Overland Water Flow Research Articles

Implementation of a GPU-enhanced multiclass soil erosion model based on the 2D shallow water equations in the software Iber

We present the implementation of a new fully distributed multiclass soil erosion module. The model is based on a 2D finite volume solver (Iber+) for the 2D shallow water equations that computes the overland flow water depths and velocities. From these, the model evaluates the transport of sediment particles due to bed load and suspended load, including rainfall-driven and runoff-driven erosion processes, and using well-established physically-based formulations. The evolution of the mass of sediment particles in the soil layer is computed from a mass conservation equation for each sediment class. The solver is implemented using High Performance Computing techniques that take advantage of the computational capabilities of standard Graphical Processing Units, achieving speed-ups of two orders of magnitude relative to a sequential implementation on the CPU. We show the application and validation of the model at different spatial scales, ranging from laboratory experiments to meso-scale catchments.

Debris flow at Luib on the A87 strategic road: Isle of Skye, Scotland

A rainfall-induced debris flow occurred on 30 September 2022, closing the A87 trunk (strategic) road on the Isle of Skye for around 2 h. Ground-based and aerial drone inspections were used to describe the event and a comprehensive rainfall analysis was undertaken. It is concluded that the event was triggered by overland water flow from the slopes above the source zone as a result of high rainfall. The resulting translational slide transitioned into a debris flow that reached a pre-existing channel where entrained superficial deposits were deposited, adding to pre-existing levee structures before reaching the road. The rainfall that led to the debris flow was high intensity–low duration; the rainfall analysis encompasses annual, monthly, daily, hourly and 15 min data, each aiding understanding of the climate of the area and/or the event rainfall. Comparison is made with a rainfall event the following month, which was of a greater magnitude but of longer duration and lower intensity. The hazard at this location is a concern but the risk is emphasized by the proximity of the road to the steep slopes above and the lack of a viable detour. Thematic collection: This article is part of the Geo-resilience and infrastructure collection available at: https://www.lyellcollection.org/topic/collections/geo-resilience-and-infrastructure

Simulating event-based pesticide transport with runoff and erosion; OpenLISEM-pesticide v.1

This study presents a novel pesticide transport module for the OpenLISEM runoff and erosion model. During water erosion events, high amounts of pesticides can be transported alongside the runoff. Simulating this process helps to mitigate adverse effects of pesticides in the environment. We conceptualized pesticide uptake during runoff with a mixing-layer, including mass transfer of dissolved pesticides into the runoff water and detachment in combination with enrichment of sorbed pesticides. Lateral transport of pesticides is modelled with a kinematic wave based on the overland flow of water. The model simulations were in line with observations for two events in a small agricultural catchment in South-Limburg, the Netherlands. A sensitivity analysis showed that pesticide transport was mainly influenced by the mass transfer rate, the soil-water partitioning and the exponent for the enrichment ratio. The accurate simulation of runoff and erosion by OpenLISEM, enables OpenLISEM-pesticide to simulate transport and redistribution adequately.

Seasonal variation in soil erosion resistance to overland flow in gully-filled farmland on the Loess Plateau, China

