2.1 Study area
The details of the study area and field measurement are given in Mukai (2017) and their summary is outlined below.
The Tebo and Geldia catchments (~285 km2; Figure 1) geographically contain (i) northern Tebba Gersa mountainous area that is a part of the Ethiopian highlands (2200 m asl), (ii) the southern lowland of the Rift Valley floor (~1500 m asl), and (iii) intermediate transitional area. The catchments and permanent gullies in the Tebo and Geldia catchments can be divided into two geographical sub-categories: the Rift margin sub-area (gullies) and the Valley floor sub-area (gullies; Billi & Dramis, 2003). From the Rift margin sub-area, five catchments (Boruamba, Telilo, Adare, Gebruamba, and Koka), which originate from either the southern margin of the Tebba Gersa mountainous area or the steep slope on the fault scarp, were selected as study catchments (Figure 2). From the Valley floor sub-area, seven catchments (Hadaware, Merko, Goro, Abharo, Kawa adami, Aware, and Odalega), which originate from the vicinity of the Merko hillside (1500−1600 m asl), were selected as study catchments.