REBUTTAL STATEMENT OF EVIDENCE OF BRETT BEAMSLEY (DREDGE DISPOSAL AND COASTAL PROCESSES)

Transcription

1 BEFORE THE NORTHLAND REGIONAL COUNCIL IN THE MATTER of the Resource Management Act 1991 AND IN THE MATTER APPLICATION NO: of a resource consent application by The New Zealand Refining Company Limited under section 88 of the RMA to deepen and realign the Whangarei Harbour entrance and its approaches APP REBUTTAL STATEMENT OF EVIDENCE OF BRETT BEAMSLEY (DREDGE DISPOSAL AND COASTAL PROCESSES) 1 I have read and reviewed the statement of evidence prepared by Dr Shaw Mead on coastal processes, numerical modelling and marine ecology. There is no part in his statement of evidence that would cause me to change my statement of evidence or findings. However, there are matters raised in this statement of evidence that I wish to rebut/correct. 2 In paragraph [11] Dr Mead does not accept that there will be no significant changes to waves and therefore sediment transport and geomorphology and suggests that many large-scale changes have been identified by the modelling that will impact on the form and function of the harbour entrance. 3 I disagree with this statement and do not believe that the predicted modification to the hydrodynamic and wave characteristics will impact on the form and function of the harbour entrance. I qualify this statement below. a. Firstly, I note that current mean annual wave height is approximately 0.80 m, while the predicted mean annual change to the significant wave height is ~ cm (i.e %, see Figure 1). It is highly unlikely that this scale of change could be measured using instruments, and it would not be observable. I consider these changes to be minor to less than minor.

2 Figure 1 Average annual change in significant wave height due to the deepened channel. Positive amplitudes indicate areas with a predicted increase, negative areas a decrease. b. While larger changes in the significant wave height are expected during storm events (i.e m) with wave heights exceeding 5 m, these changes still represent both a small actual change, and a relatively small percentage change (~3%). c. These modifications to the wave climate have been tested with industry standard morphological models and only minor morphological changes are predicted within the environs, and I do not expect these to change the governing dynamics. Further, storm driven morphological changes at Busby Head (for example) are noted to be within the existing natural variability of the site and do not represent a regime shift or permanent change. 4 In paragraph [12] Dr Mead accepts that industry standard models have been applied, however states his belief that the validation of the tidal model is poor and that there has been little incorporation of science and site-specific knowledge beyond the use of the models. 5 I disagree with this statement; a. Firstly, Dr Mead has fundamentally failed to understand how the various models have been applied within the context of this project. The model Dr Mead is referring to as the tidal-model (ROMS) has been principally used to define the residual current (i.e. non-tidal) component of the total current field at the offshore disposal site, and does not relate to the tidal model (SELFE) used to define the harbour hydrodynamics. b. Secondly, Dr Mead has failed to understand how these offshore current velocities have been applied within the context of this project. The ROMS model has been used to define the climatic hydrodynamics, and applied to plume and morphological responses in that context (i.e. running long period simulations to derive statistically relevant outcomes). The total bias of the ROMS model in defining the combined

3 tidal and residual current velocity is statistically small ( m.s -1 ) and as such appropriate to defining the regional hydrodynamics. c. Finally, both the regional scale ROMS model and the harbour scale SELFE model have been calibrated and validated against site-specific measured data, and both model and measured data have been used to define plume dispersions within the receiving environment. 6 In paragraph [13] Dr Mead recognises that the tools developed (inclusive of the models) have been applied considering the known impacts of channel deepening world-wide, and suggests that there is a deficit of information linking to the strong biogenic influence in the system. 7 I agree with Dr Mead s [13] statement, in that the models used have leveraged and used international studies of morphological response. 8 I accept that there is limited information available to explicitly model biological armoured substrate within the existing scientific knowledge; however model calibration and validation looked to simulate this armouring effect by assuming coarse gravel sediments over Mair Bank, thereby reproducing the overall stability of Mair Bank. Given the state of scientific knowledge, I believe this to be an acceptable approach to examine the scale of effects of the proposal. 9 In paragraph [14] Dr Mead makes reference to the large spatial scale of the changes to the wave and hydrodynamics, and consequentially the sediment transport. While spatial changes appear to be comparatively large (i.e. see Figure 1), the actual magnitude changes to waves and hydrodynamics, which govern the sediment transport, are minor to less than minor. 10 In paragraph [15] Dr Mead suggests that the proposal has potential to impact on the existing morphodynamics of the harbour which have not been well addressed, yet he acknowledges that industry standard models, which have been calibrated and validated against site-specific data, have been applied [Mead, paragraph 12]. As such I do not agree with his suggestion that the impact on the existing morphodynamics have not been well addressed. 11 Dr Mead suggests in his statement in paragraph [16] that the spatial extent of the expected changes in wave and hydrodynamics will not be absorbed within the natural variability. As I note above, while spatial changes appear to be comparatively large (i.e. see Figure 1), the actual magnitude changes to waves and hydrodynamics, which govern the sediment transport, are minor to less than minor. 12 In paragraphs [17-19], Dr Mead discusses the effect of the proposal on the tidal prism and phasing. It appears to me that Dr Mead does not seem to understand the concept of deriving a tidal phase or how models can be used to infer a potential shift (Mead, [19]). This is achieved by simulating both existing and proposed bathymetries and comparing the model outcomes. The site at which the tidal phasing change has been reported is significantly far inside the harbour such that the effect is worst case. The small phasing shift will not affect the tidal amplitudes. These model outcomes are then used to determine the potential impact of the proposed dredging on the morphological response, significantly within the entire harbour. This is accepted industry practice. 13 Dr Mead [20] suggests that the inner harbour has not been considered. This is not accurate. The modelling undertaken extended into the inner harbour regions, but no effects on those

