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River Islands Development at Lathrop November 2020 Final Phase 2 Sewer Technical Report Rev 1 #6520 After the depth of flow in each pipe was determined, the calculated wetted cross sectional area was used to determine each segments velocity under PWWF using the continuity equation D2 1 A,, = 4 (0 — 2 sin 20) •* �f \ 1 4 � f I 4 7 Where, Aw—Wetted Area, sq. ft per Section 10.7 Fluid Mechanics 10th edition D— Depth of Flow, ft 0—Central Angle (calculated based on depth of water), in radians Q = VA, Where, Q—Volumetric flowrate (PWWF in this model), cfs Aw—Wetted Area, sq. ft per Section 10.7 Fluid Mechanics 10th edition V—Velocity at PWWF, fps 4.2 Sewer Lift Stations— Firm Pumping Capacity Sewer lift stations are installed in sewer collections systems to raise the hydraulic grade line of the sewer main where gravity flow are no longer feasible. Sewer lift stations are typically installed at localized low points in the collection system. In no case shall any sewer main be deeper than 25 feet unless approved by the City Engineer. The City requires documentation demonstrating the need (i.e. gravity flow is no longer feasible) and the required firm pumping capacity of the lift station (Appendix H in the City Standards). Each lift station must be designed to provide a firm pumping capacity equal to the ultimate peak flow (PWWF) of the collection area and all potential tributary areas. Appendix H-C.5 in the City Standards defines firm pumping capacity as the total pumping capacity of all the pumps minus the capacity of the largest pump. In locations where the PWWF exceed 1.0 cfs(450 GPM or 0.65 MGD), the lift station shall be installed with a low flow pump with a pumping capacity of 5% to 10% of the design flows. The low flow pump shall operate as the lead pump to prevent excessive wear and tear on the larger pumps due to repeated starts and stops during low flow conditions. 16