SSS2.10

Fingerprint identification technology has been widely used to extract sediment source proportions, but the only indicator currently available to assess the accuracy and applicability of the results is good-fit (GOF). We have proposed a new method to evaluate sediment source results and quantitatively evaluate the applicability of sediment source mixing models. A typical check dam in the Loess Plateau was used to evaluate the new method by combining field sampling and numerical simulations. Collins (C) and modified Hughes mixing (M-H) models were used to quantitatively analyze the sediment sources of the check dams built and operated until July 2017. The results showed that the best combination for the fingerprint factors in the dam-controlled watershed, was Zn, Mg, Mn, and d (0,1), which had an 86.1% identification ability. With rainfall, the relative sediment contribution rates from gullies, sloping farmland, grasslands, and branch ditches were 54.22%, 23.56%, 15.54%, and 6.68%, respectively. The M-H mixing model had a higher comprehensive score (2.72) when compared with the C mixing model (2.54). The comprehensive evaluation method could provide an effective scientific theoretical basis for optimal allocations of water and soil conservation in small watersheds.

How to cite: Shi, P., Yu, Y., Bai, L., and Li, P.: A new method to evaluate the accuracy of the sediment source mixing model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-403, https://doi.org/10.5194/egusphere-egu21-403, 2021.

Sediment connectivity is highly influenced by landscape patchiness. In particular, linear features such as roads, ditches, and terraces, modify landscape patterns and affect sediment transport from hillslopes to surface waters. Connectivity patterns are commonly assessed by spatially-distributed models, which rely on semi-qualitative indices or numerical simulations of soil erosion and sediment transport. However, model-based connectivity assessments are hindered by the uncertainty in model structure and parameter estimation. Moreover, representing linear landscape features is often limited by the spatial resolution of the model input data. Here we demonstrate how a global sensitivity analysis of the WaTEM/SEDEM model can be used to improve our understanding of sediment connectivity in patchy agricultural catchments of the Swiss Plateau. Specifically, we explored model structural connectivity assumptions regarding road drainage and the presence of edge-of-field buffer strips, as well as the uncertainty in the input data, by means of a Monte Carlo simulation and a high resolution 2 m x 2 m DEM. Our results showed that roads are the main regulators of sediment connectivity in ameliorated Swiss landscapes. That is, our sensitivity analysis revealed that assumptions about how the road network (dis)connects sediment transport from cropland to water courses had a much higher impact on modelled sediment loads than the uncertainty in model parameters. These results illustrate how a high-density road network combined with an effective drainage system increases sediment connectivity from arable land to surface waters in Switzerland. Additionally, our approach underlines the usefulness of sensitivity and uncertainty analysis for identifying relevant processes in model-based sediment connectivity assessments.

How to cite: Velloso Gomes Batista, P., Fiener, P., Scheper, S., and Alewell, C.: A model-based sediment connectivity assessment for patchy agricultural catchments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-562, https://doi.org/10.5194/egusphere-egu21-562, 2021.

Preferential flow (PF)-dominated soil structure is often considered a unique system consisting of micropores and macropores and thus supposed to provide dual-pore filtering effects on hydrological signals, through which smoothing effects are likely to be stronger for matrix flow and weaker for PF via macropores. By using time series of hydrological signals (precipitation, canopy interception, throughfall, soil moisture, evapotranspiration, water storage in soil and groundwater, and catchment discharge) propagating through the Shale Hills Catchments and representative soil series, the filtering effects of the catchment and soil profiles were tested through the wavelet analysis. The hypothesized dual-pore-style filtering effects of the soil profile were also confirmed through the coherence spectra and phase differences, rendering them applicable for possible use as “fingerprints” of PF to infer subsurface flow features. We found that PF dominates the catchment’s discharge response at the scales from three to twelve days, which contributes to the catchment discharge mainly as subsurface lateral flow at upper or middle soil horizons. Through subsurface PF pathways, even the hilltop is likely hydrologically connected to the valley floor, building connections with or making contributions to the catchment discharge. This work highlights the potential of wavelet analysis for retrieving and characterizing subsurface flow processes based on the revealed dual-pore filtering effects of the soil system.

