CHAPTER ONE

Assessment of Groundwater and Surface

Water Resources

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1.1 Hydrologic Cycle

The hydrological cycle is the most fundamental principle of groundwater hydrology. The driving force of the circulation is derived from the radiant energy received from the sun.

Water evaporates and travels into the air and becomes part of a cloud. It falls down to earth as precipitation. Then it evaporates again. This happens repeatedly in a never-ending cycle. This hydrologic cycle never stops. Water keeps moving and changing from a solid to a liquid to a gas, repeatedly.

Precipitation creates runoff that travels over the ground surface and helps to fill lakes and rivers. It also percolates or moves downward through openings in the soil and rock to replenish aquifers under the ground. Some places receive more precipitation than others do with an overview balance. These areas are usually close to oceans or large bodies of water that allow more water to evaporate and form clouds. Other areas receive less. Often these areas are far from seawater or near mountains. As clouds move up and over mountains, the water vapor condenses to form precipitation and freezes. Snow falls on the peaks. Figure 1.1 shows a schematic representation of the hydrological cycle.

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Figure 1.1 Schematic Representation of the Hydrological Cycle

In recent years there has been considerable attention paid to the concept of the world water balance, and the most recent estimates of these data emphasize the ubiquitous nature of groundwater in hydrosphere. With reference to Table 1.1, if we remove from consideration the 94% of the earth’s water that rests in the oceans and seas at high levels of salinity, then groundwater accounts for about two-thirds of the freshwater resources of the world. Table 1.1 Estimate of the Water Balance of the World

Parameter Surface area (Km2)*106

Volume (Km2)*106

Volume (%)

Equivalent depth (m)*

Resident time

Oceans and seas Lakes and reservoirs Swamps River channels Soil moisture Groundwater Icecaps and glaciers Atmospheric water Biospheric water

361 1.55 < 0.1 < 0.1 130 130 17.8 504

< 0.1

1370 0.13

< 0.01 < 0.01 0.07 60 30

0.01 < 0.01

94 < 0.01 < 0.01 < 0.01 < 0.01

4 2

< 0.01 < 0.01

2500 0.25 0.007 0.003 0.13 120 60

0.025 0.001

~ 4,000 years ~ 10 years 1-10 years ~ 2 weeks

2 weeks – 1 year ~ 2 weeks – 10,000

years 10-1000 years

~ 10 days ~ 1 week

* Computed as though storage were uniformly distributed over the entire surface of the earth.

Hence, the water resources include all forms of occurrence of water including salt water and fossil groundwater. An interesting distinction which can be made is between blue and green water. Blue water, the water in rivers, lakes and shallow aquifers, has received all the attention from water

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resources planners and engineers. Green water, the water in the unsaturated soil responsible for the production of biomass has been largely neglected but it is green water that is responsible for 60% of the world food production and all of the biomass produced in forests and pasture. It is this resource which is most sensitive to land degradation. Fossil water, the deep aquifers that contain non-renewable water, should be considered a mineral resource which can be used once at the cost of foregoing future use.

1.2 Groundwater Resources

Groundwater can be split up into fossil groundwater and renewable (meteoric) groundwater. Fossil groundwater should be considered a finite mineral resource, which can be used only once, after which it is finished. Renewable groundwater is groundwater that takes an active part in the hydrological cycle. The latter means that the residence time of the water in the sub-surface has an order of magnitude relevant for human planning, say less than a hundred years. This criterion is clearly open to debate. Geologists, that are used to working with time scales of millions of years would only consider groundwater as fossil if it has a residence time over a millions of years. A hydrologist might use time-scale close to that. However, a water resources planner should use a time-scale much closer to the human dimension. In our definition, the renewable groundwater takes active part in the hydrological cycle and hence is "blue water" as mentioned before. In this sense, groundwater is (becomes) surface water and surface water is (was) groundwater. Two zones can be distinguished in which water occurs in the ground:

• The saturated zone, • The unsaturated zone.

For the hydrologist both zones are important links and storage devices in the hydrological cycle: the unsaturated zone stores the "green water", whereas the saturated zone stores the "blue" groundwater. For the engineer the importance of each zone depends on the field of interest. An agricultural engineer is principally interested in the unsaturated zone, where the necessary combination of soil, air and water occurs for a plant to live. The water resources engineer is mainly interested in the groundwater which occurs and flows in the saturated zone (see Figure 1.2).

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Figure 1.2 A schematic cross-section showing the typical distribution of subsurface waters in a simple “unconfined” aquifer setting, highlighting the three common subdivisions of the unsaturated zone and the saturated zone below the water table. The process of water entering into the ground is called infiltration. Downward transport of water in the unsaturated zone is called percolation, whereas the upward transport in the unsaturated zone is called capillary rise. The outflow from the groundwater to surface water is called seepage. The types of openings (voids or pores) in which groundwater occurs is an important property of the subsurface formation. Three types are generally distinguished:

1. Pores, openings between individual particles as in sand and gravel. Pores are generally interconnected and allow capillary flow for which Darcy's law can be applied.

2. Fractures, crevices or joints in hard rock which have developed from breaking of the rock. The pores may vary from super capillary size to capillary size. Only for the latter situation application of Darcy's law is possible. Water in these fractures is known as fissure or fault water.

3. Solution channels and caverns in limestone (karst water), and openings resulting from gas bubbles in lava. These large openings result in a turbulent flow of groundwater which cannot be described with Darcy's law.

The porosity n of the subsurface formation is that part of its volume which consists of openings:

volumetotal

voidsofvolumen = (1.1)

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Approximate properties such as field capacity and wilting point are used in the hydrological and agricultural literature. Field capacity is the volumetric moisture content left in the medium after it has drained under gravity from saturation for a period of two days (definitions vary), and the wilting point is the volumetric moisture content which is just low enough so that any plants growing in the medium will fail to transpire, so will wilt and die. When water is drained by gravity from saturated material, only a part of the total volume is released. This portion is known as specific yield. The water not drained is called specific retention and the sum of specific yield and specific retention is equal to the porosity (see Figure 1.3)

Figure 1.3 Specific Yield and Specific Retention

In fine material the forces that retain water against the force of gravity are high due to the small pore size. Hence, the specific retention od fine-grained material (silt or clay) is larger than of coarse material (sand or gravel). Groundwater is the water which occurs in the saturated zone. The study of the occurrence and movement of groundwater is called groundwater is called groundwater hydrology or geohydrology. The hydraulic properties of a water-bearing formation are not only determined by the porosity but also by the interconnection of the pores and the pore size. In this respect the subsurface formations are classified as follows:

1. Aquifer, which is a ground-water reservoir, composed of geologic units that are saturated with water and sufficiently permeable to yield water in a usable quantity to wells and springs. Sand and gravel deposits, sandstone, limestone, and fractured, crystalline rocks are examples of geological units that form aquifers. Aquifers provide two important functions: (1) they transmit ground water from areas of recharge to areas of discharge, and (2) they provide a storage medium for useable quantities of ground water. The amount of water a material can hold depends upon its porosity. The size and degree of interconnection of those openings (permeability) determine the materials’ ability to transmit fluid.

2. Aquiclude is composed of rock or sediment that acts as a barrier to groundwater flow.

Aquicludes are made up of low porosity and low permeability rock/sediment such as shale or clay. Aquicludes have normally good storage capacity but low transmitting capacity.

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3. Aquitard is a less permeable layer, not capable of transmitting water in horizontal direction, but allowing considerable vertical flow (e.g. shale or clay).

4. Aquifuge is impermeable rock neither containing nor transmitting water (e.g. granite layers).

1.2.1 Types of Aquifers For a description or mathematical treatment of groundwater flow the geological formation can be schematized into an aquifer system, consisting of various layers with distinct different hydraulic properties. The aquifers are simplified into one of the following types:

1. Unconfined Aquifer is one in which a water table varies in undulating form and in slope, depending on areas of recharge and discharge, pumpage from wells, and permeability. Rises and falls in the water table correspond to changes in the volume of water in storage within an aquifer see Figure 1.4. Contour maps and profiles of the water table can be prepared from elevations of water in wells that tap the aquifer to determine the quantities of water available and their distribution and movement. A special case of an unconfined aquifer involves perched water bodies, as illustrated by Figure 1.4. This occurs wherever a groundwater body is separated from the main groundwater by a relatively impermeable stratum of small areal extent and by the zone of aeration above the main body of groundwater. Clay lenses in sedimentary deposits often have shallow perched water bodies overlying them. Wells tapping these sources yield only temporary or small quantities of water.

