Effect of Excess Pumping on Groundwater Salinity and Water Level in Hail
Region of Saudi Arabia
Ahmed A. Al-Naim
Presently there is growing concern regarding groundwater quality degradation
and water level depletion in the potential agricultural areas of the Kingdom
of Saudi Arabia. The main objective of this study was to determine the effect
of excess pumping on groundwater salinity and water level for increasing agricultural
production in Region, Saudi Arabia. The study results showed that net water
withdrawal from the small aquifer was 99% with only 0.84% annual recharge. Mean
groundwater level depletion was 25 m over a period of 12 years (2002-2013 period)
i.e., 33 m in the unconfined zone and 18 m in the confined zone. Overall mean
annual water drawdown was 2.6 m in the study area i.e., 2.7 m in the unconfined
zone and 4.4 m in the confined zone. Water quality deterioration (total water
salinity) was high in the unconfined zone where TDS increased from 950-1180
ppm as compared to the confined zone where it increased from 600-700 ppm in
the Saq aquifer. In conclusion, the study provided a useful tool in the form
of mathematical equations for predicting the water salinity degradation both
in the unconfined and confined zones for planning future water management strategies
in Hail region.
Saudi Arabia is a vast country covering a total area of 2.25 million square
kilometers. It is located in an arid region with the Red Sea bordering its western
coast and the Arabian Gulf along its eastern coast. The country is characterized
by a hot dry climate with a mean annual rainfall range in between 25-150 mm
in about 80% of the country. This gives rise to serious limitations on the use
of shallow aquifers to meet the increasing demand of water for domestic, industrial
and agricultural purposes, especially during dry periods, when the extraction
from the existing groundwater aquifers often exceeds the replenishment in arid
regions. Water resources in their natural state are limited and non-renewable
in Saudi Arabia similar to any arid region of the world. Since, the country
falls in arid to semi-arid climate zone and there are no rivers, lakes or permanent
running streams. But the country is blessed with many aquifers containing huge
reserves of groundwater. Therefore, efficient management of these aquifers is
of great importance for sustainable irrigated agricultural activities in the
country. In Saudi Arabia, there are seven major deep aquifers, covering hundreds
of square kilometers and extending from the Jordanian boundary in the north
to the southern and eastern boundaries of the country.
Agriculture sector is next to oil as a source of economy in the Kingdom of
Saudi Arabia. Generally, around 80-85% of water requirements are met from groundwater
sources (Ministry of Agriculture and Water, 1984). The
Saq aquifer, a water-bearing formation in Hail Region, is considered as
the oldest and the largest aquifer in the northern part of the country. According
to an estimate (Khordagui, 1996), the population of
Saudi Arabia is expected to increase from 20.7 millions in 2000-44.7 millions
in 2025 which is expected to place great stress on the existing limited water
sources. Groundwater quality is one of the main factors determining its suitability
for drinking, domestic, agricultural and industrial purposes (Subramani
et al., 2005). As such, water is the most important constraint for
future development in this region (Lashkaripour et al.,
2005). A review of literature showed that a very little work has been accomplished
on the effect of pumping on the degradation of water quality, especially the
total water salinity for irrigation, in the potential agricultural areas of
Qahman et al. (2009) applied two multi-objective
management models in a coastal aquifer to maximize the total volume of water
pumped, minimizing the salt concentration of the pumped water and controlling
the drawdown limits on a part of the aquifer with 9 existing pumping wells located
at various depths. The study showed that the optimum pumping rate is in the
range of 26-34% of the total natural replenishment and the proposed technique
is a powerful tool for solving this type of management problems. Soni
and Pujari (2010) analyzed the hydro-chemical data of groundwater samples
of three different limestone mine sites, which are in close proximity and covers
a tract along the Gujarat Coast of Indian peninsula. They found sea water intrusion
in the coastal aquifer in the study area and recommended measures for sustainable
use of groundwater by the mining companies and other stake holders. Kenabatho
and Montshiwa (2006) stated that Water is an essential resource affecting
many aspects of development and the natural environment. They concluded that
with the current fragmented, uncoordinated institutional and legal arrangements
in water resources management, there is an urgent need to adopt integrated water
demand management as envisaged in the overall concept of Integrated Water Resources
Management (IWRM). Segosebe and Parida (2006) stated
that water is one of the most important elements essential not only to attain
food and health security but also for the economic development of a country.
