Analytic Assessment of the Water Table Drawdown, Seepage, and Back Pressure at Rudbar PSPP

Abstract

The impoundment of the Rudbar dam raised underground water level. On the right bank, the elevation of the water table is monitored in exploratory boreholes. The water table has remained below the level of the reservoir. The lower level of the water table is due to underground tunnels and galleries that behave as drains. Special analytic developments have been carried out to analyze the behavior of the water table during impoundment. The peculiarity of the model is that it considers a draining tunnel in an open aquifer with a free water table. Two new equations are obtained: one for inflow of water and the other for the water table drawdown. These equations are used to assess the water table elevation in the exploratory boreholes, calculate the hydraulic conductivity of the rock mass from the measured seepage in the conveyance tunnel, and determine the efficiency of the sealing from the measured back pressure on the extrados of the drainage gallery. The comparison of the calculated hydraulic conductivity with the available information from measurements with packer tests and DFN predictions will reveal the importance of scale effects and uncertainties.