Runoff Initiation Research Articles

A simple analytical method to estimate runoff generation and accumulation

The study of runoff formation in semiarid regions relies generally on the solution of Richards equations using numerical approaches such as those provided by Hydrus-1D. We demonstrate here that a Simple Analytical Method (SAM) could be easily applied to estimate areas under flooding risk, under different soil and rainfall conditions, without the need to run burdensome numerical models. The impact of antecedent soil moisture condition was expressed quantitatively, conferring to SAM a predictive capability based on a-priori information on soil properties, rainfall characteristics, and initial conditions. The SAM was applied to the Shikma catchment, in the center of Israel, to illustrate its capability to estimate the spatial distribution of time of runoff occurrence and runoff coefficient for a prescribed rainfall event. The results suggest that SAM can be used as part of early warning systems of flood risks. Radars, carried by satellites and drones, can be used to provide refined data on rainfall intensity and soil surface initial conditions. SAM could be then coupled with these remotely sensed data to improve runoff initiation and accumulation estimates, thus reducing the time interval required to reach operational decisions regarding potential floods and inundations, and related water erosion hazards.

Evaluating the influences hedgerow on soil erosion and nitrogen loss of purple soil sloping farmland under simulated rainfall

Hedgerow is a vital soil and water conservation technology for sloping farmland that can significantly reduce erosion and nutrient loss via their above- and below-ground parts. The effect of hedgerow on erosion and nutrient loss has been widely investigated, while the respective effects of their above- and below-ground parts are still unclear. Therefore, the purple soil from the Three Gorges Reservoir Area was used, and 3 slope conditions of control check, whole hedgerow and hedgerow roots only combined with 2 slope gradients (15° and 25°) were constructed and the simulated rainfall tests were researched at 3 rainfall intensities (60, 90 and 120 mm h−1). The runoff initiation time, runoff and erosion rates, and loss of nitrogen via runoff and sediment were analysed. In comparison to the control check slope condition, it was indicated that hedgerow increased the runoff initiation time by 43.38 %, decreased runoff and erosion by 15.59 % and 78.37 %, and decreased nitrogen loss via runoff by approximately 40 % and via sediment by approximately 70 % on average, respectively. The average contribution rates of the below-ground part of the hedgerow was 49.89 % for the increase in runoff initiation time, 33.99 % for runoff reduction, and 39.91 % for erosion reduction. In addition, more than 2/3 and 58.49 % of nitrogen loss reduction via runoff and sediment, respectively, was contributed by the above-ground part of the hedgerow. These results are beneficial for comprehending the control mechanism of hedgerow on soil erosion and nitrogen loss, thereby provide a scientific foundation for the sustainable and efficient utilization of soil and water resources on sloping farmland.

Mulch and Grass Cover Unevenly Halt Runoff Initiation and Sediment Detachment during the Growing Season of Hazelnut (Corylus avellana L.) in Croatia

Hazelnut orchards are popular for cropping on sloped sites, which are often highly erodible. This study aimed to assess the impact of soil management and season in a hazelnut orchard on soil properties and hydrological response. Three treatments (Tilled, Straw, and Grass) were established in Munije (Croatia) on Stagnosol. In Spring, Summer, and Fall, a rainfall simulation was performed (intensity of 58 mm h−1 for 30 min). Results reveal higher water stable aggregate values were observed for the Straw treatment in all seasons. Higher soil organic matter (SOM) content was noticed for the Grass treatment in all seasons, while lower values were recorded for the Tilled treatment. Sediment loss in Summer was up to 650% and 1300% higher for the Tilled treatment compared with the Straw and Grass treatments. This study strengthens the comprehension of utilizing a permanent ground cover in hazelnut orchards as a sustainable practice, contributing to the mitigation of soil erosion processes and the improvement of soil properties. The Straw treatment is a viable option since it increases soil stability and SOM, consequently preventing high soil erosion.

