Runoff Yield Research Articles

Influences of conservation measures on runoff and sediment yield in different intra-event-based flood regimes in the Chabagou watershed

The Loess Plateau in China has suffered severe soil erosion. To control soil erosion, extensive conservation measures aimed at redistributing rainfall, hindering flow velocity and intercepting sediment were implemented on the Loess Plateau. To accurately evaluate the combined effect of conservation measures in the Chabagou watershed, this study classified intra-event-based floods into four regimes via cluster and discriminant analyses. Regime A was characterized by short flood duration and low erosive energy, regime B was characterized by short flood duration and high erosive energy, regime C was characterized by long flood duration and low erosive energy, and regime D was characterized by long flood duration and high erosive energy. The results indicated that peak discharge (qp), runoff depth (H), mean discharge (qm), and runoff erosion power (E) decreased by 75.2%, 56.0%, 68.0% and 89.2%, respectively, in response to conservation measures. Moreover, area-specific sediment yield (SSY), average suspended sediment concentration (SCE), and maximum suspended sediment concentration (MSCE) decreased by 69.2%, 33.3% and 11.9%, respectively, due to conservation measures. The nonlinear regression analysis revealed a power function relationship between SSY and E in both the baseline (1961–1969) and measurement period (1971–1990) in all regimes. Conservation measures reduced sediment yield by not only reducing the runoff amount and soil erosion energy but also transforming the flood regime, for example, transforming a high-sediment-yield regime into a low-sediment-yield regime. Moreover, conservation measures altered the SSY-E relationship in regime A, whereas no obvious difference in regime B or C/D was observed between the measurement period and the baseline period. This study provides a better understanding of the mechanism of runoff regulation and the sediment yield reduction under comprehensive conservation measures in a small watershed on the Chinese Loess Plateau.

Erosion process of loess slope and influencing factors in the loess hilly-gully region, China

Rainfall intensity, slope length, and slope gradient are the important factors affecting runoff and sediment yield. In order to quantitatively analyze the effects of rainfall intensity, slope length, and slope gradient on the erosion process of Ansai loess slope in loess hilly and gully region, we analyzed the variation of runoff and sediment yield on Ansai loess with two slope lengths (5, 10 m), three slopes (5°, 10°, 15°) and two rainfall intensities (60, 90 mm·h-1) in an indoor simulated rainfall experiment. The results showed that the initial runoff generation time decreased with the increases of slope length, though the overall change was not significant. The initial runoff generation time decreased with the increases of rainfall intensity. Compared with the intensity of 60 mm·h-1, the initial runoff generation time decreased by 5.7-18 min under the intensity of 90 mm·h-1. Among them, the runoff initiation time on the slope of 10° was the fastest. With the duration of rainfall, runoff yield rate increased rapidly at first, and then gradually fluctuated around a certain value. The sediment yield rate increased rapidly in a short period of time at the initial stage of runoff generation, and then decreased after reaching the maximum, and being gradua-lly stable. The rates of runoff and sediment yield increased with the increases of slope length and rainfall intensity, but the law of change with slope was not obvious. With the increases of rainfall intensity, slope length and gradient, the total sediment yield increased accordingly. Under the rainfall intensity of 90 mm·h-1, the slope surface with the length of 10 m and slope of 15° generated rill, leading to the highest total erosion amount (11885.66 g). Under the rainfall intensity of 60 mm·h-1, the erosion amount per unit area decreased with the increases of slope length, and there was a critical erosion slope length in 5-10 m slope section. Slope length, slope and rainfall intensity all played a promoting role in runoff process. Rainfall intensity, slope length, and their interaction contributed more to runoff yield rate and total erosion amount. Rainfall intensity contributed the most to runoff yield rate, with a contribution rate of 49.8%. The contribution rate of slope length to the total erosion was the largest, which reached 37.8%.

