ORIGINAL ARTICLE

Measurement of field-saturated hydraulic conductivityon fractured rock outcrops near Altamura (Southern Italy)with an adjustable large ring infiltrometer

Maria Clementina Caputo Æ Lorenzo De Carlo ÆCostantino Masciopinto Æ John Robert Nimmo

Received: 4 November 2008 / Accepted: 23 May 2009

� Springer-Verlag 2009

Abstract Up to now, field studies set up to measure field-

saturated hydraulic conductivity to evaluate contamination

risks, have employed small cylinders that may not be

representative of the scale of measurements in heteroge-

neous media. In this study, a large adjustable ring infil-

trometer was designed to be installed on-site directly on

rock to measure its field-saturated hydraulic conductivity.

The proposed device is inexpensive and simple to imple-

ment, yet also very versatile, due to its large adjustable

diameter that can be fixed on-site. It thus allows an

improved representation of the natural system’s heteroge-

neity, while also taking into consideration irregularities in

the soil/rock surface. The new apparatus was tested on an

outcrop of karstic fractured limestone overlying the deep

Murge aquifer in the South of Italy, which has recently

been affected by untreated sludge disposal, derived from

municipal and industrial wastewater treatment plants. The

quasi-steady vertical flow into the unsaturated fractures

was investigated by measuring water levels during infil-

trometer tests. Simultaneously, subsurface electrical resis-

tivity measurements were used to visualize the infiltration

of water in the subsoil, due to unsaturated water flow in the

fractures. The proposed experimental apparatus works well

on rock outcrops, and allows the repetition of infiltration

tests at many locations in order to reduce model uncer-

tainties in heterogeneous media.

Keywords Large ring infiltrometer �Fractured limestone � Field-saturated hydraulic

conductivity

Introduction

The measurement and monitoring of hydrological pro-

cesses within the vadose zone is difficult and expensive

(Castiglione et al. 2005). When the vadose zone consists of

rock, rather than soil or regolith, the difficulties are greater

in several ways. Indeed, up to now infiltrometer tests have

rarely been performed directly on-site on fractured rock

outcrops. Castiglione et al. (2005) developed in laboratory

a tension infiltrometer ring (height 4 cm, diameter

27.5 cm) suitable for accurate measurements of infiltration

into fractured tuff at very low flow rates, over long equil-

ibration times. In fact, most field infiltrometer tests employ

cylinders of the order of 1–50 cm in diameter. However,

such small cylinders only allow a poor representation of

heterogeneous fractured rock materials, in which hydrau-

lically important fractures may typically be spaced further

apart than the cylinder’s diameter.

In this study, a ring infiltrometer with a large (*2 m)

adjustable diameter was developed and adapted for mea-

suring quasi-steady infiltration rates on outcrops of frac-

tured rock. Moreover, certain practical problems related to

the installation of the cylindrical ring on the rock surface

were solved in order to achieve a continuous and imper-

meable joint surface between the rock and the ring wall.

The infiltrometer tests were coupled with subsurface elec-

trical resistivity measurements to monitor, qualitatively,

the water infiltration depth and to ensure that the decrease

in the water level in the ring was caused mainly by vertical

water infiltration and not by lateral diversion of water flow.

M. C. Caputo (&) � L. De Carlo � C. Masciopinto

Water Research Institute, IRSA-CNR, via F. De Blasio, 5,

70123 Bari, Italy

e-mail: maria.caputo@ba.irsa.cnr.it

J. R. Nimmo

USGS, 345 Middlefield Rd., Menlo Park, CA 94025, USA

123

Environ Earth Sci

DOI 10.1007/s12665-009-0198-y

Usually, different kinds of probes are used to monitor the

field water infiltration in soils, such as time-domain

reflectometry (TDR) or time-domain transmissiometry

(TDT) sensors to measure water content, together with

tensiometers to measure water pressure (Masbrucha and

Ferre 2003). In this study, electrical time-lapse resistivity

measurements (e.g., Binley et al. 2002; Deiana et al. 2007),

which allow a rapid visualization of the change in water

content in the subsurface, were preferred to the above-

mentioned probes, due to sidestep the difficulty of inserting

the latter in the rock.

