Cumulative Runoff Volume Research Articles

Vegetation patterns affect soil aggregate loss during water erosion

AbstractSoil aggregates are important for improving the soil quality and structure. Soil erosion causes the fragmentation and migration of soil aggregates. Vegetation restoration is an effective method for controlling soil erosion, and the vegetation distribution on the slope changes the hydrological processes. However, there is a dearth of studies investigating the regulation of vegetation patterns in relation to soil aggregate loss. This study employed a physical model of a slope gully system to examine the characteristics of soil aggregates loss during erosion processes under four distinct vegetation patterns: no vegetation (pattern A), up‐slope vegetation (pattern B), middle‐slope vegetation (pattern C), and down‐slope vegetation (pattern D), utilizing simulated rainfall experiments. The results showed that under various patterns of vegetation, the loss of soil aggregates is predominantly driven by microaggregates (<0.25 mm), A (65.2%) < B (72.4%) < C (77.7%) < D (87.7%). On the contrary, there is an opposite trend of change observed in macroaggregates(>0.25 mm). The vegetation pattern had different effects on the enrichment rate of aggregates in sediments: the enrichment ratio of macroaggregates decreased by 20.9%–64.7% and the enrichment ratio of microaggregates increased by 11.1%–34.5%. The cumulative loss of soil aggregates and the cumulative runoff volume can be described by a linear equation: y = ax + b, where ‘a’ denotes the rate of soil aggregate loss. Vegetation patterns had the capacity to decrease the rate of macroaggregate loss. Among these patterns, pattern D exhibits the lowest rate, followed by patterns C, B, and A. These results indicated that down‐slope vegetation pattern is effective in reducing the loss of soil aggregates especially macroaggregates.

Experimental Study on the Influence of Substrate Properties on Rainfall Infiltration and Runoff from Ecological Slopes

Rain is an important factor influencing the instability of ecological slopes. There is little research on the inherent quantitative influence of substrate properties on slope runoff and water infiltration to support accurate ecological slope protection design. In this paper, the influence of substrate characteristics on slope runoff and water infiltration is quantitatively analyzed by constructing large physical models with different substrate characteristics for artificial rainfall simulations. The experimental results showed that the cumulative runoff volume and slope runoff rate were positively correlated with the cement content and substrate thickness in a 4 h, 60 mm/h artificially simulated rainfall. Specifically, the cumulative runoff volume increased by 2.06% for every 1% increase in cement content, and the cumulative runoff volume increased by 3.93% for every 1 cm increase in substrate thickness. The substrate inhibited the advance of the wetting front, and at different slope locations, the transport rate of the wetting front exhibited a mid-slope > upslope. Moreover, the transport rate of the wetting front showed a non-linear relationship with time as a power function V = a·tb, with the cement content showing a linear relationship with parameters a and b, and the substrate thickness showing a non-linear relationship with parameters a and b. The cumulative infiltration and infiltration rate were negatively correlated with cement content and substrate thickness, as shown by a 2.2% decrease in cumulative infiltration for every 1% increase in cement content and a 4.73% decrease in cumulative infiltration for every 1 cm increase in substrate thickness.

New conceptualization and quantification method of first-flush in urban catchments: A modelling study

A major challenge for runoff pollution control lies in the quantification and identification of the first-flush. At present, there is a lack of reasonable theoretical methods to guide engineering practices. To remedy this deficiency, a novel method of cumulative pollutant mass vs. cumulative runoff volume (M(V)) curve simulation is proposed in this study. Subsequently, the first-flush phenomenon was redefined based on the M(V) curve simulation and demonstrate that the first-flush exists until the derivative of the simulated M(V) curve is equal to 1 (Ft′ = 1). Consequently, a mathematical model for first-flush quantification was developed. The Root-Mean-Square-Deviation (RMSD) and Pearson's Correlation Coefficient (PCC), as objective functions, were used to evaluate the performance of the model and the Elementary-Effect (EE) method was used to analyze the sensitivity of the parameters. The results indicated the satisfactory accuracy of the M(V) curve simulation and first-flush quantitative mathematical model. The NSE values exceeding 0.8 and 0.938, respectively, were obtained by analyzing 19 rainfall-runoff data for Xi'an, Shaanxi Province, China. The wash-off coefficient “r” was demonstrably the most sensitive factor influencing the model performance. Therefore, interactions between “r” and the other model parameters should be focused on to highlight the overall sensitivities. Overall, this study posits a novel paradigm shift from the traditional dimensionless definition criterion to redefine and quantify first-flush, which has significant implications for urban water environment management.

