2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 6
Presentation Time: 3:05 PM

Controls on the Retreat Rate of the Israeli Coastal Cliff and Its Estimated Location at Year 2100

KATZ, Oded, Division of Engineering Geology and Geological Hazards, Geological Survey of Israel, 30 Malkhe Israel St, Jerusalem, 95501, Israel, odedk@gsi.gov.il

The Israeli coastal-cliff rises up to 50m and extends about 60km along the Eastern-Mediterranean shores. In past few decades cliff-top inland local retreat-rates of few tens centimeters per year were recorded with a consequent hazard to shore-communities. Cliff retreat is a result of wave-impact induced slope-failure events.

It consists of alternating eolionite and paleosols. These low-strength materials fail along the rather steep slopes of the coastal-cliff. Failed material is deposited at the cliff base and temporarily shields the cliff from wave-impact. When washed by waves in winter-storms, a new failure-cycle begins.

The average local retreat-rates (for every few hundred meters) are estimated by comparing cliff-top locations in 1945 and 2004 using aerial photos. The 2100 cliff-top location is modeled using the calculated retreat-rates, expected sea-level rise, time constants of failure in the cliff, and anthropogenic activity. Calculated average retreat-rates are less than 0.2m/year and 0.3m/year at 77% and 88% of the cliff length, respectively. The temporal window from which retreat-rates were calculated includes only a part of the accelerated recent sea-level rise period and as a consequence the calculated rates are an underestimate of the rates expected toward 2100. To include the effect of the expected up-to 1m sea-level rise by 2100, a model which considers sea-shore width (waterline to cliff-base) as a few tens of meters and constant is referred. Thus, the above sea-level rise will bring the waterline to the cliff-base that, as a consequence, will retreat inland tens of meters to keep sea-shore width constant. The expected cliff-top line in the year 2100 is mapped 20-30 meters inland from its current location using the estimated retreat-rates. This line defines a hazard zone in which without engineering efforts will be lost by 2100. Presently, this zone includes only tens of houses.