How to model depressional area in HEC-HMS
How to model depressional area in HEC-HMS
(OP)
For a project I'm working on, a subbasin 1A flows to a depression which then overflows to an existing culvert. I am unsure what is the correct way to model this. I tried both these ways:
Method 1. I modeled the depressional area as a reservoir with a spillway outlet. I had to add an arbitrary orifice outlet at the bottom of the depression with diameter 0.001 to effectively produce 0 CSS discharge under the overflow elevation.
Method 2. I divided the depressional storage by the drainage area and included it as an initial abstraction over the entire subbasin 1A under the Simple Surface input. I made a separate reservoir with the spillway set at the depression overflow elevation to model discharge flows.
However, I get different discharges for both methods. Method 1 results in an increased discharge over method 2.
Method 1. I modeled the depressional area as a reservoir with a spillway outlet. I had to add an arbitrary orifice outlet at the bottom of the depression with diameter 0.001 to effectively produce 0 CSS discharge under the overflow elevation.
Method 2. I divided the depressional storage by the drainage area and included it as an initial abstraction over the entire subbasin 1A under the Simple Surface input. I made a separate reservoir with the spillway set at the depression overflow elevation to model discharge flows.
However, I get different discharges for both methods. Method 1 results in an increased discharge over method 2.
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RE: How to model depressional area in HEC-HMS
RE: How to model depressional area in HEC-HMS
if you know the size of the depression or volume then use storage discharge curve in reservoir..do not apply any arbitrary outlet or orifice..follow below steps
1- calculate what is the peak discharge from 1A including depression storage area...but donot use reservoir in this run
2- once know the peak discharge...now apply reservoir with storage discharge curve.
3- in storage discharge curve if apply maximum discharge at full volume for example: say your full volume of depression is 10000m3 and peak discharge is 3m3/s.
Volume Discharge
0 0
500 0
5000 0
8000 0
10000 3
11000 3
by this the pond will act as natural pond and you will get exact outflow discharge from the pond.