Preliminary Assessment of the Spreading of Pollutants from a Sewage Outfall
Along the Gaza Strip
By Prof. Steve Brenner 8 Sept. 2005
[Appendix to the Petition of Professors Eidelberg, Zaritsky and Hanukoglu
against the Prime Minister, Ariel Sharon, in H.C.J. 8637/05.
A copy of the Petition is at
www.fandz.com/Downloads/Zell_Goldberg_HCJ_Enviro_11Sep05.pdf ]

In many parts of the world, including developed countries, sewage from large
cities along the coast is disposed of at sea by either dumping the sludge
far offshore (usually tens of kilometers) or by discharging the treated
wastewater into the sea through an outfall located beyond the breaker zone.
In the former case, the assumption is that the sludge will remain cohesive
and sink to the bottom in deep water where the environmental impacts will be
minimal. In the latter case, it is assumed that the ocean currents will mix
and dilute the wastewater with seawater and spread the pollutants over a
large area, thereby reducing the concentrations to environmentally
acceptable levels. It is important to locate the outfall beyond the breaker
zone (typically several kilometers) in order to avoid problems of the
pollutants washing up on the immediate shore. By the generic term
"pollutants" we refer to dissolved and suspended inorganic and organic
material as well as to various bacteria. The latter generally pose the
greatest immediate health risk, and high concentrations usually lead to the
closing of bathing beaches.

The current situation in Gaza City, with more than one million residents, is
to discharge the domestic sewage into a holding pool north of the city where
the wastewater slowly percolates into the ground. As the population of the
Gaza Strip grows, it is clear that an alternative disposal system will have
to be established and it is most likely that the choice will be discharge
into the sea. Until the present, this has not occurred due to the
environmental controls and restrictions enforced by the State of Israel.
Upon the Israeli withdrawal from this region, nothing will prevent the
Palestinians from switching to the very simple and attractive option of
ocean disposal. If this is not properly planned, assessed, and monitored,
the dire consequences for Israel will be the equivalent of an ecological
time bomb.

Based on direct current measurements that were conduced over a period of
several years off the coast of Ashkelon and Ashdod, as well as extensive
studies of the circulation in the southeastern Mediterranean Sea based on
simulations and forecasts with a state-of-the-art ocean circulation model,
it has been shown conclusively that throughout the year the predominant
direction of flow in this region is along the coast, directed from south to
north. The cross-shore component of flow is weaker and fluctuates between
onshore and offshore depending upon the depth, the precise current
direction, and the wind speed and direction. There is little doubt that any
effluents discharged into the sea off the coast of Gaza will spread
northward into the territorial waters and the coastal zone of Israel.

The potential concentrations and dilution of these effluents as well and the
potential environmental impacts cannot be quantitatively assessed without
conducting a proper environmental impact study. Nevertheless, we can draw
some preliminary qualitative conclusions based on the experience of the Gush
Dan sewage outfall, which services the greater Tel Aviv area. This outfall
is located 4.5-5 km offshore where the water depth is 38 m. The zone around
the outfall has been extensively studied and monitored by scientists from
Israel Oceanographic and Limnological Research (IOLR) for many years. Their
long-term results clearly show that the seabed and sediments are affected by
the effluents at distances of as much as 5 km to the north and 1 km to the
south (due to the mainly northward currents). It should be noted that this
is for the case of treated effluents. Perhaps a better indication of the
potentially dire environmental consequences of an unplanned and unmonitored
outfall can be seen in the accident that occurred in February 2003 when the
pipeline ruptured and partially untreated wastewater was discharged directly
into the sea over a period of several weeks. Satellite images of the sea
surface as well as numerical simulations of the circulation at this time
clearly showed the north to northeastward spread of the plume, which came
ashore and affected the entire coastline of Tel Aviv and the area to the
north. The bathing beaches in this area were closed by the Ministry of
Health and the Ministry of the Environment for an extended period due to the
deterioration of the water quality.

Based on this preliminary assessment, there is little doubt that an
improperly designed sewage outfall from Gaza will adversely affect the coast
of Ashkelon within a very short period of a few weeks or less. Since the
outfall would presumably operate continuously, the detrimental effects in
Ashkelon will grow with time while the longer term environmental impacts may
very well be felt in Ashdod and even further north.
===

Prof. Steve Brenner is a physical oceanographer specializing in numerical
simulations of ocean circulation. He has spent the past twenty years
studying the circulation of the eastern Mediterranean Sea and the Gulf of
Eilat and has coordinated several major environmental impacts studies of the
Haifa Bay region. He is currently the head of the Department of Geography
and Environment at Bar Ilan University and previously served for 18 years as
a senior scientist and the head of the Department of Physical Oceanography
at the National Institute of Oceanography in Haifa. He has been the author
or co-author of more than 150 scientific papers and reports and has served
on various local and international scientific committees and advisory
boards.