Materials and methods

Large ring infiltrometer

A ring infiltrometer for studying water flow in fractured

rock formations needs to be made from a tough material,

suitable for installation on the rock surface. At the same

time the material must be both flexible, to allow a cylinder

to be built that is adjustable to the field conditions, and

light, to facilitate transport and set up. Where the ground

surface is very irregular, small adjustments to the ring

diameter ensure efficient sealing, thus facilitating the set-

ting up of the device. If electrical methods are to be used

for the detection of water content or salinity, the ring must

also be made of a non-metallic material. The large ring

infiltrometer was therefore designed in a light and flexible

plastic material to allow easy installation on the rock sur-

face, and adaptation of its size to the field conditions. Strips

of flexible plastic 30 cm wide and 0.2 cm thick were used

to build two in situ rings of internal diameter 2 and 1.8 m

for tests #1 and #2, respectively, by sealing the two ends of

the strip with impermeable adhesive tape to form the

cylinder.

Among a variety of materials tested both in the labo-

ratory and in the field, gypsum was shown to be the most

suitable because it is cheap, easy to prepare in situ and to

apply on the ground in a previously hollowed furrow,

ensuring good sealing. Clay, instead, needed to be worked

for a long time in order to obtain a consistency that would

allow the ring to be sealed to the ground. It nevertheless

gave poor results, because the clay did not firmly grip the

ring wall on the ground. Moreover, tests carried out with

clay at the IRSA laboratory showed water losses from

cracks in the clay due to its characteristics of swelling and

shrinking. Silicon was also tested, although using it for

sealing a large-diameter infiltrometer would be expensive.

However, it was also discarded, as it did not seal well due

to the dissimilarity of the soil, rock, and plastic materials

being sealed. Polyurethane foam was easy to apply and

proved impermeable, but was also discarded because it

would be expensive and did not grip well on the rock and/

or soil.

Field tests

The infiltration experiments were performed in the

study area located in Southern Italy (Fig. 1) on the Murge

plateau formed from Cretaceous limestone during the

Paleogene and Neogene periods. The limestones are part of

Fig. 1 Schematic geological

map of the study area

(Altamura, Southern Italy)

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123

a sedimentary sequence of a carbonatic platform some

thousands (up to 3,000) meters thick. The main rock units

consist in calcilutites, which in the study area constitute a

unit known as ‘‘Calcare di Altamura’’ and ‘‘Calcare di

Bari’’ (Ciaranfi et al. 1988). During a large part of the

Neogene, the area was uplifted and affected by tectonic

stress and karst morphogenesis. The experimental tests

were conducted on the top of a karstic fractured limestone

formation constituting the deep Murge aquifer, which has a

water table ranging from 400 to 500 m depth below ground

surface. The fractured limestone studied is characterized by

a low effective matrix porosity with respect to fracture

porosity. Borgia et al. (2002) measured the effective matrix

porosity of the limestone, at field scale, and found values

up to 0.1%, together with a permeability lower than 24 mD

(millidarcy) and a hydraulic conductivity of 2.1 9

10-2 m day-1 (for water at 20�C), on average. These

values indicate a conductivity 1,000 times lower than that

of the fracture network (8–77 m day-1) of the same

limestone formation (Masciopinto 2005), which is char-

acterized by an effective fracture porosity at field scale up

to 0.4% (Borgia et al. 2002). In light of these results, it is

clear that the water flow rate component in the rock matrix

can be considered negligible as compared to the water flow

rate component in the network of fractures.

The site for testing the newly developed large ring in-

filtrometers was chosen because it has recently been

affected by untreated sludge waste deposits that have

contaminated the soil and subsoil.

The infiltrometer tests were carried out at two locations,

300 m apart, to evaluate the quasi-steady vertical flow rates

in outcrops of limestone that showed different fracture

frequencies and sizes at a visual inspection. Specifically,

the site of test #1 showed prominent visible fractures of

about 5 cm spacing and about 1 mm aperture, whereas the

site of test #2 showed no visible fractures. A 2 m diameter

ring coupled with an external ring was used in test #1. In

this case, the infiltration area consisted of a central part

with numerous visible fractures (Fig. 2a), while the rest

was partially covered by soil, 5–10 cm thick, on average.

