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Watershed Hydrology and Irrigation Water Management

A. Sarangi1, N. H. Rao2, P. B. S. Sarma1, Sheena M. Brownee1, A. K. Singh1
1Indian Agricultural Research Institute New Delhi-12, India
2NAARM, Hyderabad, India
Email: [email protected]    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.

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 geomorphological features of the watershed. The Banha watershed under Damoder Valley Corporation, Hazaribagh was digitised along with the available contours. The entire watershed was analysed in the PC ARC/INFO (ver 3.5) GIS domain. 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. The landuse information data was incorporated and landuse feature of the watershed was developed which is shown in figure 1. 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 (HRUs) 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 is shown in Fig 2. 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.

Table 1: The values of the dimensionless geomorphologic parameters

Sl. No. 
Dimensionless Geomorphologic Value
Average slope (%)
Relief Ratio
Relative relief
Elongation ratio
Basin shape factor
Form factor
Length width ratio
Circulatory ratio
Compactness coefficient
Drainage density
Stream frequency
Drainage factor

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.3 (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 IDs and attribute data was added on these IDs for each distributary.

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.

Fig 3: Patna Canal System (Water requirement at head)

The Future
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 irrigation management decision making is very crucial for both efficient water use and increased yield of crops, in which the GIS tool plays a significant role.

The output from the process based models can be displayed effectively within GIS environment and the information stored in a particular region will be handy for use. Linking the information obtainable from Remote Sensing Satellite Imageries, GIS assisted topographical analysis and process-based models for hydrological response of watersheds, the water availability and water demand scenarios can be developed on watershed basis.