Detention Storage Calculator
Reference page for estimating stormwater detention storage concepts, outlet controls, and the information needed before performing formal routing calculations.
What detention storage does
Detention storage temporarily holds runoff and releases it through a controlled outlet. The required storage depends on inflow hydrograph, allowable outflow, outlet geometry, stage-storage relationship, design storm, tailwater, and local criteria.
Inputs to collect
- Drainage area, land use, imperviousness, and time of concentration.
- Design storm depth, duration, and rainfall distribution.
- Pre-development and post-development runoff targets.
- Basin geometry, bottom elevation, side slopes, freeboard, and overflow route.
- Outlet type, orifice/weir size, invert elevation, and tailwater assumptions.
Conceptual sizing workflow
- Estimate inflow hydrographs for the applicable design storms.
- Set allowable release rates and design objectives.
- Create a stage-storage curve for the proposed basin.
- Create a stage-discharge curve for the outlet.
- Route the hydrograph and adjust storage or outlet controls until objectives are met.