Investigation of contaminant profile in highway stormwater runoff and risk assessment by statistical analysis

Highway stormwater runoff pollution has become a severe risk factor for water bodies nowadays. The conventional risk analysis protocols for directly discharging highway runoff are prone to systematic and judgmental errors. Therefore, a numeric and straightforward risk assessment protocol has been developed in this study that minimizes the errors. For this study, three highway segments were selected in the city of Rawalpindi, Pakistan. Event mean concentrations have been used as baseline numeric values for calculating the risk of discharging highway stormwater directly into the water bodies. These values are also correlated with highway characteristics (area, slope, and traffic count) and storm characteristics (storm depth, cumulative runoff volume, antecedent dry days, and cumulative flow). The highway stormwater was monitored for organics, metals, solids, and macro-nutrients at three highway sections. The event mean concentrations of dissolved organic carbon (50–145 mg/L), total suspended solids (1500–3900 mg/L), chromium (0.25–0.45 mg/L), and lead (0.1–0.8 mg/L) are found to be higher than the environmental quality standards. The risk assessment was conducted by the analysis of variance. The analysis showed that the highway characteristics significantly affect contaminant concentrations, but storm characteristics on contaminant concentrations are not found to be significant. Total suspended solids are the most threatening contaminant in highway runoffs. The study concluded that the risk from contaminants in highway stormwater depends particularly on the specific highway sections’ properties. The first flush portion (initial 25% of runoff) of highway runoff poses a higher threat to the receiving environment than the later runoff volumes.

Event mean concentration and first flush from residential catchments in different climate zones

Most studies on EMC (Event mean concentration) and first flush are reported as local studies; however variations of EMC and first flush across catchments in different climate zones has not been studied. This research collected continuous flow and discrete water quality data and rainfall measurements from 17 catchments, EMC and rainfall data from 14 catchments, and an additional dataset where only average EMC values are reported (19 catchments). The data are from residential sites across temperate, tropical, dry, and continental climate zones and include water quality parameters in particulate (total suspended solids), mixed (total nitrogen and total phosphorus) and dissolved (orthophosphate and ammonium nitrogen) forms. Our study shows that EMC differs significantly between climate zones. The average EMC is highest in dry followed by continental and temperate, with lowest in the tropical zone. Pearson's correlation analysis revealed that the rainfall depth is negatively correlated with EMC for particulate and mixed form parameters for the tropical, temperate and dry zones, but positively correlated for the continental zone. The discrete time-series data from the 17 catchments were used to evaluate first flush and it was found that catchments in the tropics exhibit stronger first flush than temperate zone catchments, for all the water quality parameters with particulate showing a stronger first flush compared to dissolved forms. Based on the distribution of the data, new limits for very strong, strong, moderate, and very weak to no first flush are suggested for TSS for different climate zones. The new limits were quantified by fitting the function L^=V^bwhere L^and V^are the normalized cumulative runoff load and volume, respectively. For catchments in the tropics, this corresponds to b < 0.47, 0.6 > b > 0.47, 0.76 > b > 0.6 and b > 0.76, respectively. For the temperate zone, b < 0.5, 0.67 > b > 0.5, 0.85 > b > 0.67 and b > 0.85, are appropriate. From a design perspective, the FF20 concept defined as the load corresponding to 20% runoff volume, is often used. The ranges FF20 < 0.27, 0.36 > FF20 > 0.27, 0.45 > FF20 > 0.36 and FF20 > 0.45 and FF20 < 0.24, 0.31 > FF20 > 0.24, 0.31 > FF20 > 0.39 and FF20 > 0.39 are proposed for tropical and temperate catchments, respectively. Other limits for TP, TN, OP and NH4-N are also suggested. This is the first study of its kind and an expended dataset especially for continental and dry regions is needed to further validate the findings.

