Ground Water in the

Sirte Area, Tripolitania

United Kingdom of Libya

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1757-C

Prepared in cooperation with the 

U.S. Agency for International 

Development Mission to Libya
Ground Water in the 

Sirte Area, Tripolitania 

United Kingdom of Libya

By WILLIAM OGILBEE

CONTRIBUTIONS TO THE HYDROLOGY OF AFRICA 

AND THE MEDITERRANEAN REGION

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1757-C

Prepared in cooperation with the 

U.S. Agency for International 

Development Mission to Libya

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1964
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402
CONTENTS

Faga

Abstract-- ____ ___--_-_____________________-___-_.__-_-_____-_.-.-__ Cl

Introduction._ ____________________________________________________ 1

Geographic and climatic features.____-__-__---________-_____________ 3

Geology ____--_-______-__--_____________-----__-_____-__--_-_-_-__ 5

Ground water__ ___________________________________________________ 8

Occurrence ___________________________________________________ 8

Chemical quality______________________________________________ 9

Fresh-water aquifer in the Qa§r Bu Hadi area.__----__--_______-__ 10

Conclusions.._____________________________________________________ 13

Selected references,________________________________________________ 14

ILLUSTRATIONS

FIGURE 1. Map showing location of the Sirte area and average annual rainfall in northern Tripolitania__-_--___---_--_-_-----_----_ C3

2. Map of the Sirte area showing location of wells and geologic

and hydrologic features_____________-_____-____-_------_ 4

3. Graphic logs of typical wells in the Sirte area.-______________ 6

4. Generalized north-south geologic section A-A', Sirte to Qasr

Bu Hadi____.____________________________ 7

5. Predicted decline of water level in fresh-water aquifer at prescribed pumpingrates-____-_-_----_---_----__--__--_--- 12

6. Predicted decline of water level in fresh-water aquifer at prescribed distances after pumping 10 years at prescribed rates. 13

TABLES

TABLE 1. Chemical analyses of water from wells in the Sirte area, Tripolitania, United Kingdom of Libya_________-__---__-_--___ CIO

2. Hydrologic data from pumping test near Qa§r Bu Hadi________ 11

in
CONTRIBUTIONS TO THE HYDROLOGY OF AFRICA AND THE 

MEDITERRANEAN REGION

GROUND WATER IN THE SIRTE AREA, TRIPOLITANIA, 

UNITED KINGDOM OF LIBYA

By WIULIAM OGILBEE

ABSTRACT

The present study of the ground-water conditions in the Sirte area was made 

during December 1961 and March-April 1962 at the request of officials of the 

Government of Libya. Particular attention was given to the potential of the 

fresh-water aquifer near Qasr Bu Hadi as a source of water for Sirte.

The Sirte area lies on the southern coast of the Mediterranean Sea about 450 

kilometers east-southeast of Tripoli, cocapital of Libya. Although tl e area receives some winter precipitation, the climate is arid. The surface rocks of the 

area are chiefly Miocene limestone containing marl, clay, and some sandstone, 

though Quaternary deposits occur along the wadis and mantle the Mio?ene rocks 

in the coastal plain.

Fresh ground water occurs locally in Recent sand dunes near Zaafran and in 

Miocene limestone near Qa§r Bu Hadi, south of a probable fault. Elsewhere 

in the Sirte area, ground water occurs generally in Tertiary rocksi but contains 

3,000 or more parts per million of dissolved solids.

To establish the hydraulic characteristics of the fresh-water aquifer in the 

Qasr Bu Hadi area, two test wells were drilled and a controlled pumping test was 

made. The coefficient of transmission!ty was found to be about 25,0'K) gallons 

per day per foot (13.68 cubic meters per hour per meter), and the coefficient of 

storage, about 0.00055. The pumping test also established the presence of two 

barrier-type hydraulic boundaries for the aquifer, one about 250 meters westward 

and another about 535 meters northward from well 9a. The first boundary is 

probably the small anticline on which stands the fort of Qa§r Bu Hadi; the second boundary is probably a northwest trending fault. Using the trans^iissibility 

and storage coefficients derived from the pumping test, the writer concludes that 

(1) the total draft from the fresh-water aquifer should not exceed 13.5 cubic 

meters per hour and (2) production wells should be at least 3 kilometers south of 

well 9a.

