## Stage-Storgae Calculations

## Stage-Storgae Calculations

(OP)

I need to calculate the stage-storage relationship for a detention basin. I am trying to design a Dry Detention basin and I need to come up with the TOB, and Control elevations. I am not sure how to do the stage-storage calculations. Can someone help me? Thanks in advance.

## RE: Stage-Storgae Calculations

1. Determine the stage increments that you need.

2. Start at the bottom (depth = 0) of the facility and for each stage (elevation) determine the surface area

3. Determine the incremental volume between each stage. Incremental Volume = (Average Surface Area between adjacent stages) x (difference in elevation)

4. Once all incremental volumes are determined, do a cumulative summation to determine the stage-storage relationship.

Set-up a spreadsheet and this becomes easy as pie. When you get to it, your spreadsheet can also include some columns for the discharge calculations.

I typically determine my S-S relationship in 0.100 m (4") increments. With the help AutoCad, this is what I do:

1. Start with an AutoCad drawing of the facility in which the outline of the bottom (depth = 0) of the facility is a PLINE (a closed polygon with an associated area)

2. OFFSET the PLINE to the depth = 0.100m (4") level. For example: If your pond side slopes are 3:1, then you would offset the PLINE 0.300m (12"). If the pond side slopes vary, then you may have to make some adjustment of account for the different slopes. Determine the area at this stage.

3. Repeat step 2 for depth = 0.200 (8") by either offsetting the bottom by 0.600m (24"), or offsetting the 0.100m depth contour by another 0.300m (12"). [These numbers are still assuming 3:1 pond side slopes]

Hope this helps.

## RE: Stage-Storgae Calculations

For detention basins, we use Hydraflow, which calculates our in- and out-flow hydrographs using either the SCS or Rational method (we use SCS as it's more conservative). Hydraflow is simple software to use, but it's not free.

I believe that SWMM can do this task and a whole lot more, but I haven't had much chance to play with it yet. SWMM is free software distributed by the EPA. http://www.epa.gov/ednnrmrl/swmm/

## RE: Stage-Storgae Calculations

## RE: Stage-Storgae Calculations