Technical data

Chapter 3 Performing Hydrologic Studies

Estimating TR-55 Detention Basin Storage

Typically, most agencies, charged with reviewing storm water

management plans for developing sites, require that post-

development discharges from the site are equal to or less than pre-

development discharges for one or more storm frequencies. To meet

this governing requirement, most designers generally employ

detention type facilities in strategic locations across the site. The

detention basin is generally the least expensive and most reliable

measure for controlling post-development peak discharges.

After calculating the peak pre-development outflow and the peak

post-development inflow for a site, you can use the TR-55 Detention

Basin Storage feature to estimate the storage volume required by your

detention pond to control post-development generated runoff.

The TR-55 Detention Basin Storage procedure is based on the average

storage and routing results obtained from analyzing many detention

structures and is biased in favor of oversizing the designed detention

facility. The procedure should not be used for final pond sizing design

if an error of 25% in calculated storage volume is not acceptable.

Key Concepts

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You can use the runoff methods outlined earlier to determine the

peak inflow discharge into the detention pond and the peak

outflow discharge from the detention pond.

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You can build a surface and model the watershed before calculating

storage requirements by using the AutoCAD Land Development

Desktop Terrain Model Explorer.

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You can use existing data when you calculate the required storage

volume. Some of the different files you can use are *.tab files

generated by the TR-55 Tabular Hydrograph Method, *.ssc stage-

storage curve files, *.hdc hydrograph files, and *.bsn files.