Quantifying the effects of watershed subdivision scale and spatial density of weather inputs on hydrological simulations in a Norwegian Arctic watershed

Abstract The effects of watershed subdivisions on hydrological simulations have not been evaluated in Arctic conditions yet. This study applied the Soil and Water Assessment Tool and the threshold drainage area (TDA) technique to evaluate the impacts of watershed subdivision on hydrological simulations at a 5,913-km2 Arctic watershed, Målselv. The watershed was discretized according to four TDA scheme scales including 200, 2,000, 5,000, and 10,000 ha. The impacts of different TDA schemes on hydrological simulations in water balance components, snowmelt runoff, and streamflow were investigated. The study revealed that the complexity of terrain and topographic attributes altered significantly in the coarse discretizations: (1) total stream length (−47.2 to −74.6%); (2) average stream slope (−68 to −83%); and (3) drainage density (−24.2 to −51.5%). The spatial density of weather grid integration reduced from −5 to −33.33% in the coarse schemes. The annual mean potential evapotranspiration, evapotranspiration, and lateral flow slightly decreased, while areal rainfall, surface runoff, and water yield slightly increased with the increases of TDAs. It was concluded that the fine TDAs produced finer and higher ranges of snowmelt runoff volume across the watershed. All TDAs had similar capacities to replicate the observed tendency of monthly mean streamflow hydrograph, except overestimated/underestimated peak flows. Spatial variation of streamflow was well analyzed in the fine schemes with high density of stream networks, while the coarse schemes simplified this. Watershed subdivisions affected model performances, in the way of decreasing the accuracy of monthly streamflow simulation, at 60% of investigated hydro-gauging stations (3/5 stations) and in the upstream. Furthermore, watershed subdivisions strongly affected the calibration process regarding the changes in sensitivity ranking of 18 calibrated model parameters and time it took to calibrate.

Experimental Study of Runoff and Sediment Yield Affected by Ridge Direction and Width of Sloping Farmland

Water and soil losses from sloping farmlands potentially contribute to water eutrophication and land degradation. However, few studies explored the combined effects of ridge direction and ridge width on surface runoff and soil losses of sloping farmlands. Twenty-seven experimental plots (8 m long and 4 m wide) with nine treatments (three ridge direction: cross ridge, longitudinal ridge, and oblique ridge; and three ridge width: 40, 60, and 80 cm) were adopted under natural rainfall conditions for two years in the Luanhe River Basin of China. Results indicated that ridge direction had significant effects on runoff and sediment yield (p < 0.05). The ridge width had no significant effect on runoff and sediment yield. No significant interaction effect was found between ridge direction and width on runoff and sediment yield of the sloping farmland based on statistical analyses. Compared with cross-ridge (CR) tillage and oblique-ridge (OR) tillage, longitudinal-ridge (LR) tillage significantly decreased runoff by 78.9% and 64.9% and soil losses by 88.2 and 83.5%, respectively (p < 0.05). The effects of ridge directions on runoff and sediment yield were related to rainfall grade. When the rainfall grade reached rainstorm, the runoff yield under CR, LR, and SR had significant differences (p < 0.05). The runoff under LR and OR treatment was 5.16 and 3.3 times, respectively, of that under CR. When the rainfall level was heavy rain or rainstorm, the sediment yield under LR was significantly greater than that under CR. The sediment yield was 13.45 times of that under CR. Cross-ridge tillage with a ridge width of 40 cm is an optimally effective measure of soil and water conservation on sloping farmland in arid and semiarid regions of China.

Research on flood forecast of dashimen reservoir in xinjiang based on melting snow and runoff yield under excess infiltration

In China, the distribution of water resources is uneven in time and space. The effective allocation of water resources can realize the rational utilization of water resources. Reservoirs are an important part of the basin system, and the rational operation of reservoirs can realize the optimal allocation of water resources. Flood forecast is of great significance for reservoir operation. In order to realize the optimal operation of Dashimen reservoir in Xinjiang, aiming at the flood forecast in the dry area affected by melting snow, this paper expanded and improved the traditional hydrological forecast model, built the flood forecast model in the dry area with the coupling snowmelt based on the northern Shaanxi model and Elman neural network, and using the typical rainfall and runoff data in this area The results show that the relative error of the model is less than 10% and the accuracy is high, which can be used in the actual forecast. This model realizes the flood forecast in the drought area affected by snowmelt, and provides a new idea for the flood forecast of reservoir in the drought area affected by snowmelt, which has a certain guiding significance for the flood forecast in the drought area.

