Nomograph development for water erosion quantification in Wadi Cheliff’s catchment, Northern Algeria

Abstract

Water erosion study is regarded as one of the most important axes in scientific researches. The erosive effect of water on the surface layers can have major consequences on soil loss and land degradation. The objective of our work was the development of a water erosion nomograph that represents a practical and precise tool that is adapted to local conditions for a direct quantification of erosive action in the absence of basic data. Regarding the magnitude of the phenomenon in Algeria, the catchment of Wadi Cheliff was taken as an experimental site where a significant spatio-temporal variability of liquid and solid flows was observed and the measurement network in different locations was either dispersed or non-existent. The developed methodological approach permitted the identification of 149 experimental sites (20 hydrometric stations, 15 large dams and 114 hill dams) where existing data allowed the erosion quantification. A flow coefficient variography was performed in addition to a principal component analysis (PCA), leading to the identification of three distinct groups. Moreover, the modeling of the studied variable was achieved through the application of multivariate analysis to the third group of 100 observations. Applying the principles of nomography on the final model, a nomograph of the semi-arid area of Wadi Cheliff catchment was realized for surfaces ranging from 500 to 25 000 ha. This nomograph enabled the direct quantification of water erosion from the product (Es1 Es2), taking into account the area of the catchment, its average slope and its flow coefficient with a mean absolute percentage error (MAPE) of 2%.