Evaluation of options The evaluation criteria have been applied each option, where the comparison is in relation to the other groyne options. It does not consider other protection solutions / coastal structures or scenarios. Each criterion rated on a scale from Very Low to Very High. As each criterion had a varying scale, rating have been coloured coded to convey well performing options, where green shading is a good result and red shading is a poor result. provides a summary of the evaluation while presents further context around each of the ratings provided, consider for each individual option. Table 5-2 Evaluation of Options – Summary Criterion Technical Effectiveness Technical Effectiveness - long term (changing Cost (Design, construct, maintain) Environment /Effects on Intertidal Reef Communities in Required /work Design Life Amenity Key Risks Option – Do Nothing LOW LOW LOW LOW LOW LOW N/A MODERATE Option – Extend existing groynes BELOW AVERAGE BELOW AVERAGE MODERATE HIGH LOW MODERATE HIGH MODERATE Option – Add additional groynes – Rock VERY HIGH HIGH VERY HIGH VERY HIGH VERY HIGH ABOVE AVERAGE ABOVE AVERAGE HIGH Option – Add additional groynes – Timber/Polymer MODERATE MODERATE BELOW AVERAGE BELOW AVERAGE MODERATE MODERATE MODERATE ABOVE AVERAGE Option – Combination: Rock & Timber Groynes VERY HIGH ABOVE AVERAGE HIGH HIGH HIGH ABOVE AVERAGE HIGH HIGH Option – Combination: Rock & Timber Groynes with Small Breakwater VERY HIGH HIGH VERY HIGH HIGH VERY HIGH ABOVE AVERAGE VERY HIGH VERY HIGH NB. The colour coding assigned to the rating changes due to varying rating scales for each criteria. In general, green is considered a GOOD rating, while red is considered a POOR rating.
Table 5-3 Evaluation of Options – Detailed analysis Criterion Technical Effectiveness Technical Effectiveness in the longer term (changing climate) Cost (Design, construct, maintain) Design Life Amenity Key Risks Environment /Effects on Intertidal Reef Communities in PPH MNP Further work Required (Design, analysis monitoring) Option – Do Nothing Some sand is being held on beach, but not continuous. Strong dependence on seasonal influence. Conditions are likely to remain similar, if not worsen overtime. Similar to existing, though likely to erosion effects. Likely to be exacerbated with SLR and increases in strength and frequency of storm events Design & Construction - N/A Continual maintenance is likely required to structures due to existing design (poor alignment, undersized, no core and filter layers). Associated costs will be minor ongoing repairs to relay and replace displace rocks Existing structures currently damaged. Already failing. Alignment and size appear to be ill-designed, but are still functional. Likely to worsen with time unless significant repairs are undertaken. Beach connectivity same as existing. Footprint same as existing. Noting that structures are undersized. Public Safety - Large height offset between compartments from being too full in corners. Creates a drop off between compartments. Sand blown over footpath. No further influence. No change to current effects experienced by the intertidal reef communities Run a controlled trial of the redistribution sand within the compartment at calmer times of year. RANKING LOW LOW LOW LOW LOW LOW N/A MODERATE
Criterion Technical Effectiveness Technical Effectiveness in the longer term (changing climate) Cost (Design, construct, maintain) Design Life Amenity Key Risks Environment/ Effects on Intertidal Reef Communities in PPH MNP Further work Required (Design, analysis monitoring) Option – Extend existing groynes Some minor improvement, though not across entire beachfront Small increases in beach width at select spots along coastline. Average beach width increase - Compartment 1: 0 m Compartment 2: Up to +15 m Compartment 3: Up to +5 m Minor improvement, but not an effective long term solution Will require some upgrade of existing structures to improve structure integrity. Rock is more expensive material. Approximately $5000/m of structure. Less new materials required only extending existing and upgrading structures. Construction effort increased working further offshore (deeper, larger waves) Structure will be exposed to bigger waves being deeper. Retaining existing orientation means structure is exposed to higher wave energies on this alignment Design will need to consider conditions in sizing material and structure design. Rock is long lasting and structure will last if suitably designed Connectivity same as existing. Increased offshore footprint. Large height offset between compartments from being too full in corners. Sand blown over footpath. Structure extends further offshore exposing public to larger waves and deeper water Extends into More sensitive zones of the MNP, closer to reefs. Small change to sediment transport through Marine National Park. Construction efforts entering Marine National Park. Detailed design of groyne extension Site Survey RANKING BELOW AVERAGE BELOW AVERAGE MODERATE HIGH LOW MODERATE HIGH ABOVE AVERAGE
Technical Effectiveness Technical Effectiveness in the longer term (changing climate) Cost (Design, construct, maintain) Design Life Amenity Key Risks Environment/ Effects on Intertidal Reef Communities in PPH MNP Further work Required (Design, analysis monitoring) Shortened compartments improves beach holding capacity Large Improvement across entire beach front Large Improvement across entire beach front with more spread and symmetrical compartments Rock is expensive material. Approximately $5000/m of structure Works will be onshore and offshore. Rock is long lasting and structure will last with site specific design. If kept on same alignment as existing groynes, experiencing higher wave loads. Advise angling structure more in to average wave direction More groyne structures on the beach will alter connectivity. More large groyne structures extending offshore. Increased number of beach structures. Large rocks on rock flats. Moderate change to region sediment transport. Construction efforts within Marine National Park. Works onshore and offshore Detailed design of timber groynes Site Survey Improved width across entire study area. Average beach width increase - Compartment 1: Up to +25 m Compartment 2: Up to +30 m Compartment 3: Up to +30 m Advise that structure is designed on an orientation that aligns with average wave direction. RANKING VERY HIGH HIGH VERY HIGH VERY HIGH VERY HIGH ABOVE AVERAGE ABOVE AVERAGE HIGH
