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

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.