Ideally, such levies should have a spacing of 30 to 50 meters for slopes that possess a gradient of five to twelve degrees. Every levee can cater to an area of about 3 hectares with a total length that is less than 400 meters. Care must be taken to establish a grass cover immediately after creating a levee or the channel could quickly erode. 4. Grassed Waterways A grassed waterway is typically quite shallow and may be narrow to a few meters in width. These can be used to regulate drain outflows going down slopes, so as to cheaply prevent erosion. The ratio be- tween the vertical and horizontal sections of the waterway needs to be in 1:4 proportion. A necessary prerequisite of such a waterway is a dense expanse of grass. The quantity of water to be evacuated as well as the steepness of the slope will have a bearing on both the size and the shape of the waterway. The steeper the slope, the wider should be the waterway. It is important that the bottom of the waterway be as horizontal as is possible to enable the water to spread out evenly. It is important that such waterways not be constructed in areas prone to erosion or they will fail. Final Thoughts Surface drainage systems are an essential part of any holistic drainage system. Not having a well designed surface drainage system can wreak havoc with a landscape unable to permeate excessive runoff. It, there- fore, makes eminent sense to keep it at the forefront in site planning, design and engineering. These systems are used in conjunction with other drainage applications such as catch basins and heavy duty trench drain systems (https://swiftdrain.com/heavy-duty-trench-drain/). The methods of surface water evacuation described are some of the more popular sustainable methods used to deal with a myriad of po- tential waterlogging issues. A well-designed surface drainage system ensures that the duration of ponded water is never long enough to cause any damage on a particular landscape. A free-flowing surface drainage system enables free flowing of water thereby preventing flooding of a specific area. That apart, such systems decrease the health implications associated with stagnant water buildup such as those caused by mosquitos. Managing surface drainage can often be done with simple but effec- tive designs that don’t have a relatively large capital expenditure and impact to the natural topography.
3. Levees Levees are surface channels usually created on land with a gradient in such a manner that the soil removed to create these forms a levee on the downslope of these channels. This helps the surface runoff not build so much velocity while flowing down a slope that it starts eroding the land. The banks or levees have to follow the lay of the slope and make the water flow down gently and not create make the lane below susceptible to landslips.
ANKIT SEHGAL is the President and Head of Engineering at Swiftdrain Inc., a global drainage and infrastructure products manufacturing company. He oversees all product design and development at the firm, including engineering, materials sourcing and production. https://swiftdrain.com
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csengineermag.com
may 2020
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