The impact of dams on floodplain geomorphology: are there any, should we care, and what should we do about it? (10822)
The majority of the world’s floodplains are dammed. Although some implications of dams for riverine ecology and for river channel morphology are well understood, there is less research on the impacts of dams on floodplain geomorphology. We conducted a literature review of the impact of dams on floodplain geomorphology, resulting in a conceptual model of the impact of dams on floodplain geomorphology. We tested the validity of the conceptual model by reviewing the cause and effects relationships in the model using the Causal Criteria methodology. We included studies from dammed and undammed rivers and include influences on vertical and lateral accretion, meander migration and cutoff formation, avulsion, and interactions with floodplain vegetation. Impacts of dams on floodplain geomorphology were considered both in a downstream direction, and over the lifetime of a ‘typical’ large dam. Based on this two stage review process, we conclude that there are a range of causal linkages whereby dams might impact on floodplain geomorphology, although there is limited empirical evidence of this at present, mostly due to a lack of studies over relevant timescales.
Based on these findings, in this paper, we ask two questions: (1) are the impacts of dams on floodplain significant, in terms of their extent, occurrence over human timescales or their potential to impact on river and floodplain structure or ecology? (2) Are there environmental flow strategies which could maintain or aid geomorphic functioning of a floodplain? (And will these ‘geomorphological flows’ have benefits for floodplain ecology at the same time?). We suggest that there are number of impacts which are severe enough, and occur over short enough timescales that they should be considered in assessing the impacts of dams, and that there are potential environmental flow strategies for dealing with them.