Differential water distribution over dune slopes as affected by slope position and microbiotic crust,Negev Desert,Israel

Runoff is one of the main water sources responsible for water redistribution within a given ecosystem. Water redistribution is especially important in arid regions, and may be of great importance on sandy dunes, where the likelihood of runoff is low owing to the high infiltration rates of sand. Redistribution of water may significantly affect plant and animal distribution, and may explain vegetation patterns within an ecosystem. Runoff yield over sandy dune slopes in the western Negev Desert was measured under natural conditions during 1990–1994. The magnitude of runoff yield on different slope sections and on north and south exposures was established. The results demonstrate that while slope position controlled the microbiotic crust cover, crust cover and crust biomass controlled the amounts of runoff obtained. Whereas no runoff was measured on the upper dune sections devoid of crust, only meagre quantities were measured on the midslope sections, characterized by discontinuous crust cover. Substantially larger amounts were, however, obtained at the bottoms of the slopes, characterized by continuous crust cover. North‐facing slopes, usually characterized by a chlorophyll a content of 29–41 mg m⁻², yielded on average 3·2 times more runoff than south‐facing footslopes, characterized by a 17 mg m⁻² chlorophyll a content. Whereas microbiotic crust was found to be responsible for runoff generation, additional water supply owing to runoff may also explain the occurrence of a high biomass crust and the dense vegetation belt at the dune–interdune interface of the northern exposure, where runoff tends to collect. Thus, whereas crust may reduce infiltration in certain habitats, runoff generated by crust may also be responsible for the promotion of crust growth in other habitats. Runoff may also be used to promote vegetation growth at the dune footslopes. The possibility of using runoff to facilitate agroforestry is discussed. Copyright © 1999 John Wiley & Sons, Ltd.     

Runoff‐induced sediment yield over dune slopes in the Negev Desert. 2: Texture,carbonate and organic matter

Runoff‐induced sediments were collected in the Hallamish dune field for four years (1990–1994). Runoff and consequently water‐transported sediments were generated on the dunes owing to the presence of a thin microbiotic crust. These sediments were analysed for their particle‐size distribution and carbonate content. In addition, the organic matter content was calculated by measuring the chlorophyll content within the runoff. The results were compared to the slope parent material, i.e. the crust and the underlying sand, as well as to playa sediments, which are scattered within the Hallamish interdunal areas, and which were previously hypothesized to originate from runoff‐induced sediments. Higher amounts of fines (silt and clay) and carbonate characterize the footslopes in comparison to the midslopes. Intermediate contents of fines (17 per cent) and carbonate (8 per cent) characterized the sediments in comparison to the fines (27 per cent) and carbonate (15 per cent) of the crust and to the fines (4 per cent) and carbonate (4 per cent) of the underlying sand. The runoff‐induced fines and carbonate contents were significantly different from those of the playas, suggesting that the playa flats do not originate from runoff‐induced sediments. The sediments were enriched with organic matter. Organic matter which originates from the crust amounted to 0·3–0·4 per cent as compared to ≤0·1 per cent in the bare sand. Nevertheless, the crust was found to be relatively resilient to water flow. Only 0·1–0·5 per cent of the crust was annually eroded off the slope by water, with south‐facing crusts showing higher resilience than north‐facing crusts. The data may thus assist in the evaluation of the crust's residence time. Copyright © 2001 John Wiley & Sons, Ltd.     

Goat trampling affects plant establishment,runoff and sediment yields over crusted dunes

Mainly attributed to goat and sheep trampling, the sand dunes at the Israeli and the Egyptian sides of the border present contrasting geomorphological conditions. In an attempt to assess the trampling effect upon vegetation, runoff and sediment yield, two pairs of plots and miniplots (each pair contains a trampled plot and a control) were constructed during 1991 and monitored during 1991–1995. In order to assess the impact on vegetation, three pairs of vegetation plots, subjected to light, medium and heavy trampling, were established during 1993 and monitored. In addition, the effect of the micro structures created by the goat hooves (mounds and depressions) were studied in three pairs of plots subjected to medium trampling during 1993 and monitored during 1993–1996. As far as trampling intensity is concerned, the findings indicate an increase in species diversity, density and biomass from the intact crusted surface to the plots subjected to light and medium trampling with a decrease thereafter at the plots subjected to heavy trampling. As for the micro scale, the findings indicate significantly higher plant biomass for the first 2 years at the hooves‐formed mini mounds and mini depressions in comparison to intact crusted surfaces, with no significant difference during the third year. Significantly lower runoff and sediment yields characterized the trampled plots implying a reduction in water redistribution. The data point to the differential effect that trampling has upon plants and soil. While increasing annual plant growth along the slope, it hinders runoff flow to the footslope, negatively affecting water availability for footslope vegetation. Recovery, as also supported by chlorophyll and microrelief measurements, was scale dependent (attributed to differential supply of aeolian sand) with estimated recovery for the plots and miniplots being 4–5 and 8–10 years, respectively. The data indicate that upon the cessation of grazing and under similar precipitation regime, recovery time of the biocrust in the Sinai sand dunes may be short, within 5–6 years. Copyright © 2016 John Wiley & Sons, Ltd.     

