Virden Creek Pumping Station and Gravity-Flow Outlet Structure Waterloo, Iowa. Hydraulic Model Investigation

摘要

The model study was conducted to evaluate the characteristics of the pumped and gravity flows through the proposed structures from Virden Creek into the Cedar River and to develop practical modification if required to improve the hydraulic performance of the structures. Hydraulic performance of the original design four-conduit gravity-flow structure was inadequate with unsymmetrical flow. This was attributed to the existing structures and the indirect approach to the gravity structure. This unsymmetrical flow through the original four-conduit gravity-flow structure was improved by a three-conduit structure which enhanced the hydraulic and structural adequacy of the gravity-flow outlet structure. Hydraulic performance of the original converging-sidewall, low-submergence pump sump indicated that air-entraining surface vortices would occur intermittently in the vicinity of the pump intakes. A modified pump sump with rounded approach pier noses and a horizontal baffle wall prevented the adverse vortices and resulted in good hydraulic performance. Sediment deposition expected during gravity-flow operations was simulated with results indicating that normal sand and gravel deposits should not affect performance of the pumping station with the gates to the pump sump closed during gravity-flow conditions. (Author)