Sediment Detachment Research Articles

Infiltration Characteristics and Hydrodynamic Parameters in Response to Topographic Factors in Bare Soil Surfaces, Laboratory Experiments Based on Cropland Fields of Purple Soil in Southwest China

Topography is an important factor that impacts the hydrological processes on sloping farmlands. Yet, few studies have reported the combined influences of slope gradient and slope position on infiltration characteristics and hydrodynamic parameters on sloping croplands in purple soil regions, an important area for agricultural productivity in Southwest China. Here, laboratory-simulated rainfall experiments were conducted in a steel trough (5 m long, 2 m wide, and 0.45 m deep), and rainfall lasted for 1 h at a rate of 90 mm h−1 to examine the variations in the infiltration rates and hydrodynamic parameters under varying slope gradients (i.e., 3°, 6°, 10°, 15°, 21°, and 27°) and slope positions (i.e., upper, middle, and lower), and explore the relationships between the infiltration rate and the soil detachment rate. The results showed that the infiltration rate decreased gradually with duration rainfall and ultimately approached a steady state in the six slope treatments. Cumulative infiltration ranged from 15.54 to 39.32 mm during rainfall, and gradually reduced with the increase of slope gradient. The Horton’s model outperforms other models for predicting the infiltration rate with an R2 value of 0.86. Factors such as Darcy–Weisbach friction, flow shear force, Manning friction coefficient, unit energy, and runoff depth varied in the following order: upper slope > middle slope > lower slope, whilst the Reynolds number and Froude number gradually increased along the slope transect from the upper to lower slope positions. A significant linear function was fitted between the soil detachment rate and the infiltration rate at the gentle slopes (3°, 6°, 10°), whereas an exponential relationship was observed at the steep slopes (15°, 21°, and 27°). Observation also suggested that 15° was the critical slope gradient of sediment detachment, infiltration characteristics, and hydrodynamic parameters. Our results provide theoretical insight for developing models that predict the impacts of topographic factors on hydrological characteristic and soil erosion in hilly agricultural landscapes of purple soil fields.

Soil hydro-physical variables and crop residues determinate runoff, soil loss, and glyphosate and AMPA concentration in the aqueous phase under simulated rainfall events.

Soil structural degradation and water erosion processes were observed even in no-tillage schemes in the Pampas region. Within these conservation systems, agrochemical application per hectare is one of the highest globally. Thus, this entails a serious risk of water contamination. The objectives of this study were to (1) test the hypothesis that the hydrological dynamics and sediment concentration related to surface runoff were conditioned by soil structure regardless of the presence of maize (Zea mays L.) crop residue and (2) assess the incidence of maize crop residue on glyphosate and aminomethylphosphonic acid (AMPA) concentration in runoff. The soil under study corresponded to Arroyo Dulce Series (Typic Argiudoll silty loam soil). Rain simulations were performed in the laboratory on undisturbed soil samples. Total runoff and infiltration rate were similar between treatments with C(+) and without C(-) maize crop residues (C(+) 1381.40mL and 14.27mm h-1, C(-): 1529.70mL and 21.67mm h-1). The C(-) treatments showed a higher sediment concentration than C(+) (1.58 and 0.42g 100mL-1, respectively). Glyphosate and AMPA average values in runoff were 15.9 and 33.9µg L-1. High variability of the hydro-physical properties and occurrence of soil structure, particularly platy ones, were detected. The hydrological variables were conditioned mainly by the occurrence of platy structures regardless of crop residue presence. Glyphosate concentration was increased in the first runoff event by the presence of corn residues, while AMPA concentrations were higher in the second runoff event in both residue treatments. In this study, maize residue on the soil surface protected the soil from sediment detachment but did not change runoff or infiltration. Thus, the implementation of agricultural management practices that promote vegetative residue cover has shown positive results to erosion.