Large areas of farmland have been established in China’s Loess Plateau region by backfilling forest and grasslands in gullies with topsoil from hillslopes. High amounts of plant litter are incorporated into the topsoil during such processes; however, their effects on soil erosion resistance under natural conditions are not fully understood. Therefore, the present study investigated seasonal variation in soil erosion resistance to overland flow and the underlying factors in the gully-filled farmland. Two typical plant litter species were selected in this study, i.e., Artemisia sacrorum Ledeb. (ASL) and Bothriochloa ischaemum (L.) Keng. (BIL). Overland water flow was tested under six shear stress levels (5.66–22.11 Pa) in natural soil samples incorporated with plant litter and without plant litter to determine soil erosion resistance parameters (rill erodibility Kr and critical shear stress τc). The study was conducted over 524 days (through May 6, 2017, to October 11, 2018), covering two rainy seasons and one winter. Soil properties changed significantly over time, with physical crust thickness and cohesion increasing from 0 to 10.7 mm and 2.9–13.4 kPa, respectively. In contrast, the mass density of incorporated plant litter decreased from 0.7 to 0.2 kg m−2. Soil erosion resistance increased with time, which showed that Kr decreased (from 0.516 to 0.021 s m−1) and τc increased (from 0.49 to 7.98 Pa). Compared with the initial state of new farmland (Kr = 0.507 s m−1,τc= 0.48 Pa), Kr decreased by 77–96% and τc increased 8–14 times at the end of the study. Plant litter incorporation markedly enhanced soil erosion resistance in a time- and species-dependent manner. Compared with the bare soil without plant litter, the Kr values of ASL and BIL treatments were 3–64% and 2–83% lower, and their τc values were 0–81% and 0–55% higher, respectively. Kr was significantly and positively correlated with cumulative precipitation, cumulative rainfall kinetic energy, soil cohesion, and physical soil crust thickness, while τc was negatively correlated with the influencing factors. Further, both Kr and τc could be well predicted by physical soil crust thickness and cohesion (R2 = 0.79 and 0.87, p < 0.01, n = 27). According to the results, seasonal patterns of soil erosion resistance in the gully-filled farmland established under plant litter incorporation were mainly controlled by rainfall and physical soil crust structure. This study provides a reference resource for soil erosion prediction in farmland ecosystems on the Loess Plateau.

Bi-directional coupling of an open-source unstructured triangular meshes-based integrated hydrodynamic model for heterogeneous feature-based urban flood simulation

Urban pluvial flash floods have become a matter of widespread concern, as they severely impact people’s lives in urban areas. Hydrological and hydraulic models have been widely used for urban flood management and urban planning. Traditionally, to reduce the complexity of urban flood modelling and simulations, simplification or generalization methods have been used; for example, some models focus on the simulation of overland water flow, and some models focus on the simulation of the water flow in sewer systems. However, the water flow of urban floods includes both overland flow and sewer system flow. The overland flow processes are impacted by many different geographical features in what is an extremely spatially heterogeneous environment. Therefore, this article is based on two widely used models (SWMM and ANUGA) that are coupled to develop a bi-directional method of simulating water flow processes in urban areas. The open source overland flow model uses the unstructured triangular as the spatial discretization scheme. The unstructured triangular-based hydraulic model can be better used to capture the spatial heterogeneity of the urban surfaces. So, the unstructured triangular-based model is an essential condition for heterogeneous feature-based urban flood simulation. The experiments indicate that the proposed coupled model in this article can accurately depict surface waterlogged areas and that the heterogeneous feature-based urban flood model can be used to determine different types of urban flow processes.

The Effect of Trails on Soil in the Oak Openings of Northwest Ohio

Trails are a form of recreational disturbance affecting natural areas. Trail disturbances can cause soil degradation such as compaction, which facilitates soil erosion and overland water flow. This study analyzed the effects of four different types of trails—paved, gravel, equestrian, and hiking—on soils in the Oak Openings of Northwest Ohio, a globally rare ecosystem that harbors more than a third of Ohio's rare plant species. Bulk density and soil moisture content were measured in order to determine physical impacts of trails. Soil pH, ammonium, nitrate, phosphate, and dissolved organic C and N concentrations were measured to determine effects on soil chemistry. Finally, soil microbial biomass and exoenzyme activities were measured to determine biological responses to trail disturbances. Soils from the gravel trail were the most affected by the trail, with significant effects on chemical (PO43-concentration) and biological (phosphatase and NAG activity, and MB-N) properties. The soils near the paved trail were the second most affected after the gravel trail, with a trend toward a pH change and a significant biological (microbial peptidase activity) effect of this trail. The soils of the horse and natural trails were generally not significantly different from the soils in the surrounding ecosystem. The only significant disturbance in the horse trail was increased bulk density in the trail, while the natural hiking trail had no statistically significant differences, but trends lean toward increased bulk density and reduced microbial phosphatase activity. These results suggest that the natural and horse trails have the least impact on the Oak Openings ecosystem.Jared Hawkins and Michael N. Weintraub. 2011. “The Effect of Trails on Soil in the Oak Openings of Northwest Ohio.” Natural Areas Journal 31(4):391-399.

