DECEMBER, 2014 NEW ENGLAND INTERSTATE WATER POLLUTION CONTROL COMMISSION GREAT KILLS HARBOR BREAKWATER STUDY: HYDRODYNAMIC MODELING
TASK 3 SUMMARY REPORT
ADDRESS SCAPE / LANDSCAPE ADDRESS Ocean and Coastal ARCHITECTURE PLLC Consultants, Inc. 277 Broadway 35 Corporate Drive Suite 1606 Suite 1200 New York, NY 10007 Trumbull, CT 06611 TEL 212-462-2628 TEL 203-268-5007 FAX 212-462-4164 FAX 203-268-8821 WWW scapestudio.com WWW ocean-coastal.com
GREAT KILLS HARBOR BREAKWATER STUDY: HYDRODYNAMIC MODELING
TASK 3 SUMMARY REPORT
PROJECT NO. 214038
DOCUMENT NO. T3_01
VERSION 2.0
DATE OF ISSUE December 19, 2014
PREPARED BRCO
CHECKED TPMA
APPROVED AZSL
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TASK 3 SUMMARY 5
Task Introduction and Scope The Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor is co-led by Ocean & Coastal Consultants, a COWI Company and SCAPE Landscape Architecture (OCC/SCAPE) along with project partners ARCADIS US, Inc., Parsons Brinckerhoff, Biohabitats, and SeArc Marine Consulting. This feasibility study will provide guidance on the use of offshore breakwaters as an adaptation strategy to reduce wave action while maintaining or enhancing habitat value. The project’s objective seeks to determine the technical feasibility and marine habitat benefits and impacts offered by an offshore breakwater system outside of and adjacent to Great Kills Harbor. The results of the study will serve to inform New York City's Office of Recovery and Resiliency (ORR), New York City Department of City Planning, New York State's Department of Environmental Conservation (DEC) and the Hudson River Estuary Program (HREP), and other agencies and community groups for use in community planning, shoreline adaptation, and resiliency.
Project team member ARCADIS US, Inc. is the designated task lead for Task 3: Hydrodynamic Modeling. The purpose of Task 3, in cooperation with the development of the selected approaches in Task 4, is to utilize ocean surface wave propagation computer models of the baseline scenario and the two selected shoreline protection strategies recommended during Task 2 of this study to determine the effectiveness of the strategies. The options modeled include:
Option 0: Baseline Existing Conditions
Option 1: A breakwater on the ocean-side of Crooke's Point with a harbor-wide breakwater at the mouth of Great Kills Harbor
Option 2: Dune on Crooke's Point with a segmented breakwater along Crescent Beach
This report presents an evaluation of the wave conditions in the study area as predicted by the hydrodynamic models under various storm, sea level rise (SLR), and project conditions. Storm and SLR wave conditions were assessed based on four storm scenarios: (1) A storm similar to the December 1992 Nor’easter, (2) A storm similar to Hurricane Sandy, (3) the nor'easter storm including 31 inches of SLR, and (4) the Sandy-like storm including 31 inches of SLR.
The following is a synopsis of the modeling report. The full modeling report, appended below, further details available data near the study site, model setup and outputs, and conclusions, and recommendation for further analyses.
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6 TASK 3 SUMMARY
Method Offshore wave propagation and attenuation with and without study conditions was assessed using the Refraction/Diffraction (REFDIF) numerical wave model. REFDIF captures the propagation of waves over complex bathymetry, topography, and coastal structures and accounts for the interaction of many processes including shoaling, refraction, diffraction, reflection and dissipation. However REFDIF does not account for locally-generated wind driven waves.
Preliminary results illustrated that there is limited wave propagation into the harbor from offshore due to wave shoaling and the geometry of the harbor entrance. Thus only a small portion of the total wave energy within Great Kills is attributable to waves propagating into the harbor from offshore. In order to gain a better understanding of the wave climate within the harbor, a local wind wave analysis was conducted using the Automated Coastal Engineering System (ACES) numerical analysis tool. The combination of the ACES wind wave analysis and REFDIF offshore waves assessment describes the overall wave climate in the harbor.
Results & Recommendations As a result of the modeling efforts, the project team reached the following conclusions and recommendations:
Waves inside the Harbor
The model results indicated a small portion of the total wave energy expected within Great Kills Harbor comes from waves propagating into the harbor from offshore. The secondary analysis using ACES indicated a strong influence on the wave climate comes from local wind generated waves in this area. These results indicate that breakwaters placed outside the harbor will have limited effect on wave conditions within the harbor as the current harbor configuration already effectively attenuates the majority of offshore waves before they enter the harbor. The use of localized wave attenuating structures within the harbor such as floating breakwaters or wave screens are recommended to mitigate the effects of waves within the harbor.
Breakwater crown elevations
The crown elevation of 11.0 feet NAVD88 studied shows considerable benefits for both the 1992 Nor’easter event (9.0 feet NAVD88 stillwater elevation) and 1992 Nor’easter event with SLR (11.6 feet NAVD88 stillwater elevation), particularly for Option 1. Less substantial benefits are seen for the Hurricane Sandy event (12.3 feet NAVD88 stillwater elevation). Minimal to no benefits are shown for the Hurricane Sandy event with SLR (14.9 feet NAVD88 stillwater elevation) in both modeled options. The falloff in effectiveness of the breakwaters with increasing sea level rise suggests the height of the breakwaters relative to the underlying water (surge) elevation is a critical factor in the magnitude of wave reduction. If the breakwater is
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TASK 3 SUMMARY 7
designed in future phases to attenuate waves at a stillwater elevation higher than 11.5 feet NAVD88, a higher design elevation than 11.0 feet is recommended.
Breakwater openings
Option 1 generally performs better than Option 2 in attenuating waves due to the continuous breakwater structure, though Option 2 has a more ideal position relative to the shoreline. The current openings (85 feet average) in Option 2 allow for waves to penetrate through the breakwater. Breakwater openings should be smaller than the wave lengths in the area, which are on the order of 90 to 100 feet. Opening sizes in the range of 20 to 40 feet would attenuate waves with increased efficiency. A staggered or overlapping opening design would further limit wave penetration and is recommended. Water quality and circulation modeling would be necessary to determine the appropriate opening size to maintain adequate circulation.