2. Confined Aquifers also known as artesian or pressure aquifers, occur where

groundwater is confined under pressure greater than atmospheric by overlying relatively impermeable strata. In a well penetrating such an aquifer, the water level will rise above the bottom of the confining bed, as shown by the artesian and flowing wells of Figure 1.4. Water enters a confined aquifer in an area where the confining bed rises to the surface; where the confining bed ends underground, the aquifer becomes unconfined. A region supplying water to a confined area is known as a recharge area; water may also enter by leakage through a confining bed. Rises and falls of water in wells penetrating confined aquifers result primarily from changes in pressure rather than changes in storage volumes. Hence, confined aquifers display only small changes in storage and serve primarily as conduits for conveying water from recharge areas to locations of natural or artificial discharge.

Figure 1.4 Schematic Cross-Section of Aquifer Types

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3. Leaky Aquifers are completely confined or unconfined occur less frequently than do leaky, or semi-confined, aquifers. These are a common feature in alluvial valleys, plains, or former lake basins where a permeable stratum is overlain or underlain by a semi-pervious aquitard or semi-confining layer. Pumping from a well in a leaky aquifer removes water in two ways: by horizontal flow within the aquifer and by vertical flow through the aquitard into the aquifer (see Figure 1.5).

Figure 1.5 Different types of aquifers; A. Confined aquifer, B. Unconfined Aquifer, C. and D. Leaky aquifers, E. Multi-layered leaky aquifer system.

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1.2.2 Groundwater Flow

The theory on groundwater movement originates from a study by the Frenchman Darcy, first published in 1856. Darcy’s result is of fundamental importance and remains at the heart of almost all groundwater flow calculations.

Darcy discovered that the discharge Q of water through a column of sand is proportional to the cross sectional area A of the sand column, and to the difference in piezometric head between the ends of the column, h1– h2, and inversely proportional to the length of the column L. That is:

L

hhKAQ 21 −= (1.2)

Darcy’s experiment is shown schematically in Figure 1.6. The constant of proportionality K is known as the hydraulic conductivity [LT–1]. The implication here is that the specific discharge is proportional to the applied force. Darcy’s experiments were one-dimensional. In this section, we generalize the results of the experiments to give Darcy’s Law in three dimensions.

Figure 1.6 A schematic diagram of Darcy’s experiment

Rather than referring to the total discharge Q, it is often more convenient to standardize the discharge by considering the volume flux of water through the column, i.e. the discharge across a unit area of the porous medium. In the context of groundwater, the volume flux is called the specific discharge q [LT–1] and is given simply by Q/A. Darcy’s result can then be written in terms of the specific discharge and the difference in head between the ends of the column.

L

hhKAQq 12 −−== (1.3)

The fraction L

hh 12 − is called the average hydraulic gradient over the length of the column. As L

tends to zero, the average hydraulic gradient becomes an increasingly close approximation to the point value of the derivative of head with respect to distance x. Darcy’s experimental result then becomes:

dxdhKq −= (1.4)

which describes Darcy’s Law at any point in the porous medium. The spatial derivative of head dh/dx is called the hydraulic gradient at that point. There are two important points to note:

If the hydraulic gradient is positive, the specific discharge is negative. This reflects the fact that the groundwater moves from high to low head. So, for example, since the water table in Figure 1.7 slopes upwards away from the origin (i.e. dh/dx > 0), the water moves back towards it (i.e. q < 0).

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Figure 1.7

Although we have referred to Darcy’s Law at a point, specific discharge, hydraulic

conductivity and hydraulic gradient can be defined only as averages taken over a volume of rock. The assumption implicit in everything that follows is that this volume is small in comparison with the scale of any problem under consideration. The volume will vary in size depending upon the scale of the problem. For example, at the scale of a study in the laboratory the value of hydraulic conductivity at a point will be taken as an average over a few cubic centimeters, whereas at the regional scale the point hydraulic conductivity may be an average taken over hundreds of cubic meters which may include a variety of different rock formations.

However, the actual velocity actv of a fluid particle is much higher because only the effective pore

space en is available for transport, thus

e

act nqv = (1.5)

The effective porosity en is smaller than the porosity n , as the pores that do not contribute to the

transport are excluded (dead-end pores). The actual velocity is important in water quality problems, to determine the transport of contaminants.

1.2.3 Groundwater as a Storage Medium

For the water resources engineer, groundwater is a very important water resource for the following reasons:

• It is reliable resource, especially in climates with a pronounced dry season. • It is a bacteriological safe resource, provided pollution is controlled. • It is often available in situ (wide-spread occurrence). • It may supply water at a time that surface water resources are limited. • It is not affected by evaporation loss, if deep enough. • There is a large storage capacity. • It can be easily managed.

It is also has a number of disadvantages:

• It is a strongly limited resource; extractable quantities are often low as compared to surface water resources.

• Groundwater recovery is generally expensive as a result of pumping costs. • Groundwater, if phreatic, is very sensitive to pollution. • Groundwater recovery may have serious impact on land subsidence or salinization.

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Especially, in dry climate the existence of underground storage of water is of extreme importance. The water stored in the subsoil becomes available in two ways. One way is by artificial withdrawal (pumping) the other is by natural seepage to the surface water. The latter is an important link in the hydrological cycle. Whereas in the wet season the runoff is dominant by surface runoff, in the dry season the runoff is almost entirely fed by seepage from groundwater (base flow). Thus the groundwater component acts as a reservoir which retards the runoff from the wet season rainfall and smoothes out the shape of the hydrograph. A recession curve, which is a useful method for the evaluation of surface water resources in the dry season, shows the variation of base flow with time during periods of little or no rainfall over a drainage basin (see Figure 1.8). In essence it is a measure of the drainage rate of groundwater storage from the basin. If large, highly permeable aquifers are contained within drainage area, the base flow will be sustained even through prolonged droughts; if the aquifers are small and of low permeability, the base flow will decrease relatively rapidly and may even cease. The baseflow recession equation is: at

oeQQ −= (1.6)

where Q is the flow at some time t after the recession started (L3/T;m3/s)

oQ is the flow at the start of the recession (L3/T; m3/s)

a is the recession constant for the basin (1/T; d-1) t is the time since the recession began (T; d)

Figure 1.8 Typical annual hydrograph for a river with a long dry summer season

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1.3 Surface Water Resources

Surface water resources are water resources that are visible to the eye. They are mainly the result of overland runoff of rain water, but surface water resources can also origin from groundwater. Surface water is linked to groundwater resources through the processes of infiltration (from surface water to groundwater) and seepage (from groundwater to surface water). Surface water occurs in two kinds of water bodies:

• Water bodies, such as rivers, canals, estuaries and streams. • Stagnant water bodies, such as lakes, reservoirs, pools, tanks, etc.

The first group of water bodies consists of conveyance links, whereas the second group consists of storage media. Together they add up to a surface water system. The amount of water available in storage media is rather straightforward as long as a relation between pond level and storage is known. The surface water available in channels is more difficult to determine since the water flows. The water resources of a channel are defined as the total amount of water that passes through the channel over a given period of time (e.g. a year, a season, a month). In a given cross-section of a channel the total available amount of surface water runoff R over a time step Δt is defined as the average over time of the discharge Q.

∫Δ+

Δ=

tt

t

dtQt

R 1 (1.7)

The discharge Q is generally determined on the basis of water level recordings in combination with a stage discharge relation curve, called a rating curve. A unique relationship between water level and river discharge is usually obtained in a stretch of the river where the river bed is stable and the flow is slow and uniform, i.e. the velocity pattern does not change in the direction of flow. Another suitable place is at a calm pool, just upstream of a rapid. Such a situation may also be created artificially in a stretch of the river (e.g. with non-uniform flow) by building a control structure (threshold) across the river bed. The rating curve established at the gauging station has to be updated regularly, because scour and sedimentations of the river bed and river banks may change the stage discharge relation, particularly after a flood. The rating curve can often be represented adequately by an equation of the form:

boHHaQ )( −= (1.8)

Where Q is the discharge in (m3/s), H is the water level in the river (m), Ho is the water level at zero flow, and a and b are constants. The value of Ho is determined by trial and error. The values of and b are found by a least square fit using the measured data, or by a plot on a logarithmic paper and the fit of a straight line. Equation 1.8 is compatible with the Manning formula where the cross-sectional area A, and the hydraulic radius R are functions of (H-Ho).

