Mapping the Ground Water Vulnerability of the Vjose ... - balwois

BALWOIS 2012 - Ohrid, Republic of Macedonia - 28 May, 2 June 2012 1

Mapping the Ground Water Vulnerability of the Vjose-Shushice Quaternary Aquifer Using the SINTACS Method.

Elsa Dindi

Polytechnic University of Tirana, Faculty of Geology and Mining, Tirana, Albania [email protected]

Abstract The Vjosë-Shushicë Quaternary aquifer lies on the Western Lowland of Albania, which contains alluvial plain conditioned from the Pliocene-Quaternary tectonic movements and river activity. Situated in this area are important confined and unconfined gravel aquifers. In relation to their quantity and quality, the ground waters serve as a very important resource of drinking water supply for cities and tourist activities in the western part of Albania. Based on the SINTACS parametric system (point count system models), the vulnerability of ground waters of the Vjose-Shushice area is evaluated by analyzing the representative parameters of the chemical composition, the human activity, as well as the geologic and hydrogeologic context. Based on the socio-economic analyze of the studied area, the normal line of weights are selected based upon the SINTACS system. This article aims modestly to suggest the importance of ground water vulnerability on policies of protection and management of ground waters in the Quaternary aquifer Vjose-Shushice. Key words: Western Lowland; Vjose-Shushice Quaternary aquifer, vulnerability of ground waters. Introduction The Vjose-Shushice region plays an important role in the economic longevity of the country because of its rich natural resources, geographic location, population density, and industrial development of its agriculture. Concentrated in this region are large centers of oil and gas extraction and processing industries, chemical, food and building material industries. Most important is also its role in road and rail transit due to the intersection of main land and sea transport routes. Vjosa-Shushica River aquifers are very important water resources in Albania. These resources must be exploited rationally in concordance with the development plans of the region. This article aims modestly to suggest the importance of ground water vulnerability on policies of protection and management of ground waters in the Quaternary aquifer Vjose-Shushice. Groundwater vulnerability maps belong to environmental maps and are used for groundwater protection planning, decision making and management (16). Organization that might benefit from the vulnerability mapping of Vjosa-Shushica quaternary aquifers are local and central government. Physico-geographical data The Vjosa-Shushica River aquifer is the largest confined and unconfined aquifer of the Western Lowland. It is build from rocks of good permeability, has suitable climatic conditions, dense hydrographic network, and flat terrain. This facilities richness in its groundwaters. The study area is included in the Central sub zone of the Mediterranean Field Climatic Zone. Soft and wet winters and hot and dry summers are the main characteristics of this sub zone. The climate of the Albanian coastal plain is highly influenced by the Adriatic Sea. This influence can be seen in the absolute


minimum, maximum and average air temperature. The average annual temperature is 15.5°C. Rainfalls reach an annual average from 912mm (Vjosa field) to 994mm (Vjosa and Shushica Rivers valleys)(10). Socio-Economic analysis of the study region The study region plays an important role in the economic longevity of the country because of its rich natural resources, gegraphical location (fig.1), population density and the development of its agriculture industry. Favorable climate, good arable land and proximity to the sea and the national Fier-Vlore route, have created a habitat relatively more populated than the average population of the country. On this perspective, the oil and gas extraction and processing industry has had an effect as well, which, due to spatial expansion of these facilities has resulted in the employmeny of a large number of residents in villages around this area. Economic activity of these region’s villages is related to many of its natural riches which consists of arable land, pastures, forests, sea, beaches, waterways and other assets, oil and gas reserves, etc. The main economic activity is agriculture, which is favored by the large areas of agricultural lands, climate and freshwater reserves. However, villages located nearby the coast, have a portion of their agricultural land consisting of higher salt content which limits agricultural production. The hilly areas are mainly cultivated by olive trees and vineyards (9, 17). Geologic and hydrogeologic settings The study region belongs to the Western Lowland, filled with Neogene deposits of the Miocene and Pliocene age (fig.1). Above the later are Quaternary desposits which lie along the valley and alluvial field of Vjosa. In the upper part they are represented by subclayey sandy covers, while at the bottom by gravel. The thickness of gravel and sands changes from a few meters southeast of this depression to tens of meters northwest (fig.2).

Figure 1. Study area (according to the hydrogeological map of Albania, sc. 1:200 000, Eftimi et al, 1985).

(Qh: Holocene; Qph: Pleistocene-Holocene; N2h: Lower Pliocene; Helmesi unit; N2

r: Middle Pliocene, Rrogozhina unit)


Figure 2. Sketch of the geological cros section of the study area (P : West, L : East)

According to lithological stratigraphical and hydrogelogical criteria, are distinguished the following waterbearing complexes: -Waterbearing complex of molassic desposits; and -Waterbearing complex of loose deposits (fig.2). Based upon the lithological composition, Quaternary deposits in the study area can be divided into three groups.: -Groudwater of gravelly deposits (which have practical importance); -Groundwater of coastal sands; and -Groundwater of subclayey sandy cover (7).