Agronomic and environmental performance of biochar amendment in alluvial soils under subtropical sugarcane production

AbstractThis study investigated the amendment of sugarcane bagasse biochar (SCBB) on soil fertility, crop yield, and nutrient loss in two different‐textured soils under sugarcane (Saccharum spp.) production. Eleven megagrams per hectare of freshly incorporated biochar increased yield of plant cane by 22% in light‐texture soil (LS) and 12% in heavy‐textured soil (HS). Although the overall yield of the ratoon crop was lower, the biochar treatment produced 20 and 14% higher yields than the control at the LS and HS sites, respectively. Biochar increased soil carbon (Csoil) across LS and HS sites by 15% and decreased the soil C/N ratio by 19%. Over the two growing seasons and sites, cumulative runoff volume, and loads of NO3––N, PO4–3–P, biological oxygen demand (BOD5), total organic C (TOC), and total suspended solids (TSS) were reduced by 33, 35, 39, 25, 24, and 54% with biochar. Calcium and K losses in runoff were also reduced by 43 and 24% with biochar. It reduced NH4+–N leaching in LS and HS soils over the two growing seasons by 33–167% and 66–81%, respectively, and reduced PO4–3–P leaching by 45–57% in HS over 2 yr. Although biochar is not considered a fertilizer, SCBB acted as a source of nutrients, increasing soil fertility and crop yield. It also reduced nutrient losses during heavy rain events typical of the subtropical climate of Louisiana.

Silage storage runoff characterization: Annual nutrient loading rate and first flush analysis of bunker silos

Bunker silos produce a runoff that is a source of nutrient loss and a threat to surface water quality. Little information is available on the water quality of stormwater produced from bunker silos. This research evaluated the runoff characteristics from six horizontal bunker facilities at dairy farms to determine runoff water quality and nutrient loading throughout a storm and annual nutrient losses. On average, at 50% of the cumulative runoff volume the difference between cumulative nutrient load and volume did not exceed 20%, which is a threshold required for a first flush scenario (cumulative loads of P and N were 1.5 to 4.5% and −2.8 to 4.0% greater than cumulative volume, respectively). During the storage of silage in horizontal bunker silos an estimated 0.3 to 1.8% of ensiled P and 0.4 to 1.7% of ensiled N was lost annually with silage runoff. Assessment of a theoretical dairy farm in WI has a calculated runoff loss from horizontal feed storage of 30% and 55% of the total farmstead N and P runoff losses, respectively. Nitrogen (N) and phosphorus (P) loading from bunker silos were relatively consistent throughout a storm with no evidence of a first flush scenario. Annual variability in low flow N and P concentrations were impacted by the production of silage leachate, and bunkers with subsurface collection reduced the nutrient concentrations in overflow runoff. Dairy bunkers provide an opportunity to decrease nutrient loading, through management of a small land base, as compared to other farmstead runoff areas. Reducing the amount of silage runoff lost from dairy farms has strong potential for N and P conservation.

Stormwater Runoff Characteristics and Effective Management of Nonpoint Source Pollutants from a Highland Agricultural Region in the Lake Soyang Watershed

The dense highland field area in the upstream region of the Lake Soyang watershed is subject to excessive soil erosion during the wet season. In this study, stormwater runoff from the Lake Soyang watershed was monitored during four rainfall events at 10 locations throughout 2016. The maximum SS concentration at Naedongcheon, which is located in the upper part of the Soyang River, reached 4598 mg/L. The event mean concentration (EMC) of SS loads in Naedongcheon ranged from 82.2 mg/L to 926.3 mg/L. We found that, although the first flush events were usually concentrated in highly paved urban areas, a first flush occurred in the agricultural area of the dense highland field region. The first flush phenomenon was identified by a dimensionless cumulative runoff mass and volume curve (M(V) curve), and the intensity of the first flush was analyzed by the coefficient of the nonlinear regression model and the FF30 and FF25 values (the fraction of pollution load transported by the first 30% and 25% of runoff, respectively). Nonlinear regression models using the power function were applied to fit the M(V) curve, the FF30 values were inversely proportional to the coefficient a of the regression model. A long-term seasonal trend decomposition for monthly turbidity and precipitation was performed for the Lake Soyang. Long-term turbidity trend was approximately coincident with the trend in long-term precipitation. In addition, the present status of the best management practices (BMPs) in the upper part of the Soyang River basin was investigated, and a survey of the management and operation of the BMPs was conducted for selected farmers.

