Groundwater Quantity and Quality Management in a Mountainous Aquifer System in NE Greece ^†

Abstract

This research work investigates the Myki Municipality’s aquifer system in the mountainous region of Xanthi Prefecture, Northeast Greece, with regard to the area’s groundwater exploitation and management requirements for drinking water supply. During the period 2021–2023, the work involved (i) groundwater discharge measurements and groundwater sampling from forty-seven (47) springs and five (5) groundwater wells, followed by groundwater chemical analyses; (ii) appropriate analysis, elaboration, and presentation of the results obtained; and (iii) formulation of related proposals that would improve the conditions of the water supply in the study area. The study revealed that water shortage circumstances exist in the study area, which may be due to low aquifer capacity in some areas, deficient groundwater recovery facilities, and water losses in the water supply network.

1. Introduction

According to Allen et al. [1], groundwater flow in mountain regions has been extensively studied, covering regional flow characterization [2,3], interaction with mountain and valley bottom streams [4,5,6,7,8,9], and mountain block recharging [8,10,11].

About 12% of the world’s population currently resides in mountainous areas and mostly relies on groundwater for their water supply. The majority of mountains are composed of fractured rocks that have little ability to store water and have steep topography. As a result, groundwater usually flows and frequently discharges into mountain streams or springs [12].

Mountains provide high-quality water to streams, rivers, and aquifers in the plains, particularly during periods of droughts, making them an important part of the hydrological cycle. Despite the limited permeability of many mountain rocks, aquifers commonly develop as precipitation infiltrates through fractures. These aquifers are essential for sustaining baseflow in rivers during dry seasons and droughts, and they also provide a reliable supply of water to springs [13].

Examining a geological cross-section of a mountainous area in general reveals the intricate nature of water movement within the rock and overlying formations. This analysis frequently clarifies the irregularities and anomalies encountered in hydrological processes [14].

Chen et al. [15] note that mountainous regions can be categorized according to their topography and elevation, ranging from low to high mountains [16], while mountainous groundwater systems have complicated geological structures and diverse hydraulic characteristics. In certain instances, particularly in subalpine regions, heavily weathered crystalline rocks may exhibit permeability at shallow depths, offering a rather increased porosity that allows them to serve as shallow aquifers [17,18,19].

Marti et al. [20] point out that despite their critical significance, mountain hydrogeological systems are still not well comprehended [21] due to the complexities arising from pronounced topographic, climatic, and geological variations. Specifically, the interactions among geology, geomorphology, and climate concerning groundwater flow and associated factors are not well understood [22,23,24]. Mountain hydrogeological systems are largely uncharacterized, as their steep gradients and inaccessibility pose substantial challenges for data collection and site instrumentation.

According to Espinha Marques et al. [25], an issue that contributes to the socioeconomic drawbacks of mountain villages’ physical isolation is the inadequate water supply, particularly to those in isolated regions. Depending on the hydrological, climatological, and socioeconomic conditions, a variety of solutions, including the use of surface water, groundwater, and even rainwater, may be implemented to overcome this situation [26,27,28].

This research investigates the aquifer system of Myki Municipality located in the mountainous region of Xanthi Prefecture, NE Greece, focusing on the management and exploitation of local groundwater resources for the purpose of supplying drinking water.

2. Material and Methods

2.1. Study Area, Geological, Hydrological, and Hydrogeological Information

The study area is situated in the northern mountainous region of Xanthi Prefecture, NE Greece (Figure 1), covering a total area of 633.3 km². According to the 2011 census, the Municipality of Myki has a population of 15,540. The municipality is characterized by its mountainous terrain and water supply issues. Τhe main crops cultivated in the Municipality of Myki include tobacco, fodder plants, other grains, and potatoes.

The mountainous area under investigation is one of the most underdeveloped areas in Greece in terms of economic and tourist development. It faces several problems, with a primary issue being drinking water shortages. Tourism in the research area is at such a low level that it cannot affect water demand.

The majority of the mountain mass in the study area is composed of impermeable metamorphic rocks, which are characterized by an extensive hydrographic network (with elevations ranging from 131 to 1696 m) and a highly varied relief morphology.