EVALUATING HYDRAULIC PROPERTIES OF SOILS: A MANAGEMENT STRATEGY TOWARDS FIGHTING THE 21ST CENTURY FLOOD DISASTER

The continual destruction of the environment due to anthropogenic and natural factors has played a role in increasing global flood disaster, acting like a hindrance in meeting the target of global sustainability. Flood has been looked at as an overland flow of water into land which is naturally dry after filling-up of natural open and close water holding bodies. The impact caused by flood disaster has been recorded and include death of humans and animals, apart from the massive destruction of properties and infrastructures, thereby limiting human development. Looking at land and water as a scare and unrenewable natural resources, then it follows that effective management of land and water resources is one way a society can maximize it economic growth and development. Studying the flux of fluid especially water into the soil profile is a great approach in investigating a soil towards the tendency for flooding. Infiltration is the key to soil water conservation and management. The ability of the soil to act as a sponge in-other to cut-down the raising cases of loss of lives and property with associated impact due to flood disaster lies on its infiltration capacity. The study evaluated the strength of soils of University of Abuja Flood meadows to absorb hydrological shock as flood. Outcome of the study revealed that dry land of University of Abuja flood meadow is able to absorbed reasonable quantity of water as flood, with coefficient of variability value of (CV=12%) for the hydraulic conductivity of the site. While bulk density of the area was found to be (2.30 g cm-3) and Porosity of (8%). Conclusion of the study states that most of the sites investigated have a weak hydrological potential in regards to adsorbing and transporting of the water down the soil profile, hence the area should be put to vegetation cover to reduce the flooding impact, alongside an advance drainage system in the area.

Flow velocity on cultivated soil slope with wheat straw incorporation

Water flow velocity is of great importance in quantifying overland water flow hydrodynamics, related to rainfall infiltration, runoff energy, and soil erosion. Mixing the straw into the cultivated soil can change its physical properties and in turn affect the velocity of water flow. Laboratory investigations were made to measure the velocities of rainfall runoff water flow under four incorporation rates (0, 2, 4 and 8 ton/ha), three rainfall intensities (80, 120 and 160 mm/h) and three slope gradients (10, 15 and 20°), on straw incorporation soil slopes, at slope distances of 5, 6 and 7 m from the top end of the slope, using an electrolyte tracing system. The results show that the flow velocity decreased exponentially with straw incorporation rate. The mean flow velocity ranged from 0.17 to 0.23 m/s over the bare soil slope, while the mean flow velocity ranged from 0.10 to 0.17 m/s, 0.09 to 0.13 m/s, and 0.06 to 0.11 m/s over the soil slopes with straw incorporation rates of 2, 4, 8 t/ha respectively. The 2, 4 and 8 t/ha straw incorporation rates reduced flow velocities by 28.44%, 44.09% and 55.56%, respectively. Higher rainfall intensity and slope gradient caused increase in flow velocity. There was no significant difference between the two adjacent rainfall intensities and slope gradients. A nonlinear multiple regression model was used to fit the measured velocities, which predicts well the effect of straw incorporation rate, rainfall intensity, and slope gradient. Increase in straw application rate had a good effect on reducing the flow velocity which may influence soil erosion and sediment delivery. Velocity over soil slope with straw incorporation can help interpret soil erosion and sediment transportation.

Fragmentation and thresholds in hydrological flow-based ecosystem services.

