USING SOIL ADJUSTED VEGETATION INDEX TO ASSESS LAND DEGRADATION ALONG SECTIONS OF MUTONGA RIVER CANYON

Abstract

Mutonga River canyon forms an important social economic strip spanning about 8 km East and West along upper Mutonga River Bridge. The 8 km strip is an area of dense human activities comprising of quarry stone mining and settlements. The canyon contains extensive stone mining sites as well as a permanent river serving the communities of Meru County in the upstream and Tharaka-Nithi County in the downstream respectively. Uncontrolled quarrying along the canyon’s river bank has resulted to geomorphic failures in the recent past leading to fatal landslides in 2002 and 2010. To assess the extent and effects of these mining activities on the canyon’s slope stability, satellite images of years 2014 and 2017were comparatively used. The severity of degradation was then assessed using Soil Adjusted Vegetation Index (SAVI). Calculated vegetation cover threshold values across the two epochs were taken as indicators of degradation. The study revealed that the strip along Mutonga river Canyon has undergone massive de-vegetation and slope de-stabilization. Soil creep from the quarry sites has also resettled into the watercourse way reducing the river depth, benthic life and degrading river water quality.