The hydrogeological system of the study area is part of the aquifer system with assigned code EL1208 of the Water District EL12 in Greece (Government Gazette Issue 81/A/12.06.2024). The mountainous part of the Xanthi Prefecture is located in the Rhodope geotectonic zone. Metamorphic rocks occupy a large part of this zone. These are rocks of a high degree of metamorphism, among which gneiss and mica schist predominate. In addition to these types, a whole series of intermediate types can be distinguished, such as gneiss schist, amphibolite gneiss, and amphibolite. Finally, a part of the area is occupied by marbles as well as various igneous occurrences (Figure 2).

It should be noted that the study area is structured for the most part by igneous occurrences, mainly volcanic rocks. While the springs that are found within the marbles are typically of low potential discharge, the marbles themselves appear fractured and partly karstified (Figure 2).

With the exception of the cracked zones, where low-potential aquifers may appear, the mountain zone’s crystalline formations are thought to be impermeable except the fractured zones (or fractured matrix). Cook [29] notes that in entirely fractured media, groundwater flows only through discontinuities, and the aquifer structure between is impermeable and lacking porosity, while in a fractured porous medium, water also stays in the aquifer matrix between the discontinuities. He also mentions that in certain circumstances, matrix permeability is insignificant, while in others, it can greatly influence flow, as well as that the majority of fractured-rock aquifers are composed of fractured porous media. The springs found in the study area’s gneiss (Figure 1) and other similar formations are often sporadic and low potential. Because of this, they frequently fall short of meeting the water supply requirements in the summer, particularly in dry years. The exceptions are the granodiorite and volcanic rock formations, which because of their structure have created ideal aquatic conditions and host a number of exploitable springs [30,31,32,33].

Rainfall and temperature data are recorded at the meteorological station of Xanthi, located 12 km south of the settlement of Myki, as well as their value fluctuations, for the 2009–2023 period (Figure 3 and Figure 4). Annual rainfall, minimum, maximum, and mean monthly rainfall values (mm) per year are presented in Figure 3, showing annual rainfall values ranging from 277.8 mm (2011) to 1028.4 mm (2019), while the mean annual rainfall value for the period 2009–2023 reaches up to 638.5 mm. The variation of mean annual temperature values ranges from 14.6 °C (2011) to 16.7 °C (2023) (°C) (Figure 4).

A comparatively constant annual rainfall value variation for the years 2012–2015, along with low values in 2011, 2016, 2017, 2020, 2022, and 2023 is recorded (Figure 3). The value in 2011 was exceptionally low, and there was an upward trend in 2018 and 2019, as well as a notable downward trend in the 2019–2023 period (meteorological data from http://meteosearch.meteo.gr (accessed on 8 August 2024)). The mean annual temperature readings are displayed in Figure 4 and show a slight increase of about 0.8 °C.

Figure 2. The study area’s geology and geological section A–B (Dimadis and Zachos [34], modified).

Figure 2. The study area’s geology and geological section A–B (Dimadis and Zachos [34], modified).

In recent years, especially since 2020, low snowfall has been recorded at the higher altitudes of the study area, due to the prolonged decrease in precipitation, and to such a low degree that it does not affect the hydrological regime in the area.

Figure 3. Annual rainfall, minimum, maximum, and mean monthly rainfall values (mm) per year at the Xanthi meteorological station (2009–2023).

Figure 3. Annual rainfall, minimum, maximum, and mean monthly rainfall values (mm) per year at the Xanthi meteorological station (2009–2023).

Figure 4. Mean annual temperature (°C) values and trendline (dotted line) at the meteorological station of Xanthi (2009–2023).

Figure 4. Mean annual temperature (°C) values and trendline (dotted line) at the meteorological station of Xanthi (2009–2023).

2.2. Groundwater Data Collection and Analysis

The research work included the following:

i.

Measurements of groundwater discharge from 47 springs and five wells (in total 52 water points), as well as in situ measurements of pH, electrical conductivity (EC), and temperature (October 2021, April 2022, October 2022, April 2023);

ii.

Sampling of groundwater from the 52 monitoring points;

iii.

