Lessons learned from the Vietnamese Mekong Delta

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Lessons learned from the Vietnamese Mekong Delta With ‘Delta Plans’ already developed and starting to be implemented in countries like Vietnam and Bangladesh, lessons learned and adopted measures can be a useful contribution to the development of the Integrated Ayeyarwady Delta Strategy (IADS). Several lessons learned from the Mekong Delta will be summarised which should provoke some thought about the sustainability and wisdom of certain types of development measures and policies. The reader will keep in mind that deltas are unique systems with several comparable characteristics, but also differences in both physical and temporal developments. The Vietnamese Mekong Delta is at a much further stage of development in comparison to the Ayeyarwady. The economic reforms which began in 1986 have had a major influence on the socio-economic development of the delta. Policies that unshackled farmers and markets, together with new investment policies, resulted in more efficient production systems including investments to improve water infrastructure, particularly for irrigation development. Investments in high flood-control dykes and salinity-control projects in coastal areas have greatly enlarged cropping areas. Once the infrastructure was put in place, technological developments have then played a key role in increasing production. For example, although already available in the 1970s, high yield rice varieties only started to be effectively used after improvements in irrigation, drainage and flood control were implemented on a large scale.

These improvements in water management, the implementation of technical advances and policy reforms supported the delta’s rice production. Moreover, the Delta functions as source for the food security of the country for not only rice but also fruit and aquaculture products. Over the last two decades following the national trend, the economic structure of the delta has been changing with a growing industrial and services sector. However, natural and anthropogenic changes are placing significant development pressures on the Delta together with the internal delta developments where intensified production has taken a toll on the natural resources and environments of the Delta, thereby undermining the Delta’s resilience and increasing its vulnerabilities to climate change. Mekong Delta Plan In this context of declining resilience, Dutch support was provided between 2011 and 2013 to the Vietnamese government to develop a strategic vision for the Delta. While having a common heritage of Dutch expertise and experience, the methodology of the MDP which was completed in Dec 2013 is not directly comparable to the IADS. However, they do share a common vision: ‘A Safe, Prosperous and Sustainable Future’. And a similar approach of ‘backcasting’ was used.

Figure 1: The Vietnamese Mekong Delta (RFA, 2016)

Mekong Delta Facts Population: 17.5 million (19% Vietnam), 431 person/km2, 75% rural (2012) GDP: 980 US$/year, national average 1050 US$ (2012) Production: Rice dominated economy, 50% national rice production / 1976: 4.5 Mt –> 2012: 24.6 Mt (8 Mt export) / 70% of national aquaculture production Land-use: 64.3% agricultural lands, 7.4% forest (GSO, 2014)

Lessons learned from the Vietnamese Mekong Delta

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Figure 2: Backcasting methodology Mekong Delta Plan (MDP, 2013) The objective here is not to compare the methodology, but rather to present the type of measures that were identified in the MDP, and key priority no-regret measures that are currently being funded in order to restore some of the lost resilience and vulnerabilities that are summarised in the following lessons. Lesson 1. Displacing floods by poldering transfers the flood risk elsewhere Over the last couple of decades, the upper delta has been losing its flood absorption function. In particular, polder construction with high dykes (>2m) between 2000 and 2011 for rice intensification has resulted in the reduction of the total flood storage to half its original state, from 9.2 billion m3 to 4.7 billion m3 (ICEM, 2015). This floodplain loss has led to an increased downstream flood risk, which is compounded by sea level rise and subsidence (Triet et al, 2017). The last extreme flood in 2011 increased the flood areas by 1/3 that of the last extreme flood in 2000 when river flows were higher (Triet et al, 2017; ICEM, 2015). Polder failures and increased downstream flood damage were the result. For example, the downstream city of Can Tho incurred an additional US$ 3 million to US$ 11 million in flood damages (ICEM, 2015).

Figure 3: Floodplain loss from the third rice crop. A view from the Vietnamese-Cambodian border in An Giang province.

Figure 4: Flooding in downstream Can Tho City during the 2011 flood. Lesson 2. Floodplain loss has economic costs that are not always visible and can lead to growing inequality The loss of half the floodplain to poldering in the upper delta between 2000 and 2011 also represents an equivalent loss of 1500 km2 of habitat and breeding areas for aquatic organisms and the fresh-water fisheries. This in turn increased fishing pressure as fish become constrained to smaller areas within canals where they are easily fished or trapped. In the same decade, the economic loss in the fishery has been estimated to be US$1,000/ha (Dan, 2015). This economic loss impacts the poor the most since they are heavily reliant on natural resource base for their livelihoods. The decline in the fishery is a contributing factor to the growing inequality gap in the Mekong Delta (Triet et al, 2014), where income disparity between the rich and poorest has grown by 14% in the last decade (GSO, 2014). Figure 5: A farmer setting a lift-net on a canal where fish are easily trapped.

