Street Flow

[puzzler77]

Invariably, a street must come to a sump. In most cases, overflow is directed over the curb and down an open channel. However, in some cases, the overflow is directed over a hill in the street. As flow from a 100 year event (1% chance) event is allowed to reach two feet from the flow line, this hill could be a foot higher than the sump allowing for up to a foot of over topping. I am needing to model the hydrology through such a section. The cross slope is typically 3% and the curb is 6" tall. The slope behind the curb is typically 2%, mostly grass and a 4' sidewalk. Anyone else out there run into a similar situation?

 

[beej67]

http://www.fhwa.dot.gov/engineering/hydraulics/pubs/10009/

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[puzzler77]

HEC-22 by the Federal Highway Administration is a great publication and indeed it had the answers in it that I needed albeit they were answers I already had. I was looking for an easier way to model flow overtopping a hill but there is quite a variety of possible sections. FlowMaster by Hastaed Method's (now Bentley) has a feature that allows for a street section and will generate a table with a few parameters given to it. With this data, I suppose it would be possible to enter a few data points into HEC-HMS (USACE) that relates storage & flow with elevation.

 

[LincolnPE]

That's an Irregular Weir (flat) condition.

 

[gbam]

puzzler77 - I have had to model significant flows within urban areas similar to what you describe. Depending on the flow rate I have used approximate methods using weir analyses and split flows by hand or when the flow rate is really high in excess of 100-cfs I have used HECRAS to set up diversions. Guess it depends how exact you want it.

 

[puzzler77]

The trouble I run into is providing a guarantee that a residence will not get flooded if built to a certain elevation. In this community, the 100 year event is theoretically limited to a foot and a half above the curb. I know this is not an exact science but I would like to be somewhat comfortable with what this level will come to through analyzing the hydrology/hydraulics. There are cases where 100 cfs will be exceeded during the 100 year event. A street modeled as a river could be just what is needed here. Thanks for the idea!