INTRODUCTION

The town of Sirte currently (1962) is confronted with a serious 

shortage in its potable water supply. The ground water beneath the 

town and environs is too salty for normal human use, but usable 

water is obtained from shallow wells and galleries in the sand-dune 

area about 4 kilometers to the west of the town, near Zaafran. This 

supply is inadequate and is reportedly deteriorating in quality. At 

the request of the Nazirs of Agriculture and Public Health of TripoliCl
C2 HYDROLOGY OF AFRICA AND THE MEDITERRANEAN REGION

tania and of other Government of Libya officials, field studies were 

made in December 1961 and in March-April 1962 to evaluate the general ground-water conditions in the area and the particrlar potential 

of the fresh-water aquifer near Qasr Bu Hadi as a source of water 

for Sirte. The work was part of a larger program of ground-water 

investigations in Libya that have been in progress since 1952 by geologists and engineers of the U.S. Geological Survey assigned to the 

U.S. Agency for International Development (US AID) Mission to 

Libya.

In the past, several efforts have been made to obtain f ~esh water in 

the Sirte area. The Italians in 1938 drilled a deep tes% well 3, approximately 2 km (kilometers) south of Sirte, but salty water was 

found in each water-bearing zone penetrated. In 1941, during World 

War II, the Italians drilled wells near Qa§r Bu Hadi and obtained 

fresh water for their troops stationed in the area. Their well 8, which 

is 57 m (meters) deep, can yield 2.7 m3 per hr (cubic meters per hour) 

of fresh water through pumping. Further study of the fresh-water 

potential in the Sirte area was made in 1958 by H. T. Smith International (1959). A test hole, well 7, was drilled in the Wadi Tlal, the 

principal stream in the area, about 2 km northeast of Q,a§r Bu Hadi 

and 17 km south-southeast of Sirte. Because the water contained 958 

ppm (parts per million) of chloride, the well was considered to be 

unsuitable for domestic use. Based on a brief field study in 1959, a 

preliminary memorandum report on a ground-water supply for Sirte 

was prepared by R. C. Vorhis (1959, written communication) for the 

US AID Mission. In 1960, several test holes of small diameter were 

drilled under the direction of G. H. Goudarzi, chief of the U.S. Geological Survey field party with the US AID Mission, to determine the 

northern extent of the fresh-water aquifer near Qa§r Pu Hadi. A 

chemical analysis of water from one test hole, well 4, is given in table 1.

The present study of the Sirte area (fig. 1) was made with the cooperation of Essayed Mohammed Bey Derna, Nazir of Agriculture and 

Forests of Tripolitania, the District Commissioner of tl^ Sirte area, 

the Mayor of Sirte, the Shieks of the local Bedouin tribes in the Qa§r 

Bu Hadi area, and oil company officials. The pumping tests at Qa§r 

Bu Hadi were made under the supervision of the writer, assisted by 

Hadi Ali Tarhuni and Mohammed Amin Zintani, Hydro^gic Technicians of the Government of Libya, and by Bu Agela Hassen 

Belgassem, Water Well Drilling Supervisor of the Nazarat of 

Agriculture.

As part of the present study, two test wells were drilled near 

Qa§r Bu Hadi by the Well Boring Section of the Nazr.rat of Agriculture. These were drilled near existing well 8, reportedly the only 

source of fresh water from many kilometers south of the dunes of 

Zaafran. A controlled pumping test was conducted by primping from
GROUND WATER, SIRTE AREA, TRIPOLITANIA, LIBYA C3

13°________ 14° 15° 16°

M

33°

32°

Isohyetal line

Showing overage annual rainfall, In 

millimeters. Dashed where approximate. Contour interval25 and 50mm

-25.

25 75 MILES

30° -

FIGOKK 1. Map showing location of the Sirte area and average annual rainfall in northern 

Tripolitania. After Stewart (I960).

one of the test wells while the other was used to determine the effects 

of the pumping. The data obtained were used to predict the effects of 

prolonged withdrawal on the aquifer. Other work in tho area included geological reconnaissance and evaluation of available geologic 

and hydrologic data relevant to the water problem.

