Combination of Satellite Images and Numerical Model for the State Followed the Coast of the Bay of Bejaia-Jijel

Abstract

Bay of Bejaia-Jijel extends over a length of 100 km with the presence of the ports, the beaches of rivers that
 discharge of the bay. This area characterized by strong economic activity, namely tourism and fisheries.
 However, severe erosion, high hydrodynamic activity and significant silting of ports affect this bay. Hence, the
 interest of this study, which tries to explain these phenomena, based on multisource data with multitasking
 models. First, we developed an algorithm that can convert satellite images in coastline vector. This technique
 applied to three images LANDSAT TM and OLI sensed in 1987, 2011; 2015. The multi-temporal monitoring
 coastlines show that the region suffered severe erosion. This erosion is 4.6 m / year for the period of 1987/2011
 and 1.5 m / year for the period 2011/2015. To explain this phenomenon we interested to do a study of
 hydrodynamics using the SWAN software. We used a long time series of wind speed and direction to discern
 extreme cases in the region. For maximum wind, the significant wave height recorded very high values and a
 very active orbital current with a speed that exceeds 0.7 m / s. Numerical modelling has allowed us to explain
 the erosion but does not explain the speed difference coastline. To find the explanation of erosion speed
 difference between the two periods we consulted the administrative archive of the region. In the archive, the
 number of authorized hourglasses is, 12 in the 90s, but 36 quarries operate haphazardly. In this period the
 balance of suspended matter is completely unbalanced which promotes erosion. After 2008, these quarries were
 closed therefore the balance of the suspended material has improved and consequently coastal erosion has
 decreased.