Methodology
The methodology adopted for the development of comparative Lu/Lc status involve the following steps:
- Generation of thematic maps using satellite data
- Land use / Land cover
- Hydrogeomorphology
- Generation of Topographic maps using SOI Toposheets
- Slope map
- Base map
- Drainage map
- Generation of NDVI using remotely sensed digital data based on red and infrared reflectance, on the basis of the expression
NDVI = (NIR -R) / NIR + R
Where,
NIR = near infra red reflectance
R = red reflectance.
The variation in green vegetation density due to Neeru-Meeru programme can be analysed using the above equation.
Description of the area
Vemuleru watershed of Prakasam District in Andhra Pradesh (Figure 1) forms a part of the Gundlakamma catchments in heterogeneous peninsular shield and lies within 15o251 and 15o501 N latitudes and 79o81 and 790161E longitudes. The Vemuleru River flows from South to North and joins Gundlakamma near Nekunambadu. The area is known for recurring droughts and inhabited by a substantial percentage of people belonging to scheduled castes, scheduled tribes and weaker sections. The relevant toposheet and the two imageries (IRS-IC, LISS-III) of 1997 and 2001 are shown in Figures 2, 3 and 4 respectively.
Geology of the Area
Study area is situated in the eastern part of the Cuddapah basin. During upper Precambrian, large tracts of the area are a basin of submergence. (Chennaiah etal 1985) The formulations in this basin are a result of cyclic sedimentation and are relegated to foreland faces. Each cycle starts with a basal conglomerate, overlaid by limestone, shale and quartzite.
Cumbum shales, phyllites and quartzites in the Nallamalai range are the rock formations in the study area. Ground water occurs in the intergranular pore spaces in the weathered zone and the secondary structures of the rocks of Cumbum shales and phyllites. The quartzites being massive have negligible pore space.
Climate
The study area experiences tropical and semi arid type of climate. In general, winter, low rainfall and severe summer are characteristics of the seasons. The area is classified as drought prone as the occurrence of low rainfall is more than 20 % of the years recorded (CPO (1993-1994): "Manual of Statistics". Chief planning office, Prakasam district, Andhra Pradesh.). The average annual rainfall recorded in the area is 624 mm. Much of it is received during SW monsoon (Jun-Sept.) and NE monsoon (Oct. - Dec.) periods. As there are no major reservoirs and efficient water management techniques in practice for tapping the water, much of the rainfall drains as surface run-off.
Physiography and slope
The diversity in relief and topography in the area resulted in to two physiographic divisions. Moderately steep-to-steep sloping structural hills and plains. The eastern and western parts of the study area have steep terrain with higher relief. The Northern and Central portions are plains with nearly level slopping conditions. Distinct variations in relief, gradient, composition of material and the topography of plain areas have resulted in the formation of fluvial plains and pediplains. The slope map derived from SOI toposheets and prepared on ARC/Info GIS platform is shown in Fig.5. Seven slope categories (Table.2) are identified and later are integrated in the process of development of scientific indicators for impact study of Neeru-Meeru programme.