Figure 3. Map of the depth of the gravels

Gravel dep[osts are characterized by permeability and high waterbearing level, which has significant practicality for the study region and constitutes the object of study. The characteristics of the aquifer in the study area are as follows: -The depth of the waterbearing layer, in Vjosa River valley, along the Hekali field toward Adbunace, varies from 0.0m (near the river bed), up to 4.0m-5.0m from the surfice. Gravel depth capture varies from 5-15m southeast of the study area, up to 60m northwest of it (fig.3); -Thickness of the gravel aquifer rises east to west (about 30-40m). Going to south and to north direction the thickness reduces. In proximity to Vjosa River with the Shushica River confluence, the thickness of the gravel layer reaches up to 110m. While on the valley side, where it goes into contact with sandstones and conglomerates of the Rrogozhina unit deposits, it decreases up to 5-10m;


-In the area of Novosela, Ferrasi and Vjosa River valley, gravels are heterogeneous with predominance of coarse particle size and less with medium particle size. Sand is found in small quantaties (about 5%) and uniformly distributed in the gravel deposisits. Sand content rises above 15% westward; (fig.3,4) -Recharge area and unconfined aquifer lie on gravelly Shushica and Vjosa bed rivers up to the village of Ada; -In the valley of Vjosa River, along the Hekali field in Adbunace, the freatic water levels are at 2.0m depth up to 5.5m from the surface; -The aquifer becomes confined near the villages of Bishan, Ferras, and Novosel ,because the thickness of the aquifer top cover increases ; -Areas of confined aquifer (artesian) lie in the western parts of the aquifer, in the Field of Vjosa River, with difficult movement conditions of groundwater flow; -Possible directions of groundwater flow of Vjosa River aquifer are: principal direction in the southeaset-northwest, other directions by south and north (in the Vjosa field);(fig.4) -The aquifer of Shushica River is primarily without pressure, movement of groundwater flow follows the flow of the Shushica river, while the Vjosa River aquifer serves as a drainage area (fig. 4), (3, 5, 6, 8).

Figure 4. Hydrogeological map of the study area

Figure 5. Map of hydraulic conductivity (5)


Methodology

SINTACS methods of groundwater vulnerability mapping takes into account hydrogeological, geological, and socioeconomic factors affecting chemical composition of groundwater. It is classified at point count system models and takes into consideration seven parameters: Soggiaceza -depth to water table. Infiltrazione efficace- net recharge. Non saturo (effetto di autodepurazione del)- unsaturated zone. Tipologia della copertura- soil media. Acquifero (caractteristiche idrogeologiche del)- aquifer media. Conducibilita idraulica del acquifero- hydrogeological conductivity. Superficie topografica (acclivita’ della)- topographic surface. Each parameter is multiplied by a weighing coefficient, which in itself expresses the relationship between parameters and their importance in the assessment of groundwater vulnerability. For each parameter a range of values is given divided into discrete intervals. Each interval is given a value which reflects the relative degree of vulnerability. Value for each interval is multiplied by the weigh of each parameter, and the products are collected by taking the final amount of points which, as noted, are expressed in relative degree of vulnerability of a polygon to another. The higher the points, the sensible, to contaminants are the groundwater system. Vulnerability index is calculated for each elementary cell: Where Wj-relative weights of selected line, Pj-parameters points (tab.1). Thus the interval of values of vulnerability index for each cell ranges 26-260 points. Degree of vulnerability is normalized and crosses in the visualized graphic of the vulnerability map, based on the international legend (1, 2, 18).

Table 1 Line of weights Parameter Normal impact High impact Drainage

S 5 5 4 I 4 5 4 N 5 4 4 T 4 5 2 A 3 3 5 C 3 3 5 S 2 2 2

The study area is divided into cells of 500 x 500 m. While necessary reports are extracted from internal reports of the Albanian Geological Survey (AGS): -are collected and interpreted field data on stratigraphy; -hydrogeological wells at any depth (and private ones), on the basis of which are built all possible combinations of geological profiles; -data-sampling for analysis of particle size at different depths, including saturated zones; -pedologic profiles; -sedimentologic data analysis; -pumping tests data; -level data using the data of ground water monitoring project (AGS) till 2009 also are used water level data collected on third drainage system and wells in villages; and -map of geologic engineering zoning (unpublished) (Polytechnic University, Tirana).