For this reason, in this site a second ring with a larger

diameter (2.2 m) was positioned (Fig. 2b) in order to

improve the hydraulic packing during the water infiltration

test. Continuity between the ring infiltrometer wall and the

rock–soil surface was obtained by filling the space between

the external and internal rings with gypsum up to a height

of about 2.0 cm to create a seal. As a result, the second ring

improved the gypsum sealing of the first ring to the ground,

overcoming the challenge presented by the presence of

different media (rock and soil) along the edge of the ring.

In the second test (#2), located in an area with an outcrop

of limestone characterized by no visible fractures, a 1.8 m

diameter ring was inserted into a thin furrow 2 cm deep,

previously hollowed into the rock (Fig. 3) which was then

also sealed with gypsum. The difference in size of the rings

used in the two tests was simply due to the local field

conditions; in fact, the device is designed to allow the

diameter to be adjusted easily when the irregularity of the

surface at the test site so requires.

In both cases the water used for the infiltration test had

moderate salinity (electrical conductivity of 2.39 mS/cm)

to enhance subsurface electrical resistivity measurements,

which were carried out simultaneously with the monitoring

of water infiltration/redistribution in the rock.

In test #1, the resistivity data were collected using a 7.5 m

long straight-line array of 16 steel electrodes with 0.5 m

spacing, oriented in the parallel direction as the visible

fractures. In test #2, two similar linear arrays were set up,

perpendicular to each other, with the same length and elec-

trode spacing, crossing at the centre of the ring infiltrometer.

Fig. 2 Test #1. a Fractured

limestone with visible fractures

of about 5 cm of spacing (s). bPlastic ring infiltrometer resting

directly on the ground and

sealed with gypsum by using a

second plastic ring

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123

The water in the ring reached a maximum level of

0.13 m above the ground surface in both tests. During the

falling-head infiltrometer tests, the specific lateral water

leakage fluxes were about 8% (0.1 m day-1) and 3%

(0.007 m day-1) of the infiltrate water fluxes in the rings

for the first and second tests, respectively. The specific (i.e.,

per unit of ring area) leakage rates, due not to the water flux

from the edge of the ring (i.e., losses) but to the amount of

infiltrated water which flowed laterally within the subsur-

face, was estimated by dividing the total water volume of

the lateral diverted water flow by the duration of the

infiltration (2 and 3.2 h for tests #1 and #2, respectively).

This estimation was performed on the basis of the areas of

the wetted surfaces (1.6 and 1.5 m2 for tests 1# and 2#,

respectively), which were observed around the rings at the

end of each test, and multiplying them by the average

thickness of the wetted layers (5 and 3 cm, respectively)

and by their porosities (0.29 and 0.03) (Borgia et al. 2002).

The thickness of the wetted layers was derived from

measurements on core samples drilled at the tested sites.

During the experiments, water levels in the infiltrometer

ring were monitored using a submersible pressure probe.

Results and discussion

The results of infiltrometer tests are summarized in the

graph in Fig. 4, which shows a constant decrease in the

water level in the ring during the tests after the water level

had reached in both cases its maximum depth of 0.13 m.

The slope of the trend line of experimental sites gives an

average infiltration rate equal to 1.33 ± 0.0034 m day-1

for test #1, and 0.22 ± 0.0027 m day-1 for test #2, where

the standard deviations take into account the standard

errors of the best fit procedures.

By assuming a constant suction head at the wetting front

(Green–Ampt model), the quasi-steady specific flow rate qs

(L3/t) can be quantified as

qs ¼Kfs

apGe

H þ 1

a�

� �� �þ Kfs ð1Þ

where Kfs is the field-saturated hydraulic conductivity, a(L)

the ring radius (1–0.9 m for tests #1 and #2, respectively),

H(L) the height of ponded water in the ring, Ge(–) the

effective shape factor and 1/a* is the macroscopic capillary

length k(L), which takes soil type into account. The

effective shape factor, which is nearly independent of soil

hydraulic properties (i.e., conductivity and macroscopic

capillary length), can be set equal to 0.184 ? 0.316 9 d/a

(Reynolds and Elrick 1990), where d(L) is the depth of ring

insertion into the rock (or soil). The macroscopic capillary

length k, during downward water movement in a fracture

plane, is related to the fracture aperture and the interfacial

surface tension r(M/T2) between air and water (equal to

71.97 dyn/cm at 25�C) (de Gennes et al. 2002) using the

Fig. 3 Test #2. a Limestone

without visible fractures. bPlastic ring infiltrometer

installed into a thin (2 cm)

furrow hollowed in the

limestone and sealed with

gypsum

Fig. 4 Measured water level versus time during tests #1 and #2

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123

following Young–Laplace equation (Pruess and Tsang

1990):

k ¼ 1

a�¼ 2

r

qg� �bc

ð2Þ

assuming the water–air contact angle equals zero, and that

the cutoff apertures, �bc, equals the fracture aperture which

delimits the region occupied only by the non-wetting

phase; g(L/t2) is the gravity acceleration and q(M/L3) is the

water density.

