Application of a Distributed hydrological Model (IISDHM) for Northern Chao Phraya Basin, Thailand

Abstract

Physically based distributed catchment models enable simulation of catchment hydrology based on the physical properties of locality and the governing equations for different hydrological processes. Their complexity and large computational and data requirements prevented them from being applied to large catchments. However, it is necessary to apply such models at regional levels for the realization of realistic coupled systems capable of simulating atmospheric-land interaction. The rapid growth of computational power and the availability of regional level data are now making such applications possible.

In the present study we have developed a distributed dydrologic model termed "Institute of Industrial Science Distributed Hydrological mathematical Model (IISDHM) for such simulations. This model consists mainly of, interception, evaporation, surface flow subsurface flow and ground water flow components. The potential evapotranspiration, which is directly input to the model is divided into two components, potential evaporation and potential transpiration and depending upon the landuse classes and soil moisture availability, actual transpiration and actual evaporation are calculated by Kristensen and Jensen model. The surface flow is generated the rainfall exceeds the infiltration capacity of the soil or ground water level reaches to the surface level. The surface flow is routed by diffusion approximation of St. Venants equation which supply lateral flow to the river nodes. The river flow is routed by either kinematic or dynamic form of St. Venant's equation. The subsurface flow is routed by three dimensional Richard's equation for all layers below ground level, up to the ground water level. The ground water flow is treated as multi layered semi three dimensional flow, where each layer could be either homogeneous or heterogeneous aquifer and modeled by Boussinesq equation. GIS is used for pre-processing of input data and post-processing of results. An interactive software has been developed to facilitate data input.

The IISDHM is applied in Ping river basin, a sub-catchment of Chao Phraya river basin, Thailand, which is a target catchment in GAME-Tropics. The sub catchment is located to the north of Chiang Mai city and has a catchment area of 6300 sq.km. A GIS of 1 km mesh consisting of Digital Elevation Model, land use and soil was made, consisting of data collected from different sources. The river network was generated from the DEM. Thiessen polygons were used to distribut the rainfall from 8 gauges over the catchment. Available hourly rainfall records were used to distribute the daily rainfall data where hourly observations are not available.

The model works well in the Ping river basin. Hourly simulation from Jun. 1992 to Mar 1993 were carried out and the simulation results show good agreement with observed.