Page 1 of 21 CLIENT: Town of Qualicum Beach PROJECT: SIGNATURE DATE CONTRIBUTORS : M. Marti Lopez REVIEWED BY : P. St-Germain, EIT APPROVED BY: J. Readshaw, P.Eng ISSUE/REVISION INDEX Issue Details Code No. By Rev d. App. Date RI 00 MML PSG JSR 26/10/2015 Issued for Client Use Issue Codes: RC = Released for Construction, RD = Released for Design, RF = Released for Fabrication, RI = Released for Information, RP = Released for Purchase, RQ = Released for Quotation, RR = Released for Review and Comments
Page 2 of 21 NOTICE TO READERS This document contains the expression of the professional opinion of SNC-Lavalin Inc. ( SLI ) as to the matters set out herein, using its professional judgment and reasonable care. It is to be read in the context of the Agreement, and the methodology, procedures and techniques used, SLI s assumptions, and the circumstances and constrains under which its mandate was performed. This document is written solely for the purpose stated in the Agreement, and for the sole and exclusive benefit of the Client, whose remedies are limited to those set out in the Agreement. This document is meant to be read as a whole, and sections or parts thereof should thus not be read or relied upon out of context. SLI has, in preparing any cost estimates, followed methodology and procedures, and exercised due care consistent with the intended level of accuracy, using its professional judgment and reasonable care, and is thus of the opinion that there is a high probability that actual costs will fall within the specified error margin. However, no warranty should be implied as to the accuracy of any estimates contained herein. Unless expressly stated otherwise, assumptions, data and information supplied by, or gathered from other sources (including the Client, other consultants, testing laboratories and equipment suppliers, etc.) upon which SLI s opinion as set out herein is based has not been verified by SLI; SLI makes no representation as to its accuracy and disclaims all liability with respect thereto. SLI disclaims any liability to the Client and to third parties in respect of the publication, reference, quoting, or distribution of this report or any of its contents to and reliance thereon by any third party.
Page 3 of 21 Table of Contents 1.0 INTRODUCTION... 4 1.1 Background... 4 1.2 Scope of Appendix... 4 2.0 HYDRODYNAMIC MODEL... 4 2.1 CMS Model... 4 2.2 Computational Grid... 5 2.3 Bathymetry... 5 2.4 Boundary Conditions... 6 3.0 HYDRODYNAMIC MODEL RESULTS... 7 3.1 Validation... 7 3.1.1 Water Elevations... 7 3.1.2 Currents... 10 3.2 Spring Tide Existing Water Levels... 13 3.3 Neap Tide Existing Water Levels... 15 3.4 Spring Tide 1m SLR... 17 3.5 Neap Tide 1m SLR... 17 4.0 SUMMARY... 20 5.0 GLOSSARY... 20 6.0 REFERENCES... 21
Page 4 of 21 1.0 INTRODUCTION 1.1 Background The waterfront and shoreline areas of the Town of Qualicum Beach, British Columbia, Canada, are a key defining component of the town and surrounding area. In the past, development of the waterfront occurred in an informal manner that is now recognized for its limitations. The many competing interests, demands and needs to maintain its character; including commercial vitality and renewal, increasing public awareness, interest and demand for waterfront access, residential pressures, preservation of the natural values, and the implications of expected climate change to the shoreline, have become more apparent in recent years. The Town of Qualicum Beach has started a Waterfront Master planning process to bring together these interests and, in particular, to start the process of planning for expected climate change and the resulting increase in sea level. This Appendix is part of the first phase of the Master Plan process. This Appendix is a companion document to the main Phase 1 report, SNC-Lavalin document: 614088-2000-41ER-0001 entitled Qualicum Beach Waterfront Master Plan Phase 1 Coastal Processes and Assessment Report. Readers are referred to the main Report for details of terminology used in this Appendix. 