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1.
To provide coastal engineers and scientists with a quantitative evaluation of nearshore numerical wave models in reef environments, we review and compare three commonly used models with detailed laboratory observations. These models are the following: (1) SWASH (Simulating WAves till SHore) (Zijlema et al. 2011), a phase-resolving nonlinear shallow-water wave model with added nonhydrostatic terms; (2) SWAN (Simulating WAve Nearshore) (Booij et al. 1999), a phase-averaged spectral wave model; and (3) XBeach (Roelvink et al. 2009), a coupled phase-averaged spectral wave model (applied to modeling sea-swell waves) and a nonlinear shallow-water model (applied to modeling infragravity waves). A quantitative assessment was made of each model’s ability to predict sea-swell (SS) wave height, infragravity (IG) wave height, wave spectra, and wave setup ( \( \overline{\eta} \) ) at five locations across the laboratory fringing reef profile of Demirbilek et al. (2007). Simulations were performed with the “recommended” empirical coefficients as documented for each model, and then the key wave-breaking parameter for each model (α in SWASH and γ in both SWAN and XBeach) was optimized to most accurately reproduce the observations. SWASH, SWAN, and XBeach were found to be capable of predicting SS wave height variations across the steep fringing reef profile with reasonable accuracy using the default coefficients. Nevertheless, tuning of the key wave-breaking parameter improved the accuracy of each model’s predictions. SWASH and XBeach were also able to predict IG wave height and spectral transformation. Although SWAN was capable of modeling the SS wave height, in its current form, it was not capable of modeling the spectral transformation into lower frequencies, as evident in the underprediction of the low-frequency waves.  相似文献   

2.
Under natural conditions, barrier islands might grow vertically and migrate onshore under the influence of long‐term sea level rise. Sediment is transported onshore during storm‐induced overwash and inundation. However, on many Dutch Wadden Islands, dune openings are closed off by artificial sand‐drift dikes that prevent the influx of sediment during storms. It has been argued that creating openings in the dune row to allow regular flooding on barrier islands can have a positive effect on the sediment budget, but the dominant hydrodynamic processes and their influence on sediment transport during overwash and inundation are unknown. Here, we present an XBeach model study to investigate how sediment transport during overwash and inundation across the beach of a typical mesotidal Wadden Sea barrier island is influenced by wave, tide and storm surge conditions. Firstly, we validated the model XBeach with field data on waves and currents during island inundation. In general, the XBeach model performed well. Secondly, we studied the long‐term sediment transport across the barrier island. We distinguished six representative inundation classes, ranging from frequently occurring, low‐energy events to infrequent, high‐energy events, and simulated the hydrodynamics and sediment transport during these events. An analysis of the model simulations shows that larger storm events cause larger cross‐shore sediment transport, but the net sediment exchange during a storm levels off or even becomes smaller for the largest inundation classes because it is counteracted by larger mean water levels in the Wadden Sea that oppose or even reverse sediment transport during inundation. When taking into account the frequency of occurrence of storms we conclude that the cumulative effect of relatively mild storms on long‐term cross‐shore sediment transport is much larger than that of the large storm events. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

3.
This study analyses beach morphological change during six consecutive storms acting on the meso‐tidal Faro Beach (south Portugal) between 15 December 2009 and 7 January 2010. Morphological change of the sub‐aerial beach profile was monitored through frequent topographic surveys across 11 transects. Measurements of the surf/swash zone dimensions, nearshore bar dynamics, and wave run‐up were extracted from time averaged and timestack coastal images, and wave and tidal data were obtained from offshore stations. All the information combined suggests that during consecutive storm events, the antecedent morphological state can initially be the dominant controlling factor of beach response; while the hydrodynamic forcing, and especially the tide and surge levels, become more important during the later stages of a storm period. The dataset also reveals the dynamic nature of steep‐sloping beaches, since sub‐aerial beach volume reductions up to 30 m3/m were followed by intertidal area recovery (–2 < z < 3 m) with rates reaching ~10 m3/m. However, the observed cumulative dune erosion and profile pivoting imply that storms, even of regular intensity, can have a dramatic impact when they occur in groups. Nearshore bars seemed to respond to temporal scales more related to storm sequences than to individual events. The formation of a prominent crescentic offshore bar at ~200 m from the shoreline appeared to reverse the previous offshore migration trend of the inner bar, which was gradually shifted close to the seaward swash zone boundary. The partially understood nearshore bar processes appeared to be critical for storm wave attenuation in the surf zone; and were considered mainly responsible for the poor interpretation of the observed beach behaviour on the grounds of standard, non‐dimensional, morphological parameters. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

