Water Resources Management (2006) 20: 91–108DOI: 10.1007/s11269-006-4636-2 C© Springer 2006

Groundwater Rise Problem and Risk Evaluationin Major Cities of Arid Lands – Jedddah Casein Kingdom of Saudi Arabia

SALEH A. AL-SEFRY∗ and ZEKAI ŞENSaudi Geological Survey, P. O. Box 54141 – Jeddah 21514, Kingdom of Saudi Arabia(∗author for correspondence, e-mail: alsefry.sa@sgs.org.sa )

(Received: 19 July 2004; in final form: 20 March 2005)

Abstract. Arid lands are in the need of additional water supply but water transportation from outsideof the natural hydrological cycle causes the groundwater to rise within the urban areas. Additionalwater supply from surrounding areas or through the desalination plants provides comfort in domesticactivities but after the usage, its disposition is necessary in an efficient manner. Unfortunately, aridregion cities have neither sufficient nor efficient sewage system. Consequently, the water returned tosurface cesspools and leakages from insufficient sewage system makes internal groundwater rechargewithin the urban area. Additionally, water supply system leakages further raise the groundwater level.Deterioration in water quality becomes a potential danger for the infrastructure and foundations.Surface depressions in the city may be flooded due to groundwater level rise and at times bed smellsoccur at various parts of the city.

In this paper, a quantitative method is followed to assess groundwater level rise risks in addition tothe few chemical risks associated with sulfate and chloride solids. It is observed that each one of thesevariables has different probability distribution function and expose risk maps with different features.

Key words: Arid lands, groundwater, level rise, map, probability, risk, Saudi Arabia

Introduction

Jeddah as the major commercial center is one of the biggest cities in the Kingdom ofSaudi Arabia. The city expanded both vertically and horizontally due to unprece-dented rapid economic growth after 1970. Unfortunately, neither geological norhydrological features are taken into consideration in such developments. In orderto gain additional usable land locations even the topography of the metropolitanarea is changed because of huge excavations. Change in topography led to distur-bance of natural wadi courses, which have confluences within the city starting fromthe eastern mountainous area. Hence, it is not possible for wadi courses to reach theRed Sea. On the other hand, increased population and local small industries con-sume excessive water from many sources including the desalination water, whichis later returned to local cesspools, open channels and depressions leading to a sortof artificial recharge. Jeddah is located between two major wadis, namely, Wadi

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Figure 1. Location map.

Fatimah in the south and Wadi Usfan in the north with several local wadis thatmake up Jeddah basin (see Figure 1). The climate is arid, very hot with high ratesof humidity. The rainfall is scanty with temporally and spatially quality variations.Generally, rainfall occurrences are in winter season.

Presently, the metropolitan area of Jeddah expanded to 1200 km2 and its popu-lation is about 2,200,000 with the annual population growth of 4% approximately.

As a result of leakages or infiltrations from different sources such as water supplypipes and some local sewerage, the natural groundwater balance is overturned intoan unbalance where the input to water table is comparatively much more than thenatural groundwater flow towards the Red Sea. Depending on the season of theyear, the groundwater table elevation started to change about ±0.12 m annually(Basamed, 2002).

On the other hand, the studies carried out between 1996 and 2000 indicate thaton the average there has been 0.41 m water table rise within the city during thisperiod, which means that there is about 0.10 cm groundwater table rise in eachyear. Such hydrogeological effects are due to leakages from the main water supplypipes, tanker water haulages and their use for irrigation purposes, sewage waterleakages, leakages from surface water storages, garden watering, rainfall, naturalgroundwater flow through the wadis.

It is, therefore, necessary to maintain the existing sewage water collection sys-tem, to establish new and additional sewage system especially in urban areas wheresuch a facility is not available. This system must be extended over such an arealcoverage that the entrance of tankers must be canceled for water transportation.Instead of sewage water direct dumping areas in the eastern parts of the city, one

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can recommend construction of wastewater treatment plants at locations such thatleakages and surface flows of treated water are away from the city metropolitan area.Furthermore, by increasing general awareness and information, the use of pollutedwater for local irrigation must be forbidden and in this manner, the groundwatertable rise will be stopped and even reduced by time.

