Sefton Coast Research Articles

Distribution and ecology of Equisetum variegatum (Variegated Horsetail) (Equisetaceae) on the Sefton Coast sand-dunes, north Merseyside, UK

A 2022 survey of Equisetum variegatum Schleich. Ex F. Weber & D. Mohr (Equisetaceae) (Variegated Horsetail) on the Sefton Coast sand-dunes, north Merseyside, found the plant in 19 of 28 known sites for the species. Most extant localities were in relatively young, calcareous dune-slacks and scrapes with short vegetation close to the shore, having ground-water-gley or peaty-gley soils with a high pH. Quadrats in vegetation supporting E. variegatum had a total of 78 vascular taxa, 20 of them being regionally or nationally notable and 10 Red-listed. There were only four non-native species. TABLEFIT analysis found that five UK National Vegetation Classification (NVC) dune-slack communities were represented, the most frequent being SD15: Salix repens-Calliergon cuspidatum dune-slack, followed by SD16: Salix repens-Holcus lanatus dune-slack. However, statistical fits to recognised NVC vegetation types were often poor. Loss of E. variegatum from nine sites was considered to be due to overgrowth by coarse vegetation and scrub, while 11 sites appeared to be imminently threatened by scrub development. Management practices that could assist conservation of E. variegatum and other notable plants in the Sefton dunes are discussed.

The status and distribution of the nationally rare micro-moth Anacampsis temerella (Lienig and Zeller, 1846) (Lepidoptera: Gelechiidae) in Lancashire in 2021, with observations on other Salix repens L. – feeding Lepidoptera

The history of Anacampsis temerella (Lienig and Zeller, 1846) in Lancashire, as well as nationally and internationally, is discussed. An account is given of a survey undertaken in May and June 2021 to look for larvae of A. temerella amongst Creeping Willow Salix repens L. on the dunes of the Sefton and Fylde coasts in Lancashire. Twenty A. temerella moths were reared from spun leaves of S. repens, as well as nineteen other species of Lepidoptera. The information gained proved the continued existence of the moth in the Sefton coast, and allowed differences to be identified between the larvae of A. temerella and Anacampsis populella (Clerck, 1759). The species was not detected on the Fylde coast during this survey. Recommendations are made regarding habitat management and future surveying to further assess distribution.

Monitoring the Dynamics of Formby Sand Dunes Using Airborne LiDAR DTMs

Coastal dunes play an important role in coastal erosion risk management, where they act as a dynamic natural sea defence line. Formby coast is part of the Sefton coast in the Northwest of England and is one of the largest and most rapidly evolving sand dune systems in the UK. Such dune systems require continuous comprehensive monitoring activity to understand their dynamics. In this research, we investigate the use of airborne LiDAR digital terrain model DTMs for monitoring the dynamics of the sand dunes at Formby between 1999 and 2020. We found that the rate of elevation change for the beach and the dune areas ranges from −0.78 to 0.02 m/year and −0.92 to 0.73 m/year, respectively. The beach and the frontal dunes have had significant sand erosion, while the inner dunes gained sand during the measurement period. Vegetated areas remained unchanged due to the impact of vegetation in stabilizing the movement of the dunes. Formby beach had a volume loss of about 907,000 m3 in the last 21 years, while the dunes had a volume increase of about 1,049,000 m3 over the same period. The total volume of the entire dune system, consisting of both the beach and dune areas, remained unchanged, which indicates that the growth of the inland dunes is fed by sand from the beach. All the volumetric changes occurred due to sand redistribution within the system, with erosion along the beach, and deposition and erosion in the dune areas.