4.
The southwest coast of England was subjected to an unusually energetic sequence of Atlantic storms during the 2013/2014 winter, with the 8‐week period from mid‐December to mid‐February representing the most energetic period since at least 1953. A regional analysis of the hydrodynamic forcing and morphological response of these storms along the SW coast of England highlighted the importance of both storm‐ and site‐specific conditions. The key factor that controls the Atlantic storm wave conditions along the south coast of southwest England is the storm track. Energetic inshore wave conditions along this coast require a relatively southward storm track which enables offshore waves to propagate up the English Channel relatively unimpeded. The timing of the storm in relation to the tidal stage is also important, and coastal impacts along the macro‐tidal southwest coast of England are maximised when the peak storm waves coincide with spring high tide. The role of storm surge is limited and rarely exceeds 1 m. The geomorphic storm response along the southwest coast of England displayed considerable spatial variability; this is mainly attributed to the embayed nature of the coastline and the associated variability in coastal orientation. On west‐facing beaches typical of the north coast, the westerly Atlantic storm waves approached the coastline shore‐parallel, and the prevailing storm response was offshore sediment transport. Many of these north coast beaches experienced extensive beach and dune erosion, and some of the beaches were completely stripped of sediment, exposing a rocky shore platform. On the south coast, the westerly Atlantic storm waves refract and diffract to become southerly inshore storm waves and for the southeast‐facing beaches this results in large incident wave angles and strong eastward littoral drift. Many south coast beaches exhibited rotation, with the western part of the beaches eroding and the eastern part accreting. © 2015 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

5.
Deposits of late‐Holocene beach sand buried conifer forests episodically emerge on beaches of the Oregon coast. Simultaneously, sand dunes buried late‐Holocene forests growing on marine terraces landward of the beaches. Dune ramps, up to 60 m in elevation, connected the beach and dune deposits. The average age of wood samples from stumps rooted on the shore platforms is 3·07 ± 1·45 ka. The average age of wood and charcoal samples embedded in forest soil on the marine terraces is 3·27 ± 1·46 ka. Between 1994 and 2006, winter storm waves exposed more than 4·5 km2 of late‐Holocene forest soil on shore platforms at 19 localities. Rooted stumps without soil were uncovered at an additional 14 localities. Once exposed, wave action eroded the soil rapidly (one to two years). The intact forest soil and roots on the shore platforms must have been nearly continuously buried, protected and preserved prior to recent exposure. The late‐Holocene buried forest provides the basis for a conceptual model of coastal evolution. A three stage reversal of erosion and sand supply must have occurred: (1) wave erosion switched to seaward advancement of forests, (2) forest growth and soil development switched to burial beneath beach and dune sand and (3) burial and preservation switched to wave erosion, truncation of dune ramps and landward retreat of sea cliffs. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

6.
The present work deals with storm classification, using the Storm Power Index, and beach morphological response to storm events in the Gulf of Cadiz (SW Spain). Over the 1958–2001 period, 377 events divided into five classes ranging from ‘weak’ to ‘extreme’ were characterized. Classes I (weak) and II (moderate) accounted for 60% and 23% of events, respectively. Class III (significant), were 9% of the recorded events and Classes IV (severe) and V (extreme) accounted for 5% and 2%, respectively. The probability of storm occurrence per year ranged from 93% for Class I to 15% for Class V. In order to characterize beach response to storm events, 214 beach profiles carried out with a monthly periodicity over the 1996–1998 period along the Chipiona‐Rota littoral were analysed, as well as published data. Different beach types were observed: (i) ‘Intermediate’ beaches underwent important vertical relief changes ranging from 0.3 m to 1.33 m associated with average slope changes from tan β = 0.06 to tan β = 0.03; (ii) the ‘dissipative’ beaches were characterized by smaller and homogeneous foreshore vertical changes, from c. 0.36 m to 0.65 m, according to the parallel retreat mechanism characterized by small slope variations (from tan β = 0.025 to tan β = 0.035); and (iii) ‘intermediate with rock shore platform’ experienced small morphological and foreshore slope variations, related to both beach pivoting and parallel retreat mechanisms. The most important morphological changes were due to the impact of usually ‘weak’ and ‘moderate’ events during October and November that produced berm erosion and upper foreshore lowering, and the impact of ‘severe’, ‘significant’ and ‘extreme’ events in December and January which produced dune escarpment, overwash and/or damage to coastal structures. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

