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Detection of the Shoreline Changes Using DSAS Technique and Remote Sensing: A Case Study of Tyre Southern Lebanon

Raghda Saad, Jocelyne Adjizian Gerard, Pierre Gerard

Because of coastal erosion and accretion, coastal zones are increasingly vulnerable to coastal devastation. Thus, coastal or shoreline calculation is a crucial aspect in manifesting coastal erosion and accretion, and it plays an important role in shoreline morphodynamic research. To investigate previous or present coastline positions or shape, the Digital Shoreline Analysis System (DSAS) can be utilized in HTA (Historical Trend Analysis). We used a diachronic analysis of aerial photographs and satellite images obtained between 1975, 2001 and 2018, as well as a topographic map from 2015, to analyze the changes occurring throughout the research area. The used methodology is based on geometric and radiometric corrections of aerial photographs and satellite images in order to digitize Tyre shoreline by DSAS version 5. This study focuses on the shoreline change detection along Tyre Shoreline from Qasmiye till El Naqoura linked with human intervention using digital shoreline analysis system (DSAS) and Remote Sensing during the period of 1975-2001, 2001-2018. The rates of shoreline changes in the form of erosion and accretion patterns are automatically quantified by two statistical parameters functioned in DSAS namely endpoint rate (EPR) and net shoreline movement (NSM). The results indicate that the regions have detected both erosion and accretion during the two periods. A period of 1975- 2001 has witnessed erosion in different regions especially in Qasmiye, Jal AL Bhar, Rachidiye, and Bahr Slaiyeb with total rate of erosion (-308.02 m), (-160.25 m), (-241.73 m), (-258.92 m) respectively. On the other hand, in the same period, some regions have revealed a small rate of accretion. At the period of 2001 -2018 Tyre shoreline has recorded a rate of erosion and accretion in almost most regions. LULC (land use and land cover) in this research confirm that the Tyre coastal area has been exposed to a dramatically changes, so settlements area (Harbor, hotels, resorts, roads net, industry, commercials etc.) has exacerbated at the expense of wetlands, sandy area, and vegetation during the period of 1975-2001 and 2001-2018. The shape of a beach and the surrounding estate is primary affected by wave conditions and tide levels. For this reason, different kinds of coastal management including sea walls, breakwaters were applied in Tyre shoreline.