Hydraulic Engineering and Sediment TransportUniv.Prof. DI Dr. Helmut Habersack
DI Dr. Mario Klรถsch
University of Natural Resources and Life Sciences (BOKU), Vienna
โข Introduction to sediment transport and river morphology
โข Historic mophology of the Mur River
โข Human impacts and consequences
โข Hydraulic Engineering in the Basic Water Management Concept
โข Pilot measure Gosdorf
โข Monitoring of hydromorphology and verification ofconsiderations in the Basic Water Management Concept
โข Conclusions
โข Outlook
Content
Grotzinger & Jordan (2017)
Weathering Erosion
Transport
Sedimentation
Subsidence
Diagenesis
Sediment cycle
Sediment transport
L
h
๐ sin๐ผ
ฮฑ๐
๐ = ๐๐โ๐ผ
Bedload transport:(eg. Meyer-Peter and Mรผller, 1948)
Bed level change: (Exner-equation)
๐๐ = 8๐๐ โ ๐
๐๐๐3
๐
๐๐ โ ๐ ๐๐โ 0.047
32
Bed shear stress:
๐ฟ๐
๐ฟ๐ก=
1
๐ โ 1
๐ฟ๐๐ ๐ฟ๐ฅ
Degradation or Aggradation
Sediment supply and river morphology
Church (2006)
Sediment supplydeterminesmorphology
Sediment supply and river morphologyโฆ and determines slope
increased supply
decreased supplyaggradation
degradation
Slope adjustment via aggradation/degradation
Historic state of border MuraBefore rockslide near the village of Vratja vas in 15th century
Human impacts and consequencesSystematic channelisation (late 19th century)
Uniform width of 76m at low flow condition
Benefits:
โข Protect from damages from channel shifts
โข Gain land for agricultural use
โข Protect inlet structures for canals for diverse industrial uses
Hochenburger (1894)
Wagner et al. (2015)
Human impacts and consequencesReduction of sediment supply due to a chain of hydropower plants and torrent control
Hydropower plant Obervogau (Mur River) in a chain of hydropower plants, and plant Retznei affecting sedimentsupply from Sulm River catchment
ยฉ google earth
Human impacts and consequencesChannelisation:
โข Increase of radius of river bends
โข Increase of slope
โข Decrease of width
18171876
18171876
1 km
IST-Zustand
straight
Habersack, 2013
Human impacts and consequencesChange of morphological type
Historic Mur River
Channelised Mur River
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228
-10 10 30 50 70 90
Stationierung [m]
Hรถ
he [
m รผ
. A
.]
1981
1986
1989
1995
2000
2006
Profil km 114.840
Tertiรคr
Quartรคr
Human impacts and consequencesLimited thickness of gravel layer above finer sediment
Human impacts and consequencesRiverbed breakthrough at Salzach River
The Basic Water Management ConceptCollection and analysis of data
Cross section surveys showcontinuous degradation
The Basic Water Management ConceptReduction of bed shear stress: by changing slope or width?
Habersack und Schneider (2000)
Bedload transport capacity (%)
Ch
ann
el w
idth
(m)
Ch
ann
el s
lop
e(โฐ
)
The Basic Water Management ConceptMeasure types
Habersack et al. (2001)
The Basic Water Management ConceptModelling of scenarios with the sediment transport model
Hengl et al. (2001)
MeasuresPilot measure Gosdorf
โข Removal of riprap from the left bank
โข Excavation of a side-channel
โข Supply of excavated sediment from side-channel into main channel
July 2008 โJune 2009June 2009 โDecember 2009
Monitoring
Repeated bed surveys
โข Erosion of supplied sediment in Gosdorf reach
โข Transport downstream
โข (Temporary) stabilisation of bed levels
July 2008 โDecember 2009
Bed level change
Monitoring Bedload velocity
Mean grain size dm (b-axis 42mm): ~1 km per year
D90 (b-axis= 106mm): ~ 100m per year
โข Decreased velocity in restored reach due to vertical mixing
โข Increased velocity downstream
โข Most sediment now already in the downstream part ofthe border section or transported further downstream
Monitoring Bedload transport: Assessment of critical shear stress
โข Measuring tracer mobility by continuous tracer surveyโข Modelling shear stress at tracer locations with a 2D
hydrodynamic-numerical model
Determination of critical thresholds for transport
Monitoring Quantification of bedload transport
Basket sampler measurements Calculation of bedload yield
Monitoring
Simplified consideration in Basic WaterManagement Concept:
Channel widening following a simple relation, until width reached 150m (within 17 years)
Limited bank erosion
despite major flow event (> 1000 m3/s)
Measurement of riverbank erosion
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230
0 20 40 60 80 100 120 140
elev
atio
n [
m a
.s.l
.]
distance [m]
Profil 1
2007 2018
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221
222
223
224
225
226
227
228
229
230
0 20 40 60 80 100 120 140
elev
atio
n [
m a
.s.l
.]
distance [m]
Profil 2
2007 2018
Width increased by 10 m (uniform section) to 28 m (downstream ofnatural rock sill)
Monitoring Measurement of riverbank erosion
Limited bank erosion
Monitoring Relevance of river curvature and sediment supplyGosdorf vs. Sicheldorf
Conclusionsโข Disturbed sediment regime at Mur River, no input from upstream sediment deficit
โข Idea of Basic Water Management Concept: Stabilise bed and supply sediment via self-dynamic widenings
โข Monitoring showed stabilising effect at the beginning
โข According to tracer study most tracers must have been transported near the downstream end or out of the border section
โข Self-dynamic increase of channel width remained below expectations (10m to 28m erosioncompared to 150m after 15 years in Basic Water Managment Concept)
โข No change of river course โ no increased curvature
โข Consequence: Initial stabilisiation of bed level turns back to incision
โข Threat of loosing the gravel layer
โข Need for action to maintain flood protection and to save and improve ecological condition
Outlook (1) โข Necessity to analyse and verify the indicated effects at all restored sites of the border Mura
โข Identifying the role of individual components (supply, width, river course etc.)
โข Development of a Concept for future measures, focusing on the central points:
โข Sediment budget
โข Bedload supply from the banks and from upstream (goal for longterm: restoration ofsediment connectivity)
โข Increase channel width to promote the development of bars and other structures
โข Considering optimisation of river course (curvature) to increase secondary currents and bankerosion, including instream structures
โข Find optimised mix of measures in goMURra โ quantity of sediment supply, size of riverbendradius and width (and related slope change)
Outlook (2) โข Methodology: Analysis of monitoring data (cross sections, low flow water levels, satellite
images (width) etc.), Application of a 3D-hydrodynamic-numerical model coupled with a sediment transport and bank erosion model to determine the effects of scenarios of measurecombination
โข Implementation of pilot measure / adaptation of Gosdorf and monitoring
โข Find sections with potential for corridor
โข Importance of ecological evaluation of measures
โข Coordination with public water supply โ change of groundwater levels
โข Effect for flood protection
โข -> integrated river engineering approach needed
THANK YOU!Helmut Habersack
Institute of Hydraulic Engineering and River Research
University of Natural Resources and Life Sciences, Vienna
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