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Join Date: Dec 2008
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How do you treat a CB in the equation for relative access hole head loss?

12/08/2008 8:49 AM

In the equation for determining energy & hydraulic grade lines for drainage pipes, there is an initial head loss coefficient = Ko. The Equation Ko = 0.1 (b/Do)(1-sin<)+1.4(b/Do)(15) sin<) requires access hole or junction diameter. What if it is a standard (4'x3') square sump CB? Also in the eqauation to solve for plunging flow, the vertical distance of plunging flow from the flow line of the higher elevation inlet to the pipe center of the outflow pipe = h. Is this value just the flow line of the higher outlet or is this the flow line plus the plunging tailwater(dc+d/2) comming out of this higher inlet? How does a standard 2' sump in a cb relate to correction for benching? Finally, Is there software out there specifically design to compute energy and hydraulic grade lines?

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Re: How do you treat a CB in the equation for relative access hole head loss?

12/10/2008 6:35 PM

Catch basins and other structures, including valves, elbows, reducers, etc. have their own equations for losses based on the type of structure, these are minor losses separate from the pipe friction loss that must be added to determine the total loss for a system. There are many software programs you can find that compute the HGL and EGL, depending on the type of system being anaylyzed. The USEPA and USAACE both have some freeware that is pretty good for some analysis. USEPA develops SWMM and USAACE develops the HEC models. There are also programs like SewerCAD, StormCAD, and WaterCAD, which are better for design, but not free. These things are commonly available and discussed online, a little search with Google would have told you most of the answers in about 5 minutes. Generally, this is not something you should mess with if you are not an engineer, because you need to make sioome assumptions and be able to recognize issues that may have been lost in the modeling. If you are an engineer, you should sue your college program for a failure to meet the ABET educational standards required for Civil Engineering degrees.