Effects of tree and shrub species on soil quality, sediment detachment capacity caused by rills and surface slope stability in forest lands of Northern Iran

A root system is an important factor to increase soil resistance to detachment of soil particles. However, due to the large number of species, there is a need for studying the impacts of native plant species on soil quality and soil erodibility. This investigation did flume experiments at various soil slopes (9.2%, 18.1%, 25.1%, and 32.5%) and different water flow rates (0.56, 0.67, 0.74, 0.81, and 0.94 L/(m·s)), to evaluate sediment detachment capacity caused by rills (Dc) and rill erodibility (Kr) as well as the soil quality of hillslopes with three common species including Carpinus betulus (as a natural tree species), Alnus glutinosa (as a planted tree species) and Mespilus germanica (as a shrub species) in forestland of northern Iran. The variability of Dc has been associated with soil properties and root characteristics of Carpinus betulus. Dc was significantly lower (average, −45%) for soils under Carpinus betulus compared to soils with the two other plant species (p < 0.01). This was due to the higher values of soil properties including medium weight diameter of soil aggregates (MWD), organic carbon (OC), total nitrogen (TN), total phosphorous (TP), potassium (K), calcium (Ca), magnesium (Mg) as well as to the more extended root system, as confirmed by the negative correlations between Dc and the studied variables. Kr also was different among the studied soils and plant species. The root system of Carpinus betulus also played a useful role for increasing soil resistance to rill erosion yielding a safety factor (1.61) in the studied forest ecosystem. Overall, the current study supports a broader use of native species (such as Carpinus betulus) in areas exposed to surface erosion and instability, as an effective eco-engineering conservation technique and an alternative technology instead of utilizing artificial and expensive management practices.

Linkages between gully erosion susceptibility and hydrological connectivity in Tropical sub-humid river basin: Application of Machine learning algorithms and Connectivity Index

Hydrological connectivity from upslope to downslope of valley floor and main channel, triggered the gully initiation and associated land degradation continue occurring off-site erosion as considered most effective drivers on potential sediment detachment. Present study attempted to identify the linkage between gullies erosion susceptibility (GES) and hydrological connectivity pathway in sub-tropical humid river basin Kangsabati (KRB) using four machine-learning algorithms (MLALs) such as Random Forest (RF), Support Vector Machine (SVM), Extreme Gradient Boosting (XGB), Artificial Neural Network (ANN) for GES mapping, and connectivity index (IC) for hydrological connectivity mapping. Thirty-five controlling factors were selected using Boruta’s approach to produce GES mapping, while frequency ratio (FR) was applied to determine the significant role in each individual class of controlling factors on degree of gully susceptibility. To achieve the efficiency of using MLALs, AUC of ROC including sensitivity, specificity, accuracy, F, and Kappa index were employed to compare in each model. In testing datasets, AUC values reveals that RF (0.99) and XGB (0.99) were well performed and predicted to GES followed by ANN (0.97) and SVM (0.87). FR depicts the most contributing factors of barren land and laterite followed by rainfall erosivity, degraded forest, single crop, and elevation to GES. IC result showed that values range (−11.52 to 0.49) address the three connectivity categories i.e. not connected (NC), gully connected but not reach (CNR), and gully well connected (WC). Correlation analysis clarified that double crop (R = 0.82), topographical wetted index (R = 0.77) and slope (R = 0.0.44) are prolonged WC for large downslope in north-western sub-basins of upper catchment and western, eastern sub-basins of lower catchment, while dense forest (R = -0.71) and vegetation cover (R = -0.82) forms NC gullies and CNR to channel due to interrupted upslope in central sub-basins of upper and lower catchment. Finally, research findings could provide to take strategy for sustainable land uses policy.

