Resservoir simulation

[Jayandra Shrestha]

Hi,

Can anybody help me to understand the reservoir and sediment simulation in SWAT? How does it work and its flow chart etc. if any? I have gone through swat2009 theory doc but it's not enough to analyze results.

Thank you.

Regards,

JP

[Jim Almendinger]

Fundamentally, sediment is deposited in reservoirs according to a settling velocity (dependent on D50, the median particle size) and hydraulic residence time.  The larger the particles, and the longer the residence time, then the more sediment is deposited.  The exception is that sediment concentrations do not fall below the equilibrium sediment concentration (NSED), which is the suspended concentration sustained (I presume) by typical wind turbulence. 

Reservoir sedimentation is extremely sensitive to RES_NSED and RES_D50.  If NSED is too large, your reservoirs can have negative sedimentation, which is generally nonsense, and can generate a downstream sediment load that is not realistic and unconstrained (i.e., the lake could be an infinite source of sediment).  So check your reservoirs to make sure they are trapping, and not creating, sediment.  Try starting with a RES_NSED of about 1 mg/L and adjust as needed.  RES_D50 can be highly variable from reservoir to reservoir, but you could start with 10 um (micrometers). 

Sediment trapping efficiencies can be highly variable among reservoirs (say, from 25% to nearly 100%), and there are some simple engineering equations to estimate it from reservoir volumes and areas.  I would guess a typical range would about 80-95%, but your reservoir may differ.  You should find values in the literature to substantiate your results, but this should get you started.

Good luck,

-- 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

[Jayandra Shrestha]

Hi Jim,

Thank you for your valuable information.

Best Regards,

JP