SRnAQ 3

2

= (1.9)

Consequently, it can be shown that the coefficient b in equation 1.8 should have a value of 1.59 in a rectangular channel, a value of 1.69 in a trapezoidal channel with 1:1 side-slopes, a value of 2.16 in a parabolic channel, and a value of 2.67 in a triangular channel.

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To illustrate the trial and error procedure in determining the value of Ho, a plot of data with Ho=0 has been added. It can be seen that the value of Ho particularly affects the determination of low flow. For the methods of measuring water levels and flows one should refer to the lectures on Hydrometry. However, making use of the rating curve, a time series of water levels can be transformed into runoff series. Finally, the total water resources of a catchment are formed by the sum of surface water and groundwater. Both resources may not be considered separately from the water quality. Abundant water resources of poor quality are still useless for consumption. A consumer of water, who pollutes the water resources system through its return flows, consumes in fact much more water than its actual consumption, as he makes the remaining water useless.

1.4 Water Balance Water resources engineers are primarily concerned with catchment yields and usually study hydrometric records on a monthly basis. For that purpose short duration rainfall should be aggregated. In most countries monthly rainfall values are readily available. To determine catchment runoff characteristics, a comparison should be made between rainfall and runoff. For purpose, the monthly mean discharges are converted to volumes per month and then to an equivalent depth per month Q over the catchment area. Rainfall P and runoff Q being in the same units (e.g. mm/month) may then be compared. On a monthly basis one can write:

tSEPQΔΔ

−−= (1.10)

The presence of the Evaporation and the Storage terms makes it difficult to establish a straightforward relation between R and P. The problem is further complicated in those regions of the world that the distinctive rainy and dry seasons. In those regions the different situation of storage and evaporation in the wet and dry season make it difficult to establish a direct relation. While studying the relationship between rainfall and runoff in a catchment, one should recognize that:

• There will be a clear threshold rainfall which no runoff takes place. The threshold would incorporate such effects as interception, replenishment of soil moisture deficit; evapotranspiration, surface detention, and open water evaporate.

• The same amount of rainfall gives considerably more runoff at the end of the rainy season

than at the start of the rainy season. At the start of the rainy season the contribution of seepage to runoff is minimal, the groundwater storage is virtually and the amount to be replenished is considerable, the value of ΔS/Δt in Eq. (1.10) is thus positive, reducing the runoff. At the end of the rainy season the reverse occurs.

The threshold rainfall is quite in agreement with Eq. (1.10) and has more physical meaning than the commonly used proportional losses. Proportional losses are rather a result of averaging. They can be derived from the fact that a high amount of monthly rainfall is liable to have occurred during a large number of rainy days, so that threshold losses like interception and open water evaporation have occurred a corresponding number of times. By taking into account the threshold loss (D) and the groundwater storage (S), a relation can be obtained between Q and P. The following model, which can easily be made in spreadsheet, has been developed for that purpose.

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Moving Average Model for Monthly Runoff using Threshold Losses

As the amount of storage available during a particular month depends on the amount of rainfall in the previous months, a relation is sough that relates the runoff in a particular month to the rainfall in the month itself and the previous months. A simple linear backward relation is used:

( ) ( ) ( ) ...2211 +−+−+−+= −− DPbDPbDPbaQ tttot (1.11)

Under the condition that if ( ) 0<−− DP it , then ( ) 0=−− DP it . D is the threshold loss on a monthly basis, bi is the coefficient that determines the contribution of the effective rainfall in month t-i to the runoff in month t (proportional loss); and a is a coefficient which should be zero if the full set of rainfall contributions and losses were taken into account. In matrix notation Eq. (1.11) reads:

aDPBQt +−= )( (1.12)

Where Qt is a scalar, the runoff in month t, B is an (n X 1) matrix containing the coefficients bi and (P-D) is a state vector of (1 X n) containing the effective monthly precipitation values of the present and previous months. The value n-1 determines the memory of the system. Obviously n should never be more than 12, to avoid spurious correlation, but in practice n is seldom more than 6 to 7. The effective runoff coefficient C, on a water year basis, is defined as:

DPQC−

= (1.13)

Where P and Q are the annual rainfall and runoff on a water year basis. It can be seen from comparison of Eq.'s (1.12) and (1.13) that (if the coefficient a equals zero) the sum of the coefficients in B should equal the effective runoff coefficient C.

∑ ≈Cbi (1.14)

Meaning that the total amount of runoff that a certain net rainfall generates is the sum of all components over n months. Obviously C should not be larger than unity. The coefficients of B are determined through a multiple linear regression. Moreover, it should be understood that the correlation substantially improves by taking into account threshold rainfall.

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The addition of the word integrated to the term water resources refers to three aspects:

• Location of the resource: e.g. upstream, downstream, basin, sub-basin. • Type of the resource: groundwater, surface water, rainfall harvesting. • Quality: water of bad quality is no resource unless it is treated.

It is not correct to consider the different aspects of water resources in isolation. The integration of location, type and quality is a necessary condition for water resources management. In hydrological cycle, the direct link between groundwater and surface water is apparent. If we add the aspect of water quality, the picture of integrated water resources is complete. For Integrated Water Resources Management (IWRM), however, further integration is needed with regard to institutional, economical, financial, legal, environmental and social aspects (as will be discussed later). But with regard to the physical aspects of water we can limit ourselves to location, type and quality. In the field of hydrology the budget idea is widely used. Water balances are based on the principle of continuity. This can be expressed with the equation:

tStOtIΔΔ

=− )()( (1.15)

Where I is the inflow in [L3/T], O is the outflow in [L3/T], and ΔS/Δt is the rate of change in the storage over a finite time step in [L3/T] of the considered control volume in the system. The equation holds for a specific period of time and may be applied to any given system provided that the boundaries are well defined. Other names for the water balance equation are Storage Equation, Continuity Equation and Law of Conservation of Mass.

Water Balance of a Drainage Area

The water balance is often applied to a river basin. A river basin (also called watershed, catchment, or drainage basin) is the area contributing to the discharge at a particular river cross-section. The size of the catchment increases if the point selected as outlet moves downstream. If no water moves across the catchment boundary indicated by the broken line, the input equals the precipitation P while the output comprises the evapotranspiration E and the river discharge Q at the outlet of the catchment. Hence, the water balance may be written as:

( )tSQAEPΔΔ

=−×− (1.16)

Where ΔS is the change of storage over the time step Δt, and A is the surface area of the catchment upstream of the station where Q has been measured. ΔS, the storage in the amount of water stored in the catchment, is difficult to measure. However, if the account period for which the water balance is established is taken sufficiently long, the effect of the storage term becomes less important, as precipitation and evapotranspiration accumulate while storage varies within a certain range. When computing the storage equation for annual periods, the beginning of the balance period is preferably chosen at a time that the amount of water is store is expected not to vary much for each successive year. These annual periods, which do not necessarily coincide with the calendar years, are known as hydrologic-or water years. The storage equation is especially useful to study the effect of a change in the hydrologic cycle.

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To give an impression of the difference in the water balance of drainage basins, the water balances for the basins of some great rivers are given in Table 1.2. Table 1.2 Indicative Average Annual Water Balance for the Drainage Basins of Some of the

Great Rivers River Catchment

size Rainfall Evapotranspiration Runoff Runoff

CoefficientGm2 mm/yr Gm3/yr mm/yr Gm3/yr mm/yr Gm3/yr %

Nile 2803 220 620 190 534 30 86 14 Mississippi 3924 800 3100 654 2540 142 558 18

Parana 975 1000 980 625 610 382 372 38 Orinoco 850 1330 1150 420 355 935 795 70 Mekong 646 1500 970 1000 645 382 325 34 Amur 1730 450 780 265 455 188 325 42 Lena 2430 350 850 140 335 212 514 60