GEOGRAPHIC AND CLIMATIC FEATURED

The Sirte area (fig. 2) as described in this report lies in eastern Tripolitania between lat 31°00' and 31°15' N. and long 16°30' and 16°50' 

E. Sirte, the principal town, is near the coast of the Gulf of Sidra, 

an embayment of the Mediterranean Sea. The town, which is the 

administrative center of the geographic region known as Sirtica, lies 

about 450 km east-southeast of Tripoli, cocapital of Libya.

The Sirte area includes a narrow coastal plain which ester ds inland 

some 3-4 km from the shoreline. Along the shore is a belt of low-
C4 HYDROLOGY OF AFRICA AND THE MEDITERRANEAN REGION

'30' 45'

MEDITERRANEAN SEA

.

\

? BirTua"ici *

10 \ T N \

EXPLANATION

Sand dunes

u

D

Fault

Doffed where concealed. U, upthrown side; D, downfhrown side

Anticline

Showing direction of p/ung

Water well 39-° 

Showing well number (upper); chloride content, in parts per million 

(middle); and depth to water, in 

meters ?0(.

A

Altitude, In meters

FIGURE 2. Map of the Sirte area showing location of wells and geologic and

hydrologic features.
' : GROUND WATER, SIRTE AREA, TRIPOLITANIA, LIBYA C5

lying sand dunes, and just inland from these is a series of salt flats or 

"sebkas" that lie at or near sea level and are subject to flooding during 

the rainy season. South of the coastal plain the land surface rises 

gradually in a gently undulating plateau which is about 60-70 m above 

sea level near Qagr Bu Hadi. The principal stream in the area is the 

Wadi Tlal, which rises about 60 km south of the map area and drains 

north into the sea near Zaafran. This stream and its tributaries, 

which slightly incise the plateau, are all ephemeral and carry runoff 

only after heavy or prolonged rain storms.

The climate of the Sirte area includes mild winters and hot dry 

summers; it is typical of the Mediterranean region. The bulk of the 

annual rain falls during the fall and winter months that is, from 

October to March. Rainfall during the remainder of the year is 

generally insignificant. The average annual precipitation ranges 

from about 125 mm (millimeters) at Sirte to about 100 mm at Qagr 

Bu Hadi (fig. 1). South from the Sirte area, annual precipitation 

diminishes rapidly. On the fringe of the Sahara, 100 km south of 

Qagr Bu Hadi, the average annual rainfall is probably no more than 

25 mm.

GEOLOGY

The Sirte area is underlain by stratified marine and continental 

sedimentary rocks of Tertiary and Quaternary age. The oldest rocks 

cropping out in the area are principally thin to massive beds of soft 

to hard marine limestone which are white to yellow. Soft green, yellow, and gray marl, as well as clay and some sandstone, is intercalated 

with the limestone. These rocks, of probable Miocene age, lie at or 

near the surface in the plateau, but they are mantled by younger 

Quaternary deposits in the coastal plain and in the Wadi Tlal and its 

tributaries.

The coastal plain is underlain by .sand and loosely cemented sandstone of Quaternary age, and along the Mediterrranean shore these 

deposits are covereed by Recent dunes of unconsolidated sand. As 

indicated by the log of well 3, the Quaternary deposits reach a thickness of at least 46 m and, elsewhere in the area, possibly more. Quaternary stream deposits of sand and of sand and gravel occur 

extensively along the channels of the Wadi Tlal and its principal 

tributaries. In well 7, for example, fine red sand and waterworn 

gravel and sand were penetrated from the surface to a depth of 26.6 

m. The logs of typical wells in the Sirte area are shown in Figure 3.

The Tertiary sedimentary rocks form part of a regional homocline 

that dips gently toward the north (fig. 4). However, field observations by G. H. Goudarzi (1962, oral communication) indicate that the

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HYDROLOGY OF AFRICAND THWELL 37V lO.P.D.L. (H.T Smith (Wi Meters 47)/Land test well) QaE MEDITERRANEAN REGION 

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GROUND WATER, SIRTE AREA, TRIPOLITANIA, LIBYA C7

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C8 HYDROLOGY OF AFRICA AND THE MEDITERRANEAN REGION

Tertiary rocks are apparently traversed by a fault to the northwest of Qasr Bu Hadi. Information from oil companies confirms 

this observation. Accordingly, a fault trending northwest is indicated 

in figure 2. Also, a small anticlinal flexure trending north-northeast 

passes through the hill on which is Qasr Bu Hadi (fig. 2). As substantiated by the hydraulic behaviour of wells 9 and 9a during pumping tests, the junction of these two structural features may form a trap 

in which fresh ground water has accumulated. Highly mineralized 

ground water is reported in wells drilled by oil and geophysical 

exploration companies at points adjacent to the Qasr Bu Hadi area.