In this study, the data recorded during 1996 and 2002 from 118 wells are eval-uated in order to assess the groundwater quality and quantity for identifying thegroundwater rise. These data also helped to identify general and local groundwa-ter flow directions. The groundwater level rise maps and representative chemicalconstituents, namely, sulfate and chloride maps are prepared through a simple prob-abilistic risk model.

General Properties of Jeddah Watershed

Jeddah watershed lies within longitudes 21◦15′N and 22◦N and latitudes 39◦3E and39◦30′N covering 1760 km2 of area (see Figure 2). The surface elevation differencevaries from zero at the Red Sea coastal area to about 400 m at the mountainous areain the east. The general tendency of slope increase is from east to west with somelocalities of lower and higher elevations than the general trend.

The small wadis lead their water towards the Red Sea. As shown in Figure 2the whole Jeddah basin can be considered in terms of three sub-basins, which aredelineated according to surface water directions. These are,

1. In the north, the sub-basin covers 675 km2 and confluences with small Abhorbay through wadi Al-Kalah,

2. In the middle, the sub-basin covers 650 km2 and confluences with Salam Palacelake, and

3. In the south, the sub-basin covers 435 km2 and leads its water to Arbeen Lake.

It is possible to divide the aquifer material and geological layers also into threeparts as follows.

1. Wadi deposits consisting of fine sand gravel and clay,2. Marine deposits consisting of marine calcareous rocks and coral reefs, and3. Silicic plutonic rocks consisting Arabian Shield rocks, which are granite, diorite

and granodiorite.

The main groundwater table rise damages are especially at low-lying areasinclude the following undesirable results.

1. the flooding of house basements,2. deterioration of roads and highways,3. damage to building foundations,4. the contamination of soil,5. offensive smell, and,6. breeding of mosquitoes.

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Figure 2. Jeddah basin.

In the end, these damages will become more widespread, if the rising ground-water table remains uncontrolled. The potential serious risks are on public healthand the deterioration of foundation material.

Urbanization has a great effect on the hydrological cycle especially to subsur-face components of infiltration and percolation leading to groundwater recharge.The major signature of urbanization is the impermeabilization of significant landsurface in addition to major water imports from outside of urban boundaries. In anyurbanization, sanitation and drainage arrangements are of fundamental importance.The flooding possibilities increase due to impervious surface pavements in terms

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of roads, airports and buildings. During the second half of the twentieth century,worldwide emigration from rural to urban areas increased present problems man-ifolds. Especially, in the developing countries unexpected immigrations endangerthe infrastructure and municipal services in an unprecedented manner (Ribeiro,2001). Consequently, already restrictive water supply sources become under addi-tional pressure due to demand rate increase. Water supply from alternative sourcesand their distribution through the mains cause to water leakages within urban areas,which enhance groundwater table rise.

Urban developments influence the groundwater regime beneath these areas dueto reduction and changes in the recharge locations and amounts. The groundwater in-puts are the natural aquifer flow towards the urban area and artificial intentional andunintentional (mains leakage) seepages, and as the outputs, the natural groundwateroutflow in addition to groundwater abstraction by pumping. There are groundwatermoulds, i.e. groundwater level rise beneath the urban area. Hence, the groundwaterregime is modified from its original natural behavior. Although it is possible toreach a new groundwater steady state regime after considerably long time from hy-drogeological and hydrological points of view but geotechnical engineers are moreconcerned with smaller time scales and local site-specific groundwater effects. Dueto urbanization even during dry (non-rainy) periods, there will be so to speak artifi-cial recharge from mains and sewage system leakages. Their effects on groundwaterlevels are expected to depend on the following situations (Wilkinson, 1994).

