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Riverbed infiltration galleries

347 bytes added, 17:31, 7 April 2012
→‎Construction, operations and maintenance
Some rural people and most well-diggers know that water can only be found at certain places in riverbeds. They can also give a rough estimate on how deep they have to dig before reaching the water-table.Their knowledge is based on the fact that certain species of trees and vegetation must have roots reaching down and into the water-table in order to survive droughts. This traditional information (based on Kenyan plants) is compiled in the table below as an example. Make sure to find the unique regional plants specific to your site area.
Since the trees below must have their tap root in the water table, the depth of a water-table can be found by knowing the depth of the tree’s tap root. A rule of thumb states that the tap root of a tree has a depth equal to about 3⁄4 of the height of the tree. The height of a tree can be found by measuring the length of the shadow the tree is casting on the ground and comparing it with the length of the shadow of a stick 100 centimeters long. The two measurements should be taken in the sunshine of early morning or late afternoon when the shadows are longest. For example: If the stick’ shadow is 80 cm long, the ratio is: 80/100 = 0.8. If the tree’s shadow is 12 m long, then the tree is: 12 m x 5 / 4 = 15 m high and the tap root and water level is at: 15 m x 3⁄4 = 11.25 m depth.
[[File:WaterTableDepthChart.jpg]]
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