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HomeMy WebLinkAboutOak Island Renourishment Project_Appendix C - Borrow Area Modeling2019/2020 RENOURISHMENT PROJECT OAK ISLAND, NORTH CAROLINA JAY BIRD SHOALS BORROW AREA MODELING Prepared for: Town of Oak Island Prepared by: ,"q moffatt & nichol 2019/2020 RENOURISHMENT PROJECT OAK ISLAND, NORTH CAROLINA JAY BIRD SHOALS BORROW AREA MODELING M&N Project No.10128-01 Revision Description Issued Date Author Reviewed Approved A Modeling report September 6, 2019 Zw KF 1M 4700 Falls of Neuse Road, Suite 300 ,", Raleigh, NC 27609 m o f f a t t & n i c h o l (919) 781-4626 •:• Fax: (919) 781-4869 www.moffattnichol.com EXECUTIVE SUMMARY In order to investigate the potential effects of dredging material from a Jay Bird Shoals borrow area identified for the 2019/2020 Renourishment Project on neighboring shorelines of Caswell Beach and Bald Head Island, numerical models were developed to investigate hydrodynamics, waves, and sediment transport using Deltares' DeIft3D model suite. The hydrodynamics and wave models were successfully calibrated and validated against available observed water levels, currents, discharges, and wave data. The sediment transport model was not calibrated due to lack of measured data to calibrate against. Tidal current, wave, and sediment transport modeling was performed for the existing and after -dredge bathymetry scenarios. Two borrow area after -dredge templates were considered. Template 1 was designed to dredge 2.95 million cubic yards (mcy) and Template 2 was designed to dredge 2.34 mcy of available beach compatible material. For both after -dredge templates only part of the material, 1.034 mcy, will be dredged for the 2019/2020 Renourishment Project. Thus, within the proposed borrow area, the results from the DeIft3D model are believed to be a conservative overestimate of the potential effects on the tidal current and wave climates. The tidal current model results indicate that for both after -dredge bathymetry templates effects on residual tidal currents would be localized and small. This implies there would be no significant effects on sediment transport processes associated with tidal currents. The figure below shows the effects of the two after -dredge bathymetry templates on residual tidal currents over a spring -neap tidal cycle. 201912020 Renourishment Project M&N Project No.10128-01 1] 16 15 T 2 14 r 13 12 11 694 695 696 697 698 699 700 701 702 703 704 xc rtlinale- Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 4 of 70 1 694 695 696 697 696 699 700 701 702 703 704 x coordm.te —. -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 Residual Currents -(Template 1-Existing) (ftfs), magmt,de Residual Currents - (Template 2-E—ting)(flls), magmt,de After -dredge bathymetry effects on residual tidal currents over a spring -neap tidal cycle The wave transformation model results for the 2004 — 2018 average annual offshore wave climates show that the two after -dredge bathymetry templates could result in a slight redistribution of wave energy along the shoreline during moderate to severe storm events. Sediment transport modeling was also completed, to observe if the changes to wave heights and wave directions would affect the longshore transport. The sediment transport modeling results for both after -dredge bathymetry templates show that the wave -induced longshore sediment transports could be reduced leeward of the borrow area but could potentially increase on shoreline segments both east and west sides of the borrow area. The net effect of these changes could result in localized adjustments in shoreline erosion / accretion. Based on the model results of the longshore sediment transport gradients as presented below, most of the potential increases in shoreline erosion would be limited to discrete portions of Caswell Beach (between survey transects 37+00 —60+00 and 150+00 — 170+00). Generally, both templates show results close to existing conditions, with some areas above and below existing. There is no strong evidence to choose one template over the other given the model results, especially given that this is not a morphological model. The modeled sediment transport inside the surf zone is greatly influenced by the imposed model bathymetry. Thus, the model results only represent the bathymetric condition constructed based on the available data sources. There will be an additional 0.6 mcy beach compatible material available in Template 1. For this reason, Template 1 was chosen for the Town of Oak Island's permit application for the 2019/2020 Renourishment Project. The Town of Oak Island will monitor the Caswell Beach shoreline for nine (9) years post -project to investigate any potential effects which might require mitigation. 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island 1/11 100 80 60 a r 40 U c a 20 O Q 0 C C E -20 a ai o -40 L m C J -60 -80 -100 Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 5 of 70 + Caswell Beach Transects —Transport Gradient - Existing -------- ------------------- --------- I --------- Transport Gradient -After-Dredge Template 1 —Transport Gradeint- After -Dredge Template E--------- ;------------------;------------------ _________1_________ 1-0-__-0-0-1_____ _ __-0- ________ _______1 _____ L_________ I____ ____ O O O O O O O O O O O O O O O O O O O O O o0o0og0000001000000900 00 O O O O O O O "00 o , 000000 0 00 0 000�000000Qo 0 ++++++++++++ +++++++++ +++ Ou o NO W ON Om cm NON omo�'1 ON ON ++++++ + +++ ++ 00 000000 0 omomo m Y'10 NO ++ + + + + + + + 0 ++ -00 mmwcan I�i00u I Sri, MNNH 00m mW m m NL N N N N N N N N N N N N qJ N ,rl , W om [v1N 00 Omom omomOY10 rl rl rl rl rl rl rl rl O1 00 D� 1� 1� 10 10 N N � ow M N JN�rI Jrl�rLl 1 - 1 TTTT TTTT' I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 1 ------------------------------------------------------ I I I I I I I I I I I I I I I I I I I I I I I I ----- ------------- 1Jay Bird Shoal borrow Site I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 692000 693000 694000 695000 696000 697000 698000 699000 700000 Easting - NC State Plan (m) Wave -induced longshore sediment transport gradients along Caswell Beach shoreline 701000 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 6 of 70 TABLE OF CONTENTS 1. INTRODUCTION....................................................................................................................... 10 2. MODEL DEVELOPMENTS......................................................................................................... 11 2.1 Model Grids....................................................................................................................... 11 2.1.1 Flow Model Grids....................................................................................................... 11 2.1.2 Wave Model Grids..................................................................................................... 12 2.2 Model Bathymetry............................................................................................................ 13 3. MODEL CALIBRATIONS............................................................................................................ 15 3.1 Calibration Metrics............................................................................................................ 15 3.2 Flow Model Calibration..................................................................................................... 16 3.2.1 Boundary Conditions.................................................................................................. 21 3.2.2 Calibration Results..................................................................................................... 22 3.3 Flow Model Validation...................................................................................................... 30 3.4 Wave Model Calibration.................................................................................................... 31 3.4.1 Model Inputs..............................................................................................................31 3.4.2 Calibration Results..................................................................................................... 34 3.5 Wave Model Validation..................................................................................................... 41 4. JAYBIRD SHOALS BORROW AREA MODELING....................................................................... 46 4.1 Tidal Currents.................................................................................................................... 48 4.1.1 Peak Tidal Flood Currents.......................................................................................... 48 4.1.2 Residual Tidal Currents.............................................................................................. 51 4.2 Waves................................................................................................................................ 54 4.2.1 Representative offshore waves.................................................................................. 54 4.2.2 Nearshore Wave Results............................................................................................ 59 4.3 Sediment Transport........................................................................................................... 64 5. SUMMARY AND CONCLUSIONS..............................................................................................68 6. REFERENCES............................................................................................................................70 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 7 of 70 LIST OF FIGURES Figure 1-1: Jay Bird Shoals borrow area.................................................................................. 10 Figure2-1: Flow model grid.................................................................................................... 11 Figure 2-2: Wave model grids................................................................................................. 12 Figure 2-3: Flow model bathymetry under existing conditions .............................................. 14 Figure 2-4: Fine wave model bathymetry under existing conditions ..................................... 