The model study was conducted to evaluate the characteristics of flow in the inlet channel, original sump, energy dissipator (saxophone outlet), and outlet channel and to develop practical modifications required for improving the hydraulic performance of the structure. Hydraulic performance of the original design inlet channel and sump was satisfactory for all anticipated sump elevations with various numbers and combinations of pumps operating. This was attributed to the relatively long and straight approach channel to the sump, the relatively long pumping bays, and the high submergence on the pumps at the minimum anticipated sump elevation. Tests conducted to investigate various size bell diameters indicated that for the range of bell diameters evaluated, there was no significant difference in the performance of flow entering the suction bell. Hydraulic performance of the outlet structure and stability of the riprap in the outlet channel were improved by the addition of minor modifications developed during the model study. Tests results indicated that the critical hydraulic conditions occurred with one pump operating and the basin initially dry.