Loss and fragmentation of natural land cover due to expansion of agricultural areas is a global issue. These changes alter the configuration and composition of the landscape, particularly affecting those ecosystem services (benefits people receive from ecosystems) that depend on interactions between landscape components. Hydrological mitigation describes the bundle of ecosystem services provided by landscape features such as woodland that interrupt the flow of runoff to rivers. These services include sediment retention, nutrient retention and mitigation of overland water flow. The position of woodland in the landscape and the landscape topography are both important for hydrological mitigation. Therefore, it is crucial to consider landscape configuration and flow pathways in a spatially explicit manner when examining the impacts of fragmentation. Here we test the effects of landscape configuration using a large number (>7,000) of virtual landscape configurations. We created virtual landscapes of woodland patches within grassland, superimposed onto real topography and stream networks. Woodland patches were generated with user‐defined combinations of patch number and total woodland area, placed randomly in the landscape. The Ecosystem Service model used hydrological routing to map the “mitigated area” upslope of each woodland patch. We found that more fragmented woodland mitigated a greater proportion of the catchment. Larger woodland area also increased mitigation, however, this increase was nonlinear, with a threshold at 50% coverage, above which there was a decline in service provision. This nonlinearity suggests that the benefit of any additional woodland depends on two factors: the level of fragmentation and the existing area of woodland. Edge density (total edge of patches divided by area of catchment) was the best single metric in predicting mitigated area. Distance from woodland to stream was not a significant predictor of mitigation, suggesting that agri‐environment schemes planting riparian woodland should consider additional controls such as the amount of fragmentation in the landscape. These findings highlight the potential benefits of fragmentation to hydrological mitigation services. However, benefits for hydrological services must be balanced against any negative effects of fragmentation or habitat loss on biodiversity and other services.

Seeking Environmental Sustainability in Dryland Forestry

Forestry systems, including afforestation and reforestation land uses, are prevalent in drylands and aimed at restoring degraded lands and halting desertification. However, an increasing amount of literature has alerted potentially adverse ecological and environmental impacts of this land use, risking a wide range of ecosystem functions and services. The objective of this paper is to demonstrate the potentially adverse implications of dryland forestry and highlight the caution needed when planning and establishing such systems. Wherever relevant, establishment of low-impact runoff harvesting systems is favored over high-impact ones, which might cause extensive land degradation of their surroundings. Specifically, both in hillslopes and channels, scraping, removal, or disturbance of topsoil for the construction of runoff harvesting systems should be minimized to prevent the decrease in soil hydraulic conductivity and increase in water overland flow and soil erosion. In order to negate suppression of understory vegetation and sustain plant species richness and diversity, low-density savanization by non-allelopathic tree species is preferred over high-density forestry systems by allelopathic species. Wherever possible, it is preferable to plant native tree species rather than introduced or exotic species, in order to prevent genetic pollution and species invasion. Mixed-species forestry systems should be favored over single-species plantations, as they are less susceptible to infestation by pests and diseases. In addition, drought-tolerant, fire-resistant, and less flammable tree species should be preferred over drought-prone, fire-susceptible, and more flammable species.

Individual-based modeling of mangrove forest growth: MesoFON – Recent calibration and future direction

We introduce individual-based models (IBMs) of mangrove forests and criticize the tasks for their development recommended previously for being mostly related to natural threats. This is contrasted with our perspective that the key research question of today's models should be to mitigate anthropogenic threats.Core objective (1) of this article is to provide a review of mangrove threats prioritizing solution-oriented IBM approaches. Because species-specific calibration of IBMs is time-consuming, efficiency is crucial. Globally, we identify an urgent need to parametrize Asian mangrove species.We suggest IBMs to unveil management scenarios with maximum sustainable timber yield to prevent mangrove conversion and over-exploitation. The key model purpose regarding natural threats is to govern the management of mangrove forest stability for coastal protection using a combination of windthrow models and IBMs. We argue for the embedding of IBMs in ecosystem models to achieve purposes regarding eutrophication and altered hydrology/sedimentation.Core objective (2) is to describe the development of the new IBM mesoFON from a task-to a solution-oriented model. Initially, the interaction of lateral crown displacement and hurricane impacts was examined with mesoFON. Later, we introduced propagule production & local dispersal with the task to close the tree life cycle. Here, we describe the change in purpose of mesoFON accompanying its calibration for Rhizophora apiculata in Malaysia. For this we applied a Genetic Algorithm optimizer, used mesoFON as a “way-back machine”, initialized it with observed tree diameters/positions and shrank the trees backwards in time.Objective(3) is to describe mesoFON's future direction: Embedding in the General Ecosystem Model (Fitz et al., 1996) and targeting the solution of threats at larger spatial scales. Finally, we demonstrate that the new model simulates overland waterflow qualitatively right even in benchmark settings.