How to cite: Liu, H., Zhao, W., Yu, Y., Guo, L., and Liu, J.: Subsurface Preferential Flow Enhances Hydrological Connectivity in the Shale Hills Catchment: Perspective from Wavelet-based Analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2427, https://doi.org/10.5194/egusphere-egu21-2427, 2021.

In semi-arid ecosystems, basin elevation and hillslope aspect play an important role in the distribution of plant type and density. In general, north-facing aspects host mesic and denser vegetation than south-facing aspects where host xeric plants. Beside aspect, elevation plays a dominant role in vegetation distribution. The Upper Rio Salado Basin, in central New Mexico, hosts shrublands and grasslands at lower elevations and forests at higher elevations. The geomorphometric analysis shows that forest areas are steeper than the grasslands and shrublands. Shrub encroachment in the region and the increase in global temperatures may lead to the replacement of forests by shrublands and the transition from a resource-conserving ecosystem to a leaky (non-conserving) ecosystem on the north-facing aspects which is similar to current south-facing aspects. The preliminary results show these transitions will lead to emerging hotspot areas in erosion. These erosion­-prone zones should be monitored in future for sustainable management.

This study has been produced benefiting from the 2232 International Fellowship for Outstanding Researchers Program of the Scientific and Technological Research Council of Turkey (TUBITAK) through grant 118C329. The financial support received from TUBITAK does not mean that the content of the publication is approved in a scientific sense by TUBITAK.

How to cite: Yetemen, O.: Implications of Climate Change on Erosion Dynamics and Sediment Connectivity in Semi-arid Ecosystem, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14482, https://doi.org/10.5194/egusphere-egu21-14482, 2021.

In recent years, the significantly decrease of water and sediment in the Yellow River has attracted wide attention from domestic and foreign scholars. The Loess Plateau is the main source of sediment in the Yellow River, which ecological environment changes caused by large-scale ecological construction measures is considered as one of the main factors affecting the water and sediment changes in the Yellow River. In this study, the Wangmaogou small watershed in Loess Plateau was taken as the study area. On the basis of summing up the process of ecological construction in Wangmaogou watershed, and restoring the topography before ecological construction by topographic map, we set up four scenarios of ecological construction to analyzed the characteristics of sediment connectivity under different ecological construction scenarios and the effects of ecological construction on sediment connectivity, which are before ecological construction, only slope measures are built, only channel measures are constructed, and at the same time slope measures and channel measures are constructed. Under the same ecological construction scenario, the index of sediment connectivity (IC) of the basin shows a decreasing trend from ridge to gully, which mean the connectivity of the sediment at the ridge is less than that at the gully, and the gully are more prone to occur soil erosion than ridge. The distributed of large amount of construction land in the middle and lower reaches at the main gully of Wangmaogou small watershed reduces the connectivity of their surrounding sediment, and the region is prone to occur sediment deposition. Eco-construction measures have decreased significantly the sediment connectivity index (p<0.01) of Wangmaogou small watershed, and reduced the occurrence of soil erosion. Laying ecological measures lessened the possibility of local soil erosion, and increased the resistance of sediment in the transport process. Compared with the situation without ecological control, the mean of D_up index decreased by 75.27% by laying slope and gully measures, while the mean of D_up index decreased by only 6.45% by laying gully measures.

How to cite: Ma, Y., Li, Z., Hou, J., Li, P., Ren, Z., and Lu, K.: Effect of ecological construction on sediment connectivity in a typical small watershed on Loess Plateau, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13758, https://doi.org/10.5194/egusphere-egu21-13758, 2021.

