Beach Response to a Shoreface Nourishment (Aveiro, Portugal)

Journal of Coastal Research

The main purpose of this paper is to analyse the behaviour of nourished beaches in Cadiz Bay (SW Spain). Similar nourishment modalities were used in all studied beaches: sand was dredged from the sea floor and split on the beach to create a raised, flat berm. These nourishment modalities transformed the initially dissipative profiles into intermediate-reflective ones. The monitoring program showed an asymptotic stationary beach trend, tending to achieve a "minimum equilibrium volume". In fact, despite the initial, important erosion, beaches acquired a seasonal behaviour with dissipative state associated to erosive conditions and an intermediate one during constructive conditions, general beach stability. Finally, it was observed that a nourishment work carried out during fair weather conditions greatly favours beach stability because sand is relocated and distributed in a natural way under low energy conditions. : ADDITIONAL INDEX WORDS Coastal erosion, volumetric variations, nourishment works, Bay of Cádiz.

Journal of Coastal Research, 2011

In the Portuguese southern coast, national and international appeal turns it into a highly relevant area concerning the country's economy. Vale do Lobo is a resort located in the centre of this coast, where the beach has been suffering from erosion problems for several years now. Local interventions have been executed in order to prevent the erosion of the beach, yet the efficiency of such strategy has not been verified. This study's main purpose is to enable a better understanding of the evolutionary trends of the coastline between the Quarteira and Ancão inlet and to analyse the efficiency of the beach nourishment interventions as a protection technique for a coastal environment with the wave energy exposure and geomorphologic characteristics of the present one. The study focussed on a 10-year period, during which, 700x10 3 and 370x10 3 m 3 of sand with D50=0.76 mm (slightly larger than the D50 of the native beach) were extracted from offshore, and deposited in the foreshore. The wave climate in the study area was processed, analysed and used as input for modelling the nearshore processes. In addition, beach profiles measured alongshore have been analysed to obtain the representative beach profile. Coastlines of different dates have been derived from aerial photographs. The longshore transport model Litdrift and the coastline model Litline were applied to study the sediment dynamics. Litdrift was used to estimate the longshore transport capacity of the beach for the hydrodynamic series considering the representative beach profile previously obtained. These results were then used to calculate the evolution of the coastline due to the incident wave climate with Litline model. Aerial photographs were used to verify the model. The analysis of the two beach nourishments performed allowed inference on the efficiency of this coastal protection technique to delay the erosion process.

Coastal Engineering, 2011

Beach nourishment programs in estuaries can enhance shore protection, but they decrease habitat suitability by creating higher berms and wider backshores than would occur under natural conditions. Use of sediment sources from outside the area can result in sedimentary characteristics that differ from native sediments on the surface and at depth, altering conditions for both aeolian transport to dunes and interstitial fauna. Field data were gathered on an estuarine beach to determine differences in beach profile change, depth of sediment reworking, and potential for aeolian transport due to nourishment. Data were gathered over a 20-month period 6 months prior to nourishment, 3 days after nourishment, 6 months after nourishment, and 14 months after nourishment when the beach was mechanically graded to eliminate a vertical scarp in the foreshore. The nourishment consisted of 87,900 m 3 of sediment emplaced to create a 1.34-km-long, 30-m-wide berm 2.3 m above mean tide level. Seven percent of the fill was removed from the profile within 6 months after nourishment, accompanied by 7 m in horizontal retreat of the artificial berm. The fill on the backshore remained above the zone of wave influence over a winter storm season and was separated from the active foreshore by the scarp. Nourished sediments on the intertidal foreshore were significantly different from native sediments to a depth of 0.20 m below the surface. A lag surface of coarse sediment formed by deflation on the backshore, resulting in a rate of aeolian transport <2% of the rate on the wave-reworked foreshore.

Coastal Engineering, 2004

Studies of coastal morphodynamics are becoming increasingly more focused on quantification of relationships between processes, form and function of dynamic landform systems because wave climates (e.g., wave height, wave period, seasonality, cyclical patterns) and sediments (i.e., composition, size, and shape) interact in various ways to collectively produce distinctive types of beaches. This paper identifies criteria and boundary conditions that characterize beaches in terms of morphodynamic states (environmental conditions or energetic stages of development) that produce discrete beach types. Long-term hindcast wave statistics (U.S. Army Corps of Engineers, Wave Information Study), small-scale aerial photography, cross-shore beach profiles, and beach sediment data from Florida's Atlantic (Delray Beach) and Gulf (Longboat Key) coasts were used as a basis for linking beach morphology with coastal processes. The role of cross-shore sediment variation in classification of beaches is related to prediction of beach types using the dimensionless fall velocity (X), the results of which are compared with field observations and morphological interpretation of aerial photographs. A new curve-fitted equation, the morphodynamic boundary condition (MBC), identifies parametric limits that force dissipative or reflective beach conditions when new sediments are artificially placed on the beach (e.g., during beach nourishment programs). Results indicate that the X parameter of the new model is strongly influenced by cross-shore selective sorting of bimodal sediments, temporal changes in beach grain size, seasonal wave patterns, and inputs of new sediments to the littoral system. Calculation of X using beachface samples produces a bias toward reflective states (decrease in X). Sediment samples from bar systems, on the other hand, produce a bias toward dissipative states (increase in X). Composite grain size of the active profile is recommended because it more accurately predicts beach states based on X (compared to field observation of beach type). The addition of new sediment to beaches requires an understanding of form-process continuums and the MBC equation is a step in that direction. The potential impacts of beach nourishment on beach morphology can be thus determined from local wave data by calculating hypothetical X values as a function of changes in beach composite grain size and a constant K value. The MBC equation (X=Kd f À2), as applied in planning phases of renourishment projects, can predict changes in beach morphodynamic states, as conditioned by the grain size of the placed fill.