Modelling Short- and Long-Term Dependencies of Clustered High-Threshold Exceedances in Significant Wave Heights

The peaks-over-threshold (POT) method has a long tradition in modelling extremes in environmental variables. However, it has originally been introduced under the assumption of independently and identically distributed (iid) data. Since environmental data often exhibits a time series structure, this assumption is likely to be violated due to short- and long-term dependencies in practical settings, leading to clustering of high-threshold exceedances. In this paper, we first review popular approaches that either focus on modelling short- or long-range dynamics explicitly. In particular, we consider conditional POT variants and the Mittag–Leffler distribution modelling waiting times between exceedances. Further, we propose a new two-step approach capturing both short- and long-range correlations simultaneously. We suggest the autoregressive fractionally integrated moving average peaks-over-threshold (ARFIMA-POT) approach, which in a first step fits an ARFIMA model to the original series and then in a second step utilises a classical POT model for the residuals. Applying these models to an oceanographic time series of significant wave heights measured on the Sefton coast (UK), we find that neither solely modelling short- nor long-range dependencies satisfactorily explains the clustering of extremes. The ARFIMA-POT approach, however, provides a significant improvement in terms of model fit, underlining the need for models that jointly incorporate short- and long-range dependence to address extremal clustering, and their theoretical justification.

Plant diversity and community composition in managed humid coastal dune slacks in NW England.

Humid coastal dune slacks are an endangered habitat in Northwestern Europe. In the UK, dune slacks are currently classified as being in ‘unfavourable’ condition, with projected decrease in England of up to 30% by 2036. Studies in mainland Europe suggest that regional factors (e.g. slack area, age, and isolation) are more important than local factors (e.g. soil, pH, soil nutrient and water status) in driving successional vegetation processes in coastal slacks. However, this has never been tested for the UK, where approximately 14% of European slacks occur. We used previously established survey protocols to test whether regional factors are more important than local factors in UK coastal slacks, along the Sefton Coast in NW England. We found that slack area and slack age were more important than local factors in driving plant community composition and species richness. We also showed that higher levels of management, such as active grazing and invasive shrub and tree removal, are effective in increasing soil moisture levels in slacks. Our results suggest that similar successional processes are likely to be important in slacks in the NW of England, compared to mainland Europe.

Using a two-step framework for the investigation of storm impacted beach/dune erosion

Long-term coastal management of beach/dune systems requires the definition and assessment of storm events. This study presents a framework using statistical analyses and numerical modelling (XBeach) to characterize storm events and investigate their impact on beach/dune erosion. The method is developed using exemplary data from Formby Point on the Sefton coast (UK), which has a complex beach morphology and frontal dunes. Relevant storm events are classified by a versatile univariate response function taking into account both nearshore water levels and offshore significant wave heights (Hs). It is shown that compared to the established storm classification (Hs ≥ 2.5 m) 35% more storm events that are relevant for beach/dune erosion are identified. Also the events exceed critical conditions for longer durations, and cause greater erosion impact (12%) along the beach/dune profile. The proposed classification of storm events thus captures relevant events for the storm erosion and can inform coastal management strategies. This framework is widely applicable to other beach/dune systems.

Increasing status of non-native vascular plants in the Sefton Coast sand-dune system, north Merseyside, UK

Over 460 non-native (alien) taxa were recorded in a Sefton Coast sand-dune vascular plant inventory, their proportion in the flora increasing after 1999. Between 2005/06 and 2018, twice as many non-native as native plants were found. An analysis of occurrences of native and non-native taxa in six major habitat types found that a higher proportion of aliens was present in scrub/woodland and disturbed ground, while native plants had more occurrences in fixed dunes/dune grasslands, dune heath and wetlands. No differences between the two groups were detected for strandline/shingle and embryo/mobile dune habitats. Twenty-four non-native and 14 native taxa showed invasive characteristics in the duneland. The former included especially Hippophae rhamnoides and Rosa rugosa, both constituting major threats to sand-dune biodiversity. Particularly invasive native plants were Arrhenatherum elatius, Betula spp., Salix cinerea, and Ulex europaea. The main findings accord with studies elsewhere in Britain and Europe showing recent increases of neophytes in semi-natural habitats and that both non-native and native species can have invasive traits. The open habitats of coastal dunes seem to be particularly susceptible to plant invasions.