Chemical analyses in the Laboratory of Engineering Geology and Groundwater Research of the Department of Civil Engineering, DUTH, examining the following parameters: total hardness, Ca²⁺, Mg²⁺, Na⁺, K⁺, Fe²⁺, NH₄⁺, HCO₃⁻, Cl⁻, SO₄²⁻, NO₃⁻, NO₂⁻;

iv.

Analysis, processing, and presentation of the results produced;

v.

Formulation of recommendations that would improve the state of the water supply in Myki Municipality (Figure 1).

3. Results and Discussion

In situ measurement values of groundwater spring/well discharge, pH (6.02–8.59), EC (71.4–627 μS/cm), and temperature at the study area (9.0–18.8 °C) (October 2021, April 2022, October 2022, April 2023) are presented in

Table 1. Min, max, mean, and standard deviation (SD) of in situ measurement values of springs and wells discharge, pH, electrical conductivity (EC), and temperature.

	Discharge (m3/h)	EC (μS/cm)	Temperature (°C)	pH
October 2021
min	0.16	71.40	12.20	6.02
max	30.00	627.00	18.30	8.27
mean	6.03	299.22	14.40	7.24
SD	7.59	163.18	1.24	0.41
April 2022
min	0.48	78.70	9.00	6.56
max	50.40	598.00	18.80	8.59
mean	7.69	270.03	12.39	7.48
SD	9.54	154.25	1.78	0.43
October 2022
min	0.20	90.00	12.10	6.35
max	30.00	618.00	16.50	8.44
mean	4.73	340.69	13.80	7.37
SD	6.50	151.62	0.99	0.42
April 2023
min	0.42	73.20	11.90	6.59
max	43.29	614.30	16.90	8.22
mean	7.13	300.39	13.53	7.36
SD	8.71	149.07	1.01	0.36

and Figure 5.

The hydrographic network of the study area consists of three main streams in the northern, central, and western parts of the study area with a NW–SE flow direction (Figure 5). The majority of water points (40 points) are located on either side of these streams at short distances. The following details are worth mentioning: (a) nineteen water points with discharge values of 40–50 m³/h are located throughout the study area (four points in the northern part, nine in the central part, and six in the southern part), (b) there are twenty water points with discharge values of 30–40 m³/h (four points in the northern part, eleven in the central part, and five in the western part), (c) a spatial density of water points is observed in the SW part with two points with discharge values of 40–50 m³/h, six points with values of 20–40 m³/h, and four points with values of 0–10 m³/h, (d) the discharge values of the five wells are within the range of 40–50 m³/h.

The results of the chemical analyses are evaluated as follows (

Table 2. Statistical approach regarding the main chemical parameters of groundwater in the study area (SD: standard deviation, CV: coefficient of variation).