14 Figure 3-1: Locations of water levels and current measurements by RPS EH ........................ 17 Figure 3-2: Survey transects in Upper Wilmington area by RPS EH ........................................ 18 Figure 3-3: Survey transects in Lower Wilmington area by RPS EH ........................................ 19 Figure 3-4: Survey transects in Snow's Cut area by RPS EH .................................................... 20 Figure 3-5: Survey transects in Southport area by RPS EH ..................................................... 21 Figure 3-6: Water level calibration results.............................................................................. 24 Figure 3-7: Depth -averaged current calibration results......................................................... 25 Figure 3-8: Discharge calibration results (TR01— TR03)......................................................... 26 Figure 3-9: Discharge calibration results (TR04 — TR06)......................................................... 27 Figure 3-10: Discharge calibration results (TR07 — TR09)......................................................... 28 Figure 3-11: Discharge calibration results (TR10 — TR12)......................................................... 29 Figure 3-12: Discharge calibration results (TR13)..................................................................... 30 Figure 3-13: Water level validation results during Hurricane Matthew ................................... 30 Figure 3-14: Offshore waves from NOAA Buoy 41013 during calibration period .................... 32 Figure 3-15: Wind data at NOAA buoy 41013 and from CFSR during calibration period.................................................................................................................... 33 Figure 3-16: Water level data from NOAA station 8658163 for model calibration .................. 34 Figure 3-17: Significant wave height calibration results........................................................... 35 Figure 3-18: Peak wave period calibration results.................................................................... 36 Figure 3-19: Peak wave direction calibration results................................................................ 37 Figure 3-20: Comparison of Bald Head ADCP wave energy spectrum: (up) measured; (down) modeled................................................................................. 40 Figure 3-21: Significant wave height validation results............................................................ 42 Figure 3-22: Peak wave period validation results..................................................................... 43 Figure 3-23: Peak wave direction validation results................................................................. 44 Figure 4-1: Jay Bird Shoals borrow area templates................................................................ 46 Figure 4-2: After -dredge bathymetry—Template 1................................................................ 47 Figure 4-3: After -dredge bathymetry—Template 2................................................................ 47 201912020 Renourishment Project M&N Project No.10128-01 ,", Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 8 of 70 Figure 4-4: Instantaneous peak flood current velocities — existing condition ........................ 48 Figure 4-5: Instantaneous peak flood current velocities — after -dredge Template 1............. 49 Figure 4-6: Instantaneous peak flood current velocities — after -dredge Template 2............. 49 Figure 4-7: After -dredge bathymetry effects on instantaneous peak flood current velocities —Template 1......................................................................................... 50 Figure 4-8: After -dredge bathymetry effects on instantaneous peak flood current velocities —Template 2......................................................................................... 50 Figure 4-9: Residual tidal currents — existing condition.......................................................... 51 Figure 4-10: Residual tidal currents — after -dredge Template 1............................................... 52 Figure 4-11: Residual tidal currents — after -dredge Template 2............................................... 52 Figure 4-12: After -dredge bathymetry effects on residual tidal currents —Template 1............................................................................................................................ 53 Figure 4-13: After -dredge bathymetry effects on residual tidal currents —Template 2............................................................................................................................ 53 Figure 4-14: Annual percentage of exceedance of significant wave height at the offshoreboundary................................................................................................ 54 Figure 4-15: Wave rose of significant wave heights at the offshore boundary ........................ 55 Figure 4-16: After -dredge bathymetry effects on waves between 0 — 3 ft with average height of 2.5 ft (top: Template 1; bottom: Template 2) ......................... 60 Figure 4-17: After -dredge bathymetry effects on waves between 3 — 6 ft with average height of 4.5 ft (top: Template 1; bottom: Template 2) ......................... 61 Figure 4-18: After -dredge bathymetry effects on waves between 3 — 6 ft with average height of 7.5 ft (top: Template 1; bottom: Template 2) ......................... 62 Figure 4-19: After -dredge bathymetry effects on storm waves comparable to Hurricane Matthew in 2016 (top: Template 1; bottom: Template 2) .................. 63 Figure 4-20: Caswell Beach transects........................................................................................ 65 Figure 4-21: Wave -induced net longshore sediment transports along Caswell Beachshoreline..................................................................................................... 66 Figure 4-22: Longshore sediment transport gradients along Caswell Beach shoreline............................................................................................................... 67 201912020 Renourishment Project M&N Project No.10128-01 1111111111111111114 LIST OF TABLES Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 9 of 70 Table 2-1: Model bathymetry data sources........................................................................... 13 Table 3-1: Goodness -of -fit parameters for significant wave height calibration ................... 39 Table 3-2: Goodness -of -fit parameters for peak wave period calibration ............................ 39 Table 3-3: Goodness -of -fit parameters for peak wave direction calibration ........................ 39 Table 3-4: Goodness -of -fit parameters for significant wave height validation ..................... 45 Table 3-5: Goodness -of -fit parameters for peak wave period validation ............................. 45 Table 3-6: Goodness -of -fit parameters for peak wave direction validation ......................... 45 Table 4-1: Representative wave conditions used as model inputs ....................................... 56 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 10 of 70 1. INTRODUCTION Moffatt & Nichol was retained by the Town of Oak Island for professional services to execute the 2019/2020 Renourishment Project following Hurricane Matthew. The Jay Bird Shoals borrow area shown in Figure 1-1 was identified as a potential borrow area for this beach renourishment project. In order to determine if potential adverse effects to the neighboring Caswell Beach and Bald Head Island shorelines could be a possibility, numerical modeling studies were conducted. DeIft3D, an open -source, fully integrated numerical modeling suite developed by Deltares, Netherland, was selected as the modeling platform. DeIft3D can carry out numerical modeling of flows, waves, sediment transport, morphological developments, water quality and ecology in coastal, river, lake and estuarine areas. For the purpose of this study, two modules in DeIft3D were used: DeIft3D-FLOW (Deltares, 2018a) and DeIft3D-WAVE (Deltares, 2018b). DeIft3D-FLOW is the hydrodynamics and sediment transport module; whereas DeIft3D-WAVE is the wave transformation module. In this report, the effects of dredging material from a borrow area in Jay Bird Shoals on waves, tidal current velocities, and sediment transport patterns were investigated. Figure 1-1: Jay Bird Shoals borrow area 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 11 of 70 2. MODEL DEVELOPMENTS In this section, the developments of flow and wave model grids and bathymetries are discussed. The model horizontal coordinate is in North Carolina State Plane, and the vertical datum is North American Vertical Datum (NAVD88). 2.1 MODEL GRIDS 2.1.1 Flow Model Grids The flow model domain included the Cape Fear River estuary from upstream of the Cape Fear, Black, and Northeast Cape Fear Rivers to 20 miles offshore from the mouth of Cape Fear River near Southport, NC. The grid cell sizes were variable throughout the domain. In the offshore area the resolution was approximately 90 meters. For the upstream Cape Fear, Black, and Northeast Cape Fear River areas, the resolution was approximately 30 meters. Along the channel the resolution was approximately five meters. Figure 2-1 presents the flow model grid. Figure 2-1: Flow model grid 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 12 of 70 2.1.2 Wave Model Grids Wave transformation from deep water to the shoreline was accomplished by nesting three increasingly resolved model domains as shown in Figure 2-2. The coarsest grid (gray) is comprised of approximately 20,000 cells with size of 500 m x 500 m. The offshore limit of the coarse grid is near the location of the National Oceanic and Atmospheric Administration (NOAA) wave buoy 41013 from which offshore wave conditions were derived. The medium -resolved wave domain (blue) and the fine wave domain (red) were developed based on the flow model grid. The fine wave model grid has approximately 5-meter cross -shore resolution in the surf zone region of Caswell Beach. Figure 2-2: Wave model grids 201912020 Renourishment Project M&N Project No.10128-01 11 MODEL BATHYMETR`' Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 13 of 70 Bathymetric data from different sources were compiled and processed to cover the entire computational domains. All bathymetric datasets were adjusted to NAVD88. The data sources used for the development of the morphology model bathymetry are listed in Table 2-1 from high priority to low priority. The most recent bathymetry data were selected where available to create the model bathymetry. The terminal groin constructed on the western tip of South Beach on Bald Head Island between June and December 2015 was also included in the model. Figure 2-3 and Figure 2-4 show the flow model bathymetry and the fine wave model bathymetry under existing conditions, respectively. Table 2-1: Model bathymetry data sources Wilmington Harbor hydrographic surveys USACE 2016 — 2017 Fugro channel bank surveys Fugro 2016 — 2017 Oak Island post Matthew beach profile surveys TI Coastal 2016 (STA 210+00 — 700+00) Bald Head Island beach profile surveys USACE 2013 (STA 000+00 — 238+00) Oak Island beach profile surveys USACE 2012 (STA 005+00 — 210+00) Cape Fear River 2010 surveys USACE 2010 NOAA hydrographic surveys NOAA 1973 — 2007 NOAA Navigation Charts MIKE C-MAP ADCIRC bathymetry NCDPS 2011 NC LiDAR NOAA 2014-2016 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 14 of 70 100 10 0 80 -10 Co ao 60 -20 0 T Z E � � �c -30 _?