7.
Abstract

A relatively simple process-oriented, physically-based distributed (PBD) hydrological model, the distributed runoff and erosion assessment model (DREAM), is described, and a validation study conducted in the semi-forested watershed of Pathri Rao, in the Garhwal Himalayas, India, is reported. DREAM takes account of watershed heterogeneity as reflected by land use, soil type, topography and rainfall, measured in the field or estimated through remote sensing, and generates estimates of runoff and sediment yield in spatial and temporal domains. The model is based on simultaneous solution of flow dynamics, based on kinematic wave theory, followed by solution of soil erosion dynamics. As the storm rainfall proceeds, the process of overland flow generation is dependent on the interception storage and infiltration rates. The components of the soil erosion model have been modified to provide better prediction of sediment flow rates and sediment yields. The validation study conducted to test the performance of the model in simulating soil erosion and sediment yield during different storm events monitored in the study watershed showed that the model outputs are satisfactory. Details of a sensitivity analysis, model calibration and the statistical evaluation of the results obtained are also presented and discussed. It is noteworthy that the distributed nature of the model combined with the use of geographical information system (GIS) techniques permits the computation and representation of the spatial distribution of sediment yield for simulated storm events, and a map of the spatial distribution of sediment yield for a simulated storm event is presented to highlight this capability.

Citation Ramsankaran, R., Kothyari, U.C., Ghosh, S.K., Malcherek, A., and Murugesan, K., 2013. Physically-based distributed soil erosion and sediment yield model (DREAM) for simulating individual storm events. Hydrological Sciences Journal, 58 (4), 872–891.  相似文献   

8.
Cliff erosion along a section of the West Wales coastline is described. Rockfalls, mudslides, and retreating fencelines are evidence of current activity. Measurements over a two-year period (1983-85) gave mean annual recession figures of up to 0.25 m yr−1 for glacial embayments. Wave refraction modelling and longshore beach surveys confirmed the existence of ‘high’ and ‘low’ beaches. Factors influencing variation in recession rates were identified and measured. Regression analysis suggested that the volume of beach-face material was the dominant explanatory variable in short-term cliff erosion.  相似文献   

9.
For development of embryo dunes on the highly dynamic land–sea boundary, summer growth and the absence of winter erosion are essential. Other than that, however, we know little about the specific conditions that favour embryo dune development. This study explores the boundary conditions for early dune development to enable better predictions of natural dune expansion. Using a 30 year time series of aerial photographs of 33 sites along the Dutch coast, we assessed the influence of beach morphology (beach width and tidal range), meteorological conditions (storm characteristics, wind speed, growing season precipitation, and temperature), and sand nourishment on early dune development. We examined the presence and area of embryo dunes in relation to beach width and tidal range, and compared changes in embryo dune area to meteorological conditions and whether sand nourishment had been applied. We found that the presence and area of embryo dunes increased with increasing beach width. Over time, embryo dune area was negatively correlated with storm intensity and frequency. Embryo dune area was positively correlated with precipitation in the growing season and sand nourishment. Embryo dune area increased in periods of low storm frequency and in wet summers, and decreased in periods of high storm frequency or intensity. We conclude that beach morphology is highly influential in determining the potential for new dune development, and wide beaches enable development of larger embryo dune fields. Sand nourishment stimulates dune development by increasing beach width. Finally, weather conditions and non‐interrupted sequences of years without high‐intensity storms determine whether progressive dune development will take place. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

10.
A strong low‐pressure system traveled along the Japanese main island Honshu in October 2006. High waves and storm surge attacked the Kashima Coast resulting in huge erosion over the area. Airborne laser data measured in October 2005 and November 2006 were analyzed to estimate cross‐sectional changes within the subaerial zone. The results of the alongshore distribution of the changes of cross‐sectional area indicate that the amount of erosion of the 38 km‐long northern and 15 km‐long southern parts decreased toward the south in each part and that the amount of erosion was smaller in protected areas with artificial headlands than in unprotected areas. The local alongshore variation of the erosion and accretion patterns showed wavy fluctuations of several hundreds of meters. The total amounts of the estimated eroded volume of the subaerial zone over the northern and southern parts were 620 000 m3 and 600 000 m3, respectively. The Simulating Waves Nearshore (SWAN) wave model was applied to estimate wave conditions along the coast during the storm. The computational results were verified, and then the alongshore distribution of wave energies, expressed as the alongshore and cross‐shore components of the wave energy flux, was compared with the alongshore distribution of cross‐sectional change. The results show that the distribution of energy flux explains the distribution of erosion well: The alongshore variability in the cross‐shore energy flux is responsible for the large‐scale variability in erosion, and shorter‐scale variability is due to gradients in the alongshore energy fluxes, especially for the areas without coastal works. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