Soil Erosion in Extensive versus Intensive Land Uses in Areas Sensitive to Desertification: A Case Study in Beira Baixa, Portugal

The occurrence of long periods of drought followed by extreme episodes of rainfall and ineffective soil conservation practices are the main causes of soil erosion in the Mediterranean region. The objective of this paper is to assess and compare the hydrological and erosional responses related to land use changes in agricultural landscapes that are sensitive to erosion and that are a result of the significant replacement of traditional land uses. Such changes are characterized by the replacement of extensive olive groves associated with pastureland by intensive almond production, where deep plowing and heavy machinery are required. In each sampling site, runoff initiation, runoff coefficient, and soil loss were evaluated under simulated rainfall (55 mm h−1), at plot scale (0.25 m2), at the end of the hot and dry summer period. Slope gradient, soil texture, bulk density, soil organic matter content, soil water content, and plant cover were also determined. The results showed the impact of recently planted intensive almond orchards (IAOs) on accelerating soil erosion risk compared with the extensive traditional olive groves (EOGs), although runoff initiation and discharge are very similar between the studied land uses. The mean values recorded for soil loss and sediment concentration were 118 g m−2 h−1 and 12 g m−2 h−1 and 3.1 g L−1 and 0.7 g L−1, respectively, for IAOs and EOGs. Our results also demonstrated that maintaining a vegetation cover is a determining factor for the prevention and control of soil erosion, especially in IAOs, where retaining high percentages of natural plant-residue mulch layers (>70%) reduced soil loss by about 70% in this study.

The contribution rate of stem‐leaf and root of alfalfa (Medicago sativa L.) to sediment and runoff reduction

AbstractSeasonal changes in ground canopy and root density induced by the growth of alfalfa (Medicago sativa L.) may strongly influence the variation in runoff and sediment across alfalfa growth stages. In this study, eight alfalfa plots with and without ground canopy and two bare soil plots (CK) were used to investigate the effect of alfalfa growth on the regulation of runoff and sediment during one growing season (seedling stage, S1; budding stage, S2; flowering stage, S3; podding stage, S4). The experiments involved four slope gradients of 8.6%, 17.6%, 26.8%, and 36.4% and one rainfall intensity of 90 mm h−1. The time to runoff initiation (TR), runoff volume (RV), and sediment yield (SY) were recorded, and runoff reduction benefits (RRBs) and sediment reduction benefits (SRBs) were calculated. The results have shown that TR was delayed with the growth of alfalfa and advanced with an increasing slope gradient. From S1 to S4, compared with CK, alfalfa grassland reduced the runoff by 10.36% to 85.80% and the sediment by 15.34% to 94.48%. The root systems of alfalfa reduced the runoff by 1.29% to 34.86% and the sediment by 0.87% to 49.97%. RV and SY decreased exponentially with aboveground biomass and root density during the growing season. The SRBs were greater than the RRBs, and the contribution of stem leaves for SRBs and RRBs was higher than that for roots under the same growing seasons and slope gradient. This study deepens our understanding of herbaceous plants in regulating runoff and sediment at different growth stages and clarifies the contribution of vegetation components to soil and water loss control.

The Interaction of Aeolian Sand and Slope on Runoff and Soil Loss on a Loess Slope via Simulated Rainfall under Laboratory Conditions

The wind–water erosion crisscross region, where the topography is complicated, is the most severe area of soil erosion on the Loess Plateau. The wind and terrain both have an impact on the soil water erosion process. In order to evaluate the effects of sand cover on runoff and soil loss characteristics, a series of experiments was conducted in two contrasting treatments. One treatment was a bare loess soil slope serving as the control, and the others were sand-covered loess slopes with five different slopes. The results showed that the runoff time, total runoff yield, and total soil loss were different between the sand-covered slope and the loess slope on the slope of 15°. The sediment concentration of the sand-covered slope was significantly higher than that of the loess slope during the entire rainfall process (p < 0.05). The increase in the slope gradient shortened the surface runoff initiation times and enhanced the total runoff volume and soil loss. The total runoff volume and the total soil loss were 39.7 L and 44.3 kg, respectively, on the sand-covered slope of 10°. When the slope gradient increased from 10° to 30°, the total runoff volume and the total soil loss increased by 22.8 L and 42.8 kg, respectively, while the surface runoff initiation times shortened by 300 s. For the sand-covered slopes, the erosion processes appeared to be mainly dominated by sediment transport. The correlation between soil loss rates and slope gradients demonstrated the secondary polynomial function. In addition, the critical slope of sand-covered slopes was from approximately 23° to 28°. The proportion of sand cover and slope responsible for soil erosion was 3:1, which means the wind effect was more important than the terrace factor in terms of soil water erosion in the wind–water erosion crisscross region. The results provide a theoretical basis for soil erosion control in this area.

