abstract
Check dams are transverse structures built across stream-beds and gullies and made of stones, gabions, masonry, concrete, or logs. They are designed mainly to control water and sediment flows, conserve soil and improve land. Throughout the world, national, regional and local governments have spent in the past, and still currently spend, important funds for basin scale erosion-control schemes (maintenance and new implementations). These projects focus on the control of sediment supply to (i) the stream fans and valley rivers for flood protection, (ii) dam reservoirs for water storage, and basically, (iii) for the mere mountain soil conservation and agriculture protection. The stabilization role of these structures is well known, i.e. they durably constrain the stream-bed through the creation of vertical and planar fixed points. They may consequently consolidate hillslopes, but also retain sediment, and often reduce the upstream reach slope. Their functions are diverse and vary depending on the geomorphic context where the structures are built. However, some projects experience disappointing results due to many different circumstances, such as poor construction quality, inadequate check dam location and lack of adequate design criteria. In addition, these structures induce secondary effects, e.g., different studies have pointed that dams represent one of the most dominant forms of human impact upon mountain fluvial systems, as they disrupt the downstream transfer of water and sediments. Observations of channel cross sections and bed material in several studies for instance indicate that check dams may increase erosion downstream. In parallel, the advent of mobile earth-moving machinery and of reinforced concrete make now possible to design open check dams, with different purposes than their simple closed-type forefathers. Recent studies demonstrate that the functioning of these open structures is also complex and similarly lack sufficient understanding to optimize existing dams and define the best-adapted design to a given site. These lacks of understanding diminished the confidence in developing check-dams as restoration tools at watershed scale. Moreover, construction of dense networks of check-dams, or alternatively of a few large open structures, implies major economic investments, but a comprehensive evaluation of the long-term effectiveness of the varied alternatives is still lacking. This EGU session aims to achieve a detailed comprehension of check dams’ effects at watershed scale in soil restoration schemes by conceptual thinking, field observations, eventual numerical approaches and feedback from tests and trials. Using the knowledge gaps identified above as a starting point, the proposed EGU session pretend to join and share scientific and technical opinions all around the world related to the legacy effects of check-dams and the potential of open check dams, highlighting the role of complex interactions between ecological elements, geomorphic processes and engineering activities.