The connectivity of rill erosion and overland flow are significantly affected by freeze-thaw cycles. Meltwater concentrated flow laboratory experiments were carried out to assess the soil erosion connectivity of different frozen conditions based on simplified hydrological curve and relative surface connection function. The experiments were performed over frozen, shallow-thawed, and unfrozen soil-filled flumes under 1, 2, and 4 L/min flow rates with the temperature around 5 °C. The results imply that according to the spatial distribution of the high connected areas on the slope, the connectivity of the sediment structure on the slope is obviously enhanced with the increase of the flow rate. The order of the structural connectivity of the sediment on the slope with different freeze-thaw states under the same flow rate is: frozen slope > shallow-thawed slope > unfrozen slope. Under different flows and soil frozen conditions, the laws of the vertical and horizontal connectivity rates of the slope are relatively similar which increase first and then stabilize, while the horizontal connectivity rate first decreases and then stabilizes. From the perspective of horizontal connectivity, the erosion form at the beginning of the experiment was mainly surface erosion; as the experiment progressed, the erosion form gradually changed from surface erosion to rill erosion. The results of this research would provide specific implications about meltwater erosion connectivity for improving the erosion process understand.

How to cite: Wang, T., Li, P., Hou, J., Li, Z., Cheng, S., and Wang, F.: Investagation of the sediment connectivity under freeze-thaw meltwater compound erosion condition on loessal slope, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13725, https://doi.org/10.5194/egusphere-egu21-13725, 2021.

The soils are susceptible to water erosion in the hilly and ravine region of the Loess Plateau due to the readily erodible attribute of soils, erosive geomorphology, land use and land cover, and erosive rainfall. The soil and water losses induced by water erosion have the significant on-site impacts on crop growths and yields in this region because of soil nutrient depletion and adverse soil moisture condition. In addition, the crops grown in different land types frequently suffer from the seasonal draught due to climate change, which leads to the decline or failure of crop yield. Therefore, the crop yields and grain production are susceptibly stressed by soil erosion and drought in this region. Soil erosion and draught are the essential issues faced by agriculture production and eco-environment. Alternatively, effective measures of soil and water conservation can incredibly control soil and water losses induced by water erosion, alleviate the influences of draught on crop yields, and sustain grain production in this region. The check dam is one of the widely adopted engineering measures of soil and water conservation in the valleys of the hilly and ravine region on the Loess Plateau. Check dam can play multiple roles in mitigating soil erosion, trapping eroded sediments, regulating runoff and creating the lands in the valleys in the context of water erosion. The check dam can control the soil erosion to some extent because it can raise the basis level of erosion in the valley. The lost sediment and runoff can be trapped by the check dam in a watershed, which can reduce resultant loss rate of soil and water in the outlet of the watershed and mitigate sediment loads in the rive connecting to the watershed. Moreover, the check dam can make sediments or eroded soils deposit so as to develop the relatively flat lands called as the dam-trapped farmland in the valleys. The dam-trapped farmlands along with the terrace lands are regarded as the crucial farmlands due to their excellent farming conditions in this region. Some grain crops, such corn, sorghum, millet or potato, are always grown in the dam-trapped farmlands, among which corn is frequently planted in this kind of farmland. The crop yields of the dam-trapped farmlands have been increasing over the last 60 years. It is evidenced that the yield of corn increased from 2250-3000 kg/ha in 1960s to 12000-15000 kg/ha at present. The corn yield of the dam-trapped farmland is 1.5-2.0 folds of that of the terrace land. The nutrient use efficiency and water use efficiency of corn in the dam-trapped farmland are much higher than those of terrace land. It can be seen that check dam have the powerful function mitigating the losses runoff and sediment, and dam-trapped land can play the critical parts in sustaining grain production and insuring food security in the hilly and ravine region of the Loess Plateau. 

