Flood transport of dissolved and suspended matter in the El Abid river basin (Morocco)

Abstract

This study presents the results of an analysis of the transport of suspended matters (S.M.) and nutrients (phosphorus, nitrogen and silica) by flood waters in the El Abid river basin, Morocco. The transport dynamics of these elements are considered within the context of temporal variations in discharge, and an evaluation of the loads of these elements supplied by the El Abid river basin to the Bin El Ouidane reservoir is also carried out. An analysis of the S.M. and nutrient dynamics, and their relationship to discharge has led to the identification of three types of flood flow. The first flow type defines storm flows that mainly occur from June — October, inclusive. Despite their low discharges, these are characterized by a high S.M. (up to 250 g l⁻¹). The second flow type occurs during the wet season, generally between December — May inclusive. In contrast to the first flow type, these flood flows are characterized by a relatively higher discharge (up to 204 m³ s⁻¹) and an S.M. concentration not exceeding 50 g l⁻¹. In contrast, the total phosphorus, nitrogen and silica levels are significantly high and indicate the importance of chemical erosion during flood flows of the wet period. Finally, there are also flood flows of an intermediate type, which are characterized by a moderate discharge (67.5 m³ s⁻¹ – 94 m³ s⁻¹) and a shorter flood duration. This third type exhibits S.M. and nutrient load characteristics common to both other flow types.