Japanese Rose (Rosa rugosa): its invasion and colonisation of the Sefton Coast, north Merseyside, UK

A spiny shrub native to north-west Pacific coasts, Rosa rugosa Thunb. (Japanese Rose) was introduced into Britain in the 19th century as a garden plant. It has since become a well-established and widespread naturalised alien, especially on sand-dunes, shingle beaches and other dry coastal habitats. The plant is also considered invasive on coasts of many other countries in Northwest Europe. Mounting concern about its recent spread on the internationally important sand-dune system of the Sefton Coast, north Merseyside, led to a volunteer survey being organised in 2014, involving 47 participants. They searched most of the 27 km-long coastal zone, recording almost 500 patches with a total area of nearly 6 ha. R. rugosa occurred especially on younger calcareous dunes (soil pH 5.6 – 8.2) near the sea and close to roads and human habitation. Few patches were found on older, more acidic duneland, or on a 5 km erosion front around Formby Point. This pattern of occurrence accords with that reported elsewhere for R. rugosa, indicating that the sea is implicated in the dispersion of propagules and that the species also establishes from anthropogenic sources, including ornamental plantings. It is concluded that the plant is a threat to dune habitats and species on the Sefton Coast. Control measures are discussed and the early stages of patch removal are described.

Effects of environmental factors and conservation measures on a sand-dune population of the natterjack toad (Epidalea calamita) in north-west England: a 31-year study

A 31-year study monitored Britain’s largest natterjack toad population on the Sefton Coast sand-dune system in north-west England. Key objectives were to describe changes in numbers and breeding success, relate these to environmental variables and explore whether conservation efforts have been well targeted. Considerable variation was found in the number of water bodies used for spawning, the number of spawn strings laid and breeding success based on estimated toadlet production. There was a declining trend in annual totals of spawn strings and toadlets. Positive correlations were established between spring and April rainfall and both spawn count and toadlet production. April rainfall for the study area declined between 2000 and 2017. Premature desiccation of water bodies and associated poor breeding success were frequently observed, there being a positive relationship between water-table height and toadlet numbers. A long-term declining trend in the height of the water-table was established. The mean adult population of Sefton natterjacks was estimated at about 1200 individuals, with a peak around 3150. Successful breeding is increasingly reliant on management to excavate appropriately designed and managed “scrapes” that hold water long enough for metamorphosis to occur. Overgrowth of vegetation and loss of dynamism in the dune system threaten both the natural production of new breeding slacks and the natterjack’s open terrestrial habitat. Encouragement of dune dynamics by removing trees and scrub, increasing areas subject to livestock grazing and mechanical rejuvenation may offer the best hope of conserving this species in the future.

Computational modelling of morphodynamic response of a macro-tidal beach to future climate variabilities

Global climate variabilities have the potential to impact many coastlines around the world, and can have detrimental effects on the stability of coastlines and their function as natural coastal defenses. This paper investigates the impacts of future extreme storms and sea level rise on morphodynamics of the macro-tidal Sefton Coast, UK, taking a process-based model as a tool to simulate a snap-shot of future beach change during storms. Sefton Coast represents one of the largest dune systems in the UK, where frontal dunes function as a natural barrier against extreme conditions. Future storm conditions were determined from global predictions of future waves at the end of the twenty first century. Future sea levels were determined based on climate change allowances set by the UK Environment Agency (EA), while future surge conditions were determined based on the guidelines also provided by EA.A nested numerical modelling approach, that combined a regional scale model with a local scale model with high resolution, is used. The modelling suite was first validated against measured waves, water levels and beach change, before using it to simulate morphodynamic change from numerous statistically significant ‘future’ storm conditions. Future storm-induced morphodynamic change of the Sefton coast was then compared with that from the present storms. The results reveal that this beach will experience significant climate change driven impacts where dune retreat during storms will be considerably higher in future. The results also reveal that due to the shape of the beach and its orientation to predominant wave approach direction, there will be a strong longshore variability of morphodynamic response to storms. It was also found that the water level in front of the dune (and hence surge and future sea level rise) is the most critical factor that determines beach erosion during a storm.