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Figure 6: Fish traps lining canals outside polders. Lesson 3. Inappropriate land-use and poor water-sediment management leads to subsidence and can significantly compound and more than double actual sea-level rise Increasing land subsidence is compromising the ability of the delta to respond to sea level rise of 3-5 mm/year. InSAR data suggest rates of 1 cm/yr. in the upper delta, and 2 to 4 cm in coastal areas (Erban et al, 2014). Modelled subsidence rates derived from aquifer drawdown data confirm these magnitudes and suggest a 25-year cumulative subsidence of 25 to 50 cm in the coastal delta (Minderhoud et al, 2017). In the upper delta, subsidence is a combination of sediment exclusion from poldering, and flood drainage driven compaction (Chapman et al, 2017). In the coastal delta, groundwater pumping to dilute salinity on shrimp farms and to irrigate horticulture is a major cause of subsidence (MDP, 2013; Erban et al, 2014).

Figure 7: Groundwater pumping for horticulture and diluting salinity in mono-shrimp farms (MDP, 2013).

Figure 8: Modelled subsidence rates derived from groundwater extraction data (Minderhoud, et al, 2017).

Lesson 4. Permanent coastal dykes will result in a coastal squeeze that will lead to the total loss of coastal-protection mangroves Over the last 150 years of human development in the Mekong Delta, first rice growing followed by shrimp farming has moved into the coastal zone along most of the Delta’s coastline. This has resulted in large-scale-mangrove clearance. As a result, the shoreline and coastal dykes are extremely vulnerable to erosion, storm damage, and overtopping by storm surges. Maximum erosion rates are now in the order of 50 t0 60 m/yr (Anthony et al, 2015). The coastal Delta is extremely vulnerable to storm surges because much of its elevation is less than +0.5m MSL, and along large sections of coastline the coastal mangrove width is less than 500 m in front of the coastal dyke where mangroves serve to protect the coastal dykes by reducing the wave energy. Wave heights can be reduced by between 13 and 66% for every 100 m of mangroves (McIvor et al, 2012). Sea level rise driven ‘coastal squeeze’ is already stripping away the dyke-protection mangroves in the Delta leaving the coastal dykes entirely unprotected, and inland areas with no forest cover are particularly vulnerable.

Figure 9: The coastal squeeze (Coastal Wiki)

Figure 10: Coastal squeeze exposing the coastal dyke to erosion, Soc Trang Province. Note the highly exposed high-value aquaculture behind the dyke with little protection from storm surges.

Lessons learned from the Vietnamese Mekong Delta

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Implementing the Mekong Delta Plan with No Regret In July 2016, the World Bank approved the US$310 million Integrated Climate Resilience and Sustainable Livelihoods project to implement 10 no-regret sub-projects consisting of measures identified in the MDP. Governance measures are also being implemented including a new long-term integrated investment masterplan, and research data sharing initiatives for the Mekong Delta.

References Anthony E.J., Brunier G., Besset M., Goichot M., Dussouillez P., Nguyen V.L. 2015. Linking rapid erosion of the Mekong River delta to human activities. Scientific Reports, 5:14745

Chapman A., Darby S., Tompkins E., Hackney C., Leyland J., Van P.D.T., Pham T.V., Parsons D., Aalto R., Nicholas A. 2017. Sustainable rice cultivation in the deep flooded zones of the Vietnamese Mekong Delta, Vietnam Science and Technology, June 2017, Vol. 59, No. 2.

Dan, T. Y. 2015. A Cost-Benefit Analysis of Dike Heightening in the Mekong Delta. EEPSEA Research Report 2015-RR11.

Erban L., Gorelick S., Zebker H. 2014. Groundwater extraction, land subsidence, and sea-level rise in the Mekong Delta, Vietnam. Environmental Research Letters, 9.

General Statistics Office of Vietnam (GSO). 2014. Hanoi, Vietnam.

International Centre for Environmental Management (ICEM). 2015. A Guide to Resilient Decision Making in the Mekong Delta. World Bank, Vietnam.

McIvor, A.L., Möller, I., Spencer, T. and Spalding, M. 2012. Reduction of wind and swell waves by mangroves. Natural Coastal Protection Series: Report 1. Cambridge Coastal Research Unit Working Paper 40. Published by The Nature Conservancy and Wetlands International. 27 pages.

Mekong Delta Plan (MDP). 2013.

