Detention basins (retarding basins, compensation basins, balancing ponds)

Stormwater detention storages are often provided to reduce peak flowrates and to improve stormwater quality. They slow down flows and allow some sediments and pollutants to settle out. They can take many forms. Most commonly in Australia they have a (normally) dry storage area behind an earth embankment. Wet basins have a permanent pond with a storage area above this. Retention basins allow some or all of the water held to infiltrate into the soil.

DRAINS provides facilities for modelling many kinds of basin, allowing for low-level and high-level outlets and interlinked basins (where the outlet of a basin is submerged by the water stored in a lower basin).  The complex calculations are based on culvert and weir hydraulics, with additional calculations for other complex relationships.

DRAINS does not assume direct rainfall on a Detention Basin, unless you specify an attached catchment. This allows the modeller the choice of either option.

Following a run, peak water levels upstream and downstream of the basin are presented in the Main Window. If multiple storms are used, the results for a particular storm can be selected from the pull-down menu that appears in the top-left corner of the drawing area.

Water levels upstream and downstream of basins can be examined using the Pop-Up (right mouse button) menu that provides options for plotting flowrates, storages and levels calculated during a run, or for displaying the numerical values. With older calculations using 1987 rainfall patterns, the pop-up menu provides these options:

With ARR 2019 calculations involving rainfall ensembles, the inflow and outflow hydrograph is not shown, but it is possible to see the water levels and volumes for the most critical storm and the summary of results.

• Related Articles

• Detention basin drawing tool

  This tool, , allows you to place a detention basin in the Main Window. When you select it, the arrow cursor changes to a pencil. Right-click your mouse to place a detention basin where you wish to locate it. The detention basin symbol will appear. To ...

• Detention basin property sheet

  In this sheet, you must specify an elevation-surface area relationship (or an elevation-volume relationship), select the type of low-level outlet and if necessary, enter data for the low-level outlet of the basin. The characteristics of basin outlets ...

• Detention basin property sheets (superseded)

  The setting out of information defining detention basins has changed twice during the life of the DRAINS program. You might encounter older models that include basins set out in superseded formats. DRAINS will still run with these, but it is best to ...

• Detention basin volumes

  Detention basin storages can take many shapes, from natural landforms to shapes such as prisms and wedges. Volumes are calculated by taking horizontal 'slices' and calculating the volume of each slice by averaging the surface areas at the top and ...

• On-site stormwater detention (OSD)

  This is the practice of providing storage devices within properties, with the aim of counteracting the hydrological effects of urbanisation from the increase in impervious surfaces. Storages are usually small and can consist of underground tanks or ...