Task 16: Impact on Lummi Cultural Properties

Transcription

1 Gateway Pacific Terminal Vessel Traffic and Risk Assessment Study Task 16: Impact on Lummi Cultural Properties Prepared for Pacific International Terminals, Inc. Prepared by The Glosten Associates, Inc. in collaboration with Environmental Research Consulting Northern Economics, Inc. File No November 2012 Rev. P0 Consulting Engineers Serving the Marine Community

2 Gateway Pacific Terminal Vessel Traffic and Risk Assessment Study Task 16: Impact on Lummi Cultural Properties Prepared for Pacific International Terminals, Inc. Seattle, Washington File No November 2012 Rev. P0 Environmental Research Consulting Cortlandt Manor, New York Prepared by The Glosten Associates, Inc. Seattle, Washington in collaboration with Northern Economics, Inc. Anchorage, Alaska PREPARED: Thomas Mathai, PhD Project Ocean Engineer CHECKED: Rick D. Strong Project Manager APPROVED: David L. Gray, PE Principal-in-Charge Consulting Engineers Serving the Marine Community 1201 Western Avenue, Suite 200, Seattle, Washington TEL FAX

3 Contents References... ii Executive Summary... iii Scope of Work per Professional Services Agreement... iv Section 1 Introduction... 1 Section 2 Wake Energy... 2 Section 3 Wind-Generated Wave Energy... 4 Section 4 Effect of Pier Location... 6 Gateway Pacific Terminal VTS Study i The Glosten Associates, Inc. Task 16 Report, Rev. P0 File No , 30 November 2012

4 References 1. Map of historic reef net fishing sites off Lummi Island, The Lummi Nation, Kriebel, D. L. and Seelig, W. N., An empirical model for ship-generated waves, Waves 2005, Fifth International Symposium on Ocean Wave Measurement and Analysis, Madrid, CEDAS (Coastal Engineering Design and Analysis System), ACES Version 4.03, Copyright , Veri-Tech, Inc., 4. Historical data for Station CHYW at Cherry Point, Washington, National Data Buoy Center, National Oceanographic and Atmospheric Administration, accessed at Gateway Pacific Terminal VTS Study ii The Glosten Associates, Inc. Task 16 Report, Rev. P0 File No , 30 November 2012

5 Executive Summary The Vessel Traffic and Risk Assessment Study project was asked to address the impacts of increased vessel traffic on traditional cultural properties and underwater archaeology. The contracting parties agreed that an appropriate method to fulfill this request is to evaluate the impact of the wake waves of GPT-bound vessels on the shoreline at locations where traditional cultural properties and underwater archaeological artifacts exist. Virtually all anticipated vessel traffic to the proposed GPT will be comprised of bulk transport vessels (bulkers) and berthing / mooring assist tugboats (tugs). This analysis finds that tugboat wakes have a larger wave height and more energy flux than bulker wakes. The tugboat wake compares to an annual maximum storm wave as follows: Height: 13% of an annual maximum storm wave. Energy Density: 2% of an annual maximum storm wave. Energy Flux: 1% of an annual maximum storm wave. The total wave energy from a year of waves and storms and the total wake wave energy from GPT-bound vessels have not been calculated. This analysis shows, however, that the addition of the GPT-bound bulkers and tugboats will add very little to the wave energy at the chosen location in comparison to wind-generated waves. Village Point Western Shore of Lummi Island, Washington Figure 1 Historic reef net fishing sites off Lummi Island, indicator of potential nearby village sites (map provided to project by the Lummi Nation, Reference 1) Gateway Pacific Terminal VTS Study iii The Glosten Associates, Inc. Task 16 Report, Rev. P0 File No , 30 November 2012

6 Scope of Work per Professional Services Agreement 1 Assesses the impact of GPT-calling vessels on traditional cultural properties and underwater archaeology. The statistical measures of impact will be: a. The additional energy arriving at the shoreline from the wakes of passing vessels bound for or departing from GPT compared to the total energy at background levels (i.e. without GPT traffic). b. The energy arriving at the shoreline from the most extreme event of passing vessels compared to the extreme event of a winter storm. c. If it is found that this statistic is measurably affected by pier location, separate statistics will be reported for both alternative pier locations. 1 Exhibit A, Scope of Services Task 16, Professional Services Agreement between Pacific International Terminals, Inc. and The Glosten Associates, Gateway Pacific Terminal Vessel Traffic and Risk Assessment Study, Effective Date June 18, Gateway Pacific Terminal VTS Study iv The Glosten Associates, Inc. Task 16 Report, Rev. P0 File No , 30 November 2012

7 Section 1 Introduction A map of shoreline locations of interest was provided to the GPT project by the Lummi Nation (see Figure 1). With the understanding that the locations of Lummi Nation cultural sites are sensitive information and that the map does not represent all of the cultural sites, The Glosten Associates chose Village Point on the western shoreline of Lummi Island, as it is the site nearest to traffic lanes that will be used by GPT-bound deep draft ships and GPT-bound assist and docking tugs. Consequently, it will also have the highest incidence of vessel wake wave height and wake energy One method to measure the impact of increased vessel traffic on the shoreline and cultural properties is to compare the arriving wake wave energy with the wave energy at background levels without GPT-bound traffic. The background wave energy levels chosen for comparison are those produced by an average summer maximum storm and an average annual maximum storm. It is assumed that storm events characterize the energy levels to which the shoreline and cultural properties are exposed without the GPT-bound traffic. There are other locations identified as sites of cultural properties and underwater artifacts that are not exposed to significant wave and storm energy; however, these locations are also not exposed to GPT-bound vessel wakes. Gateway Pacific Terminal VTS Study 1 The Glosten Associates, Inc. Task 16 Report, Rev. P0 DRAFT File No , 30 November 2012