Changing status of Blysmus compressus (Flat Sedge) in the Sefton Coast sand-dunes, north Merseyside, UK

A 2018 survey of the nationally ‘Vulnerable’ Blysmus compressus (Flat-sedge) in the Sefton Coast sand-dunes, north Merseyside (v.c.59, South Lancashire), aimed to update information collected on distribution and habitats a decade earlier. As in 2008, the plant was mainly found in calcareous dune-slacks of recent origin, with short, open, species-rich vegetation on gley soils with a relatively high pH. Sites with a lower sward height supported a higher percentage cover of B. compressus. The largest populations were associated with sites that had been disturbed by recreational trampling, occasional vehicle use and/or grazing, especially by rabbits. Twenty-two sites were recorded, seven being new. Overall, the area occupied by B. compressus declined by 17%, two 2008 sites being lost. Similarly, an estimate of 15-20,000 plants in the earlier survey fell to 12,600. Losses were attributed to vegetation overgrowth and scrub development, partly resulting from lower rabbit numbers and reduced management input. The plant occurred in a range of vegetation types but matches to known UK National Vegetation Classification communities were generally poor. Management methods to conserve B. compressus and other vulnerable taxa are discussed.

Multi-timescale morphological modelling of a dune-fronted sandy beach

Medium/long term trends (annual to decadal scale) of beach change are mostly used to make coastal management decisions. However, short term, extreme episodic events (short term) can erode the beach to exceed sustainable erosion thresholds thereby impacting long term trends of coastal change. Therefore, understanding coastal change at short and medium-long term (years to decades) timescales is essential to provide sustainable solutions to beach erosion. In this paper, we investigate and simulate the change of a beach-dune system for a megatidal coastline in the UK at storm timescale and at medium-long term timescale corresponding to sea level rise, in order to assess their significance in terms of beach management. The field site of choice is the Sefton coast, located in Liverpool Bay, United Kingdom. The approach used here involves process based modelling to determine storm-induced beach erosion and the application of modified Bruun Rule (Dean and Houston, 2016) to determine medium-long term evolution associated with climate change impacts. The application of the process-based model, XBeach, reveals that storm-induced short term beach erosion can be in the same scale or may surpass average medium/long term erosion thresholds and therefore, should be taken in to account when managing coastlines. Despite the complexities of the megatidal Sefton coast, the modified Bruun Rule proved to be capable of capturing long term beach profile change and assures that it can be confidently used to determine medium-long term beach-dune change due to sea level rise, once reliable estimates of longshore transport and sediment sources/sinks are made.

Assessment of beach and dune erosion and accretion using LiDAR: Impact of the stormy 2013–14 winter and longer term trends on the Sefton Coast, UK

An important question for coastal management concerns the importance of individual storms and clusters of storms on longer term beach sediment budgets, beach and dune erosion, and coastal flood risk. Between October 2013 and March 2014 a series of deep Atlantic low pressure systems crossed the Northeast Atlantic, and strong winds, high waves and high water levels affected many coastal areas in the UK and other parts of western Europe. Net dune recession of up to 12.1m occurred around Formby Point. On 5 December 2013 the highest water level ever recorded at Liverpool (6.22m ODN) coincided with waves of Hs of 4.55m and Tp of 9.3s in Liverpool Bay. Wave trimming of the dune toe occurred along the entire length of the Sefton coast, but significant dune erosion occurred only where the upper beach (between the mean high water spring tide level and the dune toe) was <25m wide. Sediment budget calculations based on LiDAR surveys in October 2013 and May 2014 indicated a net loss of 127×103m3 of sediment from the beach (above 0m ODN) and a loss of 268×103m3 from the frontal dune system, mostly at Formby Point. However, some parts of the beach to the south of Formby Point gained sediment, indicating net north to south transport over the winter. When considered in a longer term context, the 2013–14 winter represents only a small perturbation on the longer-term coast trend of erosion at Formby Point and progradation to the north and south. Analysis of LiDAR data over a longer time period 1999–2014 indicated upper beach and dune sediment loss of 780×103m3 from the north-central part of Formby Point, with net gains of 806×103m3 and 2116×103m3 in areas to the north and south, respectively. This indicates a net onshore transport of 2142×103m3 from Liverpool Bay towards the coast between Birkdale and Altcar, with a further net total of 210×103m3 transported towards the shore between Altcar and Crosby. In view of the demonstrated value of airborne LiDAR surveys for the quantification of storm impacts and longer term coastal changes, it is recommended that such surveys should be undertaken before and after each winter storm period, covering the area between mean low water spring tide level and a line 200m landward of the dune toe, of as a part of the regional coastal monitoring programme.

