The significance of the issue lies in the pivotal role played by Wadi Ouergha, as a major tributary of Wadi Sebou. This watercourse directly contributes to the El Wahda dam, the largest in the Kingdom of Morocco and the second largest in Africa. With its substantial storage capacity and noteworthy annual sedimentation volume, this dam's storage capacity is notably impacted. The ongoing decline in the capacity of the El Wahda dam could potentially accelerate due to shifts in surface water mobilization rates and the worsening degradation of marl soils within the catchment, coupled with alterations in vegetation cover. The aim of this study is to examine the changes in the erosion rate within the Wadi Ouergha watershed over a span of 40 years, covering the periods 1980-2000 and 2001-2020. This comparative analysis aims to ascertain whether erosion control measures have effectively reduced the erosion rate in the region over time. To assess soil losses occurring in the Wadi Ouergha watershed, impacting the El Wahda dam, we employed the RUSLE model to determine the rate and vulnerability of the catchment to water erosion. The results indicate that erosion control measures have been effective in combating soil erosion in the potential region with high erosion risk, with a 13.83% reduction in the average erosion rate between the two periods, from 25.3 to 21.8 (tons/hectare/year). This study presents a groundbreaking contribution by unveiling, for the first time, the dynamic evolution of water erosion patterns over time. It offers a comprehensive assessment of the effectiveness of erosion control measures implemented within the most vulnerable zones.