Effects of check dams, reforestation and land-use changes on river channel morphology: Case study of the Rogativa catchment (Murcia, Spain)

Catchment-scale land-use changes and erosion-control works have geomorphic consequences as can be seen in the morphological evolution of river channels. An analysis of the consequences of check dams and reforestation works that took place in the 1970s on the channel morphology in the Rogativa catchment (53 km2) in SE Spain is conducted. A land-use change detection analysis of the catchment between 1956, 1981, and 1997 was performed. River channel changes were mapped between 1956 and 1997. Furthermore, morphological field mapping of river reaches, location of all check dams, and characterization of the areas upstream and downstream of them were carried out. Sediment sampling along 10.5 km of the channel and analysis of time series precipitation data were performed.A slight decreasing tendency of the annual precipitation and erosivity of rainfall since the 1940s has been detected. In addition, vegetation cover has increased enormously in the catchment since the 1950s. The dense forest has increased fivefold and the dryland farming areas have been reduced by a 57%. Of all 58 check dams, 72% are silted and 81% of them show erosion features downstream. The active channel has narrowed and many of the lateral bars have been colonized by vegetation. A lateral displacement of the active channel is also observed. Sediment supply has decreased because of the reduction of non-point sources of sediment (i.e., decrease in dryland farming areas and pasture land) and sediment retention behind check dams. Water flow with an increased transport capacity started erosion locally downstream of check dams. The decrease of sediment supply has caused a general armoring of channels. Currently, most of the check dams have lost much of their trap efficiency, erosion of the alluvial wedges upstream of dams is starting, degrading their structure and mobilizing the sediments retained during the past 30 years.Although seemingly clear that land-use changes, reforestation, and correction works affect the channel responses and sediment dynamics, the relative importance of each of these factors with respect to the morphological channel dynamics remains unclear, which is proposed for further research.