	Ca2+	Mg2+	SO42−	HCO3−	NO3−	Cl−	EC	pH	Temp.	Na+	Fe2+	K+	NH4+
	(mg/L)						(μS/cm)		(°C)	(mg/L)
October 2021
min	4.41	0.24	1.00	7.32	0.00	0.00	71.40	6.02	12.20	3.02	0.00	0.00	0.00
max	83.37	53.46	90.00	336.72	41.80	16.67	627.00	8.43	18.30	91.00	0.47	8.00	0.82
mean	36.66	9.33	21.00	144.04	4.35	4.67	299.22	7.11	14.40	12.97	0.07	1.84	0.19
SD	22.79	8.91	17.31	95.97	8.24	4.42	163.18	0.59	1.24	15.95	0.12	1.58	0.17
CV	0.62	0.95	0.82	0.67	1.89	0.95	0.55	0.08	0.09	1.23	1.71	0.86	0.89
April 2022
min	0.32	0.00	1.00	0.98	0.00	0.00	78.70	5.53	9.00	3.34	0.00	0.27	0.00
max	73.75	44.47	60.00	301.34	21.10	21.28	598.00	8.20	18.80	40.00	0.28	8.00	0.80
mean	30.84	8.78	16.67	121.60	2.84	4.79	270.03	7.08	12.39	9.93	0.05	1.70	0.18
SD	19.96	10.85	13.47	86.37	4.28	5.49	154.25	0.51	1.78	8.07	0.07	1.56	0.21
CV	0.65	1.24	0.81	0.71	1.51	1.15	0.57	0.07	0.14	0.81	1.40	0.92	1.17
October 2022
min	4.81	0.00	0.00	6.10	0.00	0.00	90.00	6.35	12.10	3.24	0.00	0.25	0.00
max	87.37	60.75	61.00	326.96	39.30	35.46	618.00	8.44	16.50	56.25	0.60	9.10	0.75
mean	43.67	8.28	19.75	163.69	3.43	5.61	333.02	7.37	13.80	11.11	0.04	1.74	0.11
SD	24.46	10.77	15.64	92.27	6.38	5.69	153.54	0.42	0.99	9.73	0.08	1.77	0.12
CV	0.56	1.30	0.79	0.56	1.86	1.01	0.46	0.06	0.07	0.88	2.00	1.02	1.09
April 2023
min	3.31	0.49	0.67	4.80	0.00	0.35	84.47	5.96	11.90	3.20	0.00	0.17	0.01
max	73.21	52.81	60.33	306.63	34.07	18.56	614.33	8.14	16.90	46.53	0.21	5.78	0.72
mean	37.06	8.80	19.14	143.11	3.54	5.03	300.76	7.17	13.53	11.33	0.05	1.76	0.16
SD	20.50	9.35	13.31	87.27	5.82	4.24	148.54	0.47	1.01	9.81	0.05	1.37	0.14
CV	0.55	1.06	0.70	0.61	1.64	0.84	0.49	0.07	0.07	0.87	1.00	0.78	0.88

, Figure 6, Figure 7 and Figure 8):

–

Values of calcium ions (Ca²⁺) concentration are below the maximum allowable threshold of 100 mg/L (variation of values: 0.32–87.37 mg/L);

–

Values of magnesium ions (Mg²⁺) concentration are below the maximum allowable threshold of 50 mg/L except for samples from point S24 with values of 53.46 mg/L (October 2021), 60.75 mg/L (October 2022), and 52.81 mg/L (April 2022) (variation of values: 0.00–60.75 mg/L);

–

Values of ammonium ions (NH₄⁺) concentration are below the maximum allowable threshold of 0.50 mg/L except for samples from the following points (variation of values: 0.00–0.82 mg/L): S23 with values of 0.52 mg/L (October 2021) and 0.55 mg/L (October 2022); S24 with values of 0.82 mg/L (October 2021), 0.60 mg/L (October 2022), and 0.72 mg/L (April 2023); S27 with a value of 0.58 mg/L (April 2022); W36 with a value of 0.80 mg/L (April 2022); and S37 with a value of 0.53 mg/L (April 2022);

–

Values of iron ions (Fe²⁺) concentration are below the maximum allowable threshold of 0.20 mg/L), except for samples from the following points (variation of values: 0.00–0.60 mg/L): S10 with a value of 0.31 mg/L (October 2021); W21 with a value of 0.28 mg/L (October 2021, April 2022); W22 with a value of 0.22 mg/L (October 2021); S23 with values of 0.26 mg/L (April 2022), 0.60 mg/L (October 2022), and 0.21 mg/L (April 2023); S29 with a value of 0.25 mg/L (October 2021); S30 with a value of 0.40 mg/L (October 2021); S31 with a value of 0.24 mg/L (April 2022); S34 with a value of 0.47 mg/L (October 2021); and S41 with a value of 0.40 mg/L (October 2021);

–

The quality attributes of the other water samples analyzed fall within the acceptable limits as far as it concerns chloride concentrations ions (Cl⁻), nitrate ions (NO₃⁻), nitrite ions (NO₂⁻), sodium ions (Na⁺), potassium ions (K⁺), bicarbonate ions (HCO₃⁻), and sulfate ions (SO₄²⁻) (Table 2).

The groundwater recharging springs and wells originate from surface water which infiltrates through the purely fractured media and fractured porous media mainly, and through porous media rarely. The dominance of HCO₃⁻ reflects the continuous supply from infiltrated water. Changes in the order of cations and anions imply different types of water and may indicate the difference in certain geochemical processes (such as evaporation or water–rock interactions) occurring in different waters. Over the long flow path with increasing time, the chemistry of groundwater tends to change from HCO₃⁻–type water, when entering the underground circulation, to Cl^-–type water with increasing salinity [35]. This is often accompanied by a change in the dominant cation from Ca²⁺ to Na⁺. It would be very interesting to investigate in the next stage of the research the subsurface connectivity and streamflow hydrological relationship according to Zuecco et al. [36], Schiavo [37], and Schiavo et al. [38].

