HEC-HMS Reservoir 1

[larryTHUR]

Hello again,

i got the problem that i want to use a reservoir to catch some a part of the flood (in german: Hochwasserrückhaltebecken ). The thing is, that the volume of the reservoir is really small, so HEC-HMS end most of the simulation runs because:

"ERROR 41346: Computed storage in reservoir "HRB_1_TEST" exceeded maximum value in storage table"

Okay, from this i know the maximum rainfall-time witch the reservoir can handle. But is there any possibility to work on with the reservoir and rainfall-times, greater then that witch are to handle, and a constant maximum discharge without creating a dam break?

The other point ist, that i can not really work with a constant discharge. I mean, that e want a constant discharge from 1,7 m³/s independent from the elevation.

I use the Elevation-Area and the Elevation-Discharge function. Method is Outflow Curve, Storage Method: Elevation-Area-Discharge, Primary: Elevation-Discharge, Initial Condition: Inflow=Outflow

Best regards

 

[cvg]

so add a spillway to pass the excess flow. the dam should be high enough to allow the maximum discharge through the spillway without overtopping, plus freeboard

 

[larryTHUR]

Okay, but for a spillway i have to make many details, which i don't know. I only have some pictures and a DEM. Perhaps i can add a new elevation within or above the freeboard and give her a realy great discharge for "overtopping the dam?

 

[larryTHUR]

One more question. i try it with overtop dam. For this i need the elevation of the dam. But when i enter the maximum elevation of the reservoir/waterlevel, i become the message:

Computed pool elevation is above maximum table value for reservoir "HRB_Test".

Why must i choose a elevation under the maximum high of the water?

 

[cvg]

your stage storage table must extend high enough (several feet or meters deep over the top of dam) so HMS can calculate the storage during overtopping of the dam. If the maximum stage is set to the top of dam elevation, no water will go over the dam.

 

[beej67]

Treat the top of the dam itself as if it was one long broad crested weir, and calculate the stage storage far enough over the top of the dam to catch the storm.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[psmart]

cvg and beej67 make an important point that applies to virtually all pond and reservoir routing calculations: You must define storage to some point above the spillway, so that accurate storage information is available as the WSE exceeds the spillway. You'd be surprised how many people think that "a pond has no storage above the weir, because everything just spills over." That's simply not the case: Whatever head you have over the spillway, the corresponding volume of water is being detained in the pond or reservoir, and must be included in the stage-storage data.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[larryTHUR]

Thanks, now it works. But i have an other question. There are some tables where you have to enter values for the discharge (Elevation-Discharge, Storage-Discharge). Is this the discharge from the formula: √2gh or can i enter the discharge which results from the metrics of the outlet respectively the discharge which is to handle from the underlying canalization. Quasi can i limit the discharge in this tables?

 

[larryTHUR]

I had try several initial conditions. So far, so god. When i choose elevation al initial condition, i had to enter a value which is above my elevation in the tables. Otherwise: Computed pool elevation is below minimum table value for reservoir "TEST". In the tables i had enter a value for elevation, where discharge, storage and area is zero. Why can i not choose this elevation as initial condition? The model only works with a value a little bit above. I mean i can choose initial storage 0 m³ but not 412,7 as initial elevation?

Thanks and best regards

Elevation Storage Area Discharge
412.70 0.000000 0.000000 0.00
412.80 0.001803 0.039116 1.40
412.90 0.009839 0.132953 1.98
413.00 0.029924 0.282936 2.42
413.10 0.068552 0.490934 2.80
413.20 0.127160 0.687006 3.01
413.30 0.209226 0.968337 3.43
413.40 0.322507 1.317260 3.70
413.50 0.477253 1.749064 3.96
413.60 0.673533 2.158241 4.20
413.70 0.908421 2.552598 4.43
413.80 1.189736 3.087467 4.64
413.90 1.537613 3.773121 4.85