ABSTRACT
Gully restoration check dams are usually made with construction materials and have a permanent impact on the landscape. Although earthen dams have not been used to restore gullies, they have been used around the world for water reservoirs and to control flooding. Here, we propose 'green', rammed earth check dams as a better environmental solution to restore gullies and integrate check dams in the natural landscape. This new design of earthen dam aimed at achieving a reduction in construction volume, as we propose a straight profile for the earthen wall upstream and an impervious core made of rammed earth wall. Moreover, the sloping, revegetated profile downstream enables integrating the check dam into the landscape, while the rammed earth wall allows the use of traditional materials and construction methods better adapted to the natural environment. We also present the design process, calculating its stability versus overturning, sliding and ground resistance for its weight. In addition, we compare the construction costs and carbon footprint of the rammed earth check dam with those of other frequently used check dams, such as concrete or gabion check dams. It shows that although rammed earth check dams may have a greater cost (>21%), they also have a sink effect of 23,639.36â¯kg CO2 due to the vegetation cover on the downstream embankment. This work shows their feasibility in gullied areas and ravines of fine textured soils under low runoff and rainfall erosivity conditions.
ABSTRACT
Soil organic carbon plays an important role in the global carbon cycle, accounting for 70% of the Earth's carbon. However, soil erosion can have a major impact on the stocks of soil carbon and other soil nutrients, such as nitrogen and phosphorous. Soil and water conservation techniques, such as the building of check dams, are usually employed to control sediment yields and the losses of other soil components. The aim of this research is thus to quantify the soil organic carbon (SOC), soil nitrogen (SN) and soil phosphorous (SP) retained by the check dams of a hydrologic and forest restoration project in the Sierra de Ávila mountain range (Ávila, Central Spain). Soil samples were taken from the sediment wedges of 30 check dams and from 30 native soils. Soil texture, electric conductivity, pH, C, N and P were measured in all the soil samples. The volume of sediment retained by the check dams was calculated by the Sections Method, which is very accurate in estimating the real volume of the sediment wedges. The total sediment yield in the area was thus estimated at 6.40â¯Mg·ha-1·yr-1 and the mean SOC, SN and SP densities were respectively 13.76, 0.48 and 0.05â¯kg·m-2. These findings thus are very reliable and allow us to conclude that check dams constitute an important instrument for controlling losses of SOC, SN and SP, and preventing these substances from passing into watercourses downstream of the area.
