You are designing a sanitary sewer to flow across a fairly flat floodplain. The manhole spacing…
You are designing a sanitary sewer to flow across a fairly flat floodplain. The manhole spacing is 400 ft and the ground profile is shown in the following table.
Use a PVC pipe with a 12 in. diameter. The sewer will have Manning’s n = 0.010, and there is 0.1 ft of head loss in each manhole. The tailwater elevation is 776.85 ft, and the manhole invert matches the inverts of the incoming and outgoing pipes. You want at least 3 ft of cover above the top of the pipe. Pick invert elevations and check to see if the pipe is surcharged at a maximum flow of 2.0 ft3 /s and the velocity is still reasonable at a minimum flow of 0.2 ft3 /s. Complete the following tables. If you are using manual calculations or a computer program based on normal flow, use the normal depth in the pipe table. If you are using an approach that calculates backwater curves using a gradually varied flow analysis, give both the upstream and downstream depths and the average velocity.
When you have performed the hydraulic calculations, draw a profile of the sewer showing the ground elevation and top and bottom of the pipe. Annotate the drawing so that it can be understood. It may be drawn manually, with a hydraulic analysis program, or using CAD.