-, m 40 T c � o -40 0 Q1 20 - -50 3 o -60 0- -70 -20 -80 660 680 700 720 740 x coordinate (km) -4 Figure 2-3: Flow model bathymetry under existing conditions 10 0 2a -10 1s 0 16 -20 z T 14 ¢ E � w E 12 ► 30 a M L C M 10 �0 w 00 u 0 T $ E dl 6 -50 3 m c 4 LL -60 2 685 690 695 700 705 710 715 x coordinate (km) -70 80 Figure 2-4: Fine wave model bathymetry under existing conditions 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 15 of 70 3. MODEL CALIBRATIONS 3.1 CALIBRATION METRICS Several goodness -of -fit statistical parameters were used to assess model calibration and validation results. These include the mean error (ME), root mean square (RMS) error, normalized RMS error, mean absolute error (MAE), correlation coefficient (R), index of agreement (d), and time delay or lag (AT). These parameters are briefly described here. If x and y are the measured and calculated data respectively, then the following statistics can be calculated: Mean error (ME): ME= y—x (1) Where "bar" denotes the sample mean. Root mean square (RMS) error: a ERMS =r(XY) (2) To reduce the effect of measurement error and possible outliers, a one -hour low-pass filter was applied to the measured data to compute trend xf. Then the normalized error is calculated as £norm — ERMS • 100% (3) Xf,max—xf,min Where Xfmax and Xfmin are the maximum and minimum values of the trend xf. The residual in the denominator defines the range of measured data. The root mean square error of measured data was estimated as: 2 cmeas =F x f� (4) Mean absolute error (MAE): MAE= x-y (S) 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 16 of 70 The correlation coefficient R was calculated using standard method and represents a non -squared value. The model prediction capability was estimated with an index of agreement between measured and calculated data (Willmott et al., 1985): d=1— (x—y)` 0<d<1 (x-x — Y-XT The time delay AT shows expected time difference between corresponding events in measured and calculated data. To estimate the delay, the cross -correlation function between measured and calculated data is computed and the smallest time lag at which a maximum occurs is found. Because the cross -correlation function is calculated from discrete data, resulting time resolution may not be sufficient to accurately define the maximum. Therefore, computed values of the cross -correlation function were interpolated with a piecewise polynomial of 5' order, which was then used to determine the maximum. 3.2 FLOW MODEL CALIBRATION The flow model was calibrated for the period between March 27, 2017 and April 5, 2017 when RPS Evans -Hamilton (RPS EH) conducted water level, current, discharge, salinity, and water quality measurements on the Cape Fear River (RPS Evans -Hamilton, 2017). For the calibration period, water level measurements were available at Southport and Wilmington (Figure 3-1); current measurements were available at Southport (Figure 3-1); and discharge measurements were available at the 11 transects between Wilmington and Southport (Figure 3-2 through Figure 3-5). The model was calibrated to match the measured water levels, discharges, and currents. z 201912020 Renourishment Project M&N Project No.10128-01 Station Wiliningtou ,t SS � a. -�- qr AM M y ` `.Stati6lToutl}p64` ;; 7 A 0 1 2 4 6 8 . . � � Miles Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 18 of 70 Figure 3-2: Survey transects in Upper Wilmington area by RPS EH 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 19 of 70 Figure 3-3: Survey transects in Lower Wilmington area by RPS EH 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 20 of 70 Figure 3-4: Survey transects in Snow's Cut area by RPS EH 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 21 of 70 Figure 3-5: Survey transects in Southport area by RPS EH 3.2.1 Boundary Conditions The model has seven open boundaries as indicated on Figure 2-1: four offshore — West, South, East, and North; and three upstream — NE Cape Fear River, Black River, and Cape Fear River. The model was forced using tidal water levels at the offshore boundaries 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 22 of 70 and river discharges at the upstream boundaries. Winds were applied uniformly over the entire domain. A) TIDAL BOUNDARY CONDITIONS Astronomical tidal constituents for water levels were extracted from the Oregon State University tidal database which is based on TOPEX/Poseidon satellite altimetry data (Egbert and Erofeeva, 2002). The global model with a resolution of 1/6' along with high resolution along coastal areas was used. North and West open boundary were specified as Neumann boundaries, and South and East open boundary were specified as water level boundaries. B) RIVER DISCHARGES The time series of discharges from the rivers measured at three United States Geological Survey (USGS) stations (shown in Figure 2-1) were used at the three upstream open boundaries: discharge data at Station 02105769 was used at the upstream boundary at the Cape Fear River, Station 02106500 data was used at the Black River, and Station 02108000 data was used at the Northeast Cape Fear River. The discharges from the un- gaged drainage areas between the USGS stations and the model upstream boundaries were accounted for with appropriate scale factors based on the ratio of un-gaged drainage area vs. gaged drainage area for each branch. WINDS From the analysis of available wind data, it was found that the wind field in the Cape Fear River estuary is very seasonal in nature, i.e., predominant wind direction changes according to the season, and wind speeds vary depending on the location of the station. Stations that are offshore indicate higher wind speed than stations located on the coast or on land. Wind data from Station KILM (Wilmington International Airport) shown in Figure 2-1 was used to force the model. Station KILM is located on the land and is considered to better represent wind over the estuary compared to the offshore stations. 3.2.2 Calibration Results Water levels, currents, and discharges obtained from the model results were compared with measurements available at various locations. Figure 3-6 shows the comparison of 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 23 of 70 water level time series. It can be seen that the model replicates the water levels well with a small over prediction for most of the time (Station Wilmington (NOAA)). Figure 3-7 shows the comparison of depth -averaged currents and the model also replicates the currents at Southport well. Figure 3-8 through Figure 3-12 show comparisons of the discharge measurements. The statistics shown in those figures were calculated by comparing the model and measurement values at corresponding times. The positive and negative discharge correspond to ebb current and flood current direction, respectively. The calibration results match well at all transects in the main channel. 201912020 Renourishment Project M&N Project No.10128-01 set04.v2O - multi Wilmington 2 1.5 E 1 aD 0.5 L aD is 0 -0.5 1 23/Mar 25/Mar 27/Mar 29/Mar 31/Mar 2017 Southport 2 1.5 1 a� 0.5 L 0 -0.5 -1 23/Mar 25/Mar 27/Mar 29/Mar 31/Mar 2017 Wilmington(NOAA) 2 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 24 of 70 Measured Calculated 02/Apr 04/Apr 06/Apr 02/Apr 04/Apr 06/Apr ss -0.:164 1.5 ........ ... ... rm s = 0.093 meas E 1 . ..... ...... .. ..... m Enorm--10.2% ea 0.5 c - .0 . . L a� 0 I 2 e + 0 _ .15 s -0.5 T 1 .0 in d = 0.98 -1 23/Mar 25/Mar 27/Mar 29/Mar 31/Mar 2017 Figure 3-6: Water level calibration results 02/Apr 04/Apr 06/Apr 201912020 Renourishment Project M&N Project No.10128-01 set04.v20 - Southport Current Speed 2.5 2 0 28/Mar 29/Mar 30/Mar 31/Mar 01/Apr 2017 Current Direction 350 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 25 of 70 Measured Calculated 02/Apr 03/Apr 300 ErmS = 21.209 rn s = 19.927 meas 250 E = o o CE rn 541.3 200 m as - alc m a = .8 150 _ _ . ...... .. ... .......1 IAH.4 c = .9 100 Ic 0. 88 a 2. 71 U LJ alc 1 00 0• ea 50 — - _ sec d = 1.00 0 28/Mar 29/Mar 30/Mar 31/Mar 01/Apr 2017 Figure 3-7: Depth -averaged current calibration results 02/Apr 03/Apr 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 26 of 70 set04❑ Measured TR01 0 -multi Calculated 1500 1000 v 500 E ai 2 0 cc t o -500 -1000 1500 e = 32.861 rms cal - meas 61.51 ❑ MA 103.44 R = 0.97 d = 0.98 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 30/Mar/2017 TR02 1000 50 M E 2I <0 t Aa 0 -50( ) �- J . `i . .... } ....x................. p ..x................./ ....� ................ . 8 = 13.550 rms ca - me U- 52,41 : E 91.50 ❑ R = 0.94 d = 0.96 -100G 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 30/Mar/2017 TR03 300^ 200 E 100 ai rn `m t 0 w -100( .......... .......... ......... i Erms — 8.784 ca c - meas 86.71 MAE 71.88 ❑ = 0.95 d = 0.97 -2000 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 30/Mar/2017 Figure 3-8: Discharge calibration results (TR01—TR03) 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 27 of 70 set04❑ Measured TR04 0 -multi Calculated 3000 2000 M 1000 E ai 21 0 cc t o -1000 -2000 3000 )mea 50.323 ca - 13.31 ❑219.54 R = 0.99 d = 0.99 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 30/Mar/2017 TR05 1000 500 M E 6 rn 0 m t Aa i] -500 1 ...... 