Israel Water Context

6.  Surface Water

The surface water constitutes around 30% of the natural water in Israel, and its average contribution is estimated as around 550 million m³/yr. The amount of surface water depends directly on the amount of precipitation and its distribution in the course of the season. Since the amounts of precipitation are very different from year to year, so are the amounts of surface runoff, and therefore it is more difficult to predict the potential of surface water each year or to rely on it exclusively.

The surface waters can be divided into constant flows and to flood flows. Constant flows (in perennial streams) occur only in channels fed by permanent subsurface water sources, and therefore these flow all year round. Flood flows (winter swelling) are flows that occur at the time and immediately after rainstorms, and have a high intensity that rapidly dies out. In Israel there are very few perennial streams and most of them are concentrated in the Kinneret basin; the largest of them is the Jordan River. Many streams, both long and short are ephemeral and flow only in the winter season and drain only the flood flows.

The surface runoff flows on the surface in streams and in winter swellings and are drained in accord with the topography. The primary water divide, which crosses Israel from north to south on the central mountain ridge, separates the flows to two main drainage basins. The area to the west of the water divide is drained to the Mediterranean Sea; and, except for the most southern part, which drains to the Red Sea, the area to the east of the water divide drains to the Dead Sea.

The regions that are drained to the Mediterranean Sea constitute an area of around 11,400 km².  The surface runoff in this area is estimated to be ~200 million m³/yr, flowing in approximately 20 main streams. Most of the water flows to the sea and a minor part of it is exploited in reservoirs. The largest streams are the Yarqon in the Tel Aviv area (50 million m³/yr) and the Qishon in the Haifa Bay area (30 million m³/yr).Today most of the streams in this area are ephemeral; in some there is a weak perennial flow. In the historical past the Yarqon River was fed from springs whose waters originated in the mountain aquifer, but today these are dried up. Most of the streams are today in a process of rehabilitation that includes regulating the drainage, cleaning the flow channel and preventing flow pollutants.

The area of the Dead Sea drainage basin is around 29,000 km², but only half of it is within Israel. In its northern part, the catchment basin of the Kinneret, the surface water flows from the Galilee and Golan mountains to the upper part of the Jordan River and to the Kinneret, -210 m below sea level. The basin area is around 2730 km², and is the richest area in surface runoff. The surface runoff potential is estimated to be ~500 million m³/yr, and is fully exploited by pumping from the Jordan and its tributaries, from the Kinneret, and from reservoirs in the Golan . The quality of the water in the Kinneret basin is good to medium, but requires mechanical, biological and chemical treatment to bring it up to drinking-water standard.

In the central part the water flows to the southern Jordan riverbed. The area back of the mountain, which is characterized by relatively low precipitation, is drained to this part. The streams in the area are dry most of the year, except for short segments in the slope that are fed by groundwater. The potential of the surface runoff in this area is relatively low, and a small part of it is exploited in a reservoir established in Nahal Tirza (which drains an area of around 330 km²) before its entry into the Jordan.

In the southern part, which includes the Judea Desert and the Negev, the water flows to the Dead Sea or to the Arava stream and from there to the Dead Sea. In this part the flow is only from floods. All the streams in the area, in which precipitation is meager, are ephemeral. However, during rainstorms, with the wetting, the clayey ground is immediately sealed, thus enabling the surface flow of floods. The floods occur just a few times a year in the fall and for the most part continue for only a few hours. The intensity of the floods can be particularly strong, exceeding 1000 m³/sec, even causing destruction or damage to the infrastructure (roads, bridges). In some of the streams intensities of peak discharges even greater than 1000 m³/sec were measured. The surface water coming from the Judea Desert to the Dead Sea can neither be collected nor exploited. In the south along the Arava stream and its tributaries, six dams were built in the last years that enable collecting some of the floodwaters. These waters serve the farmers in the area.

As stated, only a small part of the surface runoff potential is collectable and/or exploitable. Two plants set up on streams that drain to the Mediterranean Sea exploit the surface runoff for purposes of enriching the coastal aquifer. In the Nahal Taninim basin (an area of 180 km²) around 2/3 of the surface runoff waters (12 million m³ out of  ~18 million m³) is caught and penetrated into the aquifer. In the Nahal Shiqma basin (around 760 km2) around half the surface runoff water (3 million m³ out of ~6 million m³) is caught and penetrated. Other reservoirs enable storing the water flowing in winter and using them for irrigation in the summer season. The reservoirs have another important role in that they reduce the extreme swelling flows and prevent flooding downstream. The quality of the water in the reservoirs is medium to poor, and their use is accordingly limited to agriculture or to enriching the aquifers.