Panel of Inquiry into the Environmental Effects Statement For Mornington Safe harbour Statement of Expert Evidence of Peter Riedel of Coastal Engineering Solutions Pty Ltd CONTENTS 1 INTRODUCTION 2 QUALIFICATIONS AND EXPERIENCE 3 SUMMARY OF OPINIONS 4 RESPONSE TO SUBMISSIONS Appendix A: Matters Raised by Planning Panels Victoria – Directions & Expert Evidence Appendix B: Curriculum Vitae: Peter Riedel 20//12/2010 10-590-vic hprrp RevB Page 1 of 31 Panel of Inquiry into the Environmental Effects Statement For Mornington Safe harbour Statement of Expert Evidence of Peter Riedel of Coastal Engineering Solutions Pty Ltd 1 INTRODUCTION Coastal Engineering Solutions Pty Ltd (CES) undertook a review of the EES documentation, in relation to coastal processes and engineering, for Mornington Peninsula Shire Council (MPSC) in August 2009. I adopt this witness statement, which includes a summary of the above advice, as my evidence to the Panel insofar as they relate to my areas of expertise. 2 QUALIFICATIONS AND EXPERIENCE Appendix A contains a statement setting out my qualifications and experience, and the other matters raised by Planning Panels Victoria – Directions & Expert Evidence. 3 SUMMARY OF OPINIONS 3.1 Summary of Advice to MPSC, August 2009 1 The various EES study reports, for Mornington Boat Haven, relating to coastal processes have been capably prepared and carried out in accordance with the relevant scope of studies for each of the reports. 2 The only areas of concern in relation to the full development are: a. The degree of change likely to occur at Mother’s Beach, though it is agreed that any change will occur slowly and can be detected and managed through appropriate monitoring. b. The potential for siltation on the seaward side of the beaches in the lee of the wave screen in a similar manner as has occurred at St Kilda and Brighton. 3 It is expected that without sand management Mother’s Beach will accumulate sand at the expense of Scouts Beach and Mothers Beach will rotate in a clockwise direction and become wider as a result of the full development. 20//12/2010 10-590-vic hprrp RevB Page 2 of 31 Panel of Inquiry into the Environmental Effects Statement For Mornington Safe harbour Statement of Expert Evidence of Peter Riedel of Coastal Engineering Solutions Pty Ltd 3.2 Coastal Processes 3.2.1 Sea Level Rise and Storm Tides and Wave Climate Related Issues Proponents for the development of projects within 1 kilometre of the shoreline where the land levels are less than 5 metres (AHD – Australian Height Datum, which approximates mean sea level) have since the release of the Victorian Coastal Strategy 2008 been required to undertake a Coastal Hazard Vulnerability Assessment (CHVA). This requirement was not in place when the terms of reference for the EES were set. Overview The Victorian Coastal Strategy 2008 includes a policy to plan for a rise above present-day sea levels of not less than 0.8m by the year 2100. In conjunction with the 0.8m sea level rise, there are other climate change influences that also need to be addressed, primarily as a consequence of increased “storminess” and the associated increase in storm tide levels along Victoria’s shoreline. These various factors have been addressed by the comprehensive CSIRO report “The Effect of Climate Change on Extreme Sea Levels in Port Phillip Bay” (McInnes et al, 2009). Consequently when undertaking a CHVA, parameters associated with future sea level rise and associated increased storminess are generally adopted from the CSIRO report. Sea Level Rise When considering future climate change, this CHVA utilises the following sea level rise: • 0.47 metres for a planning horizon to 2070 (from the CSIRO report). This timeframe approximates the planning life of a typical residential structure that will be constructed within the next 10 years. • 0.8 metres for a planning horizon to 2100 (as nominated in the Victorian Coastal Strategy). Storm Tide and Surge Figure 1 illustrates the primary water level components of a storm tide event. Any increase in ocean water levels as a consequence of future climate change would be in addition to these various natural phenomena. A brief discussion of these components is offered below. 