Breakwater distance from the shoreline
The Option 1 breakwater at Crescent Beach is further from the shore (0.25 miles) than the Option 2 breakwater at Crescent Beach (0.10 miles). While the Option 1 breakwater generally shows the greatest wave reduction at its lee side because it is a continuous and relatively long breakwater alignment, Option 2 provides wave attenuation for 4.5 foot waves during the 1992 Nor’easter event for a broader area than Option 1 largely due to the proximity to the coast. An alignment closer to the coast provides a broader shadow area at the shoreline, maximizing the length of shoreline where waves are reduced relative to the length of the breakwater. Based on the limited REFDIF results and engineering judgment, a breakwater of 0.10 miles offshore is preferable to a breakwater 0.25 miles offshore.
Breakwater length
In general, the longer the breakwater length, the broader the area protected on the lee side. The shadow area shown in the model outputs illustrate this. The limited reduction provided by the Option 1 breakwater near Great Kills Park and the Option 2 breakwater (which could be considered as many short breakwaters when evaluating the effects of breakwater length) highlights the need to extend a breakwater sufficiently far beyond the target areas of protection in order to provide a sufficiently large shadow zone. The necessary length is directly correlated to the distance from the shoreline and the two should be considered together in the next design phase.
Next Steps The recommended next steps to further assess waves and breakwater options in the study area are twofold.
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8 TASK 3 SUMMARY
1) Further refinement of the breakwater design using an iterative modeling process is expected to yield an implementable design.
2) Modeling the breakwaters for additional storm scenarios provides additional data which can be used for further refinement.
3) Additional modeling of sedimentation, water quality, and water circulation for the site.
4) Modeling of breakwaters in combination with other interventions, such as dunes, house elevation, or other shoreline treatments.
Document Control Recommended Citation: Marrone, Joseph F., P.E., Sleicher, Azure Dee, P.E., Manson, Todd P. PE, Orff, Kate PLS, December 19, 2014, "Great Kills Harbor Breakwater Study- Hydrodynamic Modeling, Task 3 Summary Report, Version 2.0", prepared by OCC|COWI, SCAPE/Landscape Architecture, Arcadis US, et. al. for the Hudson River Estuary Program, New York State Department of Environmental Conservation and the New England Interstate Water Pollution Control Commission.
Table 0-1: Revision History Revision Date Prepared By Checked By Approved By Final 1.0 11/19/14 BRCO TPMA AZSL 2.0 12/19/14 BRCO TPMA AZSL
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Imagine the result
NEIWPCC New England Interstate Water Pollution Control Commission
New York State Department of Environmental Conservation (NYSDEC) Hudson River Estuary Program
Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor
Staten Island, New York
Numerical Wave Modeling
December 15, 2014
Table of Contents
1. Introduction 1
2. Data Assessment 4
2.1 Wind Conditions 5
2.2 Wave Conditions 5
2.3 Tidal Datum 8
2.4 Previous Studies 8
3. REF/DIF Model Setup 9
3.1 Bathymetry and Topography 10
3.2 Wave Conditions 11
3.3 Study Options 12
4. REF/DIF Simulations 15
5. ACES Model Setup and Simulations 27
6. Recommendations 28
6.1 Breakwater Crown Elevations 28
6.2 Breakwater Distance from the Shoreline 28
6.3 Breakwater Openings 29
6.4 Breakwater Length 29
7. References 29
Tables
Table 1: Tidal Data for Sandy Hook, New Jersey (NOAA 8531680) 8
Table 2: REF/DIF Stillwater Elevation and Wave Condition Model Inputs 12
Table 3: Wind Wave Analysis Inside the Harbor 27
Figures
Figure 1: Plan View of Study Option 1 2
Figure 2: Plan View of Study Option 2 3
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Table of Contents
Figures (continued)
Figure 3: Study Domain and Subregions for the Numerical Modeling Analysis 4
Figure 4: Study Location Map and Observed Data Locations 6
Figure 5: Wind Rose at the NOAA Sandy Hook Gauge (8531680) 6
Figure 6: Wave Rose at USACE WIS Station 63126 (USACE 2014) 7
Figure 7: Study Options of Offshore Breakwater 10
Figure 8: REF/DIF Model Bathymetry and Topography for Option 1 13
Figure 9: REF/DIF Model Bathymetry and Topography for Option 2 14
Figure 10: Wave Directions – Hurricane Sandy Option 0 (offshore waves from the south) 15
Figure 11: Wave Directions – Hurricane Sandy Option 1 (offshore waves from the south) 16
Figure 12: Wave Directions – Hurricane Sandy Option 2 (offshore waves from the south) 16
Figure 13: Wave Amplitudes – Hurricane Sandy Option 0 (offshore waves from the south) 17
Figure 14: Wave Amplitudes – Hurricane Sandy Option 1 (offshore waves from the south) 18
Figure 15: Wave Amplitudes – Hurricane Sandy Option 2 (offshore waves from the south) 18
Figure 16: Wave Heights (1.5 feet) – 1992 Nor'easter Options 0, 1, and 2 21
Figure 17: Wave Heights (1.5 feet) – 1992 Nor'easter Plus 31” SLR Options 0, 1, and 2 21
Figure 18: Wave Heights (1.5 feet) – Hurricane Sandy Options 0, 1, and 2 22
Figure 19: Wave Heights (1.5 feet) – Hurricane Sandy Plus 31” SLR Options 0, 1, and 2 22
Figure 20: Wave Heights (3.0 feet) – 1992 Nor'easter Options 0, 1, and 2 23
Figure 21: Wave Heights (3.0 feet) – 1992 Nor'easter Plus 31” SLR Options 0, 1, and 2 23
Figure 22: Wave Heights (3.0 feet) – Hurricane Sandy Options 0, 1, and 2 24
Figure 23: Wave Heights (3.0 feet) – Hurricane Sandy Plus 31” SLR Options 0, 1, and 2 24
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Figures (continued)
Figure 24: Wave Heights (4.5 feet) – 1992 Nor'easter Options 0, 1, and 2 25
Figure 25: Wave Heights (4.5 feet) – 1992 Nor'easter Plus 31” SLR Options 0, 1, and 2 25
Figure 26: Wave Heights (4.5 feet) – Hurricane Sandy Options 0, 1, and 2 26
Figure 27: Wave Heights (4.5 feet) – Hurricane Sandy Plus 31” SLR Options 0, 1, and 2 26
Appendix
A Wave Direction and Wave Amplitude Plots
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
1. Introduction
Great Kills Harbor is situated between the east and south shores of Staten Island, surrounded by Great Kills Park, which is administrated by the National Park Service. Encircled by private and public marinas, Great Kills Harbor is an economic hub and important recreational amenity for the area.
