Asian River Restoration Network (ARRN) forum 2015 (15 Apr. 2015 in Kyungju, Rep. of Korea)

ARRNSeminar,April,15,2015

Sedimentreplenishmentbelowdams
forprocessbasedriverecologicalrestoration

Giyoung Ock : Hanyang University, Korea
Tetsuya Sumi*, Yasuhiro Takemon*, Matt Kondolf***Kyoto University, Japan**University of California, Berkeley, US

Pristineriverlandscapewithcomplexstructure,
dynamicsandlinkage

TagliamentoRiver,Italy(photobyOck in2010)

Structure:Mosaicorlinearfeatures
Dynamic:Expansion/contraction;rapidsuccession
Linkage: toterrestrial,subterranean,aerialsystems
Function:Hotspotsofbiodiversityandproduction
Conservation:Morethreatenedthantheirmarineandterrestrial
counterparts(Tockner,2000)
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Asian River Restoration Network (ARRN) forum 2015 (15 Apr. 2015 in Kyungju, Rep. of Korea)

Shiftinghabitatmosaic
supports
highbiodiversity• Highsedimentsupply
withnaturalflooding• Expanding/contracting
ecosystems:• Spatiotemporal
dynamicsoflinked
aquaticterrestrial
landscapes (Photos:Ock2010)

Sediment starvation in stream channels below dams
‘hungry water’ (Kondolf 1994)¾ River channel is a conveyor belt forsediment transport (Kondolf 1994)¾ Dams interrupt the continuity of sedimenttransport through river systems-causing sediment to accumulate within
the reservoir (storage decrease)- depriving downstream reaches ofsediments (sediment starvation)¾ The sediment starvation causes loss of geomorphic features,
accompanied by- simplification of habitat structure- degradation of ecological functions in riverine ecosystem (Ligon1995, Power 1996).

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Asian River Restoration Network (ARRN) forum 2015 (15 Apr. 2015 in Kyungju, Rep. of Korea)

DamimpactsonSedimentRoutingSystem
inariverbasin(膄葄緊 )
Balancing of sediment transport
from the source of the river tothe coast

Sedimentation

Lack ofsediment supply

Check dam
Storagereservoir

Riverbeddegradation

Coastal erosion

River environment changes(physical, ecological,environmental effects)

Sediment/flow monitoring
Bed load
Suspended load
Wash load

5Integrated Sediment Management Strategies (Sumi 2010)63

Asian River Restoration Network (ARRN) forum 2015 (15 Apr. 2015 in Kyungju, Rep. of Korea)

Sediment Replenishment or Augmentation
Artificially adding sediment into stream channel in a variety ways,
in order to:(1) to make up the sediment deficit downstream and(2) to mitigate morphological and ecological changes derived by thesediment starvationjReddingqSan Francisco(> 20 rivers in Japan)(>18 rivers in CA, USA >¾ It has been an increasingly practicein Japan nationwide and the west coast of US.

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Process-based river ecological restoration•reestablishesnormativeratesand
magnitudesofphysical,chemical,
andbiologicalprocessesthatcreateandsustainriverand
floodplainecosystems(Beechie etal.

•restores3dimentionalhydrologic
connectivitywhichreferstothewater
mediatedfluxesofmaterial,energy,andorganismswithinandamongcomponents
oftheecosystem(Kondolf etal.2006)2010)

Pre-degradation
Restoration (2000s)

Impoundment(1930)

Choosing processes to restore
habitat complexity (Beechie et al. 2010)

Channel simplification(1870s)3-D river degradation andrestoration (Kondolf et al. 2006)

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Asian River Restoration Network (ARRN) forum 2015 (15 Apr. 2015 in Kyungju, Rep. of Korea)

Past restoration activities
In-stream mgmt. measures (1970-80s).
yGzGy

It was found that they were less efficient andnot sustainablezGzGyGj

Methodological development depending on purposes
and implementation techniques (Ock et al 2013)