Vegetation ring formation by water overland flow in water‐limited environments: Field measurements and mathematical modelling

AbstractVegetation rings are a unique vegetation pattern found in drylands. Most examples are found in clonal plants growing in sandy soils with confined root zones. Using field measurements and numerical simulations, we found that water overland flow is a predominant mechanism that drives ring formation in the clonal species Asphodelus ramosus. In these rings, an infiltration contrast develops due to aeolian feedback between vegetation and wind‐induced particle transport. Fine particles settle at the patch's centre, reducing water infiltrability compared with that of its perimeter. In turn, this encourages the development of biological soil crust in the ring's centre, further decreasing water infiltration in this micro‐environment. These processes cause the development of surface run‐off source–sink relations between the ring's centre and perimeter. The outcome of this process is the formation of three different micro‐environments: the centre of the patch, characterized by low soil‐water content; its perimeter, characterized by higher soil‐water content; and the matrix, also characterized by higher soil‐water content. Competition for the water resource between the ramets at the perimeter and the ones at the centre leads to dieback, resulting in ring formation. Measurements of soil‐water content in rings of A. ramosus in the semiarid Negev of Israel throughout 5 years showed that the soil‐water content in the ring's centre is lower than that at its perimeter and matrix. These results are in accord with numerical simulations of a mathematical model for plant species with confined roots grown under highly seasonal rainfalls in water‐limited environments.

R.sim.terrain 1.0: a landscape evolution model with dynamic hydrology

Abstract. While there are numerical landscape evolution models that simulate how steady-state flows of water and sediment reshape topography over long periods of time, r.sim.terrain is the first to simulate short-term topographic change for both steady-state and dynamic flow regimes across a range of spatial scales. This free and open-source Geographic Information Systems (GIS)-based topographic evolution model uses empirical models for soil erosion and a physics-based model for shallow overland water flow and soil erosion to compute short-term topographic change. This model uses either a steady-state or unsteady representation of overland flow to simulate how overland sediment mass flows reshape topography for a range of hydrologic soil erosion regimes based on topographic, land cover, soil, and rainfall parameters. As demonstrated by a case study for the Patterson Branch subwatershed on the Fort Bragg military installation in North Carolina, r.sim.terrain simulates the development of fine-scale morphological features including ephemeral gullies, rills, and hillslopes. Applications include land management, erosion control, landscape planning, and landscape restoration.

Peatland ditch blocking has no effect on dissolved organic matter (DOM) quality

AbstractThe globally widespread drainage of peatlands has often been shown to lead to increased concentrations and fluxes of dissolved organic carbon (DOC) in streams and rivers. Elevated DOC concentrations have implications for carbon cycling, ecosystem functioning, and potable water treatment. Peatland rewetting, principally through ditch blocking, is often carried out with the expectation that this will reduce DOC concentrations. Uncertainty still remains as to whether drainage, or its reversal via ditch blocking, will also lead to changes in the molecular composition of DOC/dissolved organic matter (DOM), which have the potential to affect downstream processing and treatability of U.K. drinking water supplies. To investigate this question, we used a replicated experiment consisting of 12 parallel ditches on an upland bog and took samples of ditch water, pore water, and overland flow water for 4 years. After a brief preblocking baseline period, eight ditches were blocked using two methods. A complementary suite of optical metrics, chemical measurements, and analytical techniques revealed that ditch blocking had no consistent effect on DOM quality, up to 4 years after blocking. Where significant differences were found, effect size calculations demonstrated that these differences were small and would therefore have minimal impact upon water treatability. Furthermore, some differences between ditches were evident before blocking took place, highlighting the need for robust baseline monitoring before intervention. Based on our results from a hillslope‐scale experiment, we were unable to identify clear evidence that peatland ditch blocking will deliver benefits in terms of DOM treatability in potable water supplies, although we also did not find any evidence of short‐term deterioration in water quality during the restoration period. We conclude that, although peatland restoration can be expected to deliver other benefits such as reduced carbon loss and enhanced biodiversity, it is doubtful whether it will lead to improvements in drinking water treatability.