11.
Many estuaries contain sandy beaches that provide habitats and offer protective buffers for wetlands and infrastructure, alongside cultural and recreational resources. Research underpinning coastal management tends to focus on tide- and swell-dominated sandy beaches, but little attention is given to beaches in estuaries and bays (BEBs) that exist along a continuum of wind/swell wave, tide and riverine influence. BEBs are subject to less wave energy than open coast locations because of the generally narrow window of directions for which ocean waves can propagate through the entrance. However, when storm wave direction coincides with the orientation of the estuary or bay entrance, waves can penetrate several kilometres inside. Here we focus on eight BEBs in two major bays/estuaries in Sydney, Australia and present observations from before and after a major extratropical storm with waves from an atypical direction in June 2016. We quantify magnitudes of beach erosion and recovery rates for 3 years post-storm. We show that when high-energy storm waves penetrate bays and estuaries, BEBs can undergo up to 100% of subaerial beach erosion. Three years after the storm, only 5 of the 29 (17%) eroded subaerial beach profiles had recovered to their pre-storm volume. This is likely due to the lack of low-frequency, beach-building waves at BEBs under modal weather conditions in between storms, in contrast to open coast beaches. We also show that the recovery of BEBs may be limited by the absence of adjacent sediment reservoirs due to the dominance of tidal processes mid-channel. Our study highlights the unique behaviour of BEBs relative to beaches on the open coast, and that shifting wave direction needs to be considered in long-term beach resilience under climate change. © 2020 John Wiley & Sons, Ltd.  相似文献   

12.
Analyses of shoreline and bathymetry change near Calais, northern coast of France, showed that shoreline evolution during the 20th century was strongly related with shoreface and nearshore bathymetry variations. Coastal erosion generally corresponds to areas of nearshore seabed lowering while shoreline progradation is essentially associated with areas of seafloor aggradation, notably east of Calais where an extensive sand flat experienced seaward shoreline displacement up to more than 300 m between 1949 and 2000. Mapping of bathymetry changes since 1911 revealed that significant variation in nearshore morphology was caused by the onshore and alongshore migration of a prominent tidal sand bank that eventually welded to the shore. Comparison of bathymetry data showed that the volume of the bank increased by about 10×107 m3 during the 20th century, indicating that the bank was acting as a sediment sink for some of the sand transiting alongshore in the coastal zone. Several lines of evidence show that the bank also represented a major sediment source for the prograding tidal flat, supplying significant amounts of sand to the accreting upper beach. Simulation of wave propagation using the SWAN wave model (Booij et al., 1999) suggests that the onshore movement of the sand bank resulted in a decrease of wave energy in the nearshore zone, leading to more dissipative conditions. Such conditions would have increased nearshore sediment supply, favoring aeolian dune development on the upper beach and shoreline progradation. Our results suggest that the onshore migration of nearshore sand banks may represent one of the most important, and possibly the primary mechanism responsible for supplying marine sand to beaches and coastal dunes in this macrotidal coastal environment.  相似文献   

13.
Increases in the frequency and magnitude of extreme water levels and storm surges are correlated with known indices of climatic variability (CV), including the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), along some areas of the British Columbia coast. Since a shift to a positive PDO regime in 1977, the effects of ENSO events have been more frequent, persistent, and intense. Teleconnected impacts include more frequent storms, higher surges, and enhanced coastal erosion. The response of oceanographic forcing mechanisms (i.e. tide, surge, wave height, wave period) to CV events and their role in coastal erosion remain unclear, particularly in western Canada. As a first step in exploring the interactions between ocean–atmosphere forcing and beach–dune responses, this paper assembles the historic erosive total water level (TWL) regime and explores relations with observed high magnitude storms that have occurred in the Tofino‐Ucluelet region (Wickaninnish Bay) on the west coast of Vancouver Island, British Columbia, Canada. Extreme events where TWL exceeded an erosional threshold (i.e. elevation of the beach–foredune junction) of 5·5 m aCD are examined to identify dominant forcing mechanisms and to classify a regime that describes erosive events driven principally by wave conditions (61·5%), followed by surge (21·8%), and tidal (16·7%) effects. Furthermore, teleconnections between regional CV phenomena, extreme storm events and, by association, coastal erosion, are explored. Despite regional sea level rise (eustatic and steric), rapid crustal uplift rates have resulted in a falling relative sea level and, in some sedimentary systems, shoreline progradation at rates approaching +1·5 m a–1 over recent decades. Foredune erosion occurs locally with a recurrence interval of approximately 1·53 years followed by rapid rebuilding due to high onshore sand supply and often in the presence of large woody debris and rapidly colonizing vegetation in the backshore. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

