The primary purpose of installing land drains is to capture or control surface or run off water in an efficient manner and to divert or re-direct the excess water away from the affected area to an alternative site location safely (typically a soakaway pit or percolation area) which is capable of absorbing the excess water.
The process of installing land drains is generally straightforward, this would typically entail excavating a trench, part back-filling with gravel, inserting land drain pipes (protected and wrapped in a permeable membrane) and the protected pipe and trench is back-filled with more gravel. Depending on the extent of the works, land drains pipework (available in various diameters including 100mm, 150mm etc) are usually installed in trenches at least 600mm deep and 300mm wide.
Our current project is far from typical for a number of reasons. Firstly the terrain is very steep which is adding to the complexity and volume of water which must be controlled and managed. Rather unfortunate but the excessive record levels of rainfall which we’ve had (or suffered) over the last two days has severely disrupted our progress.
In this project we will be installing two land drain pipes (150mm diameter) and the trench will be wrapping both the gravel and pipes together with the membrane. This is essential to prevent any silt or soil from entering the pipework which would eventually hamper the water flow rates. The land drains will be laid as to rely on gravity for conveying the water through the land drain pipes.
The close proximity of steep embankments to our excavation works has also hampered our access thus slowing progress during the severe wet spells. Fortunately aided with several submersible pumps we are able to control and discharge quickly excess water from our trenching which we are excavating or back-filling with drainage gravel in preparation for installation of land drains.