During Hurricane Sandy, boats in Great Kills Harbor were lifted and deposited far inland, and the maritime structures were damaged by wave action. Homes and structures in Crescent Beach (the southern shore adjacent to Great Kills Harbor) were heavily damaged.
The New York City (NYC) Mayor’s Office of Recovery and Resiliency (ORR) is working with other NYC agencies, the New York State Department of State, the New York State Department of Environmental Conservation, and the U.S. Army Corps of Engineers (USACE) to evaluate various strategies to increase New York City’s resilience to coastal hazards. The goal of this study is to evaluate the technical feasibility of a system that maximizes both coastal hazard mitigation for the Great Kills area and marine habitat value. The New York State Department of Environmental Conservation's Hudson River Estuary Program funded this study to help fulfill several targets of the Hudson River Estuary Program Action Agenda and support New York City's efforts to increase shoreline resiliency using coastal green infrastructure strategies.
Offshore breakwaters—features typically composed of rock or other robust materials located in an ocean or bay—attenuate wave energy offshore, thereby absorbing the force of destructive waves before they reach the coast and adjacent neighborhoods while not interrupting navigational needs in the harbor. By calming nearby waters, an offshore breakwater has the potential to (1) complement onshore coastal protection measures, (2) reduce coastal erosion caused by wave action, (3) provide protection for on shore uses in high wave energy environments, and (4) provide new habitat for in-water ecosystems and organisms such as oysters. Although expensive, offshore breakwaters can greatly reduce risks for areas exposed to significant wave action and erosion.
It should be noted that, while breakwaters have significant potential to reduce wave action and erosion, they are likely to have limited to no impact on stillwater elevations during storm events. This assumption underlies the analysis conducted in this study. The methods of assessment and evaluative tools selected to analyze the impact of the
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling breakwaters as a part of this study were specifically targeted to isolate and understand wave conditions and impacts.
This report presents an evaluation of the wave conditions in the study area under various storm, sea-level rise (SLR), and proposed conditions. Storm and SLR wave conditions were assessed based on four storm scenarios: an event like the December 1992 Nor’easter, an event like 2012 Hurricane Sandy, and both storms with the inclusion of 31 inches of SLR (NPCC 2013). The study options assessed include three offshore breakwaters and a sand dune in Great Kills Park on the peninsula (Crooke's Point), separating Raritan Bay from Great Kills Harbor, shown on Figure 1 and Figure 2.
Figure 1: Plan View of Study Option 1
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figure 2: Plan View of Study Option 2
The study area was broken into two subregions, referred to as Inside Harbor and Outside Harbor on Figure 3. The subregions were established to account for the unique wave conditions associated with the two areas. For both subregions, offshore wave propagation and attenuation with and without study conditions were assessed using the Refraction/Diffraction (REF/DIF) numerical wave model. REF/DIF captures the propagation of waves over complex bathymetry, topography, and coastal structures and accounts for the interaction of many processes including shoaling, refraction, diffraction, reflection, and dissipation.
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figure 3: Study Domain and Subregions for the Numerical Modeling Analysis
In addition to the REF/DIF analysis, the Inside Harbor subregion assessment included a local wind wave analysis conducted using the Automated Coastal Engineering System (ACES) numerical analysis tool. As the REF/DIF model results show, limited wave propagation into the harbor from offshore due to wave shoaling and the geometry of the harbor entrance results in a small portion of the total wave energy within Great Kills Harbor penetrating from offshore; the majority of waves inside the harbor are generated by local winds. The combination of the ACES wind wave analysis and the REF/DIF offshore waves assessment defines the overall wave climate in the harbor.
The following sections describe available data near the study area, model setup and outputs, and conclusions and recommendations for further analyses.
2. Data Assessment
To conduct the analysis, water-level, wind, and wave conditions had to be defined. Observation data have been considered where available. Additionally, available data from previous analyses were considered where necessary.
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figure 4 shows the locations of weather stations, a National Oceanic and Atmospheric Administration (NOAA) wave buoy, and NOAA tide gauges closest to the study area. Data from these observation locations were used to assess wind, wave, and water-level conditions near the study area, respectively. The study area and REF/DIF model domain are represented on Figure 4 as a blue rectangle. Data were applied for both the REF/DIF and ACES analyses.
2.1 Wind Conditions
There are two weather stations that have wind data over an adequately long time period: Newark International Airport (US Air Force 725020) and Sandy Hook, New Jersey (NOAA 8531680). Of the two locations, the Sandy Hook station is believed to record winds with less overland wind dissipation and, therefore, wind data at the Sandy Hook station were used for this study. Figure 5 shows a wind rose for the NOAA Sandy Hook station. The wind rose shows the dominant wind direction is from the west and northwest at an average speed of 17 miles per hour (7 meters per second).
