Soil Erosion in the Upper Basin of Wadi Al-Zoumar

This study discusses the issue of soil erosion in the Upper basin of Wadi Al-Zoumar (104 km2). Twenty-three measuring stations (Plots) were installed in the area to collect samples from the eroded soil and rapid flow after every rainstorm. Each station had an area of 20 m2 installed during the winter season (2009-2010) which consist to only 16 rainstorms. The measurement stations were distributed within the area of study over three different uses of land: Fruitful trees, field crops and pasture areas. Through such distribution, those stations had covered nearly most of the natural conditions of the study area. The study showed that the rate of surface runoff of water in the studied area ranged between 0.12-28.8% of the amount of rainfall during the single rainstorm with an average of 4.49%. Which is equivalent to 25.7 m3 / donum / year. The surface runoff was related to a number of factors including: a- Rain characteristics variable in terms of quantity and intensity. which explained the 46.8% of variance in the surface runoff percentage with a correlation of 0.68. b- The land uses and vegetation variable explained 9.5% of the total variance with a correlation coefficient of -0.31. so when the vegetation area is more dense, or lands were ploughed and its retaining walls are subject to maintenance, the ability of rain to cause surface runoff will be reduced. c- Soil characteristics variable : This variable explained 6.9% of the variance of the surface runoff with a correlation coefficient of -0.26. This is an inverse correlation that resulted from the increase ratio of the coarse grains. in addition to the ratio of organic material in the soil, which increased the soil's ability to leak larger amounts of rainfall; this has eventually led to a reduce surface runoff. d- Surface characteristics variable: This variable explained 3.4% of the total variance with a correlation coefficient of 0.19% because whenever the surface slope degree increased surface runoff became faster due to the earth's gravity. The study has also found out that the total amounts of the eroded soil due to surface runoff in the area of the three land uses in the studied area which was 87 km2, has been estimated to be 35400 tons per year, with an average of 0.51 tons/ donum /year. This has ranged between 9.2 - 2732.2 grams during single rainstorm. The most significant factors that determine the amount of eroded soil were: a- Rain characteristics variable which explained 29.6% of the total variance of the eroded soil with a correlation coefficient of 0.55. Rainfall in this season has revealed a huge variance explained by the 127.4 ml. which fell in 25-26/2/2010 so that exceeded the monthly averages of the area. b- The surface runoff rate variable which explained a 24.3% of the variance of the amount of eroded soil, with a correlation of 0.49. This was attributed to the fact that soil erosion is basically influenced by the rate of surface runoff. c- Soil characteristics variable: This variable explained 6.5% of the total variance with a negative correlation coefficient of -0.26. d- Land uses variable which explained 4.5% of the total variance with a correlation of -0.21. It turned out that plowed land is more Liable to erosion than fallow lands. because when vegetation cover is removed, and soil's aggregates are dismantled its ability to resist erosion forces caused by surface runoff will be reduced. e- Vegetation variable which explained 3.5% of the total variance of the amounts of eroded soil with a correlation coefficient of -0.19 because vegetation cover protects the surface soil from the impact force of rain drops which hitting the surface of the soil. It also increases the amount of organic material in the soil giving it an increased ability to filter and keep rain water. Additionally, the results of this study have shown that the surface runoff plays a major role in washing away the mineral nutrient elements from the surface soil, a fact that has been proved by the chemical tests that have been made on a collected samples from the eroded soil, which weakening of the fertility and productivity. The study recommended raising the farmers awareness regarding the danger of soil erosion, and emphasized the necessity to support and encourage them both spiritually and financially to start maintaining their land by building retaining walls and terraces, in addition to using organic fertilizers.