Runoff and road erosion at the plot and road segment scales,St John,US Virgin Islands

Previous studies have identified unpaved roads as the primary source of erosion on St John in the US Virgin Islands, but these studies estimated road erosion rates only as annual averages based primarily on road rill measurements. The goal of this project was to quantify the effect of unpaved roads on runoff and sediment production on St John, and to better understand the key controlling factors. To this end runoff and sediment yields were measured from July 1996 to March 1997 from three plots on naturally vegetated hillslopes, four plots on unpaved road surfaces and two cutslope plots. Sediment yields were also measured from seven road segments with contributing areas ranging from 90 to 700 m². With respect to the vegetated plots, only the two largest storm events generated runoff and there was no measurable sediment yield. Runoff from the road surface plots generally occurred when storm precipitation exceeded 6 mm. Sediment yields from the four road surface plots ranged from 0·9 to 15 kg m⁻² a⁻¹, and sediment concentrations were typically 20–80 kg m⁻³. Differences in runoff between the two cutslope plots were consistent with the difference in upslope contributing area. A sprinkler experiment confirmed that cross‐slope roads intercept shallow subsurface stormflow and convert this into surface runoff. At the road segment scale the estimated sediment yields were 0·1 to 7·4 kg m⁻² a⁻¹. Road surface runoff was best predicted by storm precipitation, while sediment yields for at least three of the four road surface plots were significantly correlated with storm rainfall, storm intensity and storm runoff. Sediment yields at the road segment scale were best predicted by road surface area, and sediment yields per unit area were most strongly correlated with road segment slope. The one road segment subjected to heavy traffic and more frequent regrading produced more than twice as much sediment per unit area than comparable segments with no truck traffic. Particle‐size analyses indicate a preferential erosion of fine particles from the road surface and a rapid surface coarsening of new roads. Published in 2001 by John Wiley & Sons, Ltd.     

Effects of different spatial distributions of physical soil crusts on runoff and erosion on the Loess Plateau in China

The response of runoff and erosion to soil crusts has been extensively investigated in recent decades. However, there have been few attempts to look at the effects of spatial configuration of different soil crusts on erosion processes. Here we investigated the effects of different spatial distributions of physical soil crusts on runoff and erosion in the semi‐arid Loess Plateau region. Soil boxes (1.5 m long × 0.2 m wide) were set to a slope of 17.6% (10°) and simulated rainfall of 120 mm h^?1 (60 minutes). The runoff generation and erosion rates were determined for three crust area ratios (depositional crust for 20%, 33%, and 50% of the total slope) and five spatial distribution patterns (depositional crust on the lower, lower‐middle, middle, mid‐upper, and upper slope) of soil crusts. The reduction in sediment loss (‘sediment reduction’) was calculated to evaluate the effects of different spatial distributions of soil crusts on erosion. Sediment yield was influenced by the area ratio and spatial position of different soil crusts. The runoff rate reached a steady state after an initial trend of unsteadily increasing with increasing rainfall duration. Sediment yield was controlled by detachment limitation and then transport limitation under rainfall. The shifting time of erosion from a transport to detachment‐limiting regime decreased with increasing area of depositional crust. No significant differences were observed in the total runoff among treatments, while the total sediment yield varied under different spatial distributions. At the same area ratio, total sediment yield was the largest when the depositional crust was on the upper slope, and it was smallest when the crust was deposited on the lower slope. The sediment reduction of structural crust (42.5–66.5%) was greater than that of depositional crust (16.7–34.3%). These results provide a mechanistic understanding of how different spatial distributions of soil crusts affect runoff and sediment production. Copyright © 2017 John Wiley & Sons, Ltd.     

