The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.

Effects of Cross-Sectional Geometry, Vegetation and Ice on Flow Resistance and Conveyance of Natural Rivers

Terhi Helmiö

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Civil and Environmental Engineering for public examination and debate in Auditorium R1 at Helsinki University of Technology (Espoo, Finland) on the 18th of June, 2004, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-7072-2)   [716 KB]
Dissertation is also available in print (ISBN 951-22-7071-4)


The accurate estimation of local hydraulics, i.e. local flow velocities and water depths, is necessary for the restoration and protection of biodiversity. The aim of the thesis was to develop methods and models for designing and evaluating the hydraulic aspects of restoration, rehabilitation and environmental flood management in running waters.

Methods for the estimation of flow resistance in natural complex rivers and channels that have composite flow resistance and/or a compound channel shape were tested, and an unsteady 1D flow model for partially vegetated channels with complex geometry was developed. These methods were used to quantify different factors causing flow resistance, e.g. cross-sectional geometry, vegetation, ice cover and momentum transfer, in lowland rivers of different shapes and sizes. The relationship between the flow resistance and the cross-sectional geometry was analysed.

Traditional methods used to estimate composite friction factors were found to be accurate in simple concave channels with simple hydraulic properties, but an adjustment of the methods would be necessary for reaches with significant head losses due to lateral momentum transfer. It was seen that the effect of the momentum exchange process between the main channel and the floodplain or streambank vegetation was significant. A procedure for applying the success criteria in a post-project evaluation of local hydraulics was developed, based on the hypothesis of flow resistance and cross-sectional geometry determining local hydraulic conditions in boreal streams.

Based on the results from the proposed flow model, the restoration of flood retention areas and local hydraulics is a vital component of the restoration of catchment-scale hydrology, but not sufficient by itself to restore flood peaks to their earlier state, because the changes in land use have often been drastic.

This thesis consists of an overview and of the following 7 publications:

  1. Helmiö T., 2001. Friction measurements of ice cover: theory and practise in River Päntäneenjoki. In: Proceedings of the 2nd IAHR Symposium on River, Coastal and Estuarine Morphodynamics. Obihiro, Japan, 10-14 September 2001, pages 179-187. © 2001 International Association of Hydraulic Engineering and Research (IAHR). By permission.
  2. Helmiö T. and Järvelä J., 2004. Hydraulic aspects of environmental flood management in boreal conditions. Boreal Environment Research 9, in press. © 2004 Boreal Environment Research. By permission.
  3. Järvelä J. and Helmiö T., 2004. Hydraulic considerations in restoring boreal streams. Nordic Hydrology 35, number 3, in press. © 2004 by authors and © 2004 IWA Publishing. By permission.
  4. Helmiö T., 2004. Hydraulic geometry of cohesive lowland rivers. Boreal Environment Research 9, in press. © 2004 Boreal Environment Research. By permission.
  5. Helmiö T., 2002. Unsteady 1D flow model of compound channel with vegetated floodplains. Journal of Hydrology 269, numbers 1-2, pages 89-99. © 2002 Elsevier Science. By permission.
  6. Helmiö T., 2004. Unsteady 1D flow model of a river with partly vegetated floodplains – application to the Rhine River. Environmental Modelling & Software, in press. © 2004 Elsevier Science. By permission.
  7. Helmiö T., 2004. Flow resistance due to lateral momentum transfer in partially vegetated rivers. Water Resources Research 40, in press. © 2004 American Geophysical Union (AGU). By permission.

Keywords: hydraulics, river, flow resistance, vegetation, geometry, ice

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© 2004 Helsinki University of Technology

Last update 2011-05-26