The weathering of Ca-silicate and Na-silicate minerals shapes the chemical composition of the waters. This weathering probably concerns minerals of the sandy cement materials of the fractured zones under a short stay time of water because of increasing hydraulic conductivity. The high values in the concentrations of the Mg²⁺ ions are related to the composition of the ultrabasic rocks (amphivolite) in which the springs are located. The pronounced seasonal variability (CV > 1) in the gram equivalent concentrations of Fe, PO₄³⁻, NO₂⁻, and NH₄⁺ ions suggests an increased contribution of biogenic processes—such as the nitrogen cycle and chemosynthesis—to the chemical composition of the water (Figure 9).

The decrease in the discharge of springs is related to the increase in the residence time of water in the rocks and is temporally correlated with the decrease in the amount of rainfall in 2022 and 2023. The increase in residence time is reflected in the value of the CV (>1) of the distribution of SO₄²⁻ ion concentration values of the April 2022 and April 2023 samplings, which correspond to the end of the wet season of the year.

According to the Piper diagram [39] in Figure 10a, the water samples from the springs belong to the magnesium-carbonate type. The samples from spring S14 of the second period belong to the mixed type. An increase is observed for spring S7 in the second sampling period, with an increase in the Na⁺ concentration and the formation of sodium-carbonate-type water (Figure 10a). All springs appear to be recharged by rainwater except for spring S14 in the second period, in whose sample the increased Cl⁻ concentration indicates potential recharge with water with a long flowing path through the rocks (Figure 10b).

As shown in Figure 11, in the April sampling periods, the Cl⁻ concentration values are higher in the area of the highest HCO₃⁻ and SO₄²⁻ concentration values. In the October sampling periods (which mark the end of the dry season), the highest Cl⁻ concentration values are shifted to the area of the highest HCO₃⁻ and SO₄²⁻ concentration values in 2022 compared to the values of 2021, where the maximum Cl^- concentration values are located in the zone of the average SO₄²⁻ concentration values. The comparative distributions of the anion values express the increase in the participation of water with a long residence time in the groundwater system. Taking into account that in the corresponding period there is a decrease in the amount of precipitation, it can be considered that in the 2022 period the renewal of the recharge of the springs was not achieved.

The modified Gibbs diagram of Figure 12a presents the evolution of groundwater quality based on the placement of the data in the diagram as rainwater infiltration and the dissolution of carbonate and silicate minerals. The dissolution of silicate minerals was the dominant process contributing the main ions to the groundwater, which is demonstrated in Figure 12b,c. The water of springs SΥ6, SY18, SY19, SY25, SY27, SY28, SY44, SY48, SY49, and SY51 reflects the dissolution of carbonate minerals. Considering the research area’s lithological structure, the interaction of water with igneous rocks, which include Na-silicate and Ca-silicate minerals, mainly shapes the hydrochemical character. At the same time, these rocks host areas for the recharge of the springs. The very low hydraulic conductivity values of these rocks results in an increase in the residence time of water with a decrease in the discharge of springs and difficulty in recharging from surface water. Springs, where the dissolution of carbonate minerals dominates, are located in areas of volcanic rocks and marbles. These rocks present higher values of hydraulic conductivity with greater spring discharge values but have a very small surface area resulting in a reduced capacity for recharging from surface water.

The potential of meeting the demands for water consumption was studied while evaluating the measured water supply values of the springs and wells in the research area according to the benchmark value of 250 L/capita/day according to the relevant Greek legislation (Official Gazette 174/B′/26-3-1991).

A grouping of groundwater discharge values for each settlement in the study area (in L/capita/day) and the values of surplus [+] (green color) or deficit [−-] (red color) supply relative to the value of 250 L/capita/day are shown in

Table 3. Total values of groundwater discharge per settlement (L/capita/day) and surplus [+] (green color) or deficit [−-] (red color) supply values in relation to 250 L/capita/day (October 2021 and April 2022).