14.
The effect of climate change on extreme waves in front of the Dutch coast   总被引：1，自引：1，他引：0  
Coastal safety may be influenced by climate change, as changes in wave conditions (height, period, direction) may increase the vulnerability of dunes and other coastal defences. Dune erosion depends on mean water level, storm surge height and wave conditions. In this paper, we investigate the change in wave conditions in the North Sea in a changing climate. Until now, the effect of climate change on annual maximum wave conditions has been investigated, while events with higher return periods are actually most damaging for the coast (e.g. severe dune erosion). Here, we use the 17-member Ensemble SimulationS of Extreme weather under Non-linear Climate changeE (ESSENCE) change of climate change simulations, to analyse A1b-induced changes in the mean wave climate, the annual maxima and wave conditions with return periods of up to 1:10,000?years in front of the Dutch coast. The mean wave climate is not projected to differ between 1961–1990 and 2071–2100, with both wave height (H s) and wave period (T m) remaining unaltered. In the annual maximum conditions, a decrease is projected; especially, the annual T m maximum decreases significantly by 0.3 to 0.6?s over the whole study area. Furthermore, we find that the direction of the annual maximum wave conditions shifts from north and north-west to west and south-west for both H s and T m. This is induced by a similar shift in the direction of the extreme wind speeds. Despite the decrease in annual maximum conditions, the return H s and T m are not projected to change significantly as a result of climate change in front of the Dutch coast for the period 2071–2100 relative to 1961–1990.  相似文献   

15.
Wave generation, propagation, and transformation from deep ocean over complex bathymetric terrains to coastal waters around Potter Cove (King George Island, South Shetland Islands, Antarctica) have been simulated for an austral summer month using the Simulating Waves Nearshore (SWAN) wave model. This study aims to examine and understand the wave patterns, energy fluxes, and dissipations in Potter Cove. Bed shear stress due to waves is also calculated to provide a general insight on the bed sediment erosion characteristics in Potter Cove.A nesting approach has been implemented from an oceanic scale to a high-resolution coastal scale around Potter Cove. The results of the simulations were compared with buoy observations obtained from the National Data Buoy Center, the WAVEWATCH III model results, and GlobWave altimeter data. The quality of the modelling results has been assessed using two statistical parameters, namely the Willmott’s index of agreement D and the bias index. Under various wave conditions, the significant wave heights at the inner cove were found to be about 40–50 % smaller than the ones near the mouth of Potter Cove. The wave power in Potter Cove is generally low. The spatial distributions of the wave-induced bed shear stress and active energy dissipation were found to be following the pattern of the bathymetry, and waves were identified as a potential major driving force for bed sediment erosion in Potter Cove, especially in shallow water regions. This study also gives some results on global ocean applications of SWAN.  相似文献   

16.
A two-dimensional numerical model was presented for the simulation of wave breaking, runup and turbulence in the surf and swash zones. The main components of the model are the Reynolds-Averaged Navier–Stokes equations describing the average motion of a turbulent flow, a k–ε turbulence closure model describing the transformation and dissipation processes of turbulence and a volume of fluid technique for tracking the free surface motion. Nearshore wave evolution on a sloping bed, the velocity field and other wave characteristics were investigated. First, the results of the model were compared with experimental results for different surf zone hydrodynamic conditions. Spilling and plunging breakers were simulated and the numerical model investigated for different wave parameters. The turbulence field was also considered and the spatial and time-dependent variations of turbulence parameters were discussed. In the next stage of the study, numerical results were compared with two sets of experimental data in the swash zone. Generally, there is good agreement except for turbulence predictions near the breaking point where the model does not represent well the physical processes. On the other hand, turbulence predictions were found to be excellent for the swash zone. The model provides a precise and efficient tool for the simulation of the flow field and wave transformations in the nearshore, especially in the swash zone. The numerical model can simulate the surface elevation of the vertical shoreline excursion on sloping beaches, while swash–swash interactions within the swash zone are accounted for.  相似文献   

