evaluation and rehabilitation of dam seepage problems. a case study: kafrein dam

Engineering Geology 56 (2000) 335–345www.elsevier.nl/locate/enggeo

Evaluation and rehabilitation of dam seepage problems.A case study: Kafrein dam

Abdallah I. Husein Malkawi *, Mohanned Al-SheriadehCivil Engineering Department, Jordan University of Science and Technology, P.O. Box 3030, Irbid 22110, Jordan

Received 19 January 1999; accepted for publication 27 August 1999

Abstract

The intention of this study is to locate the probable sources of the Kafrein dam seepage problem. A methodologyknown as excitation-response analysis will be considered. Analytical expressions, depicting the groundwater levelresponse in the underlying aquifer as a result of changes in the reservoir water level, were derived from a linearizedgroundwater flow equation for one-dimensional semi-infinite, isotropic and homogeneous porous media. The resultsrevealed that a large proportion of the seepage water originates from a site at a distance about 1 km from theobservation point M1 and streamlines along the existing faults. Emphasis in this work was also placed on controlingand mitigating the seepage problem. © 2000 Elsevier Science B.V. All rights reserved.

Keywords: Analysis; Dam; Excitation response; Kafrein; Rehabilitation; Seepage

1. Introduction raise the dam. The dam, built originally to storenearly 4.5 MCM of water, suffers from excessive

Where natural storage in the form of ponds is seepage, the water from which is collected in anot available, reservoirs are often constructed if retention pool, called locally Batous, located aboutoptimum development of the surface water is to 1.5 km downstream from the dam. The quantitybe obtained. For countries in arid and semi-arid of seepage has reached a value of 400 l/s, and isregions, such as Jordan, where the little rainfall is expected to rise further to 700 l/s when the reser-limited to the winter season and an acute deficit voir is completely filled. Nevertheless, this damof water is an every day fact of life, dams play a suffers from other problems, among them are thevital role in supplementing other water supplies. following. (1) The soil at the toe of the dam isBut there are many hydrogeological, geological near saturation, which may indicate the inade-and geotechnical problems associated with dams, quacy of the base drains as a result of not extendingamong them seepage, which is of major concern them at the time when the dam was built. Abecause it threatens dams’ storage purposes and probable solution to drain the soil could be tomay cause unforeseen failure. construct a finger drain, and install a number of

The Kafrein dam seepage problem has gained relief wells at about 10–20 m spacing. (2) There ismuch attention recently following proposals to good indication that the soil at the toe of the

reservoir is near quick condition. This conditionmay be aggravated if the dam height is raised* Corresponding author. Tel./fax: +962-2-710-2299.

E-mail address: [email protected] (A.I.H. Malkawi) further.

0013-7952/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.PII: S0013-7952 ( 99 ) 00117-9

336 A.I.H. Malkawi, M. Al-Sheriadeh / Engineering Geology 56 (2000) 335–345

In this paper the seepage problem was tackledanalytically by a simple approach. It enabled usto locate the spatial position of the seepagesource/s, and consequently helped us to deviseremedial measures. This approach is referred to inhydrology as an ‘excitation-response’ analysis. Inthe present work it was applied to derive analyticalexpressions governing the response of the ground-water level in an aquifer due to an imposed excita-tion which is in the form of the reservoir waterlevel, assuming a one-dimensional semi-infinite,isotropic, homogeneous aquifer. The analyticalexpressions were obtained by solving the appro-priate linearized groundwater flow equation sub-ject to suitable initial and boundary conditions. Inthe literature of conjunctive use between waterbodies this approach is common. It was used byVenetis (1968), Schwarz (1971), Maddock (1972)

Fig. 1. Map of Jordan showing the location of Kafrein Dam.and Morel-Seytoux and Daly (1975). Hall andMoench (1972) used this approach to study theinteraction between an aquifer and a stream subject material protected by compacted rockfill material

on both sides. The additional 7 m added to theto an arbitrary flood shape. In their work theyused the analytical expressions derived by Carslaw height of the dam increased its capacity by 6 MCM

and helped to overcome the volume of accumu-and Jaeger (1959) and Cooper and Rorabaugh(1963) to obtain the unit step response for four lated sediment, equal to 2.5 MCM, and meet the

ongoing demand for irrigation water in thehighly idealized cases involving finite aquifers, withand without semi-pervious stream banks. served area.

