120512 iasi morphology part 2 - mr hendrik havinga

1

Morphological challenges: morphological impact resulting from the demands of the individual interests

RESTORE – WORKSHOPPart 2

Sharing River restoration knowledge and experience in Europe,

Iaşi-ROMANIA, 9-11 May 2012

Hendrik Havinga

Rijkswaterstaat Oost NederlandDutch Ministry of Infrastructure and Environment

River restoration topics

• Goals (increase bio-diversity)• River functions• Current situation (natural river, regulated river, physics)• Restoration measures problems (challenge..)• Mitigating measures• Monitoring• Maintenance• Administration processes

Mitigating measures/maintenance

• Removal of vegetation • Dredging• Structural measures

Removal of vegetation

• Cutting trees, etc.• Concept of cyclic rejuvenation in the floodplains

– Measures are taken to restore the discharge capacity and increase natural diversity. These measures “rejuvenate” the area, e.g. silted up floodplains are excavated, on the bare ground pioneer vegetation will start to develop, thus restarting vegetation succession.

General concept of Cyclic Rejuvenation

• Cyclic sediment- and vegetation management: solution to combine flood protection and ecological rehabilitation

• Measures to restore the discharge capacity and to increase natural diversity, “rejuvenate” the area, e.g. excavation of silted up floodplains. On the bare ground pioneer vegetation will start to develop, thus restarting vegetation succession

• Tailormade approaches• Demands: Expertise of hydraulics + morphology,

ecological processes, flexibility

Design of Cyclic rejuvenation measures

• Knowledge of ecological processes• Knowledge of river engineering• Socio-economic factors• Success factors

– Legislation: Flood protection, dike stability, flora and fauna, forestry, bird- and habitat, environment, soil management, water pollution, Water Framework Directive (WFD).

– Small environmental impact– Reduced maintenance. Innovative techniques are

important:• Precise dealing with (contaminated) soil • Sub-suction of sand (leaving the top layer intact) • Complete removal of trees (including roots).

Cyclic rejuvenation of floodplains

Use of innovative techniques: Subsuction of sand

Dredging

• ..and dumping to reduce bed erosion

9

Dredging instead of structural measures• Consequences of dredging: hampering of navigation, increase of

maintenance, decrease of flood protection, CO2 emissions• However, dredging is cheaper than structural measures

Manners to cope with the situation

1. Accept the consequences of dredging.2. Start with dredging operations and begin developing mitigating

measures. In time reduce dredging efforts by executing structuralmeasures

3. Include mitigating structural measures in the Room for the River and WFD projects

1. Accept the consequences

• Natural banks and side channels will enforce dynamic rivermanagement concepts. This means regular monitoring of vegetationsuccession and morphological changes, checks of floodlevels and sailing depths. On an irregular basis maintenance is required.

• Estimated increase in maintenance costs (Netherlands): 3 M Euro/year for 200 km of river, or 15,000 euro/km/yr.

• 5-10 % of time the sailing depth’s will be less than optimal, leading to higher transport costs, estimated 15 M Euro/yr. This may effect a change in the transport modal split, i.e. more cargo by truck (>CO2).

• If maintenance is neglected also flood safety is at stake.

2. Start dredging, developstructural measures

• Dredged material has to be redeposited in the low water bed, to limit further longitudinal bed erosion.

• As dredging has become rather cheap, capitalisation of thismaintenance results in limited capital for structural measures.

• Reduction of dredging amounts are achieved by structural measures. Irrigation scheme solutions might help.

• The dredged spoil and vegetation waste could be used to buildtemporariy structures that limit shoaling.

Structural measures

• Groyne adaptations near inlets and outlets• Guide bunds• Longitudinal dams• Inlet structures

Mitigating measures to reduce impact of free banks:• Forebank protection, longitudinal dams, Island groynes

Example of temporarysructure

Groyne field protections made of vegetation

palenrij

wilgenschern

geotextiel

sedimentvulling

Doorsnede

The idea is to use these structures to minimise dredging,within a program called

Self Supporting River System

The Self Supporting River System (SSRS)

• Natural morpho-dynamics and available ‘spoil’ (sand and vegetation) are used to solve bottle-necks in a structural way

• This leads to reduction of cost• The use of natural products like biomass, sand and clay is

optimised to finance maintenance efforts

Maintenance according to SSRS• Small-scale changes in the river lay-out create a natural

equilibrium locally (e.g. local constrictions)• SSRS means: search for the local natural equilibria that

solve local problems• This is called “maintenance (building) with nature”,

SSRS-example: natural longitudinaldam• “Gabions” can be made from vegetation waste and

dredged spoil• Estimated lifetime: 2-6-10 (?) years• Can be the basis for a tradional dam made of tissue

and stone revetment, that is made later on, when more budget is available

• In the meantime research can be carried out

Reduction of maintenance

• Adequate design of structures/measures• No attitude “we will see what happens..”• Example of this attitude in next slides of Gameren side

channels

Increasing flow conveyance :The Gameren floodplain

June 2000

Upstream viewSouth and East channels

Downstream viewSouth and West channels

Erosion at intakes

Erosion of groyne root

Dealing with side channels: limiting uncertainties

Applying a Dynamic River Management System:– Quick-scan monitoring systems– Adequate Data storage and presention (GIS)– Impact assesment/design of measures

using 2-D hydraulic and morphological models – Quick implementation of correcting measures

