Reduction in Water Erosion of Uncoated Roads in Lomé in Togo: Correlation Slope, Width and Water Sheet of Roads

The unpaved roads of Lomé in Togo are increasingly eroded by runoff waters. These waters dig sometimes great gullyings on the roads. The runoff waters make the roads impracticable, and they are very often dangerous for populations. The current project consists in determining the compensation slope of the roads in Lomé in order to reduce the water erosion. 330 sediment samples are taken from 110 roads in Lomé, and then subjected to granulometric analyses and identification tests. From the slope compensation theory, the slope that makes it possible to avoid the road erosion is determined for any right-of-way of roads and water sheet. As a result compensation slopes (p) exponentially decrease with roads’ right-of-way (L) lying between 3 m and 20 m (p=aLb=aeb ln (L)) and become stationary beyond 20 m. They are also decreasing from the sheet 100 mm to 350 mm for any right-of-way of the road. The required slopes for unpaved roads are between 0.23% and 2.92% with an average of 0.92 % in order to keep them from water erosion. Equations and graphs are established to help deducting slopes no matter how long the road is (L) and how high the sheet is (h)