LAUSR

Abstract Salt intrusion is an important physical phenomenon in an estuary, and can constitute a serious problem. It has become a serious environmental problem in the Sebou estuary (Morocco) during wet–dry seasons, which has a considerable impact on residential water supply, agricultural water supply as well as urban industrial production. The goal of this paper is to study the vertical salinity stratification under different ydrological conditions in the Sebou estuary. A two-dimensional (2-D) finite-difference solution to the laterally averaged equations of fluid motion model was used for the simulation of the vertical stratification and associated water quality, with observed field data being used for model calibration and validation. Additionally, the model validation process showed that the model results fit the observed data fairly well. Model results show that the vertical salinity at the bottom and surface during spring tide is higher than that during neap tide. Also, the stratification increases a larger during the low-flow periods than during the high-flow periods in Sebou estuary. The responses of salt intrusion length to changes in important dimensional parameters are presented, showing that the salinity intrusion length is inversely correlated with the river discharge (i.e. a high river discharge results in a reduced salt intrusion and vice versa). On the other hand, several stratification indicators were calculated from the observed density or salinity: the stratification coefficient, the Brunt–Väisälä frequency and the potential energy anomaly. These indicators, showed almost identical behavior with differences only of the order of magnitude of the respective values. In addition, the classification of estuarine parameter space for Sebou estuary is illustrated and included in the recent classification. Finally, this model can predict environmental impact of future sustainable undertakings in the Sebou estuary, including recreational, agricultural, and commercial activities. Also, this study provides useful information on the vertical salinity for water resources managers in understanding amount of minimum freshwater discharge needed to maintain an acceptable salinity levels during high tide.