They examined the various strategies in a semi-arid country like Botswana to
manage the growing demand for water. These strategies encompass the use of tariffs,
water reuse/recycling and water restrictions. Other attempts encourage water
conservation through rainwater harvesting and implementation of technological
innovations with exploration of non-conventional sources. Khadim
et al. (2013) developed a mathematical formula to assess the rate
of tidal sedimentation due to Tidal River Management (TRM) in parts of Khulna
and Jessore districts. The study found the evidences of considerable advancements
in regional livelihood i.e., flood resistance, cultivated lands, cultivable
area, cropping intensities and food security due to Integrated Water Resources
Management (IWRM) approaches. Therefore, the main objective of this study is
to determine the effect of pumping on groundwater salinity and water level in
Hail Region for sustained agricultural production.
Location of study area: The study area was selected lies on the south-eastern
part of Hail Region. It situated
between longitude 42°26'-42°48' E and latitude 27°23'-27°31'
N, with total land area of about 160 km2 in conical shape 200 km2
||Location of the study area (NADIC Hail Project) (190
MATERIALS AND METHODS
Water level of the aquifer was measured from four observation wells in the
study area (Fig. 1). Water samples were also collected from
three other wells in the Arabian Shield to determine groundwater salinity from
the bottom of aquifer. These three wells are located 28 kilometres away from
the south-western part of the study area representing the base of Saq aquifer.
The thickness of the interval between the bottom of wells and the base of the
aquifer (Zb) was calculated from the well depth and the total depth
of the basement rocks. Water samples were collected from the aquifer at the
time of water level for measuring the total water salinity according to methods
described in USDA (1954).
The following equations were used to calculate water level in the study area.
where, WL is the water level (m) as a function of time in years
(X) above sea level.
Data analysis: Data were analyzed by ANOVA and regression techniques
at 5% level of significance according to SAS (2001).
RESULTS AND DISCUSSION
Temporal water quality degradation: Water quality is determined by the
concentration of different types of salts in water. It is well known that depletion
of groundwater level by continuous pumping from an aquifer may degrade water
quality resulting its unsuitability for various uses. The influence of excess
pumping of groundwater on water level in the aquifer from 2002-2013 is presented
in Fig. 2. Mean groundwater level depleted from 526-597 m
above sea level in six observation wells observation wells from 2002-2013. The
net depletion in groundwater level was around 71 m, which indicated un-necessary
pumping of groundwater in the region to meet the growing water demand for various
uses in the region with particular reference to agricultural production.
Spatial degradation of water quality: Groundwater quality in an aquifer
varies with depth due to aquifer geology and other rock formation having different
chemical characteristics. Michael (1978) observed water
quality deterioration with depth in several locations in Delhi territory, India.
The results showed that total groundwater salinity of the aquifer degraded in
the unconfined zone due to excess pumping resulting in up-coning of more mineralized
water from the lower depths. Also, deep percolation of highly saline drainage
water from over irrigation and run off losses from irrigated fields may be the
cause for water quality degradation in the aquifer. A positive relationship
was observed between the well depth and water salinity in both the unconfined
(R2 = 0.914) and confined zone (R2 = 0.998) of Saq aquifer
in the study area (Fig. 3 and 4). This suggests
that groundwater quality deteriorated with depth due to high salinity at the
deeper than the shallow depths of aquifer. The water salinity in the aquifer
showed increases towards the outcrop which may be due to the inflow of highly
saline water from bottom of the aquifer especially in the outcrop of Saq aquifer
in the study area.