2.2 Wave Conditions
There are no long-term observed wave data available near Great Kills Harbor. As shown on Figure 4, the nearest observed wave data are measured at the NOAA wave buoy and USACE Wave Information Studies (WIS) locations situated in the North Atlantic Ocean, outside Raritan Bay. The NOAA buoy location has many data gaps for extreme events. However, the USACE WIS station provides long-term wind and wave data spanning multiple decades and storm events. The dominant wave direction at the USACE WIS location is from the southeast, as shown in the wave rose on Figure 6 (USACE 2014). The wave data at the WIS location are important in defining the wave climate in the region and are used as reference data to define model boundary conditions as described later in this document.
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figure 4: Study Location Map and Observed Data Locations
Figure 5: Wind Rose at the NOAA Sandy Hook Gauge (8531680)
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figure 6: Wave Rose at USACE WIS Station 63126 (USACE 2014)
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
2.3 Tidal Datum
In order to evaluate water levels and vertical datum in the study area, tidal datums were assessed. The nearest gauge is located at the NOAA Sandy Hook (8531680) location. Sandy Hook tidal datums are listed in Table 1. All elevations for this study are referenced to the North American Vertical Datum of 1988 (NAVD88). Note that mean sea level and NAVD88 differ by 0.24 feet at Sandy Hook.
Table 1: Tidal Data for Sandy Hook, New Jersey (NOAA 8531680)
Values Values Datum (feet, Station Data) (feet, NAVD88) Mean High-High Water (MHHW) 7.74 2.41 Mean High Water (MHW) 7.41 2.08 NAVD88 5.33 0.00 Mean Sea Level (MSL) 5.09 -0.24 Mean Tide Level (MTL) 5.06 -0.27 Mean Low Water (MLW) 2.71 -2.62 Mean Low-Low Water (MLLW) 2.51 -2.82 Source: http://tidesandcurrents.noaa.gov/datums.html?id=8531680 (NOAA)
2.4 Previous Studies
In support of ORR, ARCADIS U.S., Inc. (ARCADIS), Parsons Brinckerhoff (PB), SCAPE/Landscape Architecture (SCAPE) and the City University of New York (CUNY) assessed coastal protection strategies for the New York City Special Initiative for Rebuilding and Resiliency (SIRR) (http://www.nyc.gov/html/sirr/html/report/report.shtml). The coastal protection strategies were tested for performance under multiple storm and sea level rise conditions with and without breakwater implementation, using regional numerical models. The ADvanced CIRCulation (ADCIRC) and Simulating WAves Nearshore (SWAN) models were used in the SIRR study. The SIRR ADCIRC and SWAN model outputs were utilized in this study to provide boundary conditions for the site-specific, high-resolution REF/DIF model developed to analyze the proposed study options.
The Federal Emergency Management Agency (FEMA) is currently undergoing a flood insurance study for FEMA Region II, which includes Staten Island. The Flood Insurance Rate Maps (FIRMs) being developed by FEMA are founded on hundreds of
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling hurricanes and extratropical events modeled by FEMA using the ADCIRC and SWAN models. One of the historical events modeled as part of the FEMA ADCIRC and SWAN model validation was the December 1992 Nor’easter. The data available from the FEMA study for that event were considered in this analysis. Additionally, bathymetry and topography for the region were collected by FEMA for the FIRM development. In some portions of the study area, FEMA-collected elevation data were considered.
The Living Breakwaters system proposed in Rebuild by Design (RBD) was studied by a team including Dr. Philip Orton of the Stevens Institute of Technology and using the ADCIRC/SWAN storm surge and wave modeling system (SCAPE 2014). Two scenarios were modeled for the southern shore of Staten Island, including a series of segmented exposed breakwaters at elevation 11 feet (NAVD88) and a series of segmented breakwaters at variable heights (submerged, intertidal, and exposed). Both scenarios had breakwaters located approximately 0.25 mile to 0.5 mile offshore. Results of the RBD Living Breakwaters modeling runs were presented in terms of significant wave height. Exposed breakwaters were shown to be the most effective at reducing wave heights, with wave height reductions as great as 3 to 4.7 feet in vulnerable areas in a Hurricane Sandy-type storm. Modeling of a typical nor’easter showed wave action to be dramatically reduced or entirely eliminated in critical areas. The RBD results were taken into consideration in the study scenario development and model selection for this study.
3. REF/DIF Model Setup
The REF/DIF model (Kirby and Dalrymple 1994) is a state-of-the-art wave model and is most commonly used in coastal engineering applications. The propagation of waves over complex bathymetry, topography, and coastal structures involves the interaction of many processes including shoaling, refraction, diffraction, reflection, and dissipation. The REF/DIF wave propagation model, a weakly nonlinear monochromatic wave model, accounts for all of these processes. Accordingly, REF/DIF was selected to assess the three options for this study.
The REF/DIF model simulations are completed assuming steady-state conditions. The model is initialized with a constant water elevation throughout the model domain. For this study, the water level is defined as the peak water level during a given event. Additionally, incident wave heights and periods are applied at the model offshore boundary. Similar to the definition of water levels, peak conditions are applied for incident wave conditions. During the model simulation, waves propagate throughout the model domain until a steady state is reached.
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
In order to set up the model, grid cell elevations including elevation adjustments to represent the breakwater options, peak water levels, and offshore boundary wave conditions must be defined. The following sections describe the data sources and development of the REF/DIF model.
3.1 Bathymetry and Topography
The REF/DIF model grid describes the overland, nearshore, and coastal structure elevations. Figure 7 shows the REF/DIF model domain and boundaries. The topographic data and bathymetric data outside Great Kills Harbor applied to the model were obtained from the DEM developed by FEMA as part of the ongoing flood insurance study (FEMA 2014). Comparison of the FEMA DEM and the NOAA navigation charts showed that the bathymetry outside Great Kills Harbor is similar for both datasets, with the exception of dredged channels, which were not well defined in the FEMA DEM. Those channels were incorporated into the model based on the bottom elevations and dredge template defined in the NOAA navigation charts. Similar to the dredged channels, bathymetry data inside the harbor are distinctly different for the FEMA DEM and the NOAA navigation charts. The FEMA DEM in the harbor shows an average bathymetry of generally 5 feet, while NOAA charts illustrate bottom elevations closer to 10 feet, with some areas as deep as 20 feet. Accordingly, the bathymetric data from NOAA navigation charts were applied to the model inside the harbor.