3. Geological setting of the dam site area2. General background

The recent raising of the Kafrein dam is one of 3.1. Dam site geologymany projects intended to overcome the currentand future deficit of irrigation water in the Kafrein The geological map and cross-section at the

dam axis are shown in Fig. 3. The drilled boreholesarea, as well as the fertile Jordan Valley down-stream. The dam is located on the Wadi Kafrein along the dam axis (1, 2, 3, 4 and 6) showed that

the penetrated soil underlying the dam body con-Valley (Fig. 1). Historically, the dam was built in1968 with a storage capacity of 4.5 MCM. sists mainly of thick alluvial deposits to about

60 m in depth. They are comprised of poorly sortedOriginally, the dam was built to a crest height of75.5 m above a datum which was taken arbitrarily silty clay, sandy gravel with occasional lenses of

boulders or silty sands of various cementationat 200 m below mean sea level (Fig. 2). The damis made of homogeneous material with a chimney (Fig. 3). There are two eroded channels in the

bedrock; the main one, which lies between the twodrain connected to a base drain. In 1996 the damwas raised to a crest elevation of 82.5 m, permitting faults, is about 60 m in depth, and the other one,

which is of unknown depth, lies beneath an alluvialthe maximum water level to reach about 78.0 melevation. It is basically an earthfill dam of 30 m terrace of the right abutment for at least 36 m.

The nature of the bedrock is mainly limestone,height and maximum embankment length 450 m.The dam material includes compacted clayey core marl and a massive crystalline limestone. To the

337A.I.H. Malkawi, M. Al-Sheriadeh / Engineering Geology 56 (2000) 335–345

Fig

.2.

Cro

ss-s

ecti

onof

the

rais

edda

m.


right abutment, limestone and marly limestone This behavior may be attributed to the hydrogeolo-gical units in the reservoir area, which vary information varies in thickness and is dipping steeply

to the north east. Dolomitic limestone formation composition significantly, and to the majorregional structures such as faults, folds and flux-is the bedrock of the left abutment and it is dipping

to the north west. It can be characterized as a tures, which produce vertical displacements in thebedrock to such an extent that their continuitycoarse to medium grained and well jointed forma-

tion. It is underlain by well jointed, fine grained and lateral spread become limited.limestone, marly limestone and marl.

4.1. Dam seepage response analysis3.2. Reservoir geology

Data for the seepage analysis was obtainedfrom a main report by Salzgitter and PartnersThe reservoir area consists of alluvial deposits

underlying bedrock. The alluvium is characterized (1992). The data is comprised of weekly measure-ments during 1991/92 of groundwater level at theby poorly sorted partially cemented gravel and

pebble beds which appear along with limestone observation points M1, M2, M3, M8, M9, M10and K3 shown in the location map of Fig. 4. Basedand marl talus at the edges of the valley floor. The

permeability of these materials varies in accor- on a preliminary examination of the variation ofthese measurements with time, as displayed indance with cementation. At the edge of the reser-

voir area, highly permeable silty clay was observed. Fig. 5, the following observations were made: (1)the rising limb of the groundwater levelThe types of bedrock in the reservoir area are

limestone and marly limestone. These beds occur hydrograph at the observation points M1 and M2is steep similar to the one for the reservoir; (2) theon the eastern limb of the north–south trending

anticline, are dipping steeply and disrupted by height of the rising limb of the hydrographs atM1, M2 and K3 is longer than that of the reservoir;cross faulting in the upper reservoir area and by

the major north–south fault along the edge of the (3) the time-lag between the rise of water level inthe reservoir and its response hydrograph at eithervalley. To the north west of the reservoir area a

permeable sandstone is exposed in the core of the one of the observation points M1, M2 and K3 isshort ( less than five days); and (4) all responseanticline, the minimum elevation of the exposure

