Hooghoudt

Spacing drainage pipes to reduce groundwater mounding

The yellow box represents the recommended hydraulic conductivity of bioretention filter media

In most LID underdrain applications, lateral drains should be spaced between 5 - 6 m apart.

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This recommendation is supported by an analysis of Hooghoudt's equation in relation to loamy or clayey native soils, where K_media>>K_soil, finds the first term of the numerator negligible, so that the original equation: $Drain\ spacing={\sqrt {\frac {8K_{soil}H\left(D_{i}-D_{d}\right)\left(D_{d}-D_{w}\right)+4K_{soil}\left(D_{d}-D_{w}\right)^{2}}{q}}}$ may be simplified to: $Drain\ spacing={\sqrt {\frac {4K_{media}\left(D_{d}-D_{w}\right)^{2}}{q}}}$

Where:

• K_media is expressed in m/day
• D_d is the depth to the drain pipe (m)
• D_w is the minimum acceptable depth to the water table during infiltration event
• q is the inflow volume expressed as a depth over the entire surface (m)

A parameter that describes the capability of a medium to transmit water.

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

The engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles.

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.

A perforated pipe used to assist the draining of soils.

The upper surface of the zone of saturation, except where the surface is formed by an impermeable body.

Subsurface water level which is defined by the level below which all the spaces in the soil are filled with water; The entire region below the water table is called the saturated zone.

Relating to the properties, distribution and effects of water on and below the earth’s surface, and in the atmosphere.