LANDSLIDE SUSCEPTIBILTY ASSESSMENT USING GIS MODELING - THE CASE STUDY OF ZOMBA MOUNTAIN AREAS

Landslide susceptibility mapping is a practical tool in natural and urban planning. It can be applied for determining land use zone, in construction design, and planning of a variety of projects. In this study, GIS based landslide susceptibility map were generated in the mountainous parts of Zomba district at the Southern part of Zomba Mountain plateau which has helped in determining the slope effects that can induces landslides in the study area. This was accomplished by using the weight of evidence (WoE) method for correlating the causative factors which have an effects on landslide occurrences.
The instability factors taken into account were lithology, slope angle, slope aspect, distance to stream, curvature and land use. These factors were integrated in GIS environment for constructing the thematic layers of factor dataset. For this bivariate statistical approach, significant assumptions were emphasized prior to the study to establish conditional independence between each pair of components. In addition, a detailed landslide inventory map was constructed through field investigation and Google earth image interpretation process at a scale of 1:125,000. The thematic layers and landslide map were overlapped to obtain a spatial statistical relationship. The produced susceptibility map were classified into four zones: Very Low, Low, Moderate, and High susceptible zones and validated using the other half number of the landslide events of the area. The map indicates that more than 90% of the landslides were in categories of high and moderate susceptibility zones. The causative factor classes including the slope class >55, the north facing slopes, the highly weathered Syenites and superficial deposits of Dambo soils and the bare lands were identified to considerably influence the landslide in the study area.

In this study, GIS based landslide susceptibility map were generated in the mountainous parts of Zomba district at the Southern part of Zomba Mountain plateau which has helped in determining the slope effects that can induces landslides in the study area. This was accomplished by using the weight of evidence (WoE) method for correlating the causative factors which have an effects on landslide occurrences. The produced susceptibility map were classified into four zones: Very Low, Low, Moderate, and High susceptible zones and validated using the other half number of the landslide events of the area. The causative factor classes including the slope class >55, the north facing slopes, the highly weathered Syenites and superficial deposits of Dambo soils and the bare lands were identified to considerably influence the landslide in the study area.

The study was conducted in Zomba Mountain areas within Zomba plateau in Zomba district Southern part of Malawi. Zomba Mountain is located to the South of the Zomba plateau (Zomba massif). It is a Mountain of the Shire highlands in the Southern Malawi. The study area covers a total area of about 130 square kilometers (50sq mi), with the highest elevation of 2,087 meters (6,847ft).The area is bounded within 15000S and 150300 S parallel of latitude, the 350 00E parallel of longitude and Western shores of Lake Chilwa (Bloomfield, 1965). Zomba Mountain is composed of a Mesozoic syenite pluton that intruded Precambrian high-grade metamorphic gneisses and granulites. The Southern and Eastern scarps of Zomba Mountain attain a maximum height of 914.4 meters and have been formed by the differential erosion of the syenites making up the Massif and the surrounding Basement Complex gneisses. Weathering erosion and uplift have left the syenite standing at an elevation of 2000 meters while surrounding area is between 700 and 1000 meters above sea level. Zomba town is located at the foot of the Mountain. The slopes of the plateau above the inhabited locations have experienced erosion and landslides. As a consequence, the top soil was removed, exposing rocks and making the slopes unstable. The topography of Zomba is further dominated by several hills surrounding the city and some within the city. From these hills (mainly in the north towards Zomba Plateau and south), small streams connect to the main Likangala River, which flows through the city centre from west to east.
Meanwhile, the Mulunguzi River, which originates from Zomba Plateau, flows through two of the wards in the north-east of the city. During the rainy season, increased water run-off in up-hill areas into the rivers flowing through the city causes flooding. In particular, Likangala River is the source of most floods and disasters, as it flows through densely populated areas. The risk profile of Zomba includes flooding, cyclones and strong winds. Since the city is located in the African Rift Valley, it is prone to earthquakes. Bush fires are also common, especially in the woods of the Zomba Plateau. Soil erosion, gully development, landslides and rock avalanches are common and to a certain extent linked to deforestation, which causes land degradation.

Traditional authority: TA Malemia

District: Zomba

Coordinates: -15.28605, 35.3424