Keywords: soil erosion; check dam; dam-trapped farmland; grain production; food security; hilly and ravine region; Loess Plateau

How to cite: Wang, B., Dang, W., and Dang, T.: The Roles of Check Dams and Dam-Trapped Farmlands in the Hilly and Ravine Region of the Loess Plateau: Soil Erosion Control, Grain Production and Food Security, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6838, https://doi.org/10.5194/egusphere-egu21-6838, 2021.

The over 100,000 check dams constructed across the Loess Plateau for soil and water conservation may have substantially changed the hydrological processes in the region, which, however, has not been understood yet. As a critical step towards revealing the lumped effect of check dams at the regional scale, this study explored the modified flood hydrology induced by check dams in Wangmaogou catchment, a representative small Loess Plateau watershed. A coupled hydrological and hydraulic modeling approach was applied to simulate the flooding process for different stages of deposition and topographic changes in the check dam reservoir. The results suggest a paradigm shift of the dam effect on flood attributes, which transits from a total interception in the early stage of the dam to peak reduction and flood detention, rather than a complete loss of flood control functions, when it approaches the maximum capacity of sedimentation. Under a given level of deposition, the reduction to a minor flood by a check dam was higher than that to a major flood. With the progression of siltation behind the check dam, the flood peak reduction rate, flood volume reduction rate, and flood lag time decreased accordingly. Although the check dam with a reservoir fully filled by sediment lost its ability of intercepting floods, it still exhibited a considerable ability to reduce the peaks of floods. The topographical changes contributed to the reduction of flood peak appreciably by reducing the flow velocity and retarding the flood propagation. Noticeably, this reduction augmented with the advancement of siltation and the topographic change, indicating the persistence of the hydrologic effect of check dams in a long run. As a result of hydrological changes, the reduction in flood flow velocity due to check dam suggests a substantial reduction in sediment transport and channel erosion during floods. In addition, a dam system containing multiple, cascading check dams exhibits much more significant effect in modifying both hydrologic and hydraulic properties of flood than individual dams. The current research provides a mechanistic understanding of the check dam effect on watershed hydrology under heavy rainstorms in small catchments, which sheds light on evaluating the upscaled effect of the large number of check dams on Loess Plateau regional hydrology and water resources.

How to cite: Yuan, S., Li, P., Shi, P., and Zhang, Z.: Influence of Loess Plateau check dams on catchment flood hydrology across varying stages of lifespan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2161, https://doi.org/10.5194/egusphere-egu21-2161, 2021.

Check dam is a line of defense in the comprehensive watershed management system, but with the extended operation time, the operational risk of check dam increases, coupled with the frequent occurrence of sudden heavy rainfall under the influence of climate change in recent years, further increasing the risk of dam break.

In this study, to address the current problem of untimely detection of potential dam break risk of check dam in China, we use the common variable screening based on WoE (Weight of Evidence) and IV (Information Value), establish a score card model based on logistic regression method, use KS curves and statistics, and AUC values for model evaluation, and analyze the 2016 From 22:00 on August 16 to 12:00 noon on August 17, 2016, a dam break was formed by a large rainstorm in Dalat Banner.

The following conclusions were obtained: The IV values of each variable, such as control area, total storage capacity, siltation area, storage volume, and maximum rainfall, were all greater than 0.1, and each variable had more than moderate predictive power as a function of the breaking of check dam, that is, each factor had an effect on the breaking of check dam.The IV values of precipitation factors are higher than those of check dam factors. The influence probability of precipitation factors on the breaking of check dam is about 67%, and the influence probability of check dam factors on the breaking of check dam is about 33%.Precipitation is a direct factor affecting the breaking of check dam, and the maximum 6-hour precipitation has the most significant effect; among the check dam factors, the control area, storage volume, and flood storage capacity have a greater effect on the breaking of check dam, accounting for more than 10%, while the siltation volume and depth have a smaller effect on the breaking of check dam, accounting for 2.85% and 2.89% respectively.Very low risk which check dam with a score of 95 or higher account for about 43%, low risk for 28%, average risk for 15%, and higher risk for 7%. Very high risk accounted for 5% and there was only one dam with danger which is rated below 10.

