WLW Day 1: Capacity Development on Climate Change Adaptation: Using the Decision Support System by E Hernandez

8/3/2019 WLW Day 1: Capacity Development on Climate Change Adaptation: Using the Decision Support System by E Hernandez

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Emiterio C. Hernandez, RCE

MScScProject Development, Management and Evaluation

DivisionLaguna Lake Development Authority

[email protected]



Meteorological forcing

Hydrology

Hydrology Waste loads

Waste loads

GIS

GISHydrodynamics

Hydrodynamics Water quality

Water quality

Provide predictive tools for assessment of

-Ecology

Ecology

,

environmental hazards, risk scenarios, etc

The LLDA Decision Support System The LLDA Decision Support System



LAGUNA DE BAY LAGUNA DE BAY



Flooding problems Flooding problems



Flooding problems Flooding problems



L A G U N A L A K E

MANGGAHAN

FLOODWAY

C A I N T A

Typhoon Ketsana (Ondoy) Sept 27, 2009



yp oon ar nae anOctober 31, 2009



Laguna Lake water level recordsLaguna Lake water level records



Modelling of Storm Surge…Modelling of Storm Surge…

Due to the large surface area of the lake and its shallow waters, it is possible to have a storm surge in Laguna Lake waters (e.g. periodic rise and fall of the water level created by the stormy wind, as in a typhoon event).



Modelling of Storm Surge…Modelling of Storm Surge…

Due to the large surface area of the lake and its shallow waters, it is possible to have a storm surge in Laguna Lake waters (e.g. periodic rise and fall of the water level created by the stormy wind, as in a typhoon event).



Storm surge event in Laguna Lake..Storm surge event in Laguna Lake..

Source: youtube.com



Assessment of infra developments Assessment of infra developments

’’

. aranaque p way. aranaque p way Assessment of infra develo ments Assessment of infra develo ments Open channel, affected by tidalOpen channel, affected by tidal

fluctuation;fluctuation;

==

impact on lake’s hydraulic regimesimpact on lake’s hydraulic regimes

Average depth = 2.50 m (at Average depth = 2.50 m (at

10.50 m lake level)10.50 m lake level)

w c cou ecrease ncrease e susce y

o lakeshore communities to the im act o Approximate length = 8 km Approximate length = 8 km

hazards)Using Delft3D Hydrodynamic

model of LLDA – DSS (SDLBE 2000 - 2003



Scenario SetScenario Set--upup

focusing on months of Sept to December wherefocusing on months of Sept to December where,, ..

Data for river discharges, evaporation, rainfall,Data for river discharges, evaporation, rainfall, w v y w v y

event.event.

A map showing the lake level variations and flow velocities with thespillway in operation.



Typhoon Santi Typhoon Santi Typhoon Pepeng Typhoon Pepeng

Without spillway Without spillway

Typhoon Typhoon Ondoy Ondoy

With spillway With spillway



From the model results:From the model results:

Using the assumed dimension of the spillway, theUsing the assumed dimension of the spillway, themodel predicts that the spillway may not be ablemodel predicts that the spillway may not be ableo preven e p ng up o a e wa er ur ngo preven e p ng up o a e wa er ur ng

storm events (when influx is much greater thanstorm events (when influx is much greater thanthe out flux).the out flux).

However, w ith appropriate operational rules the

water level built-up before the typhoons can be

water levels after the typhoons.

ur ng recess on o e oo , e sp way sur ng recess on o e oo , e sp way seffective in reducing the flood waters stored ineffective in reducing the flood waters stored inthe lake. Without spillway, lake level reduction isthe lake. Without spillway, lake level reduction is

. , .. , .month reduction in lake level is predicted withmonth reduction in lake level is predicted with

the spillway in place.the spillway in place.



Predicted Average Outflow Discharge:Predicted Average Outflow Discharge:

..

p way:p way:

Pasig River Outflow = 221.4 mPasig River Outflow = 221.4 m 33 / s / sParanaque Spil lway = 248.4 mParanaque Spil lway = 248.4 m 33 / s / s



Concluding Remarks:Concluding Remarks:

FeasibilityFeasibil ity of of spillw ayspillway optionsoptions (canal,(canal, tunnel)tunnel)needneed toto bebe studiedstudied iveniven thethe currentcurrent ro osedro osedlocationlocation;;

makemake useuse of of ex istingex isting know ledgeknow ledge onon thethefunctioningfunct ioning of of thethe waterwater systemsystem;;

TheThe spillwayspillway shouldshould bebe seenseen inin combinationcombinat ion w ithwithotherother measuresmeasures (improved(improved catchmentcatchmentmana ementmana ement;; creationcreation of of flood lainflood lain stora estora e inin

thethe Marik inaMarik ina catchment,catchment, dredgingdredging of of Pasig,Pasig,NapindanNapindan andand smallsmal l tributar ies,tr ibutaries, etcetc..))..




