engineering methods to control soil erosion

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Engineering methods to control soil erosion Presented by: Santosh Pathak IAAS, Lamjung cam

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Engineering methods to control soil erosion

Presented by: Santosh Pathak IAAS, Lamjung campus

Engineering methods

Engineering methods deal with the physical structures that stops or try to prevent the happening of soil erosion.

Bioengineering is different terms than the civil engineering. Bioengineering uses the plants or trees to prevent the soil erosion whereas civil engineering deals about the construction of dams, walls,terrace etc.

There are different methods of engineering for soil erosion control. They are as follows:

a) Check dams

b) Retaining walls

c) Water ways

d) Terracing

e) Embankment

f) Spurs and soilways

Check dams

A check dam is a small dam which can be either temporary and permanent built across a minor channel, swale, bioswale, or drainage ditch.

They are used to slow the velocity of concentrated water flows, a practice that helps reduce erosion.

Check dams are typically constructed out of gravel, rock, sandbags, logs or treated lumber, or straw bales. They are most effective when used with other strom water, erosion.

These dams are usually used only in a small, open channel that drain ten acres (0.040km²) or less ; are usually do not exceed 2 feet high. They are also called Jack dams.

Many check dams tends to form stream pools. Under lorow flow circumstances water either infiltrates into the ground , evaporates , or seeps through or under the dam.

Under high flow(flood) conditions, water flows over or through the structure.

Coarse and medium grained sediments from runoff tends to be deposited behind check dams, while finer grains are usually allowed through.

Extra nutrients nitrogen, phosphorus, heavy metal and floating garbages are also trapped or eliminated by the presence of check dams, increasing their effectiveness as water quality control measure.

Check dams should not be used as substitute for other sediments – trapping and erosion control measures.

Advantages :

They store surface water for use both during and after the monsoon.

They help in ground water recharge of the area. Recharge of water helps in raising the water table in the area.

Which enhances availability of water ensures the increases of agricultural yield by multi-cropping.

Check dams can be used as a pisciculture.

Waterways

Nepal is second richest country of water resources. Nepal has about 45,000km of rivers. The rivers flow from the mountains and through steep hills because of which transportation is very difficult.

A feasibility study of water transport had also been carried out in Koshi, Karnali and Mahakali rivers.

The purpose of waterways in a conservation system is to convey runoff at non erosive velocity to a suitable disposal point. Therefore it should be carefully designed.

The most satisfactory location of a waterway is in a well vegetated natural drainage lined where the slopes, cross section, soil and vegetation have naturally developed to receive and carry the runoff.

Artificial waterways are normally protected by grass like paspalum spp, kikuyu, African star grass and so referred to grassed waterways.

Grass waterways are shallow and wide to obtain the maximum spread of water over a wide cross section. This waterways can be used in areas where there is sufficient moisture available to sustain a good grass cover.

Waterways should have a parabolic cross-section and be covered densely with locally adapted grasses. The deepest cut should be between 0.5 and 1.0m.

Before the onset of rains, the grass in the waterway must be cut so that the flow of water can proceed smoothly without causing eddies. Fertilisers should be applied regularly according to the requirement of the grassland.

Retaining walls

Retaining are structures designed to restrain soil to unnatural slopes. They are used to bound soils between two different elevations often in areas of terrain possessing undesirable slopes or in areas where landscape needs to be shaped severly.

Retaining wall is a structure designed and constructed to resist the lateral pressure of soil when there is desired change in ground elevations that exceeds the angle repose of the soil.

The most important consideration in proper design and

installation of retaining walls is to recognize and counteract the tendency of the retained material to move down slope due to gravity

Retaining walls are commonly used not only for control of erosion, but also to protect shorelines and keep rainwater from seeping into unwanted areas.

They also provide soil stability in areas where there is a risk of significant changes of ground elevation due to earthquakes and floods. Although retaining walls are used in the landscape, especially where new developments appear.

The basic material used in the construction of retaining walls is concrete, which is meant to serve the function of strength and durability. Because of their weight, and the resultant expensive shipping costs, contractors.

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