This study aims to characterize karst formations and aquifers in the Louros River drainage basin in Greece. Data collected includes discharge measurements, meteorological data, water chemistry analyses, isotope ratios, and more. Models were used to complete missing discharge data and predict values for 2008-2010. The basin covers 952.8 km2 and is composed of carbonate and clastic sedimentary rocks. Analysis of the data found that total discharge accounts for 61-73% of precipitation, evapotranspiration is 29-39%, and storage in the basin is approximately 2025x10^7 m3. Statistical analysis identified three distinct karst units with different recession coefficients in the basin.

1. PHD SYNOPSIS
The present study aims to describe and characterize the Ionian zone karst formation
concerning the karstification grade of carbonate formations and the development of
aquifers, through the hydrogeological study of Louros River drainage basin,
considering hydrological, hydrogeological and meteorological data, as well as major,
trace element, rare earth element and isotope concentrations. It also aims to
investigate basic karst properties such as storage capacity, homogeneity, infiltration
coefficients and the parameters of the Louros basin hydrological balance.
To accomplish this aim daily discharge measurements obtained from Public Power
Corporation at the Pantanassa station during the years 1956-1957, along with random
discharge measurements from 15 springs along the basin performed by IGME
between the years 1979-1989, daily meteorological data from 18 stations and 18 sets
of potentiometric surface measurements from 38 sites were compiled. Additionally,
chemical analyses on major and trace element concentrations of 42 rock samples and
of five sets of water samples from 64 sampling sites, along with fourteen sets of
successive periods in order to study the seasonal variation in the chemical
composition of 11 springs and REE concentrations of 116 water samples were
analysed. Moreover isotope ratios from 129 rain samples collected at five different
altitudes, 331 samples of surface and groundwater samples, radon measurements on
21 groundwater samples and microbiological analyses on 46 samples of surface and
groundwater were evaluated. Daily runoff and random spring discharge missing data
were completed applying the SAC-SMA and MODKARST simulation algorithms and
the values of these parameters for the duration of the research (2008-2010) were
predicted. The accuracy of the predicted values was tested applying statistical
methods but also against observed values from in situ measurements performed
during the same period (2008-2010).
Louros River drainage basin is located at the southern part of Epirus and covers an
area of 952.8 km2
. It is elongated and together with the adjacent basin of River
Arachthos they constitute the major hydrographic systems discharging in the
Amvrakikos Gulf. The main morphological features of the basin are elongated
mountain ranges and narrow valleys, which are the result of tectonic and other
geological processes mainly controlled by the limestone-“flysch” alternations. The
length of the river’s major channel, which is parallel to the major folding direction
(NNW-SSE), is 73.5 km. The mountainous part of the hydrogeological basin covers
an area of 400 km2
and its endpoint was set at the Pantanassa station, where discharge
measurements are performed. The underground limits of the basin coincide with the
surface one, defined by the flysch outcrops at the western margin of the Ziros-
Zalongo fault zone to the South, the application of isotope determinations and
hydraulic load distribution maps at the North and East.
Geologically, Louros River drainage basin is composed of the Ionian zone formations.
Triassic evaporites constitute the base of the zone overlain by a thick sequence of
carbonate and clastic sedimentary rocks deposited from the Late Triassic to the Upper
Eocene. In more detail, from base to top, the lithostratigraphical column of the zone
includes dolomite and dolomitic limestone, Pantokrator limestone, Ammonitico
Rosso, Posidonia Shales, Vigla limestone, Upper Senonian limestone, Palaeocene-
Eocene limestone and Oligocene “flysch”.
The major tectonic features of the regions are folds with their axes trending SW-NE at
the northern part and NNW-SSE to NNE-SSW southern of the Mousiotitsa-
Episkopiko-Petrovouni fault system and the strike-slip fault systems of Ziros and
Petousi.