Figure 7: Study Options of Offshore Breakwater
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
3.2 Wave Conditions
With the model grid oriented with the offshore boundary parallel to the coast, a wide range of wave directions can be simulated without changing the model grid domain. As shown in the wave rose on Figure 6, waves from the southeast are dominant in this study area. Additionally, due to the geometry of the harbor, waves generally from the south are expected to deliver the largest offshore waves into the harbor. The wind rose on Figure 5 shows that winds from the south are relatively common; hence waves from the south are expected to relatively common as well. For this analysis, waves from the southeast and south were simulated.
Because there are no observed wave data near Great Kills Harbor, the REF/DIF water-level and wave conditions were extracted from previous model studies. For the Hurricane Sandy like simulations for current and future conditions, the peak-water-level, peak-offshore-wave-height, and associated offshore-wave-period data were extracted from the SIRR ADCIRC and SWAN model outputs.
For the 1992 Nor’easter simulations, no observation data are available near the study area. Water-level data are available from model outputs from the ongoing FEMA flood insurance study. No wave model outputs were saved by FEMA for this storm. However, the USACE WIS station has observed wave conditions for both the 1992 Nor’easter and Hurricane Sandy. In order to approximate wave conditions at the model boundary for the 1992 Nor’easter like event, the WIS data for Hurricane Sandy were transformed from the station location to the study boundary and compared to the SIRR model outputs. The percentage change between the WIS and SIRR model data for Hurricane Sandy was applied to the transformed 1992 Nor’easter WIS data. The 1992 Nor’easter with SLR simulation assumed a 31-inch increase in the peak water level and a 10 percent increase in wave height and 2 percent increase in wave period based on the comparison of current and future wave conditions for Hurricane Sandy.
The stillwater elevation and wave conditions applied to the REF/DIF model for Hurricane Sandy and the 1992 Nor’easter are presented in Table 2.
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Table 2: REF/DIF Stillwater Elevation and Wave Condition Model Inputs
Stillwater Peak Wave Significant Wave Events Elevation (feet, Period Height (feet) NAVD88) (seconds) 1992 Nor’easter 9.0 7.3 4.8 1992 Nor’easter + SLR 11.6 8.0 4.9 Hurricane Sandy 12.3 9.9 5.8 Hurricane Sandy + SLR 14.9 10.4 5.9
3.3 Study Options
In addition to the “without breakwater” conditions (Option 0), two with breakwater study alternatives (Option 1 and Option 2) were assessed in this analysis. The Option 0 model setup was revised to incorporate the breakwater and sand dune alignments defined in Option 1 and Option 2. Figure 7 shows the study area, REF/DIF model boundaries, and option alignments.
Option 1, as shown on Figure 1, includes two continuous offshore breakwaters. The first is located near Crooke's Point, approximately 0.25 mile from Crescent Beach. This breakwater alignment includes a bend, which shelters the entrance to Great Kills Harbor. The second breakwater is positioned on the east side of Great Kills Park, approximately 0.1 mile from coastline. The elevations applied to the model are shown on Figure 8.
Option 2, as shown on Figure 2, includes an offshore breakwater with openings located 0.1 mile from the Crescent Beach shore and a sand dune along the ridge in Great Kills Park. The elevations applied to the model are shown on Figure 9.
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figure 8: REF/DIF Model Bathymetry and Topography for Option 1
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figure 9: REF/DIF Model Bathymetry and Topography for Option 2
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
4. REF/DIF Simulations
In total, 24 simulations were completed based on combinations of the three study options, four water levels/wave boundary heights and periods (see Table 2), and two wave directions (south and southeast).
Figures 10 through 12 illustrate wave directions for Hurricane Sandy for Option 0, Option 1, and Option 2 conditions, respectively. Each of these three plots shows waves from the south. Wave direction plots for all 24 simulations can be found in Appendix A.
The wave direction plots aid in the interpretation of the impacts of topography and bathymetry, as well as breakwater and dune placement, on wave propagation from offshore to nearshore and into the harbor. The vertical scale of these plots is exaggerated to highlight changes in wave direction; the plots do not properly reflect wave heights.
Figure 10: Wave Directions – Hurricane Sandy Option 0 (offshore waves from the south)
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figure 11: Wave Directions – Hurricane Sandy Option 1 (offshore waves from the south)
Figure 12: Wave Directions – Hurricane Sandy Option 2 (offshore waves from the south)
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figures 13 through 15 show contours of wave amplitude, or half of the wave height, for Hurricane Sandy for Option 0, Option 1, and Option 2 conditions, respectively. Each of these three plots shows waves from the south. Wave amplitude plots for all 24 simulations can be found in Appendix A. These figures show the absolute wave magnitude over the wave domain and are used to interpret changes in wave height due to the breakwater and sand dune alignments.
Figure 13: Wave Amplitudes – Hurricane Sandy Option 0 (offshore waves from the south)
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figure 14: Wave Amplitudes – Hurricane Sandy Option 1 (offshore waves from the south)
Figure 15: Wave Amplitudes – Hurricane Sandy Option 2 (offshore waves from the south)
18
Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figures 16 through 19 show maximum significant-wave-height contour lines for 1.5-foot wave heights for both wave directions; the maximum wave height between the two simulations of waves from the south and southeast is shown. Each plot shows the wave heights for Option 0, Option 1, and Option 2 conditions. The four storm events are shown (1992 Nor’easter, 1992 Nor’easter with SLR, Hurricane Sandy, and Hurricane Sandy with SLR, respectively). Figures 20 through 23 similarly highlight 3.0-foot wave heights, while Figures 24 through 27 indicate 4.5-foot wave heights. These figures overlay significant wave heights for all three study options from the model results shown on Figures 13 through 15 and similar results in Appendix A.