Temporal deterioration of water quality: Data showed that overall mean
changes in total water salinity were less in the confined zone than unconfined
zone (Fig. 5). This variation of water salinity may be due
to difference in aquifer thickness which is more in the confined zone as compared
to unconfined zone in presence of shale layer preventing upward movement of
saline water from the bottom layers of aquifer.
||Influence of excess pumping on groundwater level in the aquifer
||Changes of water salinity with depth of well in confined aquifer
Changes of water salinity with depth
of well in unconfined aquifer
||Groundwater salinity (TDS in mg L-1) with time
in different aquifers
Also, this scenario can help to predict future water quality changes in the
confined and unconfined zones of Saq aquifer in the study area regarding groundwater
salinity and field crop response. According to a study, the effect of soil salinity
on crop growth is negligible if the electrical conductivity of saturation extract
is less than 2 dS m-1 at 25°C (Michael, 1978).
Generally, most common field crops are affected with irrigation water salinity
between 4-8 dS m-1. But soil salinity up to 6 dS m-1 and
above is considered critical where most of the field crops in study area are
likely to suffer according to crop salt tolerance limit described by USDA
(1954) and Withers and Vipond (1974).
Water quality vs. groundwater level: Many investigators reported groundwater
quality changes due to excess pumping of aquifer (Blaszyk
and Gorski, 1981; Appelo and Postma, 1994). Data
in Fig. 6 shows that yearly water level depletion (drawdown)
was less in the confined zone than the unconfined but nevertheless, water quality
in the unconfined zone deteriorated more than the confined zone (Fig.
3, 4). This may be attributed to the sensitivity of unconfined
zone due to low discharge and well drawdown. Furthermore, yearly water level
drawdown was higher in confined zone than the unconfined zone which may be due
to the discrepancy in the distance between the production wells as reflected
by the strength or weakness of the influence of cones of depression. This was
also indicated by the small value of storage coefficient (S) in confined zone
as compared to high specific yield (Sy) in unconfined zone. On the
other hand, the total number of wells was 117 in confined zone as compared to
73 in unconfined zone. The small storage coefficient means quick spreading of
the cone of depression thus resulting in more drawdown (Fetter,
1994) and vice versa in the case of unconfined storage.
Drawdown of a well depends on the distance between the location of two adjacent
production wells. Because, if the distance between the production wells is small,
the radius of influence will be more causing more intersection between the cone
of depression of two neighboring production wells and showing more drawdown
in wells. The distance between wells in the two-direction south-north and east-west
in both zones are given in Table 1.
A manipulative calculation showed that water withdrawal was higher from the
unconfined than the confined zone depending on the aquifer storage area. The
parameters used for the calculation were the accumulated drawdown (15 years
data), number of production wells and total area in both zones (Table
||Comparison of water withdrawal and drawdown with time in Saq
||Average, maximum and minimum well field distances in both
the confined and unconfined zones in the study area
||Comparison of well water drawdown in the confined and unconfined
To calculate the excess drawdown due to variation in area and the number of
pumping wells between the confined and unconfined zones, the ratio more than
0.13 and 0.6 was multiplied by accumulated drawdown in the confined zone which
came to 8.46 and 42.62 m, respectively. The excess drawdown, depending on the
number of wells and total area, was added to the actual accumulated drawdown
estimated in the unconfined zone (i.e., 31 m) to find out the total accumulated
drawdown in the unconfined zone which came to 82.08 m and was more than the
drawdown in the confined zone. The calculated drawdown in the unconfined zone
(82.08 m) was assumed to be equal to the currently accumulated drawdown in the
confined zone (i.e., 79 m) because the two zones were similar with respect to
total area and the numbers of abstraction wells. The difference between the
calculated accumulated drawdown in the unconfined zone and the currently accumulated
drawdown in the confined zone was 3.08 m. This difference revealed that 10%
more water was withdrawn from the unconfined zone as compared to confined zone
primarily to meet the growing crop water needs in the area.
