BREACH FORMATIONA Review of State-of-the-Art

Mark MorrisHR Wallingford

IMPACT ProjectWorkshopWallingford, 16/17 May

2002

Overview

Breach Formation

What is the problem with breach formation, and why?

What has been done in the past to predict breach conditions?

What tools exist already and what are our current capabilities?

What needs to be done? What is being done? Where does the future take us?

Breach Formation

What is the problem to be solved? Why?

Breach Formation

The Process

Breach Formation

The Process

Breach Formation

The Process

Breach Formation

The Process

Breach Formation

The Process

Breach Formation

The Process

Breach Formation

The Process

Breach Formation

The Process

Breach Formation

The Process

Breach Formation

The Process

Breach Formation

The Process

Breach Formation

The challenge...

What is the scope of the challenge?

Breach Formation

End Users / Applications

Multiple end users Multiple applications Multiple processes Multiple situations Multiple loading Different failure modes

Dam owners,emergency planning, land use etc

Risk assess., asset management, planning etc

Location, initiation, formation etc

Dams, fluvial, coastal defences

Type and duration

Overtopping, piping, foundations etc

!!!

Breach Formation

Process in relation to embankment type

Different processes are critical for different embankment types & locations

Breach Formation

Process in relation to embankment type

Different processes are critical for different embankment types & locations

Multiple combination of effects leading to breach formation via many routes...

Breach Formation

What has been done so far?

What has been done so far?

Breach Formation

Definition of approach

Non - physically based methods e.g. Equation fitting (see review by Wahl)

Semi - physically based methods e.g. Models with user / pre-defined growth patterns

Physically based methods e.g. Simulation of hydraulics, sediment transport, soil

mechanics

Breach Formation

Physically Based Models

15 models listed under Table 3 Various approaches, limitations & deficiencies

Consider how breach formation occurs Not many models combine hydraulics, sediment

movement & soil mechanics...

Breach Formation

Achievements

What have we achieved through work on these 15 models (and

others)?

CADAM

Findings: Breach modelling

Discharge through the breach (Run 2)

t [s]

0 50 100 150 200 250 300 350 400

Q [l/s]

0

5

10

15

20

25

30

35

40

1

45

0

6

70 Measured1 NWS BREACH4 Paquier 2d5 Nogues / Goutal6 Broich7 Broich 2d

Breach Formation

The Current Situation

Conclusion:

We have not yet produced a ‘reliable’ breach model

What is our real ability to predict: Peak discharge or hydrograph? Timing? Piping? Location?

Breach Formation

What Needs to be Done?

Need to develop more reliable tools based on combined hydraulics and soil mechanics theory + ?

Conclusions from CADAM are broadly consistent with US conclusions for research:

(see 8 points in paper & Greg Hanson tomorrow)

Breach Formation - Specific Processes

What Needs to be Done?

Modelling processes: Sediment transport equations not steady state Flow not 1D (USDA) Growth mechanisms not simply continuous

micro / macro bank instability ** Breach initiation? Removal of eroded material

Breach Formation - Specific Processes

Erosion Processes

Breach Formation - Specific Processes

What can be approximated - or not?

Modelling of: Valley shape Breach location Initiation mode Material properties Composite structure interaction

Breach Formation - Specific Processes

Direction of research:

Modelling of: Real geometry free breach formation Better representation of processes

sediment continuity / eqns etc. Uncertainty? Use computing power 1D or 2D or 3D?

Breach Formation

What Needs to be Done?

Breach formation processes Homogeneous, composite, non-cohesive, cohesive Flood hydrograph, timing, Overtopping, piping

Breach initiation Timing Factors Processes

Breach location Risk management

Breach Formation

Present and Future Initiatives?

IMPACT - European Commission Reducing the Risk of Embankment Failure

Under Extreme Conditions (UK EA) USDA-ARS - SITES USBR / Quebec TU Delft HR BREACH - HR Wallingford University Research

IMPACT partners Birmingham, Durham, Australia, The world!

Breach Formation

Present and Future Initiatives?

Climate Change Research (Various) Risk Based Flood Management (UK)

Dam Risk Management Modelling Decision Support Framework (MDSF) Risk Assessment for Coastal Defence Systems for

Strategic Planning (RASP)

PC-RING (Netherlands)

Breach Formation

Conclusions - Future Direction

Where from here?

Breach Formation

Future Direction

• Back to basic processes, fundamental principles (again?)

• Combine disciplines (hydraulics + soils + uncertainty + ?)

• Develop tools to support end users needs (risk management)

• Start simple complex (ensure realistic)

• Observe prototype behaviour (beware scale effects)

• Collate failure data (field data)

Breach Formation

Future Direction - Secondary Challenges

Research throws up more challenges, such as:

• Scaling effects for sediments / erosion / breach formation

• Instrumentation for monitoring tests

• Instrumentation for operation and maintenance of embankments (IMPACT-ADD?)

Breach Formation

Future Direction

IMPACT does offer an opportunity to progress work in this area by allowing researchers / end users:

• to participate with / share common data sets

• to objectively assess existing and new model performance

• to develop improved models based upon field, laboratory and case study data

By no means the only initiative - follow other initiatives worldwide...

The drive for risk based tools will return to fundamental processes...