Use of Geographic Information System (GIS) tool in watershed hydrology and irrigation...

Use of Geographic Information System (GIS) tool in watershed hydrology and irrigation water management

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A.Sarangi1, N.H. Rao2, Sheena M. Brownee1, A.K. Singh1
1IARI New Delhi
[email protected]

2NAARM, Hyderabad

Abstract
Watershed hydrology plays a significant role in generation and quantification of runoff and sediment loss from watersheds. With an aim to asses runoff and soil loss Geographic Information System (GIS) tool was used to assist in data base development which acted as input to a developed conceptual model (Small Watershed Runoff Generation Model, SWARGEM). The input to the model was in the form of data tables and digitised maps comprising of soil parameters, topological information and land use features of Banha watershed under Damodar Valley Corporation, Bihar, India. The topological information indicated the elevations of corners of square grid array. The model used 4-point pour-point technique to route surface flow from one grid to the other in an overlaid grid array of the Banha watershed. The digitised watershed topology and square grid array was created using ARC/INFO GIS tool (Version 3.5). Manning’s formulae was used to route water over the entire watershed coupled with water budgeting technique corresponding to rainfall events. The out put of the model generated event based Direct Runoff Hydrographs(DRH) for the watershed. The non-parametric statistical analysis (Wilcoxon’s matched pair signed rank test) performed on the predicted value and observed runoff rate at the oulet of the watershed revealed that there is no significant difference between the observed and predicted values at 0.05 probability level. The topological information extracted using GIS was also used to obtain the geomorphological parameters of the watershed. The hypsometric analysis which is under geologic geomorphological component was performed using GIS tool. The analysis showed the erosion status of watershed, which is moderately prone to erosion and is at equlibrium stage.

Irrigation management is a key to efficient and timely water distribution in canal command areas keeping in view the crop factors. GIS tool was used to develop a canal irrigation scheduling in form of a water indent for irrigation requirement at head of the distributary for the next irrigation. Using the ARC/INFO GIS tool the map of Patna canal system within the project area and distributaries of Sone command, Bihar state, India was digitised. Relevant design data viz. Soil information, monsoon rainfall and ground water potential were also digitised for each district within the project area. The attribute data was added resulting in the creation of polygon attribute tables (PAT). The topology was built and Arc Attribute Tables(AAT) were created. Main canals and their distributaries were assigned different ID’s and attribute data was added on these ID’s for each distributary. Following simillar sequence final coverages were developed for the canal network. 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 was predicted. The GIS of the Patna canal system, component of the command area and the rice water balance model have been dynamically linked. This linkage predicts 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.

Introduction:
Advances in the field of data interpretation and analysis have necessitated the use of powerful tools within the computer environment. The set of tools applicable to the geographical ?data constitutes the Geographic Information System (GIS). GIS is a software and hardware tool applied to geographical data for integration of collection, storing, retrieving, transforming and displaying spatial data for solving complex planning and management problems. This tool (software and hardware) has made the data handling and analysis much easier with meaningful research outcomes. GIS has the advantage of handling attribute data in conjunction with spatial features, which was totally impossible with manual cartographic analysis. It stores both spatial and non?spatial data layer by layer either in raster or vector format. The linking of modelling concepts with the GIS domain is proved useful in development of a Decision Support System (DSS) and expert system based on heuristic logic. This tool makes the data?handling job easier and meaningful. It is more versatile for analysing a large data base and large areal extent. GIS facilitates repetitive model application with considerable ease and accuracy.

Use of GIS in watershed hydrology
GIS was used in development of input data set for a conceptual small watershed runoff generation model (SWARGEM) which takes into consideration of the geornorphological features of the watershed. The entire watershed was analysed in the PC ARC/INFO (ver 3.5) GIS domain. The Banha watershed under Damoder Valley Corporation, Hazaribagh was digitised along with the available contours. In order to route the surface flow to the outlet of the watershed, the watershed was discretised to square grid arrays and the elevation of the corner points were noted using the GIS tool (Shown in Fig. 1). The landuse information data was incorporated and landuse feature of the watershed was developed, which is shown in figure 2. Hypsometric analysis of the said watershed was performed to ascertain the erosion status of the watershed. The parameters for the analysis was obtained using the capabilities of GIS tool and is displayed in Table 1. The calculation of area of watershed, length of arc and elevation of point becomes handy within the GIS environment. If done manually, the same process becomes cumbersome and human error is involved. This tool was used for development of Hydrologic Response Units (HRU’s) which indicates the composite geographic parameter having same hydrologic response. This is achieved by overlaying the soil map, landuse map infiltration rate data and other pertinent information required for producing same hydrologic response from the watershed. The input parameters generated through the use of GIS is linked with the runoff generation model, which gives the output in form of runoff rate from event base rainfall . The observed and predicted Direct Runoff Hydrograph (DRH) obtained for different rainfall events. The model validation was subjected to statistical test and the result satisfied the hypothesis that there is no significant difference between the observed and predicted values of runoff rate at 0.05 level of significance.

Use of GIS in irrigation management
The digitised map of Canal system within the project area displaying the various main/branch canal network of Patna Canal and distributaries of Sone command is shown in Fig. ( ARC/INFO GIS ver 3.5 is used). Relevant design data obtained from different sources viz. Soil information, monsoon rainfall and ground water potential were also digitised for each district within the project area. The attribute data was added resulting in the creation of polygon attribute tables (PAT). The topology was built and Arc Attribute Tables(AAT) were created. Main canals and their distributaries were assigned different ID’s and attribute data was added on these ID’s for each distributary. rocess final coverages were developed for the canal network.
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.