sewergems/stormcad composite q

Hi Brian,

Is this "composite q" based on runoffs from different sub-areas of a catchment? However, it is not possible to get individual runoffs from sub-areas, unless you model each sub-area as an independent catchment with its own CN value.

Is this what you are looking for?

Just wondering if stormcad/sewer gems can do a weighted q yet? As previously posted our agency requires separate runoffs for each curve number to be added together in a catchment. We are no to use a composite curve number for a catchment.

Could you provide details on what you are looking for? With further information on what this is, we can either see if there is a way to do this or be able to log a request to include this.

Regards,

Scott

I agree with the others - more specifics on your requirements will help us provide an accurate answer, or define your requirements for development consideration. Which numerical solver (Rational for peak flow?), how is this weighting expected to work and which results does it apply to? Without this we can only guess as to what you need.

I am not certain at this point, but you may want to take a look at the subarea feature or consider the points in this article: Multiple CN numbers for a catchment and multiple catchments with a single outlet node

• Calculate separate runoff for each CN value in each catchment.  Instead of using a single composite CN value for each catchment, the runoff is calculated separately for each sub-area and then the volumes are combined.  Sometimes referred to as a "weighted-Q" approach, this procedure preserves the full runoff volume from sub-areas with high CN values.

We use weighted q method with rational and SCS TR-20

We use weighted q method with rational and SCS TR-20

Thanks for the details, Brian. I am consulting with my colleagues and will get back to you soon.

Brian, our product managers will look into this and prioritize for a potential future release - this is recorded with reference # 538362 which I have attached to a new Service Request opened on your behalf, so that you will receive an email alert if this is implemented in a future release.

In the meantime, the solution you can use is to model each land type as a separate catchment area, with its "Outflow Element" set to a single common discharge point (the same that you would have chosen for the single catchment). This will also enable you to align your model more closely to the real system (by drawing the catchment polygons for each type of land). 

I have documented this in the following article in our Wiki: Using the Weighted Q method for catchment runoff