Alteration of Catchments and Rivers, and the Effect on Floods: An Overview of Processes and Restoration Actions

Flooding is a prevalent and growing problem involving significant economic losses worldwide. Traditional flood mitigation measures are based on the use of levees, dams, dredging, and river channelization, which can distort the perception of risk, leading to a false sense of security that can induce an increase in the occupation of flood-prone areas. An undisturbed watershed and its fluvial system provide regulating services that contribute to flood mitigation. However, anthropogenic activities can degrade and diminish such services, impacting the magnitude of floods by changing the runoff patterns, erosion, sedimentation, channel conveyance capacity, and floodplain connectivity. Restoration and natural flood management (NFM) seek to recover and improve their watershed regulation services. The bibliographic review performed here aimed to assess the degradation of the natural regulation services of watersheds, which allowed us to identify significant alterations to runoff and streamflow. Also, the review studies of NMF allowed us to identify the restoration actions oriented to recover or enhance the flow regulation capacity of catchments and their fluvial systems. A current challenge is to accumulate more empirical evidence for the effectiveness of such flood mitigation solutions. Currently, the results for large catchments have been obtained mainly by the application of hydrologic and hydraulic models. Also, the adequacy of the different NFM actions to catchments with different physiographic and climatological settings needs to be addressed.