Gully Development in the Tigray Highlands

Abstract

Landforms and landscapes vary enormously across the Earth, from high mountains to endless plains. At a smaller scale, nature often surprises us by creating shapes which look improbable. Many physical landscapes are so immensely beautiful that they received the highest possible recognition-they hold the status of World Heritage Sites. Apart from often being immensely scenic, landscapes tell stories which not uncommonly can be traced back in time for tens of millions of years and include unique geological events such as meteorite impacts. In addition, many landscapes owe their appearance and harmony not solely to the natural forces. For centuries, and even millennia, they have been shaped by humans who have modified hillslopes, river courses and coastlines, and erected structures which often blend with the natural landforms to form inseparable entities.These landscapes are studied by geomorphology-'the science of scenery'-a part of Earth Sciences that focuses on landforms, their assemblages, surface and subsurface processes that moulded them in the past and that change them today. To show the importance of geomorphology in understanding the landscape, and to present the beauty and diversity of the geomorphological sceneries across the world, we have launched a book series World Geomorphological Landscapes. It aims to be a scientific library of monographs that present and explain physical landscapes, focusing on both representative and uniquely spectacular examples. Each book will contain details on geomorphology of a particular country or a geographically coherent region. This volume presents the impressive geomorphic legacy of Ethiopia which hosts many landscapes and landforms of global significance. Examples include the otherworldly Afar Depression with its sun-baked volcanoes, high-elevation basalt plateaus, the East African Rift valley with its splendid lakes, to name just a few. Ethiopia is also a country where geomorphology and people have remained in particularly close association since time immemorial. These relationships can be examined by referring to the past-as demonstrated by the chapter on geoarcheology of Aksum, but perhaps more importantly, with the reference to the present-day environmental problems arising from land use, soil erosion, water resources depletion and settlement growth.

Gully and soil and water conservation structure densities in semi‐arid northern Ethiopia over the last 80 years

“…Possibly a clear water effect related to the expansion of bedrock outcrops may also explain the increased gully as discussed by Brancaccio et al (1997). Such clear water effect is enhanced by a decreased sediment load (Frankl et al, 2015) as also evidenced in the study area by Nyssen et al (2006). The link between slope gradient and gully density is not only the result of runoff energy but also related to land use and land management: on level lands, croplands and SWC structures are very common.…”

“…(). Such clear water effect is enhanced by a decreased sediment load (Frankl et al ., ) as also evidenced in the study area by Nyssen et al . ().…”

“…Digitizing and creating orthophotographs from these photographs is difficult due to the problem of obliqueness of these photographs and small area covered by overlapping vertical photographs (Frankl et al, 2015). Hence, transect lines (along the column or row of the grid points depending on the orientation of the gullies) were drawn, along the grids used to match Google Earth imagery and aerial photographs.…”