VULNERABILITY MAPPING OF CUBAN KARST AQUIFERS USING THE EPIK METHOD

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1 VULNERABILITY MAPPING OF CUBAN KARST AQUIFERS USING THE EPIK METHOD Sebastian Pera Ibarguren(1), Rosa Maria Valcarce Ortega(2) y Willy Rodriguez Miranda(2) (1) Istituto Scienze della Terra, Suiza, CP Canobbio, (2) Instituto Superior Politecnico José Antonio Echeverría, Cuba, 114 no La Habana. Abstract The EPIK method for groundwater vulnerability assessment of karst aquifers (SAEFL, 1998, Doerfligher, et. Al., 1999), was applied to hydrogeological basins containing up to 75% of fresh water resources from La Habana province. By assessing the four required parameters in an appropriated spaced grid a groundwater vulnerability map was produced. According with the results, in Almendares - Vento and Mamposton basins, vulnerability areas are constituted mainly by the poljes bottom with moderate soil cover as well as outcrops, quarries and dolines. High vulnerability areas correspond to zones lacking of karst features having some soil cover. The presence of moderate vulnerability areas is very limited. In Habana Southern Basin, very high vulnerability areas are linked with dolines fields and infiltrating rivers and associated alluvial plains. High vulnerability areas are associated with zones lacking of karst characteristics and with moderate soil cover. Moderate vulnerability areas are associated with the lack of karst characteristics the presence of a thick soil cover and diffuse infiltration. The method is straightforward, required information can be easily found, and has proven to be a inexpensive option to map vulnerability of karst aquifers in Cuba. INTRODUCTION Water resources are vitally important for the future of mankind. Growing population and economic development, needs water for cities, industries and agriculture. Intensifying pressure on water resources and leading to tensions and conflicts among users. At global level, Karst water resources satisfy almost 25 % of water demand (Zwahlen, 2003). In Cuba Karst terrains represents the 66% of the territory by surface and contains 80% of its groundwater resources (Molerio Leon and Parise, 2007), that fulfill 31% of Cuba s water demand (CITMA, 2001). Karst aquifers due to its characteristics could be extremely vulnerable to pollution and once polluted quality restoration is difficult often impossible, and may have negative social and/or economic consequences. As in most of the Caribbean economy in Cuba was based traditionally in agriculture, however in the last decades light industry, oil exploration, mining and tourism are rising in importance. At the same time a phenomenon of population concentration in the country s capital and main cities is observed since the 1960 s. As a result of the changes in economy and human geography, new and old threatens to drinking water resources are developing. Just to mention some of them: Farm waste, domestic sewage, uncontrolled domestic and industrial waste dumps, oil pipelines, fertilizer and biocides, saline intrusion due to overexploitation in coastal areas. Geological, geographical and economic framework of the country defines, the environmental problems that should be managed for an adequate protection of groundwater quality (Molerio Leon and Parise, 2007). Assessing the intrinsic vulnerability of groundwater resources is then a key aspect to manage them in a sustainable manner. Memorias en CD-Rom, La Habana, 4 al 8 de abril de ISBN

2 Figure 1. Study area The study area is located accross La Habana Province (figure 1) southeast form La Habana city. According with Gutierrez and Rivero ( 1999), geographically speaking, belongs to Bejucal - Madruga - Coliseo heights and the Habana Matanzas Red Plain also called Habana Matanzas Southern Plain. Two structural levels have been recognized in Habana Province according with studies from several authors (De Albear e Iturralde 1985a, 1985b, Iturralde, 1996 y García et al. 2001), The folded belt and the Neogenic Platform. In the study area the folded belt is constituted by lifted blocks corresponding to El Cangre unit, Capdevila, Añil and La Charca formations, that constitute the hilly areas. The Neogenic platform instead form Miocene, is represented by Colon Fm constituted by organogenic limestones with 80 meters thickness, Cojimar fm, constituted by marns, occasionally calcareous, organogenic, clayish with a thickness of 100 meters and Guines fm constituted by several limestones types, from organogenic to detritic with a thickness of 240 meters. Formations for from the Neogenic Platform represent the most important outcrops by surface in the study area. On the basis of water management needs, considered in the Master Plan from Provincia de La Habana, several hydrogeological basins, shown in figure 5, were established (DPPF, 1986). Some of the identified basins are partially included by the study area: Melena Nueva Paz basin (HS-5), Mamposton Basin (HMJ-1), Batabanó basin (HS-4), Artemisa Quivican Basin (HS-3), Aiguanabo Basin (HAV-1), Vento Basin (HAV-2), Jaruco Basin (HMJ-2). Memorias en CD-Rom, La Habana, 4 al 8 de abril de ISBN

