This document by the Maharashtra Remote Sensing Applications Centre (MRSAC) presents the “Atlas on Watershed Prioritisation” using resources database on 1:2,50,000 scale adopting advanced techniques such as Remote Sensing and Geographic Information System (GIS). This watershed prioritisation to plan the activities on priority basis and facilitate judicious utilization of the available financial resources was done for the Water Conservation Department (Government of Maharashtra), the nodal agency to service watershed development in the State.
The natural resources i.e., soil, geomorphology and land use are greatly influenced by the terrain features, which in turn reflect on the watershed characteristics. The satellite data provides the spatial distribution of these resources and the theme maps derived using satellite data are very useful in assessing the watershed rating (prioritisation). Since the resources are interdependent, integrated study of all the resources is significantly useful for prioritising the watershed.
The run-off characters are well reflected through the natural resources constituting that watershed and can be quantified by depicting them in the form of theme maps such as land use/land cover, soil erosion, physiography, geomorphology and slope. These thematic maps can be integrated to prioritize the watershed. The district wise thematic information on the following themes derived from satellite data on 1:250,000 scale formed the main input for the watershed prioritisation.
- Geomorphology map.
- Soil erodibility map (derived from soil map).
- Land use/land cover map.
- Watershed maps of district prepared by GSDA.
- Administrative layer showing all the village location and tahsil boundaries of the district.
The approach involves identification of watershed with high run-off using the qualitative run-off assessment method. The methodology is based on the assumption that the run-off characters are influenced largely by resources such as soil, geomorphology and land use/land cover which can be depicted in the spatial format in form of theme maps. Each theme is broadly divided into 5 to 6 classes as per the run-off characteristics. The highest weightage index is given to unit indicative of high run-off, while lowest weightage index is given to the unit indicative of low run-off. Adopting the methodology described earlier, all watershseds of the State were then prioritized, district wise into four classes such as (a) High priority watersheds (b) Moderate priority watersheds (c) Low priority watersheds and (d) Least Priority watersheds.
All the digitized thematic maps were integrated in a GIS environment using ARC-INFO software. Weightage were then assigned to individual themes. The three basic layers viz., Soil, Geomorphology and Land use / Land cover were then integrated and in the process number of smaller polygons with unique aggregate weightage index were obtained. The weighted average index of entire watershed was then worked out to derive the rating of watersheds as per the runoff characteristics.
The outputs obtained were verified with the satellite image of the respective district area and it was observed that the cut-off value varies from district to district and is in the range of 9 to 7.5. The prioritized watersheds were then again classified into 4 groups, in which watersheds with index more than 10 have been classified as high priority watersheds. The watersheds with index ranging between 10 to 9.5 have been classified as moderate and watersheds with index ranging between 9.5 to its cut off value (7.5 to 9) have been classified as low priority watersheds, while the watersheds with index less than cut-off value have been classified as least priority watersheds.
It is hoped that the atlas would find immense applicability to the planners and executives in preparing their developmental plans and would facilitate in judicious diversion of available funds towards priority areas.