DEVELOPMENT PLANNING FOR COASTAL HAZARDS JUNE 30, 2006 BY ENGINEERING SECTION COASTAL ZONE MANAGEMENT UNIT COASTAL ENGINEERING FOR NATURAL HAZARDS

This presentation will cover the following topics: Typical beach response to storm events Types of Coastal Structures Engineering Design for Coastal Hazards DEVELOPMENT PLANNING FOR COASTAL HAZARDS JUNE 30, 2006

DEVELOPMENT PLANNING FOR COASTAL HAZARDS JUNE 30, 2006 Coastal Hazards and Coastal Engineering Potential Effects of Hazards - Beach Erosion - Coastal Flooding - Infrastructural Damage to Coastal Properties

Understanding Sediment Transport Processes Stability of the coastline primarily depends on a balance between: The volume of sediment (sand) available to that section Net onshore-offshore (cross-shore) sediment transport Net alongshore sediment transport DEVELOPMENT PLANNING FOR COASTAL HAZARDS JUNE 30, 2006

Understanding Sediment Transport Processes Cross-shore Sediment Transport Determined primarily by wave steepness, sediment size and beach slope High steep waves move material offshore Low waves of long period (calmer waves) move materials onshore DEVELOPMENT PLANNING FOR COASTAL HAZARDS JUNE 30, 2006

DEVELOPMENT PLANNING FOR COASTAL HAZARDS JUNE 30, 2006 Response of Shoreline to Storm Events Sediment may be lost from the system if transported far offshore !!

SHORELINE PROTECTION For convenience, structures can be classified into three groups: – –Structures built perpendicular to the coast and usually attached to the shoreline – –Structures built offshore and approximately parallel to the shore – –Structures built on the beach face

GROYNES A structure built generally perpendicularly to the shoreline to trap longshore sand transport

Submerged breakwater at Rockley Beach A structure built parallel to the shoreline that protects the area in its lee from wave attack BREAKWATERS

Seawalls & Revetments Constructed along beach face Assist the shoreline in resisting wave attack If placed improperly could facilitate erosion (wave reflection increases offshore currents) Welches, Christ Church Barbados Flour Mill Site, Spring Garden, Barbados

What type of coastal structure is best? Objective Coastal processes (e.g. groyne is only practical when there is significant quantity of sand moving alongshore) Environmental concerns (nearshore fringing reefs, vegetation in back beach) Cost Modelling costs Construction costs (e.g. use of barge to build breakwater)

DESIGN PROCESS (COASTAL ENGINEER) Analyse wave data Determine long-term statistical trends Determine Extreme Events (e.g the storm wave which has a return period of 50 or 100 years) Design Structure (usually for 50 yr. return event)

Coastal Engineering Tools used in Design Process - Numerical Modelling - Physical Modelling

NUMERICAL MODELS Coastal processes are represented mathematically Computers used to run calculations to analyse processes and determine the result of processes on the shoreline Graphical representation of results often used to explain the model outputs

East-Northeast Waves For Rockley Nearshore Wave Transformation Higher waves (yellow) reach shoreline at South Point, calmer conditions exist to the west (blue)

PHYSICAL MODELLING -Section of shoreline reproduced on a small scale in a wave tank - Allows the simulation of waves, wave run- up, wave forces, currents and sediment transport - Provide a clear and real demonstration of the effectiveness of the structure when subjected to extreme waves and water levels

Physical Model for Holetown Beach (Chefette) Area between old Regent hotel and Cheffette reproduced at 1:30 scale in wave tank

- Data is input into physical and numerical models used to obtain design parameters for structures -Coastal structure adequately designed to withstand hazards of design event - Additionally, potentially affected areas identified by models may be mapped and appropriate mitigation measures formulated CONCLUSION

THANK YOU