00.. o❑..............:.�......... �.... 8 - 113.631 rms - ❑ - cal - mea = -33.96 o AE = 98.05 R = 0.98 d = 0.99 - 000 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 30/Mar/2017 TR06 4000 3000 2000 M E ai 1000 rn t 0 0 U)_ -1000 -2000 -3000 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 30/Mar/2017 Figure 3-9: Discharge calibration results (TR04 — TR06) 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 28 of 70 set04❑ Measured TR07 0 -multi Calculated 6000 4000 2000 ai 21 0 cc t o -2000 -4000 6000 crms413.691 _ - - - ca - mea = -44.37 _. M E = 330.34 R = 0.96 d = 0.98 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 30/Mar/2017 TR08 1000 500 M E ai 2 0 An t An 0 -500 -1000 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 30/Mar/2017 TR09 6000 4000 M 2000 E ai 2 0 m t 0 ij -2000 -4000 -6000 12:00 18:00 00:00 08:00 12:00 18:00 00:00 06:00 12:00 30/Mar/2017 Figure 3-10: Discharge calibration results (TR07 — TR09) 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 29 of 70 set04.v2O - multi ❑ Measured TR10 Calculated 400 300 v, 200 M E ai 100 m cc U N C, -100 -200 -300 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 30/Mar/2017 x 104 TR11 1 0.5 W ri E N rn 0 f0 t _N -0.5 s 1070.629 . rms Ic - me s 60.22 AE = 891.15 q ❑ R = 1.00 d = 0.99 -1 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 30/Mar/2017 TR12 Lull] 200 M E ti rn 0 m t U N -200 ter, 28.48 Rns calc meas = 12.87 _ MAE = 21.48 R = 0.99 ❑ ❑❑: d= 1.00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 30/Mar/2017 Figure 3-11: Discharge calibration results (TR10 — TR12) 201912020 Renourishment Project M&N Project No.10128-01 x 104 1.5 1 42 M 0.5 E ai rn 0 m L U 0 -0.5 -1 set04.v2O - multi TR13 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 30 of 70 ❑ Measured Calculated 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 30/Mar/2017 Figure 3-12: Discharge calibration results (TR13) 3.3 FLOW MODEL VALIDATION For the flow model validation, the water level measurements at NOAA Wilmington Station during Hurricane Matthew in October 2016 were used. The model was forced with time series of measured water levels at Wrightsville Beach (NOAA station 8658163), and wind from the KILM station. It can be seen that the model captures the more extreme water levels well during this hurricane event as shown in Figure 3-13. set04.cl7 - Wilmington(NOAA) Measured Wilmington(NOAA) Calculated 2 1.5 Erms - 0.132 s = 0.275 meas E 1.0•..%q.. 1 ........ orm ID r es 6 0.5 al - 02 E _ .1 R = .96 0 calc = 0.8671 •meas+0.0499 -0.5 - . calc = 0.9226•meas AT =-12.0min d = 0.98 -1 04/Oct 05/Oct 06/Oct 07/Oct 08/Oct 09/Oct 10/Oct 11/Oct 12/Oct 13/Oct 14/Oct 2016 Figure 3-13: Water level validation results during Hurricane Matthew 201912020 Renourishment Project M&N Project No.10128-01 I11 WAVE MODEL CALIBRATION Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 31 of 70 There are six stations (as shown in Figure 2-2) with measured wave data available inside the wave model domains: three NOAA National Data Buoy Center (NDBC) buoys — 41108, Ocean Crest Pier (OCP1), and Sunset Beach Nearshore (SSBN7); three United States Army Corps of Engineers (USACE) Acoustic Doppler Current Profiler (ADCP) gages — Eleven Mile, Bald Head and Oak Island. OCP1 and SSBN7 are owned and maintained by the Coastal Ocean Research and Monitoring Program (CORMP). The NOAA buoy 41108 is at the same location as the USACE Eleven Mile ADCP. The following bulk wave parameters are reported at both the NOAA buoys and the USACE ADCPs: significant wave height, peak and average wave periods, and peak wave direction. For the wave transformation modeling, in addition to the offshore wave data as the boundary conditions, wind and water level inputs are also important especially during storm events. Based on the contiguous data available at all wave stations along with overlapping wind and water level data, the period of August 1st, 2008 to October 1st 2008 was selected for the wave model calibration purpose. Large waves generated by Hurricane Hanna were included in this period; thus, the wave model's ability to replicate both large and normal waves can be verified. 'A.4.1 Model Inputs 'A) OFFSHORE WAVE BOUNDARY CONDITIONS The directional wave spectra from NOAA buoy 41013 were applied as spatially uniform wave conditions at all three boundaries. The wave spectra were calculated based on the spectral wave density, alphal, alpha2, r1 and r2 data using the extended maximum likelihood method. The description of variables can be found in the NDBC website (www.ndbc.noaa.gov/measdes.shtml), with the conversion method following Earle et al. (1999) and Benoit et al. (1997). Figure 3-14 shows the offshore bulk wave parameters for the calibration period. The maximum wave height of 8.4 m was observed on September 6t", 2008 during Hurricane Hanna. 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 32 of 70 Significant wave height [m] 8.0 - --- ------------------ -- --- --- --- 4.0 2.0 0.0 August September 2008 2008 Peak wave period [sec] 20 15 10 5. August September 2008 2008 Peak wave direction [deg] 360 240'14"�4 120 a August September 2008 2008 Figure 3-14: Offshore waves from NOAA Buoy 41013 during calibration period (B) WINDS The spatially varying wind data from the National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) were applied for the model calibration period. The CFSR wind data interval is three hours. Figure 3-15 shows wind data comparison between NDBC and CFSR at buoy 41013 with good agreements. 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 33 of 70 NDBC [mis] CFSR [mis] 25 20 in ....................................... --------- E � 15 m m a a 10 ----- --------- C_ 5 August September 2C08 2008 NDBC [deg] CFSR [deg] 360 it 30c z rn m � 240 C O u 180 N a 120 C_ 60 0 August September 2008 2008 Figure 3-15: Wind data at NOAA buoy 41013 and from CFSR during calibration period (C) WATER LEVELS A spatially uniform water level field was used for the model calibration. Due to the lack of available measured water level data within the model domain, the data from nearby NOAA Station 8658163 at Wrightsville Beach, NC (as shown in Figure 2-1) was used for the model calibration. Figure 3-16 presents the water level data. However, it is important to point out that Hurricane Hanna made landfall at the NC/SC border, so the surge was much greater on Oak Island/Bald Head than at Wrightsville Beach. The reported storm surge was about 5 ft at Wilmington, NC, and about 4 ft at Myrtle Beach, SC, the back side of the storm. Thus, using the measured water level data at Wrightsville Beach could adversely affect the modeled waves during Hanna. Nonetheless, it's the closest available open coast water level station for the study area and thus used for the wave model calibration without any adjustment. 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 34 of 70 2 —Water Level (m) 1.5 —Residual (m) 1 0.5 0 -0.5 -1 2008-08-0100:00 2008-08-16 00:00 2008-08-3100:00 2008-09-15 00:00 2008-09-30 00:00 Figure 3-16: Water level data from NOAA station 8658163 for model calibration 3.4.2 Calibration Results Figure 3-17 through Figure 3-19 present the direct comparison between the computed and measured time series of significant wave height, peak wave period, and peak wave direction, respectively, at the gage locations of Eleven Mile ADCP, Bald Head ADCP, Oak Island ADCP and OCP1. Based on the model bathymetry, the OCP1 ADCP location is at a water depth of 5 m which is close to the wave breaking zone. Because the wave heights during the peak of the storms were greatly under predicted, it is suspected that the depth at the ADCP location was not correct (possibly due to the surge being higher) and therefore the model output point for the OCP1 ADCP was moved offshore to a deeper area of 7 m water depth. 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 35 of 70 Figure 3-17: Significant wave height calibration results 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 36 of 70 ElevenMile 20 • Measured 15 Modeled 0 «r.. ► d 10 _ _ _ _ • _ _ _ ► _ ■ «•• w w►+. «w�ww«• w ► •ww _ _ _ _ _ • _ _ ■ w�wn 5 ..• • �.... �.........«........�..... Y a� a 0 Jul-31 Aug-10 Aug-20 Aug-30 Sep-09 Sep-19 Sep-29 Time BaldHead 20 NMeasured 15 Modeled •' _ __ _ "�, aie�■ . mna apt � • s • ►- .. sr'. d 10 14_ _ _*4004. rw•► w.r ► •�wwrr .� •wiw _ _ _ _ ■ wwy«ru ter► �«r■ Y 5��•i�.�,.....I...... ■................�.i.. ,.....'..._ �" •_•_�. •tip... a 0 Jul-31 Aug-10 Aug-20 Aug-30 Sep-09 Sep-19 Sep-29 Time Daklsland 20 yMeasured ► 0 15 Modeled •► .tr > • •«r w► ww•rww«• rwr _.__ < wr �• �wr► > w. =.wr a•wwr w■ .. rw _.__. __.. ■ ■w w. d 0 Jul-31 Aug-10 Aug-20 Aug-30 Sep-09 Sep-19 Sep-29 Time OCP1 20 V Measured -a 15 Modeled •' ' O . ! ■ Am a 10 ......... .................. rrrr rrw rr wui .......... Awww - _-11L .......... ■ • • wr rr r� .... ... . �u. C..... j • r ••��► r �■w► ■■5 pqnyr:■fir `•fit ........ ..... . . • ....; is► ...........'; . � ww= �■ jI � %�7� a� a 0 Jul-31 Aug-10 Aug-20 Aug-30 Sep-09 Sep-19 Sep-29 Time Figure 3-18: Peak wave period calibration results 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 37 of 70 ElevenMile z 360 300 Measured ° 240 Modeled - 0 180.. • ♦ •♦ _ • �♦ •♦ ' N w •i 0 a- Jul-31 Aug-10 Aug-20 Aug-30 Sep-09 Sep-19 Sep-29 Time BaldHead z 360 300 Measured =0 240 Modeled •�........ - - ___.. - -_L.. .♦ ..,• IWO Cz 60 ............. ......... ........ . . ... . . . . . . . . . . . .... co 0 a Jul-31 Aug-10 Aug-20 Aug-30 Sep-09 Sep-19 Sep-29 Time Oaklsland z 360 300 Measured 240- Modeled =0 AL ' 120 60 Co 0 • , a Jul-31 Aug-10 Aug-20 Aug-30 Sep-09 Sep-19 Sep-29 Time OCP1 z 360 300 Measured .. ............. . �........., .......... . 240 Modeled . .2 .... ................. ..• .... .... ....... ... .. . ALI 180 ....... ....rN.'lr�i�. A4 > 120 ............. ...... ......... ............. 