Unbelievably high concentrations

Hello fellow swmmers

I am running the runoff model in swmm with a rating curve to produce pollutant washoff. Within the curve I am using rcoeff = desired concentration and washpo = 1 to give constant concentrations.

At the minute the model gives unbelievably high concentrations (eg ss = 0.8*10^16) however the washoff curve is the only mechanism for generating pollutants and in the summary it seems to give reasonable results eg 50 kg of total Nitrogen over one year

Has any-one else had problems with the program generating unbelievably high concentrations who might provide me with some clues as to the reason.

As far as I know, the rating curve options works well. Remember that you have to multiply RCOEF by 28.3 L/ft3^(1/WASHPO) for a units conversion, although this might make your concentrations even higher. E.g., if you wanted a constant concentration of 2 mg/L, RCOEF = 58.6 and WASHPO = 1.

The current RUNOFF.DOC file includes two rating curve examples documented among the J3 lines, one for a constant concentration and one for a non-constant concentration, based on User's Manual Fig. 4-37(e). The output is quite reasonable and the constant concentrations are constant!

This is a long way of saying I don't know what the answer is to your problem.

Wayne H.