• Use sandtraps near the upstream end of side channels• Use surface screens and bottom vanes to direct the

sediment to a preferred (dredging-) site. • Sills

Use of inlet structures to limit sedimentload

33

Surface screen (‘bandall’)

From MSc. Thesis of Siem Troost (TU-Delft): “Experimental research on the effects of surface screens on a mobile bed”

Solutions for intakes for sidechannels

• Limited sediment inflow• No hampering of navigation• Moderate cost of construction and later adjustments

Overview of sediment handling methods(Eichenberger, 2001)

PreventivePreventive

CurativeCurative

Sediment control methods

Preventive measuresSiting of intake at outer bend

Intake at outer bend

Alignment of intake

RaisedRaised entrance sillentrance sill

Sediment excluding methods

SubmergedSubmerged vanesvanes in front of intakein front of intake

Bottom Bottom vanesvanes

Conceptual flowConceptual flow patternpattern

Vortex tubes Across the river

Other preventive measures:Skimming wallSloped training wallsBottom/surface deflectorsConcave- convex guide wallsUndersluicesTunnel (vortex) excludersBarrage regulation

River flowBed material

Secondary channel

PartiallyPartially fromfrom the the riverriver bank bank

Monitoring

• Ecological monitoring• Vegetation succession (flood levels)• Morphology

Ecological monitoring

• In the Netherlands a Hydromorphological monitoring handbook is used. Description of 45 parameters to monitor.

• Some results from study ‘Rhine in the picture’ (Rijn in Beeld).

Project Ewijkse Plaat

Situation 1989

Ewijkse Plaat

Vegetation changes 1992- 2009

Plan for extra channels

Gameren side channels

Situation 1995

Actual situation

Developments in special plants1980-2009

Distribution of special plants2009

Development in Waterplants and pioneer vegetation since 1987

Developments in birds

Developments in Bankswallows

Processes organisation

The increase of ecological potentials of riverbanks and floodplains requires:

• Application of a Dynamic River Management System:• Changes in river administration methods (cooperation, active

management)• Conditions for succes are: money, research, adequate river

management, tailor made approaches

Dynamic River Management

Separate presentation: DRM explanation

Monitoring

• Hydraulic monitoring: waterlevels and discharges through sidechannels. Indications for silting up.

• Echo-sounding for bathymetry• Frequency of Monitoring

Detailpeilingen Slijk-Ewijk - km 889 - 891 - (-3.20m) 2-8-1998

1-11-2004

MultibeamMultibeam echolood metingecholood meting

• Kribben bij Haaften

• November 2002

• Meetdienst DON

Parameter Mapping scale Frequency

Vegetation

Thicket and Forest Visual survey 1 / year

Vegetation structures 1:5.000 1/5 year

Morphology

Bedlevel floodplain (including embankments)

1:5.000 1/10 year

Bedlevel of secondary channels and lakes

1:5.000 1/5 year

Erosion near constructions

Visual survey After every high discharge

Frequency of Monitoring

Administration processes

• Different responsibilities:– Terrain manager -> nature management– River manager -> reliable river works, flood protection, good

inland navigation• So… Transparent communication is necessary• Expert team to bridge the gap!

Planning and design of projects

• Use 1D and 2D morphological analyses• Projects in river system must be technically sound to safeguard all the

functions of the river, otherwise opposition against river restorationmay rise

• Establish a masterplan with defined targets concerning:– The river’s dynamic equilibrium: bed levels, sedimenttransport

capacities.– Navigation channel dimensions (width and Least Available Depth

during low (5%) discharges). This requires a reference waterlevelgoing with this low discharge.

• The impact of individual projects may not sustainably change these targets.

Discussion

• What is the first thing you will discuss at home ?

End of part 2

Thank you for your attention !

Literature

Breen, L.E. van, Jesse, P, Havinga, H 2005: River restoration from a river manager’s point of view. In: Rehabilitating large regulated rivers, Proceedings of Lownland River Rehabilitation Conference (Archiv für Hydrobilologie), Wageningen, 2003. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart.

Ghimire, B. 2003: No-regret solutions for intakes for secondary channels. M.Sc. Thesis. International Institute for Infrastructural, Hydraulic and Environmental Engineering (IHE), Delft.

Havinga, H. & Smits, A.J.M. 2000. River management along the Rhine: a retrospective view. In: Smits, A.J.M., Nienhuis, P.H. & Leuven, R.S.E.W. (Eds.). New Approaches to River Management, Backhuys Publishers, Leiden, pp. 15-32

Havinga, H. & Smits, A.J.M. 2000: River management along the Rhine: A retrospectiveview. In: Smits, A.J.M., Nienhuis, P.H. & Leuven, R.S.E.W. (Editors.) - New Approaches to River Management. Backhuys Publishers, Leiden.

Peters, B., Kater, E., Geerling, G. 2006: Cyclic management in floodplains (in Dutch). Centrum voor Water en Samenleving, Radboud University, Nijmegen.

PIANC, EnviCom Working Group 107 2009. Sustainable Waterways Within The Context of Navigation and Flood Management.

PIANC, 2003. Guidelines for sustainable inland waterways and navigation, Report ofworking group 6.

Sustainable Development of Floodplains, report: http://www.ecrr.org/sdfproject/sdfproject.htm