		October 2021		April 2022
Settlement	Springs (S) and Wells (W)	Discharge (L/d/Resident)	Total Discharge per Settlement (L/Capita/Day)	Discharge (L/d/Resident)	Total Discharge per Settlement (L/Capita/Day)
Diasparto	S1	381.43	+350.00	683.57	+748.57
Diasparto	S2	107.14		192.86
Diasparto	S3	111.43		122.14
Ano Thermes	S4	474.95	+224.95	919.63	+669.63
Meses Thermes	S5	2582.17	+2332.17	2530.12	+2280.12
Kato Thermes	S6	1349.22	+1099.22	1432.54	+1182.54
Kidari	S7	288.98	+788.37	1665.31	+3521.43
Kidari	S8	749.39		2106.12
Loutra	S9	46,320.00	+46,070.00	92,640.00	+92,390.00
Medousa	S10	325.66	+145.11	565.66	+578.04
Medousa	S11	69.45		262.38
Kottani	S12	89.30	−160.70	396.28	+146.28
Dimario	S13	463.29	+1475.57	546.84	+2448.86
Dimario	S14	1103.54		1913.92
Dimario	S15	158.73		238.10
Kotyli	W16	936.84	+1523.16	936.84	+1588.95
Kotyli	S17	836.32		902.11
Aimonio	S18	312.00	+167.60	1032.00	+908.40
Aimonio	S19	105.60		126.40
Melivia	S20	500.00	+250.00	763.27	+513.27
Echinos	W21	162.09	+74.18	162.09	+74.18
Echinos	W22	162.09		162.09
Giannochori	S23	1015.38	+765.38	1661.54	+1411.54
Kalotycho	S24	384.00	+134.00	640.00	+390.00
Temenos	W25	995.85	+840.46	995.85	+894.23
Temenos	S26	94.61		148.38
Satres	S27	28.80	−145.20	129.60	−32.40
Satres	S28	76.00		88.00
Pachni	S29	232.31	+154.90	364.50	+242.96
Pachni	S30	172.59		128.45
Glafki	S31	168.06	−81.94	365.79	+115.79
Kentavros	S32	3.94	−220.53	6.23	−232.36
Kentavros	S33	25.53		11.41
Achladia	S34	8208.00	7958.00	12,336.00	+12,086.00
Myki	S35	103.67	−146.33	289.32	+39.32
Sminthi	W36	1983.47	+1733.47	1983.47	+1733.47
Theotokos	S39	2632.26	+2986.13	22,141.94	+28,472.58
Theotokos	S40	603.87		6580.65
Oraion	S37	735.38	+545.21	174.48	−18.02
Oraion	S41	18.38		31.09
Oraion	S42	41.45		26.41
Kyknos	S43	118.55	−131.45	118.55	−131.45
Oasi	S44	119.07	−130.93	323.72	+73.72
Kirra	S45	967.06	+717.06	1327.06	+1077.06
Kotino	S46	100.84	−36.22	629.24	+548.66
Kotino	S47	112.94		169.41
Chysosminthi	S48	118.94	−131.06	273.98	+23.98
Alma	S49	66.62	−183.38	84.79	−165.21
Trigono	S50	286.03	+36.03	302.47	+52.47
Siroko	S51	62.70	−187.30	214.05	−35.95
Rema	S38	2105.90	+4353.01	66.59	+926.42
Rema	S52	2497.11		1109.83

and

Table 4. Total values of groundwater discharge per settlement (L/capita/day) and surplus [+] (green color) or deficit [−-] (red color) supply values in relation to 250 L/capita/day (October 2022 and April 2023).