REF/DIF model results exhibit some noteworthy trends:
The protection effectiveness of Option 1 and Option 2 decreases (more wave penetration) with increased water levels;
Neither Option 1 nor Option 2 provides notable wave reduction for the Hurricane Sandy plus SLR event, as shown on Figure 17, Figure 21, and Figure 25, signifying that the breakwater crown elevation must be higher if similar conditions are targeted for wave reduction;
For the three study options including “without breakwater,” Option 0, wave heights of generally 1.5 feet or less enter the harbor from offshore due to wave shoaling and the restricted entrance of the harbor. The 1.5-foot wave contours on Figures 14 through 17 highlight the limited wave weights entering from offshore. From these model outputs, it can be concluded that higher observed wave heights inside the harbor are the result of local wind waves and will not be effectively addressed by breakwaters or other wave attenuation features outside the harbor;
Wave heights on the northwestern shore of the harbor (near Seaside Wildlife Nature Park) are reduced for Option1 and Option 2, as shown on Figures 14 through 16. This is the area within the harbor that would benefit most from the placement of a breakwater;
The “shadow area” (area of reduced waves) on the lee side of the Option 1 breakwater offshore of the Crescent Beach area is notable for some events including the 1992 Nor’easter (Figures 14, 18, and 22), the 1992 Nor’easter with SLR (Figures 15, 19, and 23), and Hurricane Sandy (Figures 20 and 24);
19
Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
The shadow area on the lee side of the Option 1 breakwater offshore of Great Kills Park is also apparent for some events (Figures 14, 18,19, 22, 23, and 24) but is less common and much smaller than the shadow area offshore of Crescent Beach. The shorter length of the Great Kills Park breakwater is the reason for a less substantial shadow area, suggesting a longer Great Kills Park breakwater may be necessary to effectively reduce erosion for that area;
The sand dune in Option 2 provides limited wave attenuation benefits. Only 1.5-foot waves for the Hurricane Sandy with SLR conditions are reduced compared to Option 0 and Option 1, as shown on Figure 17. This implies that the breakwater near Great Kills Park is potentially a more effective solution in the area, particularly if the breakwater design is improved to maximum erosion protection;
The Option 2 breakwater best reduces waves for the two 1992 Nor’easter events for 4.5-foot waves (Figures 22 and 23) and, in the case of the 1992 Nor’easter without SLR (Figure 22), provides more protection to the Crescent Beach community than the Option 1 breakwater. Waves smaller than 4.5 feet in height (1.5 and 3.0 feet) penetrate the breakwater openings for all events, suggesting that the spacing of the breakwaters would need to be altered/refined to increase effectiveness;
Because of the continuous breakwater, Option 1 generally provides greater protection than Option 2 along the Crescent Beach coastline. The shadow area is larger for Option 1 solely due to the continuous nature of the breakwater. Option 2 protected areas are limited due to the relatively small shadow areas on the lee side of each breakwater segment. The Option 2 breakwater openings allow waves to penetrate the coast. However, the Option 2 alignment is likely to provide more protection than Option 1 once the openings are optimized; and
Some events show increased waves in the Crescent Beach area with the placement of breakwaters. The 1.5-foot waves in the 1992 Nor’easter with SLR event (Figure 15) and the 3-foot waves in the Hurricane Sandy with SLR event (Figure 21) best highlight areas with increased wave heights due to the breakwaters. The wave height increase is due to two-dimensional wave shoaling effects and the resulting wave energy redistribution on the lee side of the submerged breakwater. Breakwater designs can be improved to minimize these occurrences; increasing the breakwater crown elevation is the most effective improvement.
20
Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figure 16: Wave Heights (1.5 feet) – 1992 Nor'easter Options 0, 1, and 2
Figure 17: Wave Heights (1.5 feet) – 1992 Nor'easter Plus 31” SLR Options 0, 1, and 2
21
Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figure 18: Wave Heights (1.5 feet) – Hurricane Sandy Options 0, 1, and 2
Figure 19: Wave Heights (1.5 feet) – Hurricane Sandy Plus 31” SLR Options 0, 1, and 2
22
Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figure 20: Wave Heights (3.0 feet) – 1992 Nor'easter Options 0, 1, and 2
Figure 21: Wave Heights (3.0 feet) – 1992 Nor'easter Plus 31” SLR Options 0, 1, and 2
23
Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figure 22: Wave Heights (3.0 feet) – Hurricane Sandy Options 0, 1, and 2
Figure 23: Wave Heights (3.0 feet) – Hurricane Sandy Plus 31” SLR Options 0, 1, and 2
24
Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figure 24: Wave Heights (4.5 feet) – 1992 Nor'easter Options 0, 1, and 2
Figure 25: Wave Heights (4.5 feet) – 1992 Nor'easter Plus 31” SLR Options 0, 1, and 2
25
Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Figure 26: Wave Heights (4.5 feet) – Hurricane Sandy Options 0, 1, and 2
Figure 27: Wave Heights (4.5 feet) – Hurricane Sandy Plus 31” SLR Options 0, 1, and 2
26
Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
5. ACES Model Setup and Simulations
Wave conditions inside the harbor were examined to inform mitigation measure analyses specific to the harbor. The REF/DIF wave model was used to evaluate waves propagating from offshore to nearshore and from nearshore into the harbor. However, the majority of waves inside the harbor are generated by local winds. A local wind wave analysis was applied using ACES (USACE 1992; 2008). Results are presented in Table 3. The local wind waves inside the harbor are approximately 1.7 feet for the 1992 Nor’easter and 2.3 feet for the Hurricane Sandy modeled events. Storm events with the addition of 31 inches and 58 inches of SLR were also considered as shown in Table 3. ACES is significantly less computationally intensive than REF/DIF, thus for the wind wave analysis inside the harbor, two SLR cases were assessed instead of one in order to better understand the impacts of SLR in the area. Note that the ACES methodology is more sensitive to wind speed and fetch than water depth. Therefore, wave conditions for storm events with SLR are not substantially different than those without SLR, with the exception that the waves impact the shoreline at higher stillwater elevations.
