Struma/Strymonas River basin

The basin of the Struma/Strymonas River is typically considered to be shared by Bulgaria and Greece; the shares of Serbia and the former Yugoslav Republic of Macedonia in the total basin area are small. The river has its source in western Bulgaria (Vitosha Mountain, south of Sofia) and ends in the Aegean Sea (Strymonikos Gulf – Greece).

Hydrology and hydrogeology

The total length of the river is 400 km, with its last 110 km flowing through Greece. Major transboundary tributaries include the following rivers: Butkovas, Exavis, Krousovitis, Xiropotamos, and Aggitis, shared by Bulgaria and Greece; Dragovishtitsa, shared by Serbia and Bulgaria; Lebnitsa, and Strumica/Strumeshnitsa shared by the former Yugoslav Republic of Macedonia and Bulgaria.

The basin has a pronounced mountainous character, with an average elevation of about 900 m a.s.l.

There are about 60 artificial lakes in the Bulgarian part of the river basin, used for water supply, power generation and irrigation purposes. The Kerkini Reservoir in Greece was created with the construction of a levee in 1933 for regulating the river discharges, for irrigation purposes, and flood protection (a new levee was constructed in 1982). The Kerkini Reservoir was finally developed into an important wetland, protected under the Ramsar Convention. In Greece, irrigation dams also exist at Lefkogeia and Katafyto. The Lisina Reservoir on the Dragovishtitsa River in Serbia is a part of the Vlasina hydropower production system.

There is a high risk of flooding in Bulgaria due to the basin’s geomorphological and hydrological characteristics. Bulgaria reported that climate change over the last 20 years has resulted  in an approximately 30% decrease in precipitation and a subsequent decrease in water resources in the basin; provisions to address the decrease of water resources will be included in the programme of measures of the RBMP.

In the part of the basin that is Bulgaria’s territory, surface water resources are estimated at 1,961 × 106 cu m/year (average for the years 1980-2004) and groundwater resources at some 200 × 106 cu m/year (average for the years 1980-2004), adding up to a total of 2,160 × 106 cu m/year (4,435 cu m/year).

Two transboundary aquifers were identified as hydraulically linked to the surface water system and included in the first assessment: the Sandansky – Petrich aquifer (No. 139) (shared by Bulgaria, Greece and the former Yugoslav Republic of Macedonia), and the Orvilos-Agistros/Gotze Delchev karst aquifer (No. 142) (shared by Bulgaria and Greece - as reported by Bulgaria, it also extends to and is hydraulically linked with the surface water systems of the Mesta/Nestos River basin).

Bulgaria reported that new data available suggests that the Sandansky – Petrich aquifer (No. 139) is divided into two distinct aquifers thus, should be substituted by them here: (i) the Sandansky valley aquifer (No. 140) (shared by Bulgaria and Greece) and (ii) the Petrich valley aquifer (No. 141) (shared by the former Yugoslav Republic of Macedonia and Bulgaria).

According to Greece the Orvilos-Agistros/Gotze Delchev karstic aquifer (No. 142) is not hydraulically linked with the surface waters of either Struma/Strymonas or Mesta/Nestos basins. In addition, Bulgaria expresses uncertainty whether the aquifer should be considered as transboundary.

Although a major part of the basin area in Bulgaria is cropland, only a relatively small share of total water withdrawals is used for agriculture; more than half is used to supply industry. In the part of the Strumica sub-basin that extends to the territory of the former Yugoslav Republic of Macedonia, water is mainly used for irrigated agriculture; the respective water demand is expected to increase significantly (more than 40%) by 2020.

Pressures, status and transboundary impacts

Erosion and subsequent accumulation of sediments was reported by Serbia to take place in the basin of Dragovishtitsa River due to torrents and deforestation. Bulgaria reported that there are morphological alterations in the part of the river extending through the territory of the country, due to water abstractions and possible diversions in the Serbian part. According to Bulgaria, sand and gravel extraction from the Struma/Strymonas River on the Greek side causes sliding down of the river bed, which has affected more than 40 km in Bulgarian territory along the river.