It should be noted that during the tests the depth of

ponded water was not steady. For the falling-head case

Nimmo et al. (2009) developed a modification of the

Reynolds and Elrick (1990) analytical formula:

Kfs ¼LG

tln

LG þ kþ H0

LG þ kþ H

� �ð3Þ

where LG ¼ pGea ¼ 0:993d þ 0:578a is the ring-installa-

tion scaling length and H0(L) is the falling ponded depth at

the initial instant t = 0. It should be noted that Eq. 3,

which is derived by integration of Eq. 1, compensates both

for the non-constant falling head and for the subsurface

radial spreading. Assuming that the infiltration rate

obtained in test #2 of the Altamura site is independent of k,

Eq. 3 was utilized to carry out a sensitivity analysis of

field-saturated conductivity. The results, which are repor-

ted in Fig. 5, show how sensitive field-saturated conduc-

tivity is to macroscopic capillary length: increases in k of

10–20% can produce similar decreases in Kfs for an infil-

trometer ring diameter of about 2 m. Moreover, the sen-

sitivity of Kfs increases when a smaller diameter

infiltrometer ring (0.2 m) is used. Generally, it can be said

that Kfs values are very sensitive when macroscopic cap-

illary length values are lower than 1 m. In order to estimate

the field-saturated conductivity value, Kfs, by means of

Eq. 3, the macroscopic capillary length, k, is required,

which is determined by inverse modelling, using an

unsaturated fractured flow model in the vertical 2D-frac-

ture (see Appendix). The model solutions were then cali-

brated on the basis of the maximum infiltrated water depths

(1.5 and 0.3 m for tests #1 and #2, respectively) determined

by means of time-lapse images. The computational code

(Masciopinto and Benedini 1999) was then applied to

reproduce the wetting front, as estimated from electrical

resistivity tomography, depicted in Fig. 6, 80 min after the

start of the water infiltration into the ring. The simulation

results also show that changing the boundary falling head

conditions during water infiltration (from 0.13 to 0.00 m in

tests #1, and from 0.13 to 0.10 m in test #2) produced a

negligible influence on the outputs.

After estimating the macroscopic capillary length

(k = 0.90 and 0.95 m for tests #1 and #2, respectively)

and the corresponding cutoff aperture (�bc = 16.5 and

15.5 lm), as described in Appendix, Eq. 3 gave field-

saturated conductivity values of 0.67 ± 0.01 and 0.054 ±

0.001 m day-1 for tests #1 and #2, respectively.

The notable difference between the field-saturated

hydraulic conductivity values of tests #1 and #2 highlights

the great variability in hydraulic properties which charac-

terizes the carbonate rocks studied. In fact, even though the

two test sites were only 300 m apart, and the experiments

were performed on the same geological formations, the

Fig. 5 Trend of Kfs/Kfs_max as a function of the capillary length k for

different infiltrometer ring diameters

Fig. 6 a Apparent electrical resistivity measurements carried out

simultaneously during ring infiltrometer test in site #1 80 min after

the start of the water infiltration into the ring. b Best selected model

simulation results in order to fit the shape and maximum depth of

wetting front (1.5 m) at t = 80 min. Contour lines represent model

output expressed as matric heads (m) in the fracture

Environ Earth Sci

123

infiltration rates observed in the areas tested were very

different. Quarto and Schiavone (1994), with laboratory

measurements on saturated fractured limestone cores

derived from the Murge carbonate platform, showed the

applicability of Archie’s first law (using F = 2.06 9

U-1.77, where F(–) is the formation factor and U is the

porosity), which provides a rock porosity \2%, by

including matrix and fracture porosities. For the Altamura

fractured limestone, the modified Kozeny–Carman equa-

tion (Pape et al. 1999) leads to outcrop saturated conduc-

tivity values ranging from 0.6 to 12 m day-1, considering a

rock outcrop porosity from 1–2%. It should be noted that

the former conductivity value is very similar to the field-

saturated conductivity obtained by the ring infiltrometer in

test #1 (0.67 m day-1). On the contrary, the field-saturated

conductivity (0.054 m day-1) derived from test #2, where

the limestone outcrop had no visible fractures, is close to

the value (0.02 m day-1) obtained by laboratory tests on

the rock matrix of the Murge limestone (Borgia et al.