1.2 Scope of Appendix The purpose and scope of this Appendix is to provide a description of the hydrodynamic model developed to estimate the tidal currents in the vicinity of the Town of Qualicum Beach. The model covers the majority of the Strait of Georgia and can be driven based on the predicted or the measured tidal water levels defined by the Canadian Hydrographic Service (CHS) at Point Atkinson. The hydrodynamic model was used for two main purposes: i. To define continuous tidal currents in the vicinity of Qualicum Beach for various characteristic conditions: spring and neap tides, tides concurrent with particular storms and currents that could be expected close to shore after a 1 m rise in sea level. ii. Provide boundary conditions to the smaller and more refined costal sediment processes model presented in Appendix D 2.0 HYDRODYNAMIC MODEL 2.1 CMS Model Hydrodynamics, including water levels and tidal currents were computed using the CMS-FLOW engine of the US Army Corps of Engineers (USACE) Coastal Modeling System (CMS) [A.1]. Developed at the Hydraulic Laboratory (CHL) of the USACE Engineering Research and Development Center (ERDC), CMS is an integrated system for simulating currents, waves, sediment transport, and morphology change in coastal regions. CMS- FLOW is a two-dimensional (2D) depth-averaged circulation model that can be forced by astronomical tides, wind, wave, and/or stream flow.
Page 5 of 21 2.2 Computational Grid A structured computational grid of varying resolution covering the Strait of Georgia was developed for the CMS- FLOW model, see Figure A. 1. The extent of the grid was selected such that water levels at Point Atkinson could be imposed as the forcing boundary to the model. The grid has a 5-level resolution, with 40 m x 40 m being the smallest grid size and 640 m x 640 m the largest. Larger grid cells were used in wide and deep areas, while smaller grid cells were used in narrower channels and shallower areas, near the shoreline and closer to the project site. Figure A. 1 Computational Grid of Hydrodynamic Model 2.3 Bathymetry The bathymetry underlying the computational grid was assembled from four (4) sources. Depths reported on numerous CHS nautical charts [A.2] were digitized to form most of the Strait of Georgia area covered by the grid with the following exceptions: for higher accuracy in the vicinity of the Qualicum Beach shorelines, CHS field sheet sounding data [A.3] was used as well as LiDAR data provided by the Town of Qualicum Beach. Lastly, BC Ministry of Environment topographic maps were digitized to define the shorelines to the west and to the east of the town jurisdiction [A.4]. For the assembly of the bathymetric datasets, priority was given based on their resolution and date of survey. Figure A. 2 shows the assembled bathymetry in the vicinity of the Town of Qualicum Beach.
Page 6 of 21 Figure A. 2 - Assembled Model Bathymetry in Vicinity of Qualicum Beach 2.4 Boundary Conditions To simulate astronomical tides through the computational grid, CHS predicted water levels at Point Atkinson were obtained from the Canadian Department of Fisheries and Oceans [A.5] and applied along the grid s open boundary, shown as a blue line in Figure A. 1.
Page 7 of 21 3.0 HYDRODYNAMIC MODEL RESULTS Five cases were considered for running the CMS-FLOW model (see Table A. 1): One for validation purposes, two for defining tidal currents for existing water levels and another two for 1m Sea Level Rise (SLR). The SLR water levels for model forcing were obtained by superimposing 1 m to the tidal prediction time-series. Table A. 1 - Hydrodynamic Simulation Details Run Water Level Tide Purpose 1 Existing Spring Validation 2 Existing Spring Current Definition for a Typical Spring Tide 3 Existing Neap Current Definition for a Typical Neap Tide 4 1 m SLR Spring SLR Effect on Typical Spring Currents 5 1 m SLR Neap SLR Effect on Typical Neap Currents 3.1 Validation The purpose of this model run is to demonstrate the accuracy of the CMS-FLOW hydrodynamic model for tidal forcing alone. The hydrodynamic model was used to simulate water elevations and currents in the Strait of Georgia during the month of January 2012, near winter solstice, when large spring tides occur. Figure A. 3 shows the corresponding tide predictions at Point Atkinson used to force the hydrodynamic model. Figure A. 3 CHS Predicted Tides at Point Atkinson for the Month of January 2012 3.1.1 Water Elevations The water surface elevation computed by the model was verified at Northwest Bay, the closest location to the Town of Qualicum Beach where tide levels are predicted by CHS (distance between the two locations is approximately 20 km). Tidal constituents at Northwest Bay were derived from CHS daily predictions of high and low water levels (tide tables) using the T_TIDE MATLAB toolbox developed at the University of British Columbia, BC, Canada [A.6]. These constituents were then used to generate a continuous water surface elevation time-series for comparison with the one computed by the hydrodynamic model.
