Dry ponds

Also known as infiltration basins.

Overview

Dry ponds are recommended as flood control structures to accommodate occasional excess overflow downstream of other structural BMPs. They should be integrated into the landscape as useful, accessible public space.

Design

Sizing

The surface storage volume of a dry pond (A_p) is simply determined:

$A_{p}={\frac {RVC_{T}\times A_{c}}{q\times t_{drawdown}}}$

Where:

• RVC_T = Runoff volume control target (mm)
• A_c = Area of the catchment (m²)
• q = infiltration rate (mm/hr)
• t = drawdown time (hrs)

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Modeling

Dry ponds are found in storage element in the LID TTT

The largest area is at the top, level 0 m; each subsequent lower depth has a smaller area

A dry pond as a storage element (key parameters) in the Treatment Train Tool.

Stage Storage
Name	Important to have a unique name, to connect it with the catchment area
Storage type	Dry detention ponds
Bottom elevation (m)	This is important to correspond with other components, e.g. when the overflow is coupled to another BMP within a treatment train
Maximum depth (m)
Lined/unlined	Unlined (ideally)
Underlying soil	Choose from five; sandy soils drain more quickly.
Evaporation factor	?
Suction head (mm)	?
Saturated conductivity (mm/hr)	?
Initial soil moisture deficit (fraction)	?
Curves
The Curves table is designed to accommodate the side slopes. The top line begins at 0 m, with subsequent depths in the following lines.

Ground depression acting as a flow control and water treatment structure, that is normally dry.

Depressed storage area, designed to capture flood events.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

The land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

The rate at which stormwater percolates into the subsoil measured in inches per hour.

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

The temporary storage of stormwater to control discharge rates, and allow for sedimentation.

Best management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls.

Stormwater management following the hierarchical approach: Source Control measures, Conveyance Control measure and End of Pipe treatment to achieve the water quality and water balance target for lot level development of the preferred strategy.

A combination of lot level, conveyance, and end-of-pipe stormwater management practices.

Abiotic transfer of water vapour to the atmosphere.