Table 3: Wind Wave Analysis Inside the Harbor
Nor’easter Hurricane Sandy Fetch 0.85 mile Wind Speed 50 miles per hour 62 miles per hour Depth (ft) Hs (ft) Tp (sec) Depth (ft) Hs (ft) Tp (sec) MSL 12.6 1.7 2.0 12.6 2.2 2.2 MSL+31” 15.2 1.7 2.1 15.2 2.3 2.3 MSL+58” 17.4 1.7 2.1 17.4 2.3 2.3 Depth: Relative to mean sea level (MSL) (feet); Hs: Significant Wave Height (feet); Tp: Peak Wave Period (seconds)
The wave conditions inside the harbor consist of two components: local generated wind waves and waves penetrating from offshore. A linear addition of the two wave components is assumed for this study; however, for a design-level assessment, a more in-depth analysis would be recommended. Using the average offshore wave height of 1.3 feet entering the harbor and the wind wave analysis from Table 3, the wave conditions inside the harbor are approximately 3.0 feet for the 1992 Nor’easter and 3.6 feet for Hurricane Sandy. As a means to review the quality of the wind wave analysis and the linear addition of local wind waves and offshore waves, the FEMA
27
Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
Wave Height Analysis for Flood Insurance Studies (WHAFIS) analysis from the ongoing study was reviewed (FEMA 2007; 2014). FEMA reported waves inside the harbor ranging from 3.1 to 3.3 feet, with an approximately 2.6-second wave period. The wave parameters recommended for use in preliminary wave mitigation measure analyses inside the harbor are a wave height of 3.0 to 3.6 feet and a wave period of 2.0 to 2.6 seconds.
6. Recommendations
The recommended next steps to further assess waves and breakwater options in the area are twofold. First, mitigation measures such as wave screens should be considered for the harbor to reduce the wave energy that breakwater alignments are unable to reduce. Second, some elements of the breakwater alignments should be adjusted in future study phases based on the findings of the analysis.
6.1 Breakwater Crown Elevations
The crown elevation of 11.0 feet NAVD88 shows considerable benefits for both the 1992 Nor’easter event (9.0 feet NAVD88 stillwater elevation) and 1992 Nor’easter event with SLR (11.6 feet NAVD88 stillwater elevation), particularly for Option 1. Less substantial benefits are seen for the Hurricane Sandy event (12.3 feet NAVD88 stillwater elevation). Minimal to no benefits are shown for the Hurricane Sandy event with SLR (14.9 feet NAVD88 stillwater elevation). If the breakwater is designed in future phases to attenuate waves at a stillwater elevation higher than 11.5 feet NAVD88, a crown elevation higher than 11.0 feet is recommended.
6.2 Breakwater Distance from the Shoreline
The Option 1 breakwater at Crescent Beach is further from the shore (0.25 mile) than the Option 1 breakwater at Great Kills Park (0.10 mile) and the Option 2 breakwater at Crescent Beach (0.10 mile). Yet the Option 1 breakwater at Crescent Beach generally shows the greatest wave reduction at its lee side because it is a continuous and relatively long breakwater alignment. Option 2, however, provides wave attenuation for 4.5-foot waves during the 1992 Nor’easter event (Figure 24) for a broader area than Option 1 largely due to the proximity to the coast. Both a longer breakwater and an alignment closer to the coast provide a broader shadow area at the shoreline. Based on the limited REF/DIF results and engineering judgment, a breakwater of 0.10 mile offshore is preferable to a breakwater 0.25 mile offshore.
28
Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
6.3 Breakwater Openings
As mentioned above, relative to the distance to the shoreline, Option 1 generally performs better than Option 2, though Option 2 has a more ideal position relative to the shoreline. The current 85-foot openings (on average) in Option 2 allow for waves to penetrate the breakwater. Breakwater openings should be smaller than the wave lengths in the area, which are approximately 90 to 100 feet. Smaller opening sizes would attenuate waves with increased efficiency. A staggered or overlapping opening design would further limit wave penetration and is recommended.
6.4 Breakwater Length
In general, the longer the breakwater length, the broader the area protected on the lee side. The shadow areas shown in the model outputs illustrate this. The limited reduction provided by the Option 1 breakwater near Great Kills Park and the Option 2 breakwater (which could be considered many short breakwaters when evaluating the effects of breakwater length) highlights the need to extend a breakwater far enough beyond the target areas of protection to provide a sufficiently large shadow zone. The necessary length is directly correlated to the distance from the shoreline, and the two should be considered together in the next design phase.
7. References
FEMA. 2007. Supplementary WHAFIS Documentation, WHFIS 4.0.
FEMA. 2014. Flood Hazard Resources Map. http://fema.maps.arcgis.com/home /webmap/viewer.html?webmap=2f0a884bfb434d76af8c15c26541a545. Last accessed October.
NPCC. 2013. Climate Risk Information 2013, New York City Panel on Climate Change (NPCC).
Kirby, J.T., and R.A. Dalrymple. 1994. REF/DIF 1. Version 2.5. Research Report No. CACR-94-22.
The SCAPE Team. 2014. Living Breakwaters Technical Appendix: Volume II Staten Island and Raritan Bay. New York, NY: SCAPE/Landscape Architecture.
USACE. 1992. Automated Coastal Engineering System Technical Reference Report.
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Evaluation of an Offshore Breakwater System Adjacent to and South of Great Kills Harbor, Staten Island, New York
Numerical Wave Modeling
USACE. 2002. Coastal Engineering Manual. Coastal and Hydraulics Laboratory, Engineer Research and Development Center, Vicksburg, MD.
USACE. 2014. Wave Information Studies. http://wis.usace.army.mil/. Last accessed October.
