Check dams worldwide: Objectives, functions, effectiveness and undesired effects

Check dams have been used throughout the world for a variety of purposes including torrent control, water supply enhancement, agricultural land development, and watershed restoration. National, regional and local governments have invested, and continue to invest, in basin scale erosion-control projects that may include both maintenance of existing and construction of new check dams. The functions of these structures are diverse and vary depending on the geomorphic context where the structures are built. However, although the number of check dams constructed to control floods, regulate sediment transport, reduce upstream reach slopes and stabilize torrent beds continues to increase, some projects have experienced disappointing results, and thus project objectives are not achieved. Causes of failure include poor construction quality, inadequate check dam location and lack of adequate design criteria. These failures lead to reduced confidence in using check dams as restoration tools. Moreover, both construction of dense networks of check dams and construction of a few large open structures require major economic investments, however a comprehensive evaluation of their long-term effectiveness is still lacking. This review aims to achieve a detailed synthesis of the effects of check dams based on a review of the literature that includes conceptual thinking, field observations and numerical approaches. Using the knowledge gaps identified in this work as a starting point, the review is an effort to join and share scientific and technical information from a variety of sites throughout the world based on the legacy effects of check dams. The role of complex interactions between ecological impacts, geomorphic processes and engineering activities is also highlighted. Overall, this review identifies the self-similar character of check dams and the process feedback loops they initiate across a range of spatial scales and geographic settings.