Finnish Environment Institute
Kari Rantakokko (ed.)
Flood water retention in the catchment
Survey of possibilites in Finland
http://www.ymparisto.fi/palvelut/julkaisu/elektro/sy563/sy563.htm
In this report the possibilities and suitability of flood water retention in the Finnish catchments
have been examined. Report is mainly based on literature and experiences gained from projects
and plans prepared in Finland. Some foreign experiences have also presented. In several European
countries there is intention to lower or stop the increase of flood risk by activities which
are based on flood water retention, detention basins and infiltration before the waters reach
main watercourses. In Finland a further goal is to lower the risk of ice jamming. Optional activities
enables also the improvement of ecological aspects. Assessment of impacts in the detention
areas and in downstream water courses, legal aspects and funding of detention areas are also
dealt in this report.
Possible methods for flood water retention along river valleys are restoration of naturally
flooded areas, flood forests and flood meadows in connection with different solutions of small
dams or distanced embankments. Effective mean is the use of so called dry reservoirs. Methods
to be used in the catchment are restoration of ditched forests and mires, runoff regulation, rewatering
old peat production areas or dried lakes, wetlands, sedimentation and overland-flow
basins.
The benefit of flood water retention was tested in Iijoki, Kuivajoki and Vääräjoki river basins in
some spring floods recently occurred by using watershed models. Flood peak in Pudasjärvi
area in river Iijoki could have been lowered by 50 m 3/s in spring 2000 by using four separate
dry reservoirs having a total volume of 50 Mm3. In Kuivajoki river the impacts of a heavy ice
jamming in spring 1993 could have been decreased substantially by the use of a dry reservoir
delaying the ice break-up by couple of days. In Vääräjoki the flood protection of a naturally
flooded area was tested. Optionally a regulated reservoir was used or natural flooding was
enabled to be higher. In the case of a reservoir the downstream floods were even increased.
floods, flood protection, catchments, restoration, ice dam, watershed models, watercourses
The Finnish Environment 563
Nature and natural resources
Finnish Environment Institute
1238-7312 952-11-1170-4 952-11-1171-2 (PDF)
87 Finnish
Public 12.50 EUR
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23.4.2002