Sustainable Drainage Systems and Piles - Essay Example

Firstly it would be Infiltration trenches and the second will be Detention Basins. Infiltration trenches This is a system in which a trench is made and filled with artificial layers of granular material/aggregates which are clean and dry and then this is used in combination with geotextile. These granular materials have voids which are used to trap water and retain it for some time. Where as geotextile material prevents from clogging and durability. The Granular material should be 50 mm clear stones.

Then the materials are layered in the manner shown below. There are some conditions for its construction. Almost of the trench is underground and hence its maintenance will be expensive. The trenches are constructed at least 1.5m above the maximum groundwater level and it should be at least 5 m away from the foundations or buildings lines. It is used in areas where the silt/clay content is not more than 40 %.It is made in areas with type A and Type B soils. It should not be constructed near septic tanks or water supply line and the areas near it should have good house keeping, if it is not done it will result into choking of the voids that retains waters.

Then to improve the life and decrease the maintenance of the trenches it should be provided with Leaf screens, Vegetated filter strips or grass swales and similar devices such as grit separators, goss separator etc. Then these trenches are designed with an impervious drainage area to treatment facility area ratio of between 5:1 and 20:1. Therefore its is clear that the land take is very less and this option will be suitable where areas is less such as commercial areas. Where as the maintenance of the trenches are done by cleaning out leaves, debris and accumulated sediment caught in pretreatment devices, inlets and outlets annually or as needed.

If this is not done on regular basis then the trenches will choke and then a complete overhaul needs to be done which is costly. Normally the trenches’ material is replaced in 5 years. Although the cost of construction is low but the maintenance cost is high and needs to be repeated. Then in this type of system when the water passes through the layers of the trenches the solid particles are filtered and the geotextile improves the process. Eventually the quality of the water is improved but the water does not provide microbiological purification.

Concluding the merit of the system are that they require less space, the improve water quality, have less construction cost, reduce the runoff during rainy season and reduce the erosion that might occur by heavy rainfall and its runoff. Where as the demerits are that the maintenance of the system is high and repetitive, the system doesnot purify biologically. It cannot be made in areas where underground services are present. These systems are not used in high slope areas. It is ineffective in areas where soil is contaminated and polluted.

It looks the worst when the system is choked as the water stays and do not drain. Detention Basins As the name indicates this system impound water in an excavated area or basin. Primarily this is used in areas where there is heavy rainfall and frequent flooding. These basins are used in reducing peak storm water discharges, controlling floods and preventing downstream channel scouring. There are two type of detention basins dry detention basin (storage is for specified short time) and the other is extended detention basin (used for retention for