Check dam

Abstract: The construction of transverse structures (check dams) is a widely used method in Spanish Mediterranean areas to stabilise gullies and ephemeral streams, to reduce channel incision and to prevent sediment deposition downstream. The effectiveness of check dams and their effects on the morphology of ephemeral channels (ramblas) were investigated in a semiarid, highly degraded catchment. In the study area, 36 dams were surveyed, of which 29 were filled up with sediments, 2 had been destroyed and only 5 had still not completely filled with sediments. The streams above the dams held sediments, which resulted in a decrease in the longitudinal gradient. Field observations of changes in the cross-sectional shape of the stream channel, the composition of channel bed material, and bankfull stage measurements indicated that the dams cause erosion downstream. The amount of sediments stored by the dams was found to be higher than the amount of eroded material in the downstream reaches of the dam.

Abstract: The Kali sub-watershed is situated in the semi-arid region of Gujarat, India and forms a part of the Mahi River Watershed. This watershed receives an average annual rainfall of 900mm mainly between July and September. Due to high runoff potential, evapo-transpiration and poor infiltration, drought like situation prevails in this area from December to June almost every year. In this paper, augmentation of water resource is proposed by construction of runoff harvesting structures like check dam, percolation pond, farm pond, well and subsurface dyke. The site suitability for different water harvesting structures is determined by considering spatially varying parameters like runoff potential, slope, fracture pattern and micro-watershed area. GIS is utilised as a tool to store, analyse and integrate spatial and attribute information pertaining to runoff, slope, drainage and fracture. The runoff derived by SCS-CN method is a function of runoff potential which can be expressed in terms of runoff coefficient (ratio between the runoff and rainfall) which can be classified into three classes, viz., high (>40%), moderate (20–40%) and low (<20%). In addition to IMSD, FAO specifications for water harvesting/recharging structures, parameters such as effective storage, rock mass permeability are herein considered to augment effective storage. Using the overlay and decision tree concepts in GIS, potential water harvesting sites are identified. The derived sites are field investigated for suitability and implementation. In all, the accuracy of the site selection at implementation level varies from 80–100%.

Abstract: Large-scale sediment control efforts on the Loess Plateau of China and resulting reductions in sediment yield have been documented. However, it remains unclear how these control works affect the soil erosion rates and sediment loads at the catchment scale. A combination of field work and modeling exercises was used to examine the effects of land use changes and check dams on the variation of sediment yield at the catchment scale. The Huangfuchuan catchment was selected as a case study. The sediment distributed delivery (SEDD) model was calibrated using both observed sediment load data and sedimentation rates derived from check dams. The study catchment suffered important land use changes with increasing grassland and decreasing bare land, sandy area and arable land from 1990 to 2006. By 2009, 502 check dams with a total storage capacity of 571 Mm 3 had been built in the study area. Relatively good agreement can be seen between observations and model simulation results. Model applications showed that in a scenario without check dams, the land use changes between 1990 and 2006 caused a remarkable reduction of 31.4% in sediment yield. The check dams without land use changes with respect to the 1990 scenario reduced 51.9% of the sediment yield in the study area. The combination of land uses and check dam construction in 2006 reduced the sediment yield by approximately 80%. Our results indicate that check dams are efficient sediment control measures; however, the accumulation of sediment in check dams may create costly problems in the operation of dams and failures because of their short lives. Therefore, sustainable solutions are needed for sediment management in the check dams, such as sediment pass-through, flushing, or mechanical removal, and a reasonable construction plan is also needed for flood control.