Abstract:
Water erosion presents a natural risk those results primarily from the fragility of the
environment and the anarchic socialization of the slopes. Currently, it is the leading cause of
degradation of water resources. It not only reduces cultivable areas and soil fertility, but also
leads to downstream regions in the degradation of water quality and the silting up of dams.
The aim of this thesis is to assess, on the one hand, the extent of this erosion in
waterways and, on the other hand, to understand its impact on the lifespan of dams. In order to
achieve these objectives, three sub-watersheds located in different environments in eastern
Algeria were chosen: the Kebir Hammam sub-basin (Coastals Constantinois Center basin), the
Reboa sub-basin (the Constantine Highlands) and the sub-basin of Oued El Hai located on the
southern slopes of the Saharan atlas (ChottMelrhir basin). The objective of this work is, in fact,
to estimate the suspended solid transport of the three watersheds with different physical and
climatic characteristics, and to compare the erosive dynamics. The three dams, located
downstream were the subject of a siltation study (Zit Emba, Koudiet Meddaouar and the
Fontaines des Gazelles).
The study is based on the principle of modeling. The chronicles of measured liquid and
solid flows were used to reconstruct the chronicles of unmeasured flows and those from liquid
flows. They concern four stations on four rivers. They reflect by basin, heterogeneous periods
ranging from 10 to 22 years. The statistical models making it possible to reproduce the flows of
suspended matter were carried out on 4 time scales (instantaneous or daily, monthly, seasonal
and by high and low water period).
The results obtained show strong annual, seasonal and monthly variability in the three
basins. Over an observation period of 10 years (1970/19980), the average specific degradation in
the Kebir Hammam basin is 82 tonnes / km2 / year. The largest suspended solids input come
from winter (56%). Oued Reboa and Oued Guergour in the Reboa basin produce on average 300
tonnes / km2 / year for a period of 11 years (1985/1996). In spring, the suspended solids
contributions exceed 40% of the total. In the Oued El Hai basin, the peaks are rather autumnal.
The average specific solid input is 110 tonnes / km2 / year (1970/1992).
The application of the hysteresis approach linking the suspended concentrations and
liquid flows of a few floods has shown that in the Kebir Hammam basin the response of the
concentrations is in a ""clockwise loop"" direction. This model is particularly suitable for winter
and spring floods. They reflect a contribution of suspended sediment which comes mainly from
the bed of the stream and erosion is active from the first rains. On the other hand, it follows the
opposite direction of a watch in Reboa and Oued El Hai. Suspended sediment comes from the
top of the watersheds and takes longer to reach the outlet.