Runoff and sediment generation on bench‐terraced hillsides: measurements and up‐scaling of a field‐based model

Despite widespread bench‐terracing, stream sediment yields from agricultural hillsides in upland West Java remain high. We studied the causes of this lack of effect by combining measurements at different spatial scales using an erosion process model. Event runoff and sediment yield from two 4‐ha terraced hillside subcatchments were measured and field surveys of land use, bench‐terrace geometry and storage of sediment in the drainage network were conducted for two consecutive years. Runoff was 3·0–3·9% of rainfall and sediment yield was 11–30 t ha⁻¹ yr⁻¹ for different years, subcatchments and calculation techniques. Sediment storage changes in the subcatchment drainage network were less than 2 t ha⁻¹, whereas an additional 0·3–1·5 t ha⁻¹ was stored in the gully between the subcatchment flumes and the main stream. This suggests mean annual sediment delivery ratios of 86–125%, or 80–104% if this additional storage is included. The Terrace Erosion and Sediment Transport (TEST) model developed and validated for the studied environment was parameterized using erosion plot studies, land use surveys and digital terrain analysis to simulate runoff and sediment generation on the terraced hillsides. This resulted in over‐estimates of runoff and under‐estimates of runoff sediment concentration. Relatively poor model performance was attributed to sample bias in the six erosion plots used for model calibration and unaccounted covariance between important terrain attributes such as slope, infiltration capacity, soil conservation works and vegetation cover. Copyright © 2005 John Wiley & Sons, Ltd.     

Runoff generation in a sandy area—the nizzana sands,Western Negev,Israel

This paper presents the results of sprinkling experiments conducted over the lower part of vegetated and crusted linear dunes as well as over flat playa surfaces that appear in the interdune corridors. Data obtained show that these two surface units respond quickly to rainstorms. Runoff generation can be expected for any storm exceeding 2-3 mm and runoff coefficients are high. When the topsoil algal crust, 1 to 2 mm thick, is removed from the surface of the dune, infiltration increases drastically and eliminates any possibility of runoff generation under present-day rainfall conditions. This data may be of great help in the understanding of the geomorphology and sedimentary sequence of the corridors separting linear dunes.     

Compaction and cover effects on runoff and erosion in post-fire salvage logged areas in the Valley Fire,California

Runoff and erosion processes can increase after wildfire and post-fire salvage logging, but little is known about the specific effects of soil compaction and surface cover after post-fire salvage logging activities on these processes. We carried out rainfall simulations after a high-severity wildfire and post-fire salvage logging to assess the effect of compaction (uncompacted or compacted by skid traffic during post-fire salvage logging) and surface cover (bare or covered with logging slash). Runoff after 71 mm of rainfall across two 30-min simulations was similar for the bare plots regardless of the compaction status (mean 33 mm). In comparison, runoff in the slash-covered plots averaged only 22 mm. Rainsplash in the downslope direction averaged 30 g for the bare plots across compaction levels and decreased significantly by 70% on the slash-covered plots. Sediment yield totalled 460 and 818 g m⁻² for the uncompacted and compacted bare plots, respectively, and slash significantly reduced these amounts by an average rate of 71%. Our results showed that soil erosion was still high two years after the high severity burning and the effect of soil compaction nearly doubled soil erosion via nonsignificant increases in runoff and sediment concentration. Antecedent soil moisture (dry or wet) was the dominant factor controlling runoff, while surface cover was the dominant factor for rainsplash and sediment yield. Saturated hydraulic conductivity and interrill erodibility calculated from these rainfall simulations confirmed previous laboratory research and will support hydrologic and erosion modelling efforts related to wildfire and post-fire salvage logging. Covering the soil with slash mitigated runoff and significantly reduced soil erosion, demonstrating the potential of this practise to reduce sediment yield and soil degradation from burned and logged areas.     

