Natural and artificial hydromorphological changes in Norway Agnès Moquet-Stenback – Section for erosion and sediment transport – Hydrology department

Norwegian Water Resources and Energy Directorate Regulation and changes in sediment : Beiarelva 2 Estimated sediment delivery during floods caused by intake overflows amounts to some 70,000 t year-1 Svartisen hydropowerplant

Norwegian Water Resources and Energy Directorate 3 Diversion Reservoir infilling intakes overflowed  Cleaned accumulated sediment from tributaries

Norwegian Water Resources and Energy Directorate 4 Gravel and cobble pavement Patches of sand and silt overloading the substrat Water discharge and sediment carrying capacity of the Beiarelva have been reduced. Storage of sediment supplied from the tributaries is deposited in the river channel. Change in the pattern of sediment concentration variability: From availability-controlled  more dependent on hydraulic variables.

Norwegian Water Resources and Energy Directorate 5 Before regulation (1862) the channel transported sediment all the way to the delta front during the very low water stages of late summer and autumn Before regulation Habitat for shallow water fish community established. Species: pike, ruff, perch, pikeperch, cyprinides Delta in Lake Øyeren After regulation during 123 years

Norwegian Water Resources and Energy Directorate Sedimentation zones during different regulation practices Changes in reservoir water stage, discharge and inflowing river slope influence the location of delta sedimentation zones Reduced amplitude of seasonal water level variations  reduced the longitudinal extent of sedimentation zones The new delta : - - larger subaerial delta plain - increased shallow water areas - rapidly developing lagoons Shallow-water fish communities were established, taking advantage of the new habitat. (Species: pike, ruff, perch, pikeperch, cyprinides)

Norwegian Water Resources and Energy Directorate Effect of erosion protection work on sediment transport in Gråelva Gråelva Main sources of erosion = undercutting + mass movement

Norwegian Water Resources and Energy Directorate 8 The bed of the main river was raised and covered by an armouring layer Sediment transport measurement : * Maximum sediment concentrations reduced from mg/l to 3500 mg/l * Annual sediment transport rates decreased from t/yr to 5800 t/yr A year – to year variability of sediment transport controlled by climatic variables is still present

Norwegian Water Resources and Energy Directorate Main sources of erosion = undercutting + quick-clay slides Today Main sources of erosion = surface runoff Erosion protection work reduced the erosion of the river Gråelva and stopped the slides Sediment transport take place in a number of flood events of short duration caused by heavy rain or snowmelt  A year – to year variability of sediment transport controlled by climatic variables is still present

Norwegian Water Resources and Energy Directorate Hemskilen Quarries Narrowing of the river Istreelva due to increase in sediment load caused by: - Agriculture? - Quarries? - Climate change? (see water level, hydraulics conditions) 8 m 2,5 m

Norwegian Water Resources and Energy Directorate 11 Climate change 2000 years ago caused channel changes in the river Glomma Water discharge:  in old channel: warm and dry Q bankful = 880 m 3 /s  in recent channel: cold and wet Q bankful =1165 m 3 /s Natural changes in hydromorphology: Glomma

Norwegian Water Resources and Energy Directorate Flood events and changes of river : Gudbrandsdalen  impact of climate change? 12 Floods in 2011 and 2013 have changed rivers 170 m Lågen (Leiramoen): -5100m3 / tons after the 2011-flood Dørja

Norwegian Water Resources and Energy Directorate 13 Debris flow, undercuttings,  Impact on hydromorphology? Veiklåe, 2011

Norwegian Water Resources and Energy Directorate 14 Thanks!

Norwegian Water Resources and Energy Directorate Conclusion 15 «Sediment supply and sediment transfert as precondition for sustainable morphodynamics in river reaches.» - Comparing to a reference condition… In Norway due to hydropower regulations, historic state cannot be reached! Sediment regime defines the morphology of alluvial rivers  what is the new morphodynamics of norwegian rivers, under regulation conditions.  100 years of regulation… is it enough to reach a new equilibrium ? - Impact of climate change on natural hydromorphological changes?

Norwegian Water Resources and Energy Directorate Sikringstiltak 16

Norwegian Water Resources and Energy Directorate 17 = sediment trap Short-term changes in sediment transport: Atna