This study aims to monitor and warn the operation of check dam to ensure the safe operation of the check dam system and maintain the ecological security of the Loess Plateau.

How to cite: liu, B., li, P., li, Z., yang, Y., long, S., and feng, Y.: Evaluation of the risk of the breaking of check dam based on a scorecard model., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3664, https://doi.org/10.5194/egusphere-egu21-3664, 2021.

The historical landscape condition of discontinued river before discontinued flow is one of the core research fields of river ecological restoration and an important historical reference for the ecological restoration of discontinued river corridor. In this paper, the landscape condition of Yongding River, a discontinued river in northern China, is analyzed before its cut-off. Through the early KEYHOLE satellite high-definition image data interpretation analysis, the landscape type map of the river corridor before its cut-off was drawn. The overall winding degree (1.27) and the overall horizontal and vertical structure of the river before its cut-off were determined. In addition, the area proportion of the key landscape types in river corridor, such as channel, mid-channel bar and floodplain, is 12.82%, 8.8% and 16.29% respectively, and the morphological characteristics and distribution of the above key landscape types in each section of the river can be determined by quantitative analysis. On this basis, the landscape pattern index analysis method can be used to analyze and calculate the overall landscape pattern of the river corridor before cut-off. Combined with relevant historical hydrological data, the historical state of the river before its cut-off can be restored to a certain extent. These results are of great support to the channel ecological restoration, floodplain ecological reconstruction and riverbank ecological restoration.

How to cite: Xu, X.: Historical landscape condition study of discontinued river corridor based on satellite image data analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3743, https://doi.org/10.5194/egusphere-egu21-3743, 2021.

Changes in land use patterns have important implications for soil structure and soil nutrient transport processes. This paper is based on the project of returning farmland to forests in the Loess Plateau-Ziwuling area of China. Explore the phase changes of the aggregate structure and nutrients content and its effect on soil infiltration and erodibility during the changing land use process. Identify the effective time domain for soil management in the area, which provide a scientific basis for coordinating regional land use and efficient soil erosion control. The results showed that with the increase of soil recovery/opening time, the content of soil water stable aggregates (SWAG), soil organic matter (SOM), total nitrogen (TN) and total phosphorus (TP) showed an increasing /decreasing trend. In the process of soil reclamation, the content of organic matter in large-size aggregates (>5mm) decreases first at a higher rate, while in land restoration process, the content of organic matter in small-sized (2-5mm) aggregates increases rapidly. With the increase of soil reclamation time, the initial time of runoff production is advanced. In the 30-year of the land restoration process, the erodibility K decreased by 87%, and the SOC content has reached 96% to the common forest level, indicate that the soil quality is greatly improved when the land returns to this moment, the ability to resist erosion reaches a certain level and tends to be stable, and it is considered that the input and output of the governance before the time node is relatively high.

How to cite: Zhang, Y., Li, P., and Xu, G.: Response of soil nutrient structure and aggregate strength to land use in a typical area in the Loess Plateau, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4184, https://doi.org/10.5194/egusphere-egu21-4184, 2021.

The Loess Plateau is located in arid and semi-arid region, and the fragmentation of vegetation patches is large. However, the combination of vegetation patches to the runoff and sediment yield on the slope is not clear yet. To evaluate the influence of vegetation patch type and number on runoff, sediment and hydrodynamic parameters, this study established field runoff plots with different landscape patch types, including bare land, S-road patches, strip patches, grid patches and random patches, as well as different quantities patches of 5, 10, 15 and 20. The results showed that the runoff yields of the four vegetation patch types decreased by 16.1%–48.7% (p<0.05) compared with that of bare land, whereas sediment yields decreased by 42.1%–86.5% (p<0.05). Also, the resistance coefficients of the poorly connected patch patterns, including strip patches, grid patches and random patches, ranged between 0.2–1.17 times higher than that of the well-connected S-road patch pattern, and the stream power decreased by 33.3%–50.7% (p<0.05). Under a uniform distribution of vegetation patches, the runoff rate and sediment yield decreased significantly with an increased number of patches. Although the increase in the number of vegetation patches also resulted in a decrease inflow shear stress and stream power to different degrees, the differences between the combinations with similar patch numbers were not significant. Besides, the sensitivity of soil to erosion decreased with an increasing number of the patch in the vegetation landscape, whereas the sensitivities of patch combinations with poor connectivity were lower than those with good connectivity. From this perspective, the optimization of vegetation in the Loess Plateau region requires sufficient consideration to reducing the connectivity of vegetation patches and increasing the density of patches.