Circulation weather types as a key factor on runoff initiation and sediment detachment in Mediterranean shrublands

In this research, the circulation weather types (CWTs) associated with individual surface pressure data at different atmospheric heights were used to correlate and quantify soil erosion events collecting soil loss (g m-2), runoff (l m-2) and sediment concentration (g L-1) using field plots and sediment collectors. Representative Mediterranean shrubland, located at Sierra de Enguera (Eastern Spain), was used as a case study where 213 rainfall episodes and related soil loss events were recorded for the 2010-2014 period. Average annual precipitation of 544 mm was registered, summarizing a total of 2,720.1 mm for the five years of the research period. A total of 34.4% of the registered precipitation events ranged from 10 to 29.9 mm, 23.5% from 30 to 49.9 mm, and 15.9% from 50 to 99.9 mm. The dynamic low-pressure with fronts (DLp+f) CWT was found to generate the highest precipitation amount reaching 60.6% of the total precipitation (105 of the 213 events). Over a third (35%) of the precipitation events occurred during Eastern CWT, which accounted for 48% of the total precipitation with average values of 17.6 mm per event. From the total runoff, 65.6% was related to the combined Eastern and cold drops (CD) CWT. The DLp+f CWT was found to produce 48.9% of sediment mobilization, of which 73.5% of this amount was generated by Eastern CWT. The highest sediment concentration event was found for the southern CWT under thermal low-pressure (TLp) reaching 51.65 g L-1, followed by A (anticyclones) with the Eastern CWT (42.23 g L-1). As a whole, the southern is the CWT generating the highest average sediment concentration (28.66 g L-1), followed by Easter CWT. Our findings suggest that CWTs contribute to foreseeing the periods with the highest soil losses and may help to prevent them. We discuss the need to analyse the changes in soil erosion rates due to CWT to better characterize the soil erosion process and assess the soil erosion rates, improve the current soil erosion models and investigate how climate change is changing the role CWT plays in runoff initiation and sediment delivery.

The role of straw mulching in shaping rills and stabilizing rill network under simulated extreme rainfall

Straw mulching has been widely demonstrated as a useful practice for soil and water conservation, but its effectiveness in controlling rill erosion has rarely been systematically studied. The objective of the current study was to evaluate the effects of straw mulching on rill development and rill network evolution. A cinnamon soil was mulched with corn straw segments at five different rates of 0, 2.1, 4.2, 6.3 and 8.4 t ha−1, to attain the surface coverages of 0%, 10%, 20%, 30% and 40%, respectively, and received four 30-min simulated rainfalls at the intensity of 90 mm h−1. The structure from motion (SfM) photogrammetry was applied to measure soil surface elevation changes upon each rainfall. Straw mulching was found to retard runoff initiation, but decreased soil losses were typically acquired at the mulched treatments with 20% or more straw coverages. Nevertheless, this conservation effect did not monotonically increase with mulching rate, because a larger number of straw segments were more likely to induce rill erosion via surface flow convergence, thereby increasing total soil loss. Straw mulching also changed the course of rill development. Head retreat dominated rill erosion at the control without mulching throughout the entire experiment, suggesting an early stage of rill erosion. With the straw segments around and at the bottom, the initially equivalent contributions by headcutting, bed scouring and sideward erosion quickly shifted to the predominance of bed incision and then to sidewall expansion, successively. The rapid transition of rill erosion subprocess in this way, together with the dendritic and stabilized networks, indicate a mature stage of rill development by the end of the experiment. The rill depths and main channel widths, as a consequence, were typically smaller at the mulched treatments. These findings demonstrate the effectiveness of adequate straw mulching in stabilizing rill network in addition to reducing soil erosion at the plot scale, and hold important implications for agricultural management in slope farming systems.