Effect of natural rainfall on the migration characteristics of runoff and sediment on purple soil sloping cropland during different planting stages

Abstract Due to the difficulty in monitoring subsurface runoff and sediment migration, their loss loads are still not clear and need further study. This study monitored water and soil loss occurring within experimental field plots for two calendar years under natural rainfall events. The sediment loss load was quantified by considering the corresponding water flow flux and its sediment concentration. The results showed that 60.04% of the runoff and 2.83% of the sediment were lost underground. The annual underground sediment loss reached up to 54.6 kg*ha−1*yr−1. A total of 69.68% of the runoff yield and 67.25% of the sediment yield were produced during the corn planting stage (CPS: March–July). Heavy rain and torrential rain events produced 94.45%, 65.46% of the annual runoff and 94.45%, 76.21% of the sediment yields during the corn-planting stage and summer fallow period (SFP: August–September). The rain frequency, rainfall, and rainfall duration of each planting stage significantly affected the resulting runoff and sediment yield. Measures aimed at the prevention and control of water-soil loss from purple soil sloping land should focus heavily on torrential rain and heavy rain events during the CPS and SFP. This paper aims to provide a practical reference for quantifying the water and soil loss from purple soil sloping cropland.

Improved flood forecasting using geomorphic unit hydrograph based on spatially distributed velocity field

Abstract This paper presents an energy model for determining the overland flow velocity in order to improve the low accuracy problem in flow concentration simulation. It furnishes a novel idea for studying flow concentration in ungauged basins. The model can be widely applied in analysis of spatial velocity field, extraction of instantaneous geomorphic unit hydrograph and development of distributed hydrological model. A distributed flood-forecasting model is constructed for Lianyuan Basin in Hunan Province of China. In the proposed method, gravitational potential energy is transformed into kinetic energy via an analysis of energy distribution of water particles in the basin. Based on the kinetic energy equation, the overland flow velocity simulating the geomorphic unit hydrograph is computed. Rainfall-runoff simulation is then performed by integrating with runoff yield and concentration model. Results indicate that the model based on energy conversion leads to more accurate results. The model has the following advantages: firstly, the spatial distribution of the velocity field is appropriate; secondly, the model has only one parameter, which is easily determined; and finally, flow velocity results can be used for the computation of river network flow concentration.

Weed cover controls soil and water losses in rainfed olive groves in Sierra de Enguera, eastern Iberian Peninsula

Soil erosion is a threat for the sustainability of agriculture and severely affects the Mediterranean crops. Olive groves are among the rainfed agriculture lands that exhibit soil and water losses due to the impact of unsustainable practices such as conventional tillage and herbicides abuse. To achieve a more sustainable olive oil production, alternative, greener crop management practices need to be tested in the field. Here, a weed cover (CW) treatment is tested at an olive tree plantation that has undergone conventional mechanical tillage for 20 years and results were compared against an adjacent control plantation that maintained tillage as a weed control strategy (CO). Both plantations were under the same tillage management for centuries and macroscopic analysis confirms they are otherwise comparable. Compared to the CO, where tilled soil cover was zero, 20 years of CW (weeds cover 64%; litter cover 5%) had led to significantly higher values of soil bulk density and soil organic matter. Results from rainfall simulation experiments at 55 mm h−1 on 0.25 m2 plots under CO (N = 25) and CW (N = 25) show that as a result of the improved soil structure, CW (i) reduced soil losses by two orders of magnitude (140 times), (ii) decreased runoff yield by one order of magnitude (from 2.65 till 27.6% of the rainfall), (iii) significantly reduced runoff sediment concentration (from 18.6 till 1.43 g l−1), and (iv) significantly delayed runoff generation (CO = 273 s; CW = 788 s). These results indicate that weed cover is a sustainable land management practice in Mediterranean olive groves and promotes sustainable agriculture production in mountainous areas under rainfed conditions, which are typically affected by high erosion rates such those found in the CO plots. Due to the spontaneous recovery of plant cover, we conclude that weed cover is an excellent nature-based solution to increase in the soil organic matter content and soil erosion reduction in rainfed olive orchards.

