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.     

Meso‐scale catchment sediment budgets: combining field surveys and modeling in the Dragonja catchment,southwest Slovenia

In this paper, we present a methodology to construct a sediment budget for meso‐scale catchments. We combine extensive field surveys and expert knowledge of the catchment with a sediment delivery model. The meso‐scale Mediterranean drainage basin of the Dragonja (91 km²), southwest Slovenia, was chosen as case study area. During the field surveys, sheet wash was observed on sloping agricultural fields during numerous rainfall events, which was found to be the main source of sediment. With the sediment yield model WATEM/SEDEM the estimated net erosion on the hillslopes 4·1 t ha^–1 y^–1 (91% of inputs). The second source, bank erosion (4·2%; 0·25 t ha^–1 y^–1) was monitored during several years with erosion pins and photogrammetric techniques. The last source, channel incision, was derived from geomorphological mapping and lichenomery and provided 3·8% (0·17 t ha^–1 y^–1) of the sediment input. The river transports its suspended sediment mainly during high‐flow events (sampled with automated water samplers). About 27% (1·2 t ha^–1 y^–1) of the sediment delivered to the channel is deposited on floodplains and low terraces downstream (estimated with geomorphological mapping, coring and cesium‐137 measurements). The sediment transported as bedload disintegrates during transport to the outlet due to the softness of the bedrock material. As a result, the river carries no bedload when it reaches the sea. The results imply a build‐up of sediment in the valleys catchment. However, extreme flood events may flush large amounts of sediment stored in the lower parts of the system. Geomorphological evidence exists in the catchment that such high magnitude, low frequency events have happened in the past. Copyright © 2009 John Wiley & Sons, Ltd.     

Regional grain size variations in aeolian sediments along the transition between Tibetan highlands and north‐western Chinese deserts – the influence of geomorphological settings on aeolian transport pathways

Sediment distribution is investigated applying grain size analysis to 279 surface samples from the transitional zone between high mountains (Qilian Shan) and their arid forelands (Hexi Corridor) in north‐western China. Six main sediment types were classified. Medium scale (10³ m) geomorphological setting is carefully considered as it may play an important role concerning sediment supply and availability. A tripartite distribution of sedimentological landscape units along the mountain to foreland transition is evident. Aeolian sediments (e.g. loess and dune sands) are widespread. They are used to identify aeolian transport pathways. The mU/fS‐ratio (5–11 µm/48–70 µm) among primary loess opposes the two grain size fractions being most sensitive to varying accumulation conditions. The first fraction is attributed to long‐distance transport in high suspension clouds whereas the latter represents local transport in saltation mode. The ratio shows strong correlation with elevation (R² = 0.77). Thus, it indicates a relatively higher far‐traveled dust supply in mountainous areas (>3000 m above sea level [a.s.l.]) compared to the foreland. The contribution of westerlies to high mountain loess deposits is considered likely. Hereby, the influence of the geomorphological setting on grain size composition of aeolian sediments becomes apparent: the contribution from distant dust sources is ubiquitous in the study area. However, the far‐distance contribution may be reduced by the availability of fine sand provided in low topography settings. Plain foreland areas support fine sand deflation from supplying river beds, allowing the formation of sandy loess in foreland areas and intramontane basins. In contrast, high mountain topography inhibits strong sand deflation into loess deposits. Eastern parts of the Hexi Corridor show higher aeolian sand occurrence. In contrast, the western parts are dominated by gravel gobi surfaces. This is attributed to higher sand supply in eastern parts provided by the Badain Jaran Desert and fluvial storages as sand sources. Copyright © 2014 John Wiley & Sons, Ltd.     