’’

. ort ern a es ore e. ort ern a es ore e





Water depth increases by some Water depth increases by some

8 cm during flooding event.8 cm during flooding event.

With dike

Without dike

Effect on water levels



Effect on water levels



Effect on water circulation




’’

.. ore anore an ec amat onec amat on



With reclamation

Sample Scenario: Predicted velocity

patterns w t an w t out s ore an

reclamation.

Without reclamation



Extent of Extent of ShorelandShoreland FloodingFlooding

2-yr flood

50-yr flood

100-yr flood



Climate Change ScenarioClimate Change Scenario

SCENARIO:SCENARIO: The MeanThe Mean

increases by 5 cm (dueincreases by 5 cm (due





Effect on Lake water levels….



Effect on Lake water levels….

Lake level increases by 2Lake level increases by 2 --3 cm as3 cm as

a result of a 5 cm sea level rise ina result of a 5 cm sea level rise in



Effect on Lake salinity intrusion….







Standard scenario…

with 5 cm Sea Level Rise…



ALONG RIVER BANKS ALONG RIVER BANKS



Balanac River (Pagsanjan)Balanac River (Pagsanjan)



Balanac River (Pagsanjan)Balanac River (Pagsanjan)



~6.5 m~6.5 m

There is a need to revisit existing hydrologic There is a need to revisit existing hydrologic

design parameters/standards to take intodesign parameters/standards to take intoaccount chan in climactic condition.account chan in climactic condition.



Typhoon Typhoon SantiSanti (Oct, 2009)(Oct, 2009)

BrgyBrgy CalliosCallios,, StaSta Cruz LagunaCruz Laguna



SOURCE: WWFSOURCE: WWF -- PhilippinesPhilippines



Rainfall versus ElevationRainfall versus Elevation

y = 5.0688x + 1864.3R² = 0.7701

Rainfall increases by some 500 mm/ yrw eac m opograp c r se.



watershed.



Floodplain ManagementFloodplain Management

Encroachment on floodplains (such as by artificial fil l material)- ,

streams, and increases flood hazard in areas beyond the

encroachment.




The 100-year floodplain is the standard most commonly used in the US formana ement and re ulator ur oses.

Based on Federal Emergency Management Agency (FEMA) of the UnitedStates, the 100-year flood is divided into a floodway and floodway fringe.




The floodway is the channel of a stream plus any adjacent floodplain-

year flood to be carried wi thout substantial increase in flood heights.




FEMA’s minimum standards allow an increase in flood height of 1.0foot (0.30 meter), provided that hazardous velocities are notproduced.

The floodway fringe is the portion of the floodplain that could be

completely obstructed w ithout increasing the water surface elevationof the 100-year flood by more than 1.0 foot (0.30 m) at any point.

l d l il d l i




Man ahan Man ahan Floodwa summer month Floodwa summer month

Fl d l i MFl d l i M




Man ahan Man ahan Floodwa rain season Floodwa rain season

Fl d l i MFl d l i M




. . . .The banks or rivers and streams and the shores of the seas andlakes throughout their entire length and w ithin a zone of three (3)

and forty (40) meters in forest areas, along their margins, aresubject to the easement of public use in the interest of recreation,navigation, flotage, fishing and salvage. No person shall beallowed to stay in this zone longer than what is necessary forrecreation, navigation, flotage, fishing or salvage or to buildstructures of any k ind.

C l i d R d iC l i d R d i



Conclusions and RecommendationsConclusions and Recommendations

Uncontro lled develo ments alon the shore landand riverbanks illustrates the lack of spatialplanning, enforcement and appreciation of the

.

Metro Manila is sink in : in the near future more protective works seem to be required (dikes,levees, polders, detention ponds)

C l i d R d iC l i d R d i



Conclusions and RecommendationsConclusions and Recommendations

In eneral: ive s ace to water create retentionbasins + protect floodplain areas)!

- requires spatial / environmental planning, enforcement and

Consider deepening of the Napindan River- reduction of high water levels and duration and hence creation of storage capacity (combination w ith NHCS can control water level during drought)

(Re-)consider other alternatives: Dredging of rivermouths creat ion of other stora e areas Marik inadam, detention basin) and optim ization of flood

control structures and reservoirs.



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WLW Day 1: Capacity Development on Climate Change Adaptation: Using the Decision Support System by E Hernandez