Snowmelt vs Initial Abstractions
Snowmelt vs Initial Abstractions
(OP)
I'm trying to create a model to be able to calculate the runoff induce by precipitation (of both rain and snow). To be able to access both the volume of runoff and the peak discharges...
So i've created a HEC HMS model with subbasins, reaches, etc. I decided to use the Deficit and Constant method for calculating losses (i usually use SCS and CN number) and the SCS lag time for Transform.
I have in hands, both precipitation and temperature on an hourly basis which i've entered in the model so i can use the Temperature-Index method.
The model is calibrated for "storm-events" based on measured flow rate. And the model is giving good results (i'm almost surprised myself...)
So now ... I'm trying to simulate the snowmelt for a long term event (say on a yearly basis). The model runs and everything seems fine for the months where there's no snow (when compared to measured data).
BUT... When it comes to snowmelt... nothing. It's like if the program takes snowmelt in account but when it creates a precipitation from it to put it back in the model (thats how i see the process) the runoff induced is "taken" by the losses (mainly because the Initial abstractions > runoff).
What to do ? Lower the initial abstraction? Even if it's giving good results vs measured flow rates. Model separately months with and without snow?
Any ideas would be fine right now !
So i've created a HEC HMS model with subbasins, reaches, etc. I decided to use the Deficit and Constant method for calculating losses (i usually use SCS and CN number) and the SCS lag time for Transform.
I have in hands, both precipitation and temperature on an hourly basis which i've entered in the model so i can use the Temperature-Index method.
The model is calibrated for "storm-events" based on measured flow rate. And the model is giving good results (i'm almost surprised myself...)
So now ... I'm trying to simulate the snowmelt for a long term event (say on a yearly basis). The model runs and everything seems fine for the months where there's no snow (when compared to measured data).
BUT... When it comes to snowmelt... nothing. It's like if the program takes snowmelt in account but when it creates a precipitation from it to put it back in the model (thats how i see the process) the runoff induced is "taken" by the losses (mainly because the Initial abstractions > runoff).
What to do ? Lower the initial abstraction? Even if it's giving good results vs measured flow rates. Model separately months with and without snow?
Any ideas would be fine right now !





RE: Snowmelt vs Initial Abstractions
RE: Snowmelt vs Initial Abstractions
Thanks for your time
RE: Snowmelt vs Initial Abstractions
Unless you have reservoirs in your model that need initial stages from previous segments, each time segment should be mostly independent from the previous segments.
RE: Snowmelt vs Initial Abstractions
You can also change the AMC/ARC to III (which raises all CN values for wet conditions) or IV (which increases all CN values to 98 for impervious or frozen ground)
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Snowmelt vs Initial Abstractions
Can HydroCAD automatically change Ia/S and ARC at predetermined times during the simulation? Or do they have to remain constant throughout the simulation?
I've only ever used the free version, and not very much at that. But, I never saw an option for time variable infiltration parameters.
RE: Snowmelt vs Initial Abstractions
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Snowmelt vs Initial Abstractions
RE: Snowmelt vs Initial Abstractions
Or change the Infiltration method.