reservoir editing

[Tingting Liu]

Dear users,

I am using editing reservoir options to simulate the lakes and sames in my watershed. The watershed itself is about 13 km^2 which is 1300 ha.

The problem I have is I have changed RES_ESA, PES_PSA, volume for emergency spillway and principal spillway and also number of days to reach the target volume, however the results don't change comparing to the default setting for all the reservoir parameter.

Could anyone tell me what the problem it is and what is the most critical parameter in the reservoir editing?



Thanks,
Tingting




--

Tingting Liu

Department of Environment and Natural Resources Economics

University of Rhode Island

[Jim Almendinger]

I'm not sure how sensitive the reservoir routines are to geometry, but I'd make sure that your ESA > PSA, and EVOL > PVOL, since SWAT uses these two known points to infer reservoir geometry (area as a function of volume).  I.e., SWAT keeps track of volume by mass balance considerations, and then uses the area to calculate evaporation and seepage losses.  I usually set all 12 months of my target volumes (STARG) equal to the principal volume, since I don't want SWAT to be calculating target volumes based on soil moisture.  

But your model should be sensitive to NDTARGR, as long as NDTARG > 1.  If NDTARG = 1, then the reservoir has no storage and everything leaves the same day it enters.  It is unfortunate, but NDTARGR is limited to being an integer in SWAT.  It would be better to have it typed as a real number, which would allow much finer calibration of outflow -- and it should be a trivial code change to fix this.  

To see the effect, further, your emergency volume must be substantially larger than your principal volume, since the release of water from storage only occurs at volumes intermediate between emergency and target volumes.  Everything over the emergency volume gets dumped immediately, the same day it arrives.  

And -- make sure you've selected the option to have reservoirs use the targeted release.  

Cheers,

-- Jim

Dr. James E. Almendinger, Senior Scientist
St. Croix Watershed Research Station
Science Museum of Minnesota
16910  152nd St. N
Marine on St. Croix, MN  55047
tel: 651-433-5953 X 19
fax: 651-433-5924
email: din...@smm.org
web: www.smm.org/SCWRS/

[Madusanka Thilakarathne]

Dear Sir, 

My reservior RES_ESA is about 4400 ha. But SWAT does not allow more than 3000 ha. What can I do ?

Please let me know

Thanks

[Jhon]

It is possible to do that by editing manually, the max and min values in the table (resrng) in your swat2009.mdb.

[Cva Shrestha]

Jim from your quote "I usually set all 12 months of my target volumes (STARG) equal to the principal volume."

12 months of   target volumes are the buffer level :(operation rule curve)

Does Principal volume means when filled to principal_spillway

RES_PSA Reservoir surface area when the reservoir is filled to the

principal spillway (ha).RES_PVOL Volume of water needed to fill the reservoir to the

principal spillway 

Its only a single value in option in SWAT

[Jim Almendinger]

I am not quite sure what your question is.  ArcSWAT (in the res table) allows input for 12 values of STARG (STARG1 to STARG12), and I set all of these equal to the principal volume (RES_PVOL).  I do this because I do not want my target volume to be calculated as a function of soil moisture, because my reservoirs (lakes) are not managed for water supply and flood control, which is what SWAT assumes by default. 

Yes, of course RES_PVOL is a single value, and I copy and paste it 12 times to fill in the 12 STARG values. 

-- Jim

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Dr. James E. Almendinger

St. Croix Watershed Research Station
Science Museum of Minnesota

16910 152nd St N

Marine on St. Croix, MN  55047

tel: 651-433-5953 ext 19

[Cva Shrestha]

I am sorry for not being clear.

1.I was wondering if there is a proper way to assign operation rule for rule for reservoir.

Say, In january , it has to maintain certain water level and above that all water is either used or spilled. and similar for other months

2. Is there a proper way to feed elevation-area-volume curve for reservoirs...other than what SWAT has that it uses the principal volume area 
/volume and  emergency volume/area 

3.regarding ET..the formula used by SWAT (.6*PET)...is there any other option like..inputting a measured Pan Evaporation..data ..

Again Thank you jim...

[Jim Almendinger]

SWAT does not know the elevation of your reservoir, and operates only on the volume and area (which it determines from the volume according to the relation given in the theory manual, based on the principal and emergency volumes and area you input to SWAT).  If you want your reservoir to not spill below a certain elevation (level) in a given month, then you need to calculate the volume associated with that level, outside of SWAT, and put in that volume as your STARG value for that month. SWAT will spill water above that volume according to the rate determined by NTARG. 

As for ET, I don't think you can enter your own values for the reservoir alone.  You can input your own time series of PET values as part of the weather station input, but these values will affect more than just your reservoir -- it will affect all the subbasins attached to that weather station. You can change the evaporative coefficient that relates reservoir evaporation to PET, changing it from 0.6 to whatever you choose, I think. 

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