Minderhoud P.S.J., Erkens G., Pham V.H., Bui V.T., Erban L., Kooi H., Stouthamer E. 2017. Impacts of 25 years of groundwater extraction on subsidence in the Mekong delta, Vietnam. Environmental Research Letters, 12, (2017)

Nguyen T.H., Vo T.D., Tran T.A. 2014. Impacts of sediment and wild fish to An Giang’s household livelihood in the Mekong Delta of Vietnam, World Congress on Advances in Civil, Environmental, and Materials Research (ACEM14), Busan, Korea, August 24-28, 2014

Triet N.V.K, Dung N.V., Fujii H., Kummu M., Merz B., Apel H. 2017. Has dyke development in the Vietnamese Mekong Delta shifted flood hazard downstream? Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-123, 2017, Manuscript under review for journal Hydrol. Earth Syst. Sci.

MDPMeasure1:Controlledflooding

MDPMeasure6:Dual-zonecoastalmanagement

SP1, SP2: Managing Floods in the Upper Delta (MDP measure 1) Phased 40,000 ha of flood retention area and investments in flood-based agriculture (floating rice, rice-aquaculture) facilitated by new and upgraded low dykes and sluices to control flood entry and recession. Intensive rice plans phased out. Flood hazard reduction objectives.

SP3 - Managing Floods in the Upper Delta (MDP measure 1) Phased 30,000 ha of flood retention area and investments in flood-based agriculture rice-aquaculture facilitated by upgraded low dykes and sluices to control flood entry and recession. Intensive rice plans phased out. Flood hazard reduction objectives.

SP5, SP7, SP9 - Adapting to Salinity (MDP measures 6, 7, 8) Opening up coastal salinity-control sluices in dry season and transitioning from mono-rice and sugarcane to sustainable shrimp. Combined with coastal enhancement of mangroves, wave-breakers for shoreline protection (SP9), and flood control sluices in areas affected by spring tides.

SP8, SP6, SP4 – Protecting Coastal Areas (MDP measure 6) Phased upscaling from 5,000 to 60,000 ha of organically certified Integrated Mangrove Shrimp farms. Supported by capacity building for farmers and private shrimp processors. Coastal zone protection and livelihood objectives.

Upper-Middle Delta: Flood based agriculture and flood relief measures 1 2050

“no-regret” Controlled Flooding. Flood-based agricultural production systems (flood water retention, diversification of fish and vegetables) to induce sedimentation.

2 2050 in case of no controlled flooding

Flood protection: local urban and rural in combination with room for river.

3 2100 2050 in case of no controlled flooding

Major Flood Diversion. Spatial planning reservation for Major Flood Diversion.

Middle Delta: Industrial, urban and rural flood safety, secure fresh water supply 4 2050

2100

Radical shift from groundwater supply to supply from surface water to prevent land subsidence. Bassac/Hau-Mekong/Tien River Link. Spatial planning reservation for Link Canal.

5 2100 (under extreme climate change and extreme reduction of river flows)

Flow control of fresh and salt water in the estuaries during the dry season.

Coastal Zone: Brackish water economy and advanced coastal protection 6 2050

"no-regret" Dual Zone Coastal Management. Brackish economy and dynamic shorelines. Modernisation and increased sustainability of aquaculture by adopting (mangrove) poly-culture based systems aligned with mangrove regeneration in the outer coastline. Mangrove regeneration and sedimentation along outer coast line as reinforcement of sea-shore.

7 2050 "priority" and

"no-regret" 2100

Fresh water management along the coast. Combatting land subsidence, by a) halting groundwater depletion and b) foster a brackish-aquatic environment. Use groundwater for drinking water alone. Local fresh water harvesting and storage in sandy areas for limited high-value agricultural use and diversification. Investment in saline high-value agriculture (derivatives for food, cosmetic, medicine and energy) based on salt tolerant crops, sea-weeds and algae. In the short-term investment in Research and Development.

8 2050

2100

Reinforcement of coastal defence. For non-Dual Zone Coastal Management areas, sea-defence structures (dykes) need to be revamped to keep up with sea level rise. Especially north-west coast, and Eastern Delta (Mekong Branch). The routing of the dykes needs to be in line with Dual Zone Coastal Management. Unlinking road system from dyke system. Flexibility in dyke trajectories is required to allow for natural cost effective coastal flood defence strategies. The road function impedes the flexibility for the dyke. Under extreme sea level rise, coastal defence system is upgraded to accommodate rising flood risks. This includes reinforcement of inner protection dykes.

Overall measures 9 “no- regret” Water transport. Facilitation of industrialisation and bulk transport by development of

harbour facilities in a well- designed scheme. 10 “no- regret” Research and investigation programme. 11 "priority" Integrated Governance and Planning. Risks of irreversible non-optimal developments (e.g.

Corridor Industrialisation) and negative cost-effect impacts of uncoordinated measures (e.g. urban flood protection and controlled flooding) need to be confronted.

12 "priority", "no- regret" mid-term

Well balanced foreign policy with upstream countries in order to manage the impact of upstream developments for the lower Mekong.