HEC HMS : Loss method and Impervious Area
HEC HMS : Loss method and Impervious Area
(OP)
Hi,
I am a new user of HEC-HMS and I am having some problems with the choice of the loss methods.
I have tried several of them (Initial and Constant Rate, DEficit and Constant Rate, SCS Curve Number, Smith Parlange, Green Ampt). And for all of them, the only excess precipitation I get is from the impervious area.
I have changed the amount of precipitation, and the parameters (from 100 times smaller to 5 times bigger) and there are no difference, except for the SCS Curve Number method.
If I try with "Impervious Area = 0%", I don't have any excess precipitation at all.
I don't think it is normal.
Could someone help me ?
Magali
I am a new user of HEC-HMS and I am having some problems with the choice of the loss methods.
I have tried several of them (Initial and Constant Rate, DEficit and Constant Rate, SCS Curve Number, Smith Parlange, Green Ampt). And for all of them, the only excess precipitation I get is from the impervious area.
I have changed the amount of precipitation, and the parameters (from 100 times smaller to 5 times bigger) and there are no difference, except for the SCS Curve Number method.
If I try with "Impervious Area = 0%", I don't have any excess precipitation at all.
I don't think it is normal.
Could someone help me ?
Magali





RE: HEC HMS : Loss method and Impervious Area
According to your saying , you are not getting precipitation excess, for that check your meteorological model that you have set. If you have not defined Subbasin with appropriate method in meteorological model , you won't get precipitation excess. Like if you are applying inverse distance method, you have to specify the rainfall station location or centroid location defining it .
Best wishes !
RE: HEC HMS : Loss method and Impervious Area
Thank you for your answer but I don't think this is the problem. I have used two precipitation methods and the problem remains.
First I used the "Gage Weights" method. Because it is a small watershed, I only used 1 gage point.
Then for each of my subbasins, I said "yes" to "Use Gage" for this gage, and "1" for the "depth weight" and "1" for the 2Time Weight".
I also tried with a hypohetical storm (SCS Storm with "Type 1").
Did I do something wrong or the meteorologial model is not the problem ?
RE: HEC HMS : Loss method and Impervious Area
I just don't understand why this rate has to be so low (16 mm/h for a 24h-30mm precipitation) while the technical manual suggests that it should be estimated by the saturated hydraulic conductivity. I'll see when i will have observed data...
Thnak you for your help anyway !
maraligaf