Sedimentologically significant tributaries: catchment‐scale controls on sediment (dis)connectivity in the Lockyer Valley,SEQ, Australia

The nature of catchment‐scale sediment (dis)connectivity is the primary influence on sediment delivery to trunk streams and controls the particle size distribution of channel bed sediments. Here, we examine the distribution of major sediment buffers (floodplains, terraces, alluvial fans, trapped tributary fills), barriers (weirs), and effective catchment area (i.e. sediment contributing area) to characterize the potential for coarse sediment (dis)connectivity in 20 tributaries of Lockyer Creek, in the Lockyer Valley, SEQ. We then analyse the distribution of trunk stream sedimentary links to determine how certain tributaries or disconnecting features (buffers and barriers) influence downstream patterns of bed sediment fining along Lockyer Creek. We find that buffering increases downstream in the Lockyer Valley, and that tributary position and shape influence the space available for sediment buffering. Correspondingly, the spatial extent of sediment buffers impacts the distribution of effective catchment area, which influences the sedimentological significance of individual tributaries. Tributary sediment connectivity, the extent of overbank flows (floodwater zones), and weir locations all exert an additional influence on the distribution of sediment links along the trunk stream. These controls are related to the physiographic and climatic setting of the Lockyer Valley, and anthropogenic influences in this system. We conclude that controls on sediment connectivity and bed load sediment characteristics are highly variable between catchments, and that sediment (dis)connectivity merits equal consideration with tributary basin/channel size when determining controls on tributary–trunk stream relationships and channel sediment regime. Copyright © 2017 John Wiley & Sons, Ltd.     

Seismic hazard in Buenos Aires,Argentina: A preliminary study on the effects of long‐distance earthquakes on tall buildings

The 2015 Illapel earthquake produced self‐evacuation of tall buildings in the city of Buenos Aires, Argentina, located 1280 km away from the epicenter. The ground motions in Buenos Aires due to the main event (M_w 8.3) and its aftershocks were registered by a new seismometer. The data collected allowed to estimate the maximum story drift ratios and top floor accelerations for tall buildings in Buenos Aires. The similarities between the response spectra and the Fourier amplitude spectra for the mainshock and its aftershocks show the influence that the dynamic properties of the 300‐m soil deposit have on the large acceleration amplification produced in these groups of buildings.     

Impact of wind on the spatial distribution of rain over micro‐scale topography: numerical modelling and experimental verification

The wind‐driven‐rain effect refers to the redistribution of rainfall over micro‐scale topography due to the existence of local perturbed wind‐flow patterns. Rainfall measurements reported in the literature point to the fact that the wind‐driven‐rain distribution can show large variations over micro‐scale topography. These variations should be taken into account in hillslope hydrology, in runoff and erosion studies and in the design of rainfall monitoring networks. In practice, measurements are often not suitable for determining the wind‐driven‐rain distribution. Therefore, a few researchers have employed numerical modelling. In order to provide confidence in using numerical models, experimental verification for a range of different topographic features is imperative. The objective of this study is to investigate the adequacy of a two‐dimensional Computational Fluid Dynamics (CFD) model to predict the wind‐driven‐rain distribution over small‐scale topography. The numerical model is applied to a number of topographic features, including a succession of cliffs, a small isolated hill, a small valley and a field with ridges and furrows. The numerical results are compared with the corresponding measurement results reported in the literature. It is shown that two‐dimensional numerical modelling can provide a good indication of the wind‐driven‐rain distribution over each type of micro‐scale topography that is considered in this study. It is concluded that more detailed verification procedures are currently inhibited due to the lack of available and detailed spatial and temporal rainfall data from field measurements. Copyright © 2005 John Wiley & Sons, Ltd.     

Investigating the use of spatial discretization of hydrological processes in conceptual rainfall runoff modelling: a case study for the meso‐scale

In this study a simple modelling approach was applied to identify the need for spatial complexity in representing hydrological processes and their variability over different scales. A data set of 18 basins was used, ranging between 8 and 4011 km² in area, located in the Nahe basin (Germany), with daily discharge values for over 30 years. Two different parsimoniously structured models were applied in lumped as well as in spatially distributed according to two distribution classifications: (1) a simple classification based on the lithology expressed in three permeability types and (2) a more complex classification based on seven dominating runoff production processes. The objective of the study was to compare the performances of the models on a local and on a regional scale as well as between the models with a view to identifying the accuracy in capturing the spatial variability of the rainfall‐runoff relationships. It was shown that the presence of a specific basin characteristic or process of the distribution classification was not related with higher model performance; only a larger basin size promoted higher model performance. The results of this study also indicated that the permeability generally contained more useful information on the spatial heterogeneity of the hydrological behaviour of the natural system than did a more detailed classification on dominating runoff generation processes. Although model performance was slightly lower for the model that used permeability as a distribution classification, consistency in its parameter values was found, which was lacking with the more complex distribution classification. The latter distribution classification had a higher flexibility to optimize towards the variability of the runoff, which resulted in higher performance, however, process representation was applied inconsistently. Copyright © 2007 John Wiley & Sons, Ltd.     

