Addisu, Solomon (2009) Assessment of the Impact of Road Construction on Physical Land Degradation in Central Highlands of Ethiopia: The Case of Two Selected Projects. Masters thesis, Addis Ababa University.
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Abstract
Ethiopia provides a well-known example of a severely degraded African environment with consequent implications for food insecurity and famine. Physical land degradation after road building has been observed in Central Ethiopian highlands through gully erosion. In this research work by using a number of methods such as Field observation, gully measurement, GIS technique ,the 1997topomap and socio-economic questionnaires, the impacts of the road on land degradation has been studied. It investigates how road building in the Ethiopian Highlands affects the gully erosion risk by quantifying the catchement area before and after road construction, the number of gullies created, and its characteristics in two selected cases: Addis Ababa-Fiche and Addis Ababa-Ambo. Accordingly; since the building of the road, 17 new gullies were created immediately downslope of the studied road segmensts and 8 other gullies at a radical change in its dimensions. The area drained to the gully head before road construction are smaller than after the road has been constructed. The average catchement area is now 58.28 hectares and 74.52 on the road segments of Fiche and Ambo respectively, which is significantly different (p<0.001) from the average pre-road catchment area of 8.45 and 14.52 hectares (paired average). The total surface area or gully texture occupied by gullies in the side of Fiche road and in the side of Ambo road transects was about 63,892.6 m2 and 59,214.25 m2 respectively .The volume of soil loss was calculated between 12,530.38 m3 (in segment 1, on Fiche site) and 71,420 m3 (segment 3, on Ambo site). These reveals that a linear and positive relationship exists between the top width and depth of gully erosion although its regression (R2 = 0.26) is relatively lower. The result of statistical analysis indicates that variation of the gully length contributed 95% of variation in the volume of soil loss. Regions with more clay experienced a lower top width and regions with silt indicated the largest top width. The relationship between the top width and depth of gullies is significant (p<5%). The Gully density (5.7m/ha to 14.06m/ha) implies that the sampled roadside areas were moderately to severely degraded. The damages and associated problems of the gullies, as explained by farmers, include loss of land, dissection of farms, and deposition of sediments on growing crops and in extreme cases putting agricultural fields out of production. Hence roads should be designed in a way that keeps runoff interception, concentration and deviation minimal. Techniques must be used to spread concentrated runoff in space and time and to increase its infiltration instead of directing it straight onto unprotected slopes.
| Item Type: | Thesis (Masters) |
|---|---|
| Subjects: | G Geography. Anthropology. Recreation > GE Environmental Sciences H Social Sciences > H Social Sciences (General) T Technology > TE Highway engineering. Roads and pavements |
| Divisions: | Africana |
| Depositing User: | Selom Ghislain |
| Date Deposited: | 12 Jun 2018 12:46 |
| Last Modified: | 12 Jun 2018 12:46 |
| URI: | http://thesisbank.jhia.ac.ke/id/eprint/4175 |
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