Geologists protect precipitous Mediterranean cliffs

As erosion causes coast to retreat, beach becomes increasingly dangerous, as municipalities try to stabilize the area and keep it beautiful.

By
April 17, 2011 02:01
Geologists protect precipitous Mediterranean cliffs

netanya cliffs 248.88. (photo credit: Courtesy)

Gesturing northward to an elaborate log cabin home carved into the side of the Sidna Ali cliffs along the Herzliya Pituah coastline, Dr. Ram Ben-David highlighted the dangers of inhabiting an area of such geotechnical instability.

“Nobody can take him out,” Ben-David said, referring to the owner of the house, adding that teenagers often pitch tents right underneath the eroding escarpment, despite fences with signs that warn them to stay five to seven meters away.

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“If you’re crazy enough to go down there it’s your responsibility,” he said.

Ben-David, a geological engineering consultant with several decades of experience working on geotechnical stability, is currently serves on teams generating seashore master plans in both Herzliya and Netanya.

Long before the Environmental Protection Ministry’s decision two weeks ago to allocate NIS 500 million to coastal cliff protection, engineers and planners like Ben-David were working with coastal municipalities to figure out the best solutions to both stabilize the retreating Mediterranean escarpment and at the same time keep the areas as natural and beautiful as possible.

At the Sidna Ali cliffs – located 35 meters above sea level – as well as the significantly less dangerous Tel Michal areas north and south of the Herzliya Marina – located at 20 meters above sea level – Ben- David pointed out problematic areas he is currently addressing with team members of the Herzliya Municipality’s Seafront Planning Committee.

“You have to prevent waves from getting to the cliff, and also prevent run-off,” Ben- David told The Jerusalem Post atop the Sidna Ali cliff on Thursday afternoon.

The cliffs are largely composed of kurkar, aeolianite rock formed by the lithification of sediment. After maintaining a relatively steady height from Tel Aviv through the Herzliya Marina area, the terrain begins to grow higher and higher near Rehov Galei Tchelet, one of Israel’s most expensive areas, Ben-David said.

“How to stabilize this is a big debate because you don’t use the same measurements if there is going to be a park versus buildings,” he explained.

Ben-David began the afternoon’s cliff tours with an area that for sure will be becoming parkland – the sections both slightly north and south of the Herzliya Marina, at the 4,000- year-old archeological site of Tel Michal.

Turning off the main road, Ben-David plowed his fourwheel- drive pickup truck along the dirt paths through the cliffs just north of the marina, parking amid the wild flower beds. He pointed to the line of hotels along the shore, where he said the Dan Hotel group intends to build 30-floor structure, but he considers this area generally safe from the erosion because “there is almost no cliff” here.

Yet in the relatively undeveloped section of Herzliya – basically the area that stretches from Tel Michal until the border with Tel Aviv – a string of problematic cliffs run down the coast. That entire stretch, at a width of 300 meters from the sea eastward, will become part of a future park, while land beyond that line will be dedicated to expanding Herzliya proper.

“The idea is to make it as natural as possible,” Ben-David said.

Prof. Micha Klein of the University of Haifa agreed about the benefits of keeping such an area “natural” by maintaining parkland rather than building more urban elements.

“It’s less dangerous [to build a park] than constructing buildings there. What are the chances for land use in this area? A park is a safer land use than erecting buildings that will be in danger in our generation’s time,” said Klein, an associate professor of geography and environmental studies.

He has also studied the cliffs extensively and co-wrote a 2004 paper on coastal cliff retreat in the Beit Yannai area – north of Netanya – over the past century.

Between the years 1918 and 2000, the Beit Yannai coast retreated an average of 16 meters eastward annually, at an average rate of 20 centimeters, according to Klein’s report, which used photographs from the World War Iera to take accurate measurements from the earlier years.

This is just one example of the severe coastal erosion that has occurred all down the coast.

Meanwhile, back in Ben- David’s pickup truck, the geologist weaved his vehicle through the hilly terrain and stopped just south of the marina, motioning toward a huge “unnatural pile of sand,” which he said would be removed from the eventual park to extend the Herzliya seashore for bathing. Pulling over toward the bottom of Tel Michal, he pointed to scattered piles of garbage all over this section of the cliffs – home to what he called “the country beach” prostitutes.

“This one has to be treated soon, otherwise it will be a junkyard – it already is a junkyard,” he said.

Back on the paved road again, Ben-David stopped the car under a retaining wall that separates part of the slope from the street, explaining that “the idea is to prevent the sand – the kurkar – from making landslides.”

A bit north of the wall, the cliffsides became distinctly gray and rather smooth once again, where engineers had adjusted the slope of the kurkar itself rather than building an external structure to stabilize it. This option, Ben- David said, would more likely be incorporated into the park plans, rather than using unnatural barricades. Passing through the Marina mall parking lot, Ben-David said the cliffs across the street would likely be connected to a roof that would hang over that parking lot, to extend the park.

Ben-David started his truck again and headed north to Herzliya Pituah, pointing on the way at lines running down the cliffs – what he called “the incision of the water.”

“You can see the retreat. It’s dynamic,” he said.

After ambling through the wealthy neighborhoods in Herzliya Pituah, Ben-David drove the pickup to the 13thcentury Sidna Ali Mosque that stands atop a cliff that overhangs the sea with no protective barrier.

“It’s not dangerous to just stand here,” Ben-David reassured the Post, perched atop this 35-meters-above-sea-level rocky ridge, with the blue waves splashing below him. “If people are standing on the bottom and there is some kind of landslide, they can be hurt.”

Certain portions of the cliffs in this area have negative slopes – sections that curve in the opposite direction of the normal inclination – which were formed by channels of runoff water billowing down the mountainside.

“The stairs are inviting water to go fast and go down,” he said, pointing to a set of steps that leads down the cliff.

By running drainage pipes from the urban areas and through the cliffs to the sea, “you increase the intensity of this water and you make more erosion,” he added.

This location is more of a hazard than the previous area we visited, particularly to passersby underneath the cliffs, because here during landslides “a larger quantity of material goes down,” Ben- David explained, pointing to the stone on the ground that he called “fragile” but stronger than that of the marina.

Not only is the escarpment in Herzliya Pituah more dangerous than that of the marina area, measurements for slope stabilization mechanisms and park construction must be taken with much more care and precision because of the Sidna Ali Mosque that stands on the cliff top.

“This mosque is very important, so you will make measurements to make sure that it is not touched,” Ben-David said.

“It is a complex decision to make – it’s not just a simple matter of taking NIS 500m.,” he said. “There’s no clear-cut solution.”


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