Rill length and plot‐scale effects on the hydrogeomorphologic response of gravelly roadbeds

Although unpaved roads are well‐recognized as important sources of Hortonian overland flow and sediment in forested areas, their role in agriculturally‐active rural settings still lacks adequate documentation. In this study, we assessed the effect of micro‐catchment size, slope, and ground cover on runoff and sediment generation from graveled roadbeds servicing a rural area in southern Brazil. Fifteen replications based on 30‐min‐long simulated rainfall experiments were performed at constant rainfall intensities of 22–58 mm h^?1 on roadbeds with varying characteristics including ~3–7 m² micro‐catchment areas, 2–11° slopes, 2–9.7‐m‐long shallow rill features, and 30–100% gravel cover. The contributions of micro‐catchment size and rill length were the most important physical characteristics affecting runoff response and sediment production; both the size of the micro‐catchment and the length of the rills were inversely related to sediment loss and this contradicts most of the rill erosion literature. The effect of micro‐catchment size on runoff and sediment response suggests a potentially problematic spatial‐scale subjectivity of experimental plot results. The inverse relationship between rill length and sediment generation is interpreted here as related to the predominance of coarse fragments within rills, the inability of the shallow flows generated during the simulations to erode this sediment, and their role as zones of net sediment storage. Copyright © 2015 John Wiley & Sons, Ltd.     

Inter‐annual variability in the effects of riparian woodland on micro‐climate,energy exchanges and water temperature of an upland Scottish stream

The influence of riparian woodland on stream temperature, micro‐climate and energy exchange was investigated over seven calendar years. Continuous data were collected from two reaches of the Girnock Burn (a tributary of the Aberdeenshire Dee, Scotland) with contrasting land use characteristics: (1) semi‐natural riparian forest and (2) open moorland. In the moorland reach, wind speed and energy fluxes (especially net radiation, latent heat and sensible heat) varied considerably between years because of variable riparian micro‐climate coupled strongly to prevailing meteorological conditions. In the forested reach, riparian vegetation sheltered the stream from meteorological conditions that produced a moderated micro‐climate and thus energy exchange conditions, which were relatively stable between years. Net energy gains (losses) in spring and summer (autumn and winter) were typically greater in the moorland than the forest. However, when particularly high latent heat loss or low net radiation gain occurred in the moorland, net energy gain (loss) was less than that in the forest during the spring and summer (autumn and winter) months. Spring and summer water temperature was typically cooler in the forest and characterised by less inter‐annual variability due to reduced, more inter‐annually stable energy gain in the forested reach. The effect of riparian vegetation on autumn and winter water temperature dynamics was less clear because of the confounding effects of reach‐scale inflows of thermally stable groundwater in the moorland reach, which strongly influenced the local heat budget. These findings provide new insights as to the hydrometeorological conditions under which semi‐natural riparian forest may be effective in mitigating river thermal variability, notably peaks, under present and future climates. © 2014 The Authors. Hydrological Processes published by John Wiley & Sons Ltd.     

Hydrological effects of water reservoirs on hydrological processes in the East River (China) basin: complexity evaluations based on the multi‐scale entropy analysis

Using the multi‐scale entropy analysis (MSE), we study the effects of water reservoirs on the river flow records based on long streamflow series covering January 1, 1954 and December 31, 2009 at four representative hydrological stations, i.e. the Longchuan, the Heyuan, the Lingxia and the Boluo stations. Hydrological effects of two major water reservoirs, the Xinfengjiang and the Fengshuba water reservoirs, are evaluated. The results indicate that: (1) before the construction of the water reservoirs, the complexity of the streamflow series comes to be decreasing from the upper to the lower East River and which should be attributed to the topographical properties and buffering effects of the river channel; (2) construction of water reservoirs greatly increases the complexity degree of the hydrological processes, and this influence is subjected to a damping process with the increase of distance between the water reservoirs and the hydrological stations; (3) power generation is the major function of the water reservoirs in the East River basin. The results of this study should be of theoretical and scientific merits in terms of conservation of the ecological environment and also water resources management under the influences of climate changes and intensifying human activities. Copyright © 2011 John Wiley & Sons, Ltd.     

Controls on the aerodynamic roughness length and the grain‐size dependence of aeolian sediment transport

Estimates of the wind shear stress exerted on Earth's surface using the fully rough form of the law‐of‐the‐wall are a function of the aerodynamic roughness length, z₀. Accurate prediction of aeolian sediment transport rates, therefore, often requires accurate estimates of z₀. The value of z₀ is determined by the surface roughness and the saltation intensity, both of which can be highly dynamic. Here we report field measurements of z₀ values derived from velocity profiles measured over an evolving topography (i.e. sand ripples). The topography was measured by terrestrial laser scanning and the saltation intensity was measured using a disdrometer. By measuring the topographic evolution and saltation intensity simultaneously and using available formulae to estimate the topographic contribution to z₀, we isolated the contribution of saltation intensity to z₀ and document that this component dominates over the topographic component for all but the lowest shear velocities. Our measurements indicate that the increase in z₀ during periods of saltation is approximately one to two orders of magnitude greater than the increase attributed to microtopography (i.e. evolving sand ripples). Our results also reveal differences in transport as a function of grain size. Each grain‐size fraction exhibited a different dependence on shear velocity, with the saltation intensity of fine particles (diameters ranging from 0.125 to 0.25 mm) saturating and eventually decreasing at high shear velocities, which we interpret to be the result of a limitation in the supply of fine particles from the bed at high shear velocities due to bed armoring. Our findings improve knowledge of the controls on the aerodynamic roughness length and the grain‐size dependence of aeolian sediment transport. The results should contribute to the development of improved sediment transport and dust emission models. © 2018 John Wiley & Sons, Ltd.     

Soil detachment and transport on field‐ and laboratory‐scale interrill areas: erosion processes and the size‐selectivity of eroded sediment

Field‐ and laboratory‐scale rainfall simulation experiments were carried out in an investigation of the temporal variability of erosion processes on interrill areas, and the effects of such variation upon sediment size characteristics. Poorly aggregated sandy soils from the semi‐arid environment of Senegal, West Africa, were used on both a 40 m² field plot and a 0·25 m² laboratory plot; rainfall intensity for all experiments was 70 mm h^?1 with a duration of 1 to 2 hours. Time‐series measurements were made of the quantity and the size distribution of eroded material: these permitted an estimate of the changing temporal balance between the main erosion processes (splash and wash). Results from both spatial scales showed a similar temporal pattern of runoff generation and sediment concentration. For both spatial scales, the dominant erosional process was detachment by raindrops; this resulted in a dynamic evolution of the soil surface under raindrop impact, with the rapid formation of a sieving crust followed by an erosion crust. However, a clear difference was observed between the two scales regarding the size of particles detached by both splash and wash. While all measured values were lower than the mean weight diameter (MWD) value of the original soil (mean 0·32 mm), demonstrating the size‐selective nature of wash and splash processes, the MWD values of washed and splashed particles at the field scale ranged from 0·08 to 0·16 mm and from 0·12 to 0·30 mm respectively, whereas the MWD values of washed and splashed particles at the laboratory scale ranged from 0·13 to 0·29 mm and from 0·21 to 0·32 mm respectively. Thus only at the field scale were the soil particles detached by splash notably coarser than those transported by wash. This suggests a transport‐limited erosion process at the field scale. Differences were also observed between the dynamics of the soil loss by wash at the two scales, since results showed wider scatter in the field compared to the laboratory experiments. This scatter is probably related to the change in soil surface characteristics due to the size‐selectivity of the erosion processes at this spatial scale. Copyright © 2006 John Wiley & Sons, Ltd.     

