**1. Introduction**

Water erosion is a phenomenon that results from the degradation of the surface layers of the ground cover and the displacement of the constituent materials [1] under the effect of the kinetic energy of the raindrops and the transport of soil particles from their original location [2]. It is one of the main causes of soil degradation in the world [3] leading to a significant threat to both human societies and the environment [4]. It also affects the quality of surface water and/or groundwater [5], reducing the capacity of the dams [6] and decreasing the soil fertility for agricultural activities [7]. Accordingly, the land area damaged by soil erosion is estimated

at 1100 million hectares of land worldwide [8] resulting in the transportation of 2.0 to 2.5 x 1010 Mg of soil to the oceans each year [9]. This makes it a serious problem on a global scale and particularly worrying in certain regions of the world [10].

In 1930, in the United States, 20% of arable land was severely damaged by erosion following a prolonged drought. This is the dark era of the "dust bowl" phenomenon [11]. This resulted in the establishment of a water and soil conservation service by the US government. At the same time, a network of research stations was set up, which, thirty years later, resulted in the formulation of the USLE Equation [12].

Globally, [13] showed that of 13.5 billion hectares of land affected by water erosion, only 22% of the land is cultivable. During the last decades, the losses of cultivable land increased from 7 to 10 million hectares per year and at this rate, two centuries would be enough to destroy all the cultivable/agricultural land.

According to the United Nations Report on the State of the World's Soil Resources, published in 2015, cereal production losses due to erosion have been estimated at 7.6 million tons per year [14]. As a result of this report, researchers around the world have found that if nothing is done to mitigate erosion, we could achieve a reduction of more than 253 million tons of cereals by 2050. This loss of yield would be equivalent to removing nearly 15 billion hectares of land from farming [15]. According to this author, these more dramatic figures raised the alarm in different countries of the world in order to take all the necessary measures. In fact, due to the torrential nature of the rains, the high vulnerability of the land and the unfavorable human activities impact (deforestation, fires, overgrazing, poor agricultural behavior, chaotic town planning, etc.) more degradation will affect the agricultural landscape. Consequently, due to the relevance of this problem, several studies have been carried out on agricultural plots of about 100 square meters [2, 16–19], on micro-watersheds of a few hectares [20–23], on large basins of thousands of square kilometers [6, 24–26] and over large areas (countries and/or regions of the world) [27–29].

The results of soil loss vary from 1 to 200 t/ha/year (up to 700 t/ha/year) under crops specific to forest regions where slopes ranging from 30 to 60% and 0.5 to 40 t/ha/year under millet, sorghum, peanuts and cotton on long tropical ferruginous glacis of the Sudano-Sahelian regions whose slopes vary between 4 and 25% [30]. In the United States, on cultivated land, soil losses were estimated between 5 and 12 t/ha/year [31]. In Europe, [32] estimates that 25 million hectares have been seriously affected by erosion.

In the Maghreb, the water and soil potentials are seriously threatened [22, 33–36] and the phenomenon of water erosion is very widespread. The majority of watersheds are characterized by severe degradation exceeding 20 tons/ha/year [6], which leads to an average annual siltation of dam reservoirs at a rate of 125 million m3 [37]. According to [38], water erosion in Morocco causes soil losses ranging from 5 t/ha/year to more than 50 t/ha/year depending on the region, and an average annual siltation of the reservoirs of the dams of the order of 75 million m3 . That is to say an annual reduction of 0.5% of their storage capacity, which causes deterioration in the quality of the drinking water mobilized and a decrease in water resources that can irrigate 10000 ha/year. Northern and central Tunisia currently has more than 30 dams with a total storage capacity of 3.5 billion m3 [23, 38, 39]. Monitoring the siltation of these hydraulic structures made it possible to assess a loss of their storage capacity estimated at 30 million m3 /year, i.e. an annual reduction of 1%. Soil erosion has affected nearly 3 million hectares of agricultural land in the country, or more than half of the useful agricultural area in affecting the production capacity of Tunisian agriculture [23, 40].

*Spatial Estimation of Soil Erosion Risk Using RUSLE/GIS Techniques and Practices… DOI: http://dx.doi.org/10.5772/intechopen.96190*

In Algeria, the annual volume of sediment deposited in the 74 dams is estimated at 65 million m3 [41]. Although soil erosion is characterized as a natural phenomenon, human activities such as agriculture can accelerate it further in Algeria [42]. Thus, 14 million hectares of land in the country are threatened by water erosion [43]. Therefore, Algeria is a country that witnesses an enormous deficit of water (i.e. below the theoretical scarcity threshold set by the World Bank, which is around 1000 m3 per inhabitant/year) [44]. According to [45], Algeria is qualified in the category of the poorest African countries in terms of water potential. In 1962, the theoretical availability of water/capita/year was 1500 m3 ; it was only 720 m3 in 1990, 680 m3 in 1995, 630 m3 in 1998, 430 m3 in 2020. To meet Algeria's urgent water needs, the States has implemented a strategy consisting of creating 94 hydraulic dams for the mobilization of surface water resources distributed throughout the national territory. The sector expected to build around 139 dams by 2030 [46]. One of these dams is that of wadi Mina catchment with a filling capacity of 241 million m3 . The dam Sidi Mhamed Benaouda (also named dam Es-Saada) is threatened by the silting from its site [6]. It is located at the extreme north of watershed of the wadi Mina (Algeria); its catchment area is subjected to intense water erosion with a volume of sediments which reaches the tank annually. This volume is on average about 3.2 million m3 [47]. During these last decades and in a preoccupation with a management fight by the Algerian State, the catchment area of the wadi Mina was retained within the framework of a pilot project of integrated installation and development [47, 48]. The dam Sidi Mhamed Benaouda was built in 1978 with the downstream of this zone. According to [49], the marly sector located in the northern part constitutes the major source of sediments deposited in this dam.

Thus, the problem of water erosion mobilizes the scientific community to find solutions likely to ensure soil conservation [50]. In a context marked by global climate change and sustained human pressure on natural resources, the threat of soil erosion requires special and continued attention [51].