The short-term effects of an existing channel, a single pass of tillage and their interaction on the generation of runoff and sediment

A critical time for both water and tillage erosion is the period between growing seasons when the field is tilled and thus bare or nearly bare. During this period, there is a high risk for water erosion, leading to water eroded channels. The existing channels, tillage operations and the combination of these two may strongly affect runoff and sediment generations in the following water erosion events. However, knowledge on this is limited. In this study, plot experiments were conducted to quantify the short-term effects of an existing channel, a single pass of tillage and their interaction on the generation of runoff and sediment. Four treatments: no channel, no tillage (NN, as the control); with a channel, no tillage (CN); no channel, with tillage (NT); and with a channel, with tillage (CT) were examined. Plots under the four treatments were placed under simulated rainfall for at least one hour. Runoff and sediment samples were collected every 5-minutes after runoff initiation. The effects of treatments on the amounts of runoff and sediment were analyzed with ANOVA and ANCOVA. We found that with an existing channel, runoff initiation has accelerated and runoff discharge and sediment export have increased whereas with a single pass of tillage, runoff initiation was delayed and runoff discharge and sediment export have decreased. When an existing channel was tilled, the effects of tillage dominated while the existing channel only demonstrated some minor impacts. Applying this knowledge to a cereal-potato crop rotation common in Atlantic Canada, we recommend spring primary tillage after cereal harvesting and late fall primary tillage after potato harvesting to reduce the overall soil erosion.

Effects of rainfall and the slope gradient on the soil and water loss in a purple soil area

Soil and water losses in purple soil area is becoming an increasingly severe problem, bringing enormous challenges to environmental protection in rural areas. In this study, simulated rainfall experiments were conducted to analyse the effects of rainfall and the slope conditions on the soil and water loss. Purple soil from a typical slope in the Beibei District of Chongqing was selected as the experimental soil. Twenty rainfall scenarios with varying rainfall intensities and slope conditions were created in the simulation. The results indicate that the runoff initiation time shortened with an increased rainfall intensity and slope gradient. There was a logarithmic relationship between the effect of the rainfall amount on both the runoff intensity and sediment yield intensity. Generally, both the runoff and sediment yield showed a positive linear relationship with the rainfall intensity under different slope gradient conditions. In terms of the same rainfall intensity, both the runoff intensity and sediment yield intensity increased with the slope. Furthermore, a critical slope gradient for the soil and water loss was found between 20° and 25°. This study aimed to provide a reference for soil and water conservation research in a purple soil area.

Efficacy of earthworm casts on sediment and nitrate loss with runoff in the Chinese Loess Plateau

The erosion of sediment and nutrients under rainfall conditions aggravated the degradation of soil quality in sloping farmland. It is very important to comprehensively control the sediment and nutrient loss of sloping farmland and improve the soil fertility of barren sloping farmland caused by soil erosion to improve the plant growth environment in the Loess Plateau of China. However, there is no research to combine the control of soil, water, and nutrient loss with the improvement of soil fertility. To address this issue, earthworm casts (ECs), an excellent organic soil amendment, was applied to the soil (silty loam). Ten rainfall simulation experiments were conducted in a 1.0 m × 1.0 m plot with two application methods (mixed and layered applications) and five application amounts (i.e., 0, 200, 400, 600, and 800 g/m2), and simulated rainfall for 1 h at a rate of 60 mm/h. The main results indicated that the ECs application significantly delayed the time of runoff initiation, reduced unit discharge and sediment yield rate in the early stage. The nitrate nitrogen concentration in runoff could be significantly reduced with the layered application method. The equivalent model of convection was more suitable for simulating nutrient transfer with runoff, and the effective mixing depth decreased with increased the ECs amounts. The ECs application increased the water content and nitrate nitrogen concentration of the soil profile from a depth of 0–20 cm and provided a suitable environment for vegetation growth. Runoff decreased by 18.16–33.47%, sediment decreased by 28.17–87.24%, and nitrate nitrogen loss in runoff decreased by 36.99–51.76% with the layered application. The layered application of ECs with 800 g/m2 had the significant regulation on runoff, sediment yield, and nitrate nitrogen loss. In conclusion, ECs can effectively improve the water erosion resistance of the soil, and enhance the water holding capacity and fertilizer retention capacity of the soil. The layered application of ECs can effectively control nitrogen loss with runoff. In the long run, ECs can provide sufficient nutrient sources for plant growth, improve regional vegetation carrying capacity, and fundamentally solve the problem of soil and water loss and soil degradation of bare slope farmland in the Loess Plateau of China.

