Wave climate and morphosedimentary characteristics of the Kenitra–Bouknadel sandy coast, Morocco

Abstract

The Bouknadel-Kenitra 20-km sandy coastline is of strong interest from the perspectives of beach amenity, tourism and erosion issues. This section of the Moroccan coastline has only received little attention in the literature so far and morphosedimentary characteristics as well as wave climate are poorly understood. The present paper provides the first extensive description of both wave climate and alongshore variability in the morphosedimentary behavior of these wave-dominated beaches, combined with accurate topographic surveys, 9-year long global wave model output time series and subsequently driven empirical longshore drift formula and shoreline change measurements from aerial photographs. Results show that the coast is mainly exposed to high-energy low steepness NW waves (mostly during the October-March period) generated in the North Atlantic by eastward traveling low pressure systems. Given the shoreline orientation, northward and southward longshore drift components generated by this wave regime nearly balance. In contrast, the lower-energy higher steepness N-NW wave regime (April-September period) contributes to an overall quantity of sand being transported southward similar to the yearly averaged net longshore drift. Beaches are mostly of the double-barred intermediate type. The southern beaches exhibit persistent rhythmic sandbars and rather steep beachface while the northern beaches are close to the dissipative state despite all the beaches are exposed to the same wave regimes. Beach states predicted using the Dean's number roughly match these observations. While previous studies elsewhere had shown that inherited geological factors may overwhelm contemporary dynamics in the determination of beach states, here differences are attributed to coastal protection works that appear to be important additional determinants of beach morphology.

Using automatic computation to analyze the rate of shoreline change on the Kenitra coast, Morocco

“…This research reveals that most of the study area is in accretion (286000 m²/year) while the net rate of erosion is around À 374 m²/ year. Our results, combined with the earlier study of Hakkou et al (2011), show steady seaward migration of the shoreline at Chlihat of the order of 1.4 m/year. The results exhibit good agreement with values by EPR and LR models where the back calculated RMSE error is 6.4 m.…”

“…In contrast, Chlihat beach north of the Sebou estuary exhibits a dissipative shape with spilling breakers and experiences accretion due to the littoral drift. The net longshore drift averaged over the 8-year period at Chlihat beach, Sidi Boughaba beach and Nations beach is found to be southward and about 85,000, 340,000 and 200,000 m 3 /year, respectively (Hakkou et al, 2011). Deepika et al (2014) showed the same trend on the Udupi coast, western India, where sandy beaches are subjected to erosion due to migration of the river mouth after the construction of breakwaters in the 1980s on either side of the Udyavaraestuary.…”

“…The tide is mesodiurnal (Idrissi et al, 2004) with a tidal range of 2.2 m on average, which can vary from 0.9 to 3.5 m during neap and spring tides, respectively. Tide-induced currents on the continental shelf are of the order of 0.2-0.3 m/s (Idrissi et al, 2004;Hakkou et al, 2011) with generally northward and southward currents during flow and ebb, respectively. Coastal currents, which have been observed to be highly variable and dependent on seasons and the local bathymetry, are of the order of 0.1-0.5 m/s (Idrissi et al, 2004;Hakkou et al, 2011).…”

“…Tide-induced currents on the continental shelf are of the order of 0.2-0.3 m/s (Idrissi et al, 2004;Hakkou et al, 2011) with generally northward and southward currents during flow and ebb, respectively. Coastal currents, which have been observed to be highly variable and dependent on seasons and the local bathymetry, are of the order of 0.1-0.5 m/s (Idrissi et al, 2004;Hakkou et al, 2011). Prevailing winds are westerly (63%), particularly during the winter period, with only scarce gale events, while persistent northeasterly trade winds are observed during summer (Mhamdi Alaoui et al, 2010;Maanan et al, 2013).…”

“…Polynomial georectification guarantees low spatial error in the geometric properties of remotely-sensed images, as in the case of a linear longshore (Hakkou et al, 2011). Hence, due to its implicit robustness for the geometric correction of remotely-sensed data, it was employedin the present paper (Rocchini and Di Rita, 2005;Avinash et al, 2013;Maanan et al, 2014).…”