Results

STREAMFLOW

Figure 21. Map showing trends for streamflow at selected sites during 1974–98.

Figure 22. Graphs showing annual streamflow at selected sites during 1974–98.

Annual trends in streamflow at selected sites during 1974–98 are shown in figure 21. Trends are affected by three factors

1. Precipitation, which produces floodflow and also is the main source of base flow because it recharges groundwater;
2. Discharge from springs that flow into stream channels; and
3. Effluent from wastewater-treatment plants.

Time-series plots of streamflow at selected sites on major streams are shown in figure 22. Streamflow in the Iyon River (ST–1) generally was low, and the trend was not significant (fig. 22). Nearby, streamflow at two sites on the Dan River (ST–2) was much greater. At the upstream site, streamflow decreased 1.2 MCM per year during 1974–98. At the downstream site, the decrease was much greater (-13 MCM per year), but all the change occurred from 1988 to 1991 (fig. 22) when a diversion was constructed between the sites.

At the site on the Yarmouk River (ST–3), stream-flow decreased sharply (-5.8MCM per year). Many reasons might account for this decrease, including:

1. Increased diversion from the river to provide water for recent development in the area;
2. Increased abstraction from wells in upstream wadis; and
3. Decreased precipitation during the period of trend analysis.

Streamflow in the Yarcon River (ST–4), near Tel Aviv, increased 3.1 MCM per year during 1974–98. This trend was primarily influenced by high flows in the 2 years following high precipitation in 1992.

Streamflow in the Zarqa River (ST–5) increased an average of 2.9 MCM per year. This trend is primarily due to increases in treated domestic and industrial wastewater that are discharged to the river upstream from this site.

Streamflow in Wadi Karak (ST–6) decreased at average of .0.16 MCM per year, primarily due to withdrawals of water to irrigate the land in the upstream reach. These withdrawals are not uniform and are unpredictable. Water is pumped from a well field which directly affects flow in the wadis upstream from this site.