Pond Modeling
Pond Modeling
(OP)
What is the best way to model catch basins in a street low point that is separated by the road crown, then becomes one pond after the water overtops the crown? Is it possible to model it as two ponds first, or is it best to model it as one pond with two outlets?
RE: Pond Modeling
Have Fun With it!
RE: Pond Modeling
Here in PA, PennDOT will not allow more than ½ of one cartway spread during design flow AND you must stay 1 inch from the top of curb. Gutter flow and grated inlets efficiencies based upon FHWA HEC-12 will normally be accepted for any review.
Immediately prior to the sump, calc. spread thickness with the following modified Manning’s: T=(Q*n/.56/Sx^1.67/S^.5)^(1/2.67), where Sx = roadway cross slope and S = Longitudinal slope, both decimals. Check in both directions, as Long slope is rarely the same coming both ways.
Then check depth:
Weir flow depth, ft = [Q/(Cw*P)]^(2/3)
Orifice flow depth, ft = [Q/(Co*A*2g)]^(1/0.5)
I always use the greater depth for conservative design, but there is a chart in HEC12.
A common mistake: check for composite cross slopes. If the gutter line is spec’d for a steeper cross slope than the roadway (and they often are), there is an adjustment to the T value which greatly helps the results.