# Hooghoudt

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### Spacing drainage pipes to reduce groundwater mounding

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

This recommendation is supported by an analysis of Hooghoudt's equation ^{[1]}^{[2]}^{[3]} in relation to loamy or clayey native soils, where *K _{media}*>>

*K*, 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\[Drain\ spacing=\sqrt{\frac{4K_{media}\left(D_{d}-D_{w}\right)^{2}}{q}}\]

_{soil}Where:

*K*_{media}is expressed in m/day*D*is the depth to the drain pipe (m)_{d}*D*is the minimum acceptable depth to the water table during infiltration event_{w}*q*is the inflow volume expressed as a depth over the entire surface (m)

- ↑ H.P.Ritzema, 1994, Subsurface flow to drains. Chapter 8 in: H.P.Ritzema (ed.), Drainage Principles and Applications, Publ. 16, pp. 236-304, International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands. ISBN 90-70754-33-9
- ↑ W.H. van der Molen en J.Wesseling, 1991. A solution in closed form and a series solution to replace the tables for the thickness of the equivalent layer in Hooghoudt's drain spacing equation. Agricultural Water Management 19, pp.1-16
- ↑ van Beers, W.F.J. 1976, COMPUTING DRAIN SPACINGS: A generalized method with special reference to sensitivity analysis and geo-hydrological investigations, International Institute for Land Reclamation and Improvement (ILRI) Wageningen, The Netherlands