Understanding the complex environmental management through a len of food-water-ecosystem nexus: Insights from an ecosystem restoration hotspot in dryland

The Ecosystem Restoration Project (ERP) is a critical and urgent practice to achieve the land degradation neutrality (LDN) targets. However, an insufficient understanding of the balance between contrasting sectors of the food-water-ecosystem nexus results in ineffectiveness in supporting complex environmental management (CEM), leading to undesirable ERP failures. The Ordos Plateau case identified the nexus evolution and the non-linear interactions between sectors, which were expected to support adaptive strategy formulations for CEM and achieve win-win outcomes. Revegetation in drylands substantially boosted ecosystem restoration, alleviating soil erosion. However, the excessive reliance on returning cropland to woodland and grassland has caused a significant loss of arable and grazing land. During the initial period of ERPs, this exacerbated decline in grain and meat productivity. In addition, aggressive revegetation activities have also reduced runoff yield and depleted soil water resources. Water scarcity is recognized as the most challenging issue in dryland ecosystem restoration, heavily influencing the interactions between sectors and threatening the long-term sustainability of ERPs. To accommodate for regional water carrying capacity, ERPs should adopt and properly allocate the use of suitable plant species with a proven anti-drought capability and high survival ratios without additional human interventions. In addition, the evolution regimes, driving factors, critical thresholds, and complex feedbacks between the nexus sectors should be fully understood to address the water resources constraints and reconcile trade-offs. This would enable the prevention of ecosystem shifts to undesirable failures and inform timely and cost-effective CEM to achieve the LDN targets.

Relationship between the periodicity of soil and water loss and erosion-sensitive periods based on temporal distributions of rainfall erosivity in the Three Gorges Reservoir Region, China

More variable or extreme rainfall caused by global climate change is likely to cause much uncertainty in soil erosion. Exploring the effects of changes in the timing and magnitude of rainfall erosivity on soil erosion allows to better understand the sensitivity of soil erosion to rainfall. The aim of this study was to investigate the relationships between the periodicity of soil and water loss and erosion-sensitive periods based on the temporal distributions of rainfall erosivity in the Three Gorges Reservoir Region, China. A daily rainfall erosivity model and field runoff plot monitoring were used to achieve these goals. We found that extreme rainfall has a great effect on the distributions of rainfall erosivity. The average annual erosive rainfall frequency accounts for only 21.2% of the average annual total rainfall frequency, but the average annual erosive rainfall amount accounts for 70.4% of the average annual total rainfall amount. The monthly runoff yields and sediment yields show synchronization with variations in rainfall erosivity to some extent, but the former are closer to the changes in monthly rainfall erosivity. The annual runoff yields and soil loss rates do not show synchronization, but the changes in annual soil loss rates are closer to the interannual variations of rainfall erosivity. The annual soil erosion in the study area can be divided into three periods, namely, highly sensitive periods, moderately sensitive periods and slightly sensitive periods, which indicate the erosion risks from high to low, respectively. Additionally, low vegetation coverage in highly sensitive periods and human activities in moderately sensitive periods can aggravate soil erosion.

Effects of the distribution of biological soil crust on the hydrodynamic characteristics of surface runoff.

The distribution pattern of biological soil crusts (biocrusts) is one of the main factors affecting runoff and sediment yield. The relationship between runoff and sediment yield and biocrusts' distribution pattern is not clear, which hinders understanding the mechanism underlying the effects of biocrusts on runoff and sediment from slopes. To fill the knowledge gap, we investigated the relationship between the landscape indices of three biocrusts' distribution patterns, i.e. zonation, chessboard and random, and the hydraulic parameters, using of simulated rainfall experiments and landscape ecology methods. The results showed that biocrust significantly affected the erosion force of slopes and that its distribution pattern could affect slope erosion dynamics. Compared to bare soil, the presence of biocrusts significantly reduced the runoff velocity (54.6%) and Froude number (67.0%), increased the runoff depth (86.2%) and Darcy-Weisbach resistance coefficient (10.68 times), but did not affect the Reynolds number and runoff power. Expect for the runoff depth, there were significant differences in the hydraulic parameters of the three biocrusts' distribution patterns, with the random pattern having the strongest impacts on the dynamics of slope erosion. Based on factor analysis and cluster analysis, five indices of percentage of patch to landscape area, patch density, landscape shape index, patch cohesion and splitting could be used as the indicators for the distribution characteristics of biocrust patches. The patch cohesion and splitting of biocrust patches were the main distribution pattern indices of the hydrodynamics of surface runoff. As the patches patch cohesion decreased, the splitting increased, which caused the surface runoff velocity increase, the resistance decrease, and the slope erosion became more severe.