Short communication: Concentrated impacts by tree canopy drips – hotspots of soil erosion in forests

Abstract. The degradation of ground vegetation cover caused by large grazing herbivores frequently results in enhanced erosion rates in forest ecosystems. Splash erosion can be caused by drop impacts with a high throughfall kinetic energy (TKE) from the tree canopy. Notably larger canopy drips from structurally mediated woody surface points appear to induce even higher TKE and generate concentrated impact locations causing severe focus points of soil erosion. However, TKE at these locations has rarely been reported. This pilot study investigated the intensity of TKE at a concentrated impact location and compared it with general TKE locations under the canopy and freefall kinetic energy (FKE) outside the forest. We measured precipitation, TKE and FKE using splash cups at seven locations under Japanese beech trees and five locations outside the forest during the leafless and leafed seasons in 2021 in a mixed forest with evergreen coniferous trees and deciduous broadleaved trees in Japan. The TKE at the concentrated impact location was 15.2 and 49.7 times higher than that at the general locations under the beech and FKE, respectively. This study confirmed that canopy drip from woody surfaces could be a hotspot of soil erosion in temperate forest ecosystems. Throughfall precipitation at the concentrated impact location was 11.4 and 8.1 times higher than that at general locations and freefall, respectively. TKE per 1 mm precipitation (here, “unit TKE”) at the concentrated impact location (39.2 ± 23.7 J m−2 mm−1) was much higher than that at general locations (22.0 ± 12.7 J m−2 mm−1) and unit FKE (4.5 ± 3.5 J m−2 mm−1). Unit TKE in the leafless season was significantly lower than in the leafed season because of fewer redistribution of canopy drips induced only by woody tissue. Nevertheless, unit TKE at the concentrated impact location in the leafless season (36.4 J m−2 mm−1) was still higher than at general locations in the leafed season. These results show that potentially high rates of sediment detachment can be induced not only by throughfall precipitation but also by larger throughfall drop size distributions at the concentrated impact location, even in the leafless season. Further studies with more replication building on this first report are necessary to investigate how many of these concentrated impact locations may occur on average with different tree species to better assess the extent of the erosion risk under forests.

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.

Urbanization as a limiter and catalyst of watershed-scale sediment transport: Insights from probabilistic connectivity modeling

The conversion of rural lands to urban areas exerts considerable influence on the hydrologic processes governing sediment transport at the watershed scale. While the effects of urbanization on hydrology have been well-studied, the corresponding impact to the spatial and temporal variability of sediment detachment, transport, and connectivity is less certain. To address this knowledge gap, we apply process-based hydrologic simulation, probabilistic connectivity modeling, and in situ turbidity sensing to five watersheds positioned along a steep land use gradient in Kansas, USA. Connectivity modeling results show that urbanization systematically decreases the maximal extent of watershed-scale connectivity on the wettest days of the study period, from 51 % in the most rural watershed to 28 % in the most urban watershed. On the other hand, urbanization focuses sediment transport into fewer, more frequently wetted pathways, such as roadway drainage networks, which are activated 3.5 times more frequently than the equivalent pathways in rural basins. In this way, urbanization limits maximal connectivity as impervious surfaces indefinitely disconnect source zones from the sediment cascade, but also catalyzes hot spots of connectivity as these same impervious areas generate excess runoff and channel it to drainage systems. The 23.9 ± 4.2 % of days that exhibit watershed-scale functional connectivity account for 85.0 ± 9.5 % of sediment export with most of the export tied to a few highly connected days. Sensing results show that increases in watershed-scale connectivity only translate to larger fluvial sediment loads after a connectivity threshold (the median connected day) has been exceeded, suggesting a transition from functional to structural connectivity control on sediment dynamics after sufficient wetting. This study highlights the role of land use impacts on the sources and mechanisms of sediment transport, which will be an important consideration for land managers as urban areas continue to expand to accommodate global migration patterns.