3 Materials and methods The EPIK Method for intrinsic groundwater vulnerability assessment (SAEFL, 1998, Doerfligher, et. Al., 1999), is based on a conceptual model considering the karst aquifer constituted by small volume of high hydraulic conductivity (K ) ranging from 10-2 to 10-3 m s -1 network conduits, surrounded by a large volume of low K ( m s -1 ) fractured and/or fissured rock. The aquifer is also characterized by absence of surface or near surface drainage, existence of large springs, swallow holes, dolines and karst conduits. As vulnerability of karst waters is a function of direct and retarding mass transport, the EPIK method uses the parameters linking the mass transport process with flow conditions in such environments for the proposed conceptual model. Giving also for each one, the relative weight in overall vulnerability. The parameters are: Epikarst (E) meaning the presence/absence of karstic landforms (i. e. dolines, karren fields, caves) and high permeability zones due to the presence of fractures; Protective cover (P) which includes the soil cover and other overlying geological formations with possible protective effects; Infiltration conditions (I) that identifies the areas where infiltration concentrates and assessment of diffuse infiltration areas; Karstic network (K) evaluates the existence and development of a karst conduit network. Evaluation of the 4 described parameters is carried out in a semi quantitative manner. Assessment of the E parameter, was carried out by using aerial imagery, digital terrain model (DTM), and information from topographic and geologic maps. Concerning the protective cover, the only parameter that is evaluated is soil thickness. No matter about the mineralogical composition, texture, or content of organic matter. EPIK method assumes that the more important is the thickness, the more protected the aquifer. Since hypothetical pollutants released, can be intercepted by soil and/or geological formations, giving enough time for depuration process retarding or blocking their migration to groundwater. Information about the soil thickness was provided by the National soilmap 1:25000 (Paneque et Al., 1991). The analysis of infiltration conditions is addressed to differentiate between areas where infiltration concentrates and therefore more vulnerable, and areas where diffuse infiltration occurs. The evaluation of concentrated infiltration areas was performed by direct identification of karst features like swallow holes, ponors, sinking and loosing streams by using aerial imagery and field trips. Identifying diffuse infiltration areas is carried out by using the runoff coefficient, that is a function of slope and land use. Areas generating large amount of runoff are considered more vulnerable than diffuse infiltration areas, since runoff can then, reach concentrated infiltration areas penetrating directly in the aquifer. the necessary information was provided by the DTM, aerial imagery and landuse maps.the network development of karst aquifers, is assessed directly by the identification of its components (caves and conduits), and where this is no possible trough indirect methods like spring discharge measurements, geophysical surveys and/or tracer tests. The parameter is assigned globally for, unless there is information enough to divide the studied area in more categories. Memorias en CD-Rom, La Habana, 4 al 8 de abril de ISBN

4 Table I assumed values for each parameter according with the geological context. (SAEFL, 1998, Doerfligher, et. Al., 1999). Karstic morfology observed E1,1 Caves Swallow holes, dolines, karren fields, ruine like relief, cuestas E2, 3 Intermediate zones along doline alignements, uvalas, dry valleys, canyons, poljes Karstic morfology absent E3, 4 Rest of the catchment Protective cover absent P1, 1 A) Soil resting directly on limestone formations 0 20 cm of soil B) soil resting on > 20 cm of low hydraulic cond. formation P2, cm of soil P3, 3 > 1m of soil cm of soil and low hydraulic cond. formation > 1 m of soil and low hydraulic cond. Formation Protective cover important P4, 4 >8 m of low hydraulic cond formation or > 6 m of very low hydraulic cond formation with >1 m of soil Concentrated infiltration I1, 1 I2, 2 I3, 3 Perennial or temporary swallow hole banks and beds of temporary or permanent stream supplying swallow hole, infiltrating surficial flow areas of the water course catchments containing artificial drainage Areas of a water course catchment which are not artificially drained and where the slope is greater than 10% for ploughed (cultivated) areas and greater than 25% for meadows and pastures Areas of a water course catchment which are not artificially drained and where the slope is less than 10% for ploughed (cultivated) areas and less than 25% for meadows and pastures Outside the catchment of a surface water course: bases of slopes and steep slopes (greater than 10% for ploughed (cultivated) areas and greater than 25% for meadows and pastures) where runoff water infiltrates Diffuse infiltration I4, 4 Rest of the catchment Well developed karstic network K1, 1 Well developed karstic network with decimeter to metre sized conduits with little fill and well interconnected Poorly developed karstic network K2, 2 Poorly developed karstic network, poorly interconnected or infilled drains or conduits, or conduits of decimetre or smaller size. Mixed or fissured aquifer K3, 3 Porous media discharghe zone with a possible protective influence fissured non-kartic aquifer Memorias en CD-Rom, La Habana, 4 al 8 de abril de ISBN