Rates of spread of Rosa rugosa (Japanese Rose) determined by GIS on a coastal sand-dune system in Northwest England

The invasive non-native shrub Rosa rugosa (Japanese Rose) is well-established in many northwest European countries where, especially on coastal sand-dunes, it forms large dominant stands with adverse effects on semi-natural vegetation and biota of high conservation status. Its recent increase in England’s largest dune system on the Sefton Coast in north Merseyside led to an investigation into its rate of spread. Using digitised aerial photographs and GIS methodology, sample patches of old-established R. rugosa were found to have grown in area by an average of 22 % per annum between 1989 and 2013. This rate of increase is comparable to that found in Denmark and higher than reported for several other woody plants in coastal dunes. In the absence of management, R. rugosa could soon dominate large areas on the Sefton Coast, with serious consequences for amenity and the nature conservation interest of the dune system.

Effects of storm clustering on beach/dune evolution

Impacts of storm clustering on beach/dune morphodynamics were investigated by applying the state-of-the-art numerical model XBeach to Formby Point (Sefton coast, UK). The adopted storm cluster was established by analysing the observed winter storms from December 2013 to January 2014 using a storm threshold wave height. The first storm that occurred during this period is regarded as exceptionally intense, and the occurrence of such a cluster of events is very unusual. A 1D model was setup for the highly dynamic cross-shore at Formby Point. After initial calibration of the model parameters against available post-storm profile data, the model was used for the simulation of the storm cluster. It was assumed that no beach recovery occurred between adjacent storms due to the very short time intervals between storms. As a result, the final predicted post-storm profile of the previous storm was used as the pre-storm profile of the subsequent storm. The predicted evolution during each storm was influenced by the previous storms in the cluster. Due to the clustering effect, the bed level change is not proportional to the storm power of events within the cluster, as it would be in an individual storm case. Initially, the large storm events interact with the multi-bared foreshore enabling the subsequent weaker storms to influence the upper beach and lower dune system. This results in greater change at the dune toe level also during less severe subsequent storms. It is also shown that the usual water level threshold used to define dune erosion is over predicted by about 1m for extreme storm conditions. The predicted profile evolution provides useful insights into the morphodynamic processes of beach/dune systems during a storm cluster (using Formby Point as an example), which is very useful for quantifying the clustering effects to develop tools for coastal management.

Comparison of storm cluster vs isolated event impacts on beach/dune morphodynamics

