Verbist B.,Geo Institute |
Poesen J.,Geo Institute |
van Noordwijk M.,ICRAF SEA |
Widianto,Brawijaya University |
And 3 more authors.
Catena | Year: 2010
Tropical deforestation and land use change is often perceived as the major cause of soil loss by water erosion and of sediment load in rivers that has a negative impact on the functioning of hydropower storage reservoirs. The Sumberjaya area in Sumatra, Indonesia is representative for conflicts and evictions arising from this perception. The purpose of this study as part of a Negotiation Support System approach was to assess sediment yield both at plot and catchment scale and to relate it to a variety of possible clarifying factors i.e. land use, geology, soil and topography. Sediment yield at catchment scale per unit area, was found to be 3-10 times higher than soil loss measured in erosion plots. A stepwise regression showed that the dominant factors explaining sediment yield differences at catchment scale in this volcanic landscape were a particular lithology (Old Andesites) and slope angle followed by the silt fraction of the top soil. In lithologically sensitive areas soil loss at the plot scale under monoculture coffee gardens decreases over time from on average 7-11 Mg ha- 1 yr- 1 to 4-6 Mg ha- 1 yr- 1, mainly because of the development of surface litter layers as filters and top soil compaction in the areas without litter, but remains higher than under shade coffee systems or forest. The runoff coefficient under monoculture coffee remains on average significantly higher (10-15%) than under forest (4%) or under shade coffee systems (4-7%). In lithologically stable areas soil loss remained below 1.8 Mg ha- 1 yr- 1 and the runoff coefficient below 2.5% under all land use types, even bare soil plots or monoculture coffee gardens. Less than 20% of the catchment area produces almost 60% of the sediment yield. The reduction of negative off-site effects on e.g. the life time of a storage reservoir would benefit greatly from an improved assessment of the lithologies in volcanic landscapes and the consideration of potential sediment source and sink areas. In lithologically sensitive areas, a shift from sun to shade coffee systems may result in reducing surface runoff and soil loss, although water erosion at the plot scale is not the main contributor to sediment yield at the catchment scale. The quantification of land use effects on dominant erosive processes such as river bank and river bed erosion, landslides and the concentrated flow erosion on footpaths and roads can contribute to more targeted efforts and relevant incentives to reduce (or live with) sediment load of the rivers. © 2009 Elsevier B.V. All rights reserved.
Kitutu M.G.,National Environment Management Authority |
Muwanga A.,Makerere University |
Poesen J.,Geo institute |
African Journal of Agricultural Research | Year: 2011
This study assesses the farmer's understanding and perception of the causes and impacts of landslides in Bududa district in Eastern Uganda. Open-ended questions were designed to guide farmers in providing their experiences, understanding and observations in relation to the scientific findings. Steep slopes, areas with concavities and those with flow of water from underground were identified as areas prone to landslides. The soil characteristics for areas prone to landslides are stoniness, sandy and high water infiltration. Low lands and areas with sticky and strong soils were identified as stable. Rainfall was listed as the main triggering factor and most landslide occurrences are in rainfall events of low intensity but prolonged for days. Terraces are not popular in some of the areas because they promote water infiltration and trigger landslides. Loss of income from farms was mentioned as the main impact from these landslides. However, the damage to infrastructure such as roads and bridges was not identified as a problem to the farmers. Farmers in areas without landslides are less knowledgeable about the cause-effect issues related to landslides. © 2011 Academic Journals.