Gotranskarstba

5.2 The Dobrutsa transboundary aquifers

INTEGRATION OF ΤΗΕ DINARIC ΚARSΤ TRANSBOUNDARY AQUIFERS ΙΝΤΟ SUSΤAINABLE ECOSYSTEMS OF ΤΗΕ BALΚANS

As shown in Figure 5.4, the Dobrutsa transboundary aquifers are located in the Black Sea coastal area of North-eastern Bulgaria and are shared between Bulgaria and Romania. Since 2007 both countries have been full members of the EU and they have to implement the requirements of the EU Water Framework Directive 2000/60 (EU-WFD) for the integrated management of groundwater resources, including transboundary aquifers. This case study summarises the main findings of the project “Integrated Management of Transboundary Groundwater between Bulgaria and Romania in the Dobrudja/Dobrogea Area” suggested and implemented under the Phare Bulgaria-Romania Cross Border Cooperation (CBC) bilateral Programme). Most of the results presented relate to the work done in the Bulgarian part of the aquifer as far as the monitoring activities are concerned (Matchkova, 2007).

The case study contains the geological and hydrogeological characteristics of the transboundary aquifers in the Dobrudja area as well as the corresponding monitoring network used in the Bulgarian part, following the requirements of Article 8 of the EU-WFD. Also the physicochemical characteristics of the Upper Jurassic - Valanginian aquifer (Deep Aquifer) and the Sarmatian aquifer (Upper Aquifer) are reviewed. The groundwater monitoring network developed in the transboundary aquifers in the Dobrudja area is assessed and its scheme selection approach is explained.
The area is located in North-eastern Bulgaria and has a surface of about 5.500 km². The western boundary coincides with the watershed of the Suha River valley. The south-western border is the watershed of the Karamandere River, being a tributary of the Suha River






Figure 5.4. Geographical location of the Dobrudja area.

From a hydrogeological point of view, the area is a large artesian reservoir named “Lower Danube artesian basin” or “Moesian artesian basin” in Bulgaria. This is the largest hydrogeological structure in the country and is of particular hydrogeological and economic significance.

Upper Jurassic – Valanginian (Deep Aquifer)

The hydraulic gradient toward East, North and West ranges from 0.0075 to 0.002. The filtration characteristics are rather varied due to alterations in the karsting and cracking of sediments. Local permeability values vary from 8 - 10 m²/d to more than 2000 - 3000 m²/d, with an average rate of 200 - 600 m²/d.The permeability coefficient is predominantly between 2 m/d and 5 m/d. The values of specific yield are between 0.01 - 0.10. The aquifer is characterised by a vast groundwater resource (for the Varna artesian basin, the natural resources are about 13 - 14 m³/s) and it is the main source used for different purposes including water supply in the region.

The Deep Aquifer is subject to intense exploitation as it is a primary source of fresh and drinking water in North-eastern Bulgaria. As a result, several water-supply wells have been drilled, which are distributed unequally over the territory. The water consumption is more considerable in the regions around the larger settlements and the resorts. Along the Black Sea coastal border from Krapetz to Balchik and Varna, there are several boreholes for self-discharge thermal water, which are used for sporting and recreational activities as well as being a source of thermal energy for the needs of hotels. Some of them have no closure systems, so the water flows continuously without regulation. Although this latter effect has not been firmly established, it is clear that this situation represents a steady bleeding of the aquifer as well as a waste of great quantities of resources. Thus, in some wells drilled in the Krapetz (the eastern zone), which were originally artesian, the piezometric level has fallen by over 4 m over the last 20 years. The long-term observation of the groundwater levels in the western part of the area also shows steady downward trends

Mixing processes of freshwater and saline water (mainly fossil or connate) are apparently the origin of this spatial distribution of the concentrations. Since the aquifer is confined over practically the entire area, the NO3- contents are low, between 4 and 12 mg/l. Some local values greater than “the contamination threshold” i.e. 30 mg/l are due to the mixing of water from the Upper Aquifer and/or possible pollution through the annular space of the wells.

Sarmatian Aquifer (Upper Aquifer)

The Upper Aquifer represents the upper part of a common heterogeneous water-bearing complex with different water-transmitting and water storage properties. The bottom part of the aquifer is built up of unconsolidated sands. Above them lie the detritus and shelly limestone separated locally by carbonate clays. The total thickness of the complex is more than 240 m. The layers are almost horizontal with a slight dipping of 1 to 5º from the east towards the south-east and north. The rocks have a high porosity resulting from the spaces between sand grains and organogenic remains. The limestones are significantly karstified. Depending on the density of the limestone and their clay content, the volume of the caverns is 10 - 30% of the total volume. The Evksinovgrad formation clay is the bottom aquiclude for a large part of the area. The water-bearing rocks are almost 80% covered by loess, diluvia and diluvia-alluvial deposits of varying thickness. The aquifer is mainly unconfined.
The distribution of nitrates and chlorides is related to three main processes of pollution: scattered discharge of urban liquid waste and unpurified animal waste; excess fertiliser applied in cultivated areas; and incipient sea-water intrusion on the eastern coastal strip (Machkova, 2007). The nitrate content exceeds 200 mg/l in extensive areas of the aquifer, with maxima at certain points such as the central sector, where values reach over 600 mg/l. In general, the maximum values are registered in the principal infiltration area of the entire aquifer, coinciding with developed agricultural sectors and some of the major urban agglomerations. In the southern and eastern coastal sectors, except near the discharge area of Lake Durankulak, the nitrate values are generally below 30 mg/l, thus indicating a major dilution of the polluting discharge along the flow.
The highest chloride contents are closely related to local processes of sea-water intrusion near the eastern coast. Mean values for most of the aquifer are around 50 mg/l, which are considered normal for this region. Along a 5 km strip, parallel to the eastern coastline, values exceed 500 mg/l and reach almost 1000 mg/l.
Monitoring network
The main goal of the improved groundwater monitoring scheme in the transboundary aquifers in the Dobrudja area was to apply the requirements of Article 8 of the EC Water Framework Directive 2000/60/EC (WFD). Taking into account the significance of both aquifers for the sustainable development of the settlements in the area, it is essential to preserve the groundwater resources and use them in a sustainable manner. The groundwater monitoring should facilitate the process of their management and contribute further to determining and reversing the negative qualitative and quantitative tendencies. This is related to the calculation of water balance, establishment of databases and geographic information systems (GIS) including groundwater modelling, none of which would be possible without reliable specific monitoring data.
The analysis of the present monitoring network shows that it is not sufficient to provide reliable information on natural or affected groundwater abstraction, irrigation and land use conditions in both aquifers, nor on the problems related to groundwater pollution. The pre-existing scheme cannot be used for water management in the transboundary aquifers between Bulgaria and Romania. This leads to the need for increasing the density of the observation points and improving their spatial distribution, especially in the areas characterised by transboundary groundwater transfer, as well as in the areas facing a high risk of pollution and overexploitation.
Conclusions
The Dobrudja aquifers case study is a very good example of cooperation and data exchange between two countries in SEE sharing common groundwater resources. Although the results presented here refer only to the Bulgarian part and focus mainly on the development of an effective monitoring network, the good knowledge of groundwater resources in the area will provide the necessary background information for implementing integrated quantitative and qualitative management plans within the EU-WFD.