Rainfall-runoff characteristics and their threshold behaviors on a karst hillslope in a peak-cluster depression region

Water balance characteristics and rainfall-runoff relationships of karst slope, are poorly understood worldwide, even though karst landscapes occupy 10–15% the planet’s land surface. Dynamic hydrological responses were monitored for 43 rainfall events on a karst slope in southwest China over two years (2018–2019). The responses included surface, subsurface, and epikarst seepage runoff (abbreviated as SR, SSR, and ESR, respectively) and soil water content at different depths (10 cm, 30 cm, and the soil-epikarst interface) in twelve plots (5 m× 20 m, total 1200 m2). Results showed that: (1) The hillslope-scale SR, SSR, and ESR coefficients were 2.2% (0.4%–5.2%), 3.8% (0.2%–12.4%), and 31.2% (0.6%–89.1), respectively. SR and SSR were relatively rare and of short duration, while ESR was a crucial component of the karst hillslope water balance and its duration was longer, demonstrating the critical role of epikarst zone in regulating flow functions such as water storage and release; (2) Soil depth exerted the greatest direct effect on SR, which increased as soil deepened. Factors controlling the rainfall-SSR response were difficult to identify. They require other geophysical exploration methods; (3) Threshold-like runoff responses to rainfall inputs were observed on karst slope, and the rainfall depth (P) runoff initiation thresholds for SR and SSR were 36±2 mm and 43±7 mm, respectively. The strength of the threshold-like input–output relationships was slightly greater when the P + ASI (antecedent soil water content index) was used as the hydrological input variable rather than without consideration of ASI. The differing shapes of nonlinear hydrological behaviours, such as the ‘hockey stick’, ‘heaviside’ function, or the sigmoid function were detected in karst slope. This suggests karst hydrological system complexity. Threshold values should be determined according to the shapes of nonlinear hydrological behaviours. These results extend the understanding of karst hydrological processes.

The role of biocrust-induced exopolymeric matrix in runoff generation in arid and semiarid zones – a mini review

Abstract Although playing an important role in shaping the environment, the mechanisms responsible for runoff initiation and yield in arid and semiarid regions are not yet fully explored. With infiltration-excess overland flow, known also as Hortonian overland flow (HOF) taking place in these areas, the uppermost surface ‘skin’ plays a cardinal role in runoff initiation and yield. Over large areas, this skin is composed of biocrusts, a variety of autotrophs (principally cyanobacteria, green algae, lichens, mosses) accompanied by heterotrophs (such as fungi, bacteria, archaea), which may largely dictate the infiltration capability of the surface. With most biocrust organisms being capable of excreting extracellular polymeric substances (EPS or exopolymers), and growing evidence pointing to the capability of certain EPS to partially seal the surface, EPS may play a cardinal role in hindering infiltration and triggering HOF. Yet, despite this logic thread, great controversy still exists regarding the main mechanisms responsible for runoff generation (runoff initiation and yield). Elucidation of the possible role played by EPS in runoff generation is the focus of the current review.

Effects of anecic earthworms on runoff and erosion on the slope with soil from the Loess Plateau under a rainfall simulation experiment

Earthworms are ecological engineers that play an important role in hydrological processes and soil erosion by their burrowing and casting activities. Little is known, however, about the ecological function of the activities of an anecic species (Metaphire guillelmi) from the Loess Plateau in China where the soil is severely eroded. We conducted rain-simulation experiments on artificial slopes (mesocosms) filled with soil from Loess Plateau. Two rain intensities (90 and 120 mm h−1) and slope gradients (5° and 15°) were used to investigate the influences of earthworm activity on runoff and soil loss under multiple conditions. Data from 15 d of earthworm activity and 1 h of rain indicated that earthworm activity significantly reduced runoff but aggravated soil erosion. Runoff initiation time increased 2.7–3.1-fold, contributing to the promotion of water infiltration, and the amounts and rates of runoff were 35.8–61.6% and 35.1–60.8% lower under earthworm activity than the controls, respectively. Earthworms greatly influenced the physical and chemical properties of the soil, and these properties were strongly correlated with runoff initiation time and cumulative runoff. The surface casts produced by the earthworms on the soil surface were completely dispersed, increasing the cumulative sediment by a maximum of 169%. Both rain intensity and slope gradient greatly influence runoff and soil detachment, but with earthworm activity, slope gradient was more influential due to its superior contribution to sediment transport. This study quantified the effects of M. guillelmi on runoff and soil erosion and provides basic data for developing a more integrated control of soil erosion on the Loess Plateau.

