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8Environmentally friendly drainage

practices Jukka Jormola, Liisa Laitinen and Auri Sarvilinna

Finnish Environment Institute SYKE 10th International Drainage Workshop

Helsinki, Finland | Tallinn, Estonia July 6th - 11th 2008

How to combine drainage and ecological restoration of small watercourses?Natural recovery of dredged streamsAgricultural streams for fish, even trout production2-stage profiles

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How to combine drainage and ecological restoration of small watercourses?

Drainage is needed in changing climateFrom degradation to ecological restoration of small streamsDrainage practices mustbe developedMethods of Environmentalhydraulic engineering and restoration

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Natural recovery of dredged streams

Siltation and vegetationgrowth – need for new dredgingAlso start for naturalecological recoveryFish, even trout can returnCan be utilized in drainage works

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8Agricultural streams for trout production

Restoration of straightened brooksMeander excavation, if no natural recoveryStones and gravel for fishhabitats and erosioncontrol

Longinoja brook, March 2006

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Gravel for spawning groundsGravel riffles, water shouldgo through for trout eggdevelopment over winterSiltation of gravel may be a problem

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Channels with drainage needsTraditional excavation:

- straight, monotonous- broad and shallow bed on dry

seasons- Slope gradients < 1:2 help for vegetation recovery

- water turbidity as the whole bed is excavated form on e side

2-stage profile-digging only from the side of machine position

-widening flood terraces in stead of the whole bed

-narrow low flow bed with enough depth for fish can be preserved

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8Traditional and 2-stage profile - new goal for dredging

Development from natural to new good ecological statefrom A to D

(Järvenpää, L. 2004)

A. Natural stream with floodsB. Dredging by traditional profileC. Siltation and recovery, need for

maintenance dredgingD. Excavation with 2 -stage

profile with flood terrace- recoverycan continue to good state

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Experience of 2 –stage profile at Juottimenoja brook, July 2007 (highly eroding circumstances)

No or little turbidity of waterduring excavationVegetation and stumpsprotects the remaining lowflow bedTerrace level adjustement as low as possible

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Eperience after 2 months

Slight erosion could benoted, collapsing of banksDevelopment of new terrace to 3-stage profile

Sedimentation behindvegetationTrout observations on the excavated section

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Experience after one yearErosion and widening of lowflow bed (construction of onlyone weir was possiblebecause of missing winterfrost 2007-08)Vegetation has developed on flood terracesStone material will beneeded to stop bottomerosion

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Experience of fish on restoration sitesJuvenile trouts, locally bornand self migrated fromstocking in the main riverAdult trouts migrated fromthe sea, preparing for spawning

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Electro fishing results, Longinoja brook

High densities, 140 trouts/100 m2 after restorationRestoration site better than reference sections

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140

160

2005 2006 2007

Indi

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Ref. lower partRestoration sectionRef. upper partRestoration

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Electro fishing reslults, Kocksbybäcken brook

Good reference section downstream of the restoration siteNo fish in restoration year, bad water circumstancesNext year increase of trout juvenile amount to half of the reference section

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2005 2006 2007

Indi

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Ref. lower partRestoration sectionRef. upper part

Restoration

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8Conlusions of 2-stage profile

Good water quality duringexcavationDiversity could be preservedErosion control by stonematerial, wood material and vegetation is needed on highgradient, also for fishhabitatsWetlands and pools neededdownstream for sedimentation

Monitoring needs:- erosion on different soils- conveyance during flood after vegetation growth- flood terraces as sedimenttraps- fish habitat development

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Conclusions of restoration for fish

High trout juvenile production is possible in agricultural streamsErosion control is essential to preventdisadvantages for fish and whole downstreamwatercourseTechnical drainage needs, water quality and restoration for valuable fish species can becombined

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8Thank you!