Two-dimensional numerical simulations were used to investigate the impacts of storm clustering on the beach/dune evolution of the Sefton coast, Liverpool Bay, UK. A storm cluster consisting of a series of closely spaced seven events was identified using observed wave and surge data during the 2013/2014 winter period. First event in this cluster is regarded as exceptionally intense and the occurrence of seven storms within a very short time period, is unique. The XBeach coastal area model was used to simulate beach change from 1) the storm sequence (Clustered events) and 2) the same storms considering them as isolated events. Offshore metadata was transformed to the nearshore area using the Delft3D and SWAN models. Resulting evolution was first compared with the available post-storm profiles measured at a number of locations along the Sefton coast. Analysis of the Clustered and Isolated simulations showed the effect of clustering on the Sefton beach/dune system when compared to the impact of isolated events occurring on a fully recovered beach system. Morphological change occurred during each storm in the Cluster was influenced by the preceding storm(s), such that the evolution is not proportional to the storm power of the event, as it would be for Isolated events. Both storm cases resulted in heavy erosion at Formby Point (i.e. central of the Sefton coast) and accretion in the north and south. The Cluster prevented system recovery with the area of erosion continually extending south along the coast compared with that in Isolated events. The initial storm within the Cluster caused large bed level changes in the nearshore ridge-runnel system, enabling the subsequent storms to penetrate further south. The local convex geometry of the Sefton coast is found to have more influence on the beach/dune morphodynamics than the clustering effect. This study enhances the understanding beach/dune response to storm clusters, to interpret observed morphological changes and to develop tools for sustainable coastal management particularly in the Sefton coast and generally in similar systems worldwide.

Impacts of storm chronology on the morphological changes of the Formby beach and dune system, UK

Abstract. Impacts of storm chronology within a storm cluster on beach/dune erosion are investigated by applying the state-of-the-art numerical model XBeach to the Sefton coast, northwest England. Six temporal storm clusters of different storm chronologies were formulated using three storms observed during the 2013/2014 winter. The storm power values of these three events nearly halve from the first to second event and from the second to third event. Cross-shore profile evolution was simulated in response to the tide, surge and wave forcing during these storms. The model was first calibrated against the available post-storm survey profiles. Cumulative impacts of beach/dune erosion during each storm cluster were simulated by using the post-storm profile of an event as the pre-storm profile for each subsequent event. For the largest event the water levels caused noticeable retreat of the dune toe due to the high water elevation. For the other events the greatest evolution occurs over the bar formations (erosion) and within the corresponding troughs (deposition) of the upper-beach profile. The sequence of events impacting the size of this ridge–runnel feature is important as it consequently changes the resilience of the system to the most extreme event that causes dune retreat. The highest erosion during each single storm event was always observed when that storm initialised the storm cluster. The most severe storm always resulted in the most erosion during each cluster, no matter when it occurred within the chronology, although the erosion volume due to this storm was reduced when it was not the primary event. The greatest cumulative cluster erosion occurred with increasing storm severity; however, the variability in cumulative cluster impact over a beach/dune cross section due to storm chronology is minimal. Initial storm impact can act to enhance or reduce the system resilience to subsequent impact, but overall the cumulative impact is controlled by the magnitude and number of the storms. This model application provides inter-survey information about morphological response to repeated storm impact. This will inform local managers of the potential beach response and dune vulnerability to variable storm configurations.