17.
A series of airborne topographic LiDAR data were obtained from May 2008 to January 2014 over two coastal sites of northern France (Bay of Wissant and east of Dunkirk). These data were used with wind and tide gauge measurements to assess the impacts of storms on beaches and coastal dunes, and particularly of the series of major storms that hit western Europe during the fall and early winter of 2013. Our results show a high variability in shoreline response from one site to the other, but also within each coastal site. Coastal dune erosion and shoreline retreat occurred at both sites, particularly on the coast of the Bay of Wissant where shoreline retreat up to about 40 m was measured. However, stability or even shoreline advance were also observed despite the occurrence of an extreme water level with a return period >100 years during the storm Xaver in early December 2013. Comparison of shoreline change with variations of coastal dune and upper beach volumes revealed only weak relationships. Our results nevertheless showed that shoreline behavior seems to strongly depend on the initial sediment volume on the upper beach before the occurrence of the storms. According to our measurements, an upper beach volume of about 30 m3 m?1 between the dune toe and the mean high water level is sufficient at these sites to protect the coastal dunes from storm waves associated with high water levels with return periods >10 years. The identification of such thresholds in terms of upper beach width or sediment volume may represent valuable information for improving the management of shoreline change by providing an estimate of the minimum quantity of sand on the upper beach necessary to ensure shoreline stability in this region. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

18.
An 8‐year time series of weekly shoreline data collected at the Gold Coast, Australia, is used to examine the temporal evolution of a beach, focusing on the frequency response of the shoreline to time‐varying wave height and period. Intriguingly, during 2005 the movement of the shoreline at this site changed from a seasonally‐dominated mode (annual cycle) to a storm‐dominated (~monthly) mode. This unexpected observation provides the opportunity to explore the drivers of the observed shoreline response. Utilizing the calibration of an equilibrium shoreline model to explore the time‐scales of underlying beach behavior, the best‐fit frequency response (days?1) is shown to be an order of magnitude higher post‐2004, suggesting that a relatively subtle change in wave forcing can drive a significant change in shoreline response. Analysis of available wave data reveals a statistically significant change in the seasonality of storms, from predominantly occurring at the start of the year pre‐2005 to being relatively consistent throughout the year after this time. The observed change from one mode of shoreline variability to another suggests that beaches can adapt relatively quickly to subtle changes in the intra‐annual distribution of wave energy. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

19.
The paper focusses on connectivity in the context of infiltration‐excess overland flow and its integrated response as slope‐base overland flow hydrographs. Overland flow is simulated on a sloping surface with some minor topographic expression and spatially differing infiltration rates. In each cell of a 128 × 128 grid, water from upslope is combined with incident rainfall to generate local overland flow, which is stochastically routed downslope, partitioning the flow between downslope neighbours. Simulations show the evolution of connectivity during simple storms. As a first approximation, total storm runoff is similar everywhere, discharge increasing proportionally with drainage area. Moderate differences in plan topography appear to have only a second‐order impact on hydrograph form and runoff amount. Total storm response is expressed as total runoff, runoff coefficient or total volume infiltrated; each plotted against total storm rainfall, and allowing variations in average gradient, overland flow roughness, infiltration rate and storm duration. A one‐parameter algebraic expression is proposed that fits simulation results for total runoff, has appropriate asymptotic behaviour and responds rationally to the variables tested. Slope length is seen to influence connectivity, expressed as a scale distance that increases with storm magnitude and can be explicitly incorporated into the expression to indicate runoff response to simple events as a function of storm size, storm duration, slope length and gradient. The model has also been applied to a 10‐year rainfall record, using both hourly and daily time steps, and the implications explored for coarser scale models. Initial trails incorporating erosion continuously update topography and suggest that successive storms produce an initial increase in erosion as rilling develops, while runoff totals are only slightly modified. Other factors not yet considered include the dynamics of soil crusting and vegetation growth. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

20.
A simplified process-based approach for evaluating onshore sandbar migration is presented in this study. This approach takes wave-averaged parameters as input and computes sediment transport processes using a reconstructed intra-wave orbital velocity signal. The proposed method guarantees good predictive skills for multiple onshore sandbar migration cases without an ad hoc calibration for each scenario. The study differs from previous onshore sandbar migration models, where calibration and testing are performed on just one or few events, and model assessment for uncalibrated realizations is rarely carried out. The present version of the model only addresses onshore sandbar migrations. For the onshore migration cases analyzed, the model has better predictive skills than state-of-the-art morphodynamic models (XBeach and Unibest-TC).  相似文献   

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