1. Aquifer transmissivity value plays significant major role in the vertical rechargeand horizontal groundwater flow rates,

2. The aquifer beneath the urban area is exploited heavily with continuous ground-water level drops provided that there is not enough recharge. The groundwaterlevel falls are not uniform due to the heterogeneity and anisotropy of the aquifermaterial,

3. Due to heterogeneous and anisotropic subsurface soil and geological composi-tions there may appear perched aquifers at some places,

Aforementioned facts and general experience indicate that the most troublesomegroundwater mounds under urban areas are likely to develop in low-lying areas ofrelatively low permeability aquifers, especially if they are not exploited for watersupply perhaps as a result of naturally poor, or deteriorated water quality.

Water Situation in Jeddah City

Leakages from different water sources lead to groundwater table level fluctuationsand consequently, disturbance of natural groundwater storage balance, and rightafter the rainy periods due to infiltration, the groundwater level rises but dropsduring summer seasons. Various types of leakages during the period from 1996 to2002 caused to groundwater level rise on the average at about ±0.12 m in additionto seasonal fluctuations (Basamad, 2002).

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The groundwater rise indicates the changes in the groundwater storage, directionand velocity. It is necessary to know the temporal change of groundwater velocity inorder to identify depression and moulds locations within the city. The effect of tideshas also been noticed in some parts of the city. This situation is observed duringlarge excavations for construction purposes. During the nights, there is loweringand in the daytime rising because during the night pumps are able to lower thegroundwater level easily, but in the day time the same pumps are not enough tolower the groundwater level to the same elevation. This is a good indication thatthe tidal effects cause seawater intrusion into some of the inland localities.

From the groundwater elevation contour map as shown in Figure 3 the followingpoints can be identified.

1. The general groundwater direction is from the east towards the west,2. The contour lines are more or less very regular from the east up to the west,3. Calcareous rocks and coral reefs play the role of subsurface dam at the Red Sea

coastal area, which cause significant groundwater velocity changes,4. There is a noticeable variation in the groundwater level from 1996 to 2000, the

groundwater rise is obvious in the city, and the total amount is 0.41 m, whichmeans that on the average there has been 0.1 m groundwater rise, annually(Basamad, 2002).

The continuous fluctuations in the groundwater level cause the interaction be-tween the permeable and semi-permeable geological and the saturated layers withinthe wadis. Hence, there is groundwater exchange between these layers. Addition-ally, there is effect of groundwater flow from the eastern parts and especially inthe northern part of the city. The coral reefs along the seashore play the role of aconvenient media for groundwater flow to the sea or vice versa. Consequently, insome coastal-close areas, the depth to water level is less than 2.5 m. Such areas areobservable from the city center towards the northern part. The extent of groundwa-ter rise coverage locations has increased in 2002 more than 1998. It covers about61% (910 km2) of the total area, which was about 56% in 1998. Hence, there hasbeen 1.25% increase yearly, which corresponds to 18.75 km2.

Groundwater Rise and Quality Variations

Adequate and reliable water supply to cities and removal of wastes has been con-tinuous problems in many civilizations. The chemical composition of groundwatercan be identified based on its chemical concentrations or ratios of different con-centrations. Such simple techniques are used in hydrogeology literature in orderto identify the classification of groundwater quality (Lloyd and Heathcote, 1985).Similar ideas can also be used for the identification and classification of urbanarea groundwater. According to Barrett et al. (1991), an ideal recharge marker isan easily analyzed solute that is unique to one source and to one pathway, at aconstant concentration in the source, and non-reactive in all conditions. It is not

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Figure 3. Jeddah city groundwater level map.

possible to find such solutes easily. They have categorized potential marker solutesinto categories as follows.

1. Inorganic concentrations that are further grouped into major cations (Ca, Mg,K and Na) and anions (HCO3, SO4, CO3 and Cl), nitrogen species (NO3 andNH4), metals (Fe, Mn, and trace metals), and other minor ions (B, PO4, Sr, F,Br, and CN),

2. Organic concentrations starting from the most relevant ones are chlorofluorocar-bons (CFCs), trihalomethanes (THMs), faucal compounds, such as coprostanoland I-aminopropanone, detergent-related compounds, such as optical brightness

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and EDTH, and industrial chemicals, including chlorinated solvents and manyhydrocarbons.

