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. Light or indepth? Light NUTS Code Kontinentalna Hrvatska Transboundary 1 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 11 Mean evaportranspiration 650 Mean evaportranspiration unit mm/year Mean runoff 27 Mean runoff unit 600 - 750 mm Type Case Study Info 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 Arrangement type Responsibility Role Comments Name Design consultation activity Activity stage Key issues Name Comments Design land use change Land use change type Design authority Authority type Role Responsibility Name Comments Regional / sub-national water authority Financing Slovenian government Regional / sub-national water authority Financing Croatian government 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) Success factor type Success factor role Comments Successful coordination between authorities main factor Financing Financing type Comments National funds The reservoir was built as part of the joint water management plans of Croatia and Slovenia. Barrier Barrier type Barrier 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 Driver type Driver role Comments Other main driver The main purpose was drinking water supply for both, Slovene and Croatian, settlements and flood protection of downstream areas. Financing share Financing share type Share Comments Policy, general governance and design targets Part of wider plan 0 Policy target Target purpose Peak-flow reduction Policy pressure Pressure directive Relevant pressure Policy area Policy area type Policy area focus Name Comments Policy impact Impact directive Relevant impact Policy wider plan Wider plan type Wider plan focus Name Comments Policy requirement directive Requirement directive Specification 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 1 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 1 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 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. Full Context Pathway(aka Context) Default view Area(aka Level or Site) ALL