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Line 1: − 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.+ + + Line 8:
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Underdrains comprise a length of perforated pipe embedded into a reservoir gravel layer.
*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 75 - 100 mm pea gravel may then be included on top of the reservoir gravel to provide a smoother surface and reduce tearing to the geotextile.
*A layer of 75 - 100 mm pea gravel may then be included on top of the reservoir gravel to provide a smoother surface and reduce tearing to the geotextile.
*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.
A pair of small wells are recommended to inspect and periodically flush accumulated sediment from the underdrain pipe.
==Recommendations for material specifications==
==Recommendations for material specifications==