Impacts of revetments and seawalls in a fetch limited coast
Tutor / director / evaluatorGracia Garcia, Vicente
Document typeMaster thesis
Rights accessOpen Access
Found on the NW Mediterranean, the Catalan coast is not only subjected to morphological changes driven by physical natural processes but also by significant changes in local dynamics that result from the numerous coastal structures that are found on its realm. The armoring of coastal stretches is a common selected option for protecting valuable infrastructure and the hinterland. Nonetheless, the induced effects of these kinds of structures are still an open question that can be only answered by local means and remain unrevised for the area. In the present study an inventory of all the armored structures found along the Catalan coast was carried out. An approximate estimation of 110km of total armoured coast that accounts for 19% of the total Catalan coast was found and synthesized into eight associative structure-beach pattern groups by considering: morphological classification of beach and seawall characteristics. Los Vascos at the northern Ebro hemi delta and Sant Pol de Mar in the Maresme region were selected as representative sites of two of the associative structure-beach proposed groups for in depth analysis. A review of the reported effects accrued to structures on the adjacent beach found on literature was updated and tested at each representative site. The effects of found structures at each site were analyzed in the longshore and crosshore dimension through numerical simulations. For the longshore dimension, GENESIS (Generalized Model for Shoreline Changes) was used to simulate the changes in the plan shape due to longshore transport accounted for wave angle of approach and longshore gradient in wave height at both sites. Seasonal, yearly and long term analysis were performed, exhibiting differences in magnitudes of sediment transport rates and dominant mechanisms between sites as denoted by the different parameter values found during calibration .At Los Vascos the average net sediment transport was estimated in 37095.16m3/year where finer sediments are distributed by an almost unidirectional longshore current towards the northern part of the hemi delta. While for the case of Sant Pol de Mar, the sediments are redistributed in both north and south directions along the year, producing a relatively lower net average transport rate obtained in 14785.47m3. Through simulations with and without the presence of structures, the effects in the longshore transport and shoreline response accrued to the structures only were found. Maximum beach erosion and areas of influence were obtained. Expected effects in the long term were found through 10 years simulations. Furthermore, variations in 0.25m and 0.5m water level increments, 5% and 10% Hs and Tp increments, and 5% and 10% storm frequency increments were tested individually and in combination for the year 2057 as possible future conditions. An additional sensitive analysis was gained during the future condition simulations. Increments in storm frequency as the main driver for shoreline change resulted in higher shoreline variability than water level increments. As expected, combinations in 10% increments of wave parameters (i.e., 10% Hs and 10% Tp ) simulations produced larger shoreline responses and it was proved that the Hs plays a dominant role in the longshore sediment transport. Furthermore, it was found that in places as Sant Pol de Mar where significant diffraction effects governs wave transformation, increments in wave period result in higher shoreline variability than increments in wave heights. iv As for the cross-shore dimension, the SBEACH model (Storm Induced Beach Change Numerical Model) was used to analyze the effects in the beach in front of the structures at each site. Formation of scour and beach width diminishing were successfully obtained in a qualitatively basis and proved to be the cross-shore induced effects when comparing theoretical non walled final profiles obtained through simulation. Moreover, higher insight was achieved regarding the obtained GENESIS responses by setup performing tests of the two available solutions of the one line analytical model developed by Hanson and Krauss (1987) fed by the most representative wave for Los Vascos site in morphological terms. The solution for a semi infinite wall where no flanking effect possible resembled in higher accurate manner the obtained GENESIS responses proving that this was the solution offered by the model. Finally, it was proven that if the erosion behind the structure and downdrift erosion are subjects to be quantitatively analyzed the solution for a semi infinite wall where flaking effect is possible can is very useful aid in addition with GENESIS simulations.