Impact Assessment of Water Conservation Measures: A GIS Approach
Drainage
The Drainage of the area is mainly dendritic to sub-dendritic in its pattern (Strahler 1952) and the basin is elongated in shape. The fine drainage density in southeast and southwest part confirms to physiography of the area, which has the lower infiltration levels. The central portion of the watershed with nearly level sloping condition depicts the medium to high infiltration rate resulting into the incremental groundwater levels. Because of the erratic nature of rainfall and impermeable nature of rocks, shallow stream channels are formed. The drainage pattern is indicated in Figure 6.
Land use / Land cover study
The satellite digital data of 1997 and 2001 are processed using EASI/PACE image processing software for its georeferencing by extracting ground control points with the help of SOI toposheet (fig.2) and the field data. (Land use / land cover field manual, Integrated surveys division, National Remote Sensing Agency, Hyderabad, A.P. India 1995) The Hard copies for the two years are generated for subsequent visual analysis of satellite data. Based on visual image interpretation of these hard copies (Figs.3 and 4), the land use/land cover maps for both the years are generated. The final land use/land cover maps are prepared on field validation with ground checks. The flowchart showing stepwise method is provided. A digital database of land use/land cover for the years 1997 and 2001 is created using ARC/info GIS software. This database is then used for impact analysis of Neeru-Meeru programme. Four broad categories of land use/land cover are identified and mapped in the study area for the years 1997 and 2001 for comparative analysis to carryout impact assessment of the Neeru-Meeru programme. The satellite imagery of 2001 exhibits an increase in area for the land use categories namely agricultural land, forestland, and water bodies. compared to that of 1997. The 2001 imagery exhibits sizeable decrease in the area of waste/degraded land. The total increase during 2001 compared to 1997 for the three classes agricultural land, forestland and water bodies is 69.59 Sq. Kms. The decrease during 2001 compared to 1997 for the waste degraded land class is around 69.59 Sq. Kms. The area statistics of land use/land cover study are presented in Table1. All the four categories of land use/ land cover patterns are indicated in Figures 7 and 8.
Topography and Ground Water status
A critical look at the topography of the study area reveals the occurrence of land form features such as denudation hills, residual hills, dykes and intermontane valley. Cumbum quartzites and dolomites are present as structural hills, whereas cumbum shales and phyllites appear as shallow to moderately weathered pediplains and intermontane valleys. The structural hill located in the SE direction covered by velikonda south reserved forest has a relief of 438 m above MSL while the one located in the SW direction covered by velikonda reserved forest has a relief of 499 m above MSL.
The central portion is nearly flat occupying 39.19% of the total area. In the eastern and western portions, area has moderately to steep slopes.
NDVI Map Generation
Normalised differential vegetation index (NDVI) values are generated for the years 1997 and 2001 for the same season. The positive rise of the index is witnessed for the categories agricultural land, forest land and water bodies for the year 2001 compared to 1997. The negative index values have disappeared for the category waste/degraded land for the year 2001 compared to that of 1997. The comparative NDVI values for different land use/land cover categories for the years 1997 and 2001 are given in Table 3 The status and incremental growth of vegetation in the form of normalised difference vegetation Index (NDVI) are indicated in Figures 9 and 10.
Summary and Conclusion
A pilot study is carried out on the evaluation of impacts of Neeru-Meeru (WATER AND YOU) programme, the most popular development programme of the Government of Andhra Pradesh. This study is based on scientific parameter; NDVI and land use/land cover change detections etc. A scientific methodology is developed to monitor assess and evaluate the Neeru-Meeru programme.
The study leads to the following conclusions. Cursory examination of the land use/land cover maps depicted an increase in the areas under agricultural land, forestland and water bodies to the tune of 69.59 sq. km during post launching of Neeru-Meeru. This comparative study revealed that the soil and water conservation practices being in practice/adopted are yielding fruitful results besides other development factors.
The considerable decrease in areas of waste/degraded land conveys that the structural measures taken up have increased the soil moisture status and paved the way for rising chlorophyll status. The positive rise in the vegetative index for all the land use/land cover categories and the absence of the index values for waste/degraded class corroborates with the observations. The scientific approach through the methodology developed in this pilot study can be adopted for the overall evaluation of watershed activities elsewhere.
By adopting this scientific evaluation methodology, it will be possible for the Government of Andhra Pradesh to assess the returns for the investments made under this programme and to steer the programme in future.