Transcript - UNDP-ALM

Hydrological Modeling for Upper Chao
Phraya Basin Using HEC-HMS
UNDP/ADAPT Asia-Pacific First Regional Training Workshop
Assessing Costs and Benefits of Adaptation: Methods and Data
March 11-14, 2013
Dr. Dilip K. Gautam
RIMES, AIT Campus, Bangkok
Hydrological Model
 A 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 melt
 Interception, infiltration, soil moisture accounting
 Evapotranspiration
 Regulated 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 Model
 Runoff 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 Required
 Digital Elevation Model (DEM), land use, soil
types and other physiographic data
 Precipitation, temperature data
 Evaporation/evapotranspiration data
 Discharge, Water level and Rating curve data
 Channel and reservoir hydraulic data
 Generated sequence of meteorological data
representing various scenarios of future climate
Upper Chao
Phraya Basin,
Thailand
Catchment Area
= 105553 sq. km.
Dams and Reservoirs
 Bhumibol 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-GeoHMS
 Delineate catchment and river network
 Obtain catchment characteristics data (area, slope etc)
 Make Thiessen polygon
 Obtain Thiessen weights
 Prepare basin file
Data preparation using HEC-DSSVue
 Time series data (rainfall, discharge etc.)
 Pair data (elevation-storage)
Model Setup
 Basin model
 Meteorological model
 Time series data
 Pair data
 Control specification
Meteorologic model
 Precipitation
 Evapotranspiration
 Snowmelt : not applicable for upper Chao Phraya
Precipitation methods
 Gauge weights : selected for upper Chao Phraya
 Inverse distance
 Gridded precipitation
 Frequency storm
 SCS storm
 Specified Hyetograph
 Standard project storm
Evapotranspiration methods
 Monthly Average : selected for upper Chao Phraya
 Priestley-Taylor
 Gridded Priestley-Taylor
Snowmelt methods
 Gridded temperature index
 Temperature index
Control Specifications
 Simulation start date/time
 Simulation end date/time
 Time interval
Model Calibration
 Finding optimal parameter values
 Minimizing difference between simulated flow
and observed flow
 Objective functions
 Peak weighted RMS error
 Percent error peak
 Percent error volume
 RMS log error
 Sum of absolute residuals
 Sum of squared residuals
 Time weighted error
Search Algorithms
 Nelder Mead
 Univariate Gradient
The Basin Model
Simulated Hydrograph at Basin Outlet
R2 = 0.71
BIAS = 6.7 %
NS = 0.71
Conclusions
 Semi-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, RIMES
E-mail: [email protected]
Website: www.rimes.int