Semi‐empirical model for site effects on acceleration time histories at soft‐soil sites. Part 1: formulation and development

A criterion is developed for the simulation of realistic artificial ground motion histories at soft‐soil sites, corresponding to a detailed ground motion record at a reference firm‐ground site. A complex transfer function is defined as the Fourier transform of the ground acceleration time history at the soft‐soil site divided by the Fourier transform of the acceleration record at the firm‐ground site. Working with both the real and the imaginary components of the transfer function, and not only with its modulus, serves to keep the statistical information about the wave phases (and, therefore, about the time variation of amplitudes and frequencies) in the algorithm used to generate the artificial records. Samples of these transfer functions, associated with a given pair of soft‐soil and firm‐ground sites, are empirically determined from the corresponding pairs of simultaneous records. Each function included in a sample is represented as the superposition of the transfer functions of the responses of a number of oscillators. This formulation is intended to account for the contributions of trains of waves following different patterns in the vicinity of both sites. The properties of the oscillators play the role of parameters of the transfer functions. They vary from one seismic event to another. Part of the variation is systematic, and can be explained in terms of the influence of ground motion intensity on the effective values of stiffness and damping of the artificial oscillators. Another part has random nature; it reflects the random characteristics of the wave propagation patterns associated with the different events. The semi‐empirical model proposed recognizes both types of variation. The influence of intensity is estimated by means of a conventional one‐dimensional shear wave propagation model. This model is used to derive an intensity‐dependent modification of the values of the empirically determined model parameters in those cases when the firm‐ground earthquake intensity used to determine these parameters differs from that corresponding to the seismic event for which the simulated records are to be obtained. Copyright © 2004 John Wiley & Sons, Ltd.     

Large‐scale sediment bodies and superimposed bedforms on the continental shelf close to the Strait of Gibraltar: interplay of complex oceanographic conditions and physiographic constraints

A previously unknown field of large‐scale sedimentary bodies has been mapped and studied on the continental shelf off the Cape Trafalgar near the Strait of Gibraltar with particular emphasis on the relationship between large‐scale sediment bodies and the superimposed bedforms. This study is based on a grid of 975 km of high‐resolution seismic profiles collected at water depths ranging between 15 and 60 m. High variability of large‐scale sedimentary bodies is attributed to the complex interaction of hydrodynamic agents. The most prominent sedimentary features are sand banks and ridges that indicate long‐term southwest and southward‐directed sediment transport patterns, possibly due to the interplay of two dominant current systems flowing southward and westward. These sediment bodies evolve laterally to distinct external geometries, such as sand shoals in shallow water and sand sheets in the vicinity of larger sand banks that indicate moderate current velocities. In addition, pre‐existing physiography is considered to play a role in the generation of certain sediment bodies, developed over inclined surfaces or confined laterally by elevations. Relationships between superimposed bedforms (mostly very large dunes) and underlying sediment bodies vary across the study area. Most superimposed bedforms occur over the complex mosaic of sediment banks and sheets, suggesting the interaction of several high‐energy currents with different directions, such as tidal and/or wind‐driven currents. Copyright © 2010 John Wiley & Sons, Ltd.     

A macro‐element model for non‐linear soil–shallow foundation–structure interaction under seismic loads: theoretical development and experimental validation on large scale tests

In this paper, different formulations of a macro‐element model for non‐linear dynamic soil‐structure interaction analyses of structures lying on shallow foundations are first reviewed, and secondly, a novel formulation is introduced, which combines some of the characteristics of previous approaches with several additional features. This macro‐element allows one to model soil‐footing geometric (uplift) and material (soil plasticity) non‐linearities that are coupled through a stiffness degradation model. Footing uplift is introduced by a simple non‐linear elastic model based on the concept of effective foundation width, whereas soil plasticity is treated by means of a bounding surface approach in which a vertical load mapping rule is implemented. This mapping is particularly suited for the seismic loading case for which the proposed model has been conceived. The new macro‐element is subsequently validated using cyclic and dynamic large‐scale laboratory tests of shallow foundations on dense sand, namely: the TRISEE cyclic tests, the Public Works Research Institute and CAMUS IV shaking table tests. Based on this comprehensive validation process against a set of independent experimental results, a unique set of macro‐element parameters for shallow foundations on dense sand is proposed, which can be used to perform predictive analyses by means of the present model. Copyright © 2011 John Wiley & Sons, Ltd.     

