The evolution of gully erosion in the Rift Valley of Kenya over the past 50 years

Abstract

Gullies are common in areas of unconsolidated deposit soil, and relatively steep-sided erosion that spread quickly in depth and width over short periods may occur during heavy or extended rainfall and. Soil erosion has been recognized as the major cause of land degradation worldwide, especially in the East African Rift Valley of Kenya where thick layers of volcanic ash have been deposited. This paper reports the results of studying the evolutionary process of gully erosion and types of gullies in the East African Rift Valley in Kenya over the last 50 years using remote sensing images, field investigations, and UAV (Unmanned Aerial Vehicle) aerial photography. Forward expansion, backward expansion, new gullies, and road culvert gullies were classified according to their morphological evolution characteristics and then identified throughout the history of the valley over the past 50 years. The erosion length increase from forward expansion was the largest of the four categories, followed by backward expansion, new gullies, and road culvert gullies. Human activity and rainstorms are the main factors of gully erosion in the study area. Additionally, four types of gullies were also categorized according to their causes of formation via field investigation and testing: physically-induced gullies, artificially-induced gullies, pipe erosion-induced gullies, and fissure-induced gullies, and artificially-induced and fissure-induced gullies were the most common type of gully in the study area. The evolution of gullies poses a serious threat to the ecological environment since it can lead to grassland degradation, segmentation of landscape ecology, and the erosion of the survival environment of wildlife. In this regard, man-made and fissure-caused gullies are the most severe and should be investigated further.