2. The evaluation of the daily meteorological data revealed that December is the most
humid month of the year followed by January, whereas July and August are the driest
months. Approximately 40-45% of the annual precipitation is distributed during the
winter time and 30% during autumn. The mean annual precipitation ranges from
897.4 to 2051.8 mm and the precipitation altitude relationship suggests an increased
precipitation with altitude at a rate of 84 mm/100 m. The maximum temperature is
recorded during August and it may reach 40°C and the minimum during January. The
temperature variation with the altitude is calculated at 0.61°C/100 m. The maximum
solarity time is 377.8 h, recorded during July at the Arta station. December displays
the highest relative humidity with a value of 84.2% recorded again at the Arta station.
The highest wind velocity values are recorded at the Preveza station and similar
velocities are also recorded at the Ioannina station. The real evapotranspiration in
Louros drainage basin ranges between 27-39%. The potential evapotranspiration was
calculated from the Ioannina station meteorological data, which are considered more
representative for Louros basin, at 785.8 mm of precipitation according to
Thornthwaite and at 722.0 mm according to Penman-Monteith.
According to the SAC-SMA algorithm the total discharge (surficial and underground)
for the years 2008-2010 ranges between 61-73% of the total precipitation. The
algorithm simulates the vertical percolation of rainwater in both unsaturated and
saturated zones taking into account 15 parameters including the tension water
capacity of the unsaturated zone, the maximum water storage capacity of both
unsaturated and saturated zones, the water amount escaping into deeper horizons and
not recorded at the basin’s outlet, the percentage of impermeable ground which is
responsible for instant runoff, etc. These parameters are correlated to the hydrograph
and are recalculated according to it. Two interesting aspects were pointed out from the
discharge measurements and the algorithm application. The first is related to the
maximum amount of free water, which can be stored at the basic flow of the karstic
system, which is very high for the whole basin, reaching 1200 mm of precipitation
and the second is the amount of water filtered to the deeper horizons, which reaches
0.098.
The discharge of individual karstic units was simulated applying the specialized
MODKARST code. The code, which transforms precipitation to discharge resolving
mathematical equations of non-linear flow using the mass and energy balance,
successfully completed the time series of available data of spring discharge
measurements for the period between the years 2008-2010.
Additionally, a number of useful parameters including spring recharge, delay period
between precipitation and discharge, the storage capacity of the discharge area were
also calculated by the MODKARST code. These data enabled the calculation of the
annual infiltration coefficient for each one of the 15 springs and for the whole basin;
the latter was found to range between 38-50% of annual precipitation. The total
supply area was estimated approximately at 395 km2
, which is consistent with the area
of Louros hydrogeological basin calculated from hydrogeological data.
The 18 sets of water table measurements, each one corresponding to a different
period, revealed that the aquifers of the intermediate part of Louros basin, which are
developed in Quaternary alluvial sediments, are laterally connected to the carbonate
formations of the individual karstic spring units, forming a common aquifer with a
common water table. Groundwater flow follows a general N-S direction from the
topographic highs to the coastal area with local minor shifts to NE-SW and NW-SE
directions. The artificial lake at the position of the Public Power Corporation’s Dam at
the south of the region is directly connected to the aquifer and plays an important role
in water-level variation. The water table contours display a higher gradient to the

3. southern part due to the decreased hydraulic conductivity of the limestones close to
Agios Georgios village. The decreased hydraulic conductivity is believed to be the
reason for the development of the homonymous spring although the hydraulic load
distributions suggest the extension of the aquifer to the south and a relation to the
water level in Ziros Lake, boreholes and the Priala springs. The hydraulic gradient in
the broader region ranges between 4-16‰. The absolute water level variation between
dry and humid season ranges from 2 m at the South to 15-20 m to the North with an
average of 9 m.
The hydrological balance of Louros River mountainous basin according to the
aforementioned data is calculated as follows: The total precipitation between the years
2008-2010 ranged between 5.67E+08-9.8E+08 m3
and the discharge at Pantanassa
site between 3.47E+08-6.83E+08 m3
. The real evapotransiration ranged between 29-
39% of the precipitation. The total discharge (runoff and groundwater) accounted for
61-73% of the precipitation, whereas the basic flow due to the percolation ranged
between 34-38%. Considering a mean water level variation of 9 m, between the dry
and humid season, the water amount constituting the local storage is 2025Ε+07 m3
.
Statistical evaluation on spring discharge data and the recession curves analysis
revealed three distinct levels with diverse karstic weathering along Louros basin
coinciding to the upper, intermediate and low flow of Louros River, respectively. The
developed karstic units are generally complex but simple individual units develop as
well. The response of spring discharge to the stored water amounts is immediate but
with relatively large duration suggesting the storage of large quantities of water and a
well-developed system of karstic conduits, which however has not yet met its
complete evolution. The karst spring’s units are homogeneous and each one is
distinguished from different recession coefficients.
The three levels of flow are also distinguished from the duration curves, which point
to individual units upstream, complex units receiving and transmitting water to the
adjacent ones in the middle part and complex that only receive water from the upper.
This distinguishment is also enhanced by the groundwater’s major ion concentrations,
which reveal Ca-HCO3 water-type upstream, along with the isotopic composition at
the same part. The prevalent Ca-HCO3-Cl-SO4 water-type in the middle part, the Na-
Ca-Cl-SO4 water-type downstream and isotope variation confirms this
distinguishment. Moreover, REE variation is also consistent with the three levels. The
assumption of relatively large stored water reserves, which contribute to analogous
“memory” of spring karstic units, as pointed out by autocorreletion functions is
enhanced from SAC-SMA algorithm which premises an increased capacity at the
lower zone of basic flow, as well as from the hydrochemical and isotopic composition
of groundwater. Monitoring of the seasonal variation in groundwater composition
revealed minor variations of hydrochemical parameters and remarkably stable
isotopic composition.
Both aspects can be explained by the existence of a considerable water body acting as
a retarder to external changes. The crosscorrelation functions suggest a well-
developed karstic system, which however has not yet reached its complete maturity
also confirmed from field observations. The same conclusion is extracted from the
homogeneous evolution at the interval of each karstic unit as demonstrated from
recession curves on spring hydrographs.
The results from hydrochemical analyses also revealed the effect of evaporitic
minerals and phosphate-rich rocks in groundwater composition and confirmed the
hydraulic relationships between surface and groundwater.

4. The study of the isotopic composition also contributed to exclude the potential
connection between the Ioannina and Louros basins, confirmed the meteoric origin of
groundwater and revealed the effect of seawater in the chemical composition of
Sykies and Petra springs.
The microbiological research only revealed minor incidents of contamination (e.g.
Skala spring-LP7) and significant attenuation of microorganisms during periods of
high discharge.