		October 2022		April 2023
Settlement	Springs (S) and Wells (W)	Discharge (L/d/Resident)	Total Discharge per Settlement (L/Capita/Day)	Discharge (L/d/Resident)	Total Discharge per Settlement (L/Capita/Day)
Diasparto	S1	323.57	+296.43	582.86	+615.71
Diasparto	S2	117.86		164.29
Diasparto	S3	105.00		118.57
Ano Thermes	S4	780.56	+530.56	771.40	+521.40
Meses Thermes	S5	462.65	+212.65	2547.47	+2297.47
Kato Thermes	S6	691.40	+441.40	1404.77	+1154.77
Kidari	S7	97.96	+514.08	1206.53	+2610.41
Kidari	S8	666.12		1653.88
Loutra	S9	46,320.00	+46,070.00	77,200.00	+76,950.00
Medousa	S10	283.22	+164.41	485.66	+433.73
Medousa	S11	131.19		198.07
Kottani	S12	128.37	−122.00	293.95	+43.95
Dimario	S13	455.70	+1206.71	518.99	+2124.43
Dimario	S14	773.16		1643.80
Dimario	S15	227.85		211.65
Kotyli	W16	936.84	+928.95	936.84	+1567.02
Kotyli	S17	242.11		880.18
Aimonio	S18	721.60	+503.60	792.00	+661.47
Aimonio	S19	32.00		119.47
Melivia	S20	454.29	+204.29	675.51	+425.51
Echinos	W21	162.09	+74.18	162.09	+74.18
Echinos	W22	162.09		162.09
Giannochori	S23	516.92	+266.92	1446.15	+1196.15
Kalotycho	S24	360.00	+110.00	554.67	+304.67
Temenos	W25	995.85	+820.54	995.85	+876.31
Temenos	S26	74.69		130.46
Satres	S27	35.20	−176.40	96.00	−70.00
Satres	S28	38.40		84.00
Pachni	S29	294.24	+103.52	320.44	+213.60
Pachni	S30	59.29		143.17
Glafki	S31	175.78	−74.22	299.88	+49.88
Kentavros	S32	4.25	−237.13	5.46	−228.42
Kentavros	S33	8.61		16.12
Achladia	S34	4128.00	+3878.00	10,960.00	+10,710.00
Myki	S35	97.32	−152.68	227.43	−22.57
Sminthi	W36	1983.47	+1733.47	1983.47	+1733.47
Theotokos	S39	101,41.94	+15,977.10	20,438.71	+28,493.23
Theotokos	S40	6085.16		8304.52
Oraion	S37	21.73	−199.86	154.21	−42.65
Oraion	S41	15.71		29.42
Oraion	S42	12.70		23.73
Kyknos	S43	109.88	−140.12	118.88	−131.12
Oasi	S44	163.72	−86.28	292.09	+42.09
Kirra	S45	515.29	+265.29	1035.29	+785.29
Kotino	S46	231.93	+66.64	511.60	+408.15
Kotino	S47	84.71		146.55
Chysosminthi	S48	127.43	−122.57	222.30	−27.70
Alma	S49	39.37	−210.63	70.66	−179.34
Trigono	S50	164.38	−85.62	298.08	+48.08
Siroko	S51	64.86	−185.14	205.41	−44.59
Rema	S38	31.91	+44.10	57.80	+1380.06
Rema	S52	262.20		1572.25

, considering spring and well discharge measurements and the population of each settlement from the 2021 census.

More specifically, Table 3 and Table 4 concern the groundwater discharge values (in L/capita/day) for the various settlements in two time periods, October 2021 and April 2022, and October 2022 and April 2023, respectively. The tables include the discharge values measured from springs (S) and wells (W), the total discharge for each settlement, and the difference from the reference supply quantity (250 L/capita/day). This difference is displayed as a “surplus” [+] (green color) or “deficit” [−-] (red color) in relation to the reference value. The calculation of the total discharge per settlement is calculated as follows: for each spring/well, a discharge value has been measured and is presented in the table in L/capita/day. The total discharge per settlement is obtained as the sum of the discharge values measured at the water points (spring/well) located in the settlement. For example, in Table 3, in the Diasparto settlement, discharge at springs S1, S2, and S3 were measured in October 2021, with measured values of 381.43, 107.14, and 111.43 L/capita/day, respectively, and with a total amount of 600.00 L/capita/day. The surplus or deficit results from subtracting the limit of 250 L/capita/day from the total flow. It is clear that in the Diasparto settlement, in October 2021, there was a water surplus with a value of +350 L/capita/day (600.00–250.00 L/capita/day).