Offshore aeolian sediment transport across a human‐modified foredune

Concepts derived from previous studies of offshore winds on natural dunes are evaluated on a dune maintained for shore protection during three offshore wind events. The potential for offshore winds to form a lee‐side eddy on the backshore or transfer sediment from the dune and berm crest to the water are evaluated, as are differences in wind speed and sediment transport on the dune crest, berm crest and a pedestrian access gap. The dune is 18–20 m wide near the base and has a crest 4.5 m above backshore elevation. Two sand‐trapping fences facilitate accretion. Data were obtained from wind vanes on the crest and lee of the dune and anemometers and sand traps placed across the dune, on the beach berm crest and in the access gap. Mean wind direction above the dune crest varied from 11 to 3 deg from shore normal. No persistent recirculation eddy occurred on the 12 deg seaward slope. Wind speed on the berm crest was 85–89% of speed at the dune crest, but rates of sediment transport were 2.27 times greater during the strongest winds, indicating that a wide beach overcomes the transport limitation of a dune barrier. Limited transport on the seaward dune ramp indicates that losses to the water are mostly from the backshore, not the dune. The seaward slope gains sand from the landward slope and dune crest. Sand fences causing accretion on the dune ramp during onshore winds lower the seaward slope and reduce the likelihood of detached flows during offshore winds. Transport rates are higher in access gaps than on the dune crest despite lower wind speeds because of flatter slopes and absence of vegetation. Transport rates across dunes and through gaps can be reduced using vegetation and raised walkover structures. Copyright © 2017 John Wiley & Sons, Ltd.     

EFFECTS OF SOIL CRUSTING ON SOIL MOISTURE, RUNOFF AND EROSION: FIELD OBSERVATIONS

1 INTRODUCTION Soil crusting, or soil sealing, is one of the common phenomena in agricultural lands or semi-arid and arid soils. Due to the breakdown of soil aggregates by raindrops, soil surface develops a very thin, often less than a few millimeters, dense layer. Many studies indicated that such a thin layer significantly reduces infiltration capacity and increases surface runoff (i.e. McIntyre, 1958; Edward and Larson, 1969; Agassi et al., 1985; Bradford et al., 1986; Romkens et al.,…     

Geomorphic and sediment volume responses of a coastal dune complex following invasive vegetation removal

This paper documents application of an established geostatistical methodology to detect significant changes in a foredune–transgressive dune complex where Parks Canada Agency (PCA) implemented a dynamic restoration program to remove invasive marram grasses (Ammophila spp.) and enhance dynamic dune habitat for an endangered species. Detailed topographic surveys of a 10 320 m² site in the Wickaninnish Dunes in Pacific Rim National Park, British Columbia, Canada for the first year post‐treatment are compared to a pre‐restoration LiDAR baseline survey. The method incorporates inherent spatial structure in measured elevation datasets at the sub‐landscape scale and models statistically significant change surfaces within distinct, linked geomorphic units (beach, foredune, transgressive dune complex). Seasonal and annual responses within the complex are discussed and interpreted. All geomorphic units experienced positive sediment budgets following restoration treatment. The beach experienced the highest differential volumetric change (+1656 m³) and net sediment influx (+834 m³, 0 · 19 m³ m^–2) mostly from supply to the supratidal beach and incipient dune. This sediment influx occurred independent of the restoration effort and was available as a buffer against wave erosion and as supply to the landward dunes. The foredune received +200 m³ (0 · 13 m³ m^‐2) and its seaward profile returned to a similar pre‐restoration form following erosion at the crest from vegetation removal and scarping by high water events. Sediment bypassing and minimal change was evident at the mid‐stoss slope with appreciable extension of depositional lobes in the lee. The transgressive dune complex experienced high accretion following restoration activity (+201 m³) and over the year (+284 m³, 0 · 07 m³ m^–2) mostly from depositional lobes from the foredune, precipitation ridge growth along the downwind boundary, and growth of existing lobes within the complex. Further integration of this methodology to detect significant geomorphic changes is recommended, particularly for applications where sampling densities are limited or logistically defined. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of microbiotic crusts under cropland in temperate environments on soil erodibility during concentrated flow

