Rajashree V Bothale, Vinod M Bothale, G Srinivasan and J R Sharma
Regional Remote Sensing Service Centre, ISRO,
Department of Space, Jodhpur
Phone 91 0291 – 740004,
Fax – 741516,
Email : [email protected]
Present study uses decision support system “WARIS” for identification of suitable sites for water harvesting structures. The study has been conducted for upper Betwa watershed of Betwa basin, which covers 1385.61 sq km area. Theme layers viz , landuse / landcover, soil, slope, hydrogeomorphology etc which affect the identification of suitable sites were generated in Arc/INFO environment. The themes were then integrated to generate a composite coverage. A buffer of 1 km around second and third order drainage was constructed. Suitable weights were given to all the categories in each theme. The cumulative weighted values were calculated for each polygon of the composite theme map falling within buffer area. Three suitability zones viz most suitable, more suitable and suitable were generated from cumulative weighted value. Lineament map was also superimposed over the suitability zones. Various water harvesting structures like nala bund, anicuts, farm ponds etc were suggested in the area. WARIS has provided a guided flexible approach for identification of suitable sites making it versatile for any type of terrain.
Water harvesting has to be done on watershed basis, as watersheds are natural hydrologic units. Management of water resource done in this way is more effective. Watershed is characterisied by many parameters like land use, soil, hydrogeomorphology, morphometric characteristics etc. Output from similar watershed is often similar. With a suitable structure it is possible to harness maximum amount of water from the watershed. Location and type of structures depend upon soil, land use / landcover, drainage pattern, geomorphology etc.
To analyse all the affecting themes and come up with a solution for water harvesting, resource information and decision support systems are need of the time. Water Resources Information and Decision Support System package (WARIS) is designed as a system that uses geographic data, with associated ancillary data to derive information required by resource managers in a time effective manner. WARIS is intended to provide data to resource managers, in a way that allows the manager to understand data and its implications so as to construct a tactical knowledge model before making a management decision. WARIS has various analysis facilities and identification of water harvesting sites is one of them. Present study analyses upper Betwa watershed for identification of water harvesting sites using package WARIS developed over Arc/INFO GIS.
The study area covers 1385.61 sq km and falls in parts of Bhopal and Raisen districts in Madhya Pradesh. Agricultural land use covers 38.57% of the study area. Notified forest covers 26.07% of the area. Nearly 10.85% area is in forest category but falling outside notified forest. Land with scrub category covers 14.01% of the area. Water bodies cover 1.88% area under study. Watershed is mostly level plain with 37.15% area under 0 – 1 percent slope category. Around 12.77 % area is under 5 – 10 percent slope category. Higher slopes occupy around 10% of the watershed. Around 85% of the area falls under slope categories less than 10%. Hydrogeomorphically area is dominated by ridge type structural hills, which cover 44.79 %. Dissected lower plateau covers 51.54% of the area. 13 different soil units are also found in the area. Ground water prospect map shows that 51.53% area is under good to moderate category and 44.78% is under poor to nil categories. There is hardly any area under excellent category. Total length of drainage is 2377.61 km with order of drainage being 6 in the area. General elevation in the area varies from 660 m to 420 m.
IRS LISS III data for August 1999 and March 2000 were used for generation of resource themes. Collateral data from various other sources were also utilized in the analysis.
For identification of water harvesting sites following analysis was done:
- Generation of various theme maps
- Customization of maps in WARIS
- Analysis through WARIS for identification of structures
Generation of various Theme Maps
Various theme maps, which affect the water harvesting in any area, were generated either through satellite data or through other sources. The coverage’s were generated in Arc/INFO as per standard NRIS format.
Customisation of Maps in Waris
WARIS is a generalized package, which accepts data for any area. A WARISCUSTOM file integrates all the themes with the package WARIS. The package has many analysis facilities out of which generation of water resources development plan is one.
Analysis through Waris for identification of Structures
Selection of theme: WARIS provides an option to user for selection of themes to be used in the identification of structures. The major themes selected for the analysis are shown in figure 1. The themes are land use / land cover, soil, slope and hydro geomorphology. The selected themes are combined together in GIS environment.
Extraction of buffer area: The water harvesting structures are preferred along streams and 500 m area on either side of the river is sufficient. Buffer of 1 km is extracted for 2nd and 3rd order drainage only. Drainage of lower order is not selected, as these drains will not be able to give required volume of water. Velocity and volume of water in higher order drainage are also avoided by not selecting them.
Defining weights: WARIS provides interactive facility to provide weights for all categories in each theme. Different weights can be given for water harvesting and recharge sites. Weights are given according to structure for which analysis is being carried out. E.g. for nala bund less than 2 percent slope is preferable, where as for anicut 2 to 8 percent slope is required.
Selection of suitable zones: Cumulative weights are then calculated for each polygon in combined output. Total weights are divided in three zones for further analysis. The three zones are most suitable, more suitable and suitable. Figure 2 shows the suitable zones for structures. Statistics of suitable zone map was calculated. An area of about 57 sq km was found to be in most suitable zone for identification of water harvesting sites. More suitable zone occupies 453 sq km of the watershed and suitable area covers 523 sq km area.
Identification of water harvesting sites: The suitable zone map thus prepared was used for identification of water harvesting sites. Following structures were suggested as shown in figure 3.
- Anicut: For anicut sites buffer of 1 km was constructed around 2nd to 3rd order streams. Medium slope areas between 2 to 8% were taken. Favorable soils were given weights to allow storage of water. A total of 10 sites were marked in the area.
- Nala bund: Nearly plain, (up to 2%), upper reach, catchments greater than 40 ha, permeable soils were the criteria according to which the weights were decided. After the analysis 16 sites were marked which are suitable for nala bund.
- Farm pond: Flat topography, low permeability, absence of faults, joints were the criteria for site suitability.
- Dug cum bore well: Lineament map pertaining to study area was studied and 9 suitable sites were marked on the output.
Generation of water resource development plan is a tedious task but a guided semi automated way helps analyst to achieve the task in a better and faster way. WARIS helps in identification of suitable sites. Its facility to take user input for providing weights to the entire category makes it versatile to be used in all types of terrain. For Upper Betwa watershed area, around 4.17 % area, which falls in most suitable zone, is further chosen for identification of water harvesting sites. Total 38 sites for different structure were suggested within study area.
The authors wish to acknowledge the help and support received from Shri S Adiga, Director NNRMS/RRSSC during course of study.