Land subsidence due to groundwater withdrawals: Prediction of subsidence
of ground surface overlying heavily exploited aquifers is important for efficient
water management. The occurrence of land subsidence in many places in the world
is the result of groundwater pumpage from unconsolidated aquifer-aquitard systems.
In addition, Poland and Davis (1969) and Poland
(1972) provided descriptive summaries of all the well-documented cases of
major land subsidence caused by overdraft pumping. In Saudi Arabia, till to-date,
no case of land subsidence has been reported, although steady depletion in water
level is expected due to agriculture expansion (Al-Ibrahim,
Discharge and drawdown relationships: Well flow rate (discharge) causes
great influence on the cone of depression, which indirectly affect the drawdown
of the production well. For example: If the pumping rate (Q1) of
a well is 300 gpm with all other factors being constant and the drawdown (s)
of an observation well located 50 m away is 2 m, then the drawdown will be 4
m if the discharge rate (Q2) is increased to 600 gpm. Also for a
given discharge, drawdown decreases with an increase in aquifer transmissivity
and decreases in storability as described by the USDI (1977).
A negative relationship was observed between the total water withdrawal per
annum and water level elevation from 1984-1993 period (Fig. 7).
Effect of water withdrawal on water depletion
in Saq aquifer (2006-2013)
||Effect of time on water level in Saq aquifer
The regression analysis showed a negative relationship between
the water level depletion and the water withdrawal with time as given in the
WL = -4.1576X+670.27; R2 = 0.987
where, WL is the water level elevation (m) above sea level, X is the water
withdrawn from the aquifer storage per season in Million Cubic Meters (mcm).
Temporal water level changes: Data in Fig. 8 show
the water level changes with time in both the confined and unconfined zones
in the study area. Generally, the average water level for the study area in
2004 was 682 m above sea level, but only 652 m in 2013 indicating 30 m water
level depletion over a period of 10 years i.e. 66 m in the unconfined zone and
30 m in the confined zone. Thus, overall the mean annual water drawdown was
3.6 m in the study area i.e., 2.38 m in the unconfined zone and 5.31 m in the
confined zone. Based on the annual calculated water well drawdown in both zones,
the time period in terms of years can approximately be predicted when the water
level will approach the well screen level in both zones.
A rough prediction of water depletion in future over time in the study area
was also considered. The model used assumed that the annual rate of water level
depletion is the same. Two linear equations showed links between the water level
and time in terms of years for both zones (Fig. 8). An appropriate
digital groundwater computer model was used to predict future aquifer behavior
in terms of depleting water level in Saq aquifer. The two lines of graphs show
the total quantity of water withdrawn from the aquifer in the two zones (unconfined
and confined) thus indicating the differences in cultivated areas in both zones.
The two regressions equations obtained were as below.
WL = -2.3879X+676.33; R2 = 0.985
WL = -5.2788X+630.13; R2 = 0.884
where, WL is the water level as a function of year (X) in meters above sea
Water strategy for saq aquifer: The study area consisted of around 0.5%
of the total exposed surface Saq formation in the Kingdom of Saudi Arabia (about
65,000 km2 or 25,000 m2) plus 3,000 km2 in
Jordan (Ministry of Agriculture and Water). Also, total annual recharge of 250
mcm (million cubic meters)/year was from the rainfall for the total outcrop
area of Saq aquifer and the total volume of water discharged from the entire
Saq aquifer was 290 mcm/year for various uses (Al-Watban,
1976; Noory, 1983). Al-Shammary
(1986) estimated total annual recharge rate as 166 mcm over an area of 12,900
km2 of the Saq aquifer, while the total water extraction from this
area was 248.43 mcm/year. But, in study area, the total annual water extraction
was 150.2 mcm and the total annual recharge was 1.3 mcm according to water balance
method and 1.23 mcm using the Chloride method.
