The Vonarje flood storage reservoir in Croatia

General

National Id:

Croatia_03

Site name:

Sutlansko lake

Summary:

The Sutlansko Lake area is a wetland with a high biological diversity. The Vonarje reservoir was initially built for drinking water supply and flood protection. The reservoir was drained due to difficulties encountered to manage its water quality. Now it operates as a dry retention basin for flood protection. At the bottom of the reservoir, wetland ecosystems developed. For this reason, the area of the reservoir on the Slovene side has been declared as a Natura 2000 site.

NUTS Code:

Kontinentalna Hrvatska

Transboundary:

Data provider:

Adriana Raveau, ACTeon

Source(s):

Analysis of inadequate water quality of the Vonarje reservoir / Sutla Lake and the possibility of restoration and utilisation.

NWRM(s) implemented in the case study:

Basins and ponds

Longitude:

15.628

Latitude:

46.181

Site information

Climate zone:

cool temperate moist

Mean rainfall:

1200

Mean rainfall unit:

mm/year

Average temperature:

Mean evaportranspiration:

650

Mean evaportranspiration unit:

mm/year

Mean runoff:

Mean runoff unit:

600 - 750 mm

Type:

Case Study Info

Light or indepth?:

Light

Biophysical impacts

Retained water:

12400000

Retained water unit:

m3/day

Information on retained water:

Capacity is 12.4 million m3, of which 3.7 million m3 is required for 100-year flood protection.

Water quality overall improvements:

Not relevant for this application

Information on Water quality overall improvements:

Due to the implementation of the European industrial and urban waste water treatment legislation and environmental agricultural policy in Slovenia and Croatia (Croatia becoming a new EU member State in 2013), emissions to water and risk to water quality in the Vonarje reservoirs are expected to be much lower in the future than in the 1980's. Nevertheless, past pollution residuals in the lake bottom, pollution due to higher traffic, pressure on the water environment from fisheries, touristic and recrational facilities, intensification of agricultural activities and expected changes of climate patterns do not necessarily support this expectation. Furthermore, uses of the catchment on the Slovene an Croatian side are a different. On the Slovene side, there is more industry, "industrial like" tourism (large congress, termal and wellness facilities) and larger urban areas. On the Croatian side, the catchment uses are mostly traditional agriculture. The water uses are less intensive. Waste water collection and treatment depend on settlement patterns and differ in the technologies applied.

Soil quality overall soil improvements:

Positive impact-SQ improvement

Information on Soil quality overall soil improvements:

At the bottom of the reservoir wetland ecosystems developed. For this reason, the area of the reservoir on the Slovene side has been declared as Natura 2000 site.

Lessons, risks, implications...

Key lessons:

The Sutlansko Lake area is a wetland with a high biological diversity. The Vonarje reservoir was initially built for drinking water supply and flood protection. The reservoir was drained due to difficulties encountered to manage its water quality. Now it operates as a dry retention basin for flood protection. At the bottom of the reservoir, wetland ecosystems developed. For this reason the area of the reservoir on the Slovene side has been declared as a Natura 2000 site.

Success factor(s):

Type	Role	Comments
Successful coordination between authorities	main factor	Both EU countries, Slovenia and Croatia, are expected to apply for new development and cohesion funds to develop environmental and other infrastructure in the catchment. For the water management, it is important to take into account the two national institutional systems and the different economic developments in the past two decades: Although there are strong cultural ties between local communites on both river sides, the challenge for catchment water quality management to secure good ecological and chemical status of the Sotla river today is even greater than it has been in the past.

Financing:

Type	Comments
National funds	The reservoir was built as part of the joint water management plans of Croatia and Slovenia.

Barrier:

Type	Role	Comments
Other	main barrier	Shortly after filling, water in the reservoir became eutrophicated. Furthermore, other extreme water quality problems have been detected not only in the lake water, but also in the river water downstream. There was a high risk to human and environmental health that has hardly been managed successfully. In the absence of better remediation measures, the reservoir was completely drained in 1988 and now operates only as a dry retention basin for flood protection.

Driver:

Type	Role	Comments
Other	main driver	The main purpose was drinking water supply for both, Slovene and Croatian, settlements and flood protection of downstream areas.

Socio-economic

Direct benefits information:

No information found

Ancillary benefits information:

No information found

Costs investment information:

No information found

Costs operation maintenance:

No information found

Costs total information:

No information found

Ecosystem improved biodiversity:

Information on Ecosystem improved biodiversity:

The Vonarsko Lake area with its specific geographical features, as well as ecological and economic characteristics, has numerous water resources and an extremely rich flora and fauna. This area is considered as a wetland, the value of which is reflected in the biological diversity of the flora and fauna, ecosystems, and landscapes. This region is also extremely important for research and education. In short, there are many reasons for preservation and protection.

Ecosystem provisioning services:

Information on Ecosystem provisioning services:

In the course of the past decade, the area of the Sutla (Sotla) catchment developed touristically. At present, there are many local and regional initiatives to fill the Vonarje reservoir with water again and develop touristic and recreational facilities along its shore. There are also initiatives to use water for irrigation and drinking water supply. Both Slovenia and Croatia, being the new EU Member State, are now faced with the great challenge to achieve not only the good ecological and chemical status of the Vonarje lake and the river Sutla (Sotla) (as directed by Water Framework Directive), but also to achieve good or excellent quality for bathing and protection from adverse effects of water. Furthermore, both have also to harmonise touristic, recreational, fishing and irrigation needs at the same time.

Information on Ecosystem impact climate regulation:

No information found

Policy, general governance and design targets

Part of wider plan:

Policy pressure:

Policy requirement directive:

Policy impact:

Policy wider plan:

Policy area:

Policy target:

Target purpose
Peak-flow reduction

Design & implementations

Application scale:

Field Scale

Installation date:

1980

Area (ha):

590,6

Area subject to Land use change or Management/Practice change (ha):

590,6

Design capacity description:

The Vonarje reservoir or Sutlansko Lake with a volume of 12.4 million m3 was built and filled in 1980 as drinking water supply and for flood as part of the joint water management plans of Croatia and Slovenia. Due to high risk to human and environmental health that has hardly been managed successfully, the reservoir was drained in 1988. Now it operates as a dry retention basin for flood protection.

Max water retention capacity:

12,4

Max water retention capacity unit:

mio m3/day

Design contractual arrangement:

Design consultation activity:

Design land use change:

Design authority:

Authority type	Role	Responsibility	Name	Comments
Regional / sub-national water authority	Financing		Slovenian government
Regional / sub-national water authority	Financing		Croatian government

Last updated: 06 Jan 2015 | Top

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The Vonarje flood storage reservoir in Croatia

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