GROUND WATER

OCCURRENCE

The principal ground-water reservoir in the Sirte area is in the 

Tertiary sedimentary rocks and probably extends beneath and beyond 

the report area (fig. 2). This reservoir is probably recharged by occasional infiltration from sporadic heavy rains and from resulting 

runoff in ephemeral streams of the area. Water circulates through 

the reservoir and is stored chiefly in porous or cavernous beds, bedding 

planes, and fractures in limestone. Typical are permeable and saturated limestone beds penetrated between depths of 38.6 and 50.6 m in 

well 7,48 and 56 m in well 8, and 60 and 66.5 m in well 9 (fig. 3). The 

beds of marl and clay have fairly low permeability and, although they 

may be saturated, probably yield little water to wells. Sandstone 

beds may also contain water in some places in the area, but as indicated 

in the logs of figure 3, such beds do not appear to be common in the 

Tertiary sequence.

Generally, the first water reached in drilling in the Tertiary rocks 

is under water-table, or unconfinecl, conditions; but water at deeper 

levels is under artesian, or confined, conditions. For example, water 

in well 8 in limestone between depths of 48 and 56 m rose to 43.3 m 

below the surface. The depth to water in wells depends on the relative 

difference between altitudes of the land surface and thq water table. 

Among the wells in the Tertiary rocks shown in figure 2, depth to 

water ranges from about 35 to 44 m below the land surface. Sufficient 

data were not available from the present investigation to construct a 

\vater-table map of the area; however, it is evident from the known 

water levels in existing wells that the water table has a northerly slope. 

These data indicate that the water which moves through the groundwater reservoir in the Tertiary rocks discharges principally in the 

Gulf of Siclra or in the "sebkas" near the sea.

A local ground-water body is also found in the coastal sand dunes 

near Zaafran and is probably sustained chiefly by recharge from local
GROUND WATER, SIRTE AREA, TRIPOLITANIA, LIBYA C9

rainfall. This water body, which is tapped by wells and galleries 

at depths of 10 m or less, has been used the past several years for the 

potable water supply of Sirte. The quality of the water, however, has 

deteriorated progressively in recent years probably because of salt 

water encroachment, resulting from overpumping, lack of recharge, 

or both. The depth to water in wells tapping this water body is generally less than 6 m below the surface.

CHEMICAL QUALITY

As is common in many arid to semiarid regions of the world, the 

ground water in most of the Sirte area is moderately to highly mineralized. According to available analyses (table 1) and reports from 

oil-well tests, the water in the Tertiary rocks of the area commonly 

contains more than 3,000 ppm of dissolved solids; however, water 

of low dissolved-solids content is found in the wells drilled along or 

near the Wadi Tlal (fig. 2). From this relation it is inferred that 

infiltration of fresh water from runoff in the wadi system locally may 

have diluted or perhaps partly flushed out the prevalent, more highly 

mineralized water of the Tertiary rocks. Also, for wells drilled in 

or near the Wadi Tlal, it is inferred that the water found in shallow 

water-bearing zones may have better chemical quality than, that at 

deeper levels. For example, in well 7 (table 1) the water from limestone between 38.6 and 50.6 m contained 860 ppm of chloride, but in 

water from limestone between 65.6 and 74.6 m the chloride content 

increased to 958 ppm. Elsewhere in the area the shallov ground 

water may also be of better quality than deeper water. In deep well 

3 (table 1), for example, water from 368 m contained 1,120 ppm of 

chloride, but a sample taken from a depth of 515 m contained 4,780 

ppm of chloride.