Page 8 of 21 Figure A. 4 shows the comparison between the predicted tides at Northwest Bay and computed by the hydrodynamic model. Beyond the 3-day ramp that was used to gradually start-up the hydrodynamic model, reasonable agreement in both the phase and magnitude of the tides is observed. Root Mean Square Error (RMSE) and Skill Level [A.7] were used as statistical measures to assess the model s accuracy and are defined as follows: 1 2 1 where and are the model computed value and tidal prediction at time, respectively; is the number of time records compared; and is the mean of the tidal predictions. These parameters serve to aggregate the magnitudes of the differences, in this case between the computed water levels and the predicted tides, for various times into a single measure of accuracy. The more accurate is the model, the closer the RMSE is to zero and the closer to one is the Skill Level. Table A. 2 shows these two accuracy measures with respect to water levels at Northwest Bay. Overall, the model is considered to be reliable for the computation of the water levels in the vicinity of the project site.
Page 9 of 21 Figure A. 4 Comparison between Computed and T_TIDE derived Predictions of Water Surface Elevation at Northwest Bay Table A. 2 Hydrodynamic Model Water Level Accuracy RMSE (m) Skill Level 0.17 0.99
Page 10 of 21 3.1.2 Currents Further validation of the hydrodynamic model was achieved by comparing the computed current field in the Strait of Georgia against the Juan de Fuca Strait to Strait of Georgia Current Atlas from Fisheries and Oceans Canada [A.8]. Figure A. 5 shows the current directions and velocities in the Strait of Georgia at the moment of maximum flow during a falling typical spring tide (modified Chart 53 of the Current Atlas). Figure A. 6 show the current field in the Strait of Georgia at the corresponding time computed by the hydrodynamic model. Figure A. 7 shows the current directions and velocities in the Strait of Georgia at the moment of maximum flow during a rising typical spring tide (modified Chart 60 of the Current Atlas). Figure A. 8 show the current field in the Strait of Georgia at the corresponding time computed by the hydrodynamic model. From these 4 figures it can be observed that: i. The maximum ebb and flood velocities calculated by the numerical model in the Strait of Georgia were generally below 0.25 knots (0.13 m/s) and some areas of the Strait of Georgia showed current velocities up to 0.50 knots (0.26 m/s). This is in agreement with the current velocities shown in the Current Atlas at the moments of maximum flow. ii. The areas with current velocities between 0.25 to 0.50 knots (0.13 to 0.26 m/s) shown by the numerical model are generally the same areas with higher velocities in the Current Atlas. iii. Specifically, in the area of Qualicum Beach, both the numerical model and the Current Atlas show higher velocities (up to 0.50 knots or 0.26 m/s) off Columbia Beach and French Creek. Overall, reasonable agreement in both current direction and current velocity was observed in the area of Qualicum Beach, therefore the model is considered to be reliable for the prediction of the current field in the vicinity of the project site.
