Reservoir volume-area coefficients

[Julia Glenday]

Hi!

I am modelling a catchment with large water supply reservoirs and I am having several issues in getting these accurately represented in my SWAT+ model.  A first question is about the area and volume inputs in SWAT+ and if/how the shp_co1 and shp_co2 coefficients are used.

I have entered values for these constants in my model, but when I look at the volumes and areas in the model output, it appears not to have used them... 

I have a rating table for each reservoir based on bathymetry survey. I fit a Surface Area = beta*(Volume^alpha) relationship to this to get the shape coefficients (beta - scalar, alpha - exponent) relevant to the SWAT units (Area in ha and Volume in 10^4 m3). 

I used this relationship to get the volumes and areas to use in the model for the emergency and principal spillway levels and entered these in the model interface. 

I entered the shp_co1 and shp_co2 values from my fitted curve into the SWAT+ interface (assuming shp_co1 is the scalar (beta) and the shp_co2 is the exponent (alpha) as well.) 

However when I look at the model outputs of volume and area for the reservoirs, what it seems to have done is assumed the exponent alpha is 0.9 in all cases and then calculated the beta using the two areas and volumes given (pvol and evol). 

It does this despite me inputting values for shp_co1 and shp_co2 (with shp_co2 not being 0.9). The model output actually comes out the same if I put 0 for shp_co1 & 2.

 

Has anyone encountered this? 

Is there another way I should input the information so that the model better reflects the known bathymetry?  Evaporation is very high in the area I am working with and so I'd like this to be accurate. 

Thanks,

Julia