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Aquifer Hydraulics
how do aquifers respond to pumping under various situations
Question | Answer |
---|---|
what is the purpose of pumping tests? | 1. Determine aquifer parameters T and S at larger scales 2. Evaluate the aquifer response to pumping - check for “non-ideal” conditions - confined vs. unconfined response 3. Estimate well efficiency 4. Estimate a suitable long-term pumping rate |
what is static water level [SWL] (ho)? | equilibrium water level before pumping commences |
what is pumping water level [PWL] (h)? | water level during pumping |
what is drawdown(s = ho - h)? | the difference between static and pumping water levels greatest at the pumping well |
what is pumping rate (Q)? | volume of water pumped per unit time |
what is radial flow? | flow towards the well from all directions |
what is a cone of depression? | drawdown centered around a well, due to radial symmetry |
what is the radius of influence (R)? | drawdown and hydraulic gradient decrease as one moves away from the pumping well the outer limit of cone of depression is R |
what happens if we install observation wells at different radial distances from the pumping well? | we can evaluate aquifer response to pumping should be close enough to the pumping well that the drawdowns are measureable |
what is well head loss? | is related to the efficiency of screen and the material adjacent to it |
influence of time | Assuming all other factors are constant, drawdown increases with the log time. Increasing time does not alter the shape of the drawdown cone |
influence of discharge rate | Increasing the pumping rate causes a linear increase in drawdown. That is, doubling the pumping rate will double the drawdown |
influence of transmissivity | Higher gradient is needed to get the same flow volume in the low T case |
influence of stroativity | Less drawdown is needed for the high S case because the aquifer releases more water from storage per unit unit decline in head |
radius of influence | distance from the pumping well where the drawdown is negligible (s ≈ 0) |
what is the principle of superposition? | used to evaluate the influence of varying pumping rates in a single well, determine the influence of regional hydraulic gradients, or estimate drawdown at a single location from multiple pumping wells |
what is a capture zone? | the region of water around a pumping well that will (eventually) be captured by the well |
recovery | water levels will rise and gradually return to their static levels |
residual drawdown | amount of drawdown during recovery |