A synthesis of space–time variability in multicomponent flood response

Abstract. Catchment flood response consists of multiple components of flow originating from different surface and subsurface layers. This study proposes an extension of Viglione et al. (2010a) analytical framework to represent the dependence of catchment flood response to the different runoff generation processes. The analytical framework is compared to simulations from a distributed hydrologic model. A large number of rainfall–runoff events from three catchments of Tar River basin in North Carolina are used to illustrate the analytical framework. Specifically, the framework is used to estimate three flood event characteristics (cumulative runoff volume, centroid, and spreadness of hydrograph) through three corresponding framework parameters: the rainfall excess and the mean and variance of catchment response time. Results show that, under the smooth topographic setups of the study area, the spatial and/or temporal correlation between rainfall and runoff generation are insignificant to flood response; delay in flood response due to runoff generation and routing are of equal importance; the shape of the flood is mainly controlled by the variability in runoff generation stage but with non-negligible contribution from the runoff routing stage. Sensitivity tests show that the framework's main error source is the systematic underestimation of the flood event's centroid and spreadness, while the random error is relatively low.

Volume Reduction Provided by Eight Residential Disconnected Downspouts in Durham, North Carolina

AbstractOne major concern of increased development is the proportion of directly connected impervious areas (DCIA) in urbanized watersheds. A cost-efficient opportunity to treat stormwater within existing residential and small-scale commercial developments is to disconnect roof gutter downspouts and direct impervious surface runoff over lawns. Four paired residential downspout disconnection sites in Durham, North Carolina, were studied to quantify volume and peak flow reduction. Hydrologic data were collected from January 22, 2013, to October 8, 2013. For each site, the performance of disconnected downspouts discharging water over existing lawn was compared for three varying factors: slope of lawn, length of run over lawn, and proportion of contributing roof area to receiving lawn area. Data were analyzed from approximately 60 storm events. Performance was evaluated by calculating volume reduction with and without the direct rainfall on the lawn, resulting in cumulative runoff volume reduction ranges of 5...

Selecting rainfall events for effective Water Sensitive Urban Design: A case study in Gold Coast City, Australia

The current approach for protecting the receiving water environment from urban stormwater pollution is the adoption of structural measures commonly referred to as Water Sensitive Urban Design (WSUD). The treatment efficiency of WSUD measures closely depends on the design of the specific treatment units. As stormwater quality is influenced by rainfall characteristics, the selection of appropriate rainfall events for treatment design is essential to ensure the effectiveness of WSUD systems. Based on extensive field investigations in four urban residential catchments based at Gold Coast, Australia, and computer modelling, this paper details a technically robust approach for the selection of rainfall events for stormwater treatment design using a three-component model. The modelling results confirmed that high intensity-short duration events produce 58.0% of TS load while they only generated 29.1% of total runoff volume. Additionally, rainfall events smaller than 6-month average recurrence interval (ARI) generates a greater cumulative runoff volume (68.4% of the total annual runoff volume) and TS load (68.6% of the TS load exported) than the rainfall events larger than 6-month ARI. The results suggest that for the study catchments, stormwater treatment design could be based on the rainfall which had a mean value of 31mm/h average intensity and 0.4h duration. These outcomes also confirmed that selecting smaller ARI rainfall events with high intensity-short duration as the threshold for treatment system design is the most feasible approach since these events cumulatively generate a major portion of the annual pollutant load compared to the other types of events, despite producing a relatively smaller runoff volume. This implies that designs based on small and more frequent rainfall events rather than larger rainfall events would be appropriate in the context of efficiency in treatment performance, cost-effectiveness and possible savings in land area needed.

