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|Title:||PUMPIN TEST ANALYSIS BY MODELLING MULTI AQUIFER FLOW|
PUMPIN TEST ANALYSIS MODELLING
MULTI AQUIFER FLOW
|Abstract:||On the basis of hydraulic characteristics an aquifer can be classified as Unconfined, Confined or Leaky confined. In nature we normally find a leaky confined aquifer hydraulically connected to the overlying Unconfined aquifer through a semi pervious aquitard. Such an aquifer system may be described as 'Unconfined-Leaky Confined'. The hydraulic performance of the system can be described in terms of parameters e.g. specific yield, hydraulic conductivity, storage coefficient, drainage factor, hydraulic resistance, transmissi- bility and leakage factor. These parameters need to be known for various groundwater studies e.g. , well -design, planning of regional groundwater development, subsurface drainage, artificial recharge etc. The conventional method of estimating these parameters is a Pumping test. The observed data of such, tests are analyzed by graphical procedure (also known as 'type curve analysis') and parameters are estimated. In graphical procedure, parameter estimation is based on assumptions like radiality of flow, linear infinite boundaries•, absence of interfering pumpage in the - vicinity of test site, constant watertable position during a test. In practice, all these assumptions are. rarely met. As a result, the estimation of aquifer parameters also get deviated from their correct value. In the present study, a model has been adopted to simulate two dimensional horizontal unsteady state flow in, an 'unconfined leaky confined aquifer system'. The model permits estimation of watertable and piezometeric heads fluctuation in response to known patterns of withdrawls/recharge. The use of the model has been suggested for analyzing the pumping test data from leaky confined aquifer, accounting for non- radiality of flow (i.e. two dimensional horizontal flow), falling water table in the overlying unconfined aquifer, non linear and/or finite boundaries, interfering pumpages in the vicinity of the test site. Two sets of published pumping test data for two locations in the Punjab (CGWB, 1982) have been analyzed by the proposed model. In one site the intervening semi pervious layer (aquitard) has low hydraulic resistance and in the other, the aquitard has high hydraulic resistance. After analyzing through the model it is found that the extent of underestimation of transmissibility for the first location (where hydraulic resistance is low) is to the extent of 25%. The drawdown of watertable is found to be 11% of the drawdown of the piezometric head. In the other case, due to higher hydraulic resistance, the underestimation of transmissibility is marginal (3%). It is recommended to use the model for analyzing the test data of leaky confined aquifer for locations where aquitard has low hydraulic resistance. The data like interfering pumpage, non linear boundaries also need to be collected during the test since these form a component of input data of the|
|Appears in Collections:||MASTERS' DISSERTATIONS (Hydrology)|
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