P. D. Sreedevi

Drainage morphometry and its influence on hydrology in an semi arid region: using SRTM data and GIS

An attempt has been made to study drainage morphometry and its influence on hydrology of Peddavanka watershed, South India. Drainage networks for the sub-basins were derived from topographical map (1:50,000) and Shuttle Radar Topographic Mission (SRTM) Digital Elevation Model (DEM) data used for preparing elevation, slope and aspects maps. Geographical information system (GIS) was used in evaluation of linear, areal and relief aspects of morphometric parameters. The study reveals that SRTM DEM and GIS-based approach in evaluation of drainage morphometric parameters and their influence on hydrological characteristics at watershed level is more appropriate than the conventional methods. The mean Bifurcation ratio (Rb) of the entire basin is 3.88 which indicate that the drainage pattern is not much influenced by geological structures. VIII sub-basin have high elongation ratio (Re), basin relief (Bh), Ruggedness number (Rn) and time of concentration (Tc). It indicates that the erosion and peak discharges are high in these basins. Therefore, the construction of the check dams and earth dams will help in reducing peak discharge on the main channel. These studies are very useful for implementing rainwater harvesting and watershed management.

Simulation of Flow in Weathered-Fractured Aquifer in a Semi-Arid and Over-Exploited Region

The granites in and around Hyderabad, India, form part of the largest of all granite bodies recorded in Peninsular India. Alcaline intrusions, aplite, pegmatite, epidote, quartz veins and dolerite dykes traverse the granite. There are three types of fracture patterns (Fig. 1) in the area, viz. (i) mineralised or weathering fractures, (ii) fractures traversed by dykes, and (iii) late-stage fractures represented by joints. The vertical fracture pattern is partly responsible for the development of the weathered zone and the horizontal fractures are the result of the weathering. Hydrogeologically, the aquifer occurs both in the weathered zone and in the underlying weathered-fractured zone. The Maheshwaram watershed of about 53 km2 in the Ranga Reddy district (Fig. 2) of Andhra Pradesh, India, is underlain by granitic rocks. This watershed is a representative Southern India catchment in terms of overexploitation of its weathered hard rock aquifer, its cropping pattern, rural socio-economy, agricultural practices and semi-arid climate. The objective of this study is to develop and test well-suited modelling approaches to simulate the flow in the existing aquifer system that consist of two layers with any separating strata.

Relevance of hydrological parameters in artificial recharge sites selection and assessment in a granitic aquifer

Due to increasing demand of groundwater and indiscriminant pumping groundwater levels have been declined beyond economic levels and the natural recharge is not enough. Thus enhancing recharge to the groundwater system through artificial means has been evident. Depending on the situation, a variety of methods have been in practice but assessing their efficacy as well as optimal site selection has been lacking. In this study, it has been decided to use relevant hydrological parameters for an effective artificial recharge experiment using defunct dug-wells. A small watershed in a granitic terrene heavily exploited for irrigation, has been hydrologically investigated, monitored and characterised for flow parameters. The indiscriminant pumping (from about 700 bore-wells in an area of 55 Km2) has resulted in lowering of the water table and making all the 160 dug-wells in the area, perennially dry and defunct. Out of this one defunct dug-well having considerable catchment area in its vicinity was selected for demonstration of the experiment and monitoring the processes. It has been proved that the artificial recharge through defunct dug-wells are the best method to revive the aquifers and at almost no cost.

Assessment of groundwater resources using climatic and hydrologic budget methods

The Pageru River basin is situated in drought prone areas of the Rayalaseema region, Andhra Pradesh, South-India. In the absence of perennial surface water bodies, groundwater is an important source of water and has played an important role in developing industry, agricultural and domestic supply. In the present study, the efforts have been made to assess the groundwater resources using both climatic and hydrologic budget methods as quantification of groundwater balance are essential. The study reveals that the amount of recharge to the groundwater system is estimated as 5,434.5 ha.m from all sources viz, direct infiltration of rainfall seepage from water bodies and irrigation returns. The total draft accounts for 4,649.5 ha.m, providing a net groundwater balance of 785 ha.m in the catchment area. The results indicated that the groundwater balance is too little in the study area. These types of studies are more important for implementing groundwater management plans in this basin. Planning for groundwater management by precisely estimating the fluxes are necessary as groundwater balance is small and any changes in the climatic conditions may be disastrous.

Vertical disparity in electrical conductivity of groundwater: inferring water-bearing fractures in granitic aquifer

A detailed study was conducted in hard rock terrain for delineating water-bearing fractures using electrical conductivity (EC) logs. The EC logs of groundwater were taken both in pre- and post-monsoon seasons of the year 2001; in 25 borewells in a small granitic watershed at an interval of 1 m right from the water table (though narrow spacing wherever required) till the depth to bottom of the well. The EC values in various borewells have showed the changes, which were attributed to the presence of water bearing fractures zone(s). In addition, the results were compared with a number of studies carried out in the area viz., lithologs of the wells from the drilling data, sub-surface geophysical logging and also with an additional experiment of injected flow tests in the same borewells. A clear correlation is found among the anomalies and hence, it is to delineate the fractures at a desired depth using EC logs and nevertheless supported by geological information.