Groundwater ‐ the disregarded component in lake water and nutrient budgets. Part 1: effects of groundwater on hydrology

Lake eutrophication is a large and growing problem in many parts of the world, commonly due to anthropogenic sources of nutrients. Improved quantification of nutrient inputs is required to address this problem, including better determination of exchanges between groundwater and lakes. This first of a two‐part review provides a brief history of the evolution of the study of groundwater exchange with lakes, followed by a listing of the most commonly used methods for quantifying this exchange. Rates of exchange between lakes and groundwater compiled from the literature are statistically summarized for both exfiltration (flow from groundwater to a lake) and infiltration (flow from a lake to groundwater), including per cent contribution of groundwater to lake‐water budgets. Reported rates of exchange between groundwater and lakes span more than five orders of magnitude. Median exfiltration is 0.74 cm/day, and median infiltration is 0.60 cm/day. Exfiltration ranges from near 0% to 94% of input terms in lake‐water budgets, and infiltration ranges from near 0% to 91% of loss terms. Median values for exfiltration and infiltration as percentages of input and loss terms of lake‐water budgets are 25% and 35%, respectively. Quantification of the groundwater term is somewhat method dependent, indicating that calculating the groundwater component with multiple methods can provide a better understanding of the accuracy of estimates. The importance of exfiltration to a lake budget ranges widely for lakes less than about 100 ha in area but generally decreases with increasing lake area, particularly for lakes that exceed 100 ha in area. No such relation is evident for lakes where infiltration occurs, perhaps because of the smaller sample size. Copyright © 2014 John Wiley & Sons, Ltd.     

Investigation of the relationship between runoff and atmospheric oscillations,sea surface temperature,and local‐scale climate variables in the Yellow River headwaters region

The Yellow River headwaters region (YRHR) contributes nearly 40% of total flow in the Yellow River basin, which is suffering from a serious water shortage problem. Investigation of the relationship between runoff and climate variables is important for understanding the variation trend of runoff in the YRHR under global climate change. Global and local climate variables, including the West Pacific subtropical high; northern hemisphere polar vortex (NH); Tibetan Plateau Index B (TPI‐B); southern oscillation index; sea surface temperature; and precipitation, evaporation, and temperature, were fully considered to explore the relationship with runoff at Jimai, Maqu, and Tangnaihai stations from 1956 to 2014. The results reveal that runoff had a decreasing trend, which will likely be maintained in the future, and there was a significant change in runoff around 1995 at all stations. Correlation analysis indicated that runoff was dominated by precipitation, NH, temperature, and TPI‐B, and a substantial correlation was observed with sea surface temperature and evaporation, but there was little correlation with West Pacific subtropical high and southern oscillation index. Furthermore, impacts of climate change on runoff variations were distinctly different at different temporal scales. Three dominant runoff periodicities were identified by a singular spectrum analysis‐multitaper method and continuous wavelet transform, that is, 1.0‐, 6.9‐, and 24.8‐year runoff periodicities. In addition, runoff was positively correlated with temperature at a 1‐year periodicity, negatively correlated with TPI‐B at a 6.9‐year periodicity, and positively correlated with NH at a 24.8‐year periodicity, that is, temperature, TPI‐B, and NH‐controlled runoff at annual, interannual, and interdecadal scales. Further, all analyses of the stations in the YRHR showed excellent consistency. The results will provide valuable information for water resource management in the YRHR.     