Response of particle detachment and hydrological processes on windward slope in laboratory flume experiments at different wind velocities and rainfall intensities

Wind-driven rain (WDR) is a natural phenomenon that causes soil erosion, a decline in land productivity, water pollution, and other environmental problems. Owing to the influence of topography on atmospheric circulation, WDR occurs most frequently on windward slopes. Studying the physical mechanisms of soil erosion on windward slopes is challenging because of the complex co-occurrence of wind and rainfall. This study aimed to investigate the effects of rainfall intensity (30, 60, and 90 mm h−1), wind velocity (0, 2, 3, 5, 7, and 8 m s−1), and induced flow hydraulic characteristics on the processes of runoff occurrence, infiltration, and sediment detachment on windward slopes based on an indoor artificial simulated WDR soil flume experiments with three replicates. The results showed that both rainfall intensity and wind velocity exerted significant effects on runoff and sediment transport on the windward slopes (P < 0.05). The contribution rates of wind velocity on runoff occurrence time, steady infiltration rate, runoff rate, and sediment detachment rate were 20.53 %, 39.44 %, 3.36 %, and 6.24 %, respectively. When the rainfall intensity was constant, the steady infiltration rate on the windward slope increased linearly with the increasing wind velocity, whereas the runoff and sediment detachment rates decreased with increasing wind velocity. The decrease in hydraulic parameters of average flow velocity (v), stream power (Ω), unit stream power (U), and unit energy of cross-section (E) influenced by wind blowing on overland flow is the main reason for the decrease in the sediment detachment rate on the windward slope. Meanwhile, the increase in flow depth (h) and shear stress (τ) caused an increase in the infiltration rate. Because of the inclusion of Ω and E in the total work done and total energy consumption of overland flow, respectively, the relationship between Ω and E of the windward water flow with the sediment detachment rate showed an exponentially increasing curve for all treatments (R2 greater than 0.97). The hydraulic parameters Ω and E of the windward water flow are the optimal factors for constructing an erosion dynamic model under WDR conditions.

Straw Mulch Effect on Soil and Water Loss in Different Growth Phases of Maize Sown on Stagnosols in Croatia

Soil and water loss due to traditional intensive types of agricultural management is widespread and unsustainable in Croatian croplands. In order to mitigate the accelerated land degradation, we studied different cropland soil management strategies to obtain feasible and sustainable agro-technical practices. A rainfall simulation experiment was conducted at 58 mm h–1 over 30 min on 10 paired plots (0.785 m2), bare and straw covered (2 t ha−1). The experiment was carried out in maize cultivation (Blagorodovac, Croatia) established on Stagnosols on slopes. Measurements were conducted during April (bare soil, after seeding), May (five-leaves stage), and June (intensive vegetative growth) making 60 rainfall simulations in total. Straw reduced soil and water losses significantly. The highest water, sediment loss, and sediment concentrations were identified in tillage plots during May. Straw addition resulted in delayed ponding (for 7%, 63%, and 50% during April, May and June, respectively) and runoff generation (for 37%, 32%, and 18% during April, May and June, respectively). Compared with the straw-mulched plot, tillage and bare soil increased water loss by 349%. Maize development reduced the difference between bare and straw-mulched plots. During May and June, bare plots increase water loss by 92% and 95%, respectively. The straw mulch reduced raindrop kinetic energy and sediment detachment from 9, 6, and 5 magnitude orders in April, May, and June, respectively. Overall, the straw mulch was revealed to be a highly efficient nature-based solution for soil conservation and maize cultivation protection.

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 IMPACT OF CLIMATE CHANGE ON SEDIMENT TRANSPORT CAPACITY: A CASE STUDY OF THE BOUBO COASTAL WATERSHED

For soil erosion modeling, determining sediment transport capacity (Tc) is essential because it plays a key role in sediment detachment, transport, and deposition research. This paper provides insights into the seasonal spatial distribution of sediment transport capacity, excess runoff depth in response to the distribution of precipitation, and land use at a watershed scale, using SCN Curve Number (CN) method, Remote Sensing (RS), and Geographic Information Systems (GIS). Spatial distribution in runoff production on hillslopes and sediment transport are explained. We integrated the effect of slope gradient in the curve number to model the landscape effect on sediment transport. The findings show that seasonal variation in sediment transport capacity is influenced by climate change. During June and October, the transport capacity is higher and coincides with channel areas in the Boubo watershed. Potential applications of this map may help the decision-maker to deal with problems associated with watershed development and management.