Several studies illustrate the wind and water erosion‐reducing potential of semi‐permanent microbiotic soil crusts in arid and semi‐arid desert environments. In contrast, little is hitherto known on these biological crusts on cropland soils in temperate environments where they are annually destroyed by tillage and quickly regenerate thereafter. This study attempts to fill the research gap through (a) a field survey assessing the occurrence of biological soil crusts on loess‐derived soils in central Belgium in space and time and (b) laboratory flume (2 m long) experiments simulating concentrated runoff on undisturbed topsoil samples (0.4 × 0.1 m²) quantifying the microbiotic crust effect on soil erosion rates. Three stages of microbiotic crust development on cropland soils are distinguished: (1) development of a non‐biological surface seal by raindrop impact, (2) colonization of the soil by algae and gradual development of a continuous algal mat and (3) establishment of a well‐developed microbiotic crust with moss plants as the dominant life‐form. As the silt loam soils in the study area seal quickly after tillage, microbiotic soil crusts are more or less present during a large part of the year under maize, sugar beet and wheat, representing the main cropland area. On average, the early‐successional algae‐dominated crusts of stage 2 reduce soil detachment rates by 37%, whereas the well‐developed moss mat of stage 3 causes an average reduction of 79%. Relative soil detachment rates of soil surfaces with microbiotic crusts compared with bare sealed soil surfaces are shown to decrease exponentially with increasing microbiotic cover (b = 0·024 for moss‐dominated and b = 0·006 for algae‐dominated crusts). In addition to ground surface cover by vegetation and crop residues, microbiotic crust occurrence can therefore not be neglected when modelling small‐scale spatial and temporal variations in soil loss by concentrated flow erosion on cropland soils in temperate environments. Copyright © 2007 John Wiley & Sons, Ltd.     

Contrasting hydrological response of coastal and desert biocrusts

Biocrusts abound in southern Israel, covering the Hallamish dune field near Nizzana (NIZ) in the Negev (mean annual precipitation of 95 mm) and the coast of Nizzanim (NIM) near Ashdod (mean annual precipitation of 500 mm). While the hydrological response of the NIZ crust to natural rain events was thoroughly investigated, no data is available on the hydrological response of the NIM crust. Runoff was monitored in runoff plots during the years 2005–2008, and in addition, sprinkling experiments were carried out on NIM and NIZ crusts. For the evaluation of the possible factors that may control runoff initiation, fine content of the parent material, crust thickness, compressional strength, hydrophobicity, surface microrelief, organic matter, biomass (chlorophyll a and total carbohydrates) and the crust's species composition of NIM were studied and compared to that of NIZ. The data showed that in comparison to the NIZ crust that readily generated runoff, no runoff was produced by the NIM crust. This was so despite the fact that (1) Microculeus vaginatus predominated in both crusts, (2) the substantially higher rain intensities in NIM, (3) the greater thickness and higher chlorophyll content and (4) the lower microrelief at NIM in comparison to NIZ. The lack of runoff in NIM was explained by its low amounts of exopolysaccharides that did not suffice to affectively clog the surface and in turn to facilitate runoff initiation. The absence of runoff and its consequences on the NIM ecosystem are discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

The relative role of constructive and destructive processes in dune evolution on Cape Lookout National Seashore,North Carolina,USA

Coastal dunes are dynamic features that are continuously evolving due to constructive (e.g., wind- and wave-driven sediment transport) and destructive (e.g., elevated total water levels during storm events) processes. However, the relative importance of these processes in determining dune evolution is often poorly understood. In this study, ten lidar datasets from 1997 to 2016 are used to determine the relative role of erosion and accretion processes driving foredune change on the coast of Cape Lookout National Seashore, North Carolina, USA. Beach and dune morphometrics reveal that dune toe locations have generally retreated since 1997, while dune crest heights accreted by 0.01–0.02 m/year. We develop three univariate metrics that represent (1) the potential for erosion, i.e., total water level impact hours per year, (2) accretion, i.e., dune building hours per year, and (3) the relative net effect of foredune accretion and erosion processes, i.e., constructive–destructive dune forcing (CDDF) ratio, and test the correlative power of these metrics in explaining changes in foredune morphology. The total water level impact hours per year metric explained as much as 66% and 67% of the variance in dune crest and toe elevations, respectively, across the nearly two decades of dune evolution. The greatest number of dune building hours per year and largest dunes within the study site co-occurred at locations exposed to the dominant cross-shore wind direction as a result of varying shoreline orientation. The CDDF ratio was positively correlated to changes in the dune toe elevation in approximately 70% of dunes within the study site, outperforming the impact and dune building hours per year metrics. Our results show that these three metrics can provide first-order estimates of dune morphometric change across multiple spatial and temporal scales, which may be particularly useful at sites where lidar acquisition is intermittent.     