Long‐term effects of management practices on water‐driven soil erosion in an intense agricultural sub‐watershed: monitoring and modelling

The overarching objective of this research was to provide an improved understanding of the role of land use and associated management practices on long‐term water‐driven soil erosion in small agricultural watersheds by coupling the established, physically based, distributed parameter Water Erosion Prediction Project (WEPP) model with long‐term hydrologic, land use and soil data. A key step towards achieving this objective was the development of a detailed methodology for model calibration using physical ranges of key governing parameters such as effective hydraulic conductivity, critical hydraulic shear stress and rill/inter‐rill erodibilities. The physical ranges for these governing parameters were obtained based on in situ observations within the South Amana Sub‐Watershed (SASW) (～26 km²) of the Clear Creek, IA watershed where detailed documentation of the different land uses was available for a period of nearly 100 years. A quasi validation of the calibrated model was conducted through long‐term field estimates of water and sediment discharge at the outlet of SASW and also by comparing the results with data reported in the literature for other Iowa watersheds exhibiting similar biogeochemical properties. Once WEPP was verified, ‘thought experiments’ were conducted to test our hypothesis that land use and associated management practices may be the major control of long‐term erosion in small agricultural watersheds such as SASW. Those experiments were performed using the dominant 2‐year crop rotations in the SASW, namely, fall till corn–no till bean (FTC‐NTB), no till bean–spring till corn (NTB‐STC) and no till corn–fall till bean (NTC‐FTB), which comprised approximately 90% of the total acreage in SASW. Results of this study showed that for all crop rotations, a strong correspondence existed between soil erosion rates and high‐magnitude precipitation events during the period of mid‐April and late July, as expected. The magnitude of this correspondence, however, was strongly affected by the crop rotation characteristics, such as canopy/residue cover provided by the crop, and the type and associated timing of tillage. Tillage type (i.e. primary and secondary tillages) affected the roughness of the soil surface and resulted in increases of the rill/inter‐rill erodibilities up to 35% and 300%, respectively. Particularly, the NTC‐FTB crop rotation, being the most intense land use in terms of tillage operations, caused the highest average annual erosion rate within the SASW, yielding quadrupled erosion rates comparatively to NTB‐STC. The impacts of tillage operation were further exacerbated by the timing of the operations in relation to precipitation events. Timing of operations affected the ‘life‐time’ of residue cover and as a result, the degree of protection that residue cover offers against the water action on the soil surface. In the case of NTC‐FTB crop rotation, dense corn residue stayed on the ground for only 40 days, whereas for the other two rotations, corn residue provided a protective layer for nearly 7 months, lessening thus the degree of soil erosion. The cumulative effects of tillage type and timing in conjunction with canopy/residue cover led to the conclusion that land management practices can significantly amplify or deamplify the impact of precipitation on long‐term soil erosion in small agricultural watersheds. Copyright © 2009 John Wiley & Sons, Ltd.     

Testing the influence of topography and material properties on catchment‐scale soil moisture patterns using remotely sensed vegetation patterns in a humid temperate catchment,northern Britain

In order to evaluate the relationship between the apparent complexity of hillslope soil moisture and the emergent patterns of catchment hydrological behaviour and water quality, we need fine‐resolution catchment‐wide data on soil moisture characteristics. This study proposes a methodology whereby vegetation patterns obtained from high‐resolution orthorectified aerial photographs are used as an indicator of soil moisture characteristics. This enables us to examine a set of hypotheses regarding what drives the spatial patterns of soil moisture at the catchment scale (material properties or topography). We find that the pattern of Juncus effusus vegetation is controlled largely by topography and mediated by the catchment's material properties. Characterizing topography using the topographic index adds value to the soil moisture predictions relative to slope or upslope contributing area (UCA). However, these predictions depart from the observed soil moisture patterns at very steep slopes or low UCAs. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of depression storage capacity on overland‐flow generation for rough horizontal surfaces: water transfer distance and scaling

Overland‐flow triggering on rough surfaces was investigated using an understanding‐oriented model. The model was based on conditioned‐walker technique and developed to simulate and analyse the evolution of puddle connection on numerically generated rough surfaces. The percolation theory gave a theoretical framework to formalize model outputs and to study overland‐flow scaling. Overland‐flow triggering appeared consistent with a percolation process. A scale‐change exponent was suggested. New insights based on the concept of transfer distance of water were emphasized. Transfer distance enabled us to analyse the water redistribution inside a field and helped to define rainfall efficiency when infiltration occurred. Copyright © 2002 John Wiley & Sons, Ltd.