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
NWRM(s) implemented in the case study
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 |
|---|---|---|---|---|
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.
|
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.
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.
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.