Global spatial sensitivity of runoff to subsurface permeability using the active subspace method

Hillslope scale runoff is generated as a result of interacting factors that include water influx rate, surface and subsurface properties, and antecedent saturation. Heterogeneity of these factors affects the existence and characteristics of runoff. This heterogeneity becomes an increasingly relevant consideration as hydrologic models are extended and employed to capture greater detail in runoff generating processes. We investigate the impact of one type of heterogeneity – subsurface permeability – on runoff using the integrated hydrologic model ParFlow. Specifically, we examine the sensitivity of runoff to variation in three-dimensional subsurface permeability fields for scenarios dominated by either Hortonian or Dunnian runoff mechanisms. Ten thousand statistically consistent subsurface permeability fields are parameterized using a truncated Karhunen–Loéve (KL) series and used as inputs to 48-h simulations of integrated surface-subsurface flow in an idealized ‘tilted-v’ domain. Coefficients of the spatial modes of the KL permeability fields provide the parameter space for analysis using the active subspace method. The analysis shows that for Dunnian-dominated runoff conditions the cumulative runoff volume is sensitive primarily to the first spatial mode, corresponding to permeability values in the center of the three-dimensional model domain. In the Hortonian case, runoff volume is sensitive to multiple smaller-scale spatial modes and the locus of that sensitivity is in the near-surface zone upslope from the domain outlet. Variation in runoff volume resulting from random heterogeneity configurations can be expressed as an approximately univariate function of the active variable, a weighted combination of spatial parameterization coefficients computed through the active subspace method. However, this relationship between the active variable and runoff volume is more well-defined for Dunnian runoff than for the Hortonian scenario.

Effects of gravel on infiltration, runoff, and sediment yield in landslide deposit slope in Wenchuan earthquake area, China.

Amounts of landslide deposits were triggered by the Wenchuan earthquake with magnitude8.0 on May 12, 2008. The landslide deposits were composed of soil and rock fragments, which play important roles in hydrological and erosion processes in the steep slope of landslide deposits. The mixtures of soil and gravels are common in the top layers of landslide deposits, and its processes are obviously different with the soil without gravels. Based on the data of field investigation, a series of simulated scouring flow experiments with four proportion of gravel (0, 25, 33.3, and 50%) and three scouring flow rates (4, 8, 12L/min) under two steep slopes (67.5, 72.7%) were conducted sequentially to know the effects of proportion of gravel on infiltration capacity, runoff generation, and sediment production in the steep slope of landslide deposit. Results indicated that gravel had promoted or reduced effects on infiltration capacity which could affect further the cumulative runoff volume and cumulative sediment mass increase or decrease. The cumulative infiltration volume in 25% proportion of gravel was less than those in 0, 33.3, and 50% proportion of gravel. The cumulative runoff volume was in an order of 25 > 0 > 33.3 > 50% while cumulative sediment mass ranked as 25 > 33.3 > 0 > 50% with different proportions of gravel. A significant power relationship was found between scouring time and cumulative runoff volume as well as cumulative sediment mass. The relationship between average soil and water loss rate and proportion of gravel was able to express by quadratic function, with a high degree of reliability. The results have important implications for soil and water conservation and modeling in landslide deposit but also provide useful information for the similar conditions.

Modeling middle and final flush effects of urban runoff pollution in an urbanizing catchment

Summary In current literature, the first flush effect of urban runoff pollution has been studied and reported extensively. However, the effects of middle and final flushes on pollutant flushing were not given much attention. In addition, few previous studies have discussed the suitability of the widely used exponential wash-off model for describing the middle or final flush processes. In this paper, the Shiyan River catchment, a typical rapidly urbanizing catchment in China, is chosen as a study area to analyze the effects of first, middle and final flushes based on monitoring hydrographs and pollutographs. In order to simulate the middle and final flush processes observed in storm events, a new, realistically simple, parsimonious model (named as logistic wash-off model) is developed with the assumption that surface pollutant loads available for wash-off increase with cumulative runoff volume following a logistic curve. The popular exponential wash-off model and the newly developed model are used and compared in simulating the flush processes in storm events. The results indicate that all the three types of pollutant flushing are observed in the experiment; however, the first flush effect is weak, while the middle and final flush effects are substantial. The exponential model has performed well in simulating the first flush process but failed to simulate well the middle and final flush processes. However, the logistic wash-off model has effectively simulated all the three types of pollutant flush, and particularly, it has performed better in simulating the middle and final flush processes than the exponential model.