Aeolian processes across transverse dunes. II: modelling the sediment transport and profile development

This paper discusses a model which simulates dune development resulting from aeolian saltation transport. The model was developed for application to coastal foredunes, but is also applicable to sandy deserts with transverse dunes. Sediment transport is calculated using published deterministic and empirical relationships, describing the influence of meteorological conditions, topography, sediment characteristics and vegetation. A so-called adaptation length is incorporated to calculate the development of transport equilibrium along the profile. Changes in topography are derived from the predicted transport, using the continuity equation. Vegetation height is incorporated in the model as a dynamic variable. Vegetation can be buried during transport events, which results in important changes in the sediment transport rates. The sediment transport model is dynamically linked to a second-order closure air flow model, which predicts friction velocities over the profile, influenced by topography and surface roughness. Modelling results are shown for (a) the growth and migration of bare, initially sine-shaped dunes, and (b) dune building on a partly vegetated and initially flat surface. Results show that the bare symmetrical dunes change into asymmetric shapes with a slipface on the lee side. This result could only be achieved in combination with the secondorder closure model for the calculation of air flow. The simulations with the partly vegetated surfaces reveal that the resulting dune morphology strongly depends on the value of the adaptation length parameter and on the vegetation height. The latter result implies that the dynamical interaction between aeolian activity and vegetation (reaction to burial, growth rates) is highly relevant in dune geomorphology and deserves much attention in future studies. Copyright © 1999 John Wiley & Sons, Ltd.     

Measuring effectiveness of three postfire hillslope erosion barrier treatments,western Montana,USA

After the Valley Complex Fire burned 86 000 ha in western Montana in 2000, two studies were conducted to determine the effectiveness of contour‐felled log, straw wattle, and hand‐dug contour trench erosion barriers in mitigating postfire runoff and erosion. Sixteen plots were located across a steep, severely burned slope, with a single barrier installed in 12 plots (four per treatment) and four plots left untreated as controls. In a rainfall‐plus‐inflow simulation, 26 mm h^?1 rainfall was applied to each plot for 1 h and 48 L min^?1 of overland flow was added for the last 15 min. Total runoff from the contour‐felled log (0·58 mm) and straw wattle (0·40 mm) plots was significantly less than from the control plots (2·0 mm), but the contour trench plots (1·3 mm) showed no difference. The total sediment yield from the straw wattle plots (0·21 Mg ha^?1) was significantly less than the control plots (2·2 Mg ha^?1); the sediment yields in the contour‐felled log plots (0·58 Mg ha^?1) and the contour trench plots (2·5 Mg ha^?1) were not significantly different. After the simulations, sediment fences were installed to trap sediment eroded by natural rainfall. During the subsequent 3 years, sediment yields from individual events increased significantly with increasing 10 min maximum intensity and rainfall amounts. High‐intensity rainfall occurred early in the study and the erosion barriers were filled with sediment. There were no significant differences in event or annual sediment yields among treated and control plots. In 2001, the overall mean annual sediment yield was 21 Mg ha^?1; this value declined significantly to 0·6 Mg ha^?1 in 2002 and 0·2 Mg ha^?1 in 2003. The erosion barrier sediment storage used was less than the total available storage capacity; runoff and sediment were observed going over the top and around the ends of the barriers even when the barriers were less than half filled. Published in 2007 by John Wiley & Sons, Ltd.     

Field measurements of interrill erosion under ­different slopes and plot sizes

Despite numerous studies, the effect of slope on interrill erosion is not clearly established. Several interactions exist between erosion parameters that are not taken into account under experimental laboratory measurements and results need to be validated in the field. The influence of slope steepness (2 to 8 per cent) on soil loss for a crusted interrill area and the detachment and transport processes involved in the interaction between slope, rain characteristics and plot size were investigated. Sediment discharge and runoff rates were measured in bounded plots (1 m2 and 10 m2) under natural and simulated rainfall, allowing the analysis of a combination of detachment and transport processes at various scales in the field. Runoff rate increased from 20 to 90 per cent with increasing slope and rain intensity for both plot sizes, whereas sediment concentration increased from 2 to 6 g l−1 with increasing slope only for the 10 m2 plots. At the 1 m2 scale, erosion was transport‐limited due to the reduced rain‐impacted flow. Interactions between slope angle and rain intensity were observed for detachment and transport processes in interrill erosion. Results show the importance of an adapted experimental set‐up to get reference data for interrill erosion model development and validation. Copyright © 2000 John Wiley & Sons, Ltd.     

