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Combining hydrologic modelling and boundary shear stress estimates to evaluate the fate of fine sediments in river Juktån: Impact of ecological flows
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2018 (English)Independent thesis Advanced level (degree of Master (Two Years)), 40 credits / 60 HE creditsStudent thesis
Abstract [en]

Altered flow regimes following river regulation can result in significant changes in river bed geomorphology and subsequent negative ecological impacts caused by re-suspended sediments deposited on the riverbed. This study aimed to evaluate the consequences of implementing an ecological flow regime on sediments accumulated within the regulated river Juktån. Sediments were sampled and analysed for particle size distribution to estimate sediment stability. Flow alteration following the ecological flow regime was analysed with HEC-RAS unsteady flow simulation serving as a basis for calculations of forces acting to erode or retain deposited sediments. Additional analyses regarding critical flow were made with HEC-RAS steady flow simulation. Results show that 4 out of 15 cross-sections analysed would have the potential to erode and re-suspend sediments. The estimated average critical flow for when sediments become unstable with potential to re-suspend is 17 m3/s. The total sediment inventory of the studied reach is ~25000 ton, with ~3000-ton sediments potentially eroding into re-suspension. This is approximately 3% of river Umeälvens annual 100 000 ton suspended sediments before being regulated. Results indicate that river bed heterogeneity in river Juktån could benefit from implementing the ecological flow regime while not mobilizing such amounts of fine sediments that would cause clogging effects downstream the site of interest. The study also introduces the erosion rate equation which compares the annual erosion between two different flow regimes.

Place, publisher, year, edition, pages
2018. , p. 31
Keywords [en]
: Stream geomorphology, Clogging, Flow alteration, Ecological flow regime, Erosion, Fine sediments, Boundary shear stress, Critical shear stress, Critical flow, Competence, HEC-RAS, River modelling.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:umu:diva-145948OAI: oai:DiVA.org:umu-145948DiVA, id: diva2:1192621
Educational program
Master's Programme in Geoecology
Supervisors
Examiners
Available from: 2018-04-04 Created: 2018-03-22 Last updated: 2018-04-04Bibliographically approved

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CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf