Morphodynamic responses of nourished beaches in SW Spain

Coastal Engineering, 1984

Engineer: Journal of the Institution of Engineers, Sri Lanka

Beach nourishment is a viable engineering solution for shore protection by stabilizing beaches. However, beach nourishment may not be technically or economically feasible or justified for some sites, particularly those with high erosion rates. The frequency of re-nourishment is one of the important parameters that could be used to justify beach nourishment process for a given shoreline. Mathematical models could be effectively used for the above purpose. A mathematical model was developed for the simulation of shoreline changes due to both the longshore and cross-shore sediment transport and there by, frequency of re-nourishment could be estimated. This model is an improved version to the typical 'one-line model'. The model has been calibrated and verified against the field data collected from a beach nourishment project implemented in 2003 in a coastal stretch leading from Maha Oya to Lansigama in the west coast of Sri Lanka. The model results proved that the model is capable of simulating shoreline changes with a reasonable accuracy. Median grain size of beach sand and depth of closure are more sensitive to the model predictions compare to other input parameters. The applicability of the model is limited to straight coastlines without the presence of structures.

Coastal Engineering Proceedings, 2018

When erosion occurs, sandy beach cannot maintain the sufficient sand width and the foreshore slope becomes steeper by the frequent erosion effect. As a result, the beach is trapped in a vicious circle of becoming vulnerable by the incident waves. In order to repair or protect the erosive beach, beach nourishment can be used as a countermeasure while minimizing the environmental impacts. However, beach nourishment is not a permanent solution and requires periodic renourishment after several years. To alleviate such problem, minimizing the period of renourishment must be an economical alternative. In that respect, selecting the optimum grain size of the sand for the beach nourishment is very important. Generally, larger grain sized sand is more resistant to the erosion, thus extending the period of renourishment. In addition to selecting the optimum grain size of the sand nourishment, determining the durability as well as maintaining the familiarity of the users of the native sand sho...

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.

Journal of Coastal Research, 1996

The erosion of a nourished beach may be conveniently described as the sum of the linear coastal retreat and a surcharge which decreases exponentially in time. Application of this model to data from eight nourishment projects in north-western Europe has shown on average only 52% of nourished volume becomes a permanent part of the coastal volume. Allowing for an initial loss of some 10%, the results obtained indicate that in practice computed nourishment volumes should be multiplied with a factor of about 2.2, somewhat higher than in previous recommendations.

Science of The Total Environment, 2018

The erosion of the world's coasts and the shortage of sand to mitigate beach erosion is leading to the increasingly common use of gravel for coastal protection and beach nourishment. Therefore, in order to determine the amount of gravel required for such actions, it is important to know perfectly the equilibrium profile of gravel beaches. However, at present, this profile is obtained from formulas obtained mainly after channel tests, and therefore most of them do not adapt to the real profiles formed by gravel beaches in nature. In this article, 31 variables related to sedimentology, waves, morphology and marine vegetation present on the beaches are studied to determine which are the most influential in the profile. From the study carried out, it is obtained that these variables are the steepness and probability of occurrence of the wave perpendicular to the coast, the profile starting slope (between MWL and-2m), the energy reduction coefficient due to Posidonia oceanica as well as the width of the meadow. Using these variables, different numerical models were generated to predict accurately the gravel beach profile, which will lead to a saving in the volume of material used in the order of 1300 m 3 /ml of beach with respect to current formulations, and a greater certainty that the beach nourishment carried out will have the desired effect.

Coastal Engineering 1996, 1997

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

fish.kagoshima-u.ac.jp

Hard engineering approaches such as seawalls, groins, detached and submerged breakwaters to stabilize or restore beaches are used to counteract beach erosion. However, none of these shore protection structures adds more sand to the beach system to compensate for natural and artificial erosion. Thus, beach nourishment, also called "artificial nourishment", "replenishment", "beach fill", and "restoration" involves the addition of sand in designed contours to extend a beach. In the United States, Europe and Australia, beach nourishment has grown in acceptance as major shore protection and beach restoration measure for more than fifty years. In Japan, "hard" structures are also commonly used but after a new coastal law was approved in April 2000, beach nourishment as a legal shore protection work was accepted. However, at present, beach nourishment is not yet widely used as shore protection method in Japan. Specifically, this paper deals with beach nourishment projects in carbonate material (coral reef) beach in Okinawa, Japan and in Florida, USA. Data on beach fill length, volume, nourishment volume density, frequency of beach fill, borrow source and cost of beach fill material from different beach nourishment projects were reviewed, assessed, analyzed and consolidated．Range of values and mean values of nourishment project parameters were calculated and then were used as basis for the comparative analysis of beach nourishment in normal sandy and coral sandy beaches. The consolidated results will serve as database for implementing future restoration projects in coral sandy beaches in tropical and subtropical countries like the Philippines.

Coastal Engineering 1986, 1987

Geomorphology, 2010

The relationship between beachface slope and sand grain size has been established based on multiple observations of beach characteristics in many parts of the world. We show that this observational result may be understood in the light of the Constructal Law (Bejan, 1997). A model of wave run-up and run-down along the beachface (swash) was developed to account for superficial flows together with flows through the porous sand bed of average porosity 0.35, the permeability of which may be related to grain diameter and sphericity (0.9 for sand grains) through the Kozeny–Carmán equation. Then, by using the Constructal Law, we minimized the time for completing a swash cycle, under fixed wave height and sand grain diameter. As the result, a relationship involving sand grain size, beachface slope and open ocean wave height has been obtained, and then discussed and validated against experimental data. In addition, this relationship has also been used to illuminate beachface dynamic processes, namely the reshaping of sandy beachfaces in response to changes in wave height. Though the model used in this work may be improved further, the results appear to show, as with other natural systems, that beachface morphing in time may be understood based on a unifying principle — the Constructal Law.