Marokopa Coastal Hazards
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Marokopa Coastal Hazards Prepared for the Waitomo District Council By Jim Dahm Bronwen Gibberd Focus Resource Management Group Objectives Waitomo District Plan review – natural hazards. Work with local communities, landowners and Iwi to: • Identify areas potentially at risk with existing sea level • Identify the additional areas that could be affected with projected future sea level rise • Develop adaptive management strategies that clearly identify how existing and potential future risk will be managed • Focus on: Mokau Awakino Marokopa TeWaitere Kinohaku Methodology Overview Community & CMT Research and Analysis Identification of Hazard Meetings Areas & Draft Information Gathering Processes, Values, Management Erosion, Flooding Community Values Recommendations Draft Adaptive Management Plan Community Discussion Council Discussion of Recommendations Final Adaptive Management Plan/District Plan Provisions HERE WE WE ARE Purpose of this Meeting Second round of community meetings to: Outline findings in regard to areas of existing and potential future risk (and associated uncertainties) Outline and discuss options for the management of current and potential future hazard risk areas Sea Level Rise National Policy: Scenario 2070 2120 must plan for 100-150 years Huge uncertainty, cannot simply Lower bound 0.32 m 0.55 m extrapolate past trends “surprise” Must use “plausible scenarios” Intermediate 0.36 m 0.67 m Intergovernmental Panel on Climate Change (“IPCC”) scenarios Relate to future emissions and High+ (85th 0.61 m 1.36 m management percentile) National guidance from Ministry for the Environment from these studies – tells us what to use. Adaptive Planning – Decision Cycle Much uncertainty so need a flexible and adaptable approach to planning Five key stages: 1. Building a shared understanding (processes, hazards, community resilience) 2. Exploring the future and how communities are affected and identifying objectives 3. Building adaptive pathways 4. Implementing the strategy in practice 5. Monitoring the strategy using early signals and triggers (decision points) for adjusting between pathways. This study is currently working with WDC, WRC and local communities and stakeholders on Items 1-3 Management Options and Philosophy: National and Regional Policy (NZCPS 2010, RPS) Risk avoidance - Managing land use in hazard risk areas to avoid risk. Landward relocation of assets to a safe location Risk reduction - Managing land use and development to reduce existing risk exposure over time Living with erosion – accepting erosion where appropriate Mitigation of erosion through protection and restoration of natural buffers (e.g. beaches, dunes, wetlands) Soft engineering measures which mitigate erosion using natural buffers Decreasing Decreasing preference (e.g. beach nourishment) “Hard” engineering structures, including new or existing sea walls or rock revetments. This used to be the immediate response, is now last resort for most areas. Significant challenge. National Policy (NZCPS 2010) - Key Policies https://www.doc.govt.nz/Documents/conservation/marine-and- coastal/coastal-management/nz-coastal-policy-statement-2010.pdf - simple, readable document Policy 24: Identify areas in the coastal environment that are potentially affected by coastal hazards (including tsunami), giving priority to the identification of areas that are at high risk of being affected… Policy 25: In these areas… Avoid increasing the risk… Avoid redevelopment or land use changes that will increase the risk… Encourage redevelopment or change that will reduce the risk… including managed retreat by relocation… designing for relocatability from hazard events… Encourage location of infrastructure away from areas of hazard risk… Discourage hard protection structures… promote alternatives… National Policy (NZCPS 2010) - Key Policies Policy 26 Natural defences against coastal hazards Provide where appropriate for the protection, restoration or enhancement of natural defences that protect coastal land uses… Recognise that such natural defences include beaches, estuaries, wetlands, intertidal areas… Policy 27 Strategies for protecting significant existing development … long term risk reduction approaches including relocation or removal of existing development or structures… recognising that hard protection structures may be the only practical means to protect existing infrastructure of national or regional importance… recognising and considering the environmental and social costs of permitting hard protection structures to protect private property… Planning for transition mechanisms and timeframes to more sustainable approaches focus on approaches to risk management that reduce the need for hard protection structures