Storm Sewer Systems and the Energy Grade Line
Storm Sewer Systems and the Energy Grade Line
(OP)
Many jurisdictions have a storm sewer system design requirement that the calculated energy grade line be below the rims of manholes and the throats of inlets. This is in additional to the requirement that the hydraulic grade line be 2' (or something close to that) below rims and throats, which I understand completely. What is the purpose of the separate Energy Grade line requirement? Wouldn't the HGL line criteria alone be enough? Is there a reason the EGL should be considered separately?
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RE: Storm Sewer Systems and the Energy Grade Line
RE: Storm Sewer Systems and the Energy Grade Line
RE: Storm Sewer Systems and the Energy Grade Line
RE: Storm Sewer Systems and the Energy Grade Line
When I started engineering, everyone sized their storm drains with 'the wheel,' such that all your storm pipes were sized for Manning's open channel flow capacity. We also stuck to a minimum slope of 1%, and we matched crowns. If you follow those three guidelines, you basically never have a problem in your storm sewer unless there's a tailwater issue. But then along came computer models such as StormCAD, which allowed engineers to justify undersizing pipes based on an HGL analysis and pressure flow, which in turn caused sinkholes and failures from putting non-watertight pipes into pressure conditions, which in turn caused the regulators to start imposing additional restrictions on the HGLs, EGLs, and the like. So now, even if you wanted to, you can't size your pipes with 'the wheel.'
Sad to say, this is a layer of complexity that the private engineering firms brought upon themselves, at least in this region.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Storm Sewer Systems and the Energy Grade Line
Our Design criteria specifically says no pressurize pipes (unless we have a really really good reason), so we do it that way and sumbit the old manning's pipe spreadsheet showing the pipes meet the minimum slopes, and the the hgl calcs. Is running the HGL calcs completely unnecessary?
RE: Storm Sewer Systems and the Energy Grade Line
RE: Storm Sewer Systems and the Energy Grade Line
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com