Field Investigation of Selective Withdrawal

A field investigation of the steady-state thickness and extent of a withdrawal layer in a stratified reservoir is reported. Existing theory indicated that, throughout the study period, the withdrawal layer was in a steady state in the regime governed by a balance between buoyancy and viscous forces. A natural salt tracer in the water enabled estimates of the mean withdrawal layer thickness, δ, over a 10-km (6.2-mile) length upstream from the sink for two different time periods. To achieve good agreement between theoretical predictions and field measurements it was necessary to postulate transport coefficients of momentum approximately ten times the molecular value. Comparisons with model simulations over the same time period suggest an effective average Prandtl number of 20 in the hypolimnion.