MONITORING CHANGING POSITION OF THE SHORELINE ALONG BURULLUSBALTIM, NILE DELTA, EGYPT, AND THE RULE OF COASTAL DUNES AS A NATURAL DEFENSE AGAINST EROSION IN A GEO-HERITAGE SITE: REMOTE SENSING APPLICATION

Abstract

Monitoring the coastal area along the Burullus-Baltim coast shows that it is a fragile coastal area composed of loose sand eroded from the old Sebennitic Promontory since historical time of more than 1000 years, then enhanced after the construction of Aswan High Dam (AHD). The interplay of waves, wind and sands along this coast led to construction of a unique geomorphosite with the characteristic barchan and linear sand dunes. Due to the high threshold velocity that reached at Baltim (Vt) 19.38 cm sec, such velocity is able to blow sands with diameter D50 of 250 m. The velocity need for suspending the D50 to an elevation Z (Vz=5m) is equal to 630 cm sec-1. Contrary is the case to the east at Gamasa where the Vt equal to 16.3 cm sec-1 and the Vz for suspending the D50 (180 m at Gamasa) is equal to 560 cm sec . This may explain why the dunes at Baltim are coarser in grain diameter and together withthe tight back desert strip explain the presence of Baltim dunes at elevations more than 20m, while at Gamasa not exceeds 5m. These dunes represent natural defence measures for the barrier beach separating the Burullus Lake from the Mediterranean Sea. Due to human intervention including urban extension and agricultural activities much of these dunes were deteriorated and diminished from 174.8km to 6.4km. The project of extraction and concentration of heavy minerals from sand dunes seem uneconomic. Although the heavy mineral concentration is more than 5%, more than half of the detected minerals is Ilmenite, which is neitherstrategic nor economic mineral. Such project may add new form of hazards. Although the defence measures seem effective in protecting the coast, several rates of erosion and accretion were detected along the studied sectors, and the shoreline does not retain its present position in many areas of the coast since 1984.