Previously, based on the total recharge and discharge parameters, the total
annual withdrawal of water from the whole Saq aquifer was 40 mcm per year as
against 82.39 mcm per year estimated by Noory (1983)
and Al-Shammary (1986). Lloyd and
Pim (1990) estimated that the total water extraction from the whole area
of the Saq aquifer was 3195x106 m3 year-1.
Noory (1983) previously estimated that the total water-strategy
of the entire area of Saq aquifer was 200 Billion Cubic Meters (BCM) per year.
Thus, the net non-renewable water extraction from the entire Saq aquifer was
about 2.95 bcm/year (Noory, 1983; Lloyd
and Pim, 1990).
The study results indicated that both the water level and the water quality
deteriorated due to excess pumping of aquifer in order to meet the growing water
needs for domestic, agricultural, industrial and other beneficial uses. The
percentage net overdraft volume of water withdrawn from the small aquifer storage
in the study area came to 99 with 0.84% annual recharge. The average water level
in the study area was 675 m above sea level in 2002, but only 620 m in 2013,
indicating 25 m depletion over a period of 12 years i.e. 18 m in the unconfined
zone and 33 m in the confined zone. Thus, overall mean annual water drawdown
was 2.6 m in the study area i.e. 2.7 m in the unconfined zone and 4.4 m in the
confined zone. Thus, overall mean annual water drawdown was 3.6 m in the study
area i.e., 2.38 m in the unconfined zone and 5.31 m in the confined zone. The
study results agree with the findings of Lashkaripour and
Ghafoori (2011) who reported that manifold increases in water demand with
little recharge have strained groundwater resources resulting in water level
depletion and deterioration of groundwater quality in the major parts of the
plain. They further mentioned that primary cause of sharp depletion in the groundwater
level in recent years is attributed to excess pumping as compared to the level
of natural recharge. As a result, the average water level dropped from 1036.47-1002.75
m from 1987-2006 with an annual rate of depletion to about 1.77 m. Similarly,
water level depletion is often associated with increasing groundwater salinity
(OHara, 1997). Also, El-Fadel
et al. (2001) reported that severe water level depletion and the
increase in groundwater salinity will be different, with regard to the amount
of aquifer recharge, as well as the thickness of fresh water layer. Similarly,
overexploitation and pollution of groundwater in the semi areas were reported
by Ballukraya (2001) and Rao (2003)
who referred shortage of surface water supplies as the main causes for this
type of scenario. Similar views were expressed by Fischer
et al. (2011) who observed that groundwater levels in the capital
Hanoi decreased dramatically when excessive pumping at certain individual wells
lowers the potentiometric surface locally and causes up-coning of the inter-face
between fresh water and saline water. Also, Qahman et
al. (2005) investigated the optimal and sustainable extraction of groundwater
from a coastal aquifer for seawater intrusion into the aquifer. Their physical
model was based on the density-dependent advective-dispersive solute transport
The net volume of water withdrawn from the small aquifer storage in the study
area came to 99% with 0.84% annual recharge. Mean groundwater level depletion
was 25 m over a period of 12 years (2002-2013 period) i.e. 33 m in the unconfined
zone and 18 m in the confined zone. Overall mean annual water drawdown was 2.6
m in the study area i.e. 2.7 m in the unconfined zone and 4.4 m in the confined
zone. The study area covered approximately 5% of the total water exploitation
from Saq aquifer and 46 % of the total volume of water exploitation from the
whole Saq aquifer in the Al-Hail region. Therefore, the aquifer storage in the
study area is under stress as a result of water exploitation as compared to
other locations in the Saq aquifer. According to the study observations, it
may take around 21 years for the groundwater salinity to each critical level
for salt stress on most of the field crops and upto 36 years for the water level
to reach the well screen levels. In conclusion, the study area needs careful
planning and adoption of improved water management practices to avoid water
shortage problems for sustainable irrigated agriculture.
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