Submission to KCDC Prepared by Peter Katz 10 Stonewall Grove Waikanae Beach
Background to Submission Beachfront property owner since 1981 30 years of paranoia observing the interaction between the Waikanae river mouth, dunes and sea Been enagaged in some council workshops and active grass planting on the dune.
Key points Shand s analysis does not: Explain and take account of the dunes accreting and growing in height. Consider man made factors that increase the likelihood of dune erosion which could be mitigated to delay the rate of erosion and push back the estimated lines. Factors which I believe should be considered in more depth in Shand s analysis to make it neutral and credible are: Cutting/not cutting the Waikanae River. Centralized co ordinated grass planting of the dunes Managing storm water outlets onto the beach. Identifying high risk areas where dunes has broken down Waikanae boat club, high use houses ie Army house which weaken the overall dune defense.
Cutting the Waikanae River The sandspit accumulates sand supports the build up of sand on the northern beach side. The build up of sand north supports the development of sandbars that assist absorbing wave energy hitting the dunes. I have observed that cutting the river and blocking the old channel has on previous occasion lead to severe erosion on the north head and back along the beach. Also, over the following years: The river turns south and slowly erodes the spit The sand bars are less prominent Storm seas push through to the current riverbank adding to sea land erosion. Observation of the NZ coastline demonstrates it is natural for rivers to form spits as a natural protective buffer against sea erosion. Submission is the River should not be cut unless it naturally occurs. If the river naturally cuts itself, the main channel remains open and the cut leaves the river pointing south, limiting the erosion impact on the north end.
Centralized co ordinated grass planting of the dunes The photos demonstrate that: where there was active grass plant the dune was more resistant to erosion Where grass planting was not prominent, the sea erosion line is determined by the point of least resistance the effectiveness of grass planting is diminished.
Centralized co ordinated grass planting of the dunes Co ordinated grass planting: Ensures uniform protection for the dunes. in my view the dunes would be 1 metre further forward or more if a program of uniform planting was adopted. The cost of managed uniform planting: could be justified in terms of councils responsibility to make a reasonable effort to protect property. Increase property values and rates. Maintain a dry rather than wet beach as a social benefit
Identifying high risk areas boat club, high use houses ie Army house where dunes has broken down. On Tutere Street has three highly used units owned by the NZ army. KCDC should engage owners to manage beach access to protect dune. Waikanae boat club is an area of high erosion affecting the dune either side. KCDC should work with them to address this problem
Properly managing storm water outlets onto the beach. Add photo
Conclusion The analysis should be consistent with and explain the current dune accretion. It should be able to identify and explain the tipping points for a reversal. What would the analysis have predicted if applied 10, 20 years ago? Is it robust, does it show accretion? The KCDC lines should be drawn only after: There is a clear understanding of the impact of the waikanae river mouth on erosion. KCDC has identified measures under its responsibility that could enhance dune protection uniformly along all the foreshore to get maximum benefit. The analysis should reflect these measures
Comment on neutrality and transparency There should be a uniform approach to Global warming. The $0.8million project was recently completed but clearly under global warming assumptions it has a limited life. See picture below. Many properties in the Beach area are close to sea level, below beach front properties. It is likely that the indfrastructure sewerage in particular will come under pressure. KCDC should be equally open and honest about its plans for these properties and the risks they face if they continue with the firm lines and assuptions applied to the beachfront.