|Development of Water Resources|
Applied Research Institutes, Ben-Gurion University of the Negev
". . . and the scorched land will become a pool, and the thirsty ground springs of water"
Scarcity of water has always been the dominant factor in agriculture in the Land of Israel, as it has been throughout most of the arid Middle East. Man has had to rely on scanty and erratic seasonal rains or on rivers for his water throughout the area. In Egypt, for example, the Nile river was the only stable source of water in an otherwise desert landscape. In ancient times, sustained agriculture was limited to narrow strips of land on either side of the river. Even today, farming in Egypt is localized mainly along the banks of the Nile.
The climate of Israel and the areas west of the Jordan River is strongly affected by the proximity of the desert to the south and east. Most of Israel’s territory is classed as arid (60%) or semi-arid. Rainfall is confined to the winterand occurs mainly between November and March. Average annual rainfall ranges from 400 to 800 mm. in the northern and western parts of the country and declines sharply toward the south and east. A dry season with practically no rain prevails from about the beginning of April to the end of October.
Until the beginning of the 20th century, agriculture in the Land, being almost entirely rainfed, was limited to the northern part of the country and the coastal area. In some northern localities, where springwater was available, fields were irrigated. The water was conveyed by gravitation from the source to the fields in open dirt canals. Each farmer was supposed to get his share of water for several hours once every few days or weeks. However, due to heavy loss of water along the transportation route, resulting from fast percolation into the ground, the water was distributed unevenly – and farmers furthest from the source were left with little water. Along the coast, underground water was raised from shallow wells with the help of ‘norias’ (bucket-type water-wheels) driven by donkey or ox. The water was collected in a pool and from there conveyed by gravitation to adjacent plantations, mainly orange groves. Such wells were dug manually and the output was low. The notion that agriculture requires a reliable water supply began to take hold only at the end of the 19th century and beginning of the 20th century. This revolutionary change in attitude was introduced to the area mainly by the Jewish settlers, who were ready to adopt advanced – for the time – technologies and know-how. Such technologies were introduced by immigrants with specialized skills and professional training – among them people experienced in advanced methods of drilling through hard layers and pumping large quantities of water from deep wells.
The Role of Irrigation in Advanced Agriculture
The use of irrigation in traditional farming is hampered by several constraints:
* Sources of water, especially under arid and semi-arid conditions, are usually very limited.
* Water is conveyed to the fields in canals by gravitation, which means that the ground needs to be level. Hilly terrain and slopes, therefore, cannot be irrigated by this method.
* The traditional practice of constructing dirt canals results in large losses of water due to percolation of water into the soil, with longer canals generating larger losses.
* The supply of water declines along the line of distribution, leading to unequal sharing of the limited resources.
* Water supply – which depends on rainfall – is inevitably irregular, resulting in inability to meet the needs of the crops and thus in poor yields.
In view of the circumstances prevailing at the turn of the century in this area, notably the predominance of dry farming with its almost exclusive reliance on seasonal rains, the introduction of new concepts into agriculture involved not merely technical changes but also profound modification of the strategy and scale of agricultural progress.
Two main elements are responsible for the passage from traditional to modern water utilization in agriculture: the human factor, and the introduction and use of newly imported technologies.
Following the establishment of the British Mandate at the end of the First World War, many Jewish immigrants came to Palestine, mainly from Europe. This wave of immigration was unique. Many of the immigrants were highly motivated and keen to establish new agricultural settlements. They were inclined to examine and apply new agrotechnologies, they understood the significance of modern know-how based on scientific studies, and they were eager to adopt advice from scientists and professionals. But perhaps the pivotal factor in their success was their ability to join together and establish organizations for the purpose of raising funds, formulating strategic policies, and drawing up plans for physical development. All these efforts culminated in the twenties and thirties in the establishment of a large number of new agricultural settlements.
As part of the settlement movement, geologists were recruited to search for underground water. Modern drilling equipment capable of drilling to great depths through hard rock layers, new efficient pumping machines, and newly introduced materials such as cement and metal pipes, were all enlisted to help develop dependable systems of water supply. However, over and above these technical efforts, the challenge was met by radically modifying the concept of an adequate water supply.