Technical Effectiveness Technical Effectiveness in the longer term (changing climate) Cost (Design, construct, maintain) Design Life Amenity Key Risks Environment/ Effects on Intertidal Reef Communities in PPH MNP Further work Required (Design, analysis monitoring) Option – Add additional groynes – Timber/Polymer Shorter compartments improves beach holding capacity, though timer structure unable to extend as far offshore Notable increase in Compartment 3. Little change elsewhere. Average beach width increase - Large improvement through Compartment 3; Little to no effect in Compartments 1 and 2 Timber is cheaper than rock. Smaller structures. Less material. Works largely on shore. Approximately $3500/m of structure Timber is less durable and not a strong as rock. Improved alignment will reduce repeat wave impact structure. Increased number of smaller groyne structures on the beach will alter connectivity. Increased number of beach structures. Timber structures create vertical drop-off between compartments Climbing, trip hazards. Smaller structure. Piling into beach. Small to moderate change to region sediment transport. Detailed design of timber groynes Site Survey Compartment 1: 0 m Compartment 2: 0 m Compartment 3: Up to +10 m Timber structure should be designed on an orientation that aligns with average wave direction RANKING MODERATE MODERATE BELOW AVERAGE BELOW AVERAGE MODERATE MODERATE MODERATE ABOVE AVERAGE
Criterion Technical Effectiveness Technical Effectiveness in the longer term (changing climate) Cost (Design, construct, maintain) Design Life Amenity Key Risks Environment / Effects on Intertidal Reef Communities in PPH MNP Required design/analysis /work Option – Combination: Rock & Timber Groynes Improved width across entire study area. Even spread of sand across compartments Average beach width increase - Compartment 1: Up to +25-30 m Compartment 2: Up to +10 m Compartment 3: Up to +10 m Improved width across entire study area. Even spread of sand across compartments Combination of timber and rock proves nearly as effective, but at cheaper cost Timber Approximately $3500/m of structure Rock Approximately $5000/m of structure Works will be onshore and offshore. Timber is less durable and not a strong as rock. Improved alignment will reduce repeat wave impact structure. But shorter structures to limit exposure to wave energy Rock is long lasting and structure will last with site specific design. Advise angling structure more in to average wave direction Less impact on beach connectivity with less large rock structures Increased number of beach structures. Timber structures create vertical drop-off between compartments Climbing, trip hazards. Large rocks on rock flats. Moderate change to region sediment transport. Construction efforts within Marine National Park. Works onshore and offshore Detailed design: Rock groynes Timber groynes Site Survey RANKING VERY HIGH ABOVE AVERAGE HIGH HIGH HIGH ABOVE AVERAGE HIGH HIGH
Criterion Technical Effectiveness Technical Effectiveness in the longer term (changing climate) Cost (Design, construct, maintain) Design Life Amenity Key Risks Environment / Effects on Intertidal Reef Communities in PPH MNP Further work Required (Design, analysis monitoring) Option – Combination: Rock & Timber Groynes with Small Breakwater Improved width across entire study area. Even spread of sand across compartments Average beach width increase - Compartment 1: Up to +25-30 m Compartment 2: Up to +10 m Compartment 3: Up to +10 m Limits wave energy reaching the location where beach most desired, enabling sand build up near shops. Improved width across entire study area. Even spread of sand across compartments As waves and storm get bigger limits wave energy reaching the location where beach most desired, enabling sand build up near shops. Combination of timber and rock proves nearly as effective, but at cheaper cost Timber Approximately $3500/m of structure Rock Approximately $5000/m of structure Works will be onshore and offshore. Timber is less durable and not a strong as rock. Improved alignment will reduce repeat wave impact structure. But shorter structures to limit exposure to wave energy Rock is long lasting and structure will last with site specific design. Advise angling structure more in to average wave direction Less impact on beach connectivity with less large rock structures but large rock structure within vicinity of key location on the site. Increased number of beach structures. Timber structures create vertical drop-off between compartments Climbing, trip hazards. Structure extends further offshore exposing public to larger waves and deeper water Large rocks on rock flats. Moderate change to region sediment transport. Construction efforts within Marine National Park. Works onshore and offshore More environmental impacts with structure located nearer to headland – rock pools Detailed design: Rock groynes Timber groynes Breakwater Site Survey Requires further environmental assessment and monitoring at and around headland RANKING VERY HIGH HIGH VERY HIGH HIGH VERY HIGH ABOVE AVERAGE VERY HIGH VERY HIGH