As indicated by chemical data given in table 1 and chloride concentrations shown in figure 2, ground-water salinity gradually increases downgradient in wells drilled along the Wadi Tlal. For 

example, between wells 10 and 4 (fig. 2) the chloride concentration 

increases from 149 to 2,700 ppm, respectively, in the shallow ground 

water of the Tertiary rocks. Perhaps the most pronounced change 

takes place between wells 8 and 7 where the chloride increases from 

217 to 860 ppm (fig. 2) in a lateral distance of about 2 km. A probable 

fault (fig. 2) passes between these two wells and acts as a partial, 

but probably not complete, obstruction to the northerly flow of ground 

water through the Tertiary rocks. Thus, fresh water tends to accumulate to the south of the fault, which probably also impedes tl x °, mixing 

of this water with brackish and salty water to the north.
CIO HYDROLOGY OF AFRICA AND THE MEDITERRANEAN REGION

TABLE 1. Chemical analyses of icater from wells in the Sirte arer, Tripolitania, 

United Kingdom of Libya

[Chemical analyses in parts per million. Analyses by Chemical Laboratory. Libyan-American Joint

Services]

a

1. _

1 __

2

2.....

3.....

3.....

4.....

5

6. ..

7...-

?-.. 

8..... 

9..... 

10....

Depth of water-bearing zone 

(meters)

5.0±

5.0± 

5.0±

368

515 

42

35+

38±

50±

75±

57 

67 

47

Date collection of 

2-W

5-57 

2-57

5-57

7-39

8-39 

8-60

1958

1958

10-58

10-58

1940 

12-61 

1957

Temperature (°C)

....

22

35

"26"

Silica (Si0 )2

20

Ifi

13

23

7 

20

Calcium (Ca)

857

86

740 

328

52 

70 

63

Magnesium (Mg)

322

44

306

38 

3 

44

Sodium (Na)

1,520

Q4.

2,910 

1,420

182 

126 

137

Potassium (K)

104

19

108 

33

s"

12

Bicarbonate 

(HCOs)

114

165

542

284 

152

O

OJ

"3

OJ

346

112

2,260 

1,100

73 

54 

99

Chloride (Cl)

512

2,180

153

1,120

4,780 

2,700

1,540

1,260

860

958

217 

124 

149

Dissolved solids 

(residue on 

evaporation at 

180°C.)

1,440

4,880 

945

712

11, 670 

6,150

720 

541 

688

Specific conduct- 

(micromhos ance 

at 25°C.)

5,970

1,050

14,900 

8,770

1,120 

760 

1,150

Hardness as

CaCOa

570

773 

400

391

2,600

3,020 

1,950

277 

314 

334

%

7.4

7 6

"7"?,

7.4 

7.5 

7.5

The quality of the water in the local ground-water body near 

Zaafran is indicated by the analyses for wells 1 and 2 (table 1). Apparently its quality deteriorated markedly in 1957 (table 1), and the 

water currently (1962) is reported to have an even higher concentration of dissolved solids.

FRESH-WATER AQUIFER IMF THE QASR BIT HAD! AREA

Two major hydraulic characteristics that affect development of 

the fresh-water aquifer near Qa§r Bu Hadi, as well as of all aquifers, 

are the ability of the aquifer to transmit water and the capacity of the 

aquifer to yield water from storage. These characteristics, which affect the water levels and yields of wells, are called the coefficient of 

transmissibility, first defined by Theis (Ferris and otters, 1962, p. 

72-73), and the coefficient of storage (Ferris and others, 1962, p. 

74-78), respectively. When these coefficients are known for an aquifer 

or part of an aquifer, it is possible to forecast approximate water-level 

trends at different rates of withdrawal from production wells.

To establish the transmissibility and storage coefficients of the 

fresh-water aquifer near Qasr Bu Hadi, two test wells were drilled 

for a controlled pumping test. The first test well (well 9, fig. 2), 

completed in December 1961, was drilled and cased to a depth of 

67 m. Fresh water with 124 ppm of chloride was tapped in porous 

limestone between depths of 44 and 67 m, and the caging between 

those depths was perforated. A pump was then installed temporarily and operated for 72 hours at a pumping rate of 9 m3 per hr.
GROUND WATER, SIRTE AREA, TRIPOLITANIA, LIBYA Cll

During this period no change in chemical quality was observed. 

The second test well (well 9a, fig. 2), 75 m north of well 9, was completed in March 1962 at a depth of 67 m.

