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The effect of water harvesting structures on groundwater recharge and water quality was evaluated in a watershed situated in a semi-arid region in Andhra Pradesh, India. Two percolation tanks and two check dams with a total storage capacity of 4.209 ha m were selected to assess their effect on groundwater recharge and water quality within the influence zone of the water harvesting structures. Daily rainfall, evaporation and storage depth in structures were measured to quantify percolation. Using rainfall–run-off relationship with antecedent precipitation index as a factor, complete water budgeting was carried out. Results show that the threshold value of rainfall for ensuring 1 mm potential recharge is 61 mm. Potential recharge is only 3% of annual rainfall received. Water quality analysis revealed that except pH, all other water quality parameters like electrical conductivity, sodium adsorption ratio, residual sodium carbonate, total hardness, nitrate and fluoride content reached desirable limits in close vicinity (<100 m) to the water harvesting structures. Increased availability of groundwater led to subsequent over-exploitation in below-normal rainfall years and the number of bore wells increased by three times.

Discussions on the merits and demerits of energy resources and their availability are centred on the renewable/non-renewable or conventional/non-conventional energy resources. The prime candidate between non-conventional and renewable energy sources is solar energy, which is projected as a big supplier of our future energy requirements super(1,2), but production of energy is not large so far even today. Once boiling, liquid ball earth cooled to the present condition by gradual loss of heat over billions of years. The hot interior funds the incessant loss of heat from every part of the earth, which flows out unevenly through the surface apparently in small amounts (84 mWm super(-2)), depending upon the geological set-up of the area. The net annual heat loss by this conduction mechanism from the earth is 4 x 10 super(13) W; this is more than the energy released by all earthquakes in a year super(3). On the contrary, nature has geologically controlled but sporadically distributed high-temperature anomalous thermal manifestations with economic potential such as the presence of magma pockets, volcanic eruptions, geysers, fumaroles, solfatara, hot grounds, hot dry rocks, geopressurized water and the highly useful hot-water springs. Springs emitting water more than 5 degree C than the average annual temperature of the area fall under the hot-water category. The water temperature and quantity are controlled by the geological characteristics of the region. Inside the earth water is heated up by magma pockets, cooling crystalline igneous rocks, tectonic activity located within the range of a few hundred metres to a few kilometres depth and by the downward increasing geothermal gradient. This is 30 degree C/km under normal conditions; however, it ranges from as low as 10 degree C/km to exceptionally high values near the mouth of a volcano. The quantity of emitted water is controlled by depth of the heat source, porosity and permeability of the rocks, quantity of percolating meteoric water or source of water, fractures and structural set-up of the area. The geothermal water cycle comprises downward percolation of meteoric water inside the earth through pores and fractures to lateral migration over the heat source and finally emergence of water on the surface. The entire process from percolation to re-emergence of water may be completed in hundreds to ten thousands of years. Once the cycle is established, it may survive up to a million years super(4).

One particular practical problem in oil recovery is to predict the time to breakthrough of an injected fluid in one well and the subsequent decay in the production rate of oil in another. Because we only have a stochastic view of the distribution of rock properties, we need to predict the uncertainty in the breakthrough time and post-breakthrough behavior in order to calculate the economic risk. In this paper, we apply scaling laws from percolation theory to predict the distribution of breakthrough times that can be calculated algebraically rather than directly via very time-consuming numerical simulation of large number of realizations. The main contribution is to show that percolation theory, when applied to a realistic model, can be used to obtain the same results as calculated in a more conventional way but significantly more quickly. Specially, when the parameters of scaling law optimized, we found that a previously proposed scaling form for the breakthrough time distribution when applied to a real oil field is in good agreement with more time consuming simulation results. Consequently, these methods can be used in practical engineering circumstances to aid decision making for real field problems.

The percolation method has been recently considered in evaluation and prediction of reservoir parameters. This theory has been applied in estimating the connectivity of the reservoir in conventional and fractured reservoirs. Application of this method for predicting the breakthrough time was compared with the field simulation results and this comparison lead to obtaining the results quickly made by estimating the above-mentioned parameters in the reservoirs. In this paper, by using the percolation theory, new parameters generated for breakthrough time prediction via modification and optimization. These new parameters were tested in some oil reservoirs and eventually optimized parameters in scaling law were identified and presented in one of the tested fields.

The main objective of the paper is to estimate the costs of groundwater over exploitation and examine the costs and benefits from groundwater replenishing mechanisms in different ecological contexts. Using the public good and externalities framework, the study shows how groundwater exploitation in Andhra Pradesh, India is resulting in economic losses to individual farmers apart from ecological degradation. It is argued that policies towards strengthening the resource base (replenishment mechanisms) and equitable distribution of the resource (property rights) would be beneficial, economically as well as ecologically. The analysis is in favour of investment in replenishment mechanisms such as irrigation tanks and percolation tanks. The situation of over extraction and the resultant environmental degradation is a consequence of lack of appropriate and adequate policies (policy failure) for managing the subsurface water resources. Hitherto, groundwater policies (subsidized credit, power, etc.) are in the nature of encouraging private initiatives in groundwater development. It is argued that community-based investments in replenishment as well as extraction of groundwater would make better economic as well as ecological sense.