Runoff coefficients for sloped regions and hydraulic soil groups

[backseatpockets]

I am tasked with calculating the runoff coefficient for a rather large drainage area (50+ acres). Using Carlson Hydrology, I was able to create an index of all the HSGs and their respective coverages. My PM has requested that I adjust my calculations to account for the slope of the regions (i.e., 0-2%, 2-6%, 6%+).

I can easily create the slope zones. My concern, however, is that calculating the areas of the slope regions while ensuring they align with the correct HSGs is going to be very tedious.
Any suggestions would be much appreciated!

 

[zelgar]

I would ask your PM why they want you to adjust your calculations. Before you do, you might run the model adjusting for doing the areas as a whole with the different runoff coefficients. If the best case won't get the results your PM wants, there is no point in spending a lot of time to go into the minutiae in trying to model it to the nth degree they want.

 

[backseatpockets]

The reviewing engineer is kind of a psycho and he has asked for this in the past but for smaller designs. My guess is that PM is the trying to avoid that comment by just doing the calc. I honestly think that it's a waste of time I'll probably just grab the area of the sloped region and use the highest coefficient. The design engineer likes to under design BMP. I'll probably just have to amend the design just so we can meet the volume and runoff requirement.