As mentioned earlier, rainfall in Israel is limited to winter and declines from north to south and from west to east. Furthermore, total annual rainfall fluctuates considerably, drought years being frequent. Planning and building a reliable water supply system must take these constraints into account, that is, it must assure bridging between seasons (winter and summer), regions (north and south), and years (with adequate and inadequate precipitation).
Thus, in the early stages, settlements joined together on a local basis, invested money to search for underground water, and succeeded in providing a more or less uninterrupted water supply. Later on, a broader view of the problem of water supply was adopted. The first concerted effort to build a large-scale project dates to 1935. The leaders of this project were Levi Eshkol, later Prime Minister of Israel, and Simcha Blass, an engineer who later became prominent in the design and development of all the main water projects in the country. The project was designed and carried out between 1935 and 1938 by Mekorot, the newly established public water company. The source of the water was three wells drilled into the western flanks of the valley of Jezreel.
The main features of the project were:
1. Conveyance of the water in metal pipes under high pressure, allowing uninterrupted supply over long distances. The high pressure made it possible to irrigate the fields with sprinklers, superseding traditional flood irrigation.
2. Incorporation of two concrete tanks and two open reservoirs, instrumental in providing a constant water supply. The water was pumped into the reservoirs at night, when the cost of electricity was relatively low; thereafter the water was supplied into the irrigation system without interruption.
The issue of water resources availability and the potential for further development of advanced systems to provide adequate supply was not merely an academic or technological question. It also had political implications. Indeed, national rights to the land lay at the heart of the conflict between the Jewish and the Arab communities. British government policy was to place restrictions on the purchase of land by Jews, establishment of new settlements and also on immigration to Palestine, based on the argument that physical conditions prohibited further growth of the existing population. One of the measures taken by the leadership of the Jewish community to counter British policy was to demonstrate that, with proper development, the land could sustain a much larger population. Hence, considerable effort was invested in conceiving and designing water projects.
Water supply projects – planning
In the late thirties it was accepted by the leading figures in the field that the following principles should guide future planning of water projects:
* Any system developed to provide water must bridge between areas where water is available and those where water is in short supply, as well as between the rainy and the dry season. Therefore, water from rivers, floods and springs should be stored in reservoirs, underground aquifers and tanks for eventual conveyance in supply lines according to needs. Also, water surplus from rainy years should be stored for use in dry years.
* Water should be conveyed under pressure in pipes. While requiring substantial financial inputs, this approach circumvents topographic limitations and minimizes water losses, thus promoting long-term water saving. It also guarantees balanced and fair distribution among end users.
* Planning must be comprehensive. That is, the water projects must convey water to sites all over the country to meet the needs of the growing population and of extensive agricultural development, especially in the Negev.
Several plans for conveying water to the Negev were drawn up from 1939 onward, mainly by Simcha Blass. A comprehensive study titled "Water resources in the Land of Israel: prospects for irrigation and hydro-electric development" was prepared by Mekorot Water Company, in 1944, and at about the same time, experts on water and land conservation from the US became involved in studying and presenting schemes for water projects in Palestine. W.K. Lowdermilk, a highly reputed American expert on soil conservation and hydrology, published, also in 1944, a book ("Palestine – Land of the Promise") on the possibilities of developing water projects in Palestine. In the same year, J.B. Hays, an American expert on dams and water conservation, visited the country to examine the prospects for planning a water project. His book, "Tennessee Valley Authority of the Jordan," was published a few years later. Hays continued his studies after the establishment of the State of Israel and presented several versions of a master plan for the development of hydroelectric power and irrigation. He was later joined by his colleague, J.S. Cotton, who submitted a master plan in 1955 which was eventually adopted by the government and served as the blueprint for the National Water Carrier.
Water supply projects – construction
As part of a drive to settle the Negev, the more arid southern region of the country, three experimental settlements were established there in 1943. The aim was to explore soil conditions in the region, the availability of water (including data on annual precipitation), and which crops could be cultivated under prevailing conditions. Another eleven settlements were established in the Negev in 1946 and a further five in 1947, financed and equipped as before by the Jewish national institutions.