Modern augmentation (after 2000s): to support geomorphic processes forchannel complexity and substrate quality
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Asian River Restoration Network (ARRN) forum 2015 (15 Apr. 2015 in Kyungju, Rep. of Korea)

Missing Link ofSediment augmentation to Ecological functions
Gravel Augmentation
Sediment quality and quantity
Dam release flow regulation

Geomorphological Responses
Geomorphic process (Erosion-Transport-Deposition)
Riffle and Pool structure
Bar and Island structure

Habitat Diversity
Physical (substrate, flow depth, velocity)
Biochemical (DO, pH, nutrients)
Water temperature (Hyporheic exchange)
Food source (Organic Matter)

Ecological Function
Biodiversity: life form for fish, invertebrates

9 Much river restoration projects have a
missing link between geomorphologicalchanges caused by gravel augmentationand subsequent contribution toecological functioning.

This study aims to- compare gravel augmentation
implementation- focusing on geomorphologicalresponses (in-channel Riffles andBars),- and their effects on ecologicalbenefits, particularly in Organic
matter retention and Hyporheicexchange

Material cycle: Organic matter retention,
Ecosystem energy flow, Foodweb, Purification

High-flow stockpile in the Nunome River, Japan(2) Frequency: 1-3 times a year depending on
natural flood-runoff
Peak duration: 2-4 hours
Flow discharge(1) Source of sediment: Upstream end of reservoir

Check Dam

Reservoir

2006

2007

2008

2009

Nunome Dam
Location ofHigh-flow
injection(3) Volume of sediment: depending on release flow (upto 500 m3 per event)Size of sediment : mixed sand and gravel (0.075-19mm)

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Asian River Restoration Network (ARRN) forum 2015 (15 Apr. 2015 in Kyungju, Rep. of Korea)

Downstream effects on geomorphic featuresand subsequent ecological functions¾ Geomorphological responses
Repeated high-flow stockpile prevents riverbed fromlowering (degradation) in the regulated channel,- supplementing existing riffles- maintaining long riffles along channels(accounting for 68% )¾ Ecological responses(2) Benthic macroinvertebrates (BMI) distribution(1)Relative contribution of suspended POM(particulate organic matter) sources
Reservoir plankton• Riffles show high retention capacity ofreservoir plankton (ecosystem food quality)• Species richness increased• Functional feeding group responses(predators & grazers increased)

Trinity River Restoration Program (TRRP)

Primary goal:
Restore and sustain natural production ofSalmon fish populations downstream ofLewiston Dam to pre-dam levels.

Restoration Strategy:
A combination of(1) Re-introduction of naturalized flow
regime with peak flow(2) Coarse sediment augmentation(3) Mechanical channel rehabilitation
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Asian River Restoration Network (ARRN) forum 2015 (15 Apr. 2015 in Kyungju, Rep. of Korea)

High-flow injection & Gravel placement (2009-2011)
Before (2009)

After (2011)

alcove¾ High-flow injection created a ěMedial Bar(island)’ 400 m downstream through a dynamic
process (supply-scour-transport-deposition)¾ Gravel placement constructed a ‘Point Bar
with an alcove’(Gaeuman 2013)

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Asian River Restoration Network (ARRN) forum 2015 (15 Apr. 2015 in Kyungju, Rep. of Korea)

Ecological functions of Restored gravel barsby gravel augmentation (Ock & Kondolf, 2014)

17Summary Recent river restoration projects have increasingly applied for a various
sediment augmentation with the aim of enhancing geomorphic processes
along with environmental flow restoration
 Sediment replenishment below dams is increasingly used for processbased ecological restoration strategies, but still needs a linkage between
the physical habitat diversity and ecological functions.
 This study summarized sediment augmentation processes by comparisonof two different cases in Nunome River (High-flow stockpile) and Trinity
River (High-flow injection) in the context with riffle-pool reconstruction
and gravel bar restoration.
 Restored riffle-pool feature and gravel bars provide (1) a complex habitat
structures for fish spawning and rearing, (2) function as a strong naturalfilters for riverine organic matters, and (3) induce hyporheic flows,
providing hydrological and thermal heterogeneity
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