5 Once obtained the value for each single parameter a Protection Index (F) is calculated by using the following equation: (1) Low parameters values gives low F values indicating more vulnerable situations. Table 2 illustrates the equivalence among protection index values, vulnerability degree. Table II equivalence between protection index values, vulnerability degree (SAEFL, 1998, Doerfligher, et. Al., 1999). Protection index value Vulnerability 9 to 19 Very high High 20 to 25 High Greater than 25 Moderate Greater than 25 with the presence of P4 + (I3-3) categories Low Applying the EPIK method, implies handling a large number of spatial data from different sources and often at different scales. For this work, we used aerial imagery, topographic and geologic maps, digital terrain model (DTM). The operation is significantly simplified if a geographical information system (GIS) is used. For this work the information concerning the parameters mapping was integrated in a GIS and layers for all them created. Successively raster images were derived, where each pixel takes the value of the parameter. finally by using raster calculation tools, F parameter was calculated and, from table II vulnerability assessed. RESULTS Epikarst - E Among karst features present in the area, dolines are the most common and associated mainly to Guines and Cojimar formations. They are often placed along, or near mapped faults indicating that structural control on their development may be present. In some cases dolines showed a vegetal cover of trees making the identification on the basis of aerial imagery difficult, however the DTM provided the necessary complementary information to recognize them. The presence of Cuesta like relief was identified along the road from San Jose de las Lajas to Guines. In the same area, there are several active and abandoned quarries for rock extraction. although quarries are not natural features, they constitute areas where the limestone is exposed, and according with the method should be considered as having developed epikarst. Check on the field allowed us to confirm the mapped features, and therefore to all previous cited areas were assigned to E1. From previous studies from Molerio Leon (1975) the Almendares Vento basin was classified as a polje, by analogy the Mamposton river basin included in the study area was also considered as a polje, and both basins Memorias en CD-Rom, La Habana, 4 al 8 de abril de ISBN

6 recognized as E2 according with the method. The rest of the study area lacking of karst features was classified as E3. Figure 2 shows values distribution for the E parameter in the study area. Figure 2. E parameter values distribution Protective cover - P Ferralic and Cambisol soils are predominant in the area, developed from limestone under tropical climate conditions. Soil depth ranges from 0.5 to 1 meter, and more than 75% of soil material is constituted by caolinic clay. In most of the area the soil cover is relatively thin (less than 1m) and laying directly on the limestone, especially in the hilly areas and in the southern plain. Only locally soil cover present thickness above 1 meter, figure 3 shows the distribution values for the P parameter in the area, obtained by classifying the layer containing the soil depth. Memorias en CD-Rom, La Habana, 4 al 8 de abril de ISBN

7 Figure 3. P parameter values distribution Infiltration conditions - I Geomorphology of the area is characterized by large flatlands and gently hills. Slope derived from the DTM shows high values only in a limited portion of the study area, generally in correspondence with outcrops from non karst geological formations. Concerning land use, hilly areas are covered by forest (palm trees and other species) and meadows, while, in flatlands, intensive agriculture under irrigation prevails. The combination of land-use and geomorphology, results in large areas where diffuse recharge occurs (I2, I3). Concerning concentrated infiltration areas, I1 value was assigned to rivers in Southern Plain because all were considered loosing streams. An I1 value was also assigned to swallow holes, dolines and associated streams that were identified on the basis of aerial imagery, as well as, to areas subject to flooding identified by Campos (2004), since water accumulates on them until infiltration. Rivers within the Almendares Vento basin were considered concentrated infiltration points, since the Ejercito Rebelde Dam, placed within the basin has been recognized as a recharge point (Peralta, 2005). Figure 4 shows the values assumed by I parameter within the study area. Memorias en CD-Rom, La Habana, 4 al 8 de abril de ISBN

8 Figure 4. I parameter values distribution Karst network development K Whithin the study area up to 10 distinct cave levels have been recognized. Karst processes evidenced by large development of caves, dolines presence and terrain collapse, have been identified (Campos 2004). Those phenomena are mainly associated with Guines formation that shows more developed karst features. However all calcareous formations present important degree of karsification. K parameter was consequently globally estimated for the area and a K1 value was assigned as shown in figure 5. Memorias en CD-Rom, La Habana, 4 al 8 de abril de ISBN

