A set of modular soil water balance models for rice and other crops and canal flow models, developed and tested in earlier studies were adopted for use in the Sone project area. From the soil water balance model, information on scheduling (depth and timings) of crops is derived and the canal flow model helps account for seepage losses. Based on this the biweekly irrigation requirement at the head of each distributary can be derived. The GIS of the Patna canal system component of the command area and the rice water balance model have been dynamically linked. This linkage facilitates:
- Selection of the distributary of interest from the canal network GIS,
- Running the rice field water balance model in real time up to current date in any year after entering the date in response to screen queries,
- Preparing a report of the current water status in rice fields in the command area of the distributary transplanted on up to five different dates, and
- Preparing a water indent for the irrigation
requirements at the head of the distributary for the next 14 days of the
irrigation cycle after accounting for conveyance losses.
Individual distributaries can be selected at random from the GIS and reports of water status in fields and indents for water for the next irrigation cycle on any given date can be prepared.
GIS for spatial distribution of recharge: The spatial distribution of recharge for variable weather, soil, landuse and water supply conditions over the command area of an irrigation project was assessed using GIS. Field data of Godavari Delta Central Canal Irrigation Project In Andhra Pradesh were used as a case study to develop the procedures (Chowdary et al, 1997a). Rice is the dominant crop grown in this project area. Daily data of 7 raingauge stations, discharges in 4 main canals, soil and command area maps, groundwater structures in each block/mandal were available. The soil map, raingauge thiessen polygons, command area map and the block map were digitized to obtain the respective coverages using PC ARC/INFO (ver 3.4.2). By performing overlay operations sequentially with all the 4 coverages a fifth coverage was obtained. The very small polygons of this coverage were edited to merge with the adjacent large polygons. Each polygon of this coverage is homogeneous with respect to the soil parameters and the daily rainfall and water supply data input to the soil water balance model. The polygons of the newly derived coverage are designated as basic simulation units. A total of 39 such basic simulation units were obtained for the command area of the Godavari Delta Central Canal Project.
Seepage losses were assessed by using rating curves of canal discharges vs seepage losses derived from a simple model of canal flows developed in earlier studies. A generalized daily soil water balance model was developed to estimate the percolation losses for all crops. The model includes a separate subroutine for rice, which is grown under flooded conditions and under a distinct water management regime. The daily soil water balance model was run for each unit to obtain the annual percolation losses from various fields. The coupling between the GIS and model was achieved by developing suitable preprocessors for linking the input and output routines of the soil water balance model . The percolation losses and seepage losses were added to obtain the total annual recharge and displayed on the GIS. To validate the recharge rates derived from GIS, a finite element grid was overlaid on the recharge GIS. The recharge at each node was input to a groundwater basin simulation model. The groundwater pumping was distributed among the nodes by adopting a set of heuristic guidelines for deriving pumping distribution coefff6ients. The groundwater levels predicted by the model were close to the observed levels at the end of the year.
GIS of Nitrate Pollutant Loads to Groundwater: Nitrate losses from fertilizer applications vary spatially and in time with weather, soil, and water supply conditions over the command area of an irrigation project. The coupled soil water balance?nitrogen balance model developed was used to assess spatially and temporally varying nitrate pollutant loads from rice fields over the Central Godavari Delta Canal Project area using GIS (Chowdary et al,1997b). Urea is the main fertilizer. Daily data of 7 raingauge stations, discharges in 4 main canals, soil and command area maps, groundwater structures in each block of the project used above for estimating recharge were also used to estimate the nitrate loads to groundwater.
The same 39 basic simulation units derived for the command area of the Godavari Delta Central Canal Project were applicable in this study also. The coupled daily soil
water balance ? nitrogen balance model was run for each unit to obtain the annual percolation and nitrate leaching losses from various fields. The link between the GIS and model was achieved by modifying the input and output routines of the model. The annual nitrate loads in leached water were displayed on the GIS. The pollutant loads were input to a finite element groundwater transport assess the nitrate concentrations in groundwater at the end of each season. The estimated pollutant loads and the transport model were validated by compared data of nitrate concentrations in wells at the end of monsoon season 1995
Development of realtime irrigation management decision support system: This is being developed for the Sone Irrigation Project in Bihar. A GIS of the Canal of the project area displaying the various main/branch canals and distributaries has been developed. A set of modular soil water balance models for rice and other crops and canal flow models, developed and tested in earlier studies were adopted for use in the Sone project area. From the soil water balance model, information on scheduling (depth and timings) of crops is derived and the canal flow model helps account for seepage losses. Based on this the biweekly irrigation requirement at the head of each distributary can be derived. The GIS of the Patna canal system component of the command area and the rice water balance model have been dynamically linked. This linkage facilitates:
- Selection of the distributary of interest from the canal network GIS,
- Running the rice field water balance model in real time up to current date in any year after entering the date in response to screen queries,
- Preparing a report of the current water status in rice fields in the command area of the distributary transplanted on up to five different dates, and
- Preparing a water indent for the irrigation
requirements at the head of the distributary for the next 14 days of the
irrigation cycle after accounting for conveyance losses.
Individual distributaries can be selected at random from the GIS and reports of water status in fields and indents for water for the next irrigation cycle on any given date can be prepared.
GIS assisted research under progress:
The cartographic and data overlaying capability of GIS coupled with its dynamic linking ability with models plays a vital role in water management decision making process. It is also useful in preparing the processed data bases pertaining to watershed geomorphology as an input to runoff and sediment yield models. The model output can be displayed effectively and the information stored in a particular region will be handy for use. Recently the GIS is being used for development of input data set to be used in rice wheat cropping system models. In order to use the hydrologic soil groups of India for runoff prediction using Curve number method, the hydrologic soil group map of India being prepared using the capability of Arc-view GIS tool.