is approximately 50 m. To the east of the reservoir hydrographs have only one single peak. Theseobservations led to the conclusion that only onearea, dolomitic limestone, massive limestone, chalk

and marl formations in addition to limestone and major source might be responsible for seepagewater downstream of the dam site.marl are the materials of the bedrock, which are

partly disrupted by minor folds and faults. On the Therefore, to locate the probable source ofseepage, we simply made the problem amenablevalley floor the bedrock is massive limestone, marl

and marly limestone. It looks like a syncline fold to excitation-response analysis of systems. Themain idea behind this analysis is to impose ancomprised by the two north–south faults. These

faults probably mark the boundary between allu- excitation, for example a change of the reservoirwater level with time at the upstream face of thevium and bedrock in most places.dam, and trace the response to it in the form ofgroundwater level hydrograph at some point inthe aquifer, using the appropriate governing equa-4. Seepage study programtion and suitable initial and boundary conditions.In this work the analysis was applied in thisBased on the available geological information

in Fig. 3, and the well known groundwater aquifers manner: a probable seepage scenario was chosenfirst where an anonymous location of the seepagein the area, the seepage under Kafrein dam was

studied. The flow system beneath the reservoir source was assumed already known. By knowingthe location of the seepage source a hydrographarea seems complex, as shown by the piezometric

heads which vary significantly over short distances. displaying the change of water level with time was


Fig. 3. Geological and dam section map with boreholes.

imposed on the steady groundwater flow before infinite aquifer. If the obtained response at theobservation point agrees well with the observedthe excitation. The response to this excitation in

the form of groundwater level changes at an obser- one, it can be concluded that this source locationis that from which seepage originates, otherwise avation point, say M1, was obtained by solving

analytically the groundwater flow equation, assum- different seepage source location should beinvestigated.ing one-dimensional groundwater flow in a semi-


Fig. 4. Location map for water level observation points.

In this work two seepage scenarios describing abutments, respectively. Other points like M3, M5,M6, M8 and M10 show similar trends to K3, M1,the probable sources of seepage were investigated:

one which depicts seepage occuring between the M2 and M9. However, one should notice that theheight of the rising limb of the groundwater levelreservoir left side bank and passing through the

dam left abutment to the observation point K3; hydrograph is inversely proportional to the down-stream distance from the dam. Points K2 and K8and the other which depicts water percolating from

a location at some distance upstream from the appeared dry during the observation period. Thesetwo scenarios were selected following the con-mouth of the reservoir and flowing to the observa-

tion points, say M1, through the alluvium aquifer tractor recommendations, which were based onthe hydrogeological investigation (Salzgitter andbeneath it. Both points K3 and M1 were selected

because they are the closest to the left and right Partners, 1992). Other possible scenarios describ-


ing seepage through the reservoir bed and the level were drawn, it was noticed that the ground-water level between the point designated by * andbottom of the embankments were discarded as the

imperviousness of the fine textured sediment accu- K3 can be represented by a straight line with smalldeviations (actually it was a concave up flat parab-mulated over the years precludes seepage.ola). For boundary conditions (B.C.) one bound-ary condition was assigned at the point designated4.2. Seepage under the left abutmentby *, representing a variable head boundary whichcorresponds to the rising limb of water level in theFor the first seepage scenario an excitationreservoir. This boundary condition was repre-representing the rising limb of water level in thesented by a linear function in time of water levelsreservoir was imposed on the dam left abutmentbetween the times when the reservoir started fillingat a point designed by * in Fig. 4, and the responseand when it reached a constant level of −130.95 mwhich represents the groundwater level hydro-after four days. The other boundary condition forgraph at the observation point K3 was thus sought.semi-infinite domain was assumed at 2 (physi-To apply excitation-response analysis for this sce-cally, during the time of simulation and at a farnario the problem statement was formulated as:distance downstream from the dam site thethe groundwater flow in the dam abutments undergroundwater level was assumed constant, and thusthe dam water level and in the alluvium aquiferhad no effect on the simulation). In mathematicalbeneath it can easily be verified to be under fullterms the above can be formulated as:saturation, and thus it is governed by the well

known transient groundwater flow equation (ana-logous to the heat conduction equation in solids). ∂h