60 a Jul-31 Aug-10 Aug-20 Aug-30 Sep-09 Sep-19 Sep-29 Time Figure 3-19: Peak wave direction calibration results 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 38 of 70 The calculated goodness -of -fit parameters for the wave calibration results are listed in Table 3-1 through Table 3-3 for the significant wave height, peak wave period and peak wave direction, respectively. The results suggest that: • For the significant wave heights, the model predictions agree very well with the measured data at all four ADCP locations, with MAE and RMS errors less than 0.2 m, and R and d values greater than 0.9. • For the peak wave periods, the MAE and RMS errors are less than 2.5 s, and R and d values around 0.7 and 0.8, respectively. The data indicates there are periods when at least two wave systems exist — long period waves from offshore and locally generated waves from onshore. In the presence of the two systems, determination of peak period may not be consistent and may alternate between two values. This negatively affects the statistics. • For the peak wave directions, the model predictions have large deviations from the measured values. It is more pronounced at the Bald Head Island ADCP during period of September 17-26, when the reported ADCP peak wave directions are from between 90 and 180°N, whereas most of the modeled values are from between 330 and 360°N. Figure 3-20 presents both the measured and modeled Bald Head ADCP wave energy spectrum at 1:00 am EST on September 24, 2008. Two wave systems are evident from both the measured and the model predicted spectra: waves coming from SSE —SSW (offshore) with the frequency of around 0.1 Hz; and waves coming from NNW—N (locally wind -generated) with the frequency of around 0.4 Hz. The measured spectrum has some noise at higher frequencies beyond 0.8 Hz. It appears that the peak wave direction from the measured spectrum was calculated to be from offshore; whereas the peak wave direction from the modeled spectrum was calculated to be from onshore. This supports the fact that two or more wave systems can exist at the same time and one can dominate the wave field, which can result in large peak wave direction differences between the measurement and the model prediction. Per communication with USACE personnel' who is familiar with the handling of ADCP data, an upper cutoff frequency was used when post -processing the raw ADCP data to the bulk wave parameters. The cutoff frequency was the lesser of the two: when the wavelength is less than two times of the beam separation; or when the pressure response correction for amplitude is 0.1. 1 Personal communication with Kent Hathaway from the USACE. 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 39 of 70 Table 3-1: Goodness -of -fit parameters for significant wave height calibration Eleven Mile ADCP 0.14 0.19 4.3 0.96 0.97 Bald Head Island ADCP 0.11 0.15 5.3 0.91 0.95 Oak Island ADCP 0.10 0.13 4.6 0.92 0.96 OCP1 ADCP 0.08 0.11 3.5 0.94 0.97 Table 3-2: Goodness -of -fit parameters for peak wave period calibration Eleven Mile ADCP 1.3 2.0 0.74 0.86 Bald Head Island ADCP 1.4 2.4 0.65 0.81 Oak Island ADCP 1.4 2.3 0.64 0.81 OCP1 ADCP 1.4 2.2 0.71 0.85 Table 3-3: Goodness -of -fit parameters for peak wave direction calibration 201912020 Renourishment Project M&N Project No.10128-01 0 330 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 40 Figure 3-20: Comparison of Bald Head ADCP wave energy spectrum: (up) measured; (down) modeled 201912020 Renourishment Project M&N Project No.10128-01 140 3.5 WAVE MODEL VALIDATION Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 41 of 70 Based on the contiguous data availability at all wave stations along with overlapping wind and water level data, the period of July 1, 2009 to December 1, 2009 was selected for the wave model validation purpose. Similar to the wave model calibration period, the directional wave spectra from NOAA buoy 41013 were applied as spatially uniform wave conditions; spatially varying wind fields from CFSR were used as the wind inputs; and measured water level data from NOAA station 8658163 were used as a spatially uniform water level field. Figure 3-21 through Figure 3-23 present the direct comparison between the computed and measured time series of significant wave height, peak wave period and peak wave direction, respectively, at the gage locations of Eleven Mile ADCP, Bald Head ADCP, Oak Island ADCP and OCP1. The goodness -of -fit parameters for the wave validation results are listed in Table 3-4 to Table 3-6 for the significant wave height, peak wave period and peak wave direction, respectively. The results suggest that: • For the significant wave heights, the model predictions agree very well with the measured data at all four ADCP locations except Oak Island ADCP, with MAE and RMS errors less than 0.2 m. The wave heights were consistently over -predicted at the Oak Island ADCP. The measured wave heights at Oak Island were lower than OCP1 ADCP; whereas the predicted wave heights were similar. It is possible that the deployment of the Oak Island ADCP during the validation period was in a different depth than previous deployment periods. • For the peak wave periods, the MAE and RMS errors are less than 2.6 s, and R and d values around 0.6 and 0.8, respectively. • For the peak wave directions, the model predictions have large deviations from the measured values. After checking the measured and model predicted directional wave spectra, the presence of a double peaked spectrum is what caused the issue. 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 42 of 70 ElevenMile 3 Measured -- Modeled v� 2-1...... _....... A... ................. CD '.. 2 _ ■ ■ ' « 0 Jul-06 Jul-26 Aug-15 Sep-04 Sep-24 Oct-14 Nov-03 Nov-23 Time BaldHead 3 Measured L Modeled CD • t s ! # ! 1 .4. Ch i 0 Jul-06 Jul-26 Aug-15 Sep-04 Sep-24 Oct-14 Nov-03 Nov-23 Time Oaklsland 3 Measured L Modeled m2 ........ ......... a, _ ; ■ m t 0 Jul-06 Jul-26 Aug-15 Sep-04 Sep-24 Oct-14 Nov-03 Nov-23 Time OCP1 3 Measured L Modeled o) 2 ......... ..... ......... . a cn 0 Jul-06 Jul-26 Aug-15 Sep-04 Sep-24 Oct-14 Nov-03 Nov-23 Time Figure 3-21: Significant wave height validation results 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 43 of 70 ElevenMile 20 NMeasured ■ -a 15 Modeled....... ........ ......... ! ......... .......... .......... ►....... . .............. o ass ♦ N W 1MNA�� M • ■ A ■ i111 AlkF N a 0 Jul-06 Jul-26 Aug-15 Sep-04 Sep-24 Oct-14 Nov-03 Nov-23 Time BaldHead - 20 • Measured ► a 15 Modeled ..... o ♦ d 10 •: w. • ♦ M • : w • w w •wow � ► •r t.. iW � • wi a� w w •i i � • � • dw a 0 Jul-06 Jul-26 Aug-15 Sep-04 Sep-24 Oct-14 Nov-03 Nov-23 Time Oaklsland 20 i Measured « 0 15 Modeled s s •i � N w ♦ ■ •� w wr w w w w: w w . r w rw •: • :. ► ii r ►► r r r err li► r r�r r ■ d 1 • • • r� • w► • • .w ■ w r w rNr w ■•.• .. . _ .01 a 0 .• Jul-06 Jul-26 Aug-15 Sep-04 Sep-24 Oct-14 Nov-03 Nov-23 Time OCP1 20 N L] ( Measured a 15 « Modeled "" a 10 •- �► • r< wwr ♦ « rrw•r •NMI : � ...... . ........... ......... ... _... �...N..•F�.wAw■... _. ........•►•..... ...... /•wIN•...f■..rwwN. w.. (D a 0 Jul-06 Jul-26 Aug-15 Sep-04 Sep-24 Oct-14 Nov-03 Nov-23 Time Figure 3-22: Peak wave period validation results 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 44 of 70 ElevenMile z 360 •, , 300 r Measured �, 240 '•= j _ Modeled0— .•4.f s AAA -2 css i .. • • • a 0 Jul-06 Jul-26 Aug-15 Sep-04 Sep-24 Oct-14 Nov-03 Nov-23 Time BaldHead 360 (D 'E� 300 Measured ' Modeled _: _ _ _ _ __� __ $s _ o L7 • ♦ .. •..... ..... ..;d� a 120 lr......*....!!l• • •i �1�....My ;!_+. .i3..�,. .del......... ........ ; . .......... .. ... IR! . .. Y ca a) 0 a Jul-06 Jul-26 Aug-15 Sep-04 Sep-24 Oct-14 Nov-03 Nov-23 Time Oaklsland 360 1�. 300 Measured 240 Modeled 0 180 * — Y 0 - • • • • ♦ N a Jul-06 Jul-26 Aug-15 Sep-04 Sep-24 Oct-14 Nov-03 Nov-23 Time OCP1 z 360 =s 300 Measured T° 240 Modeled ....... . J;1 0 180 - � . 60 ' a 0 Jul-06 Jul-26 Aug-15 Sep-04 Sep-24 Oct-14 Nov-03 Nov-23 Time Figure 3-23: Peak wave direction validation results 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 45 of 70 Table 3-4: Goodness -of -fit parameters for significant wave height validation Eleven Mile ADCP 0.14 0.18 8.7 0.88 0.93 Bald Head Island ADCP 0.12 0.15 8.6 0.87 0.92 Oak Island ADCP 0.19 0.22 20.3 0.88 0.77 OCP1 ADCP 0.09 0.13 8.2 0.90 0.94 Table 3-5: Goodness -of -fit parameters for peak wave period validation Eleven Mile ADCP Head Island ADCP 1.3 2.1 70.66 7827Bald 1.5 2.5 0 Oak Island ADCP 1.6 2.6 0.57 0.76 OCP1 ADCP 1.4 2.3 0.68 0.82 Table 3-6: Goodness -of -fit parameters for peak wave direction validation 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 46 of 70 1. JAY BIRD SHOALS BORROW AREA MODELING To investigate the potential effects of dredging the identified Jay Bird Shoals borrow area on tidal currents, nearshore waves, and sediment transports along the adjacent shorelines, the existing model bathymetries were modified to reflect the after -dredge conditions. Two borrow area templates were considered as shown in Figure 4-1. Template 1 includes three zones with dredging elevation down to -26 ft-NAVD88 (Zone 1), -31 ft-NAVD88 (Zone 2), and -27 ft-NAVD88 (Zone 3), respectively. For Template 2, the Zone 2 dredging elevation was reduced to -27 ft-NAVD88 (the same dredging elevation as Zone 3 in Template 1) and its footprint was also reduced. The maximum dredging scenario was considered for both templates, i.e. assuming to remove all the available material identified as beach compatible (2.95 million and 2.34 million cubic yards for Template 1 and 2 respectively). Only part of the available material, 1.034 million cubic yards, will be dredged for the 2019/2020 Renourishment Project. Figure 4-2 and Figure 4-3 illustrate the after -dredge bathymetries at the Jay Bird Shoals borrow area for Template 1 and 2, respectively. Figure 4-1: Jay Bird Shoals borrow area templates 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Figure 4-2: After -dredge bathymetry —Template 1 17 16 �r 15.-mom m c a 14 � � �v o 13 12 694 695 696 697 698 699 700 701 x coordinate (km) 702 703 -40 -35 -30 -25 -20 -15 -10 After -dredge bathymetry - Template 2 (ft-NAVD88) -5 0 Figure 4-3: After -dredge bathymetry —Template 2 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 48 of 70 The modeling results based on the after -dredge bathymetries were compared with the modeling results from the existing bathymetry to identify the potential effects. 