2002). The above comparison supports the field-saturated

hydraulic conductivity values obtained using the large ring

infiltrometers.

Simultaneous electrical subsurface measurements,

inverted by using the Res2Dinv software (Loke and Barker

1996), also show a difference in behaviour between the two

tests as a consequence of the water infiltration during

the tests (Fig. 7). Before the infiltrometer tests (t B 0 min),

the subsurface resistivity was above 500 Xm at the first site

and 800 Xm at the second site. In test #1, the low resis-

tivity area, below 150 Xm, was visualized after 80 min up

to 1.5 m of depth; similar results were obtained for the

electrode arrays in the perpendicular direction. The same

resistivity was visualized at depth of 0.3 m at the same

time during test #2. The low resistivity zones can be related

qualitatively to fractured rock with high water content and

moderate salinity. This assumption is consistent with the

classification of different resistivity zones made by Quarto

and Schiavone (1994) using similar electrical resistivity

measurements recorded for the same geological formation.

For both tests the electrical resistivity measurements

Fig. 7 Electrical resistivity

profiles during tests #1 and #2,

before (t = 0 min) and during

(t = 80 min) water infiltration

tests

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123

confirmed the effectiveness of the ring sealing, showing that

the water infiltrated from within the ring and not from

outside (Fig. 7) to a maximum depth of 1.5 m in test #1 and

0.3 m in test #2. Additionally, electrical resistivity imaging

highlights not only that the water reached different depths in

the two infiltrometer tests, but also that its variable redis-

tribution within the investigated vertical plane results from

the structural characteristics of the limestone outcrop. As

expected, in test #1 the deepening of the level of the low-

resistivity anomaly associated with the infiltration of mod-

erately saline water was much greater than in test #2, and

was, in fact, consistent with the different number and size of

the fractures observed visually in the limestone.

Conclusions

The large ring infiltrometer coupled with subsurface elec-

trical resistivity measurements, described in this work, has

proved to be a simple and inexpensive field tool, capable of

evaluating the field-saturated hydraulic conductivity of

fractured rock formations even if it requires numerical

elaboration supported by mathematical models. It is

designed to be installed directly on an outcrop of fractured

rock, easily constructed on-site with inexpensive, light-

weight materials and with an adjustable diameter. These

characteristics improve the versatility of the infiltrometer

method and its adaptability to various geological condi-

tions. Thus, it expands the potential for exploring hydraulic

conductivity of fractured rock, which until now has been

more frequently investigated in laboratories, mainly

because of the practical difficulties involved in field

investigations. Simultaneous electrical resistivity mea-

surements are used to monitor the subsurface water infil-

tration instead of TDR and TDT sensors or tensiometers,

thus sidestepping the difficulty of inserting probes into the

rock. Further technical difficulties related to the installation

in the field of the large ring infiltrometer, were solved using

non-commercially available equipment during the on-site

installation procedure. Specifically, the set up of the

experimental apparatus requires the hollowing out of a

furrow in which to install the ring and seal it to the rock

surface with gypsum. The efficacy of the seal of ring in-

filtrometer with soil/rock surfaces was confirmed by the

simultaneous electrical resistivity measurements that show

the deepening and spreading of the water during the infil-

tration tests. The time required for the installation was

about 2 h and the water volume used for each infiltration

test was about 0.5 m3, depending on the local rock per-

meability. On the whole, the field data obtained from the

infiltrometer tests (0.67 and 0.054 m day-1, for tests #1

and #2, respectively), and the range of electrical resistivity

measurements are consistent with the nature of the rocks

tested and are corroborated by laboratory measurements

carried out by other authors (Quarto and Schiavone 1994;

Borgia et al. 2002). The difference between the field-sat-

urated hydraulic conductivity values obtained for tests #1

and #2 highlights the heterogeneity of the outcrop studied,

due to differences in both the number and the size of the

fractures at the different locations.