Linking Dominant Rainfall‐Runoff Event Hydrologic Response Dynamics With Nitrate and Chloride Load Estimates of Three Boreal Shield Catchments

AbstractUnderstanding hydrological dynamics in boreal Shield catchments is critical for projecting changes in stream runoff and chemistry in a region that is, sensitive to climate change. Previous work has mostly focused on a limited number of events over one or a few seasons because of the relative scarcity of high‐frequency datasets and automated tools for rainfall‐runoff event delineation. For the boreal region, a greater understanding of seasonality in hydrologic response and solute export related to rainfall‐initiated events is needed, as significant shifts in hydrologic regimes from climate change are expected. This study aimed to help resolve these knowledge gaps by assessing event‐scale hydrologic response dynamics and stream loads of nitrate and chloride using long‐term data from three boreal Shield catchments. Hydrometric and stream chemistry data from 2001 to 2018 were analyzed to delineate rainfall‐runoff events and estimate event nitrate and chloride loads. Event hydrologic response and loads were highly variable, especially with respect to catchment runoff initiation. Only subtle differences in hydrologic response dynamics were observed between summer and fall events, while seasonal differences in event nitrate and chloride loads were most statistically significant. Interestingly, a wide range of rainfall‐runoff events classified by response magnitude and timing was associated with differences in nitrate and chloride export. This study further confirms the utility of long‐term high‐frequency datasets and illustrates the need for additional work to further assess long‐term changes in event‐based hydrologic response and stream solute concentrations in the boreal region.

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%.

Sand cover enhances rill formation under laboratory rainfall simulation

Soil erosion was severe in the wind-water erosion crisscross region of the northern Loess Plateau of China, where aeolian sand cover may enhance water erosion. In order to evaluate the effects of sand cover on runoff, soil loss and rill information, a series of rainfall simulation experiments was conducted in two contrasting treatments. One is a bare loess soil slope serving as a control, and another is a sand-covered loess slope (namely sand cover treatment). Nine simulated rains, 60 min each, were applied to each treatment in duplicates. The results showed that the runoff generation mechanism changed from infiltration-excess runoff in the control to subsurface saturation-excess runoff in the sand cover treatment. The runoff initiation was delayed about three folds in the sand cover treatment as compared to the control. Total runoff volumes and total soil loss in the sand cover treatment in each event were 1.1–1.2 times and 1.9–9.3 times those in the control treatment. A paired t-test showed that the runoff rates were greater in sand cover than in control in all events except for the last run at P < 0.05. The soil loss rates were greater in sand cover than in control for all events except the first rain at P < 0.05. Measured total rill length, width, and degree of rill dissection in the sand cover treatment were much greater than those in the control. The rill erosion of sand cover slope was dominated by the shallow and wider rills, while loess slope was dominated by the narrow and deeper rills. The results clearly indicated that a sand layer overlying a less pervious loess soil facilitated return flow and thus accelerated rill formation and development. This finding is in line with the common understanding that return flow in layered soil can promote rill formation and cause severe rill erosion, which is also important to understand the effect of wind-blown sand cover on water erosion in the wind-water erosion crisscross region.

Integrating depression storages and their spatial distribution in watershed-scale hydrologic modeling

Surface depressions are important topographic characteristics for surface runoff initiation, and the spatial distribution of depressions may further affect the timing and quantity of surface runoff reaching channels and outlets. However, many hydrologic models simulate the fill-spill processes for depression-dominated areas in a lumped manner and release outflows from depressions to channels or outlets directly. As a result, the progressive formation of contributing area (CA) and the dynamic runoff contribution process are not well characterized. The objective of this study is to improve depression-oriented hydrologic modeling by incorporating the influence of depression storages and their spatial distribution into the simulation of surface runoff generation and flow routing. To achieve this objective, a modified depression-oriented variable contributing area (MD-VCA) model is developed to simulate the depression-dominated catchment response during rainfall events, which employs a new depressional time-area zone scheme to deal with the spatially distributed depression storages, tracks the intrinsic changing patterns of the connected areas and depression storage, simulates the connected area-based surface runoff generation dynamics, implements a new CA-based surface runoff routing technique, and quantifies the likelihood of occurrence of outlet CA and runoff contributions using the joint probability distribution associated with depression storages and their spatial distribution. The performance of the MD-VCA model was evaluated through the application to a depression-dominated watershed in the Prairie Pothole Region of North Dakota. Simulation results demonstrated that the MD-VCA model was able to simulate the threshold-controlled overland flow dynamics under different rainfall conditions, and it effectively revealed the influences of depression storages and their spatial distribution on surface runoff generation and propagation processes.

