River Kokemäenjoki – Flood risk management & WFD Brussels 17.4..2008 Juha-Pekka Triipponen Southwest Finland Regional Environment Centre

8 River basin districs in Finland (WFD) The Kokemäenjoki River is located in the southwest part of Finland and flows to the Baltic sea. The catchment area is about 27 000 km2 8 River basin districs in Finland (WFD) 15.2.2019

The hydrology of the Kokemäenjoki River is characteristic by the high proportion of lakes (11 %) in the catchment area. The length of the main Kokemäenjoki River is about 110 km. The river has been harnessed to generate hydropower which means water level regulation of the main lakes and the river flow. 15.2.2019

Flood risk management in the Kokemäenjoki river basin district The pilot project of the Flood Directive implementation in Finland Preliminary flood risk assessment -> Potential flood risk areas: The City of Pori (80 000 inh.) at the mouth of the river Flat agricultural area with some smaller municipalities and towns in central parts of the river Thousands of rural houses and summer cottages in the lake district 15.2.2019

Flood hazard maps and flood risk maps – partly done already, new height model by National Land Survey will help in the lake district Flood risk management plan Prevention: Possibilities to regulate water levels of four lakes in upper catchments is the most important mean to prevent and mitigate flood damages in the lower river reach (an extensive run-off forecast system available) -> some contradictions between flood risk management, hydro power generation and recreational use. Climate change -> Need to change the regulation permits? Protection: The needed flood protection measures Preparedness: Co-operation between rescue authorities and water resources authorities -> operational action plan for floods in the city of Pori (2008) 15.2.2019

Flood hazard map of Pori during a serious ice jam flood : - Probability: 1/200 years - 5 000 buildings wet - Damages to housing and industry: 200-300 mill.€ Flood protection project in The City of Pori 2007-2013: Dredging 700 000 m3 New embankments 25 km

Ice jam in the centre of the City of Pori January 1975 Cumulative factors affecting to winter floods in the river Kokemäenjoki: - High discharge at the same time with freezing due to the heavy rainfall in late autumn -> frazil jams - Warming up and rainfall during winter -> frazil jams and ice break-up jams The high sea level 15.2.2019

Connection between the flood risk management and the WFD - The run-off from the catchment areas to the Baltic sea during winter has increased -> significant part of the total nutrient loading (even 90 %) comes during warm and rainy winters because lack of vegetation on the fields (erosion & leaching) What is the significance of the flood risk management for the nutrient loading? the retention of the run-off on land areas -> relative significance and effect on the water quality 15.2.2019

The Kokemäenjoki river – a heavily modified water body The Harjavalta hydropower plant –the first barrier for the fish migration 40 km from the sea Almost totally dammed up by 4 hydropower plants which carry out short-term water level regulation (permit) Assessment of hydromorphological alterations  HMWB Is good ecological potential already achieved? - potential hydro-morphological mitigation measures are identified - assessment how much it is possible to improve the current status with the combination of measures unfinished 15.2.2019