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Dangerous soil erosion? : A study on soil erosion in the Voi River catchment, South-East Kenya

Kort, A.J.K. (2006) Dangerous soil erosion? : A study on soil erosion in the Voi River catchment, South-East Kenya.

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Abstract:This report is about water erosion in a part of the Voi River catchment, Taita-Taveta District, Coast Province, Kenya. Population pressure in this area is resulting in unsustainable fuel wood collection, overgrazing, inappropriate land use techniques, and deforestation. Furthermore climate changes are likely to cause more droughts. The area is under present conditions semi-arid and therefore vulnerable to erosion. These facts result in the following problem definition: in the Voi River catchment erosion is too high because of decreasing vegetation cover. The objective of this research is to give soil conservation recommendations based upon an erosion hazard assessment and socio-economic analysis. The method used for collecting data is Rapid Rural Appraisal (RRA). RRA is used widely in developing countries for pre-project exploratory work. It has been used because it gives fast accurate social and technical data by triangulation of interviews, secondary data and observations. Also it takes local conditions into account what is very important for giving good conservation recommendations. During fieldwork the area has been mapped and divided in different sub-areas. The sub-areas are: Voi town & Mwakingali Hills, Sagala Hills, Voi River, Plains, Sisal estate and Taita Hills. Erosion hazard has been determined by erosion intensity and erosivity. To determine erosion intensity drainage density and drainage texture are used. For erosivity slope, soil characteristics under wet conditions, and difference between recommended and present land use. For the whole research area a rainfall aggressiveness rate has been determined with weather data of Voi. Rainfall aggressiveness was highest in April and was quite high, taken the aridity of the area into account. Erosion intensity was highest at the foothills of Mwakingali Hills, Sagala Hills, and Small Taita Hills. Gullying in these areas was severe. The hill-areas had very steep slopes and were susceptible to erosion. Erosion risk was highest in the foothills. Erosion risk was high north of the Small Taita Hills and south of Voi River. Results of the erosion hazard assessment, conducted with the indicators mentioned above except of rainfall aggressiveness, are that especially the foothills are vulnerable to erosion. In the Small Taita Hills erosion risk was especially severe. The theory of Poiesz, in combination with interviews and observations, has been used to analyze the behaviour of people in taking conservation measures. It became clear that the environment was forcing people to take conservation measures. Awareness of erosion as a problem was high throughout the research area. The motivation of people however to take measures was moderate as experienced by Westerveld Conservation Trust (WCT) and observations made clear. Only in the Small Taita Hills people were motivated. The capacities of people were differing for each sub-area. In general local people were taking already quite some measures, but most of the time they were inadequate or badly constructed. Maintenance of simple techniques is over the whole research area very well, but maintenance of more advanced techniques, as terraces, was moderate to bad. Community or NGO projects were also maintained badly. The overall conclusion was that erosion prevention practiced in the Taita Hills by local farmers is quite high, but most of the time still inadequate, on the Sisal estate soil prevention is good, and for Plains and Voi River it is moderate to low and inadequate, because most people are not actively preventing erosion. There are many soil conservation measures needed. In the whole area farmers have to be taught appropriate farming techniques, such as replanting of trees, use of mulch and so on. Along roads gutters have to be installed, so that gullying is prevented. Furthermore in most sub-areas vegetation cover has to be restored and gullies to be reclaimed. At the foothills waterways are recommended to prevent gullying. Trenches are recommended on the plains and foothills to increase water infiltration and plant cover. In the Small Taita Hills ladder terraces are recommended on agricultural plots. Social consequences of recommendations have to be taken into account. People must have opportunities to get fuel wood and pasture. Therefore it is needed to teach them sustainable fuel wood collection and the animal-land ratio has to be made sustainable. The latter however is very difficult to obtain. Concluding, erosion in the research area is especially severe at the foothills. It is damaging roads, houses, plots and nature. Erosion risk of the foothills is high and local soil erosion prevention is not adequate enough, except of Sisal estate. Soil conservation measures are therefore needed fast. It is recommended to do research at soil loss in the rainy season to compare results with other studies of erosion in East-Africa and with results of soil loss models as Universal Soil Loss Equation (USLE) to get more insight in specific local conditions and the severity of erosion in the area. Also measurements on soil loss for the research area and for trenches are recommended, so that conservation measures can be designed and the effectiveness of trenches could be determined. More data on local weather of the sub-areas is needed, because it is differing much and determines greatly soil conservation that is possible. It is strongly recommended to implement soil conservation combined with water storage measures and to make a catchment wide plan, so that areas downstream are not neglected. Before implementing projects it is wise to determine who will benefit of the project and how to give the locals ownership over the project. Gender and the powerless have to be taken into account to make the project sustainable. Before the soil conservation recommendations are implemented, it is necessary to make more detailed plans for the implementation per sub-area.
Item Type:Essay (Bachelor)
Clients:
Westerveld Conservation Trust, The Netherlands/Kenya
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
Link to this item:http://purl.utwente.nl/essays/74567
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