Modeling Precipitation data with out a gage

[ALBUD1962]

I am doing a small drainage study for an area less than an acre.
The purpose of the study is to recommend solutions to correct basement flooding for a series of homes. Homeowners being as they are, really can't give me alot of information on the flow rate entering their basements or the depth of water ponding for any given flooding event. I am having to make some assumptions which will preface any design that I develop. I am looking at one major storm event which occured last fall which was particularly bad. I have NOAA data which I can use to get total rainfall volumes for the area that I am studying. The drainage shed is rather small, less than 2 acres. Since the area was small, and developed I was not planning to adjust my peak estimated inflows for time of concentration. Does any have any insight, comments or suggestions for this approach?





Al Budinsky
Skelly and Loy
Harrisburg, Pa

 

[civilman72]

"I was not planning to adjust my peak estimated inflows for time of concentration."

Can you explain what you mean by this? How will you determine rainfall intensity (assuming you are using the rational method)?

 

[ALBUD1962]

I am using a local rainfall distribution and estimating the peak inflow from the maximum depth of rainfall for any given interval. Rainfall is given in 15 minute increments. Since I am looking at the worse case scenario I am estimating that none of the rainfall is abstracted. I am not really using the rational method, but dealing with total rainfall volumes because the water is collecting in the basements. It has no where to runoff.

 

[gbam]

Sounds like an underdrain problem unless runoff is entering the baement from surface runoff. Then it would be a grading problem. Back to the hydrology; in order to transform from precipitation data to runoff data you must have a unit hydrogragh for the watershed. If you have enough historic rainfall/runoff data for your watershed or a similar one nearby then you can develop your UH. Why not just use the Rational Method or other acceptable UH and synthetic design storm from NOAA. If the basements capture 100% of the runoff from the storms, then you can use the storm volume. Otherwise you must transform your precipitation to runoff an then compute the capture.