Suspended sedimentary dynamics under Mediterranean semi-arid environment of Wadi El Maleh watershed, Algeria

Soil degradation due to erosion by water is a serious environmental problem for the integrated management of basins, affecting the soil and water resources in Algerian region. Pluvial flood has been increasingly understood as a major threat that has presented a significant risk for many watersheds worldwide, estimation of runoff and sediment yield is primarily required for watershed development planning involving soil and water conservation measures, considering runoff is responsible for sediment detachment and their transport during the erosion processes. In this context, the phenomenon reaches spectacular values in many Algerian watersheds; in this case, it is very severe in flood period, many models have been developed and their application has been spread. In this study, water flow discharge and suspended sediment concentration have been modelled using sediment rating curve approach, this model is the large discussed model; it is the best significant equation for the majority of Algerian basins, this equation which has a power law form (i.e. C = aQb, where a and b are fitted parameters), explains, more than 72% for the whole floods observed during 17 years in Wadi El Maleh watershed, the flood contribution in annual suspended yield is variable; it can reach more than 92%, which is the case of flood; January 19, 1985, while, at inter-annual scale, the percentage is 24% and 43% in total water and suspended sediment yields, respectively; for all studied floods, a good logarithmic correlation between sediment rating curve parameters is observed, this outcome can help to extrapolate this model to other events.

Quantitative Analysis of Geomorphologic Characteristics for Surface Runoff Determination in Amala River Catchment in Kenya

Hydrological response of a catchment is a function of rainfall as influenced by catchment characteristics comprising geomorphology, land cover, and management practices. In this study, the analysis mainly focused on how geomorphological characteristics influence the catchment hydrological response. Geomorphological analyses of catchment geometry, stream patterns, relief, and slope can be used to characterize the catchment features that affect the drainage network. These characteristics are catchment specific and therefore unique to provide an insight into its hydrologic response. The objective of this research was to quantitatively analyze geomorphologic characteristics; linear, areal, drainage pattern, and relief aspect, of Amala River catchment, using ArcGIS tools and infer its hydrological behavior. The morphometry of the catchment was derived from the DEM within the ArcMap environment. These parameters as well as mathematical map equations were used to derive geomorphological characteristics such as bifurcation ratio, rho coefficient, drainage density, infiltration number, form factor among others. The results show that the Amala River catchment is elongated with uniform lithology and a higher probability of delayed peak hydrographs due to longer lag time and time of concentration. The catchment exhibits a dendritic drainage pattern with an average bifurcation ratio of 4.26 which is closer to the upper bound value of 5. This indicates a reduction in peak flows and a delayed time to peak. The surface runoff yield efficiency was low and non-uniform with an average drainage density of 1.073 km/km2. The catchment was characterized by higher infiltration characteristics as compared to surface flows, this varied spatially, with sub-basins far North of the outlet having high infiltration than those near the outlet. The catchment relief was characterized as steep and therefore high stream velocity was inferred. The investigation and findings of this study on catchment geomorphology and inferred hydrologic behavior will be of great importance in catchment management, water resource planning within the catchment, and water harvesting at a spatial scale. Thus, the outcomes provide a baseline for informed water pan and water harvesting structures site.

Normalized Antecedent Precipitation Index Based Model for Prediction of Runoff from Un-Gauged Catchments

The ‘Normalized Antecedent Precipitation Index (NAPI)’ model developed based on water balance equation was found capable to predict runoff yields from ungauged catchment when its parameters estimated from the gauged catchment are updated using the linear relationship of geomorphologic parameters of an ungauged to that of the gauged catchment, and cumulative geomorphologic index (CGI). The CGI was developed by assigning a relative weight on each geomorphologic parameter multiplied by the ratio of characteristic value of that parameter of the ungauged and gauged catchment. Influence of land-use and land-cover (LULC) on the model’s parameters was also analyzed by developing an index for LULC. The NAPI model has three parameters and its mathematical structure has rational form and the parameters possessed resonance with curve number (CN) of the SCS (Soil Conservation Services) model. The NAPI model demonstrated ability to simulate rainfall-runoff events both as direct and inverse problem. Performances of the model to predictions of runoffs from ungauged catchments were also tested with the data of two observation sites of the Bina basin in Madhya Pradesh (India) considering the data of one site as the runoffs from the ungauged catchment. The results exhibited a close match between the computed and observed values when the model’s parameters were also updated by the index of LULC.