For the pumping test, made between April 5-17, 1962, well 9a was 

equipped with a pump which was operated for 159 hours at a pumpage rate of 18 m3 per hr. Water-stage recorders were installed on 

well 9 and on well 10, an Arab-dug well known as Bir Tuama about 325 

m south of well 9a, to determine the time and rate of drawdown caused 

by pumping in well 9a. Water levels in well 8, which is about 195 m 

north of well 9a, were measured using a steel tape during the pumping period and during part of the recovery period. Data obtained 

from measurements in well 10 were inconclusive because the well 

penetrates only the top 1.5 m of the aquifer. Also, during the recovery period, water-level measurements in well 8 were disrupted so that 

the well could be pumped to serve the water requirementr of local 

Bedouin tribesmen. Pertinent hydrologic data from the pumping test 

are given in table 2.

TABLE 2. Hydrologic data from pumping test at well 9a near Qa§r Bn Hadi

Well

9a. __ . ____

9 ____ . ___ ...

8 __ .... .........

10 .............

Depth of 

well (m)

67.6

67.0

66.7

47.0

Static 

water level 

below landsurface 

datum (m)

44 n

43.9

43.3

44.6

Dynamic 

water level 

below landsurface 

datum (m)

62.1

44.5

43.4

Pumping 

period 

(hrs;

Drawdown 

(m)

18.2

.57

.14

.04

Yield 

(m3 per hr)

18

Distance 

from well 

9a (m)

75

196

325

After 159 hours, pumping in well 9a was discontinued, and water 

levels were observed during the recovery period in both wells 9a and 

9. The coefficients of transmissibility and storage were corrputed by 

the nonequilibrium formulas of Theis and Jacob (Ferris and others, 

1962, p. 92-100). The computed coefficient of transmissibility was 

about 25,000 gpd per ft (U.S. gallons per day per foot) or 13.68 M3 

per hr per ft (cubic meters per hour per foot). The coefficient of 

storage, computed as about 0.00055, suggests that the aquifer may be 

semiartesian or perhaps a water-table aquifer grading into an artesian 

aquifer.

During the pumping of well 9a, the outward spread of tl>Qs cone of 

depression was rather rapid; however, breaks in the slope of the 

time-drawdown curves for wells 9 and 9a indicate the preserve of two 

hydraulic boundaries that do not transmit water readily. The first 

boundary, computed as 250 m westward from well 9a, is attributed to 

the small anticline on which stands the fort of Qasr Bu Hadi. The 

second boundary, computed as about 535 m northward from well 9a,
C12 HYDROLOGY OF AFRICA AND THE MEDITERRANEAN REGION

corresponds to the northwesterly trending fault shown ir figure 2, the 

possible attitude of the fault is indicated in figure 4. Apparently, 

this fault partly limits the flow from the fresh-water aquifer on the 

south to the brackish-water transition zone on the north. Therefore, 

prolonged pumping from a well or wells near the fault conkl probably 

reverse the hydraulic gradient and induce flow of brackish water 

from the north. To minimize this possibility, production wells in the 

fresh-water aquifer should be drilled as far south of the fault as 

practical.

To forecast approximate water-level trends at prescribed pumping 

rates in production wells that may be constructed in the- fresh-water 

aquifer, the pumping-test data were evaluated taking into account the 

limitations of accepted formulas and also compensating for the two 

hydraulic boundaries. Having well 9a as the focal point, figure 5 

shows the computed decline of water level (drawdown) that would 

occur at prescribed rates of pumping. For example, at a pumping rate 

of 13.5 in3 per hr, the pumping water level would decline about 1.7 m 

at the end of 1,000 days of pumping. As shown in figure 5, the decline 

of water level increases at comparable rates in the first three curves 

but diverges sharply in the lowest curve. These predictions indicate 

that a pumping rate of 18 m3 per hr is beyond the capacity of the 

fresh-water aquifer. In fact, pumping from well 9a at 18 m3 per hr 

for 10 years would result in a pumping water level of 61" m, which is 

the bottom of the well. For this reason, it is believed that the pumping

1000 

TIME, IN DAYS

10,000 100,000

FIGURE 5. Predicted decline of water level (drawdown) in fresh-water aquifer at prescribed

pumping rates.
GROUND WATER, SIRTE AREA, TRIPOLITANIA, LIBYA C13

rate from the fresh-water aquifer in the Qasr Bu Hadi area should not 

exceed 13.5 m3 per hr.