The effect of physicochemical properties of bottom sediments on nitrogen and phosphorus sorption

River and reservoir bottom sediments are characterized by their physical and chemical properties, which affect the quality of water and deposited sediments in reservoirs. The grain composition of sediments is their fundamental property that determines the detachment, transport and sedimentation of sediments. In addition to understanding the dynamics of transport and distribution of particles in the watershed, the granularity is closely related to the mineral and chemical composition of the sediment and plays an important role in terms of its ability to bind contaminants. Other important property of sediment includes the specific surface area, which determines the nature of sediment surface reactions and influences ecosystem level, biological processes.This study investigates sediment properties, including physical properties such as grain-size distribution, specific surface area, organic matter and chemical composition, and their reflections on nitrogen and phosphorus adsorption by the sediments deposited in the small water reservoir. The results clearly indicate the dependence of the content of nutrients (nitrogen and phosphorus) in reservoir sediments on their grain size and specific surface area.

Impacts of raindrops increase particle sedimentation in a sheet flow

AbstractInterrill erosion is driven by raindrops and sheet flow. Raindrop impacts cause sediment detachment and splash, but can also affect flow transport. Even if these processes have been studied for long, the actual effect of raindrop impacts on particle settling velocities has not been experimentally assessed. This leads to unconstrained adjustments in the soil erosion models, the settling velocity of particles being a freely adjustable parameter allowing for better fitting the particle flux measured at the outlet. To address the effect of raindrop impacts on the settling of particles in sheet flow, a laboratory flume experiment was designed, using an upstream feeder of sediment (100–200 μm) and simulated rainfalls. It reproduced conditions close to sheet flow, while not allowing for the detachment of particles from the flume bottom. Two series of experiments were run: a series with a high rainfall intensity (175 mm/h) generated by an oscillating‐nozzle rainfall simulator, and a series with lower rainfall intensities (10, 15, 25, 35, 55 mm/h) generated by a drop‐former rainfall simulator. When a rainfall was applied, it systematically decreased the sediment concentration at the outflow compared to the no rain condition; however, no obvious relationship was found with the rainfall intensity. This shows that raindrop impacts increase particle settling velocities in sheet flow. Two underlying mechanisms are suggested, related to the momentum of the raindrops or to the turbulence caused by the raindrops into the flow. Further studies should be carried out, using computational fluid dynamics and collaboration with the fluid mechanics community.

Evaluating sediment connectivity and its effects on sediment reduction in a catchment on the Loess Plateau, China

Sediment connectivity is a principal element for revealing sediment yield variations in catchments. Although several methods for quantifying this element have been tested, there is still much room for improvement as manifested in many recent discussions on this issue. In this study, we defined a new revised sediment connectivity index (RIC) by incorporating the functional with the structural components of a sediment routing system. The index was applied to the Gushanchuan catchment on the Chinese Loess Plateau to produce yearly RIC maps of sediment connectivity based on the datasets of topography, rainfall erosivity, land use and land cover, soil erodibility in 39 years (1980–2018). The RIC maps were combined with the distribution histogram of RIC to identify hotspots of sediment detachment and transport. Moreover, the temporal evolution of sediment connectivity was tested by using sediment discharge observed at the outlet. The results showed that values of sediment connectivity were higher in the gullies than in the hill slopes. After differentiating the impacts of rainfall, land use and land cover change (LUCC), check dams on the sediment reduction in the catchment, the contribution rates of the check dams were estimated to be 63% (1990–1999) and 9% (2000–2018) of the total sediment yield reduction. The remaining 37% and 91% were explained by the variations of sediment connectivity induced by rainfall change and LUCC. Among them, the average sediment reduction benefit was −33% and −39% for rainfall variation, and 70% and 130% for LUCC. The land use statistics showed a decreasing trend of cropland (231.91 km2) from 1980 to 2018. The cropland conversion resulted in an annual sediment reduction of 757 × 104 t in the 1990s and 1 408 × 104 t in 2001–2018 compared with the period of 1980–1989. The new RIC was illustrated to be an easy-to-run and suitable tool for studying the changing soil erosion and sediment delivery in catchments.

