peter246
Civil/Environmental
- Mar 9, 2006
- 45
Hello, i'm doing a review of runoff calculations & noticed that the applicant hasn't set up the model as they described the actual conditions, and i've been asked how the shoulda/coulda done it. there are a series of subcats that flow to a continuous roadside ditch that has culverts and they've delineated the subcats from the culverts, so that each subcat flows to a culvert.
as the ditch is (presumably) continuous, and they have not described different, whatever can't flow through each culvert should cascade downstream through the ditch - this is how their Drainage Diagram is set up for routing, as dashed lines connect the nodes, but their output shows zero flow from the Secondary Outflow for all storms and each culvert, and impossibly high flows through the roadside culverts (54 cfs for an 18-inch CMP?! c'mon...)
please note that they did not set up the culverts as catch basins, and their output reports don't include details on how they set up any sort of storage, which they must have, otherwise HCAD won't let you save a pond node, right?
Anyway, at each design point (culvert), I think they should:
1) define the culvert as the primary outlet;
2) define a trapezoidal weir as secondary outlet at the same or slightly
higher invert as the culvert (the weir having the same geometry as the ditch); and
3) provide for overflow along the road through a broad-crested weir as tertiary outlet routed to same place as the culvert (it's a small ditch).
they also should use reaches in-between the culverts to represent the roadside ditch.
sound reasonable? not having done this particular physical setup before, i'd appreciate input. thanks in advance!
as the ditch is (presumably) continuous, and they have not described different, whatever can't flow through each culvert should cascade downstream through the ditch - this is how their Drainage Diagram is set up for routing, as dashed lines connect the nodes, but their output shows zero flow from the Secondary Outflow for all storms and each culvert, and impossibly high flows through the roadside culverts (54 cfs for an 18-inch CMP?! c'mon...)
please note that they did not set up the culverts as catch basins, and their output reports don't include details on how they set up any sort of storage, which they must have, otherwise HCAD won't let you save a pond node, right?
Anyway, at each design point (culvert), I think they should:
1) define the culvert as the primary outlet;
2) define a trapezoidal weir as secondary outlet at the same or slightly
higher invert as the culvert (the weir having the same geometry as the ditch); and
3) provide for overflow along the road through a broad-crested weir as tertiary outlet routed to same place as the culvert (it's a small ditch).
they also should use reaches in-between the culverts to represent the roadside ditch.
sound reasonable? not having done this particular physical setup before, i'd appreciate input. thanks in advance!