8 Section 2 Wake Energy The impact of vessel wakes on traditional cultural properties has been evaluated by analyzing the wakes from a Capesize bulker and a tugboat in terms of height, period, energy density, and energy flux. In this study, the western shore of Lummi Island is chosen as an example site for evaluation because of traditional cultural properties located there, and also because it is the closest point of approach for passing GPT-calling vessels. The sailing line is at least onequarter nautical mile from the shoreline at this location. The speed of the bulker is assumed to be 12 knots, and that of the tugboat is assumed to be 14 knots. The water depth is assumed to be 180 feet. Vessel wakes comprise of a set of transverse waves propagating in the same direction as the vessel, and a set of diverging waves propagating at an acute angle to the sailing line (Figure 2). The height of the transverse waves diminishes faster than that of the diverging waves, as the distance from sailing line increases. Therefore, waves reaching the shoreline are expected to be comprised primarily of diverging waves. The maximum height of these diverging waves is estimated based on Reference 2. The wave pattern remains steady in a vessel-fixed frame of reference. Therefore, wave period and length can be estimated from the vessel speed and the angle the direction of wave propagation makes with the sailing line. Here, this angle is taken to be 35 16' (see in Figure 2), though this is theoretically correct only at the cusp locus line. y CUSP LOCUS LINE o V SAILING LINE 0 TRANSVERSE WAVE Cd DIVERGING WAVE Figure 2 Pattern of wave crests generated by a moving vessel (Reference 2) Gateway Pacific Terminal VTS Study 2 The Glosten Associates, Inc. Task 16 Report, Rev. P0 DRAFT File No , 30 November 2012

9 Once the wave parameters are estimated, the average energy density, E, is given by: 2 gh E (1) 8 The energy flux, P, is obtained by multiplying the average energy density by the group velocity, c G : P Ec G (2) The group velocity can be determined as follows: c G 1 2kd 1 2 kd sinh 2 c Here, is density of water, g is gravitational acceleration, H is wave height, k is wave number, d is water depth and c is wave celerity (e.g., wave speed). The calculated height, period, energy density, and energy flux of wakes generated by a Capesize bulker and a tugboat, at a distance of one-quarter nautical mile from the sailing line, are shown in Case C and Case D, respectively, in Table 2. Comparisons with similar results for wind-generated waves are shown in the next section. (3) Gateway Pacific Terminal VTS Study 3 The Glosten Associates, Inc. Task 16 Report, Rev. P0 DRAFT File No , 30 November 2012

10 Section 3 Wind-Generated Wave Energy In order to estimate the severity of wind-generated wave conditions at Lummi Island, a wave hindcast is performed using Coastal Engineering Design and Analysis System software (Reference 3). The average of summer maximum and the average of annual maximum wave conditions are hindcast by applying the corresponding wind speeds for Cherry Point taken from Table 1. The seasonal maximums in Table 1 are summarized from National Data Buoy Center historical records for the years (Reference 4). The calculated wave height, period, energy density, and energy flux corresponding to the average of summer maximum and the average of annual maximum wave conditions are shown in Case A and Case B, respectively, of Table 2. Results for vessel wakes are shown in the last two rows. Table 1 Seasonal maximum wind speed (2 minute average in knots) for Cherry Point Season\Year Average Spring Summer Fall Winter Annual Table 2 Case A B Comparison of wave energy from wind-generated waves in summer (Case A) and in winter (Case B), and from vessel wake by a Capesize bulker (Case C) and by a Tugboat (Case D) Source Wind-generated waves, average summer maximum Wind-generated waves, average annual maximum Height ft Period sec Energy Density ft-lb/ft^2 Energy Flux ft-lb/ft-sec 4.7 * 5.8 ** 179 2, * 7.4 ** ,215 C Capesize bulker, 12 knots D Tugboat, 14 knots 1.1 (22% of A, 13% of B) * Root-mean-square wave height ** Modal period (5% of A, 2% of B) 86 (3% of A, 1% of B) Table 2 illustrates that the wake created by a Capesize bulker (Case C) is small relative to that created by a tugboat. The tugboat wake (Case D) could be 22% of a summer maximum storm wave in terms of height. However, the tugboat wake is only 5% of a summer maximum storm wave in terms of energy density and only 3% of it in terms of energy flux. The tugboat wake is 13% of an annual maximum storm wave in terms of height. It is only 2% of an annual maximum storm wave in terms of energy density and only 1% of it in terms of energy flux. Gateway Pacific Terminal VTS Study 4 The Glosten Associates, Inc. Task 16 Report, Rev. P0 DRAFT File No , 30 November 2012

11 Criteria are not well established for vessel wake height, energy density, and energy flux, that will minimize adverse effect on shoreline morphology and damage to nearshore underwater properties. Nonetheless, this analysis shows that the addition of the GPT-bound bulkers and tugboats will add very little to the wave energy arriving at Lummi Island relative to the energy of wind-generated waves. Gateway Pacific Terminal VTS Study 5 The Glosten Associates, Inc. Task 16 Report, Rev. P0 DRAFT File No , 30 November 2012

12 Section 4 Effect of Pier Location The two alternative pier locations are close to each other and differ mainly in their alignments by about 20 degrees (Figure 3). The vessel route to either alternative will be identical except for the final approach and berthing. The final approach and berthing involve slow speed maneuvering which does not produce significant wake. In view of the above, no measurable difference is expected in the potential impact to cultural properties by choosing one alternative over the other. Figure 3 Second Wharf Alignments to be Studied Alternative #4 Gateway Pacific Terminal VTS Study 6 The Glosten Associates, Inc. Task 16 Report, Rev. P0 DRAFT File No , 30 November 2012