Thursday February 15 2018

Prevent erosion of water-sensitive materials

Prevent erosion water-sensitive materials

To help prevent loss of water sensitive material, produce a backup storage plan for any and all the materials. In case you get a delivery early or cannot use the materials as quickly as you may have thought, have a plan in place for a dry and secure place to store the materials to prevent water damage. PHOTO BY RACHEL MABALA  

By Roland D. Nasasira

Edwin Mugume is building a double storeyed house at Bunamwaya hill on Entebbe Road. It has been under construction for a bit of time due to inconsistency in his income. When you visit the site, deep gullies are visible. They stretch from one corner of the levelled ground that lies on a hill, to another. He says these gullies developed during the rainy season of 2017.
“I noticed that whenever it rains, the water carries soil from one area to another. Rain water from the roof also tended to dig the house foundation. What I did was to set up water gutters and direct the water to a direction where the house foundation would not be affected. I also had to dig water drainage channels to direct erosive water to a more controlled direction,” Mugume explains.

Much as water erosion is the commonest kind at building sites such as Mugume’s, other kinds of erosion such as wind are in most cases ignored.
Jimmy Sserwadda, an independent engineer, says when well attended, both water and wind erosion can be controlled and minimised to avoid damaging effects. This, he reasons, helps you minimise unexpected costs that arise as a result of erosion.
“After levelling the ground, when you are sure you will not do any more digging or levelling, plant compound grass to prevent erosion from water and wind. When the grass has grown, it will control mobility of soil,” Sserwadda advises.

Be prepared
Sserwadda adds that, unfortunately, most common erosion types at a site come as a result of ignorance from site owners.
“A levelled ground is also considered a construction site. As you raise the required money to start the construction, take off time to visit your site to check if there is erosion occurrence or not. If it exists, find mechanisms of controlling it instead of waiting to spend more on levelling further,” Sserwadda advises.
“If you are constructing on a hilly area, the easiest way to control erosion especially water is by covering the soil because hilly areas are characterised by a lot of wind that might blow it away. Water tends to carry away materials such as sand which will lead to added costs,” Sserwadda says.

As it is imperative to visit a site to make sure builders are doing what they are supposed to do, Sserwadda says a developer should take time to study his construction site and know how erosion happens. “For example, visit the site during heavy rain so that you know how erosion happens in cases it does and how the water can be guided,” he says. This, Sserwada says, will help you understand how to deal or go about different approaches to control erosion.

Effects of erosion
Much as water and wind erosion can be controlled, their effects on the environment, site occupants, community and the neighbourhood is something that is often ignored.
Moses Senfuka, a site safety officer, says when water erosion at your site is not controlled, the gullies the water creates are a threat to site occupants or visitors such as children.
“If someone steps in a gulley that was left uncovered after it developed, they might fracture or twist their ankle joints. The gullies also dig deep into the already levelled ground, meaning you will have to spend more money to either have the ground levelled again or the gullies filled with soil,” Senfuka says.

Environmentally, he says, eroded water carries with it harmful substances such as cement and tiny metals that are deposited into the community water wells and other water bodies. In some cases, uncontrolled erosion can also cause the falling of trees which endangers lives.

Methods of erosion control
Unlike flat areas, Senfuka says erosion on steep construction sites can be controlled by partitioning or applying steps on the levelled ground especially if it is the compound that is left open and exposed. This method, he reasons, prevents high and fast water runoff and also maintains the quality of the soil.
According to the balance.com, an online portal, some of the principles of construction erosion control at a site include dividing the project into smaller phases by clearing smaller areas of vegetation, scheduling excavation during low-rainfall periods, when possible, fitting development to the terrain and excavating immediately before construction instead of leaving soils exposed for months or years.

Other principles include covering soils as soon as possible with vegetation or other materials. You can also mulch to reduce erosion potential, divert water from disturbed areas and control concentrated flow and runoff to reduce the volume and velocity of water from work sites. This will in the end prevent formation of gullies and minimise length and steepness of slopes using bench terraces.
Where wind erosion happens, the portal says, plan and install windbreakers and avoid soil compaction by restricting the use of trucks and heavy equipment to limited and supervised areas.

Apply sediment control methods
Any additional water runoff can usually be controlled using additional sediment control methods:
• Straw rolls can be applied on slopes, at the base of slopes, in trenches and around drainage devices. Ideally they should be placed along the natural contours of the land and staked down to keep them in place.
• Slit fences are designed to capture sediment at the base of slopes but are not intended for use on slopes or around storm drains. Incorrect installation and use of slit fences can actually increase erosion damage so use best practices when implementing this method.
• Gravel bags work similarly to sand bags but are filled with drain rocks and are used to protect drain inlets. The larger rocks allow sand to filter through without creating a dam.
• Rock entrances and roads to mitigate the disturbance to exposed soils. You can also use large rock or concrete pieces as energy dissipaters at the outlet of outlet of pipes, conduits or channels to slow the speed of water that flows through them.

Effects of erosion on the environment
•Soil erosion reduces crop yields when valuable cropland is lost, so it can raise prices or reduce food availability.
•It can reduce food by making it difficult to catch fish when waters are turbid, and can cause fish die-offs, especially when soil erosion carries toxic chemicals with it into the watershed, and into streams or lakes.
•If you appreciate nature, it can cause your outdoors experience to be less enjoyable when habitat is lost or spoiled from erosion, but at the same time, marvelous works of nature like the Grand Canyon are appreciated by millions.
•When the top layer is removed, the soil’s ability to store water and other nutrients are reduced. It also exposes the subsoil, which is the second layer of the soil.

rnasasira@ug.nationmedia.com

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