Selection of bio-engineering techniques 

Various bio-engineering techniques can be used depending upon site condition and availability of resources possible combination or integration of the vegetative system with small scale engineering structures are endless. However, some techniques that are commonly used are as follows:

a. Planting trees, shrubs, and grasses

Trees, shrubs, and grasses can be planted on degraded slopes either alone or in combination for the protection of slope against erosion. Method of planting should be selected depending upon the purpose, site condition, and availability of resources. However, on a hilly slope, contour line planting at regular interval is the general practice.

b. Planting stumps system

Stump cutting woody vegetation can be planted along the contour to trap soil particles and debris falling down the slope.

c. Seeding grass, trees, and shrubs

Seeds of grass, trees, and shrubs can be sown directly on-site either alone or in combination. The method and timing for seeding depend upon site condition and availability of resources. Seeding can be done on the steep, rocky and unstable slope where direct plantation cannot be done.

d. Bamboo/ Bamboo grass planting

Bamboo and Amliso can be planted directly on slopes. They perform effectively once they are established.

e. Wattling

Bundles of live branches with buds are put into a trench along the contour and covered with a thin layer of soil. When the branches are emerged out and catch the soil, a strong vegetative barrier is formed which holds the soil particles moving down the hill slope. This techniques is not popular since it is expensive and work only in a gentle slope.

f. Brushwood check dams

Brushwood check dams using bamboo and wood are commonly used to stabilize the gully slope after the construction of check dams grass and shrubs are planted on gullies gully head and slide slope.

fig: Brushwood check dams

g. Vegetated rip-rap

Side slope of gullies and gully bed are sometimes protected by constructing dry stone walls and then grass seeds are sown or planted in the gap between the stone in order to reinforce toe walls and gullies beds.

h. Loose stone and gabion check dams

Construction of loose stone and gabion check dams is very common for stabilizing slopes. After the construction of check dam, seeding of trees, shrubs, and grass are done either separately or in the combination of gully heads, slide slopes, gully beds and in an around the surface for reinforcement.

i. Jute netting 

Jute netting is another way to protect the slopes using grass slips or seeding. This method can be useful on steep and hard slopes where the establishment of vegetation is difficult. Although this method is expensive it is commonly used in Nepal but results have not been evaluated yet.

fig: Jute Netting

Note:

Mulching

Mulch is a non-living material spread over the soil surface to provide protection from surface erosion by rainwater and retention of soil moisture. Various types of mulches are straw, grass fiber, wood fibers, seaweeds, and paper products, etc.

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