Mapping vulnerability “S” depth to water table is in inverse proportion to the natural vulnerability. SINTACS points reduce with increasing depth of water table level, of the aquifer, according to a hyperbolic type of declining performance. Values start from 10 for all cases where the water table level is on the ground surface such as in the cases of recharge areas with asymptotically tendencies leading toward the value of 1 for greater than 60m depths(1, 18). Data on water levels in hydrogeological wells are powered by hydrogeological monitoring projects (2009, Albanian Geological Survey). Taken under consideration are also data on water level of private wells in villages, as well as in drainage channels of the third level. In the valley of Vjosa and Shushica River the aquifer is unconfined. Depths of groundwater table in these areas vary generally from 0.0-0.5m up to 20m. In the Field of Vjosa River aquifer, where the aquifer is confined (artesian) for the depth of the gravel aquifer, larger than 30m, the phenomenon of inverse leakage takes place. Taking under consideration this fact, corrections have been made and rates are 1(6, 4,) (fig. 8). “I” net recharge describes the infiltration. The main source of recharge from the infiltration is precipitation. Basic information, necessary for its assessment, is obtained from a series of continuous data (50 years), registered from the Institute of Hydrometeorology. As part of the Western Lowland, the assessment of infiltration is made through the traditional method of calculating the elements of balance. It is mainly distributed as follows: -10% of precipitation infiltrates, percolating underground waters; while, -90% are for evapotranspiration and surface run off (10). Based on these models, infiltration values of Vjosa River aquifer and Shushica River aquifer, consist of 87mm/year and 92mm/year respectively (averages for all over the areas). According to SINTACS methods, in the case when the cover has considerable thickness, the full value of precipitation is used for each cell P, without considering evapotranspiration. While specific infiltration is I = P *χ mm/year. The coefficient of potential infiltration χ (tab.2) is a function of thickness and lithological composition of geological formations which are exposed on the surface as well as slope of topographical surface. This parameter is corrected as well for thickness of the water table level, land usage, etc (1, 2, 6).

Table 2. Potential infiltration depending on the coverage type Type of top cover Potential infiltration

χ sub clay 0,10 sub sand 0,15 sand 0,40

In the recharge areas, without sub clayey cover or with sub clayey cover thinner than 1.0m, for the parameter “I”. is given the highest rate 10. In the western part of the aquifer due to the composition and large thickness of the cover and artesian character of groundwater, recharge aquifer impact is practically inexistent, therefore parameter “I” is given a value of 0 (fig. 9). “N” The unsaturated media is the second obstacle for the pollution to get in the aquifer media (the first is soil media), where physical and chemical factors take part. The texture of the unsaturated media determines the time of travel of a contaminant.


In order to create a conceptual model of the hydrogeological system of the unsaturated zone, first hand importance is given to the stratigraphy observed directly. Then, the data is compared with information from the same cell. When necessary, they were interpolated with cell and/or neighboring wells data as well. In determining lithotypes, the geologic engineering zoning is taken under consideration (fig.6) (12, 13).

Table 3. Lithotypes of the unsaturated zone and SINTACS ratings

Figure 6. Map of geologic engineering zoning

Based on the above analysis and on all available data, the construction of the relative stratigraphic column was made possible for each elementary cell of the discrete zone with the definition of the present lithotype thickness. For each elementary cell, according to the lithology of the unsaturated zone, the value

of parameter “N” was defined utilizing the weighted average calculation. hPh

N ii∑= )*(

Where: Pi-sintacs points for each lithotype; hi-thickness of each lithotype; h-thickness of unsaturated zone of recharge area. The rates of this parameter range from 10 to recharge area, to the lowest values in the western part of the study region (tab.3, fig. 10).

Lithotype Ratings Clay 1 Loam 2 Subclay 6 Subsand 6,5 Sand 7 Gravel&sand 8 Without topcover

10


“T” Soil media is the first barrier that the pollution is faced with. A large number of physico-chemical analysis have been effectuated in the study area from the Institute of Land Study. These analysis, realized under the special project context, are synthesized in the Peodological and Land Classification Map (world Reference Base for Soil Resources), (fig.7, fig. 11), (15, 19).

Figure 7. Peodological and Land Classification Map (World Reference Base for Soil Resources)

“A”- Aquifer media. Aquifer media refers to the grade of the consolidation of the aquifer. The larger and more homogenious the granular size of gravels higher is the permeability. The rating is based on the sorting and amount of fine material within the aquifer such as sand (3, 5, 6). Within the same layer, dependent on analyzed conditions, potential changes of groudwater vulnerability are observed. In accordance with the methodology used, the rating system of this study ranges from 9 for gravel to 6 for sand (fig. 12). “C”- Conductivity. Hydraulic conductivity controls the rate at which the water flows through the porous media. The higher is the conductivity the higher the vulnerability of the aquifer. Based on experimental data of the hydraulic conductivity as well as those extracted from the permeability map, assessment of the possible real values of the hydraulic conductivity is effectuated (5, 6,8). For permeability > 4000m2/day, the ratings of parameter “C” is 9, and for permeability <4000m2/day, this value is 8 (fig. 13). “S”- Topographic surface slope refers to the slope of land surface. The terrain slope map of the study area is based on the topographic surface slope of each elementary cell. Topography controls if the pollutant will run away or will infiltrate underground. The study area is located largely on field terrain, with the exception of a few elementary cells with slight slope. By classifying the entire study region at a slope of 2-3%, the evaluation of parameter “S” (topographic surface slope) according to the SINTACS classification is at 9 points (fig. 14).