Page 11 of 21 Figure A. 5 Ebb Currents for a Typical Spring Tide according to CHS Current Atlas (modified from [A.8]) Figure A. 6 Computed Ebb Currents on a Typical Spring Tide
Page 12 of 21 Figure A. 7 - Flood Currents for a Typical Spring Tide according to CHS Current Atlas (modified from [A.8]) Figure A. 8 Computed Flood Currents on a Typical Spring Tide
Page 13 of 21 3.2 Spring Tide Existing Water Levels A large spring tide was predicted at Point Atkinson for the night of 2011/11/25 with an ebb tide range of 4.4 m, followed by a flood tide range of 4.7 m. The hydrodynamic model was used to simulate water levels currents in the Strait of Georgia for the period of 2011/11/05 to 2011/12/05. Figure A. 9 shows the tide predictions at Point Atkinson for that period. Figure A. 9 CHS Predicted Tides at Point Atkinson for the Period of 2011/11/05 to 2011/12/05 Figure A. 10 and Figure A. 11 show the computed tidal current field in the vicinity of the Town of Qualicum Beach 3 hours after and 5 hours before high water (HW) at Point Atkinson, respectively. These are the times when higher velocities are observed in this area. Weak tidal currents are observed at the Town Waterfront, being less than 0.05 m/s at the peak flood and less than 0.1 m/s at the peak ebb. Stronger currents are observed at either W and E limits of the waterfront area. In front of Little Qualicum River Beach current velocities of up to 0.2 m/s can be observed during falling of a typical spring tide. In front of Columbia Beach velocities of up to 0.25 m/s appear quite close to the shoreline during tidal rising. Maximum current velocities are observed off French Creek at depths or around 10 m with respect to Chart Datum, where velocities reach 0.35 m/s during both ebb and flood.
Page 14 of 21 Figure A. 10 Computed Spring Ebb Current Field in the vicinity of Qualicum Beach 3 hours after HW at Point Atkinson (Existing Water Levels) Figure A. 11 - Computed Spring Flood Current Field in the vicinity of Qualicum Beach 5 hours before HW at Point Atkinson (Existing Water Levels)
Page 15 of 21 3.3 Neap Tide Existing Water Levels A small neap tide was predicted at Point Atkinson for the day of 2011/09/13 with an ebb tide range of 2.0 m, followed by a flood tide range of 2.2 m. The hydrodynamic model was used to simulate currents in the Strait of Georgia for the period of 2011/08/29 to 2011/09/28. Figure A. 12 shows the tide predictions at Point Atkinson for that period. Figure A. 12 CHS Predicted Tides at Point Atkinson for the Period of 2011/08/29 to 2011/09/28 Figure A. 13 and Figure A. 14 show the computed tidal current field in the vicinity of the Town of Qualicum Beach 2 hours after and 4 hours before high water (HW) at Point Atkinson, respectively. These are the times when higher velocities are observed in this area. The current field show a similar pattern to the one previously observed for a typical spring tide. Currents in front of the Town Waterfront are very weak, especially during flood. The stronger currents are observed off Columbia Beach and French Creek, where up to 0.25 m/s currents can be observed.
Page 16 of 21 Figure A. 13 - Computed Neap Ebb Current Field in the vicinity of Qualicum Beach 2 hours after HW at Point Atkinson (Existing Water Levels) Figure A. 14 - Computed Neap Flood Current Field in the vicinity of Qualicum Beach 4 hours before HW at Point Atkinson (Existing Water Levels)
Page 17 of 21 3.4 Spring Tide 1m SLR 1 m SLR was superimposed to the tidal predictions associated to the typical spring tide used for model forcing. Figure A. 15 and Figure A. 16 show the computed tidal current field in the vicinity of the Town of Qualicum Beach 3 hours after and 5 hours before high water (HW) at Point Atkinson, respectively. Patterns in the current field are very similar to the ones obtained with existing water levels although overall current velocities are slightly reduced in the case of the ebb tide by <0.05 m/s. 3.5 Neap Tide 1m SLR 1 m SLR was superimposed to the tidal predictions associated to the neap spring tide used for model forcing. Figure A. 17 and Figure A. 18 show the computed tidal field in the vicinity of the Town of Qualicum Beach 2 hours after and 4 hours before high water (HW) at Point Atkinson, respectively. Patterns in the current field are very similar to the ones obtained with existing water levels although overall current velocities are slightly reduced in the case of the ebb tide by <0.05 m/s.