∂t=k

∂2h

∂x2(1)

By knowing that the groundwater level decreasesso slowly when the dam is empty, the functionrepresenting initial condition (I.C.) was deduced I.C.: h(x,0)=b+axfrom the water levels in the reservoir when it wasalmost empty, and the observation point at K3 B.C.: h(0,t)=c+mt 0<t<4 dayswhen it was at its lowest groundwater level (thiscorresponds to day 336 of the year in Fig. 5). h(0,t)=V t>4 daysWhen the contour lines of the groundwater levelat the time when the dam was at its lowest water where k=KH/S, K is the hydraulic conductivity,

H is the average saturated thickness of the aquifer,and S is the storativity. Further, b and c are thelowest reservoir water level, a is the slope of thestraight line connecting the initial water levelsbetween the points * and K3, m is the slope of therising limb of water level with time in the reservoir,and V is the highest water level in the reservoirwhen it was full. Solution of Eq. (1), subject tothe above initial and boundary conditions, is givenby Carslaw and Jaeger (1959) as:

h(x,t)=CmAt+x2

2kB+cDerfcx

2Ekt

−mxEt

Epke−x2/4kt+ax+b erf

x

2EktFig. 5. Hydrograph of ground water levels at the observationpoints. 0<t<4 days (2)


water comes from percolation of baseflow waterh(x,t)=CmAt+

x2

2kB+cDCerfcx

2Ekt at a point upstream from the reservoir and flowsdirectly into the alluvium strata beneath the reser-voir bed. To verify that the flow is only through

−erfcx

2Ek(t−4)D+ mx

Epk the alluvium or in combination with some faultedbedrock, mainly beneath the right abutment of the

×[Et−4 e−x2/4k(t−4)−Et e−x2/4kt ] dam, as depicted in Fig. 3, a rough estimate of kin the alluvium became necessary. Estimation of k

+V erfcx

2Ek(t−4)+ax+b erf

x

2Ektin alluvium was made by performing the excita-tion-response analysis once again, but herebetween observation points M8 and M9 down-t>4 days. (3)stream of the dam. These points were selected

The response at the observation point K3 at abecause we thought that the flow between them isdistance x=150 m from * can be obtained byentirely through the alluvium. By recalling theinserting the following specific values into Eqs. (2)previous assumptions, the flow between the pointsand (3) above: m=1.5125, a=−0.2306, b=c=M8 and M9 can be formulated mathematically as:−137 m, V=−130.95 m.

What is left unknown in Eqs. (2) and (3) is k. ∂h

∂t=k

∂2h

∂x2(4)It was difficult to estimate k, given the available

data and the complexity of the hydrogeologicalformations, therefore it was decided to estimate it I.C.: h(x,0)=b+axby what is called an inverse problem by which

B.C.: h(0,t)=c+mt t>0 daystrial values of k are substituted into the responseequations at K3. The one value that makes the where all symbols are defined as before. Solutiontheoretical response match well with the observed of Eq. (4) is given generally by Carslaw and Jaegerone is selected to depict the situation in hand. But (1959) as:unfortunately, in this case, a match was impossiblewhatever the value of k, as illustrated in Fig. 6.

h(x,t)=CmAt+x2

2kB+cDerfcx

2EktTherefore, seepage from this source was unable toproduce the observed response at K3 and thus itmay contribute little to seepage.

−mxEt

Epke−x2/4kt+ax+b erf

x

2Ekt. (5)

4.3. Seepage through the alluviumFor a particular solution at point M9 distant x=

The second scenario was attempted as men- 148.62 m from point M8, the following values oftioned before by assuming that the bulk seepage

Fig. 7. Coincidence of observed and simulated response betweenFig. 6. Comparison between actual and simulated response atobservation point K3. M8, M9 through alluvium to estimate alluvium permeability.