Figure 8. Depth of water table, and SINTACS ratings

Figure 9. Map of net recharge

Range Ratings 0-5 9 5-10 7 10-20 4 20-30 2,5 >30 1


Figure 10. Map of unsaturated zone

Figure 11. Map of Soil media, and SINTACS ratings

Soil type Symbol Texture SINTACS ratings

Haplic Calcisol

CLha Sandy-Clay-Loam

5

Eutric fluvisol

FLeu Loam 5

Calcaric Cambisol

CMca Loam 4,5

Calcaric Fluvisol

FLca Loam 4,5

Gleyic Cambisol

Cmgl Sandy-Loam

5

Gleyc Fluvisol

FLgl Sandy-Clay-Loam

5

Haplic Gleysol

GLha Sandy-Clay-Loam

5

Gleyic soloncac

SCgl clay 1


Figure 12. Map of Aquifer media, and SINTACS ratings

Figure 13. Map of Hydraulic conductivity, and SINTACS ratings

Lythotype of saturated zone

Ratings

Gravel 9 Gravel, 15% sands 8 Gravel > 15% sands

7

Sands 6

Hydraulic conductivity (m/s)

Ratings

5*10-3 - 1*10-3 9 1*10-3 - 6*10-4 8


Figure 14. Map of Topographic surface slope

Figure 15. Groundwater vulnerability Map


Results and discussion In order to describe the hydrogeologic conditions and their impact is taken into account a range of factors such as topographical gradient, unsaturated zone, saturated zone, etc., as well as human impact. Human impact in the study region, on the perception of land use, is not very intensive. Considerable area is covered by spontaneous vegetation or barren agricultural land. A portion is comprised of agricultural land, in which the use of fertilizers and pesticides is limited in small quantities. There are no large concentrations of live stokes in these areas. Based on the previously mentioned scale of territorial usage, deemed reasonable, for all of the study area, is the use of the line of weight of normal impact (fig. 15). According to the SINTACS method, based on the index of vulnerability (normalized), there are 5 the classes of vulnerability: low, moderate, high, very high, and extremely high. The recharge areas located to Vjosa and Shushica Valley River are of extremely to very high vulnerable. The other part of aquifer mainly freatic the groundwater vulnerability is high. Going to northern western and southern part to Ferras, Novosele and Cerven, the vulnerability degree of underground waters is high to medium. As a main reasons are: the aquifer becomes confined, the thickness of the top cover increase, and granular size and heterogeneity of the aquifer. The largest reduction of the groundwater vulnerability scale is observed in the western direction of the study region because of a considerable number of factors such as changes in hydrodynamic conditions, increasing cover thickness, reduction in infiltration values, etc, (3). Conclusions The groundwater vulnerability of Vjosa–Shushica quaternary gravel aquifer is assessed using SINTACS methhod.This method take into consideration seven parameters: depth to water, net recharge, unsaturated zone, soil media, aquifer media, hydrogeological conductivity and topographic surface. The vulnerability parameters are classified to range and ratings. Second of the socio-economic analyses of the studied area is selected the line of normal weights and computed the index of vulnerability for each sell. The resultant vulnerability map shows the areas of different vulnerability degree in the same aquifer with different hidrogeological conditions in spatial extension. Groundwater vulnerability maps do not consider the chemical nature of the pollutant in assessing vulnerability. The maps concern only the hydrogeologic settings that make the groundwater susceptible to contamination from surface sources (18). Based on geologic-hydrogeological settings; the data gathered on the local and national usage of the ground waters and the land use; and the vulnerability of ground waters, there are defining the following areas:

-belonging to extremely - high vulnerability areas; -contributing to well yield or pumping stations (capture zone); -with high exploitable and potential resources; and -the recharge areas.

Accurate analysis and research, as well as implementation of rational and long-term policies, is dependent to a considerable extent by the study and assessment of quantity and quality groundwater, use of appropriate vulnerability models, their verification and accuracy, as well as the interaction of economic aspects of sustainable use of these waters along with all of the territories in which these policies are developed (3, 11, 14).


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Mapping the Ground Water Vulnerability of the Vjose ... - balwois

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