The possibility of building a ring with a large adjustable

diameter on-site has the advantage of including fractures

and other features of the rock in order to obtain field-sat-

urated hydraulic conductivity data at a more representative

scale of measurements, with negligible border effects. The

proposed installation procedure of a large ring infiltrometer

on limestone outcrops extends the possibility of performing

field infiltrometer tests on rocks that would previously have

been very difficult to test.

Acknowledgments This research was supported by the Italian

Government (Regional Authority) under the 2007 Toxicological

Data-Base studies.

Appendix

The unsaturated water flow in a vertical section can be

described by the Richards’ equation:

ohow

owot¼ � o

oxKfrðwÞ

owox

� �� o

ozKfrðwÞ

owoz� 1

� �� �ð4Þ

where Kfr(L/t) is the variable hydraulic conductivity as in

the vertical fracture plane with variable apertures. It should

be noted that, following Hestir and Long (1990), the

fracture network in a vertical section xz (or yz) of a

fractured rock can be assumed equivalent to a fracture

lattice, as in a fracture with variable aperture.

Consequently, Kfr can be defined using the following

equation (Bear 1993, p. 15)

Kfr wð Þ ¼ k wð Þkfr x; zð Þqg

lð5Þ

where g(L/t2) is the gravity acceleration; q(M/L3) the water

density; l(N/L2, centipoises) the dynamic water viscosity;

kfr ¼ hsbðx;zÞ2

12the saturated fracture permeability within

which b(x, z) is the nodal aperture of the vertical fracture

and hs the saturated water content; k(w)(–) the relative

permeability coefficient and w(L) is the suction head. The

coefficient k(w) is related to the water suction head (or to

the water content, h) by means of an unsaturated hydraulic

conductivity function (Reitsma and Kueper 1994; Abdel-

Salam and Chrysikopoulos 1996; Bockgard and Niemi

2004, p. 789) and it can be calculated using:

kðwÞ ¼ kfrðwÞkfr

ð6Þ

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123

The field-saturated hydraulic conductivity, Kfs is related to

fracture hydraulic conductivity, Kfr(w), at saturation and to

the mean aperture of vertical fracture, by means of the

permeability of the rock matrix and mean spacing between

fractures of the outcrop (Hestir and Long 1990).

Equation 4 was solved by applying a finite difference

grid in x and z. An iterative numerical method was used to

solve the above equation and an infiltrated water mass

balance check was carried out at every instant of simulation.

Some numerical improvements of the Crank–Nicholson

implicit method (Bear 1979) allowed an automatic increase

(i.e., adjustment) of the temporal discretization step during

numerical iterations in order to reduce the total computa-

tional time. A computational code calibrated in a previous

work (Masciopinto and Benedini 1999) was then applied to

reproduce the pressure head distributions during infiltration

tests at the Altamura site. As boundary conditions at the

topsoil, a variable pressure head versus time was imposed to

simulate the water ring infiltration. The van Genucthen

parameters for the retention curves considered for test #1

were a* = 1.11 m-1, m = 0.65, hr = 0.01 and hs = 0.99,

respectively. It should be noted that a* was reassigned at the

end of the simulation, when the output of the simulation

fitted the real infiltrated water depth (about 1.5 m). The

parameters for nodal aperture generation in the fracture

plane (x, z) were mean of aperture 102.1 lm in x, 102.47 lm

in z; standard deviations of Log aperture 0.34 in x and 0.49

in z, nugget 0.02 (in x and z), sill 0.10 (in x and z) and spatial

correlation length 3 m in x and 2 m in z. The details

describing the geo-statistical and computational methods

used for fracture aperture generation in the vertical outcrop

section are reported in other works (Masciopinto 2005;

Pruess and Tsang 1990). Several simulations were carried

out by considering different mean fracture apertures (i.e.,

the model parameters) in x and z. The best model solution

(see Fig. 6b) was determined when the maximum simulated

depth of infiltrated water was equal to 1.5 m, 80 min after

the start of the infiltration into the ring. Thus, the corre-

sponding model output, in terms of matric head distribution

also enhanced the macroscopic capillary length of 0.90 m

(or a* = 1.11 m-1) and the corresponding cutoff apertures

bc(16.5 lm) defined by the Young–Laplace equation. This

pressure head is clearly visible in Fig. 6b, as the contour

line -0.90 m divides the zone of fracture filled only by air

from that with larger apertures filled by water and air.

