Assessing in-stream rehabilitation with a two-dimensional model of river hydrodynamics and fish habitat, a case study - the River Kiiminkijoki

Timber floating was practiced in most of the Finnish rivers and float worthy brooks for many years. In the broadest state there were over 40 000 km of float ways from which about one third were dredged rivers. Rehabilitation of these dredged channels to stony and heterogeneous rapids started in early 80's and is still ongoing.

Results of in-stream restorations may be reliably assessable at the ecosystem level only after a considerable period following the restoration. Recovery from physical disturbance alone may take up to a decade with concurrent uncertainty about the success of restoration. Surveying only ecological changes (e.g. fish population) for short periods may seriously under- or overestimate the actual long-term outcome of the restoration. Physical habitat models are a promising tool to predict the future outcome of restoration or provide an estimate of the site's restoration potential for certain target species.

Physical habitat modeling is mostly based on hydraulic and morphological variables, such as water depth, velocity and substrate. These physical parameters are thought to be the main factors influencing the distribution and abundance of organisms and species in aquatic ecosystems. The River2D model (Steffler and Blackburn, 2002) predicts depth and velocity laterally and longitudinally throughout a length of river channel. Life stage specific habitat suitability criteria (HSC) for depth, velocity and substrate are applied to this hydrodynamic model. Model predictions are combined with substrate data into a quantification of target species preferred habitat known as weighted usable area (WUA).

This project quantifies how the restoration of the River Kiiminkijoki changed WUA for salmon (Salmo salar) fry and juvenile. Model estimates are compared to the actual short term changes in salmon fry and juvenile densities monitored over a 6 year period. We hypothesized that: (1) the restoration projects would result in an increase in WUA; and (2) the modelled increase in WUA would be seen as an actual increase in juvenile salmon densities.

Lammassaari, V. 1985. Uitto meillä ja muualla. Floatage in Finland and in other countries. Oulun yliopisto, vesitekniikan laboratorio.

Steffler, P., & Blackburn, J., 2002, Two-dimensional depth averaged model of river hydrodynamics and fish habitat: Introduction to depth averaged modeling and users manual: Edmunton, Alberta, Canada, University of Alberta, 119 p.

(Christison, K.J., P.M. Steffler & C. Katopodis. 1999. Two-Dimensional Hydrodynamic Modeling of a Braided River – A case Study. Proceedings of the Third International Conference on Ecohydraulics, Salt Lake City, Utah, CDROM.

Published 2013-04-25 at 13:11, updated 2013-04-25 at 13:10