Page 18 of 21 Figure A. 15 - Computed Spring Ebb Current Field in the vicinity of Qualicum Beach 3 hours after HW at Point Atkinson (1 m SLR) Figure A. 16 - Computed Spring Flood Current Field in the vicinity of Qualicum Beach 5 hours before HW at Point Atkinson (1 m SLR)
Page 19 of 21 Figure A. 17 - Computed Neap Ebb Current Field in the vicinity of Qualicum Beach 2 hours after HW at Point Atkinson (1 m SLR) Figure A. 18 - Computed Neap Flood Current Field in the vicinity of Qualicum Beach 4 hours before HW at Point Atkinson (1 m SLR)
Page 20 of 21 4.0 SUMMARY The CMS-FLOW hydrodynamic model was developed and validated to provide tidal currents for typical spring and neap tide cycles in the vicinity of the Town of Qualicum Beach and for use in the coastal process modelling undertaken for the overall assignment. The validation of the model included comparison of computed water levels with predicted water levels at Northwest Bay, which is located ~20 km east of the Town of Qualicum Beach. A Skill Level of 0.99 and a Root Mean Square Error of ±0.17 m indicated good model accuracy in the computation of water levels at this location, which is considered to be representative of the project site. Further validation was achieved with the comparison of computed currents published in the Juan de Fuca Strait to Strait of Georgia Current Atlas [A.8]. Good agreement was observed especially near the project site. The CMS-FLOW hydrodynamic model was utilized to develop current definitions for a typical spring tide and neap tide cycle in the vicinity of Qualicum Beach and to discuss the possible effect of 1 m sea level rise on currents. The current field pattern was similar in all simulations, showing very weak currents (<0.1 m/s) in front of Town Waterfront area, especially on a flood tide, and stronger currents at the W and E limits of the study area. Current velocities in front of Little Qualicum River Beach reached 0.2 m/s on a typical spring ebb tide. Maximum current velocities were observed in front of Columbia Beach and French Creek, reaching up to 0.35 m/s in a typical spring tide ebb and flood. Simulations with an additional 1 m of sea level rise imposed to the CHS tidal predictions showed very little change in the overall current patterns although ebb currents appeared slightly weaker by <0.05 m/s. The hydrodynamic model described here was also used to provide hydrodynamic boundary conditions to the smaller and more refined costal sediment processes model presented in Appendix D. 5.0 GLOSSARY Please refer to Main Report for list of terms and acronyms.
Page 21 of 21 6.0 REFERENCES [A.1] Reed, CW., Brown, M.E., Sánchez, A., Wu, W., and Buttolph, A.M. (2011). Validation of the Coastal Modeling System: Report III, Hydrodynamics, ERDC/CHL-TR-11-10, US Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory, Vicksburg, MS. [A.2] Canadian Hydrographic Service, Nautical Charts # 3538, 3539, 3512, 3513. [A.3] Canadian Hydrographic Service, Field Sheet # 1300818. [A.4] Ministry of Environment 1:2000 Topographic Maps # 92F.038.067, 92F.039.043, 92F.039.051, 92F.039.052, 92F.039.053. [A.5] Canadian Hydrographic Service Tide Predictions, Department of Fisheries and Oceans. [A.6] Pawlowicz, R., Beardsley, B., and Lentz, S. (2002). Classical tidal harmonic analysis including error estimates in MATLAB using T_TIDE, Computers and Geosciences, 28, 929-937. [A.7] Willmott, C.J. (1981). On the validation of models, Physical. Geography, 2, 184-194. [A.8] Fisheries and Oceans Canada (2010), Juan de Fuca Strait to Strait of Georgia Current Atlas, ISBN 0-660-62300-5. DOCUMENT END