9 Figure 5. K parameter values distribution By using the produced maps for each parameter, the protection factor index was calculated with formula (1) for the analyzed area. Then values were reclassified according with table II to obtain the vulnerability map as shown in figure 6. DISCUSSION According with the results, large part of the analyzed area shows very high and high vulnerability, with limited areas having moderate vulnerability (figure 6). In we refer the results to specific hydrogeological basins differences in distribution of vulnerability may be noted: in Almendares - Vento and Mamposton basins high vulnerability areas prevail constituted mainly by the poljes bottom with moderate soil cover. Very high vulnerability areas are represented by fractured outcrops, Cuesta relief and quarries along the road from Guines to San Jose de las Lajas, as well as doline fields within Mamposton river basin. Only limited very high vulnerability areas are linked to rivers and related alluvial plains, since just those within Almendares Vento Basin were considered loosing streams. Moderate vulnerability areas are little represented only by zones lacking of any karst features, and characterized by diffuse infiltration through thick soil cover. In Habana Southern Basin, instead, very high vulnerability areas are linked largely to infiltrating rivers and associated alluvial plains, and to the Memorias en CD-Rom, La Habana, 4 al 8 de abril de ISBN

10 presence of karst features like dolines fields placed southern of San Felipe. High vulnerability areas are associated with zones lacking of karst characteristics and moderate soil cover (0.20 to 1 m). As in Almendares vento basin, moderate vulnerability areas are associated with the lack of karst characteristics, and diffuse infiltration through thick soil. No low vulnerability areas were identified. Figure 6. Groundwater vulenrability map CONCLUSIONS Vulnerability maps are an essential tool in groundwater management and protection. The EPIK method for intrinsic groundwater vulnerability mapping, was originally developed to protect catchments intended for drinking water, according with the Swiss Water Protection Act. However it has proven to be efficient and fully applicable also to Cuban context, since is based on parameters defining the transport process common to all karst aquifers, independently of the geographic framework. The method is straightforward, and vulnerability can be assessed economically through measurement of simple and clear parameters. By using geographic information systems, the vulnerability assessment process can be facilitated and improved as new information is acquired. On the basis of produced information, policy makers can emanate directives, restrictions and eventually plan land-use in order to minimize negative impacts on groundwater. Memorias en CD-Rom, La Habana, 4 al 8 de abril de ISBN

11 BIBLIOGRAPHY CITMA, Situación ambiental cubana ISBN Ciudad de La Habana, Cuba. Campos, M., M. Guerra, E. Jaimez, y J. Olivera Caracterízación geólogo - ambiental de las provincias habaneras. Informe Final, Proyecto Evaluación geólogo ambiental de las provincias habaneras Código 30302, Instituto de Geofísica y Astronomía, Ciudad de La Habana. De Albear, J. F., Iturralde Vinent, M. A. 1985a. Estratigrafía de las provincias de La Habana. En Contribución a la Geología de las provincias de La Habana y Ciudad de La Habana, Editorial Científico Técnica, La Habana, pp De Albear, J. F., Iturralde, M. A. 1985b. Pisos estructurales en el territorio de las provincias de La Habana. En Contribución a la Geología de las provincias de La Habana y Ciudad de La Habana, Editorial Científico Técnica, La Habana, pp Direccion Provincial de la Planificacion Fisica DPPF, Plan director de la Provincia de La Habana Doerfliger N., Jeannin, P. Y., Zwahlen, F Water vulnerability assessment in karst environments: a new method of defining protection areas using a multi attribute approach and GIS tools (EPIK method). Environmental Geology 39, issue 2, ,1999 García D. et al., Informe proyecto generalización y actualización geológica de la región Habana Matanzas, escala Fondo Geológico Nacional. Molerio Leon, L. F., Aplicacion del metodo de recesion al estudio hidrodinamico de las fuentes del Rio Mayabeque. Simposium XXXV. Aniversario Sociedad Espeleologica. Cuba, La Habana 67. Molerio Leon, L. F. and Parise M., Managing environmental problems in Cuban karst aquifers. Paneque, j., Fuentes, E., Mesa, A., Echemendía, A., El mapa nacional de suelos escala 1: Memorias del XI Congreso Latinoamericano y II Congreso Cubano de la Ciencia del Suelo, La Habana Memorias, D. R. Villegas, D. Ponce de Leon, editores. Peralta Vital, J. L., Gil Castillo, R., Leyva Bombuse, D., Molerio Leon, L., Pin, M., Uso de técnicas nucleares en la evaluación de la cuenca Almedares Vento para la gestión sostenible de sus recursos idricos. SAEFL, (1998). Guide pratiche Cartographie de la vulnerabilitè en régions karsiques (EPIK) 20 pp. Zwahlen, F Cost Action 620. Vulnerability and Risk mapping for the protection of Carbonate (Karst) Aquifers. Final report: Memorias en CD-Rom, La Habana, 4 al 8 de abril de ISBN