dsd-int 2016 local effects of the reshape of the niers - walter

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• Riparian rights (watermills) has been revoked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

Model

Cross-sections from hydraulik model Cross-sections in iMOD

Results

hydraulic head (in m above sealevel)

Computed (top) highest HAG; topographical image for reference purposes

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

iMOD International User Day, 1st November 2016

Local effects of the reshape of the Niers

Christian Walter

Niersverband, Germany

Thanks for your attention!