How to cite: Sun, R., Zhang, J., and Ma, L.: Landscape Patches Influencing Runoff and Sediment Yield and Flow Hydrodynamics in The Loess Plateau, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5930, https://doi.org/10.5194/egusphere-egu21-5930, 2021.

In order to improve the accuracy of the inflow forecasting of Shiquan Reservoir in the Han River Basin, this paper compared the application effects of Xin'anjing model and Wetspa model. The study collected the rainfall and runoff data from 2009 to 2015, as well as the DEM, land use and soil data with 1000´1000m grid size. The model calibration and verification periods were from 2009 to 2012 and from 2013 to 2015, respectively. In addition to using the runoff depth and the determination coefficient to evaluate the accuracy of the two models, the flow relative error CR1, model confidence coefficient CR2, Nash-Sutcliffe efficiency CR3, logarithmic version of Nash-Sutcliffe efficiency CR4 for low flow, improved Nash-Sutcliffe efficiency CR5 for high flow were adopted to analyze the simulation results of the two models. The results showed that the simulation results of the Wetspa model could be used as a supplement to the simulation results of the Xin'anjiang model, providing high-precision flood forecasting results for the scheduling decisions of Shiquan Reservoir in terms of time and space.

How to cite: Cai, S., Yuan, R., Liao, W., and Wu, L.: Application of Xin'anjiang Model and Wetspa Model in the Inflow Forecasting of Shiquan Reservoir, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1933, https://doi.org/10.5194/egusphere-egu21-1933, 2021.

In karst environments, soil erosion is a  prominent environmental issue that can cause many other problems. Researching the erosion and deposition rates at the hillslope scale in small watersheds is important for designing efficient soil and water conservation measures for the small watersheds even the large scale areas. In our research, the closed watershed, a representative depression in karst gabin basin, located in the Yunnan province, Southwest China, was selected to assess the soil erosion and sediment mobilisation at different hillslope positions using the ¹³⁷Cs tracing technique. The results showed that the soil erosion rates in the shoulders, backslopes and footslopes were 0.87, 0.35 and 0.49 cm a^-1, respectively, meanwhile the soil sediment rate in depression bottom was 2.68 cm a^-1. The average annual soil erosion modulus of the complete hillslope was 632 t km^-2a^-1, which confirmed the serious gradation according to karst soil erosion standards. The sediment delivery ratio would summarize 0.82 in the whole catchment according to the square of hillslope and depression bottom. To identify which factor could play the most important role in influencing the estimations using ¹³⁷Cs, a linear correlation and Principal Component Analysis were conducted. The results showed ¹³⁷Cs concentration of different soil depth at different hillslope positions were significantly correlated with soil organic matter (SOM) and total nitrogen (TN) (P<0.05). As the typical karst geomorphological types, these findings are expected to provide data support for the whole watershed soil erosion management and ecological restoration in  fragile karst ecosystem.

How to cite: Li, Y., Yu, Y., Lan, F., and Liu, P.: Evaluating soil erosion and sediment deposition rates by  137Cs fingerprinting technique at different karst hillslope positions  in Yunnan Province, southwest China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13863, https://doi.org/10.5194/egusphere-egu21-13863, 2021.