Abstract
Abstract. Here we investigate the changes of temperature, precipitation, river runoff and sediment transport in the Wadi Abd in northwest Algeria over a time series of 40 hydrological years (1970–2010). Temperature increased and precipitation decreased with the reduction in rainfall being relatively higher during the rainy season. A shift towards an earlier onset of first rains during summer was also found with cascading effects on hydrology (hydrological regimes, vegetation, etc.) and thus on erosion and sediment yield. During the 1980s, the flow regime shifted from perennial to intermittent with an amplification of the variations of discharge and a modification of the sediment regime with higher and more irregular suspended particulate flux. Sediment flux was shown to almost double every decade from the 1970s to the 2000s. The sediment regime shifted from two equivalent seasons of sediment yield (spring and fall) to a single major season regime. In the 2000s, autumn produced over 4 times more sediment than spring. The enhanced scatter of the C–Q pairs denotes an increase of hysteresis phenomena in the Wadi Abd that is probably related to the change in the hydrologic regime. At the end of the period, due to irregularity of the discharge, the ability of a rating curve to derive suspended sediment concentration from river discharge was poor.
Highlights
Fluvial and estuarine suspended sediment fluxes are changing dramatically under the combined effects of anthropogenic activities and climate change
AO2007, showing the advantage of working with over 22 years of measurement, stressed the difficulty of defining a reference period, and the need to extend the study over a longer period of time. The objectives of this additional study are to (1) describe precipitation, discharge and sediment flux variability of the Wadi Abd basin over a 40-year period; (2) detect the shift, if any, in temperature, runoff and sediment yield; (3) determine the relationship between sediment load and runoff over the last 40 years; (4) detect when a shift occurred in the runoff–sediment load relationship; (5) analyse the possible causes of the change in flow regime and its consequences on suspended sediment discharge; and (6) assess the use of rating curves and the physical signification of their parameters when a river is experiencing a transition and shifts from a perennial regime to an intermittent regime
This method, used by Agence Nationale des Ressources Hydrauliques (ANRH) at all hydrologic stations in Algeria, underestimates the suspended load as compared to its value averaged over the cross section under low turbulence since water is sampling near the surface (Touat, 1989)
Summary
Fluvial and estuarine suspended sediment fluxes are changing dramatically under the combined effects of anthropogenic activities and climate change. AO2007, showing the advantage of working with over 22 years of measurement, stressed the difficulty of defining a reference period, and the need to extend the study over a longer period of time The objectives of this additional study are to (1) describe precipitation, discharge and sediment flux variability of the Wadi Abd basin over a 40-year period; (2) detect the shift, if any, in temperature, runoff and sediment yield; (3) determine the relationship between sediment load and runoff over the last 40 years; (4) detect when a shift occurred in the runoff–sediment load relationship; (5) analyse the possible causes of the change in flow regime and its consequences on suspended sediment discharge; and (6) assess the use of rating curves and the physical signification of their parameters when a river is experiencing a transition and shifts from a perennial regime to an intermittent regime
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