BREACH FORMATION A Review of State-of-the-Art Mark Morris HR Wallingford IMPACT Project Workshop Wallingford, 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 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 Measured 1 NWS BREACH 4 Paquier 2d 5 Nogues / Goutal 6 Broich 7 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...