4.1 TIDAL CURRENTS For the existing and the two after -dredge templates, the flow model was simulated for a full spring -neap tidal cycle with astronomical tides and annual average river flows without winds. 4.1.1 Peak Tidal Flood Currents Figure 4-4, Figure 4-5, and Figure 4-6 present the instantaneous peak flood current velocities during a spring tide under existing and the two after -dredge templates, respectively. Figure 4-7 and Figure 4-8 show the peak flood current velocity differences between the existing and the two after -dredge templates, respectively. The model results indicate that Template 1 would have no measurable changes from existing, Template 2 could cause a 1 ft/s increase of peak flood currents in highly localized areas. Since the project peak current velocity magnitude in these localized areas is less than 1.5 ft/s under all conditions, effects on shorelines are expected to be negligible. 17 ED Y = - - U 14 a 13 12 694 695 696 697 698 699 700 701 702 703 x coordinate (km) 0 1 2 3 4 5 6 Flood Currents - Existing, magnitude (ftls) Figure 4-4: Instantaneous peak flood current velocities —existing condition 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 49 of 70 _ rrrr/rr cg g'- a 14ssi$s� 13 12 694 695 696 697 698 699 700 701 702 703 x coordinate —> 0 1 2 3 4 5 6 Flood Currents - Template 1, magnitude (fUs) Figure 4-5: Instantaneous peak flood current velocities —after-dredge Template 1 16 I - irJJJ/� T �JII/J - - Jr i O ' S { r 335 T ?' tf :. 13 12 RON 694 695 696 697 698 699 700 701 702 703 x coordinate (km) 0 1 2 3 4 5 6 Flood Currents - Template 2, magnitude (fUs) Figure 4-6: Instantaneous peak flood current velocities — after -dredge Template 2 201912020 Renourishment Project M&N Project No.10128-01 17 16 15 T is -2 14 `0 0 V 13 12 11 694 695 696 697 698 699 700 701 x coordinate -� Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 702 703 704 -3 -2 -1 0 1 2 3 Flood Currents - (Template 1 - Existing), magnitude (fUs) Figure 4-7: After -dredge bathymetry effects on instantaneous peak flood current velocities — Template 1 17 16 T 15 E Y_ N 14 `0 0 V a 13 it 11 694 695 696 697 698 699 700 701 x coordinate (km) -+ 702 703 704 -3 -2 -1 0 1 2 3 Flood Currents - (Template 2 - Existing), magnitude (fl!s) Figure 4-8: After -dredge bathymetry effects on instantaneous peak flood current velocities — Template 2 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 51 of 70 4.1.2 Residual Tidal Currents Residual tidal currents over a spring -neap tidal cycle is the "net" flow that remains after subtracting the flood flow vectors from the ebb flow vectors. The residual tidal current pattern is an indicator of potential net movement of sediment over a tidal cycle. In DeIft3D, the residual currents are calculated based on Fourier analysis for the current velocities over a specified period. Figure 4-9 to Figure 4-11 presents the residual tidal currents under the existing and the two after -dredge templates, respectively. The difference of residual tidal currents are shown in Figure 4-12 and Figure 4-13 for Template 1 and 2, respectively. The model results indicate the two after -dredge bathymetry templates could cause negligible residual tidal current increase (less than 0.05 ft/s). 17 15 0 14 T 'f 13 , ti: 694 695 696 697 698 699 700 701 702 703 x coordinate 0 0.2 0.4 06 0.8 1 1.2 1.4 1-6 1.8 2 Residual Currents - Existing (ff/s), magnitude Figure 4-9: Residual tidal currents — existing condition 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 52 of 70 17 15 - _ c -= v CU a 14 •'•x T 13 12 694 695 696 697 698 699 700 701 702 703 x coordinate 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Residual Currents - Template 1 (ftls), magnitude Figure 4-10: Residual tidal currents — after -dredge Template 1 Figure 4-11: Residual tidal currents — after -dredge Template 2 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 53 of 70 17 �V 0 �' C� Q � 16 15 r a 14 L� o U � T 13 12 11 694 695 696 697 698 699 700 701 702 703 704 x coordinate -4 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 Residual Currents - (Template 1 - Existing) (fVs), magnitude Figure 4-12: After -dredge bathymetry effects on residual tidal currents — Template 1 16 15 �d ? ?3 Ca P } oil 0 14 8 N, a 13 12 11 694 695 696 697 698 699 700 701 702 703 704 x coordinate 425 42 -0.15 41 405 0 0.05 0.1 0,15 0.2 0,25 Residual Currents - (Template 2 - Existing) (ftls), magnitude Figure 4-13: After -dredge bathymetry effects on residual tidal currents —Template 2 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 54 of 70 4.2 WAVES As stated previously, there were concerns that any potential nearshore wave climate changes caused by the project could affect the adjacent shorelines. For this study, a representative wave approach was adopted to investigate this concern. 4.2.1 Representative offshore waves The offshore wave data at the NOAA buoy 41013 from 2004 to 2018 was the primary source for deriving the representative input wave conditions. The data gaps in the buoy data were filled with available USACE Wave Information Studies (WIS) hindcast data and NOAA WW3 hindcast data at locations close to 41013. The WIS hindcast data were only available to 2014, so WW3 data were used to fill the data gaps afterwards. The combined wave data were in an hourly time interval. Figure 4-14 shows the annual percentage of exceedance of the significant wave height from the combined offshore wave data. The annual mean significant wave height at the offshore location is about 4.4 ft. Figure 4-15 plots the wave rose for the significant wave height from the combined wave records at offshore. It indicates that the dominant wave direction in the offshore region of the project area is from the ESE. Wave heights less than 6 ft comprise about 80% of the 15-year record. Station 41013_comb_NDBC_WIS_WW3 Percent Exceedance (Annual) 100 N = 131478 µ=4.42,a=2.24 mode = 2.70 75 2.84 0 U a 50 3.86 aD U X W 25 5.44 10 7.38 1 8.73 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Significant Wave Height, ft Figure 4-14: Annual percentage of exceedance of significant wave height at the offshore boundary 201912020 Renourishment Project M&N Project No.10128-01 Total L •CD 15 2 ro 12 c 9 6 W in 3 0 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 55 of 70 Significant Wave Height (Annual) Station 41013 comb NDBC WIS WW3 Period 01-Jan-2004 to 31-Dec-2018 N NW, - - \ NE 20% 15% \ I \ � ! , , 10% v i f f 1 I I WI------L 0.00 -L- -- E 1 i L f 4 1 \ \ I / SW v _ SE \ � I � I � S n Ez15 ❑ 12 - 15 �9-12 ❑6-9 r73-6 No-3 Direction FROM is shown Center value indicates calms below 0 ft Total observations 131478, calms 0 About 0.01440% of observations missing Percentage of Occurrence 0.60 1.77 4.31 9.39 12.76 17.84 14.62 9.15 9.75 8.62 6.16 1.66 0.99 0.95 0.72 0.72 100.00 0.23 0.10 0.11 0.11 0.12 0.13 0.80 0.15 0.55 0.33 0.22 0.34 0.37 0.49 0.37 0.24 0.12 3.34 0.36 1.14 2.56 1.20 1.45 1.34 1.44 1.88 1.32 1.05 0.33 0.30 0.24 0.18 0.19 15.07 0.42 1.17 2.57 4.53 5.91 8.30 7.23 4.55 5.33 5.10 3.74 0.85 0.47 0.52 0.42 0.43 51.5 0.22 0.44 1.64 5.17 7.73 5.56 2.67 1.89 1.74 1.10 0.36 0.16 0.14 29.03 N NNE NE ENE E ESE SE SSE S SSW SW WSW W WNW NW NNW Total Figure 4-15: Wave rose of significant wave heights at the offshore boundary 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 56 of 70 In order to derive representative wave conditions, the 15-year wave record was sorted by peak wave direction and significant wave height. The sorting routine contained 24 direction bins (15 degrees each) and nine significant wave height bins (1 m each). Only waves which would reasonably be expected to affect the project shorelines were considered specifically including waves originating from between East (90 degrees) and West (270 degrees) azimuth. This resulted in 86 wave cases used as model input and which represent approximately 75.4% of the 15-year record by occurrence (waves from east to north to west were excluded). The average wave parameters were calculated in each wave case. Table 4-1 lists the characteristics of each wave case as they were applied to the wave modeling. Table 4-1: Representative wave conditions used as model inputs MWD-Ibin 0-1 90 -105 Bin average sig. 2.5 Bin average peak periodHs-bin 9.0 Bin average Wave Percentage Occurrence 97.7 4.854 1-2 90 - 105 4.4 9.5 98.0 3.973 2-3 90 - 105 7.8 3-4 90 - 105 11.3 10.1 11.8 97.3 0.635 97.1 0.164 4-5 90 -105 14.2 12.4 98.0 0.054 5-6 90 - 105 17.5 13.9 99.0 0.016 6-7 90 -105 20.7 13.1 98.0 0.002 0-1 105 -120 2.4 8.9 112.5 6.297 1-2 2-3 105 - 120 4.4 9.4 112.4 112.8 5.030 0.714 105-120 7.7 9.6 3-4 105 -120 11.3 10.9 112.2 0.129 4-5 105 -120 14.1 12.2 112.0 0.038 5-6 105-120 17.6 11.2 115.9 0.005 6-7 105 -120 20.7 12.3 115.8 0.002 7-8 105 -120 23.3 15.3 115.1 0.002 0-1 120 -135 2.5 8.6 126.9 5.573 1-2 120 -135 4.4 9.0 127.3 4.728 2-3 120 -135 7.7 9.6 127.1 0.789 3-4 120 -135 11.1 10.1 128.1 0.135 4-5 120 -135 14.4 10.2 126.9 0.035 5-6 120-135 18.0 11.3 128.7 0.010 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 57 of 70 6-7 120 -135 20.2 12.2 130.1 0.002 8-9 120 -135 26.8 14.8 128.6 0.002 0-1 135-150 2.5 8.0 141.6 3.391 1-2 135 -150 4.5 8.3 142.0 3.696 2-3 135 -150 7.8 8.9 142.5 0.646 3-4 135 -150 11.3 9.9 142.2 0.193 4-5 135 -150 14.1 10.4 142.1 0.054 5-6 135-150 18.3 11.1 142.9 0.011 6-7 135 -150 20.2 12.3 142.6 0.003 7-8 135 -150 25.2 15.9 141.2 0.002 8-9 135-150 27.6 14.8 143.3 0.001 0-1 150 -165 2.6 7.1 156.9 2.225 1-2 150-165 4.6 7.4 157.3 2.810 2-3 150 - 165 7.8 8.1 157.7 0.739 3-4 150 - 165 11.0 9.2 157.3 0.174 4-5 150 -165 14.6 9.7 157.6 0.035 5-6 150 -165 17.4 11.1 154.1 0.007 6-7 150 -165 20.5 11.9 154.8 0.003 7-8 150 -165 23.9 13.0 159.0 0.001 0-1 165 - 180 2.7 6.1 172.3 1.770 1-2 165-180 4.6 6.7 172.6 3.194 2-3 165-180 7.8 8.0 172.5 1.012 3-4 165 -180 11.1 9.0 172.9 0.204 4-5 165 -180 14.3 9.6 173.7 0.029 5-6 165 -180 17.6 11.2 169.7 0.004 6-7 165 -180 20.7 12.0 175.7 0.004 7-8 165 -180 25.8 13.8 169.7 0.002 8-9 165 -180 26.8 14.2 170.8 0.002 0-1 180 -195 2.7 5.5 187.0 1.607 1-2 180 -195 4.5 6.4 187.2 3.474 2-3 180 -195 7.9 8.0 186.7 1.063 3-4 180 -195 11.2 9.2 186.9 0.232 4-5 180 -195 14.2 10.0 186.9 0.050 5-6 180 - 195 17.6 11.2 186.6 0.005 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 58 of 70 6-7 180 -195 20.2 