Hydro-technical constructions in the Bulgarian part, such as dams (serving hydropower generation, irrigation and drinking water supply purposes), are pressure factors. Small hydropower stations may exert pressure on the environment. Bulgaria reports that the issue is under investigation.

Diversion of watercourses towards artificial reservoirs used for drinking water supply was reported by Bulgaria. There is intensive groundwater abstraction from some aquifers in the region. Water distribution infrastructure is degraded and results in water losses and problems for drinking water quality in some areas. Measures are being taken by regional water companies to improve water distribution infrastructure, so as to reduce water losses.

Untreated wastewater is an important pressure factor and organic matter from wastewater discharges is of concern in Bulgaria. The construction of wastewater treatment plants has started (to be finished until 2014 for settlements with more than 2,000 inhabitants) and will address the issue in many of the settlements. Strumica town (the major town in the part of Strumica sub-basin extending in the former Yugoslav Republic of Macedonia) lacks a wastewater treatment plant.

Agricultural run-off is a source of pollution in Bulgaria, as are the many small illegal dumpsites; livestock breeding units’ effluents and fish-farming are additional significant sources. Gravel extraction was reported as a very important issue; research on the effects of this pressure is being conducted. According to Bulgaria, gravel extraction in the Greek part of the watercourse influences the water table on the Bulgarian side, and alters the morphology of the Struma/Strymonas River.

The water quality is generally “good”. The water is suitable for use, especially for irrigated agriculture. Decreasing industrial activity after 1990 in Bulgaria resulted in water-quality improvements.

Due to decrease of industrial and agriculture activities, the concentrations of phosphates measured in 2008 are lower than the minimum for 2000-2005. The same applies to ammonia (for three out of four values provided).

Responses and trends

The part of the Struma/Strymonas Basin that is within Bulgaria’s territory has been assigned to the West Aegean Basin District, the part that is within Greece’s territory has been assigned to the Central Macedonia District, as well as to the Eastern Macedonia and Thrace Basin District. In Bulgaria, there is a management authority that has the primary responsibility for water resources management and a basin council (a consultative body) at the level of the river basin district. The RBMP for the West Aegean Basin District was prepared to cover the part of the basin falling within Bulgarian territory.

There is a monitoring station in Bulgaria, near the Bulgarian– Greek border. Monitoring programmes are being established in
both countries in accordance to the WFD. Bulgaria reports that joint monitoring of the aquifers should be established.

The increase of tourism in the Bulgarian part is expected to result in increased water consumption needs.

Transboundary cooperation

According to the agreement signed between Bulgaria and Greece in 1964, both countries are bound, inter alia, not to cause significant damage to each other, arising from the construction and operation of projects and installations along the valleys of the Struma/Strymonas, Mesta/Nestos, Arda/Ardas and Maritsa/Evros rivers. The agreement provides for exchange of information and data between parties for preventing floods, as well as an exchange of information concerning the installations subject to the agreement.

According to the Agreement signed between the two countries in 1971, a Bulgarian-Greek Commission on cooperation in the field of electric energy and water use of the rivers flowing through their territories was set up. Bulgaria reports that the agreement is not active for the time being, and that discussions regarding its renewal and possible updating are ongoing. Finally, an Agreement was signed between the Ministry of Environment and Water of the Republic of Bulgaria and the Ministry for the Environment, Physical Planning and Public Works of the Hellenic Republic in 2002 on Cooperation in the field of Environmental Protection. In 2010, ministers responsible for water issues in Bulgaria and Greece stated in a joint declaration their political will to start a new dialogue with the aim to promote cooperation for the
preservation and protection of shared water resources. As a result, a joint Bulgarian-Greek Working Group on cooperation on water protection was established in May 2011. The joint Working Group will focus its work on: legislative issues linked to transposing the WFD and the Floods Directive; support to the implementation in both countries of the WFD, through RBMPs, and of the Floods Directive; implementation of the basin water management principle in both countries; monitoring of water quantity, water resources assessment and flood early warning systems; and water management bodies and administrative structures.71