Geodiversity decreases shrub mortality and increases ecosystem tolerance to droughts and climate change

AbstractMass mortality of shrubs, especially the Noaea mucronata species, has been observed in the semi‐arid Negev of Israel since the early twenty‐first century. This has followed a long‐term drought episode, and suggests a hysteresis‐like effect. However, recent studies have revealed that the mortality has been varied across the region. Therefore, we assessed the depth and stoniness of the soil profile, in homogeneous and heterogeneous hillslopes. Then, we studied the volumetric moisture content during two consecutive growing seasons, in the topsoil of shrubby patches and of inter‐shrub spaces in these hillslopes. The study shows that geodiversity – characterized by shallow soil, a high content of stones in the soil, and a high cover of rock fragment on the surface – reduced shrub mortality. This was attributed to the soil moisture content, which was considerably greater in the heterogeneous hillslopes, than that in the homogeneous hillslopes. It is proposed that the shallow soil halted the growth of herbaceous vegetation in the inter‐shrub spaces of the heterogeneous hillslopes. Therefore, under rainstorms, this hillslope configuration results in considerable generation of overland water flow in the inter‐shrub spaces. The water accumulates in the shrubby patches, allowing them to thrive, even during long‐term dry episodes. In hillslopes with a deep soil layer, no stoniness in the soil profile, and no cover of rock fragments, the herbaceous vegetation is well developed, covering a considerable share of the inter‐shrub spaces. This negates runoff formation and source–sink relations, limiting water availability for the shrubs, and resulting in their mass mortality. Despite no direct pastoral value for livestock, the shrubs play an important role in overall ecosystem functioning. This is due to their capacity to transect hydraulic connectivity, and negate ecosystem collapse. We propose a conceptual model for demonstrating the role played by geodiversity in alleviating drought stress in drylands. Copyright © 2018 John Wiley &amp; Sons, Ltd.

Identification of karst sinkholes in a forested karst landscape using airborne laser scanning data and water flow analysis

Karst sinkholes (dolines) play an important role in a karst landscape by controlling infiltration of surficial water, air flow or spatial distribution of solar energy. These landforms also present a limiting factor for human activities in agriculture or construction. Therefore, mapping such geomorphological forms is vital for appropriate landscape management and planning. There are several mapping techniques available; however, their applicability can be reduced in densely forested areas with poor accessibility and visibility of the landforms. In such conditions, airborne laser scanning (ALS) provides means for efficient and accurate mapping of both land and landscape canopy surfaces. Taking the benefits of ALS into account, we present an innovative method for identification and evaluation of karst sinkholes based on numerical water flow modelling. The suggested method was compared to traditional techniques for sinkhole mapping which use topographic maps and digital terrain modelling. The approach based on simulation of a rainfall event very closely matched the reference datasets derived by manual inspection of the ALS digital elevation model and field surveys. However, our process-based approach provides advantage of assessing the magnitude how sinkholes influence concentration of overland water flow during extreme rainfall events. This was performed by calculating the volume of water accumulated in sinkholes during the simulated rainfall. In this way, the influence of particular sinkholes on underground geomorphological systems can be assessed. The method was demonstrated in a case study of Slovak Karst in the West Carpathians where extreme rainfalls or snow-thaw events occur annually. We identified three spatially contiguous groups of sinkholes with a different effect on overland flow concentration. These results are discussed in relation to the known underground hydrological systems.

Use of shrub willows (Salix spp.) to develop soil communities during coal mine restoration

Afforestation or reforestation in highly degraded environments (e.g., surface mines) is often complicated by the total removal of vegetation and severe soil degradation that occurs during mining operations, necessitating revegetation to be undertaken in tandem with the re-establishment of soil developmental processes. Shrub willows (Salix spp.) are effective as colonizer species initiating revegetation dynamics; however, it is unclear if they also serve as nurse plants facilitating the establishment of soil communities such as those of nematodes. We established a study in a former coal mine site in New Brunswick, Canada, to assess whether the presence of willows on otherwise bare, poorly developed soil contributed to nematode community development and to what degree landform design (e.g., slope) may influence these dynamics. Our results demonstrate that willows can facilitate nematode communities at this site, but that slope strongly influences these effects, likely as a consequence of hydrology and overland water flow. These results confirm the beneficial role that willows can play in reforestation of highly degraded environments both for revegetation and for the re-initiation of soil ecosystem processes.