Yenisei 2440 450 1100 220 540 230 561 51 Ob 2950 450 1350 325 965 131 385 29

Rhine 200 850 170 500 100 350 70 41

1.5 Available Renewable Water Resources 1.5.1 Water Scarcity In the eyes of the public, water scarcity is associated with lack of drinking water. That is not so strange. Drinking water, although in terms of quantity a very small consumer of water resources, is closest to people's environment and experience. Consequently, in the discussion on water scarcity, the image most commonly conveyed by the media is that of thirst. We see pictures of people standing next to a dry well, or people walking large distances to collect a bucket of water. Or, on a more positive note, people happily crowded around a new water point that spills crystal clear water. Thirst, however, is not a problem of water scarcity; it is a problem of water management. There is enough water, virtually everywhere in the world, to provide people with their basic water needs: drinking, cooking and personal hygiene. Shortage of water for primary purposes (essentially household water) is much more a problem of lifestyles and poor management than of water availability. As a result of the "sanitary revolution" of the Victorian age, drinking water is mainly used to convey our waste over large distances to places where we then try to separate the water from the waste. This way of sanitation, which probably was highly efficient at the beginning of this century when there was neither scarcity of water nor an environmental awareness, is now highly inefficient in terms of energy consumption, money and water alike. An extra-terrestrial visiting the Earth would be very surprised to see that clean and meticulously treated drinking water, which is considered a precious and scare commodity, is used for the lowest possible purpose: to transport waste. Subsequently, the waste is removed through a costly process, after which the water is often pumped back and re-treated to be used again. We need a new sanitary revolution, to restore this obvious inefficiency. If drinking water is not the problem of global water scarcity, then what is? Of the 1700 m3/cap/yr of renewable fresh water that is considered an individual's annual requirement, close to 90% is needed for food production. For primary water consumption 100 l/cap/day may be considered sufficient. After the second sanitary revolution it may become even less! On an annual basis this consumption amounts to about 40 m3/cap/yr. Industrial use may be several time this amount, but also in the industrial sector, a sanitary revolution could seriously reduce the industrial water consumption.

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The water scarcity problem is primarily a food problem. The production of a kilogram of grains under proper climatic and management conditions, requires about 1-2 m3 of water, but it can reach as much as 4 m3 of water per kg in tropical dry climates. A kilogram of meat requires a multiple of this amount. Apparently, the per capita water requirement primarily depends on our food needs and habits. Consequently, the main question to address is: how are we going to feed an ever growing population on our limited land and water resources? 1.5.2 A Rainbow of Water Of all water resources, green water is probably the most under-valued resources. Yet it is responsible for by far the largest part of the world's food and biomass production. The concept of green water was first introduced by Falkenmark (1995), to distinguish it from blue Water, which is the water that occurs in rivers, lakes and aquifers. The storage medium for green water is the unsaturated soil. The process though which green water is consumed is transpiration. Hence the total amount of green water resources available over a given period of time equals the accumulated amount of transpiration over that period. In this definition irrigation is not taken into account. Green water is transpiration resulting directly from rainfall, hence we are talking about rainfed agriculture, pasture, forestry, etc. The average residence time of green water in the unsaturated zone is the ratio of the storage to the flux (the transpiration). At a global scale the storage in the unsaturated zone is about 500 mm, whereas the average global transpiration is 100 mm/month. The average residence time of green water is hence approximately 5 months. At a local scale, depending on climate, soils and topography, these numbers can vary significantly. Green water is a very important resource for global food production. About 60% of the waorld staple food production relies on rainfed irrigation, and hence green water. The entire meat production from grazing relies on green water, and so does the production of wood from forestry. In Sub-Saharan Africa almost the entire food production depends on green water (the relative importance of irrigation is minor) and almost of the industrial products, such as cotton, tobacco, wood, etc. There is no green water without blue water, as their processes of origin are closely related. Blue water is the sum of the water that recharges the groundwater and the water that runs-off over the surface. Blue water occurs as renewable groundwater in aquifers and as surface water in water bodies. These two resources can not simply be added, since the recharge of the renewable groundwater eventually ends up in the surface water system. Adding them up often implies double counting. Depending on the climate, topography and geology, the ration of groundwater recharge to total blue water varies. In some parts the contribution of the groundwater to the blue water can be as high as 70–80%, in some parts (on solid rock surface), it can be negligible. Generally the groundwater contribution to the blue water is larger than one thinks intuitively. The reason that rivers run dry is more often related to groundwater withdrawals, than to surface water consumption. Engineers always have had preference foe blue water. For food production, engineers have concentrated on irrigation and neglected rainfed agriculture, which does not require impressive engineering works. Irrigation is a way of turning blue water into green water. Drainage is a way of turning green water into blue water. To complete the full picture of the water resources, besides green water and blue water, there is white water. White water is the part of rainfall that feeds back directly to the atmosphere through evaporation from interception and bare soil. Some people consider the white water as part of the green water, but that adds to confusion since green water is a productive use of water whereas the white water is non-productive. The white and green water together form the vertical component of the water cycle, as opposed to the blue water, which is horizontal. In addition, the term white water can be used to describe the rainfall which is intercepted for human use, including rainwater harvesting.

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Table 1.3 presents the quantities of fluxes and stocks of these water resources, and the resulting average residence times, at a global scale. For catchments and sub-systems similar computations can be made. The relative size of the fluxes and stocks can vary considerably between catchments. Not much information on these resources exists at sub-catchment scale. Table 1.3 Global Water Resources, Fluxes, Storage and Average Residence Times

Resource Fluxes [L/T] or [L3/T] Storage [L] or [L3] Residence time [T]

Green T 100 mm/month Su 500 mm Su/T 5 months White I 5 mm/day* Ss 4 mm* Ss/I 0.8 days Blue Q 46x1012 m3/yr Sw 124x1012 m3 Sw/Q 2.7 years

Deep Blue Qs 5x1012 m3/yr* Sg 750x1012 m3* Sg/Qg 150 years Atmosphere P 510x1012 m3/yr Sa 12x1012 m3 Sa/P 0.3 months

Oceans A 46x1012 m3/yr So 1.3x1018 m3 So/A 28000 years * indicates rough estimates. Finally, the last color of the rainbow is the ultra-violent water, the invisible water, or the virtual water. Virtual water is the amount of water required to produce a certain good. In agriculture, the concept of virtual water is used to express a product in the amount of water required for its production. The production of grains typically requires 2-3 m3/kg, depending on the efficiency of the production process. Trading grains implies the trade of virtual water. For example; assume that in a certain basin, blue water applied to tobacco has productivity of around 3.5 $/m3, whereas productivity of water for wheat is only around 0.5 $/m3. Since wheat and tobacco can be both traded on the international market, the best use of water resources would be to produce tobacco, export it and buy the required wheat on the international market. One cubic meter of water applied to tobacco would allow the importation of 7 m3 of virtual water in the form of grains. A net gain to the basin of 6 m3 of water! Supplementary irrigation during the rainy season of rainfed crops has a relatively high productivity. In the communal areas, one cubic meter of blue water applied to a rainfed crop as supplementary irrigation results in production gains valued at 1 $ to 1.3 $. In water scare regions, the exchange of water in its virtual form is one of the most promising approaches for sharing international waters.

How to Determine the Blue and Green Water? The blue water (B) can be determined through rating. The difficulty lies with the green water (G). On an annual basis, the sum of the white (interception) and the green water equals the overall average evaporation from a catchment E = W+G = P-Q (E is the total annual evaporation, P is the annual rainfall and Q is the annual runoff (Q=B), all in mm/yr). The white water (W) consists of the open water evaporation, the bare soil evaporation and the direct evaporation from interception. Hence, the sum of the blue and green water differs from the total rainfall P by the direct evaporation losses (interception, bare soil and open water evaporation). The blue and green water is productive, or can be made productive. Savenije (1997) developed a method to determine the direct evaporation losses (W), which in fact corresponds to the actual threshold losses of Eq. (1.11), where W=min(D,P). On the monthly basis, the transpiration equals the amount of green water (G) consumed by the vegetation: G= E-W.

Is evaporation a Loss? In most water balances, evaporation is considered a loss. Hydrological engineers who are asked to determine surface runoff, consider evaporation a loss. Water resources engineers who design reservoirs, consider evaporation from the reservoir a loss. For agricultural engineers, however, it depends on where evaporation occurs, whether it is considered a loss or not. If it refers to the water evaporated by drop (transpiration), then evaporation is not a loss, it is the use of the water for the

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intended purpose. If it refers to the evaporation from canals or from spill, then evaporation is considered a loss which reduces the irrigation efficiency. 1.5.3 The Water Balance as a Result of Human Interference Attempts have been made to incorporate the interference of the man in the hydrological cycle through the introduction of the water diversion cycle, which includes water withdrawal and water drainage. The diversion cycle is exerting significant influence on the terrestrial water cycle; especially in highly economically develop regions with a dense population. The water diversion cycle including human interference results in the following annual average water balance equation (neglecting storage variation):

DHRRUUCQCEP

gsgs ++−−+=++=

(1.17)

where, P precipitation E total evaporation from the land surface (transpiration + interception + open water evaporation). C net water consumption due to water use Q runoff from land to ocean Us+Ug intake from surface and groundwater Rs+Rg return flows to surface and groundwater H rain harvesting D desalination In this respect it is important to note that re-use of return flows (Rs and Rg) are no additional resources, but merely a way to make water use more efficient (minimizing drainage).

