Historical & Technological Aspects in Development of Limited Water Resources
by Dr. Dov Sitton
Historical
background
". . . and the scorched land will become a
pool, and the thirsty ground springs of water" (Isaiah
35:7)
Scarcity of water has always been the dominant
factor in agriculture throughout most of the arid Middle East, with
its population relying on scanty and erratic seasonal rains or on
rivers for their water supply. In Egypt,
for example, the Nile 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 present-day Israel 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. Rain
falls only in the winter, 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 was almost entirely rain-fed, and therefore
was limited to the northern part of the country and the coastal area.
In some northern localities, where spring-water 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 the 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 technologies and know-how. Such
technologies were introduced by immigrants with specialized skills
and professional training. Among them were people experienced in
advanced methods of drilling through hard layers of rock 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 in quantity and
are not readily available.
- Water is conveyed to the fields in canals by
gravitation, which means that the ground needs to be leveled.
Hilly terrain and slopes, therefore, cannot be irrigated by this
method.
- The traditional practice of constructing dirt
canals results in considerable loss of water due to percolation
of water into the soil. The longer the canals, the larger the
loss.
- The supply of water declines along the line of
distribution, leading to unequal sharing of the limited
resources.
Another disadvantage of traditional irrigation is
that the water supply is inevitably irregular, resulting in an
inability to meet the needs of the crops and thus in poor yields.
In view of the circumstances prevailing at the
turn of the 20th century in the 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. Many of their number were
highly motivated and keen to establish new agricultural settlements.
They were inclined to examine and apply new agro-technologies, they
understood the significance of modern know-how based on scientific
studies, and they were eager to take 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 policies, and drawing up plans
for physical development. All these efforts culminated in the 1920s
and 1930s in the establishment of a large number of new agricultural
settlements.
As part of the settlement movement, geologists led
by Prof. L. Picard (who immigrated from Germany in 1924) were
recruited to search for underground water. Modern drilling equipment
capable of drilling to great depths through hard rock layers,
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, beyond these technical efforts, the
challenge was met by radically modifying the concept of what an
adequate water supply should be.
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 was in 1935. The leaders of this project were Levi
Eshkol, later Prime Minister of Israel, and Simcha Blass, an
engineer who 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 water came from three wells drilled into
the western flanks of the valley of Jezreel. The main features of the
project were:
- Conveyance of 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.
- 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 channeled 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
In the late 1930s it was accepted by the leading
figures in the field that the following principles should guide
future water projects:
Planning
- Any system developed to provide water should
bridge between areas where water is available and those where it
is in short supply, as well as between the rainy and the dry
seasons. 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 input, 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 should be comprehensive. That is, the
water projects must convey water all over the country to meet the
needs of the growing population and of extensive agricultural
development, especially in the Negev, the southern region of the
country (the scarcity of rainfall characterizes the Negev region
as arid land).
From 1939 onwards, several
plans for conveying water to the Negev were drawn up, mainly by
Simcha Blass. A comprehensive study entitled, "Water resources
in the Land of Israel: prospects for irrigation and hydro-electric
development" was prepared by Mekorot 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. W.K.
Lowdermilk, a highly reputed American expert on soil conservation and
hydrology, published a book ("Palestine - Land of the
Promise") on the possibilities of developing water projects in
Palestine, also in 1944. 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 (1948) and presented several versions of a master
plan for the development of irrigation and hydroelectric power. He
was later joined by his colleague, J.S. Cotton, who submitted a
master plan in 1955 that was eventually adopted by the government and
served as the blueprint for the planning and construction of the
National Water Carrier.
Construction
As part of a drive to settle
the Negev, the arid southern region of the country, three
experimental settlements were established in 1943. The aim was to
explore soil conditions in the region, the availability of water
(including data on annual precipitation), and what crops could be
cultivated under prevailing conditions. Another eleven settlements
were established in the Negev in 1946 and a further five in 1947,
equipped and financed as before by the Jewish national institutions.
From the very start, it was
clear that in the Negev the main limiting factor from the standpoint
of 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 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 the quantity and intensity of the floods, as
well as technical difficulties. Eventually, it was concluded that the
only way to secure a dependable and sufficiently large supply of
water was to transport fresh water from northern sources via pipes.
The first 'Negev pipeline',
became operative in 1947 and assured a reliable if limited supply of
water to most of the settlements in the Negev (although several
settlements still had to rely on local wells). This modest pipeline
transported water from wells in the northwestern Negev, an area
relatively rich in underground water. The first stage consisted of
190 km. of 6"-diameter pipes supplying one million cubic meters
(MCM) annually. Later on this line was converted to a
20"-diameter pipeline supplying 30 MCM annually. 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.
This pioneering endeavor was
followed by two large-scale projects to supply water to the Negev.
The first was the 'Yarkon-Negev pipeline', constructed soon after the
establishment of the State. This 66"-diameter pipeline
transported 100 MCM of water annually from the Yarkon River to the
Negev over a distance of 130 km
Although this was an
ambitious project in terms of the means available at the time, it
soon became clear that a larger and more comprehensive system was
necessary. This perception culminated in a second large-scale
project, the ambitious National Water Carrier. The main function of
the Carrier was to convey water to the southern region of the country
from the Sea of Galilee (Hebrew, Yam Kinneret, Lake Kinneret) in the
north. The original plan was to draw water from the Jordan River
before it entered the lake. The first stages of the groundwork began
in 1953. However, because of strong opposition by Syria and a United
Nations resolution, Israel was forced to suspend work and modify the
initial 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.