3. Particulate matters including faecal microbiological species, and various col-loidal particles, and finally,

Groundwater level rise and hydro-chemical analysis results provide a basis forthe characterization of groundwater variation within each hydrogeological unit.It is possible to interpret different processes that may occur within the aquifers;the effect of groundwater upon dewatering structures; the effect of groundwaterabstraction on the aquifer host rock; and the suitability of groundwater for someuses.

The solution of calcium sulphate and sodium chloride are important mecha-nisms in the groundwater environment. Ion exchange, removing calcium ions andreleasing sodium ions to the groundwater, is also indicated as a potential mecha-nism for the modification to the groundwater chemistry at higher total dissolvedsolids concentrations. The factors that limit the rock solubility include the followingpoints.

1. Solution of calcium and possibly magnesium carbonate by the infiltrationgroundwater,

2. Restrictions of the solution of calcium sulphate by availability within the aquiferrather than other factors such as ion exchange or availability of sodium chloridein the groundwater,

3. Change of calcium for magnesium in dolomites within the aquifer releasingmagnesium to the groundwater,

4. Solution of sodium chloride within the aquifer concentration being restricted byavailability,

5. Ion exchange between calcium in the groundwater and sodium in the aquiferresulting in the release of sodium ions to the aquifer, and

6. Solution of nitrates from the aquifer in higher total dissolved solids concentrationwaters.

It must be stated herein, that the abovementioned statements are tentatively validand may be an over-simplification of a much more complex system.

In this paper, the risk maps SO4 and Cl are prepared because they are the mostdamage inflicting ions on the foundation materials in Jeddah.

Reasons of Groundwater Rise in Jeddah City

It is possible to summarize groundwater rise within the metropolitan area of Jeddahcity due to the following causes (Basamed, 2002).

1. Leakages from water supply systems: This is due to high-pressure water dis-tribution system and cracks or loose binding locations along the pipelines. Thedaily water supply to Jeddah city is about 750,000 m3 and only 85% of this

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amount is distributed through the water supply distribution system. The averageamount of leakage in the city is about 30% which gives 750,000×0.85×0.30 =191,000 m3/day,

2. Exfiltration from cesspools: Because of the sewerage water collection systemin the city, the tankers are effective to carry away the sewage water. This waterrecharges the soil. Unfortunately, the extra sewage water is carried away from thecity to fallout locations, which are within the city confluence wadis on the easternmountainous rural areas. Presently, wastewater pool volume is at 20 × 103 m3and this pool gives rise to infiltration towards the subsurface layers. About 75%of sewage water comes from water consumption, i.e., about 446,250 m3/day.The leakage from the tankers is about 20% which corresponds to 89,250 m3/dayapproximately,

3. Rainfall recharge: The rainfall period within each year is considered fromNovember to April. The maximum monthly rainfall amount varies between15 mm and 39 mm whereas the annual average rainfall within the Jeddah cityis almost 50 mm in the north and 65 mm in the south and in the eastern partof the catchment it reaches to 70 mm annually. The volume of rainfall waterover the Jeddah city annually is equal to about 275,000 m3. Small amount fromthis volume appears as infiltration because the urban areas have small surfacepermeability due to roofs and asphalt roads. Depending on the comparison ofgroundwater levels before and after the rainy period, it is found that at the north-ern parts of the city the water table fluctuations have variations ±0.16 m and theaverage annual rise is 0.37 m,

4. Excess landscape irrigation: The green area in Jeddah is about 9.3 × 106 m2and its watering requires daily 26,300 m3. In general not very large quantitiesinfiltrate from this amount and especially the watering is carried out duringnights and therefore the evaporation rates are almost negligible,

5. Leakage from underground storage tanks: In general, reinforced concrete stor-ages are not suitable for water conservation, and generally, there are fracturesthat may lead to water leakages from such storages. It is estimated that about5% to 10% of stored water lead to leakage and hence to groundwater rise,