4 areas are expected. In addition, the extensive intertidal areas are expected to be morphologically dominated by locally generated waves. 14 Dr Mead [21] notes that the fundamental laws of physics indicate that change will occur. I agree with this broad statement, and note that these physical processes are accounted for in the hydrodynamic and morphological models applied. 15 In paragraph [31] Dr Mead suggests that on the eastern flank of the channel there is a 20% increase in potential sediment flux and this is significant. I recognise that this appears to be a significant value; however increases in potential sediment flux do not mean that the sediment erosion and accretion will similarly increase, as shown in Figure 2. Dr Mead [31] goes on to note that the relative effect of changes should be related to impacts on the processes; I agree and note that the overall effect on the morphological process is expected to be minor (e.g. Figure 2). Mr Reinen-Hamill in his evidence-in-chief discussed the likely effects of these modelled changes. Figure 2 Changes in sedimentation and erosion patterns between the existing and postdeepening configurations over a 5-day storm event. 16 In paragraph [32] Dr Mead suggests that relatively small changes in the percentage of time critical shear stresses are exceeded < 5% of the time are significant and presumably occur throughout the harbour. I disagree with this statement. Comparisons between the existing and proposed deepened channel bathymetry show similar spatial patterns, and extensive areas of <5% difference are not expected (see Figure 3).

5 Figure 3 Percentage of time the bed shear stress exceeds the critical shear stress threshold for 200 µm sand at flood tide. Calculated from a 28-day simulation of the existing harbour (left) and the deepened channel (right).

6 17 Further, Dr Mead [32] criticises the use of a 28 day period to consider these modelled changes in the percentage of time critical shear stress, stating that the duration of change is not 28 days, it is permanent. I find this statement to be inflammatory and misleading. The use of 28 days captures two complete Spring-Neap tidal cycles, ensuring that the expected range of conditions are accounted for. 18 In paragraph [36] Dr Mead expresses his opinion that the modelling investigations show that there are a wide range of changes of varying magnitudes over a large spatial extent. I agree with this statement in general, but when examined in more detail, while there are spatially broad extents to the absolute wave height change (see Figure 1), as described in 3 a b and c the actual scale of change is small. Further, Dr Mead in paragraph [44] suggests that relying on the relative change of individual processes should not be solely used to interpret the model outcomes; however in paragraph [36] Dr Mead appears to do exactly that. In my experience, it is important to understand the relative changes in the underlying processes, but to also understand the effect of those processes and their relative change on the morphological response of the harbour system. Accordingly, my evidence-in-chief should be read together with that of Mr Reinen-Hamill. 19 In paragraph [39] Dr Mead discusses the predicted changes to various hydrodynamic and wave parameters (but does not explicitly state which) occurring over large areas, and goes on to note that he does not consider 20-30% change in bed shear stress to be insignificant. Dr Mead appears to be taking these values out of context, and they need to be considered with respect to the absolute magnitudes and how they relate to sediment transport (see Figure 4). I reiterate my observation that Dr Mead appears to contradict himself (paragraph 18 above) with respect to placing emphasis on the underlying processes. In my view, Dr Mead either misrepresents or misunderstands the outcomes of the modelling and the impact of the changes on the overall sediment transport capacity and morphological response of the system to predicted changes in the hydrodynamics. While changes of 20-30% may seem significant, these represent only a very small actual increase in current velocities (of the order 1-5 cm.s -1 ). As such, Dr Mead s statement does not change my position as expressed in my evidence-inchief.

7 Figure 4 Absolute (top) and relative (bottom) difference in tidal flows post-deepening during the peak spring ebb flows. Plots on the right show a zoomed in view of the entrance region. Positive values indicate a predicted increase in flow (red scale), while the negative values indicate a decrease (blue scale). 20 In paragraph [40-41] and again in [47] Dr Mead again raises questions around the impact of the proposed deepening and offshore disposal on the incident wave climate. I have addressed this in paragraphs 3 a, b and c above. 21 I agree with Dr Mead s paragraph [43], which is why morphological models have been applied in addition to wave and hydrodynamic models, which have been used to quantify the effects of the proposal on the underlying processes responsible for morphological response. I do not agree with Dr Mead [44] that quantifying the effect of the proposed deepening on the underlying processes is a major flaw in the interpretation of the modelling results, as to fully understand the processes and outcomes you must understand both cause and effect, i.e. processes and response. 22 I disagree with Dr Mead s statement in paragraph [64] that the cumulative impacts of the consented land reclamation at Northport have been down-played or disregarded by myself. Modelling has considered both the existing harbour configuration and that which would eventuate if Northport fully exercised their consent. With respect to tidal hydrodynamics, a 2- minute phase change is expected at a point significantly far inside the harbour, which represents a worst case location, if only the proposed deepening was to occur. If both the proposed deepening and the consented reclamation were realised, then a 7-minute phase change is expected at a point significantly far inside the harbour. With respect to the

8 sediment transport and morphological response, the cumulative effect has been considered and is not expected to change the outcomes presented in my evidence-in-chief. Brett Beamsley 23 February 2018