Water from the lake, located some 220 m. below sea level, is pumped
to an elevation of about 152 m. above sea level. From this height,
the water 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, contribute some 350 MCM and 250 MCM respectively, to the
Carrier each year.
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,
as well as 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.
Supply
and demand - management of limited water resources
The fresh water resources of
Israel, which average about 2,000 MCM annually, are already being
exploited 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 seawater. Adequate treatment -
purification in the case of sewage water and desalination for saline
water and seawater - can provide the much-needed extra water
Sewage 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, a large-scale project for processing sewage
to produce highly purified water. This procedure results in two major
benefits: the aquifer serves as an underground reservoir for the
recharged water - preventing losses by evaporation - and water is
pumped off when needed, mainly in summer; percolation of the water
through soil layers provides an additional cleaning phase.
About 110 MCM of this
purified water is transported annually via a separate pipeline called
the 'Third Negev Pipeline' to the western Negev for use in
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 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 all
over the country provide treated sewage water for irrigation of
fields located a short distance from the source of the effluent. In
many cases treatment is minimal, and use of the treated water is
restricted to crops such as cotton in the summer. However, small
projects of this type are reported to be highly cost-effective
Saline water and seawater
There are two categories of
water available for desalination, saline (brackish) water and
seawater. Desalting of seawater 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, seawater 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 1960s. Among these, reverse osmosis has been shown to be
efficient and relatively inexpensive; however, today it costs about
25% more to produce potable water by reverse osmosis than to purify
sewage water.
The leading desalination
project is located near Eilat, a city
on the Red Sea at the southern tip of Israel - the driest region of
the country, with negligible amounts of precipitation. The population
of Eilat is about 40,000 plus an
annual influx of some 500,000 tourists. Until 1997, all the drinkable
water supplied to Eilat was obtained
from desalination of underground brackish water. The desalinated
water is produced by reverse osmosis in two plants with a combined
output of about 36,000 cubic meters per day (about 13 MCM annually).
As a result of the ever-increasing demand for a reliable supply of
drinkable water, a third unit for seawater desalination was added to
the already existing units (the water is pumped from the Red Sea). At
present, the annual output of this unit is about 3.5 MCM.
Desalination of saline water
is preferred to desalination of seawater, since the energy required
to produce drinkable water from saline water is 0.8 to 1.0 kWh per
cubic meter, and 73% of the water input is recovered, while the
energy required for desalination of seawater is about 3.85 kWh per
cubic meter, and only 50% of the water input is recovered. However,
underground saline water is spread over relatively large areas and
the availability of this water in the vicinity of Eilat is limited. The supply of seawater, on the other hand, is infinite.
Therefore, future production of desalinated water will have to rely
mainly on seawater.
In addition to assuring an
important 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,
including the crucial coastal aquifer.
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 those 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 a
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.
Advanced
methods of irrigation
In Israel, the agriculture
sector is the major consumer of water. Thus, in order to curtail the
total water consumption, the amount of water allocated to agriculture
has been subjected to a number of restrictions, especially since the
early 1990s. From a total consumption of 2,008 MCM in 1997, 1,264 MCM
(63%) was used for agriculture, as compared to the situation in 1985
when water consumption for agriculture was 1,389 MCM out of a total
of 1,920 MCM (72%). There is no doubt that efficient use of water for
irrigation is a paramount priority.
One of the most important
agro-technological innovations is probably the invention in Israel 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:
- 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 and the ability to extend laterals with drippers
over greater distances.
- Via the drippers,
fertilizers can be supplied to the plant together with the water
('fertigation').
- Water and fertilizers
are delivered directly to the root system rather than to the
total area of the field, thereby economizing on both water and
fertilizers.
- The quantity of water
delivered can be optimized to fit different soil types, avoiding
percolation of water beyond the root zone. Furthermore, sandy
soils, which cannot be watered by furrows or by flooding, can be
efficiently irrigated with drippers.
- The emergence of weeds
is minimized.
- Between the planted rows
the dry ground facilitates comfortable access in the field for
workers and machines throughout the season.
- Exploitation of poor
quality water (saline water or effluents) is made possible
because:
- Drip irrigation,
unlike sprinkler irrigation, makes it possible to utilize
saline water. This is 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.
- 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.
- 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 under the conditions prevailing 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.
- High-quality drip
irrigation equipment can last for fifteen to twenty years if
maintained 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
of irrigation, and that it is also superior to surface and sprinkler
irrigation in regard to water saving, especially under conditions of
limited water supply.
Conclusions
This 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 proved indispensable in this process. Yet, in
recent years, the continuously increasing demand for water, mainly
for domestic use, has created a chronic situation in which all
available water from natural sources is being used up. The only
solution to ensuring a dependable supply of water for both domestic
and agricultural use requires that several steps be taken
concurrently to implement regulations and measures for saving water
and to construct immediately large-scale plants for desalination of
seawater and reclamation of urban effluents.
Sources: Israeli
Foreign Ministry |