DSD-INT 2014 - Delft3D Users Meeting - Stream response to mining subsidence - Delft3D subsidence...

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Stream response to mining subsidence: first results of the newly developed Delft3D

subsidence module

Delft Software Days 2014

Imke Evers1, Sebastian Henkel1, Roy

Frings1, Aukje Spruyt2, Willem

Ottevanger2, Holger Schüttrumpf1

1 Institute of Hydraulic Engineering and Water Resources Management, RWTH Aachen University

2 Deltares

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04.11.2014 Delft Software Days

Coal mine and coke oven Anna Aachen-Limbourg coal mining area - WDR Digit

Introduction

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Topography

Morphology

Water level

Introduction

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Stream response to subsidence

Introduction

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Problem:

Mining subsidence cause local lowering of the river channel and its

floodplains

Consequences:

Change in sedimentation pattern on the floodplains during a flood

Accumulation of cohesive sediments polluted by heavy metals

Introduction

Objective: determine the influence of subsidence on

• frequency and magnitude of floodplain inundation

• accumulation of cohesive sediments

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Research area

Methods

Implementation of subsidence

Set up of a numerical model

Scenario development of a sink-hole

Results

Conclusion

Outline and approach

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Research area

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Research area

River Wurm:

Length 57 km

Width: 5 – 10 m

Mean discharge: 2 m³/s

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Implementation of subsidence/uplift in Delft3D

Concept:

Subsidence change of base level elevation

Time- and space-varying

Free adjustment of bed level and water level due to subsidence

Methods

Base level

Bed level

Water level

Ele

vation (

m)

Distance along cross-section n=5 (m)

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Implementation of subsidence/uplift in Delft3D

Creation of a new file: (.sdu)

Implementation in the master definition file (.mdf)

Methods

Reproduction of subsidence/ uplift

• Predefined Time-series

• Predefined location

Predefined time steps for

„bedrock surface elevation“

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Setup of the numerical model

Dimensions and discretisation:

1000 m x 600 m river section

Cell size floodplains: 100 m²

Cell size riverbed: 30 m²

Time settings:

Time step: 0.001 min.

Simulated time 10 days

General settings:

Only cohesive sediments

One type of sediment and one well mixed layer

Hydraulic roughness: Chezy = 40 m1/2/s

Methods

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Initial conditions:

Topography resolution: 1 point

per meter

Riverbed elevation mapped

with GPS

Sediment influx: 0.5 kg/m³

Boundary conditions:

Inflow: timeline discharge

Outflow: QH-Relation

Measured during flood event

Methods

Discharge Q [m³/s]

Wate

r le

vel [m

]

H measured

Rating curve

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Scenario analysis

Flood event (Peak discharge Q=39.7 m³/s)

1. No subsidence (reference)

2. Formation of a sink-hole in 1 day

Sink-hole position: midstream

Sink-hole size: 90 x 90 m

Sink-hole depth: 1 m

Methods

Analysis of

• Magnitude and frequency of floodplain inundation

• Amount of accumulated cohesive sediments

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Simulation of a flood event

Results

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3

2

1

0

[m]

Magnitude of floodplain inundation: Discharge 39.7 m³/s

Results

Sink-hole

Size of flooded area:

0.06 km²

Size of flooded area:

0.04 km²

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Results

Frequency of inundation: Discharge 17 m³/s

Sink-hole

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3

2

1

0

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Results

Amount of accumulated cohesive sediments:

Sink-hole

0.25

0.20

0.10

0.05

0

0.15

Sedimentation on

floodplains:

227 m³

Sedimentation on

floodplains:

930 m³

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First results:

It is possible to implement subsidence or uplift in a Delft3D model

Stream response to sink-hole:

Less inundation of the floodplains

Inundation starts at lower discharge

Accumulation of cohesive sediments in the sink-hole depression

Local increase of sedimentation on the floodplains

Further research:

Variation of location, size and depth of the subsidence

Simulation of longer time series

Conclusion

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Thank you for your attention

End

DSD-INT 2014 - Delft3D Users Meeting - Stream response to mining subsidence - Delft3D subsidence...

Engineering

Transcript of DSD-INT 2014 - Delft3D Users Meeting - Stream response to mining subsidence - Delft3D subsidence...