the constants were substituted: m=−0.042, a= where all symbols were defined before. The general−0.01379, b=c=−164.48 m. As before the value solution of Eq. (6) is (Carslaw and Jaeger, 1959):of k was estimated by trial and error procedure, avalue of 10 000 m2/day gave the best fit between h(x,t)=erfc

x

2Ekt+ax+b erf

x

2Ekt. (7)

the calculated and observed response at M9. Theresponse graphs are shown in Fig. 7. This value The response at point M1 which is at a distancewas no surprise to us given the fact that some

1000 m from the area of percolation, and bylenses of clay are present in the alluvium which

inserting the values of the constants given by a=makes the storativity value very low (in the range0.01379, b=−149.1 m, and V=−130 m, the par-of 0.01). Similar values were also obtained byticular solution at M1 was obtained. A value ofYachielli et al. (1995) in their work on the aquifersk=85 000 m2/day made the calculated responsenear the Dead Sea.approximately match the observed one at M1(Fig. 8). In contrast to the response at K3 in the4.4. Seepage under the right abutmentfirst scenario, the response at M1 was attainable.Therefore, this scenario might be possible, andOnce the alluvium k was evaluated, the secondseepage water thus comes from an area upstreamscenario was investigated in which the simulatedof the reservoir mouth and passes through allu-response at observation point M1 was comparedvium enhanced by the faults in the bedrock beneathwith the observed one. The response at M1 wasit. The high value of k (8.5 times higher than thatselected because it seems that there is a major faultof the alluvium) can be explained by both the highpassing through it which extends upstream to thepermeability of the bedrock faults and the lowarea beyond the reservoir (Fig. 3). As a prere-storativity of the alluvium due to the presence ofquisite to this scenario the following were assumedclay lenses.applicable: (1) baseflow water percolates from an

area upstream from the mouth of the reservoir atabout 1000 m upstream from point M1; (2) the

5. Discussionalluvium beneath the reservoir behaves as a con-fined aquifer at high water level in the reservoir

It is always articulated among workers of thewhich is bound on top by the reservoir imperme-Kafrein reservoir that the high rate of seepage isable bed sediments, and behaves as an unconfinedits main problem, but they could not figure out itsone when seepage water almost ceases to merge insources. In this study we tried to use the conceptthe dam downstream area; (3) clayey and siltyof systems in hydrology to discover these sourcessediments on the bed of the reservoir form an

aquitard of very low permeability; (4) the gradient by performing an excitation-response analysis,of the water table aquifer at low seepage water whereby an excitation (in the form of water levelwas assumed to take the same value as thatbetween points M9 and M10 at the time of theirlowest water level; and (5) at the location wherebaseflow water percolates into the alluvium, thesaturated thickness amount was assumed to extendfrom the aquifer original water table to thebaseflow channel bed. Under these assumptions,the problem was formulated as:

∂h

∂t=k

∂2h

∂x2(6)

I.C.: h(x,0)=b+axFig. 8. Comparison between actual and simulated response atobservation point M1.B.C.: h(0,t)=V t>0 days


with time) conforming to the physical system beha- be attributed, in addition to confinement, to thestaggered permeability value by the presence of avior at hand was imposed on the probable seepage

source position, and then routed by a suitable few fractures in the bedrock.governing equation (groundwater flow equation)to a point where response (in the form of ground-water level with time) was desired. If this responseagreed with the observed one, it could be con- 6. Conclusionscluded that seepage might originate from thissource, otherwise another source should be Based on the previous analytical analysis, avail-

able geological, hydrogeological data and frominvestigated.In spite of the many assumptions used in site observations, the following can be concluded

for the Kafrein dam seepage problem: (1) most ofmaking the excitation-response concept amenableto the seepage problem in the Kafrein dam, it the seepage water collected at the downstream

observation points comes mainly from water flow-turned out that the concept results were reasonablydecisive in differentiating between seepage sources ing through the alluvium superficial deposits and

the faulted bedrock beneath the abutment of the(see Figs. 6, 7 and 8). Fortunately, our results wereconfirmed lately and independently by a grouting dam; (2) seepage water originates from an

upstream location distant about 1 km away fromtreatment program developed and executed by theJordan Valley Authority (JVA) between September the dam. To the knowledge of the official workers

at the dam, this location was probably used as a15 and December 6, 1997. JVA had reported thatthe right side of the dam below 20 m depth con- borrow area when the dam was originally built.