The predicted declines of water level (drawdown) in the freshwater aquifer at prescribed distances after pumping at prescribed 

rates for 10 years are shown in figure 6. A pumping rate of 13.5 m3

100 1000 

DISTANCE, IN METERS

10,000

FIGURE 6. Predicted decline of water level drawdown) in fresh-water aquifer at prescribed distances after pumping 10 years at prescribed rates.

per hr for 10 years would result in a decline of water level of 0.63 m 

at a distance of about 3 km. This predicted decline indicates that new 

production wells preferably should be at least 3 km south of well 9a. 

Care should be taken in drilling and completing such wells, as the 

shallow aquifer probably contains water of better quality than that of 

the deeper aquifers. If wells are drilled too deep, contamination, at 

least locally, of the fresh-water aquifer may result.

CONCLUSIONS

The present study and previous work by other investigators have 

established the presence of a moderately productive fresh-water 

aquifer in the Qasr Bu Hadi area. This aquifer, if properly developed and carefully utilized, can probably sustain most, if not all, 

of the potable water requirements of Sirte for some years to come. 

To help assure proper development, the following measures are 

suggested.

1. The predicted decline of water level after 10 years of pumping 

at 13.5 m3 per hr (fig. 6) indicates that at 3 km from well 9a, the 

decline in water level would be only about 0.62 m. Thus, new produc-
C14 HYDROLOGY OF AFRICA AND THE MEDITERRANEAN REGION

tion wells should be drilled at least 3 km south of present wells 9 and 

9a. This measure would minimize the possibility of drawing brackish 

or salty water from north of the fault into the fresh-water aquifer.

2. The production wells should not be pumped at rates exceeding 

13.5 m3 per hr. At greater rates, the water level in the wells would 

decline to the point where contamination of the fresh-vmter aquifer 

would follow.

3. Two or more production wells may be desirable to give standby 

capacity for emergency, to minimize local drawdown in the aquifer, 

and to obtain the same amount of water in shorter pumping periods. 

The effects upon the aquifer would be similar if the total withdrawal 

in a 24-hour period were the same.

4. The present test wells 9 and 9a should not be used for production 

except in emergency.

5. A well should be available for periodic measurement of the effects 

of pumping on the aquifer. Either well 9 or 9a could be used for this 

purpose.

6. When the new production wells are drilled, there should be close 

supervision of the drilling to determine whether the character of the 

aquifer is the same as that at the present test wells 9 r.nd 9 a. The 

production wells should be tested as they are drilled to eh eck the yield 

and quality of the water before construction of hydraulic works is 

begun.

SELECTED REFERENCES

Bruin, Jack, and Hudson, H. B., Jr., 1958, Selected methods fo'* pumping test 

analysis: Illinois Water Survey Division Kept. Inv. 25, 38 p.

Cooper, H. H., and Jacob, C. S., 1946, A generalized graphical method for 

evaluating formation constants and summarizing well-field history: Amer. 

Geophys. Union Trans., v. 27, p. 526-534.

Ferris, J. G., 1948, Ground water hydraulics as a geophysical aid: Lansing, 

Mien., Michigan Dept. Cons. Tech. Rpt. 1.

Ferris, J. G., Knowles, D. B., Brown, R. H., and Stallman, R. W., 1962, Theory 

of aquifer tests: U.S. Geol. Survey Water-Supply Paper 153"-E, p. 69-174.

H. T. Smith International, 1959, Report on prospects for the development of 

potable water supplies from tube wells at Sirte, Libya: International Cooperation Administration, Duplicated Rept., 56 p.

Stewart, J. H, 1960, Land and water resources of Tripolitania (Libya) : International Cooperation Administration, Duplicated Rept., 248 p.

Stuart, Wilbur T., 1960, Significance of decline in ground-water levels in Tripolitania, Libya, as determined by pumping tests: U.S. Geol. Survey open-file 

report, 29 p.

Theis, C. V., 1936, The relation between the lowering of the piezometric surface 

and the rate and duration of discharge of a well using ground water storage: 

Amer. Geophys. Union Trans., pt. 2, p. 519-524.

Wenzel, L. K., 1942, Methods of determining permeability of water-bearing materials : U.S. Geol. Survey Water-Supply Paper 887,192 p.

o