Estimation of discharges of water flows and debris floods in a small watershed

AbstractFloods in small mountainous watersheds cover a wide spectrum of flow. They can range from clear water flows and hyperconcentrated flows to debris floods and debris flows, and calculation of the peak discharge is crucial for predicting and mitigating such hazards. To determine the optimal approach for discharge estimation, this study compared water flow monitoring hydrographs to investigate the performance of five hydrological models that incorporate different runoff yields and influx calculation methods. Two of the models performed well in simulating the peak discharge, peak time, and total flow volume of the water flood. The ratio (γ) of the monitored debris flood discharge (Qd) to the simulated water flow discharge (Qw) was investigated. Qualitatively, γ initially increased with Qw but then decreased when Qw exceeded a certain threshold, which corresponded to rainfall of 95 and 120 mm in a 6‐ and 24‐h event with a normal distribution of precipitation, respectively. The decrease might be attributable to a threshold of sediment availability being reached, beyond which increased flow rate is not matched by increased sediment input in the large watershed. Uncertainty of hydrological calculation was evaluated by dividing the catchment into sub‐basins and adopting different rainfall time steps as input. The efficiency of using a distributed simulation exhibited marginal improvement potential compared with a lumped simulation. Conversely, the rainfall time step input significantly affected the simulation results by delaying the peak time and decreasing the peak discharge. This research demonstrates the applicability of a discharge estimation method that combines a hydrological water flow simulation and an estimation of γ. The results were verified on the basis of monitored flow densities and videos obtained in two watersheds with areas of 2.34 and 32.4 km2.

A watershed runoff yield model based on Erlang distribution water storage capacity curve

A storage capacity curve reflects the spatial heterogeneity in water deficiency within a basin and is used for computing the production of watershed runoff. This study analyzed the spatial distributions of watershed storage capacity for several typical basins. The Erlang distribution was shown to have the best fit to the watershed storage capacity curves, which was then adopted to derive the production of runoff in the studied watersheds. This study proposes a novel watershed runoff yield model with increased adaptability based on the Erlang distribution storage capacity curve; hence, the model should be better able to represent the actual runoff yield process in a basin. The proposed watershed runoff yield model generated more accurate simulations compared to those of the Xin'anjiang model. In addition, the parameters of the proposed runoff yield model can be estimated from basin topography and soil type data, thereby providing a feasible approach for the calculation of runoff yield in data-scarce areas.

Effects of slope length on soil erosion of Karst slope under different rainfall conditions

Based on the runoff and sediment yield data from 59 erosive rainfall plots with different slope lengths (5, 10, 15, 20, 25 m) in Shiqiao small watershed of Guizhou Province from 2012 to 2014, we analyzed the relationship between runoff and sediment yield and slope length under diffe-rent rainfall conditions. The results showed that, with the increases of slope length, the runoff yield of slope showed a 'V-shape' pattern, the sediment yield of slope increased first and then decreased. According to rainfall amount, rainfall duration, and average rainfall intensity, the 59 erosive rainfall in the study area could be divided into three types, including type A with short duration, heavy rain intensity and small rainfall, type B with medium duration, light rain intensity and medium rainfall, and type C with long duration, medium rain intensity and large rainfall. The relationships between runoff and sediment yield and slope length were different under different rainfall patterns. There was about 20 m critical slope length of sediment yield under type A and B. The sediment yield gradually increased with the increases of slope length under type C. There was a good cubic function relationship between slope length and runoff and sediment yield under different rainfall patterns. The variable amplitude of runoff and sediment yield was different among different slope lengths. Except the slope length of 15-20 m, the variable amplitude of runoff and sediment yield under type C was relatively large. The variation amplitude of sediment yield was significantly higher than that under other rainfall patterns. The total runoff yield under different rainfall patterns was type A>B>C. The sediment yield under type B was the smallest, that of type A at the slope length of 20 m was the largest and that of type C at other slope lengths was the largest. The correlation between compound rainfall factors and runoff and sediment yield was better than that of single rainfall factor under type A (common rainfall type in the study area). Rainfall amount (P), the pro-duct of rainfall duration and maximum 30 min rainfall intensity (TI30), product of rainfall duration and average rainfall intensity (TI), product of rainfall amount and rainfall duration (PT) were significantly correlated with the runoff and sediment yield. Among those factors, P and TI had the strongest correlation with runoff. Further, the relationship between them and runoff under different slope lengths could be expressed by linear equation and S-curve. There was a good cubic function relationship between the sediment yield and its corresponding rainfall factors under different slope lengths.

