RTK Unit Hydrograph Method for RDII

I have a few questions about the R,T,K unit hydrograph method for
modeling RDII.

1. In what version of SWMM does this method exist? I have the

2. Is there any documentation that explains how the values of R, T & K
are derived from a set of precipitation and flow monitoring data? I am
looking for an example that gives typical values for each of these
parameters.

3. Once these parameters are determined, how is RDII computed from a
complex hyetograph?


Thanks,

Tom Barnard
tebarn@EPIX.NET <mailto:tebarn@EPIX.NET>

Tom - I think the triangular unit hydrograph routine was new to version
4.4; any historians in the group should feel free to correct me on this.

There is a WERF publication titled "Using Flow Prediction Technologies
to Control Sanitary Sewer Overflows" (Project Number 97-CTS-8) that has
a good explanation of the method (see Appendix C). Other methods are
discussed as well. Their parameters are, I suppose, as "typical" as
anyone else's, but you will need to do a fair amount of fitting with
your own monitoring data. There are, after all, 18 parameters that can
be adjusted among the three triangular hydrographs.

RDII is computed using the usual discrete convolution method, which you
can find in most hydrology textbooks. It's useful to set up a
spreadsheet that performs the convolution and allows you to compare the
results graphically with the monitored flow. For complex hyetographs
you may also want to look at the shape of the unit hydrographs
themselves (individually and summed) as well as the convolution results.


I hope this helps. Good luck!
Peter Klaver
pklaver@LIMNO.COM <mailto:pklaver@LIMNO.COM>