Landslides a growing concern

Photo: Internet

When the harmony of nature is disturbed, it takes revenge. People of Bangladesh have recently seen this devastating side of nature, when soil of Chittagong Hill Tract collapsed, causing death to so many people.
In Chittagong many plants and vegetations have developed on the hill slopes. These plants have been grown for millions of years. The hill tracts are naturally laid on a slope as 1:2 or 1:3, which indicates the proportion of vertical to horizontal distance. In this slope, soil remains safe and comparatively stable.
In Bangladesh the rainy season, the rainfall is heavy and frequently ranges between 1,500 -- 2,500 mm per year. This rainfall has a normal tendency to slide down the hill slope. When the hill is covered with plants and huge vegetations, the risk of sliding is less. The heavy raindrops first hit the plants before the slope that reduces their energy. This slowed down raindrop cannot erode the top soil easily.
But when people cause deforestation in the hilly region, this situation alters completely. People living in hilly areas practice 'Joom' cultivation. They burn plants on hills to create land. As a result, hill top becomes bare and exposed. The rain drops falling on this bare soil causes significant erosion resulting in continuous washing of topsoil.
People living at the foot of the hills in Chittagong maintain a vulnerable existence. They often cut down the soil of hills to construct their houses. In this way, the normal comfort level of this hilly zone is being disturbed hugely. The natural slope of the hill is also altered by making it 1:0, instead of 1:2 or 1:3.
Because of this imbalance in slope as well as deforestation, frequent landslide occurs in the Chittagong Hill Tract.
Is there any way to arrest such erosion of hill slopes?
Dr. Mohammad Shariful Islam, Associate Professor, Bangladesh University of Engineering and Technology (Buet) answers:
There are different solutions. To restore a slope to its former condition, filling of that particular section might be needed. But this may not be possible. An eco-friendly long-term solution to this problem is plantation of long rooted vegetation.
If we sow seeds on a slope, then a specific period will be needed to grow these plants. During this period, we can use 'geojute' on the slope surface. Geojute is an open mesh type geotextile. It is biodegradable, eco-friendly and cost effective. Moreover, geojute can absorb water of about 4-5 times its dry weight. The rough surface of jute makes the passing of rainwater difficult on the topsoil by reducing its velocity .This helps to reduce soil erosion. Tree plantation along with vegetation can hugely reduce landslide on hills.
From our experience in various projects, we have seen that some small bushy type plants possess a long and very strong root system. One example is 'Vetiver', which can go up to 5 feet, but its root system can go up to 14 feet below the ground. This strong root system protects the soil from erosion, and thus prevents landslide. At last, we all must remember that we should live in nature by respecting it.

The writer is a civil engineering graduate.