Tham khảo tài liệu 'water conservation part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Importance of Percolation Tanks for Water Conservation for Sustainable Development of Ground Water in Hard-Rock Aquifers in India 21 Fig. 1 b . Nearly horizontal lava flows comprising the Deccan Traps or Basalts of Western India. Location Western Ghat hills between Pune and Mumbai Maharashtra State. 3. 3. The aquifer parameters like Storativity S and Transmissivity T often show erratic variations within small distances. The annual fluctuation in the value of T is considerable due to the change in saturated thickness of the aquifer from wet season to dry season. When different formulae are applied to pump-test data from one well a wide range of values of S and T is obtained. The applicability of mathematical modeling is limited to only a few simpler cases within a watershed. But such cases do not represent conditions over the whole watershed. 4. 4. The phreatic aquifer comprising the saturated portion of the mantle of weathered rock or alluvium or laterite overlying the hard fractured rock often makes a significant contribution to the yield obtained from a dug well or bore well. 5. 5. Only a modest quantity of ground water in the range of one cu. meter up to a hundred cu. meters or so per day is available at one spot. Drawdown in a pumping dug well or bore well is often almost equal to the total saturated thickness of the aquifer. Ground water development in hard rock aquifer areas in India and many other countries has traditionally played a secondary role compared to that in the areas having high-yielding unconsolidated or semi-consolidated sediments and carbonate rocks. This has been due to the relatively poor ground water resources in hard rocks low specific capacity of wells erratic variations and discontinuities in the aquifer properties and the difficulties in exploration and quantitative assessment of the resource. 22 Water Conservation It should however be realized that millions of farmers in developing countries have their small farms in fractured basement
