NIH_Basin – A WINDOWS Based Model for Water Resources Assessment in a River Basin

Abstract

A detailed spatially distributed model has been developed at NIH to assess various components of hydrological cycle in a river basin. The model incorporates spatial variation of land-use, soil type, rainfall, evapo-transpiration, physiographic characteristics, cropping pattern, irrigation development, groundwater conditions, river network and hydraulic structures in a river basin. GIS is employed to link the spatial data with the simulation model and to project model results in map form. The model is under continuous development. In the present report, an effort has been made to make some modifications in the model methodology and develop a WINDOWS interface (named as NIH_Basin – NIH_Basin-Simulation) of the model for easy application by the user groups. For approximating the EAC relationships for a reservoir, the approach developed by J. Mohammadzadeh-Habili et. al (2009) has been adopted. The method has been programmed and linked to river basin model for computation of EAC table for a reservoir. This method avoids the necessity of obtaining EAC tables for various reservoirs in the river basin. The basin model has been modified to include rule curve based operation for the storage reservoirs so that control on basin water resources utilization can be analyzed and water management issues can be addressed. The option of hydropower simulation of a reservoir has also been added. An important modification of the current study is the simpler representation of GW system for long-term simulation. The revised model can now work in two modes: a) monthly mode (in which the simulation is carried out at daily time step for a month and then the spatial recharge and discharge pattern are externally used to find the revised water table in the basin with groundwater simulation model, say Visual MODFLOW, and the revised groundwater table is used for the analysis in subsequent month), and b) continuous mode (in which the simulation is carried out at daily time step for the complete period, say for 30 years of record, for which hydro-meteorological data are available). In the second case, a simplified methodology to represent GW conditions has been adopted. For each sub-basin, average groundwater elevation is computed from data of a large number of observation wells. A procedure, defined by DHI, Denmark in DSS under HP-II has been adopted for computing average GW elevation in a subbasin from irregular groundwater depth observations in different wells. A FORTRAN program has been developed for the purpose and added in the WINDOWS interface. In addition, a number of modifications have been adopted some of which include: increase in number of landuse classes from 6 to 61 and increase in number of dimensions of other variables for model application to a large river basin, separate consideration of industrial demands, inclusion of date of commissioning of projects in long-term simulation so that their effects are considered only after their occurrence, consideration of variable GW development, variable human and cattle population etc. In WINDOWS interface of the model, various data input forms have been developed for easy preparation of data files by the user groups. Four important modules of the software include: a) Database preparation, b) GIS analysis, c) Model execution, and d) Results. Now, it is planned to apply the modified model to a large basin and develop the User’s Manual for effective technology transfer to large group of users.