Soil and water losses from new citrus orchards growing on sloped soils in the western Mediterranean basin

Ten representative research sites were selected in eastern Spain to assess soil erosion rates and processes in new citrus orchards on sloping soils. The experimental plots were located at representatives sites on limestone, in areas with 498 to 715 mm year^?1 mean annual rainfall, north‐facing slopes, herbicide treated, and new (less than 3 years old) plantations. Ten rainfall simulation experiments (1 h at 55 mm h^?1 on 0·25 m² plots) were carried out at each of the 10 selected study sites to determine the interill soil erosion and runoff rates. The 100 rainfall simulation tests (10 × 10 m) showed that ponding and runoff occurred in all the plots, and quickly: 121 and 195 s, respectively, following rainfall initiation. Runoff discharge was one third of the rainfall, and sediment concentration reached 10·4 g L^?1. The soil erosion rates were 2·4 Mg ha^?1 h^?1 under 5‐year return period rainfall thunderstorms. These are among the highest soil erosion rates measured in the western Mediterranean basin, similar to badland, mine spoil and road embankment land surfaces. The positive relationship between runoff discharge and sediment concentration (r² = 0·83) shows that the sediment availability is very high. Soil erosion rates on new citrus orchards growing on sloped soils are neither tolerable nor sustainable. Copyright © 2009 John Wiley & Sons, Ltd.     

Aeolian sediment transport and morphologic change on a managed and an unmanaged foredune

Sediment transport and short‐term morphologic change were evaluated at a site where sand fences are deployed and the beach is raked (Managed Site) and a site where these human adjustments are not practiced (Unmanaged Site). Data were gathered across the seaward portion of a low foredune when winds blew nearly shore‐normal at mean speeds 8.9 to 9.3 m s^‐1. Data from traps revealed sediment transport rates at unvegetated portions of the foredune crest (40.2 to 43.5 kg m^‐1 h^‐1) were greater than on the backshore (4.9 to 11.2 kg m^‐1 h^‐1) due to onshore decreases in surface moisture and speed‐up of the wind passing over the foredune. Data from erosion pins indicate sediment input to the dune was 1.48 m³ m^‐1 alongshore at the Managed Site and 1.25 m³ m^‐1 at the Unmanaged Site. The Unmanaged Site had deposition at the dune toe, erosion at mid‐slope, and deposition at the crest. Deposition occurred at mid‐slope on the Managed Site near a partially buried (0.58 m high) fence with a porosity of about 65%. Deposition at partially buried wrack on the upper backshore and dune toe at the Unmanaged Site was about twice as great as deposition in this zone at the Managed Site. Results indicate that: (1) the seaward slope of the foredune can be a more important source of sand to the lee of the crest than the beach; (2) wrack near the toe can decrease transport into the foredune; (3) a scour zone can occur on the foredune slope above the wrack line; (4) a fence placed in this location can promote deposition and offset scour, but fences can restrict delivery of sediment farther inland. Evaluation of alternative configurations of fences and strategies for managing wrack is required to better determine the ways that humans modify foredunes. Copyright © 2012 John Wiley & Sons, Ltd.     

Aeolian sediment transport on a recovering storm‐eroded foredune with sand fences

Studies of sediment transport on developed coasts provide perspective on how human adjustments alter natural processes. Deployment of sand‐trapping fences is a common adjustment that changes the characteristics of the dune ramp and its role in linking sediment transfers from the backshore to the foredune. Fence effects were evaluated in the field using anemometer arrays and vertical sediment traps placed across a beach and dune at Seaside Park, New Jersey, USA during onshore and longshore winds. The foredune is 18 m wide and 4.5 m above the backshore. The mean speed of onshore winds at 0.5 m elevation decreased by 17% from the berm crest to the upper ramp and 36% in the lee of a fence there. Sediment transport during mean wind speeds up to 8.0 m s^?1 at 0.5 m elevation was < 0.06 kg m^?1 h^?1 on the berm crest and backshore where fetch distances were < 45 m and surface sediment was relatively coarse (0.74–0.85 mm) but increased to 5.63 kg m^?1 h^?1 on the upper ramp aided by the longer fetch distances (up to 82 m) and finer grain size of the source sediment there (0.52 mm). Sediment transport along the berm crest and backshore during longshore winds, where fetch distances were > 200 m, was up to 58.69 kg m^?1 h^?1, about three orders of magnitude greater than during the onshore winds. Fences can displace the toe of the ramp farther seaward than would occur under natural conditions. They can create a gentler slope and change the shape of the ramp to a more convex form. A fence on the ramp can cut off a portion of sediment supply to the upper slope. Decisions about fence placement thus should consider these morphologic changes in addition to the effects on dune volume. Copyright © 2017 John Wiley & Sons, Ltd.