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1.6 Brief about Water Resources in Palestine 1.6.1 Introduction The water resources in Palestine are mainly the Jordan River, Wadi flows and groundwater (utilized mainly through wells and springs). The following table is a summary of the available water from these resources. Table 1.4 Available Water for the Palestinian Water Resources

Source of water Natural flow or Recharge (Mcm/yr)

Jordan River Wadi flow Groundwater Basins Eastern

1485-1671 110-120 100-172

Northeastern 130-200 Western 335-450 Gaza Coastal 55-65

Total 2,215 – 2,678

Source: several studies At present, water demand in Palestine exceeds the available water supply which has led to low consumption rates. On average, the per capita consumption in the West Bank is about 70 l/d and water losses from conveyance systems can reach 40% and thus the actual water consumption per capita amounts of 42 l/d which is about one third of what the per capita consumption needs are according to WHO standards. In the Gaza Strip, only a total of about 8.9 Mcm/yr out of the water supplied by municipal wells may be considered acceptable (based on health considerations); this 8.9 corresponds to approximately 18 percent of the total supply quantity, and translates to an acceptable per capita supply rate for domestic use of only about 13 l/c/d. The gap between supply and demand in 2005 for all uses was 336 Mcm/yr. The main causes of increased water demand in Palestine are agriculture (accounting for 59% of total demand), demographic growth and urbanization. Urbanisation reduces aquifer replenishment and increases the risks of floods. Climate change is expected to lead to decreasing and more irregular rainfall, creating major constraints for agriculture and water supply for other purposes. Climate change could also lead to higher rates of evapo-transpiration, lower soil moisture content, growing desertification, falling water levels in aquifers and saline intrusion into coastal aquifers. Desertification has also taken place in Palestine as a result of loosing 50% of the grazing area to Israeli settlements and military camps and “nature reserves”. This has an impact on climate patterns in the region. The poor sanitation services, poor management of sewage and solid waste and over-application of fertilizers and pesticides in the agricultural sector can cause pollution to the Palestinian aquifers. In Gaza, aquifer quality is an important issue, with high nitrates and chlorides arising from over-extraction and reduction in storage volumes, leading to a continuous degradation of water quality. There are also some areas where seawater intrusion has been detected. Also, in areas of intensive pumping, saline water has been drawn upward from underlying waters or saline geological formations. Contamination of water will minimize the already limited quantities of water resources in Palestine, i.e., enlarging the gap between water supply and demand.

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There is a need to emphasize the principles of access to essential water supply and sanitation services as 40% of the Palestinian communities are not served in this respect. The Palestinian citizen pays about $1.25 per 1 m3 of water. This is a high cost compared to the average income of the Palestinian citizen This paper addresses only the environmental problem with the following general objectives, (1) providing a general description of the aquifer systems in Palestine; (2) undertaking an assessment of the water quality deterioration in the Palestinian aquifers; and (3) providing guidelines for groundwater protection from pollution. Water quality in the wider sense has an important role to play in addressing the resource of the West Bank and Gaza Strip groundwater supply. In this way, it can assist and inform the resource-based modelling that is required to support the sustainable management of the various aquifer units concerned. For many years, raw sewage effluents from the Palestinian cities and localities and from Israeli Settlements in the West Bank, have been discharged in the Wadis. Moreover, Leachate from dumping sites, zebra from olive mills, industrial wastes, agricultural returns rich with agro-chemicals and hazardous wastes from the Palestinian and Israeli sources have caused groundwater quality of Palestinian aquifers to deteriorate. Since the carbonate aquifers of the West Bank have pronounced mature karst features above and below the water table, these aquifers show high potential for extensive pollution, a case study in Nablus area shown in this paper deals with the effect of pollutants mainly wastewater on the carbonate aquifers in the Northern part of the West Bank. Moreover, the over-abstraction in the Jordan valley aquifers causes salinisation problems. 1.6.2 Aquifer Basins in the West Bank and Gaza Strip Israel controls all aquifers in Palestine; although the major part of fresh water supply in Palestine originates from the three aquifers of the West Bank. In the West Bank, the aquifer system is comprised of several rock formations that are recharged from rainfall. In years of normal rainfall, some 600-650 Mcm/yr of rain infiltrate the soil and replenish the ground aquifers (PWA, 2005). The major groundwater system in the West Bank consists of three major basins, classified according to flow direction into: the Western, Eastern and Northeastern Basins. The West Bank aquifer system discharges approximately 600-660 Mcm/y.

The Western Aquifer Basin (WAB) It is considered the most important aquifer in the West Bank and the largest of all groundwater basins in Historical Palestine as shown in Figure 1.9. It is a shared aquifer between the West Bank, Israel and Egypt, with a surface area of 11,398 km2 (Abu Saada, 2004) where the area located within the borders of the West Bank forms the main recharge area for this Basin, estimated at about 1,596km2, and located within the heavy rainfall area. This area provides the aquifer for more than 73% of the basin’s water. The ground water in this aquifer basin moves to the West and North West, where the rock layers forming the basin tend to these directions (SUSMAQ, 2005). Most of the rock formations within the borders of the West Bank are considered unsaturated and non-artesian due to close proximity to the recharge areas, and artesian and saturated towards the west, due to the increase in thickness of the rock and underlying aquitard formations. Two main aquifers are present in this basin: the upper and the lower aquifers. The average thickness of these aquifers ranges between 600-900 meters. The basin has a safe yield of 443 Mcm/yr; Israel exploits most of the water of this aquifer about 95% through more than 500 deep groundwater wells. Israel limits Palestinian use from this aquifer to 21 Mcm/yr with a total number of wells of 134 (SUSMAQ, 2005).

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The Northeastern Aquifer Basin (NEAB) The area of this basin in the West Bank as shown in Figure 1.9 is nearly 1,067.5 km2. The annual groundwater recharge of this basin is approximated to be 145 Mcm. The mountains in the southern parts of this basin have peak elevations between 600-918 m asl. The central and northern parts of the Northeastern Basin have a relatively flat to hilly topography that rises about 300 to 600 m asl. This hilly area drains surface water to the west into shallow wadis, which recharge the coastal aquifer system as they meet the flatter coastal plain. The number of the Palestinian wells in the Northeastern Aquifer Basin is 76 wells with an average abstraction of about 16 Mcm/yr, whereas the most important and the largest utilization of this basin water is by Israelis through the wells and springs located outside the borders of the West Bank (PWA, 2005).

The Eastern Aquifer Basin (EAB) Large parts of this aquifer basin are located within the eastern borders of the West Bank as shown in Figure 1.9. The area of this basin is estimated at 3,079.5 km2. The mountains forming the highlands in this basin consist mainly of carbonate sedimentary rocks with deeply incised wadis draining to the east. The surface water divide runs parallel to the axis of the mountains, and surface water drains eastwards towards the Jordan River Valley with minimal infiltration in the carbonate rocks or soil profile due to the high degree of slope in the wadis. The elevation of these mountains ranges from 600-1,000 m asl, yielding an elevation difference of more than 1,300 meters between the high mountain peaks and the adjacent Jordan River Valley. The majority of the Eastern Aquifer Basin area is located within the areas featured by scarcity of rain in general, while the western part is located within an area featured by heavy rainfall. The eastern aquifer basin has a safe yield of 175 Mcm/yr on average. The number of Palestinian wells in the eastern aquifer is 95 wells with an average abstraction of about 25 Mcm/yr, (PWA, 2005).

The Coastal Aquifer Basin (CAB)

The coastal aquifer is the main aquifer for groundwater in the Gaza Strip. Its depth ranges from several meters in the eastern and southeastern parts to about 120-150 meters in the western part. It extends along the coastal strip and consists of sand layers of kurkar with a mixture of clay and sandstone followed by non permeable layers of marl for a depth ranging between 800-1000 meters, followed by layers of limestone rock, where salinity exceeds 20 g/l of chloride (PWA, 2005) (see Figure 1.9). The aquifer is characterized by high porosity and permeability. It is divided into four sub-aquifers which extend 1-3 km from the seacoast and then unified together, forming one aquifer. Impermeable and non-porous clayey and silty layers in the form of lenses define these sub-aquifers. Towards the east, these clayey lenses thin out and disappear gradually (Al-Agha, 1997). The aquifer is unconfined in many places in the strip, thus the infiltration of contaminants (sewage, fertilizers, pesticides and other sources) is easy through the surface soil layer. The annual recharge of Gaza Coastal is about 55-65 Mcm/yr (PWA, 2005).

