iMOD International User Day, 1st November 2016 Local effects of the reshape of the Niers Christian Walter Niersverband, Germany
iMOD International User Day, 1st November 2016
Local effects of the reshape of the Niers
Christian Walter
Niersverband, Germany
Local effects of the reshape of the Niers
• Introduction
• The project
• Why iMOD ?
• Model/Results
• Next steps and conclusion
Delft
Introduction
The Niersverband:
• Headquartered in Viersen
• 330 employees
• water board responsible for the hole (german)
catchment area of the river Niers
• wastewater and rainwater treatment
• waters care and restauration of the river
Introduction
The Niers:
• length ca.116 km, last 8 km in the Netherlands
• flows into the Maas
• catchment area ca.1400 sqkm, between rhine and maas
• Source 73 m above sealevel
• Mouth 10 m above sealevel in Gennep, NL
• Slope: first 30 km ~ 0,6 ‰ (60 cm/km)
the following 85 km ~ 0,25 ‰ (25 cm/km)
• no mountains in the catchment area
Introduction
The Niers
• Since Middle Ages lots of watermills (1920: 37), though rare slope
• Population increases and industrialisation decreases water quality
(Reasons for founding Niersverband in 1927)
• Riparian rights (watermills) has been revoked
• Niers was straightend and put in the dump of the valley
regional groudwater lowering, less floodings, quicker runoff
Agriculture is possible in the floodplain
Introduction
The Niers
• Niers valley underground is builded from thick layers of sand and
gravel from the ice age
• Groundwaterlevels in the narrow Niers valley
are between 0 and 3 m below the surface
• Niers and its tributaries are fed from emerging groundwaters
Changes in waterlevels of the niers river have effects on the
groundwater levels
Introduction
• Since the 1980th a more ecological kind of view became accepted
• (Not at last) the european water framework directive has lead to
the request of removement of all weirs and such structures
• Weirs are relicts from the straightening last century
• Weirs support groundwaterlevels next to wood footed buildings
• Many Weirs has been broken down in the last years
Footing of the buildings has been replaced
Buildings has been destroyed
The project “Wissener Schleife“
• The weir „Wissen“ is the last one between the mouth and
Mönchengladbach
• Mouth km 0
Wissen km 37
Mönchengladbach km 95
• Waterlevel and bottom difference from about 1m
• Weir lies beneath Schloss Wissen with a moat, filled by Niers-
water
The project “Wissener Schleife“
• Downstream of the weir
the Niers has been straightened in 1935
• As second part of the project
the old reach will be reactivated
• Both reaches are used
(one for ecology; the other for high water and canoes)
• What questions have to be answered now ???
The project “Wissener Schleife“
• Why actual to consider about changes?
Only few plots possessed by the Niersverband
Landowners want to know the effects on land use
(agriculture and forestry)
castle „Wissen“: can any subsidence happen to the buildings?
Parts of the planning area are under nature protection
Enough reasons to calculate with a groundwater-model
From DELTARES(2015):
Actualisatie en Kalibratie IBRAHYM
Why iMOD ?
Easy question - easy answer!
• In the province Limburg/NL exists an iMOD-based Model „IBRAHYM“
since years
• In 2012 the NAGREWA-project takes place. That was an EU-project
with 5 different water boards in NL and in D
• The dutch water board Peel en Maasvallei and the german
Niersverband have developed it for the lower reaches of the Niers
• The Niersmodell was worked out bei DHV, ahu and Deltares
• Through the NAGREWA-project a first part from the Niersverbands-
catchment area became part of the IBRAHYM-model.
Why iMOD ?
Once again:
• Model is existing and could be used to answer the questions!
Changes in groundwaterlevels should be estimated
Sensitivity analysis minimization of encroachment
• The project has two big aims:
- to remove the weir „Wissen“
- to reactivate a historical river course
Model description
Input
• rearrangement-planning; measured timeseries
• Hydraulic 2D-modell delivers waterlevels, (steady state)
• projected on the new water reaches and timeseries adapted
Border conditions (for the river)
• waterlevels upstream the weir should be the same as today
(wetland should be protected)
• runoff division 50/50 between both reaches (mean water)
• high water: bigger part runs through existing reach
Results
Computed differences between the averaged
groundwater level and the renewed Niers-“Altarm”
• absolute levels of groundwater cannot show the difference
between present situation and planning
Use of the computed differences instead.
• There is a wide range of differences in the modelled period
We decided to take the mean differences
Results
Sensitivity analysis • bed resistance is one of the key parameter in this project
• Another one is width of the river (less sensitive)
• Variation of 4 types:
I. Gravel (Cb = 0.01 days)
II. Sand (Cb = 0.1 days)
III. Loam (Cb = 1.0 days)
IV. Silty/clayey (Cb = 10.0 days)
Computed
differences between
the averaged
groundwater level
and the renewed
Niers-“Altarm” for
(top left) gravel,
(top right) sand,
(bottom left) loam,
(bottom right) clay
Results
• Further planning with szenario “sand bed resistance”
• Drillings have confirmed this meanwhile
• Opportunity to influence this parameter
through different bedmaterial while renaturation
• The outline of this szenario (> 10 cm difference)
is used as investigation area
Results
• Intersection with landuse
Different consultants to estimate
changes for agriculture and forestry
• Intersection with land owners
• With each owner should be made
an agreement or contract
• With regard to compensation
Next steps and conclusion
• Agreement with land owners
• Approval procedure at Bezirksregierung Düsseldorf
means participation of all public authorities
and involved private persons
• Results from groundwatermodelling are very suitable for further steps
• Resolution of the regional model was good enough
for working on a detailed question