Infiltrometer testing

SWMMers:

I'd be interested in hearing from anyone on their experience trying to measure soils characteristics for urban runoff modeling. Have you done infiltrometer testing or detailed flow metering to try to get better estimates of infiltration parameters than can be derived from soil survey data?

In my experience, most of the soils I model in an urban setting are listed as "urban disturbed" in the soil survey and SCS/NRCS in the US doesn't report hydraulic characteristics for urban soils. I find that it's very difficult to calibrate the soils parameters as most urban runoff is dominated by the impervious response. However, the pervious area response can be significant in intense storms and we're usually left to guess whether the infiltration parameters we specify are reasonable or not.

Thanks for your thoughts.
Mitch Heineman, P.E.
Camp Dresser & McKee Inc.

Check out:
http://www.epa.gov/ednnrmrl/reports/SR00016/cover.pdf

Boyd,Bufill,&Knee (1993). "Pervious and impervious runoff in urban catchments" Hydrological Sciences Journal 38(6) 463-478.
Boyd,Bufill,&Knee (1994) "Predicting pervious and impervious storm runoff from urban drainage basins" HSJ 39(4) 321-332.

Something else to consider is that a modeler will typically setup the SWMM catchment as X percent impervious, and 100-X percent pervious, with the same length (subcatchment width) and slope, yet differing values for depression storage and roughness. If the 'typical' overland flow length over pervious land is much different than that for impervious land, then calibrated infiltration parameters can be quite different than the measured ones. That's of course assuming the infiltration measurements are good, which they often aren't. The above comments apply to determination/measurement vs. calibration of 'effective' or 'connected' impervious area as well.

Have you seen the paper by Pit et all; Infiltration Through Disturbed Urban Soils and Compost-Amended Soil Effects on Runoff Quality and Quantity.

It can be downloaded from http://www.epa.gov/ednnrmrl/news/main.htm

It shows a lot of infiltrometer testing results.

Reinhard Sprenger, P. Eng.
Sprenger & Associates Inc.