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Universität für Bodenkultur Wien (2009)

Modelling spatial rill initiation on rough soil surface using rill survey and digital photogrammetry at Angereb Watershed, Ethiopia

Gessesse, Gizaw Desta

Titre : Modelling spatial rill initiation on rough soil surface using rill survey and digital photogrammetry at Angereb Watershed, Ethiopia

Auteur : Gessesse, Gizaw Desta

Université de soutenance : Universität für Bodenkultur Wien

Grade : Thesis. Doctoral 2009

Résumé
In order to quantify and characterize spatial rill formation and development, rill survey and close range digital photogrammetry were applied on terraced hillslopes at Angereb watershed in Ethiopia. Rill initiation and development was investigated on different soil tillage surfaces, soil textures, stone terraces and slope lengths at small field plots and catchment scales during erosive storms. Low tillage frequency for faba bean seedbed preparation, which gives surfaces with high random roughness, was highly susceptible to rill erosion followed by Teff and wheat tillage management with high frequency. Although there was confounding effect of microtopographic surface roughness, clay, loam, and sandy loam soil textures were relatively susceptible to rill formation. Rill formation and development in the area between terraces was commonly observed because of wider terrace spacing and damaged stone terraces. Organized rill network development with spacing from 133 to 160 cm started after 4 m slope length in the area between terraces. The rill network was controlled mainly by the nature and size of initial soil surface roughness, soil cohesion and the slope length at small field plots ; and by the landscape structures, concavity and runoff concentration at catchment scale. Prediction of threshold area for critical rill initiation was significantly improved when soil surface roughness was taken into account. The range of threshold area was found between 0.20 and 0.50. The threshold area was determined under a minimum average rill contributing areas of 0.75 to 1.3 m2, local slope gradient of 18-30 % and surface random roughness of 4 to 9 cm. Rill prone areas decreased with increase in slope length but it was independent of slope length on tillage oriented roughness. Due to relatively low precision of photogrammetric measurements, amount of erosion and deposition involved at low rainfall events were highly uncertain. However, when high erosive storms above 50 mm occurred, then significant erosion and deposition can well be measured on irregular surface topography. Since runoff plot method constitutes potential sources of errors and unreliability, rill survey and close range digital photogrammetric measurement with high accuracy can identify erosion prone areas and can be used to enhance field erosion measurement

Mots clés : Rill initiation and development / Rill erosion / Soil surface roughness / Digital photogrammetry / Angereb watershed / Ethiopia

Présentation

Page publiée le 4 septembre 2010, mise à jour le 13 mars 2019