Water from that location percolates and seepssumed about 53 336 kg of grouting material, whilethe left side consumed only 5666 kg. Even the through the alluvial deposits and faulted bedrock

beneath the reservoir to appear at the observationreported results did not articulate the seepagesource position/s, but the grouting total depth and points downstream; and (3) left abutment of the

dam contributes little to seepage watervolume illustrate clearly the size of the faultedrocks beneath the dam right side bank. downstream.

It must be remembered that this work was notintended to incorporate each and every propertyof the hydrogeological formations. Such treatment,in addition to adding a substantial complexity in 7. Recommendations for remedial measuresthe problem statement and solution, requires moredata which is unavailable and difficult to gather. The following main points could be drawn as

remedial measures.Therefore, the parameter k reflects the gross orlumped property of the underlying porous media 1. Improving the efficiency and capacity of the

Batous retention pool, which is deemed to beas a whole. Nevertheless, the one-dimensional flowassumption on which this work was based suggests the most practical feasible solution in our case.

2. To overcome the build-up of pore water pres-that we traced the longitudinal flow lines, whilethe transverse ones were ignored, given the fact sure downstream of the dam, and to ensure

adequate dam safety, a trench at the down-that the width of the wadi flow is much smallerthan its length to induce substantial lateral flows. stream of the dam at the right-hand side of the

toe drain should be made, so as to release anyThe high value of k in the alluvial deposits(10 000 m2/day) suggests that certain portions of uplift pressure and to lower the water level of

the relief wells. Increasing the number of thesethese deposits are under confinement, probably bythin lenses of clay which made their storativity wells will certainly help solve the problem.

3. It is clear here that when the water level in thevalue low, while permeability is kept high. But themuch higher value of k (85 000 m2/day) for the reservoir increases, the soil at the toe down-

stream of the dam may be brought to a quickdeposits under the right abutment of the dam may


condition, a state which should be avoided. ReferencesTherefore, installing additional standpipe

Carslaw, H.S., Jaeger, J.C., 1959. Conduction of Heat in Solids.piezometers to monitor the pressure isClarendon Press, London.recommended.

Cooper, H.H., Rorabaugh, M.I., 1963. Groundwater move-4. The area located near the toe drain should bements and bank storage due to flood stages in surface

well cleaned in order to monitor it and to check streams. US Geological Survey, Water Supply Paper 1536-J,for any signs of piping phenomena. pp. 343–363.

Hall, F.R., Moench, A.F., 1972. Application of the convolution5. These remedial measures should be executedequation to stream–aquifer relationships. Water Resour.before impounding of the reservoir to the newRes. 8 (2), 487–493.high levels.

Maddock III, T., 1972. Algebraic technological functions froma simulation model. Water Resour. Res. 8 (1), 129–134.

Morel-Seytoux, H.J., Daly, C.J., 1975. A discrete kernel genera-tor for stream–aquifer studies. Water Resour. Res. 11 (2),253–260.

Salzgitter and Partners, 1992. Studies of Raising Kafrein Dam,AcknowledgementsMain Report, Project No. SEM/03/628/026.

Schwarz, J., 1971. Linear models for groundwater management.The authors deeply acknowledge the coopera- J. Hydrol. 28, 377–392.

Venetis, C., 1968. On the impulse response of an aquifer. Bull.tion of Eng. Maher Iskander, Former Director ofInt. Assoc. Sci. Hydrol. 13 (3), 136–139.Dams, Eng. Ziad Shehadeh, Present Director of

Yachielli, D.R., Berkowitz, B., Dershowitz, W.S., Hadad, A.,Dams of the Jordan Valley Authority and his staff, 1995. Aquifer characteristics derived from the interactionJafar Ababneh, Omar Al-Hattamleh, Rajah between water levels of the terminal lake (Dead Sea) and

an adjacent aquifer. Water Resour. Res. 31 (4), 893–902.Nasser, and Wajih Habboush.

evaluation and rehabilitation of dam seepage problems. a case study: kafrein dam

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