Purna River, Maharashtra

Abstract

Purna River and its basin area have been studied using advanced techniques of remote sensing and geographical information system. Physiographically, from north to south, the basin is divisible into four distinct regions, i.e. high relief Melghat Hill Range, alluvial plain, undulating to rolling plateau plains and Ajanta Hill Range. Morphological and lithological variations are quite distinct and clearly identifiable into consolidated sediments, unconsolidated sediments, residual capping and volcanic flows. Landforms are mostly the results of structural, denudational and fluvial processes, of which the last is mainly represented by loose to consolidated sediment cover of the area, due to the depositional activity of the Purna River and its tributaries. These are further subdivided on the basis of occurrence, relief, vegetation, nature of sediment admixture, lithological characteristics and dissections particularly in the case of basalt. The widespread alluvial sediments have been studied for its lateral variations, for which, apart from image characteristics, other supportive parameters such as number of dug wells, presence of summer-irrigated crops and moisture content have also been taken into consideration. The overall analysis indicates the occurrence of five lithofacies, i.e. boulder-pebbly facies, sandy alluvial facies, sandy-clay facies, silty facies and clayey facies. The spatial distributions of these facies are controlled mainly by structural set-up and topography of the area. The river has twelve major tributaries making a dendritic pattern in peripheral area whereas parallel to subparallel in central alluvial part. The confluences of northern tributaries with the main channel are almost at the right angle, whereas the southern tributaries have a tendency of Yazoo pattern. The basin has been divided into twenty watersheds following the criteria as proposed by AIS & LUS. Various quantitative measurements belonging to linear, aerial and relief aspects of the watersheds have been calculated and interpreted. The lineament study reveals that the main channel has a strong control of a major lineament, whereas certain tributaries bear minor reflections. In general, the density of lineaments is low in alluvial area as compared to basaltic terrain. Attempts have also been made for delineation of land use/land cover categories, palaeochannels and soil types of the basin area. Comments have also been made on the inland groundwater salinity prevailing in the central alluvial part of the basin covering an area of 2900 km². Both shallow and deep aquifers experience low to high levels of salinity creating major socio-economic problem in the area.