Offshore dredging study: Environmental ecological report

Abstract

The Government of Israel is considering the possibility of dredging about 4 million cubic meters of kurkar, a soft calcareous sandstone, each year from the shallow sea floor off the Mediterranean coast. The objective of this operation would be to supplement and eventually replace onshore sources of kurkar. Kurkar is utilized extensively for road construction and maintainance. The favoured site for the offshore mining is in the central and northern portions of Haifa Bay. A second-choice site is off Netanya. The sea floor in the vicinity of the Haifa Bay mining site is characterized by four rocky ridge systems which roughly parallel the coastline. The ridges rise from 1 to 10 m above the surrounding bottom, but in most areas the ridge crests remain 10 m or more below the water surface. Bottom areas between the ridges are characterized by rock outcrops as well as softer sediments (mud, sand and gravel). Biological productivity along the Israeli coast is relatively poor compared to other coastal waters of the world, because of the extreme depletion of nutrients in the surface waters of the eastern Mediterranean. Nevertheless, limited studies made in the soft bottom areas of Haifa Bay show that a considerable diversity of organisms inhabit the Bay floor. Commercial fishing is practiced in Haifa Bay by a variety of methods, but only gill netting and hook-and-line fishing are carried out in the rock bottom areas. During the first ten years, the proposed dredging in Haifa Bay will destroy 10–20 km2 of existing bottom habitats, including the submerged rock ridges. The lost rock bottom habitats will be replaced by new habitats, which may vary depending on the dredging plan from mostly sand and mud with a little rock, to perhaps about 75% sand and mud, and the remainder rock. It is recommended that the dredging be carried out in such a way as to maximize the area of rock outcrop and the irregularity of the bottom, in order to replace as far as possible the submerged ridges and rock outcrops lost by quarrying. All the fauna and flora inhabiting the dredged areas will be destroyed or displaced by dredging. Most of the displaced organisms will meet an early death. The new habitats will be partially repopulated with many of the same species of organisms that previously lived in the mined area. The dredging operation and particularly the washing of the recovered material will create a turbid cloud. This cloud or plume will surround the dredge or trail off downstream. It is expected that the dredging operation and the turbid plume generated will disrupt fishing in a large part of the Bay. The nutrient contribution to the coastal waters derived from the offshore dredging is not likely to be significant. Also, the adverse impact of salt brought ashore with the damp kurkar should not be of great importance. The Netanya dredging site is closer to the beach than the mining site in Haifa Bay; it lacks large rocky ridges, and it is characterized by a greater portion of sand bottom. Marine fauna in the area is expected to be less diverse, and have a smaller biomass. The deterioration of water quality, resulting from the generation of turbid waters very close to the shore, may be detrimental to the recreational and tourism values of Netanya Beach. However, this impact will be tempered considerably by the degradation of the offshore waters which is expected to result from the discharge of large quantities of wastes from the Netanya industrial outfall, presently under construction.