Juanico M. and Friedler E. (1999) - Wastewater reuse for river recovery in semi-arid Israel. Water Sci Technol. 40(4-5):43-50.  

ABSTRACT

 In the past, relatively large quantities of water flowed in the few rivers and some of the ‘nahalim’ or ‘wadies’ of Israel (streams which run dry or almost dry during the Mediterranean summer, while flowing during the rainy winter). The ‘natural’ base-flow (excluding winter floods) of the rivers amounted to about 300-400 MCM/year, while the Jordan river alone added several more MCM/year. Since the beginning of the 20th century, as a consequence of population growth and the resultant increase in water demand, most of the flowing water was captured at source and diverted to meet the growing needs for water supply. Thus, most rivers and streams turned  into dry river-beds which deliver only sporadic floods during the winter. Simultaneously, the same accelerating population growth resulted in uncontrolled discharge of raw sewage into the rivers, transforming many of them into open sewage channels. In recent years, various organizations (governmental and non-governmental) invest increasing efforts to improve the poor condition of the rivers and streams in the country. These efforts resulted in the creation of ‘The Administration for the Recovery of Israeli Rivers’, and in an official recognition of rivers and streams as ‘legitimate water users’.  

In a semi-arid country such as Israel where literally every drop of water is used, reclaimed wastewater is the most feasible water source for river recovery. Indeed, ‘The Administration for the Recovery of Israeli Rivers’ already initiated some projects where reclaimed wastewater serves as the main water source for the recovery of rivers and streams.

Two main topics concerning the use of reclaimed wastewater for the recovery of rivers and streams are addressed in the present paper:

  1.  Water quality management in rivers where most of the flowing water is treated wastewater.

  2.  Water  allocations (or reclaimed wastewater allocations) required for the recovery of rivers and streams, and their meaning within the framework of water resources management. 

Water quality management.

The management of water quality under these conditions (main water source is reclaimed effluent) must find a balance between two different approaches:

  1.  Concentrate the water quality control effort on the allocated wastewater. The allocated reclaimed wastewater is not only a source of water but also a source of pollution. This basic pollution level reduces the capacity of the river to absorb pollution from other sources. Additional waters from different sources may reach the river with varying quality and further contribute to the pollutants load.

  2.  Spread the water quality control effort among the allocated wastewater and the other sources of pollution. If the wastewater quality requirement is too strict, it may sharply increase the treatment costs while having not conspicuous effect on the quality of the water within the river, due to the contribution of other sources of pollution. A more holistic approach extending quality management to the whole catchment area may render better results. 

The main sources of pollution affecting water quality in these rivers and streams are:

Pollutants to the river can be classified as:

 Water allocations.
A request for allocation of water may be based on three different reasons, according to the planned uses of the river. Each one has a different methodology to estimate the required water allocation:

  1. Ecological needs - Water allocation needed to restore part of the ecosystem which characterized the river in the past, and to enable the development of a diverse and healthy aquatic community.

  2.  Landscape development needs - Water allocation needed to develop the river and the surrounding area to parks and ‘green belts’ which are most important in a small densely populated country with large urban areas.

  3.  Economic activity needs  - Water allocation needed to enable commercial development relying on the river as a focal point (restaurants, hotels, commercial sport centers, etc.). 

An important point is the difference between the bruto and neto allocations:

   ·   The bruto allocation is the amount of reclaimed wastewater which must be discharged into the river in order to fulfill the flow requirements for the different needs.

   ·   The neto allocation is the bruto one minus the amount of water which can be taken downstream from the river and reused for other purposes (e.g., irrigation of parks on the river banks, groundwater recharge, etc.). 

A study of the allocation needs for the recovery of 14 main rivers and streams in Israel reveled that some 122 MCM/year of reclaimed wastewater may be required, a frightening amount in a country with very limited water resources. But, the study also reveled that this amount of water is already running in the rivers, generally as raw sewage or low quality wastewater. The problem is that this flow has inappropriate quality, it enters the rivers at inappropriate places, and it is running in an inappropriate time of the year. The formal allocation of this wastewater to the rivers will make possible the investments in treatment and storage required for the release of wastewater of proper quality in proper places and time. And the implementation of this step will allow the reuse of the allocated wastewater downstream, a thing which is impossible today. Thus, surprisingly, the bruto allocation of 122 MCM/year of wastewater for the recovery of rivers may result in a small neto allocation and in an increase of the water resources available to the country.

 Keywords

Mediterranean, river recovery, water allocation, water quality, water reuse

 

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