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Figure 1.9 Groundwater Basins in the West Band and the Gaza Strip

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1.6.3 Groundwater Aquifer Systems in the West Bank

First Aquifer: The Shallow Aquifer The Holocene (alluvial) aquifer, Pleistocene (Lisan Formation) aquifer, Miocene-Pliocene (Beida Formation) aquifer and Eocene (Jenin Subseries) aquifer represent the shallow aquifer. They are locally important. Holocene (Alluvial Formation) aquifer This aquifer occurs in the Jordan Valley. It is important to agricultural uses. It is built up of sub-recent terrigenous deposits (alluvial fans) formed along the outlets of major wadis that flow eastward to the Jordan Valley and its thickness ranges from 0 to 100 m (see Figure 1.10). These alluvial fans are still accumulating after large floods and consist of debris from neighbouring lithologies which are deposited according to their transport energy. The biggest clasts are found close to the apex and the smallest close to the fan margin. Transport normally takes place along alternating channels or after heavy rain as sheet flow. Thus permeable horizons alternate with impermeable lithologies within the deposits. The yield of the wells in this aquifer is about 20-100 m3/hr. The water quality is variable (from 100 mg/1 to more than 2000 mg/l). Estimates of transmitting properties show that the aquifer varies from low potential to fair potential. The alluvial aquifer often directly overlies the Pleistocene gravel with which it is in hydraulic contact. Pleistocene (Lisan Formation) aquifer/aquitard The Lisan formation is not considered an aquifer or an aquitard but rather both: an aquifer/aquitard. It is continuous along the Jordan Valley and varies in thickness; it may be up to 200 m thick. The Lisan Aquifer consists of unconsolidated beds of sand, gravel, cobbles, and boulders separated by impermeable layers of saline marls and other lacustrine deposits (see Figure 1.10). These deposits are composed of clastic rocks of limestone, dolomite, and chert with a sand and clay matrix that form alluvial fans. It extends from Jericho in the south to Marj Na’ja and lower Wadi Fari’a to the north. The aquifer supplies agriculture in the Jordan Valley. Borehole yields vary from 20 to 100 m3/h. Water quality is variable, with chloride concentrations from 50 mg/l up to 2200 mg/l in areas influenced by salt domes, hyper saline brines and/or Dead Sea water inflows south of Jericho. The sulphate concentration rises from 100 mg/l in the west to 900 mg/l near Jericho. Miocene – Pliocene (Bedia Formation) aquifer (sometimes known as Neogene aquifer) This is the lower part of the Dead Sea group. Beida consists of three lithologies, well-cemented conglomerates, highly permeable, some indurated marl and sandstone and few freshwater limestone of minor aquifer potential (see Figure 1.10). Beida is of local importance at the northeastern boundary of the West Bank in the Jordan Valley and Wadi Fari’a especially near the Bardala and Ein Beida areas. The thickness of the three combined lithologies can be up to 350 m in places. However, the aquifer is of limited extent and in most places only about 100 m thick. Water quality in the aquiferous conglomeratic portion is good (about 70 mg/l chloride). Eocene (Jenin Formations) aquifer In this aquifer groundwater normally occurs within 100 m from ground surface and for this reason it is extensively used for irrigation. It consists of nummulitic limestone with chalk, chert bands and marl. The limestone is of limited thickness and contains chalk, chert and intercalations of marl, which reduce the groundwater supply potential of the aquifer. It has limited storage and water transmitting properties. The yield of this aquifer is highly dependent on rainfall. The thickness of this aquifer ranges between 90 – 670 m.

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An individual well yield is in the range from 20-100 m3/hr. The water quality of the aquifer varies depending on location. The Eocene is separated from the underlying Upper Aquifer by a 200-500 m thick sequence of chalks and marls belonging to the K/T-C series which serves as a confining unit to the Upper Aquifer. Water Quality tends to deteriorate towards the Jenin area due to over-pumping and heavy irrigation activities. TDS reaches 1650 mg/l in some parts of the aquifer, while chloride concentration reaches 679 mg/l, whereas the average nitrate concentration in the aquifer is 41 mg/l. The Eocene is separated from the underlying Upper Aquifer by a 100-500 m thick sequence of chalks and marls belonging to the Nablus Group (Senonian series), which acts as the confining unit to the Upper Aquifer (see Figure 1.10). In some parts of the Northeastern Aquifer Basins, the Nablus Group may form a local aquifer.

Second Aquifer: The Upper Aquifer This aquifer consists of the Turonian (Jerusalem Formation), Upper Cenomanian (Bethlehem and Hebron formations). Turonian (Jerusalem) aquifer This formation consists of massive limestone (sometimes thinly bedded limestone), and dolomitic limestone with well developed karst features. It is part of the Upper Aquifer, but it is isolated from the main part of the Upper Aquifer in the south and parts of the eastern West Bank wherever the underlying Bethlehem Formation becomes a weakly permeable aquitard (see Figure 1.10). The Jerusalem Formation is of large lateral distribution and thickness in the Tulkarem and Qalqilya areas (approximately 130 m thick). It forms a good aquifer especially where the saturation thickness is in tens of meters. Water quality is generally good but in some areas there is evidence of deterioration because of pollution by sewage and agro-chemicals. Upper Cenomanian (Bethlehem and Hebron Formations) aquifer The Upper Cenomanian aquifer consists of the Bethlehem and Hebron Formations which are mainly interbedded dolomite and chalky limestone (see Figure 1.10). In the southern and eastern part of the West Bank, the Bethlehem Formation is considered an aquitard, while to the north and west it has aquiferous characteristics. The Aquifer is an important regional source of water supply for domestic uses. It is heavily exploited in the areas near Tulkarem and Qalqilya. The well yields range from 40-400 m3/hr. The well depths are less than 400m with some exceptions. The depth to water is rarely more than 200 m below ground surface. The Aquifer has high recharge values. Its water quality is generally good (30-70 mg/1 of chloride). The Lower Yatta Formation hydraulically separates the two regional aquifers (Upper and Lower Aquifers) across most of the West Bank, although to the north, the presence of Yatta limestone gives rise to minor springs and seepage. Water levels (heads) in the Upper Aquifer are generally higher than in the Lower Aquifer.

Third Aquifer: The Lower Aquifer The Albian (Lower Beit Kahil Formation) and to a lesser extent the Albian (Upper Beit Kahil Formation) and sometimes the lower part of Yatta Formation form the Lower Aquifer, which is a deep confined aquifer across most the West Bank. It is a regional source of drinking water. Individual well yields across the West Bank range from 150-450 m3/hr. Well depths vary from 500 to 850 m. The high water bearing capacity and productivity is owed to the great thickness of dolomitic limestones and limestones (see Figure 1.10). Water quality is generally good with chloride values in the 20-50 mg/1 range, though slightly higher salinities have been encountered towards the Jordan Valley.

