Morphological challenges: some Dutch examples.

1. Morphological challenges: morphological impact
resulting 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

2. 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

3. Mitigating measures/maintenance
• Removal of vegetation
• Dredging
• Structural measures

4. 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.

5. 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

6. 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).

7. Cyclic rejuvenation of
floodplains
Use of innovative techniques: Subsuction of sand

8. 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
9

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

11. 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.

12. 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.

13. Structural measures
• Groyne adaptations near inlets and outlets
• Guide bunds
• Longitudinal dams
• Inlet structures

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

15. Example of temporary
sructure

16. Groyne field protections made of vegetation

18. palenrij
Doorsnede
wilgenschern
geotextiel
sedimentvulling

19. The idea is to use these structures to minimise dredging,
within a program called
Self Supporting River System

20. 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

21. 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”,

22. 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

23. 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

24. Increasing flow conveyance :
The Gameren floodplain
June 2000

25. Upstream view
South and East channels

26. Downstream view
South and West channels

27. Erosion at intakes

28. Erosion of groyne root

31. 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

32. 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

33. Surface screen (‘bandall’)
From MSc. Thesis of Siem Troost (TU-Delft):
“Experimental research on the effects of surface screens on a mobile bed”
33

34. Solutions for intakes for side
channels
• Limited sediment inflow
• No hampering of navigation
• Moderate cost of construction and later adjustments

35. Sediment control methods
Curative
Preventive
Overview of sediment handling methods
(Eichenberger, 2001)

36. Preventive measures
Siting of intake at outer bend
Intake at
outer bend
Alignment of intake

37. Sediment excluding methods
Raised entrance sill

38. Bottom vanes
Submerged vanes in front of intake
Conceptual flow pattern

39. Vortex tubes Across the river
Partially from the river bank
Secondary channel
Bed material
River flow
Other preventive measures:
Skimming wall
Sloped training walls
Bottom/surface deflectors
Concave- convex guide walls
Undersluices
Tunnel (vortex) excluders
Barrage regulation

40. Monitoring
• Ecological monitoring
• Vegetation succession (flood levels)
• Morphology

41. 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).

42. Project Ewijkse Plaat

43. Ewijkse Plaat
Situation 1989

44. Vegetation changes 1992- 2009

45. Plan for extra channels

46. Gameren side channels
Situation 1995

47. Actual situation

48. Developments in
special plants
1980-2009

49. Distribution of
special plants
2009

50. Development in Waterplants and pioneer
vegetation since 1987

51. Developments in birds

52. Developments in
Bankswallows

53. Processes organisation

54. 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

55. Dynamic River Management
Separate presentation: DRM explanation

56. Monitoring
• Hydraulic monitoring: waterlevels and discharges through side
channels. Indications for silting up.
• Echo-sounding for bathymetry
• Frequency of Monitoring

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

58. Multibeam echolood meting
• Kribben bij
Haaften
• November
2002
• Meetdienst
DON
1-11-2004

59. Parameter Mapping scale Frequency
Vegetation
Thicket and Forest Visual survey 1 / year
Vegetation structures 1:5.000 1/5 year
Morphology
Bedlevel floodplain 1:5.000 1/10 year
(including
embankments)
Bedlevel of 1:5.000 1/5 year
secondary channels
and lakes
Erosion near Visual survey After every high
constructions discharge
Frequency of Monitoring

60. 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!

61. 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.

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

63. End of part 2
Thank you for your attention !

64. 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 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