The impacts of porous rock check dams on a semiarid alluvial fan

A procedure for risk assessment of check dam systems: A case study of Wangmaogou watershed

Flood-based hydrodynamic damage to check dam systems on the Loess Plateau of China occurs frequently, and there is a strong desire to carry out risk assessments of such check dam systems. This study proposes a weighting method that combines the analytic hierarchy process, entropy method, and TOPSIS to assess the risk of check dam systems. The combined weight-TOPSIS model avoids weight calculation only considers the influence of subjective or objective preference and the bias of the single weighting method. The proposed method is capable of multi-objective risk ranking. It is applied to the Wangmaogou check dam system located in a small watershed on the Loess Plateau. The result of risk ranking matches the reality of the situation. The gray correlation theory model is utilized to rank the risks in the same research area and compared with the results of the combined weight-TOPSIS model. The combined weight-TOPSIS model is more favorable to risk assessment than the gray correlation theory model. The resolution level and decisive judgment of the combined weight-TOPSIS model are more advantageous. These results are in line with the actual conditions. It proves that the combined weight-TOPSIS model can provide a technical reference for the risk assessment of check dam systems in small watersheds.

Modelling Water Flow and Soil Erosion in Mediterranean Headwaters (with or without Check Dams) under Land-Use and Climate Change Scenarios Using SWAT

The use of check dams is a common strategy to reduce soil erosion in the Mediterranean headwaters. However, the effects of these control works on water flow rates and sediment yields have been scarcely investigated under possible scenarios of climate and land-use changes. On this regard, the use of hydrological models, such as SWAT, provide reliable hydrological predictions under variable environmental conditions. To fill this gap, this study has evaluated the effectiveness of check dams on the hydrological response of a forest headwater in Calabria (Southern Italy) in comparison with an unregulated subcatchment with very similar environmental conditions. In this regard, the effects of different combined scenarios of climate change (through three GCMs and two RCPs applied to a time period of the next 80 years) and land use (forest, pasture, and cropland) on water flow rates and sediment yields in the two headwaters were analysed using the SWAT model. The SWAT model was first calibrated in a third headwater with very similar climatic, soil, and land-use conditions, and this verification showed a satisfactory prediction capacity of water flow rate. The water flow rate prediction capacity of the model was satisfactory (coefficients of determination and efficiency of Nash and Sutcliffe equal to 0.71 and 0.67, respectively, and percent bias of 14.9%). No significant differences were detected for the water flow rates and sediment yields between the two subcatchments (with or without check dams) among the different land-use and climate change scenarios. This was linked to the low hydrological response of both headwaters to the forcing actions, which influenced the low effectiveness of the control works. SWAT estimated higher values of both mean and maximum values of water flow rates and sediment yields under RCP2.6 compared with RCP8.5. Both water flow rates and sediment yields were predicted to be very low under all climate and land-use scenarios. The regulated headwater with check dams was predicted to always produce more runoff and erosion compared with the subcatchment without check dams. The increases were predicted to be up to 60% for the maximum flow rate and 30–35% for the sediment yield in forest land use under RCP2.6. Although there was a limitation in this study due to the lack of validation of the erosion data (due to unavailable records of sediment yield), this study demonstrated how the use of check dams in headwater catchments may be not effective for soil conservation purposes several decades after their installation in Mediterranean semiarid areas, where the water flow and erosion rate are limited.

Comparing the Hydrological Response of Forested Headwaters (Unregulated and Regulated with Check Dams) under Mediterranean Semi-Arid Conditions

This study has evaluated the runoff and erosion rates in torrents of Southern Italy, two forested headwaters with very similar climatic, hydrological and geomorphological characteristics; in one headwater, 15 check dams were installed in the mid-1950s, while the other is not regulated with engineering works. To this aim, the hydrological variables have been modeled over 15 years after check dam installation using the HEC-HMS (Hydrologic Engineering Center-Hydrologic Modeling System) model coupled to the MUSLE (Modified Universal Soil Loss Equation) equation. The model simulations have shown that check dams have not played a significant role in reducing the surface runoff compared to the unregulated torrent; in both catchments, the well-developed forest cover determined very low runoff coefficients (lower than 0.3%) with a scarce runoff generation capacity. Additionally, the reduction in peak flow due to the check dams was not significant, on average −7.4% compared to the unregulated headwater. Check dams have retained sediments for about 8–10 years after their installation, reducing erosion by about 35%, although soil loss was much lower than the tolerance limit in both catchments. After the sediment retention capacity of the dam sediment wedge was depleted, the sediment yield in the regulated torrent was even higher (by about 20%) compared to the unregulated catchment. Overall, the study has shown that the use of check dams as a catchment management strategy of forested headwaters under semi-arid Mediterranean conditions should be considered with caution, since the structures could be ineffective to reduce water and sediment flows during floods or, in some cases, check dams may increase erosion rates.

Water runoff harvesting systems for restoration of degraded rangelands: A review of challenges and opportunities

Mismanagement of rangelands worldwide has accelerated processes of overland flow and soil erosion, resulting in extensive land degradation. Wherever self-restoration processes of degraded rangelands are hindered or negated, active recovery efforts, coupled with livestock pressure management, might be needed. The objective of this review paper is to provide land managers and environmental planners with applied and practical knowledge on advantages and disadvantages of the main methodologies and practices for runoff harvesting in rangelands. Preferably, restoration efforts should focus on forming low-footprint runoff harvesting systems on hillslopes which encompass the runoff's source area. These systems should imitate natural patchiness, strengthening source-sink relations, accelerating re-establishment of herbaceous and woody vegetation, maximizing the retaining of water on hillslopes, regulating hydrological connectivity, lessening soil erosion, and minimizing transmission of water to stream channels. The resulting lower-energy floods are expected to negate the need for massive check dams in channels. If flood dissipation in streams is still necessary, then high-to medium-porosity check dams, made of local materials, might be effective for lessening scour processes and sediment transport. Furthermore, in terms of environmental sustainability, a large number of pointed (e.g., branch bundles; brush or woody piles; micro-catchments) or low-to medium-footprint lineal means for regulating surface processes in hillslopes (e.g., stone terraces; contour furrows/trenches/ditches) and channels (e.g., log check dams; loose rock check dams; porous or semi-permeable rock check dams; gabions) are expected to be more cost-effective than a small number of massive means (e.g., contour bench terraces; earth bunds/dykes; concrete check dams). If runoff harvesting systems are properly designed, restoration processes over time are expected to generate geo-ecological feedbacks and recover eco-hydrological functioning, increasing pasture productivity and sustaining rangeland carrying capacity.

The use of check dams in watershed management projects: Examples from around the world

Check dams are widespread and effective soil and water conservation structures throughout the world. This review paper presents an overview of the use of check dams for soil and water management and runoff control with examples from the literature based on field measurements from four continents. More than 150years of research has reported that check dams are civil engineering landmark structures used all over the world. Among all civil engineering structures, check dams are probably the most emblematic of torrent control works. They were used for centuries, and are located all around the world. Over the past several hundred years, people have increasingly realized the envisioned advantages of check dams such as land development, environmental improvement, agricultural production, enhancement of gully stabilities, and mitigation of intensive flood. The optimum size, location and type had great influences on the efficiency of check dams under watershed management. Moreover, in both the theoretical and practical realms, check dams have been proved to be a useful tool for controlling soil erosion and flooding at a catchment scale. This paper will be helpful for policy makers to extend check dam projects in the whole erosion-prone areas.