Simulation of Runoff for Varying Mulch Coverage on a Sloped Surface

The use of thin plastic film to cover slope surfaces can lead to slope runoff and soil erosion in Loess hilly areas in northwest China. Three main factors (slope, rainfall intensity, and coverage ratio) were selected to analyze variations in runoff dynamics for a Lou soil surface and to obtain a theoretical foundation for practical application. The results indicate that for a fixed rainfall intensity and coverage ratio, a critical slope gradient close to 26.8% was observed. For a fixed coverage ratio and slope gradient, the cumulative runoff volume increased with the rainfall intensity. Overland flow varied with the coverage ratio and this can be attributed to increases in the cumulative runoff volume and runoff velocity with increasing coverage ratio. The experimental results show that for double-ridge cultivation with film mulching, the best coverage ratio is 50:150. This ratio not only reduces moisture evaporation and promotes soil conservation, but also effectively improves rainwater utilization and reduces soil erosion. In addition, for slope gradients exceeding 26.8%, runoff decreases and the soil infiltration capacity increases, so a slope gradient of 26.836.4% is optimal for the local cultivation model.

A modelling approach to assessing variations of total suspended solids (tss) mass fluxes during storm events

AbstractConnections between the catchment hydrology and accumulation, washoff and transport of pollutants in wet weather greatly affect the management of urban drainage and its wet‐weather effluents. In recent years, the concept of the first flush has gained on prominence and was further developed for analyzing the interaction between the hydrology and transport of runoff pollutants. One of the most important definitions of the first flush can be derived from the analysis of the m(v) curves (i.e. the curves in which the normalized cumulative pollutant mass is plotted vs the normalized cumulative runoff volume). Indeed the m(v) curves, indicating the distribution of pollutant mass versus volume in wet‐weather flow (WWF) discharges, are commonly used for comparing pollutant discharges for different rainfall events and catchments. In this study, the m(v) curves were used to define the concepts of flow‐limited and mass‐limited WWF events. These two different behaviours have been analysed for rainfall/runoff events observed in the urbanized part of the Liguori catchment in Cosenza (Italy). In order to advance the understanding of the intra‐event variability of m(v) curves, the mathematical rainfall/runoff model Storm Water Management Model of the US Environmental Protection Agency (SWMM) was calibrated for eight observed rainfall/runoff events and the differences between observed and simulated m(v) curves were analysed. The results showed a good correlation between the observed and simulated m(v) curves, and this finding offers further benefits in SWMM model calibration. Copyright © 2013 John Wiley &amp; Sons, Ltd.

The development of a novel approach for assessment of the first flush in urban stormwater discharges

The management of stormwater pollution has placed particular emphasis on the first flush phenomenon. However, definition and current methods of analyses of the phenomena contain serious limitations, the most important being their inability to capture a possible impact of the event size (total event volume) on the first flush. This paper presents the development of a novel approach in defining and assessing the first flush that should overcome these problems. The phenomenon is present in a catchment if the decrease in pollution concentration with the absolute cumulative volume of runoff from the catchment is statistically significant. Using data from seven diverse catchments around Melbourne, Australia, changes in pollutant concentrations for Total Suspended Solids (TSS) and Total Nitrogen (TN) were calculated over the absolute cumulative runoff and aggregated from a collection of different storm events. Due to the discrete nature of the water quality data, each concentration was calculated as a flow-weighted average at 2 mm runoff volume increments. The aggregated concentrations recorded in each increment (termed as a 'slice' of runoff) were statistically compared to each other across the absolute cumulative runoff volume. A first flush is then defined as the volume at which concentrations reach the 'background concentration' (i.e. the statistically significant minimum). Initial results clearly highlight first flush and background concentrations in all but one catchment supporting the validity of this new approach. Future work will need to address factors, which will help assess the first flush's magnitude and volume. Sensitivity testing and correlation with catchment characteristics should also be undertaken.