6. Subsurface inflow from the eastern wadis: By using topographic maps and mod-ern satellite images, Jeddah watershed limitations are identified and in the meantime, the surface water flow directions are determined. The amount of sub-surface water flow towards the urban area is calculated as 33,000 m3 per day,

7. Hydrogeological influence: The hydrogeological parameters play significantrole in the calculations of groundwater rise. Especially, existence of clay layersin the south and north of Jeddah hinders enough infiltration and makes thegroundwater calculations rather difficult. On the other hand, clay layers exist atrather shallow depths and accordingly they hinder the further deep infiltrationinto the aquifer and as a result of this, there are additional groundwater rises.Similar effect occurs from the coral reefs along the seashore in the westerncity.

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Risk Calculations

The simple risk, R, can be defined as the probability of a variable, V , to be greaterthan the critical level (nationally or internationally allowable levels), CL , at leastonce over the time, T , of consideration. If the sequence of future likely occurrenceof V is V1, V2, . . . , Vn then the joint probability of nonoccurrence, P(N ), is definedas (Şen, 1999)

P(N ) = P(V ≤ CL = P(V1 ≤ CL , V2 ≤ CL , . . . , Vn ≤ CL ) (1)

Hence, the simple risk, R, as a complementary event is defined as,

R = 1 − P(N ) = 1 − P(V1 ≤ CL , V2 ≤ CL , . . . , Vn ≤ CL ) (2)

The calculation of the multivariate probability term on the right hand side ofEquation (2) is dependent on the data variability and, in general, can be calculatedby multiple integration of the multivariate probability distribution function (PDF)through tetrachoric series expansion (Saldarriaga and Yevjevich, 1970). However,in the case of simple dependence structure such as the first order Markov processdependence, the right hand side of Equation (1) factorizes into various terms, whichare explained by Şen (1976).

In the risk assessment of any variable, it is necessary to decide first on thefrequency of critical level exceedence, which is related to the return period, T , afterwhich it is then possible to determine the magnitude of the design variable becauseof the most suitable PDF of the variable concerned. The return period is defined asthe average length of time over which V will exceed once. The random variable) Tr ,which specifies the time between any two successive exceedences of the variable,is referred to as the waiting time. Its distribution in the case of independent discreteobservations is given by Feller (1967) as

P(Tr > j) = q j−1 (3)

or

P(Tr = j) = pq j−1 (4)

where j is discrete duration of non-exceedence. Hence, the return period, which isthe expected value of waiting time, is obtained as

E(Tr ) = T =∞∑

j=1j P(Tr = j) = p

∞∑

j=1jq j−1 = 1

p(5)

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where

p = P(V > CL ) (6)

which is the probability of exceedence. If the theoretical PDF of the variable con-cerned is denoted by f (V ) then Equation (6) can be rewritten as,

p =∫ ∞

CL

f (V )dV (7)

In order to apply Equation (7) it is necessary to specify the theoretical PDF of thevariable concerned from the available data. There are 118 groundwater-samplingpoints scattered over the whole Jeddah metropolitan area. Although many variablesare measured the three variables that are considered herein are the chloride (Cl),sulphate (SO4) and the actual groundwater level, GL . The theoretical PDFs for Cl,SO4 and GL are found as lognormal, Cauchy and Weibull distribution functions,respectively. The theoretical PDSs are obtained from the experimental histogramsas shown in Figures 4–6.

In the risk calculation the basic function is the cumulative PDF for each variable.It shows the probability of exceedence. The three variable cumulative PDFs areprovided in Figures 7–9 for Cl, SO4 and GL , respectively.

With the help of the cumulative PDFs it is possible to calculate the risk levelsat each sampling point within the city by entering the concerned variable value onthe horizontal axes and the corresponding risk is obtained from the vertical axis.The risk values at each sampling point indicate the regional variability of Cl, SO4and GL . The SURFER software is used for the mapping of risk values through thebest linear unbiased estimation method of Kriging and the results are presented inFigures 10–12 for each variable.

Figure 4. Histogram and theoretical PDF for chloride.

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Figure 5. Histogram and theoretical PDF for sulphate.