Sediment detachment by raindrop impact on grassland and arable fields: an investigation of controls

Sediment detachment by raindrop impact on grassland and arable fields: an investigation of controls

Land use and land cover change-induced changes of sediment connectivity and their effects on sediment yield in a catchment on the Loess Plateau in China

The spatial distribution of landscape pattern in catchments has a great impact on the potential sediment detachment and transport capacity. In this study, a sediment connectivity model was applied to evaluate the effect of the spatial distribution of landscape pattern on the sediment transfer in a typical catchment on the Loess Plateau in China based on land use and topography data in 1964, 2004, and 2018. Thereupon, the impacts of changes in different land use types on sediment connectivity and those of sediment connectivity changes on sediment yield reduction in the catchment were quantified. The results showed that (i) grassland and slope farmland were the main land use types in the catchment, and a decrease of the slope farmland area and an increase of the vegetation coverage occurred from 1964 to 2018; (ii) compared with 1964, most parts of the catchment in 2004 and 2018 had an overall lower connectivity index (IC); (iii) the distribution of sediment connectivity presented obvious spatial variability. The hill slopes and tributary gullies tended to be relatively well connected, and the main gully was highly disconnected. Scenario simulations showed that the potential sediment reduction effect was 20%−45% for vegetation, and <10% for terraces or dam lands in 1964, 2004, and 2018. The effect of impounding sediment by check dams was not included in IC calculation in this study, and it was found that the sediment impounded by these dams accounted for about 16% of sediment discharge reduction during 1995–2004 and 1% during 2005–2018. The IC reduction was responsible for 84% of the decrease of sediment discharge during 1995–2004 and 99% during 2005–2018, reflecting that vegetation restoration and terrace construction on slopes has become the main drivers for reducing IC value and sediment yield.

EVALUATION OF SOIL PHYSICAL PROPERTY AS A DETERMINING FACTOR OF EROSION: A CASE STUDY OF BEHIND NIGERIA INSTITUTE OF LEATHER AND SCIENCE TECHNOLOGY, ZARIA

Soil Erosion is the detachment, transportation and deposition of soil sediment from one place to another. This has led to loss of lives and infrastructure in many parts of Nigeria. Soil properties play a role in it vulnerability and extent to erosion. This study aims to evaluate selected physical properties as they interact to cause erosion in the study area. The study was conducted in 2012 in a gully site in relation to its potential to erodibility of gully channel. This was done by collection of various soil samples at different depth followed by laboratory analysis to determine the plastic limit, moisture content and other engineering properties. The Results indicated that the soil samples have Atterberg limit that might be considered low, while liquid limit (LL) ranged from 25 – 30, the plasticity index (PI) ranged from 1 – 5%, which suggested that the soils are slightly plastic. Moisture content was moderate. The soil properties investigated played a major role in exacerbating the gully erosion in the area, therefore, the existing culvert should be redesigned and reconstructed taking appropriate consideration of the underlying soil properties

Spatial simulation of forest road effects on hydrology and soil erosion after a wildfire

AbstractPost‐fire catchment and water utility managers throughout the world use predictive models to estimate potential erosion risks to aid in evaluating downstream impacts of increased runoff and erosion, and to target critical areas within a fire for applying mitigation practices. Erosion prediction can be complicated by forest road networks. Using novel GIS technology and soil erosion modelling, this study evaluated the effect of roads on surface runoff, erosion and sediment yields following a wildfire and determined that the predictive models were providing reasonable results. The GeoWEPP model was used to simulate onsite erosion and offsite sediment delivery before and after fire disturbance using a 2‐m resolution DEM as the terrain layer. Erosion rates in excess of 4 Mg ha−1 year−1were predicted mainly from steep moderate and high severity burn areas. Roads influenced surface runoff flow path distributions and sub‐catchment delineations, affecting the spatial distribution of sediment detachment and transport. Roads tended to reduce estimated erosion on slopes below the roads but increases in erosion rates were estimated for road fillslopes. Estimated deposition amounts on roads and in sediment basins were similar to measured amounts. The results confirm that road prisms, culverts and road ditches influence sedimentation processes after wildfire, and they present opportunities to detain eroded sediments.