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Fourth Aquifer: The Deep Aquifer Lower Albian (Ein Qinya) aquifer The aquifer is not yet understood and it seems there is a great change in the characteristics of this aquifer from the middle to the north of the West Bank. In general, the aquifer seems to be of low potential. However, it was tested while drilling Ein Senia Well No.7 in Ramallah District. The test shows that it has some low aquifer potential that is not really sufficient for pumping water from it. Neocomian (Ramali) aquifer It is mainly of Neocomian age (see Figure 1.10). The Ramali is composed of primarily sandstone. Very little information is available on these deeper sediments because few wells penetrated to these depths. Edwin & Pauly, Phillips, and John Mecum oil companies drilled deep exploration wells for oil in Halhul (Halhul No.1) in Hebron District, and Abu Shkeidem (Ramallah No.1). The logs for these wells suggest that Ramali aquifer consists of sandstone of older formation. Its thickness is about 70 meters. (Oxfordian) Maleh aquifer The Maleh aquifer system is mainly of Oxfordian age from the Jurassic period. It is made up of dolomitic limestone, interbedded ferruginous limestone, and marls. It is the lowest aquifer system expected in the West Bank (see Figure 1.10). There is very little information on this aquifer system because no monitoring or production wells have been drilled to this depth. 1.6.4 Groundwater Aquifer in the Gaza Strip The aquifer is composed of clastic sediment from the Pleistocene age overlaying impervious clay of the Miocene age. The Pleistocene sequence consists of continental and marine units composed of sandstone, calcareous sand, siltstone and red loamy soils. The bottom formation consists of thick compact marine clay (see Figure 1.11). This layer is dipping toward the sea at an average slope of 10 meters per Km. At the eastern part near the foothills, the limestone formation is overlapping and subsurface inflow is expected to recharge the aquifer (Abu Jabal et al, 2005). Groundwater in the Gaza Strip is found in three shallow sub-aquifers composed mainly of quaternary sand, calcareous sandstone and pebbles with interbeds of impervious and semi- pervious clay, gradually sloping westward. The three aquifers are of a thickness range from 120 meters near the coast to 10 meters in the east, where the Seat is located. They are divided into sub-aquifers that overlay each other in certain places separated by impervious and semi-impervious clayey layers. The upper sub-aquifer lies closest to the sea and extends to two kilometers inland at a depth mainly below sea level. The middle sub-aquifers are situated below the upper sub-aquifer near the coastline and rise in an eastward direction according to the general slope of the geological layers. The lower sub-aquifers extend further inland. Deeper permeable strata are present at depths of 200-300 meters and consist of carbonates and sandstone, with salinity concentration reaching a value of 2,000 mg/l, (Abu Jabal et al, 2005).

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Figure 1.10 Stratighraphical Section of the West Bank (Hydrogeological Map of the West Bank, SUSMAQ Project)

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Figure 1.11 Stratighraphical Section of the Gaza Strip 1.6.5 Surface Catchments There are two surface catchments areas in Palestine: the western catchments areas that drain in the Mediterranean Sea, and the eastern catchments areas which drain into the Jordan River and the Dead Sea Basin. The total quantity of surface runoff which originates from the Palestinian territories in the Western catchments is 72 Mcm/year with the total surface area being equal to 2950 km2 inside the Palestinian territories. The eastern catchments are all presented as part of the Jordan River and Dead Sea Basins. Jordan River Basin The Jordan River Basin is the most important surface water resource in the region. The total natural flow of the Jordan River, in the absence of extraction, ranges from 1485 to 1671 Mcm/yr at the entrance to the Dead Sea. The total area of the Jordan River Basin covered by isohyetes over 300 mm is 14847 km2. Of this area, 1638 km2 (11%) is within Palestinian territories. Israel is the greatest user of the Jordan River water where its present use is around 54% of the total flow. Israel transfers huge quantities of surface water through the National Water Carrier from Upper Jordan to Naqab, where, these quantities equal 420 Mcm/yr. At the same time, Palestinians have been denied use of the Jordan River water due to the Israeli occupation since the 1967 war. In addition, Jordan uses 22% of the Jordan River flow, Syria uses 11%, and Lebanon uses around 0.3% of total natural flow.

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The total catchments area of the eastward draining wadis of the Dead Sea and the Jordan River Basin (including Wadi Araba) is 40,650 Km2 of which Wadi Araba is 11,300 km2. The total area inside the Palestinian territories is 2750 km2 or 6.8%. Most of wadis within the Dead Sea basin originate and drain within the borders of each riparian state, except Wadi Abu Moraden which originates inside Palestinian territories and crosses the green line into Israel and then drains into the Dead Sea. The total average flow from the West Bank, as shown in the Table is 17.4 Mcm/year. Israel transfers huge quantities of surface water through the National Water Carrier from the Upper Jordan to the Naqab (about 420 Mcm/year), in addition to local consumption in the Tiberias Basin and the Huleh Valley which all sum up to the annual discharge of the three main tributaries of the Jordan River. Also, Israel gains 25 Mcm/year from the Yarmouk River and any runoff value that can be captured (around 50 Mcm/year) according to the 1995 Peace Treaty with Jordan. In essence, this is an illegal treaty that affects other riparian rights and systematically steals their water. It must be noted that the Palestinians had used and developed the water resources in the Jordan River Basin pre-1967. Around 150 pumps on the Jordan River had been used for irrigation of lands in the Jordan Valley. This fact alone solidifies the rights of Palestinians to use the Jordan River water resources according to International Water Law. Most of the Jordan River riparian countries consume the Jordan River water in order to fulfill their needs from the river basin and consequently the small quantity that reaches the West Bank is of bad quality and cannot be utilized. In addition, agricultural return flows and mismanagement of untreated wastewater by the Israeli colonies in the Jordan Valley are additional main sources of pollution to the Lower Jordan River. Wadis in West Bank and Gaza Western Wadis The total quantity of surface runoff in the western catchments surface runoff that originate from the Palestinian territories is 72 Mcm/year, whereas their total catchments area equals 2950 km2 inside the Palestinian territories. The eastern catchments are all presented as part of the Jordan River Basin and Dead Sea Basin. Wadi Gaza

The surface water system in the Gaza Strip consists of wadis, which only flood during very short periods, except for Wadi Gaza. Wadi Gaza is the major wadi in the Gaza Strip that originates in the Naqab Desert in a catchment area of 3500 Km2 and with an estimated average annual flow of 20 to 30 Mcm/year. However, rainfall varies significantly from one year to another and annual discharge can range from 0 to 100 Mcm/year. In addition, Wadi Gaza at present is diverted by the Israelis towards reservoirs for artificial recharge and irrigation. This means that nowadays, only a little water out of the huge floods may reach the Gaza Strip, if any, due to the Israeli practices. There are two other insignificant wadis in the Gaza Strip, namely Wadi El Salqa in the south and Wadi Beit Hanon in the north, that are almost always dry. Finally, it should be mentioned that the main reason for the drying-up of Wadi Gaza is the Israeli practices upstream of the Wadi. Based on the above, Palestinian surface water rights are 262 Mcm/year distributed as follows: 173 Mcm/year from the Jordan River, 17.2 Mcm from Dead Sea Basin, 72 Mcm/year from Western Wadis.

39

1.7 Worked Examples on Chapter One

Example 1.1 Evaporation A farmer has a reservoir with vertical sides and a surface area of 10,000 m2. Following the rainy season, the reservoir is filled to a depth of 3 m. During the dry season, the reservoir loses 6 cm of water per week to evaporation. If the average irrigation demand during the dry season is 350 m3/day, how many weeks can the farmer irrigate from the reservoir? Answer 1.1

• Volume of water available = 3x10,000 = 30,000 m3. • Losses to evaporation per week = 0.06x10,000 = 600 m3. • Irrigation demand per week = 350 X 7 = 2450 m3. • Water lost to evaporation and used to irrigation per week = 600 + 2450 = 3050 m3. • Number of weeks to irrigate from the reservoir = (30,000 m3)/(3050 m3/month) = 9.84 weeks.

Example 1.2 Water Balance A groundwater basin in a coastal area has an area of 510 km2. The land area is 500 km2 and the area of the river is 10 km2. There is no stream flow or groundwater flow into the basin. A water budget for the basin has the following long-term average annual values.

Precipitation Evapotranspiration Overland flow Baseflow Runoff Sub-sea outflow

875 mm/yr 575 mm/yr 75 mm/yr 150 mm/yr 225 mm/yr 75 mm/yr Notes:

• In order to prepare a water budget, identify all parameters in and out for each component assuming steady conditions.

• River flow or runoff is a combination of land flow and Baseflow. 1 Prepare an annual water budget for the basin as a whole. 2 Prepare an annual water budget for the river. 3 Prepare an annual water budget for the groundwater reservoir. 4 What is the annual river flow from the basin in m3/sec? 5 What is the average rate of groundwater recharge in million m3 per day per km2 of surface area?

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Answer 1.2

1 Water Budget for the Whole Basin

In Out

Precipitation = 875 mm Evaporation = 575 mm

Runoff = 225 Sub-sea flow = 75 mm

Sum 875 875

2 Water Budget for the River

In Out

Over land flow = 75 mm Runoff = 225

Base flow = 150 mm Sum 225 225

3 Water Budget for the Groundwater Reservoir

In Out

Prec. - Overland flow - Evap. = 875 – 75 – 575 (mm)

Baseflow = 150 mm Sub-sea flow = 75 mm

Sum 225 225

4 Runoff = 225 mm/yr = (0.225 m x 510x106 m2) / (365x24x60x60) = 3.64 m3/sec. 5 Recharge = 225 mm/yr = 0.225 m/yr = 0.225 m/ 365 = 6.164x10-4 m/day. = 6.164 x10-4 m3/m2 per day = 6.164x10-4 m3/ (m2x10-6km2/m2xday) = 6.164 x 10-4 x 106 m3 per day per km2 = 1.164x10-4 million m3 per day per km2.