Effect of rainfall intensity and duration on soil erosion on slopes with different microrelief patterns

Tillage-induced surface microrelief (TSM) is commonly thought of as an effective measure to control soil erosion on agricultural lands. The objective of this study is to discuss how rainfall intensity and duration affect the role of TSM in soil erosion. Three rainfall intensities of 60, 90 and 120 mm/h and four rainfall durations of 15, 30, 60 and 90 min for each intensity were investigated. Two slope ranges, corresponding to a gentle slope (5° to 10°) and a steep slope (20° to 25°), were considered. Two different TSMs, consisting of depressions and mounds (DM) and troughs and ridges (TR), were used for testing in a soil box that was 2 m long by 1 m wide. A smooth surface (SS) served as a control. The runoff and sediment reduction benefits (RRB and SRB), represented by the ratios of the difference between the tilled slope and SS to that of SS, were used to quantify the role of TSM in soil erosion. The results showed that DM and TR delayed runoff initiation regardless of rainfall intensity and slope. The TSM RRB and SRB decreased with increasing rainfall intensity, duration and slope. Compared to the SS, the DM RRB decreased from 43% to 6% when the rainfall duration increased from 15 to 90 min, and the TR RRB decreased from 100% to 31% on the gentle slopes; on the steep slopes, the DM and TR RRBs decreased from 24% and 46% to nearly zero when the rainfall duration increased from 15 to 90 min. When rainfall intensity was below 90 mm/h and the duration was shorter than 60 min, DM and TR were effective at controlling soil loss; when the duration increased to 90 min or the rainfall intensity was 120 mm/h, the sediment form DM and TR was much higher than that from SS. In particular, the sediment from DM and TR increased by 114% to 330% when the rainfall intensity was 120 mm/h. This indicates that DM and TR were not effective at controlling soil loss during rainfall with a high rainfall intensity and/or long duration. In addition, TR exhibited greater effectiveness at controlling soil and water loss than DM under the same situations. Therefore, rainfall conditions and slopes are important factors influencing the soil and water conservation benefits of TSMs, and the effectiveness of TSMs on soil erosion reduction needs to be further assessed in conjunction with climate change.

Initial effect of shifting from traditional to no-tillage on runoff retention and sediment reduction under rainfall simulation

Context Low precipitation and soil erosion are critical threats to sustainable agricultural development in the north-western coastal zone of Egypt. Conservation tillage may offer a good opportunity to mitigate these threats; however, switching from traditional tillage to conservation tillage causes initial challenges such as soil compaction and erosion. Aims This study was designed in order to assess the effects of various tillage practices on soil bulk density, volumetric water content, runoff rate, runoff initiation time, soil loss, sediment yield rate and wheat (Triticum aestivum L.) yield in a cultivated basin area. Furthermore, to investigate the efficacy of various rainfall intensities in generating runoff in a micro-catchment area. Methods Under rainfall simulation, five rainfall intensities (14, 21, 30, 36, and 45 mm h−1) and three tillage practices (contour tillage, CT; traditional tillage, TT; and no tillage, NT) were investigated. Key results Under various rainfall intensities, the CT treatment significantly reduced surface runoff compared with the TT and NT treatments. For the 30 mm h−1 rainfall intensity, the CT treatment decreased sediment yield rate by 58.7% and 49.4% compared with NT and TT treatments, respectively. Furthermore, the CT treatment significantly increased precipitation use efficiency by 11.8% and 19.9% compared with TT and NT treatments, respectively. Additionally, the CT increased grain yield by 12.3% more than TT and 21% more than NT. Conclusions and implications Consequently, it is preferable to encourage farmers to use CT practices when transitioning from traditional tillage to conservation tillage. Moreover, soil compaction and smoothing may contribute to enhance the generated runoff on the micro-catchment area.