31,385 research outputs found
Overtopping a truncated planar beach
No full textRun-up on a truncated impermeable beach is analysed theoretically and experimentally to find the volume of fluid, associated with a single wave event, that flows over the end of the beach. The theoretical calculations investigate the motion using the shallow-water equations and the fluid is allowed to flow freely over the end of the beach. Two models of wave events are considered: dam-break initial conditions, in which fluid collapses from rest to run-up and overtop the beach, and a waveform that models swash associated with the collapse of a long solitary bore. The calculations are made using quasi-analytical techniques, following the hodograph transformation of the governing equations. They yield predictions for the volume of fluid per unit width that overtops the beach, primarily as a function of the dimensionless length of the beach. These predictions are often far in excess of previous theoretical calculations. New experimental results are also reported in which the overtopping volumes due to flows initiated from dam-break conditions are studied for a range of reservoir lengths and heights and for a range of lengths and inclinations of the beach. Without the need for any empirically fitted parameters, good agreement is found between the experimental measurements and the theoretical predictions in regimes for which the effects of drag are negligible
Beach and cliff retreat induced by storm groups at Forte Novo,Algarve (Portugal)
No full textLittoral cell dynamics may change through time as a reaction to modifications of the coastal system. Along the Vilamoura-Quarteira coastline, the construction of a groin field limited the sediment supply to the already narrow Forte Novo beach, located downdrift, enhanced wave action on the cliff base and lead to long-term persistent cliff retreat. This research uses a set of surveys from November 2009 to March 2010 to determine short-term soft cliff erosion associated to storm groups at this sediment starved area. Following the initial LiDAR survey, three subsequent surveys were performed using a reflectorless total station for monitoring the cliff face, and RTK-DGPS to monitor the position of the cliff top, the cliff foot and the topography of the adjacent beach. Results indicate an important reduction in beach levels during successive storms (without significant beach recovery in between), allowing waves to further attack the cliff base and contributing to further enhance the structural and permanent cliff retreat. This work demonstrates how a combination of magnitude and frequency of extreme events coupled with development of the coastline, has led to increased cliff-beach recession and to the permanent dislocation of the cliff face
Modelling of wave climate and sediment transport patterns at a tideless embayed beach, Pirita Beach, Estonia
No full textNearshore sand transport patterns along the tideless, embayed Pirita beach, Tallinn, Estonia, have been investigated utilizing high-resolution modelling of wave processes combined with bathymetric surveys and sediment textural analyses of the nearshore sea floor. Textural analysis showed the mean grain size is about 0.12 mm. Fine sand (0.063–0.125 mm) accounts for about 77% of the sediments. Coarser-grained sand (0.28 mm) dominates along the waterline. Based upon the spatial distribution of the mean grain size and basic features of the local wave activity, properties of the Dean Equilibrium Beach Profile were determined.
Alongshore sediment transport was calculated based upon a long-term time series of wave properties along the beach, and the CERC formula applied to about 500 m long beach sectors. The time series of wave fields and the properties of the local wave climate were modelled using a triple nested WAM wave model with an extended spectral range for short waves. The model is forced by open sea wind data from Kalbådagrund for the years 1981–2002. Results indicate that typical closure depth at Pirita is 2.5 m. The width and mean slope of the equilibrium profile are 250 m and 1:100, respectively. Southward transport dominates in the northern sections of the beach whereas no prevailing transport direction exists in the southern sections. This pattern has several nontrivial implications for the planning of beach protection activities
Beach development, sediment budget and coastal erosion at Holderness.
No full textComplex relationships exist among offshore conditions, beach
sediment transport and morphology, and till cliff erosion. Modelled
and measured sediment transport rates established for the Holderness
coast are similar to those on comparable coasts elsewhere. The
direction of sediment drift depends on wave approach, and determining
sediment transport rates, cliff composition and cliff retreat
rates allows a sediment budget to be prepared. The beach response
predicted by the sediment budget was confirmed by field observations,
with budget surpluses and deficits coinciding with full and depleted
beach profiles respectively. The area of deficit in the north of the
study area was associated with the reduced sheltering effect of
Flamborough Head on sediment drift.
At most profiles, especially those with a sediment deficit, high
energy waves may remove the sand veneer completely, leaving the
till platform exposed. These bare till patches which elsewhere have
been called ords and have been regarded as unique, were thought, in
the present study,to represent a normal beach response to limited
sediment supply and prevailing offshore conditions.
Beach evolution was also modelled formally, the range of beach
profiles exhibited on the Holderness coast being grouped into a
number of distinct types, and evolution among them described and
predicted by a first-order Markov model. This can be refined to
provide different models for "winter" and "summer". Different modal
types occur at different locations, and certain types of transitions
between classes can be associated with particular ranges of wave
conditions.
Beach Development, Sediment Budget and Coastal Erosion at Holderness
Susan J. Mason.
Till cliff retreat at Holderness is extremely variable, both
spatially and temporally, being influenced by beach level, energy
conditions, cliff moisture content and the actions of man.
The sediment transport rates, cliff retreat data, sediment
budget and beach behaviour model are all essential elements of a
research programme currently being undertaken to find a cheap
method of protecting this coast
AN ECONOMIC EVALUATION OF BEACH EROSION MANAGEMENT ALTERNATIVES
No full textThis paper examines the relative economic efficiency of three distinct beach erosion management policies — beach nourishment with shoreline armoring, beach nourishment without armoring, and shoreline retreat. The analysis focuses on (i) the recreational benefits of beaches, (ii) the property value effects of beach management, and (iii) the costs associated with the three management scenarios. Assuming the removal of shoreline armoring improves overall beach quality, beach nourishment with shoreline armoring is the least desirable of the three alternatives. The countervailing property losses under a retreat strategy are of the same order of magnitude as the foregone management costs when the beneficial effects of retreat — higher values of housing services for those houses not lost to erosion — are considered. The relative desirability of these alternative strategies depends upon the realized erosion rate and how management costs change over time.Resource /Energy Economics and Policy,
Valuing a Beach Day with a Repeated Nested Logit Model of Participation, Site Choice, and Stochastic Time Value
No full textBeach recreation values are often needed by policy-makers and resource managers to efficiently manage coastal resources, especially in popular coastal areas like Southern California. This article presents welfare values derived from random utility maximization-based recreation demand models that explain an individual’s decisions about whether or not to visit a beach and which beach to visit. The models utilize labor market decisions to reveal each individual’s opportunity cost of recreation time. The value of having access to the beach in San Diego County is estimated to be between 23 per day.Recreation demand, repeated nested logit, labor supply, opportunity cost of leisure, time, beach recreation., Demand and Price Analysis, Environmental Economics and Policy, Institutional and Behavioral Economics, Q26, J22, Q51.,
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