Adapting HYDRUS‐1D to Simulate Overland Flow and Reactive Transport during Sheet Flow Deviations

Core Ideas HYDRUS‐1D code was adapted to solve the diffusion wave equation for overland flow. The modified code can simulate transport and fate of many different kinds of solute. The model can simulate physically nonequilibrium overland flow and transport processes. Surface runoff is commonly described in numerical models using either the diffusion wave or kinematic wave equations, which assume that surface runoff occurs as sheet flow with a uniform depth and velocity across the slope. In reality, overland water flow and transport processes are rarely uniform. Local soil topography, vegetation, and spatial soil heterogeneity control directions and magnitudes of water fluxes. These spatially varying surface characteristics can generate deviations from sheet flow such as physical nonequilibrium flow and transport processes that occur only on a limited fraction of the soil surface. In this study, we first adapted the HYDRUS‐1D model to solve the diffusion wave equation for overland flow at the soil surface. The numerical results obtained by the new model produced an excellent agreement with an analytical solution for the kinematic wave equation. Additional model tests further demonstrated the applicability of the adapted model to simulate the transport and fate of many different solutes (non‐adsorbing tracers, nutrients, pesticides, and microbes) that undergo equilibrium and/or kinetic sorption and desorption and first‐ or zero‐order reactions. HYDRUS‐1D includes a hierarchical series of models of increasing complexity to account for both uniform and physical nonequilibrium flow and transport, e.g., dual‐porosity and dual‐permeability models, up to a dual‐permeability model with immobile water. This same conceptualization was adapted to simulate physical nonequilibrium overland flow and transport at the soil surface. The developed model improves our ability to describe nonequilibrium overland flow and transport processes and our understanding of factors that cause this behavior.

Impact and Mitigation of Nutrient Pollution and Overland Water Flow Change on the Florida Everglades, USA

A subtropical watershed and wetland covering nearly 47,000 km2 in the southeastern United States, the Florida Everglades is a degraded, human-dominated environment. As a unique and important ecosystem, the Everglades provide a variety of important environmental services for society and nature. Over the past century and a half, anthropogenic actions have severely impacted the Everglades by disrupting the natural water flow and causing water pollution. As a result, the native flora and fauna have been displaced, important habitats have been lost, invasive species have become prevalent, and water contaminant concentrations have increased. Accelerating efforts are being made towards preserving the Everglades ecosystem by restoring water flow and improving water quality. To explore this complex and important aquatic ecosystem, we critically review the relevant environmental history, major terrestrial and aquatic characteristics and dynamics, engineered changes to water flow, major sources and impacts of nutrient pollution, trends in system response to pollution and mitigation actions, and recent regulatory efforts driving restoration.

Composition and design of vegetative filter strips instrumental in improving water quality by mass reduction of suspended sediment, nutrients and Escherichia coli in overland flows in eastern escarpment of Mau Forest, Njoro River Watershed, Kenya.

This study assessed the effect of vegetative filter strip (VFS) in removal of suspended sediment (SS), total nitrogen, total phosphorus and Escherichia coli (E. coli) in overland flow to improve receiving water quality standards. Four and half kilograms of cowpat manure was applied to the model pasture 14 m beyond the edge of vegetated filter strip (VFS) comprising 10-m Napier grass draining into 20-m Kikuyu grass (VFS II), 10-m Kikuyu grass draining into 20-m Napier grass (VFS III) and native grass mixture of Couch-Buffel (VFS I-control). Overland flow water samples were collected from the sites at positions 0, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25 and 30 m along the length of VFSs. E. coli removal by Napier grass VFS was on the order of log unit, which provided an important level of protection and reduced surface-flow concentrations of E. coli to below the 200 (CFU 100 mL-1) recommended water quality standards, but not for nutrients and SS. The Napier grass showed highest efficiency (99.6 %), thus outperforming both Kikuyu grass (85.8 %) and Couch-Buffel grasses VFS (67.9 ± 4.2 %) in removing E. coli from overland flow. The low-level efficiency of native Couch-Buffel grasses in reducing E. coli in overland flow was because of preferential flow. Composition and design of VFS was instrumental and could be applied with a high potential of contracting the uncertainty in improving water quality standards through mass reduction of SS, nutrients and E. coli load in watersheds.