References

Abdel-Salam A, Chrysikopoulos VC (1996) Unsaturated flow in a

quasi three-dimensional fractured medium with spatially vari-

able aperture. Water Resour Res 32:1531–1540

Bear J (1979) Hydraulics of groundwater. McGraw-Hill, New York

Bear J (1993) Modeling flow and contaminant transport in fractured

rocks. In: Bear J, Tsang CF, de Marsily G (eds) Flow and

contaminant transport in fractured rock, vol 1. Academic Press,

San Diego, pp 67–272

Binley AM, Cassiani G, Middleton R, Winship P (2002) Vadose zone

flow model parameterisation using cross-borehole radar and

resistivity imaging. J Hydrol 267(3–4):147–159

Bockgard N, Niemi A (2004) Role of rock heterogeneity on lateral

diversion of water flow at the soil–rock interface. Vadose Zone J

3:786–795

Borgia GC, Bortolotti V, Masciopinto C (2002) Valutazione del

contributo della porosita effettiva alla trasmissivita di acquiferi

fratturati con tecniche di laboratorio e di campo (Evaluation of

effective porosity contribution to the transmissivity of fractured

aquifer using laboratory and field techniques). IGEA Groundw

Geoeng 17:31–43

Castiglione P, Shouse PJ, Mohanty B, Hudson D, van Genucthen

MTh (2005) Improved tension infiltrometer for measuring low

flow rates in unsaturated fractured rock. Vadose Zone J 4:885–

890

Ciaranfi N, Pieri P, Ricchetti G (1988) Note alla Carta Geologica

delle Murge e del Salento (Puglia Centro-Meridionale) (Notes on

the geological map of Murge and Salento—Center-Southern

Apulia). Mem Soc Geol It 41:449–460

de Gennes PG, Brochard-Wyart F, Quere D (2002) Capillary and

wetting phenomena—drops, bubbles, pearls, waves. Springer,

New York (ISBN 0-387-00592-7)

Deiana R, Cassiani G, Kemna A, Villa A, Bruno V, Bagliani A (2007)

An experiment of non invasive characterization of the vadose

zone via water injection and cross-hole time-lapse geophysical

monitoring. Near Surf Geophys 5:183–194

Hestir K, Long JCS (1990) Analytical expressions for the permeabil-

ity of random two-dimensional Poisson fracture networks based

on regular lattice percolation and equivalent media theories. J

Geophys Res 95(B13):21565–21581

Loke MH, Barker RD (1996) Rapid least-squares inversion of

apparent resistivity pseudosections using a quasi-Newton

method. Geophys Prospect 44:131–152

Masbrucha K, Ferre TPA (2003) A time domain transmission method

for determining the dependence of the dielectric permittivity on

volumetric water content. An application to municipal landfills.

Vadose Zone J 2:186–192

Masciopinto C (2005) Pumping-well data for conditioning the

realization of the fracture aperture field in groundwater flow

models. J Hydrol 309(1-4):210–228

Masciopinto C, Benedini M (1999) Unsaturated flow in fractures with

anisotropic variable apertures. In: Proceedings of XXVIII

IAHR—AIRH congress, 23–27 August, Graz, Austria

Nimmo JR, Schmidt KM, Perkins KS, Stock JD (2009) Rapid

measurement of field-saturated hydraulic conductivity for areal

characterization. Vadose Zone J 8(2):1–8

Pape H, Clauser C, Iffland J (1999) Permeability prediction based on

fractal pore-space geometry. Geophysics 64(5):1447–1460

Pruess K, Tsang YW (1990) On two-phase relative permeability and

capillary pressure on rough-walled rock fractures. Water Resour

Res 26(9):1915–1926

Quarto R, Schiavone D (1994) Hydrogeological implications of the

resistivity distribution inferred from electrical prospecting data

from the Apulian carbonate platform. J Hydrol 154:219–244

Reitsma S, Kueper BH (1994) Laboratory measurement of capillary

pressure-saturation relationships in a rock fracture. Water Resour

Res 30(4):865–878

Reynolds WD, Elrick DE (1990) Ponded infiltration from a single

ring: I. Analysis of steady flow. Soil Sci Soc Am J 54:1233–1241

Environ Earth Sci

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