people live whose livelihoods will be directly or indirectly affected by the project construction and operation. In this area, the project related social impacts according to the SIA include 50-100 fishermen whose livelihoods depend on traditional fishing in Hou Sahong due to the permanent removal of fish traps in the Hou Sahong and the reduction of fishing pressure in nearby channels. Another category of social impacts is related to nuisance (noise, dust etc.) from construction and excavation activities.

A range of mitigation measures is being proposed by the developer in the SIA and the SMMP, including ‘livelihood development’ in other sectors than fisheries such as agriculture, forestry, transport and security, and ‘livelihood betterment’ measures such as education, water supply and sanitation, electrification etc. Wealth creation advisors and revolving micro-credit funds would help local people to generate benefits from the project.

The Don Sahong Hydropower Project, which includes the construction of roads and a 350m long bride across the Hou Phapheng, will change the socio-economic future of sub-region beyond the impact of the hydropower plant. Strong independent oversight

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and compliance of the implementation of the project and the proposed mitigation measures would be important to maximize the potential development and poverty reduction benefits for the population in the sub-region.

Several issues need further consideration in the SIA, CIA and SMMP. These are summarized below:

Livelihood restoration and development strategy is well prepared guideline and mentioned that livelihood restoration activities will be continued over a period of about six years (SIA, page 48). However, social development action plan of SMMP shows Table 4 budgets for SMMP planned only 2-4 years (SMMP, page 34).

Employment opportunity of local people during the construction period of DSHPP (SIA: page 67) should be ensured such as the recruitment of the best fishermen for catch and transfer ( and other fisheries related tasks) would be full-time or part-time; what type of employment for skilled boatmen for logistics and transportation would be after the 350 m long bridge between mainland and island is available.

Under point 6.3.2 Medical Care Support - Waste disposal management such as garbage and human waste disposal was not described (SMMP: on page 18).

Proposed public health mitigation found in SIA particular education and treatment programs for Schistosoma mekogi which is risk in life style and daily dietary of local people. An observation is whether the education and treatment is emphasizes and incorporated in the SMMP on primary health education or not. (SMMP, page 18 and SIA, page 68).

The Education Promotion Programme of SMMP is incorporated with Section 5.5.9 Support for Education and Training of SIA in particular formal education on primary and secondary school levels. However, adult education mentioned in the Section 5.5.9 is not incorporated in SMMP.

The community base aquaculture is not clearly defined that this will be a community based entity or cooperative or association to facilitate aquaculture sector as alternative sector to develop community economies (SIA, page 55: fisheries). This concept was not referred to in the SMMP on the Section 7: institution arrangement to be function in strengthening livelihood development (SMMP, page 25-26).

There is main gap between concept of fishery resources in livelihood system (SIA page 52: 5.3.2) and genuine practice. It is not easy to change perception of users on fisheries resources from common resources to be communal resources. In addition, this conceptual strategy was not fully adopted and applied into SMMP for enhancing and sustaining wild fisheries resources.

Section 5.5.10 of SIA: Credit and Credit Training is not as a topic listed in Section 6.3.10 Livelihood Training and Awareness Raising of SMMP to support Section 6.3.12 Livelihood Development on e) Establishment of village development and revolving micro-credit funds (SIA, page 63 and SMMP, page 24-25).

The implementation schedule of SMMP (Figure 2, page 31) has no details on task of organization of training related to fisheries sector as remarked in Section 6.3.12 Livelihood Development, in addition, training on fisheries sector is not listed in the Table 4 budgets of SMMP (SMMP, page 34).

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2.3 The transboundary scale

The transboundary scale (arguably the most important for MRC purposes) refers to the impact that the project may have on nearby Cambodia and the other countries in the Mekong Basin.

According to the project preparation documents, the project, including the proposed mitigating measures, will not have a significant transboundary impact in terms of changes in hydrology, fisheries, environment etc. (that would lead to social impacts). As a consequence, the SIA does not assess social impacts in Cambodia and the other countries. Therefore, the project developer does not propose mitigating measures (or benefit sharing options).

The project preparation reports show that theoretically the negative transboundary impacts of the project can be mitigated and can make the Khone Falls fault less of an obstacle to the migrating fish (and the potential adverse impacts this would bring upstream and downstream)2.

However, the challenge has to do with oversight and compliance assurance of the proposed mitigating measures and with adaptive management based on good monitoring of a range of parameters. This is potentially important as the design, construction and management of some of the proposed mitigating measures will pose some technical and managerial challenges.

In this context, the following recommendations are made:

The project preparation reports would benefit from a more comprehensive discussion of the best ways and means for compliance assurance of the large range and variety of mitigating actions that are being proposed. There would be a role to play for MONRE (incl. LNMC) as well as for periodic independent audits during the construction and operational phases of the project.

Similarly, a joint Lao-Cambodia technical monitoring programme could be established with support from the MRC (this would become a transbounary cooperation project). The programme would monitor fisheries and improve fisheries management in the wider Khone Falls area. Given the decreasing numbers and proportions of big fish, and decreasing catch per unit effort, such a transboundary project should be a priority even if there is no hydropower project. To prevent misperception about the impact of the project, the Government must ensure that monitoring data are made available to the public.

2 It should be recalled that in the ‘without project’ situation, fish migration over the Khone Falls is also at risk. The developer’s reports (as well as MRC reports and other papers) suggest that the Hou Sahong and other channels are heavily fished and increasingly so. Population increases, and so do fish traps. Also the deep (dolphin) pool is heavily fished. As a result, papers on fisheries in the Khone Falls region describe decreasing numbers and proportions of big (late maturing) fish, and decreasing catch per unit effort.