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<p>An underdrain comprises a length of perforated pipe embedded into a reservoir gravel layer.  A pair of small wells are recommended to inspect and periodically flush accumulated sediment from the underdrain pipe.</p>

An underdrain comprises a length of perforated pipe embedded into a reservoir gravel layer.  A pair of small wells are recommended to inspect and periodically flush accumulated sediment from the underdrain pipe.</p>

*To promote infiltration the base of the gravel reservoir and the underdrain pipe should be horizontal to optimize distribution of the water within.  

*To promote infiltration the base of the gravel reservoir and the underdrain pipe should be horizontal to optimize distribution of the water within.  

*Where drainage or conveyance to a downstream facility is a greater priority, the base of the reservoir and the underdrain pipe may have a gradient of up to 1-2%.

*Where drainage or conveyance to a downstream facility is a greater priority, the base of the reservoir and the underdrain pipe may have a gradient of up to 1-2%.

*A layer of geotextile is usually then used to prevent migration of fines into the underdrain/reservoir space.

*A layer of geotextile is usually then used to prevent migration of fines into the underdrain/reservoir space.

==Recommendations for material specifications==

===Recommendations for material specifications===

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<h5>Geotextile</h5>

<div class="NavHead"><h5>Geotextile</h5></div>

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<h5>Pipes</h5>

<h5>Pipes</h5>

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