Hydrological Modeling for Upper Chao Phraya Basin Using HEC-HMS
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Hydrological Modeling for Upper Chao Phraya Basin Using HEC-HMS
UNDP/ADAPT Asia-Pacific First Regional Training WorkshopAssessing Costs and Benefits of Adaptation: Methods and Data
March 11-14, 2013
Dr. Dilip K. GautamRIMES, AIT Campus, Bangkok
Hydrological ModelA model is a simplified representation of reality.
A mathematical model consists of series of equations defining the system we are dealing with. The function of model is to convert the given input into an output.
A hydrological model is the mathematical representation of the response of a catchment system to hydrologic events during the time period under consideration.
Hydrological phenomena are extremely complex, highly non-linear and highly variable in space and time.
A model is needed to predict the watershed runoff for the design and management of water resources utilization and flood control projects.
Classification of Hydrological Models
Hydrological Model Outputs for Climate Change Impact Assessment
Simulated flow peaks, volumes and hydrographs at the outlets of subbasins and the points of special interest such as reservoirs, weirs or other hydraulic structures
Simulated long flow sequences for water budget and drought analyses
Simulated extent of flooded areas for different precipitation events and various antecedent basin conditions
Hydrologic processes that need to be captured by the model
Single-event precipitation-runoff transformation
Continuous precipitation-runoff transformation
Snow accumulation and meltInterception, infiltration, soil moisture
accountingEvapotranspirationRegulated reservoir operation
HEC-HMS• US Army Corps of Engineers, Hydrologic Engineering
Center’s Hydrologic Modeling System software
• Designed to simulate both single event and continuous rainfall-runoff process
• Simulates precipitation-runoff and routing processes, both natural and controlled
• HEC-HMS uses a separate model to represent each component of the runoff process including:runoff volume;direct runoff (overland flow and interflow);baseflow;channel routing.
HEC-HMS representation of watershed runoff
Key Components of ModelRunoff Volume models: separate infiltration from
pervious surface, runoff from impervious surface, compute the direct runoff volume
Direct Runoff models: transform direct runoff volume from excess precipitation into fast component of flow
Base Flow models: compute slow subsurface drainage component
Routing models: compute flow attenuation and translation over channel
Reservoir models: flow regulation
Data RequiredDigital Elevation Model (DEM), land use, soil
types and other physiographic dataPrecipitation, temperature dataEvaporation/evapotranspiration data Discharge, Water level and Rating curve dataChannel and reservoir hydraulic dataGenerated sequence of meteorological data
representing various scenarios of future climate
Upper Chao Phraya Basin,
ThailandCatchment Area = 105553 sq. km.
Dams and ReservoirsBhumibol dam in the Ping River (Storage 13462
MCM)Sirikit dam in the Nan River (Storage 9510
MCM)Kwae Noi dam in Kwae Noi River (Storage 766
MCM)Kiew Kor Mha dam in Wang River (Storage 171
MCM)Kiew Lom dam in Wang River (Storage 112
MCM)
Data preparation using HEC-GeoHMSDelineate catchment and river networkObtain catchment characteristics data (area,
slope etc)Make Thiessen polygonObtain Thiessen weightsPrepare basin file
Data preparation using HEC-DSSVueTime series data (rainfall, discharge etc.)Pair data (elevation-storage)
Model SetupBasin modelMeteorological modelTime series dataPair dataControl specification
Meteorologic modelPrecipitationEvapotranspirationSnowmelt : not applicable for upper Chao
Phraya
Precipitation methodsGauge weights : selected for upper Chao
PhrayaInverse distanceGridded precipitationFrequency stormSCS stormSpecified HyetographStandard project storm
Evapotranspiration methodsMonthly Average : selected for upper Chao
PhrayaPriestley-TaylorGridded Priestley-Taylor
Snowmelt methodsGridded temperature indexTemperature index
Control SpecificationsSimulation start date/timeSimulation end date/timeTime interval
Model CalibrationFinding optimal parameter valuesMinimizing difference between
simulated flow and observed flowObjective functions
Peak weighted RMS errorPercent error peakPercent error volumeRMS log errorSum of absolute residualsSum of squared residualsTime weighted error
Search AlgorithmsNelder MeadUnivariate Gradient
The Basin Model
Simulated Hydrograph at Basin OutletR2 = 0.71 BIAS = 6.7 % NS = 0.71
ConclusionsSemi-distributed physically based
deterministic hydrological models are powerful tools for assessing climate change impact on water resources.
Continuous modeling approach could be taken to assess the impact on flow volume.
Care should be taken to interpret the results as there are lots of uncertainties in the model inputs, parameters and structure of the model. Uncertainties associated with climate models will also be carried over.
Thank You !
Dr. Dilip K. Gautam, Senior Hydrologist, RIMESE-mail: [email protected]
Website: www.rimes.int