Hack distributions of rill networks and nonlinear slope length–soil loss relationships

Abstract. Surface flow on rilled hillslopes tends to produce sediment yields that scale nonlinearly with total hillslope length. The widespread observation lacks a single unifying theory for such a nonlinear relationship. We explore the contribution of rill network geometry to the observed yield–length scaling relationship. Relying on an idealized network geometry, we formally develop probability functions for geometric variables of contributing area and rill length. In doing so, we contribute towards a complete probabilistic foundation for the Hack distribution. Using deterministic and empirical functions, we then extend the probability theory to the hydraulic variables that are related to sediment detachment and transport. A Monte Carlo simulation samples hydraulic variables from hillslopes of different lengths to provide estimates of sediment yield. The results of this analysis demonstrate a nonlinear yield–length relationship as a result of the rill network geometry. Theory is supported by numerical modeling, wherein surface flow is routed over an idealized numerical surface and a natural surface from northern Arizona. Numerical flow routing demonstrates probability functions that resemble the theoretical ones. This work provides a unique application of the Scheidegger network to hillslope settings which, because of their finite lengths, result in unique probability functions. We have addressed sediment yields on rilled slopes and have contributed towards understanding Hack's law from a probabilistic reasoning.

A review of the current state of process-based and data-driven modelling: guidelines for Lake Erie managers and watershed modellers

Elevated phosphorus (P) loading from the watersheds draining into Lake Erie, particularly from agricultural (53%) and urban (43%) sources, is identified as one of the main drivers of the severe eutrophication. In this study, we present a comprehensive evaluation of 11 process-based models to characterize the water cycle as well as nutrient fate and transport within a watershed context, and to find a robust and replicable way to optimize the modelling strategy for the Lake Erie watershed. Our primary objective is to review the conceptual/technical strengths and weaknesses of the individual models for reproducing surface runoff, groundwater, sediment transport, nutrient cycling, and channel routing, and to collectively guide the management of the Lake Erie Basin. Our analysis suggested that the available models either opted for simpler approximations of the multifaceted, nonlinear dynamics of nutrient fate and transport, and instead placed more emphasis on the advanced representation of the water cycle or, introduced a greater degree of biogeochemical complexity but simplified their strategies to recreate the roles of critical hydrological processes. Notwithstanding its overparameterization problem, the MIKE SHE model provides the most comprehensive 3D representation of the interplay between surface and subsurface hydrological processes with a fully dynamic description, whereby we can recreate the solute transport that infiltrates from the surface to the unsaturated soil layer and subsequently percolates into the saturated layer. Likewise, the physically based submodels designed to represent the sediment detachment and erosion/removal processes (DWSM, HBV-INCA, HSPF, HYPE, and MIKE SHE), offer a distinct alternative to USLE-type empirical strategies. The ability to explicitly simulate the daily plant growth (SWAT and APEX) coupled with a dynamic representation of soil P processes can be critical when evaluating the long-term watershed responses to various agricultural management strategies. Drawing parallels with the (sub)surface and sediment erosion processes, a more complicated physically based approach, e.g., the dynamic wave model provided by MIKE SHE (coupled with MIKE URBAN or MIKE HYDRO) and SWMM may be more appropriate for realistically simulating the pressurized flow and backwater effects of water routing in both open channels and closed pipes. While our propositions seem to favor the consideration of complex models that may lack the commensurate knowledge to properly characterize the underlying processes, we contend this issue can be counterbalanced by the joint consideration of simpler empirical models under an ensemble framework, which can both constrain the plausible values of individual processes and validate macroscale patterns. Finally, our study discusses critical facets of the watershed modelling work in Lake Erie, such as the role of legacy P, the challenges in reproducing spring-freshet or event-flow conditions, and the dynamic characterization of water/nutrient cycles under the nonstationarity of a changing climate.