and similar engineering interventions… Coastal Structures – why a last resort? When erosion occurs on a natural beach, the whole profile moves landward A wide high tide beach will re-establish after erosion Erosion does not destroy beaches as long as the erosion encounters sand Coastal Structures – Effect on beaches Building an effective seawall protects the land behind the wall A seawall does not stop the erosion occurring in front of the wall The beach continues to erode, and over time the beach disappears Recreational values are lost and public access alongshore also adversely affected So, generally not an acceptable long term solution on sandy shorelines Possible Management Approaches Development setbacks and associated controls – to avoid and reduce risk and to inform on existing and longer term risk Minimum floor levels to protect from flooding Controls/guidance on use of structures in the coastal margin Coastal restoration and soft approaches as relevant – e.g. restoration and enhancement of beaches, dunes and coastal wetlands, working with nature Adaptive management strategies and triggers will be required at some sites Coastal structures – limited, but may have a role in transition Adaptive Management Approaches Requires a decision-making framework that is neither “business as usual” nor a radical (expensive, impractical) “overnight” fix/change. Aim is to ensure a transition to more sustainable management over time. Will be very challenging and require time. Will take more than one meeting to reach agreement among all stakeholders. Requires patience and open dialogue. Marokopa Shoreline Change Erosion occurs largely on outside banks of river bends, with accretion on inside banks This pattern is evident since earliest photos and has likely occurred for centuries By 1940s, most of the reserve in front of worst affected properties had already been eroded. Photo: 1940s, dark line shows 2017 shoreline Marokopa Shoreline Change Most notable erosion along coastal margin between Marokopa Road and Moana Quay Ocean waves are a significant influence Some erosion of marae land. Photo: 2017, yellow line shows 1940s shoreline Coastal Erosion – Rauparaha Street Bank composed of sand but quite cemented by iron near toe, presently erodes moderately slowly Erosion linked to wave penetration into estuary and downstream migration of river meander Erosion began long before dune planting (not the cause). Sea level rise will increase coastal erosion Wave effects can be significant Marokopa Rauparaha Street Structures will further destroy beach and limit public access along foreshore. Conflict between public & private interests Not suitable long term solution Need to work with locals to develop appropriate adaptive management strategy for this area to balance interests Marokopa Rauparaha Street Adaptive management strategy likely to require: Setbacks and development controls (most sections deep – room to slowly relocate landward over time) Long term removal or landward relocation of structures – need suitable trigger Transition to more sustainable approach over time, not overnight change Shallow sections may require additional action Marokopa Coastal Erosion Other Areas Erosion rates very slow, or trend for accretion in some places. Adaptive management strategy: Setbacks and development controls (live with erosion) Dune restoration in suitable locations Marokopa Inundation Existing flooding areas (river and coastal): • Rugby Club • Southern township • Marae land • Farmland and road upstream Minimum floor levels (longer term probably raised ground levels Road levels Blue area – inundation from 1% AEP storm. Source http://coastalinundation.waikatoregion.govt.nz/ Marokopa Inundation Potential longer term flooding areas (river and coastal): • Rugby Club • Extensive flooding of Township • Marae buildings • Farmland and road upstream With increasing sea level rise, flooding will occur even with normal high tides Minimum floor levels (longer Blue area – inundation from 1% AEP storm, plus 1 m sea level rise. term probably raised ground Source http://coastalinundation.waikatoregion.govt.nz/ levels Road levels Your turn… Any further information on erosion or flooding that we have missed? Your thoughts or concerns on the different management options. Etc… Adaptive Planning: SLR Scenarios (as per national guidance) Existing at-risk development Most difficult to manage Consider all sea level rise (SLR) scenarios Minimum 1.0 m SLR until adaptive planning complete Detailed adaptive management approach with thresholds and triggers. Test performance of future actions against range of scenarios. Low-risk non-inhabitable works and activities, particularly those with a functional need to be near the coast. Plan for adaptation in long term. Consider minimum 0.65 m SLR in short term..