From the very start, it was apparent that in the Negev the main factor limiting agriculture was the scarcity of water. The awareness that successful modern agriculture hinged upon irrigation, which required a reliable supply of water, led to the launching of a series of exploratory studies. These included meteorological, geological and hydrological surveys. Attempts were made to drill wells and draw underground water near the settlements; however, the quantities obtained were quite small, and the salinity of the water was often too high for agricultural use. Attempts to build dams and reservoirs to collect seasonal floodwaters failed because of the large fluctuations from year to year in quantity, the intensity of the floods, and technical difficulties. It was concluded that the only way of securing a dependable and sufficiently large supply of water for agriculture was to transport fresh water from northern sources via pipes.
The first ‘Negev pipeline,’ installed in 1947, assured a reliable if limited supply of water to most of the settlements in the Negev (although several of them still had to rely on local wells). This modest pipeline transported water from wells in the north-western Negev, an area relatively rich in underground water. The first stage, installed and functioning by 1947, consisted of 190 km of 6"- diameter pipes supplying 1 million m3 (MCM) annually. Later on this line was converted to a 20"-diameter pipeline supplying 30 MCM annually. This pioneering endeavor was followed by two large-scale projects which will be described below. The significance of this pipeline was that the concept of transporting water from farther north to sustain the southern arid section of the country was now firmly established.
The first large-scale water supply system, the ‘Yarkon-Negev pipeline,’ was constructed soon after the establishment of the State of Israel. This 66"-diameter pipeline transported water from the Yarkon River to the Negev over a distance of 130 km. The annual output was about 100 MCM.
This was an ambitious project in terms of the means available at the time. However, it soon became obvious that a larger and more comprehensive system was called for, which culminated in a second large-scale project, the ambitious National Water Carrier. The main function of the Carrier is to convey water to the southern region of the country from the Sea of Galilee (Lake Kinneret) in the north. Originally, it was to draw water from the Jordan before it enters Lake Kinneret. The first stages of the ground-work were started in 1953. However, in view of Syrian opposition and a United Nations resolution, Israel was forced to suspend work and modify the design. The final plans were approved in 1956, and the National Water Carrier was completed and functioning by 1964. The Carrier is a combination of underground pipelines, open canals, interim reservoirs and tunnels, supplying about 400 MCM annually from Lake Kinneret, located some 220 meters below sea level. Water is pumped to an elevation of about 152 m. above sea level, and flows by gravitation to the coastal region, whence it is pumped to the Negev.
In addition to the Sea of Galilee, two large aquifers, the Mountain Aquifer and the Coastal Aquifer, respectively contribute some 350 MCM and 250 MCM per annum to the Carrier.
The National Water Carrier functions not only as the main supplier of water, but also as an outlet for surplus water from the north in winter and early spring and a source of recharge to the underground aquifers in the coastal region. Most of the regional water systems are incorporated into the National Water Carrier to form a well-balanced network in which water can be shifted from one line to another according to conditions and needs.
National Water Carrier – Longitudinal Section
Supply and demand – management of the limited water resources
The fresh water resources of Israel, which average about 2,000 MCM annually, are by now being exploited almost to the limit. However, the country’s population is growing constantly, and so is the demand for water. Urgent measures must be taken to provide additional quantities of water. An important potential source is marginal water, a category that comprises effluents, saline water and sea water. Adequate treatment – purification in the case of sewage water and desalination for saline and sea water – can provide the much-needed extra water.
Increasing quantities of sewage water have been finding their way into the environment, endangering groundwater and other sources of fresh water. The pressing need to find alternate sources of water, together with the critical condition of the environment, led the Water Commission to set up the Shafdan plant operated by Mekorot, a large-scale project for processing sewage to produce purified water. This procedure results in two major benefits: a) A nearby aquifer serves as an underground reservoir for the recharged water, preventing losses by evaporation; water is pumped off when needed, mainly in summer. b) Percolation of the water through soil layers provides an additional cleaning phase.
About 100 MCM of this purified water is transported annually via a separate pipeline called the ‘Third Negev Pipeline’ to the western Negev for irrigation. Thanks to the high degree of purification of the treated water, it can be used for all crops without risk to health.
Additional sewage water purification plants are already operative, under construction or on the planning boards. It is expected that most of the water allocated for agriculture will eventually consist of purified effluents, so that quality fresh water can eventually be shifted from agricultural to domestic uses.