12.8 183.0 0.001 0-1 195-210 2.7 5.1 202.1 1.613 1-2 195 - 210 4.5 6.0 202.4 3.239 2-3 195 - 210 7.8 7.6 201.7 0.727 3-4 195-210 11.1 8.9 201.9 0.189 4-5 195-210 14.3 9.4 201.9 0.040 5-6 195 - 210 17.0 10.0 199.6 0.003 0-1 210-225 2.7 4.9 216.8 1.319 1-2 210-225 4.6 5.8 217.1 3.141 2-3 210 - 225 7.7 7.2 217.4 0.666 3-4 210-225 11.0 8.3 217.9 0.115 4-5 210-225 14.2 9.2 215.3 0.015 5-6 210-225 16.8 8.3 219.7 0.001 0-1 225 - 240 2.6 4.6 231.3 0.688 1-2 225 - 240 4.6 5.5 230.8 1.609 2-3 225 - 240 7.8 7.0 231.2 0.367 3-4 225 - 240 10.8 8.3 231.0 0.071 4-5 225 - 240 14.2 9.2 228.9 0.007 5-6 225 - 240 17.4 8.8 231.2 0.005 0-1 240 - 255 2.6 4.9 246.5 0.301 1-2 240 - 255 4.7 5.5 246.3 0.539 2-3 240 - 255 7.9 6.7 246.4 0.190 3-4 240 - 255 10.8 7.4 246.9 0.039 4-5 240 - 255 13.5 7.5 249.3 0.002 5-6 240 - 255 17.8 8.6 248.0 0.001 0-1 255 - 270 2.6 4.8 261.3 0.169 1-2 255 - 270 4.7 5.4 262.0 0.321 2-3 255 - 270 7.8 6.3 262.3 0.168 3-4 255 - 270 10.7 6.9 261.3 0.040 4-5 255 - 270 15.0 8.2 259.0 0.002 5-6 255 - 270 17.9 8.3 263.5 0.002 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 59 of 70 4.2.2 Nearshore Wave Results Each of the 86 wave conditions listed in Table 4-1 were run for the existing bathymetric condition and of the two after -dredge bathymetry templates. Winds and water levels were not included in these model runs. For each discrete wave condition, the spatial map of significant wave height (after -dredge Hs — existing Hs) was calculated. It is expected and confirmed by the model results that nearshore waves would decrease leeward of the Jay Bird Shoals borrow area due to wave refraction caused by the excavated borrow area. At the same time nearshore waves could increase slightly on both the east and west side of the borrow area. Some results from the 86 wave conditions are presented below, all wave condition model results are included in Appendix C1 and C2 for Template 1 and Template 2, respectively. Figure 4-16 presents the model results for representative waves in the range of 0 — 3 ft originating from Southeast (SE), South (S), and Southwest (SW). The waves in this range comprise about 30% of the 15-year record. The average wave height is about 2.5 ft. The two after -dredge bathymetry templates show that effects from these small wave conditions are negligible. Vectors represent the modeled wave directions from the two after -dredge bathymetry templates. Figure 4-17 presents the model results for representative waves in the range of 3 — 6 ft originating from SE, S, and SW. The waves in this range comprise about 50% of the 15- year record. The average significant wave height is about 4.5 ft which is approximately the annual average wave conditions in the offshore area. The two after -dredge bathymetry templates could cause about 3 inches of wave height increase in highly localized areas offshore of the shoreline. Figure 4-18 shows the model results for representative waves in the range of 6 — 9 ft originating from SE, S, and SW. The waves in this range comprise about 15% of the 15- year record. The average significant wave height is about 7.5 ft. The two after -dredge bathymetry templates induced show wave changes are mostly less than 0.5 ft. Figure 4-19 shows the model results for storm waves originating from SE, S, and SW. During Hurricane Matthew in 2016, significant wave height of 21 ft was observed offshore. Similar to the model results under more frequent normal wave conditions, the two after -dredge bathymetry templates could cause wave reduction leeward of the borrow area and wave increases on both east and west sides. The magnitude of wave change is mostly less than 1 ft in localized areas. 201912020 Renourishment Project M&N Project No.10128-01 17 16 E 15 14 kk 13 12 894 696 BBB 897 SOS 699 700 701 702 703 x d dinere{km1 — .2 -1.5 -1 -0.5 0 0.5 1 1.5 2 5,9,R W Wave Height Odle— (Template 1 - Existing) (R) 17 16 ? 15 E p 14 kp 13 12 894 896 BBB 697 698 699 700 701 702 70 x doaldinare {km) — In 694 695 696 697 698 699 700 701 702 703 x coordinate (km) —> -2 -1 5 -1 -0.5 0 0.5 1 1.5 2 Sig,f.M We- Height DiRerenee (Templsle 1 - Ddsting) (R) Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 60 of 70 17 SW 2.5ft incoming wave , 15 13 12 894 898 696 697 696 699 700 701 702 703 xfA dr te(km) r -1 -0.5 0 0.5 1 1.5 2 SigniticaM Wave Height pilfer (Template 1 - Existing) (R) 17 16 ? 15 E p 14 pd 13 12 894 898 696 697 698 899 700 701 702 703 xc dmate(km)-r i -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 -2 -1.5 -1 -0.5 0 0.5 1 15 2 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Significant Wave Height D4lerenw ITemplate 2- Existing) (R) Sigm=rh Wave Height Meereroe (Template 2 - Existing) (R) SigmticaM Wave Height E),%.— (Template 2 - Existing) (R) Figure 4-16: After -dredge bathymetry effects on waves between 0 — 3 ft with average height of 2.5 ft (top: Template 1; bottom: Template 2) 201912020 Renourishment Project M&N Project No.10128-01 In 17 S�sft mtn wave.. g wave - 14 1�}}"t`1r1S1t�4t1ty41114``�4y�4`Y`k4 (�` �l' r�) 13 �'�4klk;},1�44���144���11����j��it1�, '',,;.•,:,'';,;,, '. 4,�'Yl'lllllYlY4`Y1,kY}Y1411111411�111t1�y;` t �,;";:;;:�;:', J�Jj , 12 4 1 �} y�kll4Ykk4kl`Y4kYl}kLY4lYYtYY $t4`yY`4�yy"y�'4": ti,,, t { } V f . 4 l ) 1 ; 5 444k i S i �ii',';,•�:i ,', � 4 _ 894 896 BBB 697 B98 699 700 701 702 703 x -din (km) — -2 -1.5 - -0.5 0 0.5 1 1.5 2 Significant Wave Heigh[ rifle— (Template 1 - Existing) (R) m t 15 E R 14 iS 13 694 695 696 697 698 699 700 701 702 703 x coordinate {km) —> -2 -1 5 -1 45 0 0.5 1 1.5 2 Significant Wale Height hilt— (Template 1 - F ''sting) (11) In MY 719/1 ME FEN I MP 17 16 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 61 of 70 894 896 Bs$ 597 896 699 700 701 702 703 x could -le (km) -• -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 5191ificaW Wave Height l3iftem as (Template 1 - Existing) (R) SO4 896 Bs8 697 696 899 700 701 702 703 x cohldin (km)--, -2 -15 - -0.5 0 0.5 1 1.5 2 -2 -i.5 -1 -0.5 0 0.5 1 15 2 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Significant Wave Height title.— (Template 2 - Eaialing) (R) Sig,dx a R Wale Height MOerexe (Template 2 - Existing) (R) 5ignificam! Wave Height E),% — (Template 2 - Existing) (R) Figure 4-17: After -dredge bathymetry effects on waves between 3 — 6 ft with average height of 4.5 ft (top: Template 1; bottom: Template 2) 201912020 Renourishment Project M&N Project No.10128-01 17 1e ? 15 E 14 13 12 894 896 BBB 697 898 699 700 701 702 703 x ooardinate(kml � -2 -1.5 - -0.5 0 0.5 1 1.5 2 Significant Wave Height DiOer (Template 1 - Existing) (n) 17 1e T 75 E p 14 pd 13 12 e94 896 BBB 697 e9e 699 700 701 702 703 x—rdinete (kml � m 694 695 696 697 698 699 700 701 702 703 x coordinate (km) -2 -1 5 -1 -0.5 0 0.5 1 1.5 2 SignificaM wave Height Drffe—e (Template 1 - Basting) (8) In Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 62 of 70 1E In 694 695 696 697 698 699 700 701 702 703 xc dinaia(km)-> -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Sig,i—M Wave Height Difference (Template 1 - F 'sblg) (ti) m 12 y�{TY�5g�4�'�I� �'�""+�4 l'F '' Az��j�I/���f���/�lfl.�f�j�f Y r<r r 1 x :11/lll�i/li il���f� >� �ll.Gft f.U111� 694 695 696 697 696 699 700 701 702 703 694 695 696 697 698 599 700 701 702 703 x coordinate (km) - x coordinate (km) - -2 -1 5 - -0.5 0 0.5 1 1.5 2 -2 -1.5 -1 -0.5 0 0.5 1 i 5 2 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Significant Wave Height Di$er (Template 2 - Exialing) (0) SignificaM Wave Height MOerexe (Template 2 - Exisfing) (R) SignificaM Wave Height Difference (Template 2 - Exisfing) (ff) Figure 4-18: After -dredge bathymetry effects on waves between 3 — 6 ft with average height of 7.5 ft (top: Template 1; bottom: Template 2) 201912020 Renourishment Project M&N Project No.10128-01 894 695 3W 897 998 ego 700 701 762 703 x o dinete (km) � .2 -1.5 -1 -0.5 0 0.5 1 1.5 SigMficenl Wave Height Ditlereiwa (pemplate 1 - Existing} tR) 11 �y9�fyyY4444147�y47r,✓r,"',i""r'✓f4'iyyy!{''i�111i�ti'�1' }4.45 t r.r tR�,�,E1tF a?,��✓,i.,?!d7�r!J�r>'7 r�,4t'.e4�64{i��l;�.%/�I !✓/�iii$'i�5��lf llll, f .t ! 694 695 696 697 696 699 700 701 702 703 x c—d—te (km) , 2 2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Slgnilicant Wave Haight Oitterence (Template 1 - Ex h,g) (A) T 5 tl Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 63 of 70 694 695 696 697 698 699 700 701 702 703 a coordinate {km) —> -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Signili-M Waue Height Diflerenee (Template 1 - Ewsting) (fl) 12 SS}•iti'Si'i}•1i1}1E44Qf+�1�i4'}t4+S;.SS,SS141i44i1'/d'�i'�•�•'�.:�;.;�������+�j�,e �'i1a 4ygif4'}'yf�tlryi41')'15�✓'r1,�rN�ri"`"Y,✓'r'§iiS°iJ{'ll�'11`illi''�'/�y����%/1'%'lrl i4,t44,1�ti1Il,1�,14d tS.Slit}!4 titi,iS i (4.}4.4�li al.i{�t11 y j P216 , 9,Fi�Yrtrli a:.:+S 1i111 5 4iR4t4�, ;tfiFR:4 � 1 �i5l di �tr 4 l:S�e4 L{l{} ��flr`�J/fviii P �rf . (lf, � r� i'Jl /r f���f /ll l ir!all i}%lf!/����%r/dflTffU711 894 695 3W 897 698 699 700 701 762 703 094 695 696 697 898 899 700 701 702 703 694 695 696 697 698 699 700 701 702 703 x o di.te (km) x coordinate (km) —, x coordinate (km) —> -2 -1.5 -1 -0.5 0 0.5 1 T 5 2 .2 -1.5 -1 '0.5 0 0.5 1 1.5 2 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Sig,i ce Wave Height Ditlererua (Template 2 - Existing) (fl) $IgMlicant Wave Haight OiHam—(Template 2 - ExlsOng) (fl) SignifiwM Wave Height DIfler— (Template 2- E)lsting) (fl) Figure 4-19: After -dredge bathymetry effects on storm waves comparable to Hurricane Matthew in 2016 (top: Template 1; bottom: Template 2) 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 64 of 70 4.3 SEDIMENT TRANSPORT Based on the model results demonstrated in section 4.1.2, it is reasonable to conclude that the two after -dredge bathymetry templates have negligible effects on the residual tidal currents, and thus upon the associated sediment transport processes along the Caswell Beach shoreline due to tidal currents. Therefore, only wave induced sediment transport was considered for this analysis. For each of the 86 representative wave conditions in Table 4-1, the wave induced longshore currents and associated sediment transport were estimated by coupling DeIft3D-FLOW and DeIft3D-WAVE modules using only the fine wave model grid for the existing and the two after - dredge bathymetric templates. There were no tide and wind inputs, and no morphology update. A uniform median sediment grain size of 0.25 mm was assumed. No sediment transport calibration effort was made due to lack of measured data. The sediment transport rates through shore -normal transects along the Caswell Beach shoreline (Figure 4-20) were extracted from the model results under each wave condition; and were then subsequently weighted by the percent occurrence of each wave condition to formulate the average annual potential sediment transport. Modeled sediment transport inside the surf zone is greatly influenced by the imposed model bathymetry. Thus, the model results represent only the bathymetric condition constructed based on the available data sources listed in Table 2-1. In reality, the beach bathymetry tends to be smoothed out by waves. Since this sediment transport study is not a morphological model, the sediment transport results were smoothed through a 0.5 mile moving average. 