30 Appendix A
Wave Direction and Wave Amplitude Plots
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Appendix A – Wave Direction and Wave Amplitude Plots
The wave direction plots aid in the interpretation of the impacts of topography and bathymetry, as well as project placement, on wave propagation from offshore to nearshore and into the harbor. The vertical scale of these plots is exaggerated to highlight changes in wave direction; the plots do not properly reflect wave heights.
Figures showing wave amplitude, or half of the wave height, illustrate the absolute wave magnitude over the wave domain and are used to interpret changes in wave height due to the project alignments.
A-1
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 1: Wave Directions – 1992 Nor'easter Option 0 (offshore waves from the south)
Figure 2: Wave Amplitudes – 1992 Nor'easter Option 0 (offshore waves from the south)
A-2
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 3: Wave Directions – 1992 Nor'easter Option 0 (offshore waves from the southeast)
Figure 4: Wave Amplitudes – 1992 Nor'easter Option 0 (offshore waves from the southeast)
A-3
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 5: Wave Directions – 1992 Nor'easter with 31” SLR Option 0 (offshore waves from the south)
Figure 6: Wave Amplitudes – 1992 Nor'easter with 31” SLR Option 0 (offshore waves from the south)
A-4
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 7: Wave Directions – 1992 Nor'easter with 31” SLR Option 0 (offshore waves from the southeast)
Figure 8: Wave Amplitudes – 1992 Nor'easter with 31” SLR Option 0 (offshore waves from the southeast)
A-5
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 9: Wave Directions – Hurricane Sandy Option 0 (offshore waves from the south)
Figure 10: Wave Amplitudes – Hurricane Sandy Option 0 (offshore waves from the south)
A-6
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 11: Wave Directions – Hurricane Sandy Option 0 (offshore waves from the southeast)
Figure 12: Wave Amplitudes – Hurricane Sandy Option 0 (offshore waves from the southeast)
A-7
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 13: Wave Directions – Hurricane Sandy with 31” SLR Option 0 (offshore waves from the south)
Figure 14: Wave Amplitudes – Hurricane Sandy with 31” SLR Option 0 (offshore waves from the south)
A-8
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 15: Wave Directions – Hurricane Sandy with 31” SLR Option 0 (offshore waves from the southeast)
Figure 16: Wave Amplitudes – Hurricane Sandy with 31” SLR Option 0 (offshore waves from the southeast)
A-9
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 17: Wave Directions – 1992 Nor'easter Option 1 (offshore waves from the south)
Figure 18: Wave Amplitudes – 1992 Nor'easter Option 1 (offshore waves from the south)
A-10
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 19: Wave Directions – 1992 Nor'easter Option 1 (offshore waves from the southeast)
Figure 20: Wave Amplitudes – 1992 Nor'easter Option 1 (offshore waves from the southeast)
A-11
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 21: Wave Directions – 1992 Nor'easter with 31” SLR Option 1 (offshore waves from the south)
Figure 22: Wave Amplitudes – 1992 Nor'easter with 31” SLR Option 1 (offshore waves from the south)
A-12
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 23: Wave Directions – 1992 Nor'easter with 31” SLR Option 1 (offshore waves from the southeast)
Figure 24: Wave Amplitudes – 1992 Nor'easter with 31” SLR Option 1 (offshore waves from the southeast)
A-13
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 25: Wave Directions – Hurricane Sandy Option 1 (offshore waves from the south)
Figure 26: Wave Amplitudes – Hurricane Sandy Option 1 (offshore waves from the south)
A-14
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 27: Wave Directions – Hurricane Sandy Option 1 (offshore waves from the southeast)
Figure 28: Wave Amplitudes – Hurricane Sandy Option 1 (offshore waves from the southeast)
A-15
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 29: Wave Directions – Hurricane Sandy with 31” SLR Option 1 (offshore waves from the south)
Figure 30: Wave Amplitudes – Hurricane Sandy with 31” SLR Option 1 (offshore waves from the south)
A-16
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 31: Wave Directions – Hurricane Sandy with 31” SLR Option 1 (offshore waves from the southeast)
Figure 32: Wave Amplitudes – Hurricane Sandy with 31” SLR Option 1 (offshore waves from the southeast)
A-17
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 33: Wave Directions – 1992 Nor'easter Option 2 (offshore waves from the south)
Figure 34: Wave Amplitudes – 1992 Nor'easter Option 2 (offshore waves from the south)
A-18
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 35: Wave Directions – 1992 Nor'easter Option 2 (offshore waves from the southeast)
Figure 36: Wave Amplitudes – 1992 Nor'easter Option 2 (offshore waves from the southeast)
A-19
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 37: Wave Directions – 1992 Nor'easter with 31” SLR Option 2 (offshore waves from the south)
Figure 38: Wave Amplitudes – 1992 Nor'easter with 31” SLR Option 2 (offshore waves from the south)
A-20
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 39: Wave Directions – 1992 Nor'easter with 31” SLR Option 2 (offshore waves from the southeast)
Figure 40: Wave Amplitudes – 1992 Nor'easter with 31” SLR Option 2 (offshore waves from the southeast)
A-21
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 41: Wave Directions – Hurricane Sandy Option 2 (offshore waves from the south)
Figure 42: Wave Amplitudes – Hurricane Sandy Option 2 (offshore waves from the south)
A-22
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 43: Wave Directions – Hurricane Sandy Option 2 (offshore waves from the southeast)
Figure 44: Wave Amplitudes – Hurricane Sandy Option 2 (offshore waves from the southeast)
A-23
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 45: Wave Directions – Hurricane Sandy with 31” SLR Option 2 (offshore waves from the south)
Figure 46: Wave Amplitudes – Hurricane Sandy with 31” SLR Option 2 (offshore waves from the south)
A-24
Evaluation of an
Offshore Breakwater System Adjacent to and South of Great Kills ` Harbor – Appendix A
Figure 47: Wave Directions – Hurricane Sandy with 31” SLR Option 2 (offshore waves from the southeast)
Figure 48: Wave Amplitudes – Hurricane Sandy with 31” SLR Option 2 (offshore waves from the southeast)
A-25