Smaller-scale plants located in the Negev itself provide treated sewage water for irrigation of fields located a short distance from the source of the effluent. Treatment is minimal and use of the treated water is restricted to crops such as cotton. These small projects are reported to be highly cost-effective.
Saline water (brackish) and sea water
There are two categories of water available for desalination, saline water (spring and underground) and sea water. Desalting sea water is costly owing to the high concentration of salts. Therefore, efforts to develop a cheaper process are currently focusing on saline water. In the long run, however, sea water will also have to be used as a source of potable water.
Several methods for desalting saline water have been investigated in Israel since the early sixties. Among these, reverse osmosis was found to be efficient and relatively inexpensive; yet it costs today about 25% more to produce potable water by reverse osmosis than by purification of sewage water. Eilat, a city with a population of some 37,000 plus many tourists, has relied on desalinated water for its water supply for the past three decades. Its supply comes from large plants purifying brackish water as well as from a reverse osmosis plant. The latter, making use of a mixture of 80% seawater from the Red Sea and 20% brine from an adjacent factory, provides about 27,000 cu.m/day (about 10 MCM annually).
In addition to assuring an additional source of potable water, the development of an efficient method of desalination will help reverse the current and dangerous trend towards salinization of the fresh-water aquifers.
To a limited extent, untreated saline water is already being put to use for crop irrigation. Many studies have been carried out to investigate whether saline water can be used to irrigate crops. It was found that certain crops such as cotton, tomato and melon readily tolerate saline water (up to 7-8 dS/m electric conductivity, equivalent to salinity of 0.41-0.47% NaCl). However, to minimize accumulation of salts around plant roots and facilitate leaching away of the salts that do accumulate, it is essential: a) to use drip irrigation systems to deliver the saline water; and b) to cultivate the plants in soil-less medium or in light soils (sandy or loamy-sandy soil). In the case of these tolerant crops, the use of saline water can result in the saving of fresh water.
Rain enhancement through cloud seeding has been performed in Israel since 1960. Using aircraft and ground generators, rain enhancement has resulted in an average 15% increase in rainfall in the northern part of the country.
Advanced methods of irrigation
One of the most important agrotechnological innovations of modern times is probably the Israeli invention of drip irrigation by Simcha Blass and his son (the father conceived the idea, the son developed the dripper). Drip irrigation has many advantages over other irrigation methods:
* Drip irrigation is the most efficient method of irrigation when it comes to water saving. Since the drippers emit the water directly to the soil adjacent to the root system, which absorbs the water immediately, evaporation is minimal. This characteristic is especially important in arid zones. In irrigation by sprinklers or by surface methods, evaporation is enhanced by winds, while in drip irrigation the impact of winds is minimal.
* Water is discharged uniformly from every dripper fitted onto the lateral pipe. This is true even on moderately sloping terrain. Furthermore, the development of compensated drippers enables uniform irrigation on steeper slopes over greater distances.
* Via the drippers, fertilizers can be supplied to the plant together with the water (‘fertigation’).
* The quantity of water delivered can be optimized to fit different soil types, avoiding percolation of water beyond the root zone.
* The emergence of weeds is minimized.
* Drippers with a given discharge of water (of the order of several liters per hour) can be installed at any spacing to accommodate the needs of any crop.
* Exploitation of poor quality water (saline water or effluents) is made possible.
* Saline water can be used because direct contact between water and leaves is avoided, thus obviating burns.
* Drip irrigation causes salts to be continuously washed away from the root system, avoiding salt accumulation in the immediate vicinity of the roots. This is important when irrigating salinized soils or irrigating with saline water.
* Drip irrigation allows the use of minimally treated sewage water because the water is delivered directly to the ground, minimizing health risks.
* High-quality drip irrigation equipment can last for fifteen to twenty years if handled properly.
Water use efficiency (WUE) is defined as the ratio between the amount of water taken up by the plant and the total amount of water applied. Studies show that drip irrigation has a WUE of about 95%, versus 45% for surface irrigation and 75% for sprinkler irrigation. To sum up, then, it may be concluded that drip irrigation has many advantages over other methods, and that it is also superior to surface and sprinkler irrigation in regard to water saving.
This short review describes how the constraints of limited water resources and an arid and semi-arid environment were overcome by a leadership capable of defining future needs and identifying and implementing appropriate solutions. Advanced technologies have proved indispensable in this process.