Figure 6. Histogram and theoretical PDF for groundwater level.

Environmental Impacts

There are different aspects of environmental effects from the rising groundwaterlevel in any urban area. Among these are the followings possibilities.

1. If the groundwater table rises above the ground surface and (good quality)groundwater issues from the soil, it forms flowing rivulets or it fills depressions.The extent to which this is a negative effect or environmental assets dependson the location of occurrence. If the water drains into existing, natural drainagechannels and forms flowing streams, it enhances the appeal of the urban land-scape. On the other hand, if the water interferes with the designated utilization of

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Figure 7. Cumulative PDF for chloride.

Figure 8. Cumulative PDF for sulphate.

the surface features, for instance, roads, it detracts from the urban environmentand creates a nuisance.

2. If the groundwater recharge is of poor quality such as leakages from effluentof cesspools or the sanitary sewer system, then the effect as mentioned in theprevious point is complicated by the consequent threat to public health. Althoughthere is a certain amount of self-purification to be expected from flowing water

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Figure 9. Cumulative PDF for groundwater level.

being exposed to the atmosphere, it is more likely that, particularly in the aridclimates children will be exposed to these water flows. In the case of ponding verylittle purification is likely. The most dangerous effects are due to the presence offecal coliforms and E. coli. These either themselves cause increased occurrencesof gastrointestinal diseases, or they serve as indicators of other organisms thatcause those diseases. It is possible to quantify these instances conceivably byestimation the burden of increased medical costs imposed on an area affectedby rising groundwater, in addition to the above-mentioned effect of a generaldrop in property values.

3. Spontaneous growth of vegetation feeding on the shallow groundwater may beanother environmental impact and again, this impact is not necessarily negative,and it depends on the type and location of the vegetation in the question.

4. It is possible that in unsewered areas of urban, the groundwater rise may threatenthe community public health. The impact of polluted water surrounding thepotable water supply system is serious. Cross connection will be inevitable ifpressure in the water system drops down in a leaky section. Such condition canoccur both in the municipal water network and in-house water system.

Recommendations

The sewerage collection system must be enhanced in addition construction of rain,surface and floodwaters collection networks and their proper maintenance. Thesemust be planned for long ranges with the capabilities to accommodate extra watervolumes.

Existing wastewater dumping locations must be transferred to other suitablelocations such that the seepage from them must not be within the basins that con-fluence to Jeddah city. A set of observation wells must be monitored so as to controlthe groundwater rise within the city.

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Figure 10. Risk map for chloride.

The leakages from the networks and subsurface storages must be controlled andnecessary maintenance obtained.

Planning proper number of wells and their management through suitable with-drawals, the groundwater levels can be returned to the original elevations. Automaticoperation must be preferred.

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Figure 11. Risk map for sulphate.

Arbitrary irrigation practices and garden watering must be reduced to the mini-mum with acceptable water quality.

Useful guidance for water quality, pollution and usage amounts must be givento city settlers for their awareness and alertness of the city water problems.

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Figure 12. Risk map for groundwater level.

Conclusions

Urban areas in arid regions need additional water resources by water transportationfrom rural areas where groundwater resources are available. On the other hand, inarid regions desalination plant water is also used for the city demand and hence

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the water input becomes more than output because of inefficient or nonexistenceof sewage system. Output devises are cesspools, natural channels, open pits, de-pression zones, etc., all off which recharges the underlying unconfined aquifersand consequently groundwater rise problem becomes significant. Such rises maycause many problems in urban areas such as unpleasant smells, health, construction,excavation, foundation and environmental problems.

This paper exemplifies groundwater rise problem through a case study from theKingdom of Saudi Arabia, Jeddah city, which is under the subtropical arid regionconditions. The general approach for the combat of the problem is given and thenapplications are presented for this region. Chloride and sulphate risk maps areprepared for the groundwater quality variations and their risks based on a simpleand straightforward probabilistic model. These two ions are selected because oftheir possible dangerous effects on the foundations. Additionally, the groundwaterlevel rise map is also prepared. Necessary recommendations are presented.

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