Journal of Coastal Conservation

Coastal erosion in SW Spain is affecting man-made structures and beaches that represent an important economic resource in the area. In the last decade the Spanish government carricd out several nourishment works that have limited durahility. i\:!ost of the artificial beach fills consist of a spill of natural dredged sand on the visihle beach. leading to a tlat. anificial herm with an important seaward slope and a narrow foreshore. As a result, the initial dissipative profile was transformed into a fully reflective one. A beach monitoring program was carried out to record morphological evolution after the nourishment \I/orks. Several field assessments of disturbance depth were a!so made to characterize beach morphodynamics of a nourished beach (Rota) and a natural dissi pati ve one (Tres Piedras). whose slope \vas similar to the pre-nourishment gradient of Rota beach. Natural dissipative beaches were characterized by spilling breakers that did not signifi-C:l!1tlyaffect bottom sand. The severe erosion recorded in the nourished zones \I,:as related to the new morphodynamic rcgime acting on these beaches. which was controlled by high erosive plunging breakers associated with high foreshore slopes. In conclusion. other nourishment practices should be used. better adapted to the natural beach morphodynamics of thc zone. taking also into account the original grain size and density of the beach sands, in order to obtain more durable artificial beaches.

Earth Surface Processes and Landforms, 2014

Proxies, such as changes in beach profiles and shoreline positions, are commonly used in management and research for estimating changes in subaerial beach volume; however, the accuracy of these proxies across increasing time scales and complex morphologies is unclear. Volume changes associated with along-beach morphologic variability may not be captured well by changes in profiles, while volume changes associated with across-beach morphologic variability may not be captured well by measuring shoreline change. This study assesses the impacts of morphologic variations, associated with beach cusps and nourishment material, on volume change estimates from profiles and shoreline change at 0.5 to 3.5 year time periods. Results indicate that profiles spaced ≥ 150 m apart and the shoreline-change proxy will likely estimate volume change inaccurately over periods ≤ 1 year at beaches that are consistently eroding or accreting and contain cusps. However, over longer time periods (1-3.5 years), estimates of volume change from both proxies improved at those types of beaches. Volume changes at the edges of nourishment areas are not captured well by profiles. When the nourishment material is graded to a ramped morphology, which minimizes across-beach morphologic variability, the shoreline-change proxy does accurately estimate volume changes. Both proxies estimate volume changes inaccurately at beaches where volume changes oscillate between erosion and accretion on both short and long time scales because the magnitude of small-scale changes in volume from the formation and erosion of morphologic features, such as cusps and berms, will always be similar to the longer-term net volume change. This study suggests that decadal records of shoreline change, which are commonly developed using aerial photography, can be used to help identify the best proxy for estimating volume change; however, recent anthropogenic modifications that impact patterns of beach sedimentation, including nourishment, terminal groins, and inlet-channel dredging, makes decadal records less useful.

This study contributes to the understanding of very low-energy fetch-limited environments by reporting the evolution of a back-barrier beach (Ancão Peninsula, southern Portugal). It considers two timescales: a largescale evolution for the past 60 years based on aerial photograph analysis, and a small-scale beach evolution based on monthly topographic surveys performed during three years of monitoring. Each timescale revealed a different rate of evolution, the first reporting a modified beach response-type (from human activities), and the second reporting a natural beach response-type. Human activities caused significant changes in the backbarrier shore, whereas changes under natural forcing were much smaller, were less influential on the area's evolution, and were not sufficient to counteract or mask the consequences of human activities. The findings of the study should contribute to a better understanding about the large-and small-scale changes in other back-barriers characterised by similar very low-energy conditions.

Journal of Coastal Research, 1992

Beach fill instances on the Atlantic coast of the U.S.A. generally have a life expectancy of less than five years. Although beach nourishment is viewed as viable and is often preferred to hard structures, the geomorphologic life of the fill is an important variable in evaluating the success of the venture. Two adjacent, nourished beaches on the diffed south coast of Portugal are examined to determine their morphologies following the fill and the variables that condition their temporal and spatial responses. The differential exposure to the ambient wave conditions and the nearshore circulation system differences caused by stacks and a very long jetty help to explain the contrasting history of beach fill in the two areas. Shoreline changes, surface morphologies, and sediment redistributions are traced through aerial photos, ground surveys, and a large collection of postcard views of the growing tourist area. The interpretation of this heterogeneous data set is that Praia da Rocha is r...

Journal of Coastal Research, 2013

Norte beach stands in a coastal stretch fully exposed to the high energetic North Atlantic wave regime. The beach is located updrift of the Nazaré submarine canyon head, a sedimentary sink that captures the southward directed longshore drift. Systematic monitoring of Norte beach has been conducted by a coastal video monitoring system since 2008. A total of 31 monthly coastlines were extracted and analyzed in the period between December 2008 and May 2012. Results show a rare high seasonal coastline variability which exceeds 160 m in the southward sector (adjacent to the headland) and 70 m at the central and north sectors. These coastline variations are related with modifications in the planform beach configuration: beach oscillates between a straight (generally from June to August) and an arcuate configuration (during the remaining months of the year). Results suggest that Norte beach variability depends mainly on longshore drift gradients rather than with cross-shore sedimentary transfers. The intense wave refraction over the canyon head, associated with the westerly swell waves, generates a sedimentary convergence at the centre of the beach promoting the increase of the beach curvature, while, northern and/or short waves (more frequent in summer) tend to linearize the beach. This work contributed with valuable information about the sedimentary dynamics of the Norte beach and showed that this site is a suitable candidate to evaluate longshore drift from shoreline changes.