MODELLING DUNE EROSION OF THE SEFTON COAST, LIVERPOOL BAY, UK

Dune erosion at sandy coastal systems poses significant threat to the hinterland areas due to flooding and subsequent damage to life and property. The Sefton Coast (Fig.1), bounded by Mersey (South) and Ribble (North) estuaries in the Liverpool Bay, represents about 20% of the UK’s dune system, has a high recreational value, form an effective coastal flood defense and consists of a significant number of conservation areas of national and international interest. This area is however susceptible to erosion during storm events where landward retreat occurs leading to dune breach and coastal flooding. Present study focused on an area around the Formby Point of the Sefton Coast (dashed-line polygon in Fig.1), which is a highly dynamic sedimentary system. The dune system at Formby Point beach showed continuous accretion (max ~4.7 m/year) during the last century but has become an eroding beach since early twentieth century (max. ~6.2 m/year). However, beach accretion can still be seen in far south and north of Fomby Point. The Sefton Coast experiences a semi-diurnal macrotidal regime with a mean spring tidal range reaching 8.22 m (Esteves et al., 2012). Mean annual significant wave height (Hs) is about 0.53 m while extremes exceed 5 m (Brown et al., 2010). The aim of this study is to investigate the response of the Formby Point dune system to extreme storm conditions based on the March 2010 storm event (max. Hs>3.5 m, see Brown, 2010). We use the 2DH process-based morphological model XBeach, which has been developed to investigate dune erosion under extreme conditions (Roelvink et al., 2009), in combination with the SWAN spectral wave model (Booij et al., 1999). The model set-up consists of a coarse-grid model (Sefton) and a fine-grid model (Formby Point) which encloses the area of interest. The Sefton model is driven by the Liverpool Bay WaveNet buoy wave data (Esteves et al., 2012). The outputs of the Sefton model provide wave and water level boundary conditions to the Formby Point morphodynamic model to investigate the beach response to the selected storm event. The model setup described above is then used to simulate nearshore hydrodynamics and morphodynamics. Fig. 1shows a snapshot of simulated Hs corresponding to the storm event occurred in the Liverpool Bay during 30 March and 02 April 2010, at the mean tidal level. Offshore waves are significantly attenuated when travelled from offshore to nearshore. Fig. 2 shows the model simulated exposure of the dune system and the beach during Low Water (LW) (a) and High Water (HW) (b). At LW, the beach exposes up to about 3 km while at HW, the entire beach drowns, exposing the dune system to incoming waves. Therefore, a storm event combined with HW may lead to damage the dune system and hence flooding of the hinterland of the River Alte area, due to the low dune height in this area. Relatively high morphological changes are observed around the Crosby channel area (see location in Fig. 1). The storm driven dune erosion occurred during the HW. Large storm waves propagate along the Crosby channel towards the River Alte area. The River Alte area is susceptible to coastal flooding during storms, as a result of the low dune crest in this area. Work is currently in progress to predict the dune evolution and flooding under the future climate change and sea level rise scenarios.

Modelling storm-induced beach/dune evolution: Sefton coast, Liverpool Bay, UK

Storm-induced dune evolution on a sandy coastal system is investigated using a nested modelling approach applied to the Sefton coast, Liverpool Bay, UK. Real-time offshore water levels and waves were used as model boundary forcings. A Delft3D coarse grid setup is used to simulate time and space varying sea surface elevations on which offshore waves are transformed (by applying the SWAN model) to establish the wave boundary for the high resolution morphological model (XBeach). Statistical comparisons between model predicted and measured post-storm profiles at a number of locations along the coast suggest that XBeach successfully captures storm-induced beach change along the Sefton coast. Predicted bed evolution of the beach/dune system shows alternate erosion and sedimentation areas in the nearshore. Strong bed level changes are found at the northern part of the Sefton coast when north-westerly (NW) extreme waves and winds coincide with spring-high tide. Morphological changes in the southern part are significantly lower than that in the north as a result of NW wave dissipation on the shoals located to the north of the Crosby channel, which creates low wave actions in that area. In addition, erosion of the dune foot is observed at some locations along the beach. Temporal simulation of beach/dune evolution as a result of variable forcing conditions during storms provides useful insight into the morphodynamic processes of beach/dune systems during storms (using Sefton as an example), which is very useful for developing coastal management strategies over the existing conceptual tools.

Comportamento hidráulico e impacto regional de um furo horizontal num aquífero superficial: exemplo de Sefton Coast, noroeste de Inglaterra (Reino Unido)

Horizontal wells can be utilised for groundwater abstraction in aquifers of limited saturated thickness. One feature that must be considered is the hydraulic head inside the horizontal well, since hydraulic head gradients can be substantial in long wells with relatively small cross-sectional areas. Little experimental evidence is available concerning horizontal wells, but this report describes field data collected for a 300-m long horizontal well in northwest England (UK); the well is curved in plan, in a shallow unconfined aquifer. Conceptual and computational models are presented; they represent regional groundwater flow, convergent groundwater flows towards and into the well, and also hydraulic conditions within the well. Good agreement is achieved between field and modelled values for groundwater heads in the aquifer and for hydraulic heads in the well. The computational model is then used to explore the rates of inflow along the well; the impact on regional groundwater conditions of abstraction from the well is also examined. Finally, a preliminary comparison is made between vertical well points and horizontal wells in shallow aquifers.