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 65 of 70 Figure 4-20: Caswell Beach transects Figure 4-21 presents the modeled average annual "net" longshore sediment transport rates along the Caswell Beach shoreline for both the existing and the two after -dredge templates. Positive values represent westerly sediment transport direction. The model results indicate potential sediment transport rate reduction leeward of the borrow area, and potential sediment transport rate increases along both east and west shoreline segments away from the borrow area. The net longshore sediment transport gradients along the Caswell Beach shoreline are shown in Figure 4-22. The net longshore sediment transport gradient is calculated as dQ/dx where dQ is the transport rate differential between neighboring transects and dx is the alongshore distance between transects. The transport gradient is a proxy to potential shoreline changes. Positive and negative values in Figure 4-22 indicate potential localized adjustments in shoreline accretion and erosion, respectively. Based on the model results, it would appear that areas of concern for potential increases in shoreline erosion would be limited to discrete portions of Caswell Beach (between survey 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 66 of 70 transects 37+00 — 60+00 and 150+00 — 170+00). Potential effects on shoreline erosion in other areas seem to be minimal and some areas may experience increased shoreline accretion. Generally, both templates show results close to existing conditions, with some areas showing transport rates above and below existing conditions. There is no strong evidence to choose one template over the other given the model results, especially given that this is not a morphological model. The modeled sediment transport inside the surf zone is greatly influenced by the imposed model bathymetry. Thus, the model results only represent the bathymetric condition constructed based on the available data sources. There will be an additional 0.6 mcy beach compatible material available in Template 1. For this reason, Template 1 was chosen for the Town of Oak Island's permit application for the 2019/2020 Renourishment Project. The Town of Oak Island will monitor the Caswell Beach shoreline for nine (9) years post -project to investigate any potential effects which might require mitigation. 200 150 100 50 0 -50 100 + Caswell Beach Transects I I I I I I —Net Transport - Existing —Net Transport - After -Dredge Template 1 —Net Transport - After -Dredge Template 2 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I + Westerly Transpdrt 00000 l000000 000000 0o00ooi0000000i000 00 l000 I I 00000 0th 00N �0N�[�LI00N0N 0N 0N 0N000000 00000 00 N 0N 0rl000l000000000 00�000��0+1+O+O10001�0 000 N 0�0'II00O 1O 10nOA0,Ol 0,0,0'r,OIOI0,:0, IONO' '0'JONO+++ i++ +1+ +++t+++ .CommMNoo, NN N0.1~11mmm o.'.�- N - J I I I I I I I ;Jay Bird Shoal l orrow Site I I I I I I I I Easterly Transpoq I I I I I I I I I I I ----- ---. I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 692000 693000 694000 695000 696000 697000 698000 699000 700000 701000 Easting - NC State Plan (m) Figure 4-21: Wave -induced net longshore sediment transports along Caswell Beach shoreline 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island 1/11 100 80 60 a r 40 U c a 20 O Q 0 C C E -20 a ai o -40 L Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 67 of 70 + Caswell Beach Transects —Transport Gradient - Existing —Transport Gradient -After-Dredge Template 1 —Transport Gradeint- After -Dredge Template ---------;------------------;------------------ ------------------------------------------------------------------------ _________,_________1_________ L_____ _ ________ _______1 _____L_________I_fm, ___ O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O I Oo00oo,000000,000000Qoo 00 000000 0 00 0 000 000000Q ++++++++++++ +++++++++ +++ ++++++ + +++ ++ o0 000000 ONO M0 W 0M ON OM MOM OM0lh ON 0M 0MOM0 it N NO NO ++ + +++++ 100 mm m W1,10 m N 't MNN H 0 0m mca I'W om �vt N 00 O NO1 ON ON ON M ['!lM NN NN NN NN NN NNNv N Nr,'i.-,rl ei ei rl ei ei 'i ei 'i a100 DPI, I,W tom Vl� 1 ' - ' - - I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I ,Jay Bird Shoal borrow Site I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 692000 693000 694000 695000 696000 697000 698000 699000 Easting - NC State Plan (m) Figure 4-22: Longshore sediment transport gradients along Caswell Beach shoreline 700000 701000 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 68 of 70 5. SUMMARY AND CONCLUSIONS In order to investigate the potential effects of the Jay Bird Shoals borrow area identified for the 2019/2020 Renourishment Project on the neighboring shorelines of Caswell Beach and Bald Head Island, numerical models were developed for hydrodynamics, waves, and sediment transport using Deltares' DeIft3D model suite. The hydrodynamics and wave models were successfully calibrated and validated against available observed water levels, currents, discharges, and wave data. Sediment transport calibration was not conducted, due to lack of measured data to calibrate against. Tidal current, wave, and sediment transport modeling were performed for the existing and two after -dredge bathymetric templates. The maximum borrow area dredge scenarios were considered, i.e. assuming to remove the full 2.95/2.34 million cubic yards of available material identified as beach compatible in Template 1 and 2, respectively. Only part of the material, 1.034 million cubic yards, will be dredged for the 2019/2020 Renourishment Project. Thus, within the proposed borrow area, the results from the DeIft3D model are considered to be a conservative overestimate of the potential effects on tidal current and wave climates. The model results were analyzed to determine potential effects of the two after -dredge bathymetric templates. The findings are: • The two after -dredge bathymetric templates show that effects on tidal currents would be localized and small, which implies no significant effects upon sediment transport processes associated with tidal currents; • The two after -dredge bathymetric templates could reduce waves leeward of the borrow area; however, it could slightly increase nearshore waves on both east and west sides of the borrow area in localized areas; • and similarly, the two after -dredge bathymetric templates could reduce the wave - induced longshore sediment transports leeward of the borrow area but could also cause longshore sediment transport increases on shoreline segments both east and west sides of the borrow area. The net effect of these changes could result in localized adjustments in shoreline erosion / accretion. Based on the model results, it would appear that most of the potential increases in shoreline erosion would be limited to discrete portions of Caswell Beach (between survey transects 37+00 —60+00 and 150+00 — 170+00). Potential effects in other areas seem to be minimal. Generally, both templates show results close to existing conditions, with some areas showing transport rates above and below existing conditions. There is no strong evidence to choose one template over the other given the model results, especially given that this is not a 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 69 of 70 morphological model. The modeled sediment transport inside the surf zone is greatly influenced by the imposed model bathymetry. Thus, the model results only represent the bathymetric condition constructed based on the available data sources. • Given that there will be an additional 0.6 mcy beach compatible material available in Template 1; this is the chosen scenario for the Town of Oak Island's permit application for the 2019/2020 Renourishment Project. The Town of Oak Island will monitor the Caswell Beach shoreline for nine (9) years post -project to investigate any effects predicted by the model which might require mitigation. 201912020 Renourishment Project M&N Project No.10128-01 Town of Oak Island Jay Bird Shoals Borrow Area Modeling September 6, 2019 Page 70 of 70 6. REFERENCES Benoit, M., Frigaard, Peter, and H.A. Schaffer (1997) "Analyzing Multidirectional Wave Spectra", Proceedings of the 27th IAHR Congress, San Francisco, 10-15 August 1997, IAHR Seminar "Multidirectional Waves and their Interaction with Structures", Mansard, Etienne (ed.), Canadian Government Publishing, Benoit. Deltares (2018a), "Delft3D-FLOW, Simulation of multi -dimensional hydrodynamic flows and transport phenomena, including sediments, User Manual". Deltares (2018b), "Delft3D-WAVE, Simulation of short -crested waves with SWAN, User Manual". Earle, MA K.E. Steele, and D.W.C. Wang (1999), "Use of advanced directional wave spectra analysis methods", Ocean Engineering, Volume 26, Issue 12, December 1999, Pages 1421-1434. Egbert, Gary D., and Svetlana Y. Erofeeva (2002). "Efficient inverse modeling of barotropic ocean tides." Journal of Atmospheric and Oceanic Technology 19.2 (2002): 183-204. RPS Evans -Hamilton (2017). "Cape Fear current, water Level and water quality study". Willmott, C.J., S.G. Ackleson, R.E. Davis, J.J. Feddema, K.M. Klink, D.R. Legates, J. O'Donnell, and C.M. Rowe (1985), "Statistics for the evaluation and comparison of models". Journal of Geophysical Research, 90(C5), 8995-9005. 201912020 Renourishment Project M&N Project No.10128-01