Browsing by Author "Grundeen, Gordon M."

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    Recharge from Induced Streambed Infiltration Under Varying Groundwater-Level and Stream-Stage Conditions
    (Water Resources Research Center, University of Minnesota, 1967-06) Grundeen, Gordon M.; Hills, David L.; Walton, William C.
    Recharge from induced streambed infiltration can be estimated with data on streambed infiltration rates, surface-water temperatures, groundwater levels, and stream stages. However, estimates of recharge are not valid unless the following factors are considered: the rate of leakage through a streambed increases in direct proportion to declines in the water table until water levels have receded to stages below streambed; after the water table recedes below the streambed, the rate of leakage remains constant and at a maximum value, provided the stream stage and temperature do not change. Incorrect water-table declines and incorrect potential yields of well fields will be computed if it assumed that the induced streambed infiltration continuously increases in direct proportion to the drawdown beneath the streambed regardless of the stage of the water table. An aquifer-stream system for which hydrogeologic data are available was studied using electric analog computers and analytical methods to gain insight into the magnitude of recharge by induced stream infiltration under complex stream-stage and groundwater level conditions. The profound influence of changes in stream stage or recharge from induced streambed infiltration is illustrated by the results of the analytical studies. The results of the electric analog computer studies demonstrate that much greater drawdowns are computed for an aquifer-stream system when maximum infiltration conditions are taken into account than when maximum infiltration conditions are ignored. The electric analog computers consist of low impedence analog models and excitation-response apparatus. The analog models are regular arrays of resistors, capacitors, transistors, and diodes and are scaled-down versions of the aquifer-stream system. The excitation-response apparatus consists of two power supplies, a waveform generator, a pulse generator, tow power amplifiers, and an oscilloscope. Analog model streambed elements were designed with resistors, transistors, and diodes to correctly simulate leakage through the steambed under maximum infiltration conditions. Streambeds must be simulated in mathematical and analog models in such a way that: 1)leakage of water through a streambed is directly proportional to the drawdown beneath the streambed until the water table declines below the streambed, thereafter, induced streambed infiltration remains constant provided the stream stage and temperature remains stationary: and 2) provided the water table remains below the streambed, leakage of water through a streambed is directly proportional to the average depth of water in the stream and varies with stream-stage changes and changes in the surface-water temperature.