Sediment and solute transport on soil slope under simultaneous influence of rainfall impact and scouring flow

AbstractSoil erosion and nutrient losses with surface runoff in the loess plateau in China cause severe soil quality degradation and water pollution. It is driven by both rainfall impact and runoff flow that usually take place simultaneously during a rainfall event. However, the interactive effect of these two processes on soil erosion has received limited attention. The objectives of this study were to better understand the mechanism of soil erosion, solute transport in runoff, and hydraulic characteristics of flow under the simultaneous influence of rainfall and shallow clear‐water flow scouring. Laboratory flume experiments with three rainfall intensities (0, 60, and 120 mm h−1) and four scouring inflow rates (10, 20, 30, and 40 l min−1) were conducted to evaluate their interactive effect on runoff. Results indicate that both rainfall intensity and scouring inflow rate play important roles on runoff formation, soil erosion, and solute transport in the surface runoff. A rainfall splash and water scouring interactive effect on the transport of sediment and solute in runoff were observed at the rainfall intensity of 60 mm h−1 and scouring inflow rates of 20 l min−1. Cumulative sediment mass loss (Ms) was found to be a linear function of cumulative runoff volume (Wr) for each treatment. Solute transport was also affected by both rainfall intensity and scouring inflow rate, and the decrease in bromide concentration in the runoff with time fitted to a power function well. Reynolds number (Re) was a key hydraulic parameter to determine erodability on loess slopes. The Darcy–Weisbach friction coefficients (f) decreased with the Reynolds numbers (Re), and the average soil and water loss rate (Ml) increased with the Reynolds numbers (Re) on loess slope for both scenarios with or without rainfall impact. Copyright © 2010 John Wiley &amp; Sons, Ltd.

An analytical probabilistic model of the quality efficiency of a sewer tank

The assessment of the efficiency of a storm water storage facility devoted to the sewer overflow control in urban areas strictly depends on the ability to model the main features of the rainfall‐runoff routing process and the related wet weather pollution delivery. In this paper the possibility of applying the analytical probabilistic approach for developing a tank design method, whose potentials are similar to the continuous simulations, is proved. In the model derivation the quality issues of such devices were implemented. The formulation is based on a Weibull probabilistic model of the main characteristics of the rainfall process and on a power law describing the relationship between the dimensionless storm water cumulative runoff volume and the dimensionless cumulative pollutograph. Following this approach, efficiency indexes were established. The proposed model was verified by comparing its results to those obtained by continuous simulations; satisfactory agreement is shown for the proposed efficiency indexes.

Interactions of Tillage and Cover Crop on Water, Sediment, and Pre‐emergence Herbicide Loss in Glyphosate‐Resistant Cotton: Implications for the Control of Glyphosate‐Resistant Weed Biotypes

The need to control glyphosate [N-(phosphonomethyl)glycine]-resistant weed biotypes with tillage and preemergence herbicides in glyphosate-resistant crops (GRCs) is causing a reduction in no-tillage hectarage thereby threatening the advances made in water quality over the past decade. Consequently, if environmental gains afforded by GRCs are to be maintained, then an in-field best management practice (BMP) compatible with tillage is required for hectarage infested with glyphosate-resistant weed biotypes. Thus, 1 d after a preemergent application of fluometuron [N,N-dimethyl-N'-(3-(trifluoromethyl)phenyl)urea] (1.02 kg ha(-1)) and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] (1.18 kg ha(-1)) to a Dundee silt loam (fine-silty, mixed, active, thermic Typic Endoaqualf), simulated rainfall (60 mm h(-1)) was applied to 0.0002-ha microplots for approximately 1.25 h to elucidate tillage (no tillage [NT] and reduced tillage [RT])and cover crop (no cover [NC] and rye cover [RC]) effects on water, sediment, and herbicide loss in surface runoff. Regardless of tillage, RC delayed time-to-runoff 1.3-fold, reduced cumulative runoff volume 1.4-fold, and decreased cumulative sediment loss 4.7-fold. Cumulative fluometuron loss was not affected by tillage or cover crop. Conversely, total metolachlor loss was 1.3-fold lower in NT than RT and 1.4-fold lower in RC than NC. These data indicate that RC can be established in hectarage requiring tillage and potentially curtail water, sediment, and preemergence herbicide losses in the spring to levels equivalent to or better than that of NT, thereby protecting environmental gains provided by GRCs.