120512 Iasi morphology part 2 - Mr Hendrik Havinga
Morphological challenges: morphological impactresulting from the demands of the individual interests RESTORE – WORKSHOP Part 2 Sharing River restoration knowledge and experience in Europe, Iaşi-ROMANIA, 9-11 May 2012 Hendrik Havinga 1 Dutch Ministry of Infrastructure and Environment Rijkswaterstaat Oost Nederland
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 floodplainsUse of innovative techniques: Subsuction of sand
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 9
Manners to cope with the situation1. Accept the consequences of dredging.2. Start with dredging operations and begin developing mitigating measures. In time reduce dredging efforts by executing structural measures3. 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 river management concepts. This means regular monitoring of vegetation succession 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, develop structural 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 this maintenance 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 build temporariy 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
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 longitudinal• dam “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
Dealing with side channels: limiting uncertaintiesApplying 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 of inlet structures to limit sedimentload• 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
Surface screen (‘bandall’)From MSc. Thesis of Siem Troost (TU-Delft):“Experimental research on the effects of surface screens on a mobile bed” 33
Solutions for intakes for side channels• Limited sediment inflow• No hampering of navigation• Moderate cost of construction and later adjustments
Sediment control methods CurativePreventive Overview of sediment handling methods (Eichenberger, 2001)
Preventive measuresSiting of intake at outer bend Intake at outer bend Alignment of intake
Bottom vanesSubmerged vanes in front of intake Conceptual flow pattern
Vortex tubes Across the river Partially from the river bank Secondary channel Bed material River flowOther preventive measures:Skimming wallSloped training wallsBottom/surface deflectorsConcave- convex guide wallsUndersluicesTunnel (vortex) excludersBarrage regulation
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).
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 ManagementSeparate presentation: DRM explanation
Monitoring• Hydraulic monitoring: waterlevels and discharges through side channels. Indications for silting up.• Echo-sounding for bathymetry• Frequency of Monitoring
Multibeam echolood meting • Kribben bij Haaften • November 2002 • Meetdienst DON1-11-2004
Parameter Mapping scale FrequencyVegetationThicket and Forest Visual survey 1 / yearVegetation structures 1:5.000 1/5 yearMorphologyBedlevel floodplain 1:5.000 1/10 year(includingembankments)Bedlevel of 1:5.000 1/5 yearsecondary channelsand lakesErosion near Visual survey After every highconstructions dischargeFrequency 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 restoration may 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 waterlevel going 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 ?
LiteratureBreen, 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. 15-32Havinga, 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. (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 of working group 6.Sustainable Development of Floodplains, report: http://www.ecrr.org/sdfproject/sdfproject.htm