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Example 1.3 Surface Water Resources The discharge Q is generally determined on the basis of water level recordings in combination with stage discharge relation curve, called a rating curve. The rating curve can often be represented adequately by an equation of the form:

boHHaQ )( −=

The following observations of head and corresponding discharge were obtained for a stream:

Head (m) 0.64 0.88 1.25 1.58 Q (m3/s) 0.052 0.153 0.408 0.747

1 Determine the constants a, b, knowing that the height of zero flow is 0.3 m. 2 What will be the discharge of the stream when the head = 2 m? Answer 1.3 1

boHHaQ )( −= , where Ho=0.3 m.

Taking logs gives: aHHbQ o log)log(log +−=

Now, plotting log Q against log (H-Ho), should give a straight line with a slope b and y-intercept log a.

H – Ho 0.34 0.58 0.95 1.28 log (H-H0) -0.469 -0.237 -0.022 0.107 log (Q) -1.284 -0.815 -0.389 -0.127

Rating curve

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3

log (H-H0)

log

Q

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From the rating curve, Slope = 2.01 b= 2.01 And y-intercept = -0.34 log a = -0.34 a= 0.46. 2

boHHaQ )( −=

where, a=0.46, b=2.01, H= 2m and H0=0.3 m

.sec/34.1)3.02(46.0

3

01.2

mQ=

−=

Example 1.4 Groundwater as a Storage Medium

The flow of a river at the start of a Baseflow recession is 233 m3/sec; after 60 days the flow declined to 89 m3/sec.

1 Find the recession constant for the basin. 2 What would the flow be after 112 days?

Answer 1.4 1 at

oeQQ −=

then,

123

3

106.1233

89ln

601

ln1ln

−−

−

×=⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛×−=

×⎟⎠⎞

⎜⎝⎛−=⇒=−⇒=

days

ms

m

daysa

QQ

ta

QQat

QQe

ooo

at

2 atoeQQ −=

( )

sm

memQ daysday

3

3

112106.13

8.38

1667.0sec/233sec/233

12

=

×=

×= ××− −−

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Example 1.5 Groundwater Recharge from Short Lived Wadis

Background The annual precipitation of the West Bank is much less than the potential evapotranspiration leaving a moderate scope of direct groundwater recharge. Therefore, an assessment of direct recharge by infiltration of water through wadi beds during floods is an important element of water resources evaluation. This is the subject of this question. The case study is taken about Wadi Misk. Given Data

• Figure 1.10. • Wadi Misk is 40 km long, with a uniform width of 50 m. • The flood hydrographs upstream (at distance 0 km) and downstream (at distance 40

km) of the wadi are shown in Figure 1.10. The distance between gauging stations is 40 km.

• Evaporation data are calculated by installing class A pan near the stream of Wadi

Misk to determine daily evaporation. The level in the pan is observed every 12 hours. • Rainfall and evaporation are given in Figure 1.10.

Required 1 Determine the total volume of flood water at the gauging stations upstream and down stream shown in Figure 1.10. 2 Calculate the average daily evaporation as mm/day. 3 Calculate the total volume of water evaporated over the entire event period. 4 Calculate the total recharge volume through the stream bed over the entire flood event.

44

Figure 1.10

45

Answer 1.5 1 Upstream flood volume = 0.5 x (72-12) hr x 60 min x 60 sec x 130 m3/sec = 14.04 x 106 m3

Downstream flood volume = 0.5 x (56-12) hr x 60 min x 60 sec x 50 m3/sec

= 2.88 x 106 m3

2 The average wadi evaporation per 12-hr period = (5 + 6 + 12 + 6 + 3)/5 = 6.4 mm per 12-hr period = 12.8 mm/day 3. Total evaporation rate over the 72 hours = 5 + 6 + 12 + 6 + 3 = 32 mm Volume lost to evaporation = evaporation rate x surface area of the wadi = 0.032 m x 50 m x 40,000 m = 6.4 x 104 m3 4 Total transmission over the 40 km stream = 14.04 x 106 – 2.88 x 106 = 11.16 x 106 m3 Groundwater recharge = 11.16 x 106 – 6.4 x 104 = 11.096 x 106 m3

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Example 1.6: Clear Lake has a surface area of' 708,000 m2. For the month of March, this lake had an inflow of 1.5 m2/s and an outflow of 1.25 m2/s. A storage change of +708,000 m3 was recorded. If the total depth of rainfall recorded at the local raingauge was 225 mm for the month, estimate the evaporation loss from the lake. State any assumptions that you make in your calculations.

Figure 1.3 The water balance of (a) a lake or reservoir; and (b) a catchment area

Solution:

Note:

The evaporation loss may be computed by rearranging Equation (1.2): E = P + Qi n-Qo u t - ∆S in which seepage is assumed to be negligible. The individual components are then computed as follows: precipitation, P: 225 mm x 708,000 m2 / 1000 mm/m = 159,300 m3 inflow, Qin: 1.5 m3/s x 86,400 s/d x 31 d/month = 4,017,600 m3 outflow, Qout: -1.25 m3/s x 86,400 s/d x 31 d/month = -3,348,000 m3 change in storage = - 708,000 m3 hence evaporation, E = 159,300 + 4,017,600 - 3,348,000 - 708,000 = 120,900 m3 or 120,900 m3 x 1000 mm/m / 708,000 m3 = 171 mm over the lake area.

The calculation can also be made directly in terms of mm depth; the important point is to be consistent in terms of units in any water balance as well as in the sign of each term, ie what is an input and what is an output to the control volume.

In contrast, if the control volume is a catchment or drainage area bounded by its topographic divide or watershed, as shown in Figure 1.3b, the inputs consist of precipitation, P, and possibly groundwater inflow, Gin, and the outputs comprise the discharge, Q, at the catchment outlet, transpiration from the vegetation growing within the catchment and evaporation from precipitation intercepted on the vegetal canopy held in storage on the ground, E, and possibly groundwater outflow, Gout. The changes in storage, ∆S, to be considered are principally those in the sub-surface unsaturated and saturated zones, leading to

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Q = P – E + Gin - Gout ± ∆S (1.3)

Example 1.7: During the water-year 1994/95, a catchment area of 2,500 (km)2 received 1,300 mm of precipitation. The average discharge at the catchment outlet was 30 m3/s. Estimate the amount of water lost due to the combined effects

of evaporation, transpiration and percolation to groundwater. Compute the volumetric runoff coefficient for the catchment in the water-year. Solution:

Assuming that the changes in storage, ∆S, are negligible, Equation (1.3) becomes E + Gout - Gin = P - Q the runoff, Q = 30 m3/s x 86,400 s/d x 365 d/annum x 1000 mm/m / [2,500 (km)2 x (1000 m/km)2] = 378 mm hence the combined loss = 1,300 - 378 = 922 mm The volumetric runoff coefficient, C, is the ratio of the total volume of runoff to the total volume of rainfall during a specified time interval; in this case, C = 378 mm / 1,300 mm = 0.29, ie only 29 per cent of the rainfall reached the catchment outlet within the water-year.

If the underlying geology of the catchment is such that the groundwater divide coincides with the topographic divide, ie the catchment is watertight, then the terms, Gin and Gout, may be deleted. Moreover, if the period over which the balance is considered is sufficiently long, ie the annual seasonal cycle or water year, then ∆S can be considered to be zero. Of the remaining terms, Q may be measured using standard hydrometric methods, and if sufficient raingauges can be deployed to evaluate spatial variations, P may also be estimated. Although standard methods are available to measure the evaporation from an open water surface or to estimate the evaporation from a uniform stand of vegetation, E for a heterogeneous mixture of both short and tall plants and bare soil is difficult to evaluate independently. Hence

E - P - Q (1.4)

Provided that care is taken with the boundary conditions, ie the topography and geology, and the choice of the period over which the balance applies, Equation (1.4) can provide useful results, despite its apparent simplicity. Indeed, this approach has been employed extensively to calibrate indirect methods of estimating the evaporation from an open water body.