Prioritization of critical source areas for soil and water conservation by using a one‐at‐a‐time removal approach in the upper Huaihe River basin

AbstractAppropriate land use planning plays an active role in soil and water conservation. Considering the financial investment and grain security limitations, land use planning practices should be applied focusing on the critical source areas (CSAs) rather than the complete region. In this study, the Soil and Water Assessment Tool (SWAT) model was used to identify CSAs for sediment control in the upper Huaihe River basin. A novel one‐at‐a‐time removal approach was proposed which involves individually removing the land use planning programme at sub‐basin level, after which the related runoff and sediment results were simulated by the validated SWAT model. Then, two influencing indexes (i.e., runoff yield and sediment yield) were used to evaluate the influences on runoff and sediment responses at the watershed outlet, caused by the removal of that land use planning programme. Finally, critical sub‐basins for land use planning were prioritized based on the weighted average of those influencing indexes. Calibration and validation results showed that the SWAT model well represented the monthly streamflow and sediment at the watershed outlet. The Nash–Sutcliffe efficiency values of monthly streamflow and sediment were generally greater than 0.75. Results of the integrated priorities revealed that the most CSAs affecting land use planning implementation were in sub‐basin 11, which was not the sub‐basin yielding the most sediment. The CSAs prioritization determined by the one‐at‐a‐time removal approach can achieve a better erosion control performance than that identified by the simulated sediment loads, which can be applied widely in targeting CSAs for implementation of watershed conservation practices with limited investment and disturbance.

Study on Landscape Patches Influencing Hillslope Erosion Processes and Flow Hydrodynamics in the Loess Plateau of Western Shanxi Province, China

Although vegetation restoration plays an important role in the management of surface runoff and soil erosion, the large-scale restoration of vegetation can increase water consumption and reduce surface water resources, thus affecting the health of river ecosystems. Therefore, vegetation restoration should aim to achieve a vegetation landscape pattern that optimizes protection of soil resources while limiting water consumption. 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. An artificial rainfall experiment was conducted to determine the effect of different vegetation patches in reducing runoff and sediment, and the relationship between the types and number of vegetation patches and hydrodynamic parameters. The results showed that the runoff yields of the four vegetation patch types decreased by 16.1–48.7% compared with that of bare land, whereas sediment yields decreased by 42.1–86.5%. In addition, 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%. Under a set vegetation coverage rate, an increase in the number of vegetation patches resulted in a significant reduction in runoff velocity, runoff yield, and sediment yield, increases in surface roughness and flow resistance, and reductions in runoff shear force and stream power. 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. The results of this study highlight the importance of vegetation patch type and quantity for control of soil erosion.

Erosion-induced spatial uniformity of surface runoff over an extremely degraded catchment on the Chinese Loess Plateau

Previous studies have suggested that runoff reduces with slope length, and the scaling trend diminishes with the degree of land degradation. This study further hypothesized that runoff is scale-independent and spatially uniform in extremely degraded landscapes. We tested the hypothesis on the Chinese Loess Plateau. Runoff data were collected from a densely rilled and gullied loess headwater with soil erosion intensity close to 20,000 t km−2 yr−1. The data included observations from seven arable experimental plots of various lengths (20 to 164 m) and gradients (9 to 32°), as well as the headwater outlet. The results showed that the erosion-induced network of rills and gullies lowered runoff reinfiltration and resulted in exceptional high flow connectivity, thus obscuring the effects of other environmental conditions (mainly topography) and contributing to uniform runoff from the upper hillslope to the headwater outlet. The observations held at the event, annual, and mean annual time scales, suggesting that the investigated watershed is simply the sum of individual slopes. This study highlights the effect of erosion processes on the ensuing runoff yield and suggests that scale-independent runoff is typical of highly degraded slope systems.11SSY (t km−2), area-specific sediment yield.