Surpluses in green are visible in some settlements that have significant water reserves. For example, in Table 3, in the Loutra settlement (S9), discharge values of 46,320 L/capita/day in 2021 and 92,640 L/capita/day in 2022 are noted, much higher than 250 L/capita/day. Similarly, in the Theotokos settlement (S39, S40), the discharge values are 2986.13 L/capita/day in October 2021 and 28,472.58 L/capita/day in April 2022, indicating a significant surplus in water supply. Conversely, water deficits in red are present in several settlements in relation to the limit of 250 L/capita/day. For example, in the Kentavros settlement (S32, S33), a serious deficit is shown with values of −220.53 L/capita/day in October 2021 and −232.36 L/capita/day in April 2022. Also, in the Myki settlement (S35), a value of −146.33 L/capita/day in October 2021 was recorded, although this was partially counterbalanced in April 2022 with a positive difference of +39.32 L/capita/day. The settlement of Rema (S38, S52) shows water supply surpluses, with a significant increase in 2022, with 4353.01 L/capita/day in October 2021 and 926.42 L/capita/day in April 2022. In the Satron settlement (S27, S28) a deficit was presented in October 2021 (−145.20 L/capita/day), but the second half of the year showed small improvements (−32.40 L/capita/day).

The table provides useful data for monitoring water availability at the settlement level. Settlements with surpluses may utilize large reserves to ensure adequacy, while settlements with deficits may need water supply network reinforcement or external water sources. The data in the table lead to the conclusion that the western part of the Municipality of Myki does not face serious water shortage problems as occurs in the eastern part, mainly during the summer months.

It is worth mentioning that not all the springs under investigation are discharged into tanks for water supply and that some of them give water to a small number of communities beyond the study area.

According to the findings of the chemical analysis of the samples taken from the 52 water points, these samples can be defined from a hydrochemical perspective, in the first stage, as suitable for water supply. Yet, it was found that there is not enough drinking water to meet Myki Municipality’s water needs. Aquifer capacity limitations in some locations, inadequate groundwater recovery facilities, and water losses in the water supply system are all contributing factors to the apparent water deficit.

Due to the necessary expensive improvements, the water shortage issue in Myki Municipality has persisted for many years. The potential of any of these springs and wells to supply water to more than one settlement has been substantially investigated. The results of the investigation demonstrated that, because of their large discharge values, 17 springs and all five wells (Table 3 and Table 4, data in green) may provide drinking water to several settlements.

4. Conclusions

The available water resources to meet the water needs of the Myki Municipality are partly inadequate according to the findings of the appropriate calculations shown in Table 3 and Table 4. The total discharge per settlement values (L/capita/day) in seven (7) settlements during October 2021 and October 2022 (20.6%), and eleven (11) settlements during April 2022 and April 2023 (32.3%) of all thirty-four (34) settlements exhibit deficient [−] supply values in relation to the reference value of 250 L/capita/day, with values ranging from 18.02 to 232.36 L/capita/day. In some cases, reduced performance could be considered acceptable. Also, with respect to water-saving approaches, some areas with excess consumption could consider saving and/or reducing their performance.

Water losses in the water supply system, some inadequate groundwater recovery facilities, and the restricted capacity of aquifers in some areas are all responsible for the apparent water scarcity. The central and southern parts of the research area are most affected by these shortages, although springs in the northern part could be used for supplying water to the various settlements.

The procedures that follow are suggested in order to prevent serious issues with water shortages and water-quality degradation and to improve and modernize the current water infrastructures in the study area:

–

Construction of projects to protect the narrow spaces of the springs;

–

Protection of the water supply system;

–

Gathering of separate springs inside a central network of springs;

–

Design and construction of new groundwater recovery systems at selected spring locations;

–

Inclusion of springs in the existing water supply network after relevant preparation;

–

Design and construction of suitable reservoirs as well as drilling wells in selected locations that will reinforce the existing water supply network;

–

Serious improvement of the road network to facilitate transport connections between settlements, water points, and relevant infrastructures;

–

Provision of measures and implementation of appropriate actions and arrangements to ensure, over time, a minimum environmental flow in parts of the research area, which is possible to achieve.