Measures for landslide prevention in Chittagong hill tracts of Bangladesh

Abstract

Landslide is one of the most significant natural disasters in hilly environment. It is a major concern for Bangladesh since the Hill Tracts of Bangladesh are very vulnerable to landslide because of its geological formation and soil characteristics. Devastating landslides have hit Chittagong Hill Tracts (CHT) areas repeatedly in recent years. Moreover, rapid urbanization, increased population density, improper land-use, cutting of hills, indiscriminate deforestation and agricultural practices are aggravating the landslide vulnerability in CHT. Against this backdrop, it is essential to develop suitable methods which can be effective and economic solution for landslide prevention. Disturbed and undisturbed soil samples have been collected from different landslide prone locations of Rangamati. Index and engineering properties of the collected soil samples have been determined to characterize the hill soil. To understand the behaviour of hill slopes, Finite Element Models have been developed using the soil properties obtained from the laboratory tests of the collected samples. Effect of vegetation and slope angle has been studied from the numerical models. It is observed that factor of safety (FS) decreases with the increase of slope angle. However, vegetation (rooted soil) has little contribution in increasing FS. Nailed slope with vegetated cover performs better for stability of slopes. Increasing degree of saturation for rainfall decreases FS of slope. Hence, proper drainage can effectively decrease landslides. For developing nations like Bangladesh, where soil erosion is prevalent in its extreme form, landslide is one of the most deteriorating natural processes that must be dealt with. Little has been accomplished in dealing with erosion that can be widely applied, in inexpensive, long-lived, and appealing appli¬cations. Vetiver, a tropical grass, offers a practical and inexpensive way to prevent erosion. This deeply rooted, persistent grass has restrained erodible soils for decades. Efficacy of vetiver in soil erosion has been studied with small scale laboratory model study. Performance of slope against erosion has been studied under rainfall for both bare slope and vetiver rooted slope. It is found that sediment yield for bare soil is very much higher compared to the sediment yield for rooted slope. Amount of infiltrated water increases with time resulting in reduced surface runoff and soil loss for the vegetated slope. Sediment yield tends to be zero after a certain rainfall which prove the effectiveness of vetiver grass against erosion. From this study, it can be said that the vetiver grass plantation is effective to protect the hill slopes against top soil erosion and surface runoff. It may act better in combination of soil nailing and proper drainage for overall stability of slopes. It also works against shallow depth failure. Plantation of vetiver can be a cost-effective, sustainable and eco-friendly method for the erosion control as well as shallow depth slope failure in Bangladesh.