20//12/2010 10-590-vic hprrp RevB Page 3 of 31 Panel of Inquiry into the Environmental Effects Statement For Mornington Safe harbour Statement of Expert Evidence of Peter Riedel of Coastal Engineering Solutions Pty Ltd COASTLINE BROKEN WAVES WAVES ARE BREAKING INCOMING WAVES WAVE RUNUP WAVE SETUP STORM SURGE TIDE ASTRONOMICAL TIDE LOW WATER DATUM Storm Tide = Astronomical Tide + Storm Surge + Breaking Wave Setup Figure 1 : Components of a Storm Tide Event • Astronomical Tide: The astronomical tide is the normal day-to-day rising and falling of ocean waters in response to the gravitational influences of the sun and the moon. The astronomical tide can be predicted with considerable accuracy. Astronomical tide is an important component of the overall storm tide because if the peak of a severe storm were to coincide with a high spring tide for instance, severe flooding of low lying coastal areas can occur and the upper sections of coastal structures can be subjected to severe wave action. • Storm Surge : This increase in ocean water levels is caused by meteorological effects during severe storms. Strong winds blowing over the surface of the ocean forces water against the coast at a greater rate that it can flow back to sea. Furthermore sea levels can rise locally when a low pressure system occurs over the sea - resulting in what is termed an “inverted barometer” effect. A 10mb drop in atmospheric pressure results in an approximate 10 cm rise in sea level. In order to predict the height of storm surges, these various influences and their complex interaction are typically replicated by numerical modelling techniques using computers - such as has been done for the CSIRO study throughout Port Phillip Bay (McInnes et al, 2009). • Breaking Wave Setup: As storm waves propagate into shallower coastal waters, they begin to shoal and will break as they encounter the nearshore region. The dissipation of wave energy during the wave breaking process induces a localised increase in the ocean water level shoreward of the breaking point which is called breaking wave setup. Through the continued action of many breaking waves, the setup experienced on a foreshore during a severe wave event can be sustained for a significant timeframe and needs to be considered as an important component of the overall storm tide on a foreshore. 20//12/2010 10-590-vic hprrp RevB Page 4 of 31 Panel of Inquiry into the Environmental Effects Statement For Mornington Safe harbour Statement of Expert Evidence of Peter Riedel of Coastal Engineering Solutions Pty Ltd • Wave Runup: Wave runup is the vertical height above the local water level up to which incoming waves will rush when they encounter the land/sea interface. The level to which waves will run up a structure or natural foreshore depends significantly on the nature, slope and extent of the land boundary, as well as the characteristics of the incident waves. When assessing existing coastal stability and vulnerability for a CHVA, the 100 year return period event for storm tide is usually adopted. The prediction reported by CSIRO (McInnes et al, 2009) for Mornington is +1.14m (AHD). Future climate change scenarios for the years of 2070 and 2100 indicate there will be increases in the magnitude of storm surges. The CSIRO report determines the combined effects of future sea level rise and storm tide for a 100 year return period as “Scenario 2”. These are summarised below in Table 1. Current Location 2070 2100 Climate Mornington +1.14 +1.82 +2.28 Table 1 : Sea Level Scenarios Storm (wave) Parameters The CSIRO study of future climate change effects throughout Port Phillip bay (McInnes et al, 2009) predicts a 13% increase in the strength of winds during storms by the year 2070. This is expected to produce a similar percentage increase in the storm wave heights approaching Mornington harbour. For the year 2100 scenario winds are predicted to increase by 19% again resulting in a similar percentage increase in wave heights. Facility Design Parameters The most appropriate engineering design approach to handle the impacts of sea level rise is to design the facility for present day sea level or possibly a sea level rise up to a design horizon of 50 years, but to ensure that the design elements can be practically upgraded for more distant sea level rise and storminess scenarios. Incorporation of this design approach in the detail design of the facilities at Mornington Safe Harbour would not be onerous. 20//12/2010 10-590-vic hprrp RevB Page 5 of 31 Panel of Inquiry into the Environmental Effects Statement For Mornington Safe harbour Statement of Expert Evidence of Peter Riedel of Coastal Engineering Solutions Pty Ltd Impact on Coastal Processes (sand movement) The sand movement studies for the EES and by CES for MPSC (in their review of EES documentation) show that rates of sand movement are low now and will generally be slower after the development is complete because of the wave shadow created by the wave screen walls. Higher water levels and larger storm waves in Port Phillip will result in some increase in the rate of sand movement, but the absolute magnitude would still be slow and by 2100 it is unlikely that sand movement rates would more than double. That is, sand management could still be practically implemented to maintain the required beach amenity. It is acknowledged that sand movement calculation is not a precise science. However, coastal engineers are usually comfortable that their calculations are within a factor of 2 of the real situation.