International Levee Handbook Overview of the handbook Chapter 7 Site characterisation and data requirements

Chapter 7 - context

7Site characterisation and data requirements Chapter has two principal themes –Actions on levees Determination of hydraulic actions for fluvial, coastal and shoreline, and estuarine levees at the toe Human actions on levees –Assessment of the physical characteristics of the levee and environs Geotechnical Fluvial, coast and shoreline, and estuarine dynamics

7.1Principles of site characterisation

7.1Principles of site characterisation Needs for characterisation Adopt a phased approach to characterisation Desk study –Undertaking and sources of information –Ground “truthing” by walkover survey Implementing investigations –Roles of personnel involved and H&S Reporting –Desk study data, meta-data, hydraulic, morphology and geotechnical data, and preservation and presentation of data

Phased approach – typically three –Reconnaissance (Initial assessment of viability) Utilising existing information for rudimentary hydraulic modelling and preliminary assessment of ground conditions. –Feasibility (Develop better understanding) Detailed hydraulic data and modelling Limited geotechnical investigations to support assessment 7.1Principles of site characterisation –Detailed (Final design) Detailed geotechnical assessment Update or refine hydraulic data and modelling

7.1Principles of site characterisation

7.2Morphological, hydraulic and other natural actions on levees Riverine, coastal and shoreline, or estuary settings must consider: –Interaction between levees and environmental factors –Influences of seasonal change and extreme events –Influences of long-term change –Actions from other natural processes

Actions from other natural processes include: –Windblown sedimentsChoke vegetation –Wind on vegetationForces on slope –Seismic Body forces & liquefaction –Ice on river Water levels & damage –Rainfall Soil strength & erosion –Sun Desiccation & kill vegetation –Climate change Levee structure, as above, & hydraulic actions 7.2Morphological, hydraulic and other natural actions on levees

7.2Morphological, hydraulic and other natural actions on levees

7.3Morphology and hydraulic actions for riverine levees Understanding river characteristics Determination of hydraulic actions –Data needed Measurement of flows and water levels Sediment movement Bed roughness and geometry Wind Water levels and waves –Methods of determining hydraulic actions Flow and water level analysis Modelling of hydraulic processes Influence of shipping and ice Uncertainty in data and analysis

7.3Morphology and hydraulic actions for riverine levees

7.3Morphology and hydraulic actions for riverine levees Rivers are dynamic systems that: −Are a product of their environment Soils and geology Gradients (slope of landscape) Hydrology (rainfall and runoff) −Respond to variable hydraulic actions Lateral movements Vertical movements Volume and Rate of flow

7.3Morphology and hydraulic actions for riverine levees Levees may change hydraulic conditions and alter the dynamic equilibrium of these systems Assessment of hydraulic actions is essential to establish present and expected behaviour

7.4Morphology and hydraulic actions for coastal and shoreline levees Understanding coastal characteristics

7.4Morphology and hydraulic actions for coastal and shoreline levees Determination of hydraulic actions –Data needed Sediment movement and bathymetry. Pressure and wind Water levels and waves Marine currents and tides Tsunamis –Methods of determining hydraulic actions Extreme water level and wave analysis Joint probability wave and water level Uncertainty in data and analysis

7.4Morphology and hydraulic actions for coastal and shoreline levees Coastal and shoreline systems are dynamic and highly complex Hydraulic loads acting on coastal levees vary: –Geographically –Over time (daily, monthly, seasonal, decadal and longer-term) –Comprise various combinations of water levels, currents, and waves

7.4Morphology and hydraulic actions for coastal and shoreline levees Necessary to know extreme water levels, waves, currents, and morphological response

7.5Morphology and hydraulic actions for estuarine levees Principle concern derives from how estuary characteristics influence water levels, velocities and wave heights in transition between river and coast Estuarine morphology –Processes originate from both sea and river sources –Dependant on shape and bathymetry of estuary –Series of questions presented (Table 7.38) to assist in analysis of estuaries Hydraulic action on estuarine levees –Determining hydraulic actions on estuarine levees involves a combination of river and coastal analysis techniques

7.5Morphology and hydraulic actions for estuarine levees

7.5Morphology and hydraulic actions for estuarine levees

7.6Human actions on levees Load types, and loading assumptions and restrictions. Categories considered: –Recreation –Terrorism –Boat traffic –Unplanned structures –Transport infrastructure –Construction, maintenance and operational actions Plant loads Temporary stockpiles Changes in geometry Secondary functions Crest raising

7.7Ground investigation for levees

7.7Ground investigation for levees Overview of planning and conducting a GI GI requirements relative to –Failure modes: Failure process, investigations and monitoring –Different levee scenarios: Condition assessment, improvement works and new levees –Structures and material assessment GI valuation through –Pre construction trials –Visual observation during construction

7.7Ground investigation for levees Considerations when investigating existing levees as a result of past activities –Construction Heterogeneous internal structure, including structural elements, resulting from historic raising and widening. –Improvement Side slopes and crest many be formed from different material which could include ‘dredgings’ –Repair Seepage mitigation or breach repairs may include: aprons, sheet piles or deep soil mixing

7.7Ground investigation for levees

7.8Geotechnical parameters

7.8Geotechnical parameters Properties and parameters considered Determination of parameters through –Typical values –Empirical correlations with index properties –Direct measurement: laboratory and in situ –Geophysics –Index –Compaction –Shear strength –Compressibility –Permeability –Erodibility Determination of characteristic values

7.8Geotechnical parameters Selection of a characteristic value is the probably the single most important geotechnical design task Some considerations in selecting a value: –Codes used –Degree of conservatism –Applicability to limits state –Strain hardening or softening –Derivation of correlations –Data quality and quantity Lower characteristic value: 95% probability of being exceeded by the spatial average

7.9Site investigation methods

7.9Site investigation methods Surface information –Terrain –Surface cover –Bathymetry –Sediments Hydraulic gauging methods Rivers: –Gauge height –Discharge –Sediment load Coasts and Estuaries: –Tide and wave height –Currents –Sediment load Geotechnical information –Geophysics –Intrusive –Sampling –Instrumentation

7.9Site investigation methods Geophysics –Includes broad spectrum of techniques: airborne, onshore surface and borehole, and water based –Integral part of a phased investigation –Fast screening of sites for feasibility –Gain information to target and infer conditions between points of intrusive investigation –Condition assessment of exiting levees

7.9Site investigation methods Application of surface geophysics to existing levees.

7.9Site investigation methods Phased approach: Desk study Non intrusive Intrusive –CPT –Targeted boreholes Spatial distribution of intrusive investigations: Adequate to characterise both the levee and the foundations Guidance in Codes and Standards on spacing but include targeted locations Investigate lateral variations in ground condition not just along the levee alignment

7.9Site investigation methods

7.9Site investigation methods Intrusive investigations –Levee foundations typical comprise a combination of high permeability soils and low strength, high compressible soils under conditions that may present difficult access. –Base equipment, drilling and sampling techniques need to take account of these factors to obtain required data. –Special considerations Close to water Ground stability Contamination UXO Flora and fauna Biohazards

7.9Site investigation methods Instrumentation –To better understand the levee and foundations Condition Interactions Construction Validate design and assumptions ground characteristics Considerations in selection, installation and monitoring Nature and magnitude Redundancy Reading and records Presentation of results Installation records Base line readings

7.9Site investigation methods New and involving techniques Discrete monitoring networks – Micro electro mechanical techniques Distributed monitoring systems – fibre optics

Thank you Chapter 7 Team Leads: To download the International Levee Handbook go to: Shaun Wersching CH2MHILL E: Andy Gaines USACE E: