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HomeMy WebLinkAboutAdd Info for CAMA applicationOak Island 2019/2020 Renourishment Project Additional Information for CAMA Major Permit Application For the Town to maintain adequate cash flow, the renourishment of the entire oceanfront is being completed in separate projects to ensure manageable budgets. The 2019/2020 Renourishment Project is the first of three planned over the next three years (2019, 2020 and 2021). As a result of recent hurricane activity, there is effectively no protective dune throughout most of the oceanfront. Therefore, the first two planned renourishment projects will focus on building a dune to withstand a 25-year return period storm event across the island. The design also includes a support pad with a 1V:20H slope that will move MHW seaward on average 80 ft; see Table 1 and Figure 1. This is to meet the Town's immediate need to provide protection to vulnerable infrastructure from increasingly active hurricane seasons. The third project, planned for winter 2021, will focus on repairing what dune volume is lost in the interim as well as provide additional storm protection in the form of a recreational berm in front of the dune across the island. Table 1- Summary of volume per cubic yard planned for dune and pad Station MHW Advancement Total Unit Fill Dune Unit Fill (above 7' NAVD) Pad Unit Fill (Below 7' NAVD) Pad Percentage of Total Fill Dune Percentage of Total Fill 300+00 1 0.0 1 7.4 1 7.1 1 0.2 1 3.3% 1 96.7% 310+00 64.6 28.6 8.4 20.2 70.7% 29.3% 320+00 66.7 36.1 8.7 27.4 75.9% 24.1% 330+00 97.4 55.7 10.6 45.1 81.0% 19.0% 340+00 85.2 52.9 10.8 42.1 79.6% 20.4% 350+00 80.8 37.7 8.8 28.9 76.6% 23.4% 360+00 98.6 44.7 11.1 33.6 75.3% 24.7% 370+00 111.9 56.9 12.1 44.8 78.8% 21.2% 380+00 142.1 65.2 11.8 53.5 82.0% 18.0% 390+00 106.5 51.9 12.0 39.9 76.9% 23.1% 400+00 62.2 25.6 7.8 17.8 69.4% 30.6% 410+00 91.8 40.9 9.1 31.8 77.7% 22.3% 420+00 64.2 21.1 5.4 15.7 74.4% 25.6% 430+00 99.7 38.4 8.6 29.9 77.7% 22.3% 440+00 76.7 36.0 10.5 25.5 70.8% 29.2% 450+00 67.0 31.3 9.4 21.9 69.9% 30.1% 460+00 71.3 32.4 9.0 23.4 72.3% 27.7% 470+00 82.6 37.3 9.3 28.0 75.1% 24.9% 480+00 53.3 24.7 6.5 18.1 73.6% 26.4% 490+00 47.7 20.9 4.1 16.7 80.2 % 19.8 500+00 75.9 31.4 7.7 23.6 75.3% 24.7% Average 82.3 38.5 9.1 29.4 75.7% 24.3% Min 47.7 20.9 4.1 15.7 69.4% 18.0% Max 142.1 65.2 12.1 53.5 82.0% 30.6% 1 iiiiiiiii■i■ii■i ■iiiiii■ ■iiiiiiiiiiiiiiiiiiiiii■iii■ MMmmMIIIMMmMmMMmMIM iiii■iiii■iiii■i .. .-------------- C■■■■■■■■■w■■■■■u ■■■■■■■■■■■■■■■ iiiii■■■■;1iii■!�■ (81%of Total Fill) I■■i■■iiiiii■■■ Ciiiii■iiii■i■■1�■� .iiiiiiiii■iii■ ii■■i■iiRiii■■11■i■ii.i■■iiiiiiiiiiiiiiiiiiiiii■iii■ iii■■■■■i[.117i■■J ■�■■■■i■ ■i ■iiiiiiiiiliiiiiiiiii■iii■ iiiiii■ iiiil�li■I�i ■i■■i■i■ ■i ■iiiiiiiii■iiiiiiiiii■iiii .. iii■�i■i11i11i■►1■■i iiiiiiii■iiiiiiiiii■iii■ ■■■■►I►\■■►1.■1■■ ■■■■■■■1■■■■■■■■■■■■■■■ iiiiiiili�_ !l■! ■■■■■■■■■■■■■ii■■■■■i■■ iii■■■\I►1■■1 iiiiiiiiiiiiii■iii■ ■■■■■■fi■■IL ■■■■■■■■■■■■■■■■■■■ ■■■■■■■■■■■\ ■■■■■■■■■■■■■■■■■■■ iiiiii■ i■■i■► iiiiiiiiiiiiii■iii■ , iiiiii■ iiiiii► iiiiiiiiiiiiii■iii■ ■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■ iiii■iiii■iiii■i ■L ■i■ ■iiiiiiiiiiiiiiiiiiiiii■iii■ Ciiiii■ ii■i■ii■i iiii "i■ ■iiiiiiiiiiiiiiiii■iiii■iii■ ..ii.iii■iiii■■■■■■ "�■■i■iir�ii■■i■■■iii■iiiiiiiii Eiiiii■ ii■i■i■■iiiii\ I ■i*Miia�iii■iiiii■iiii■iii■ ..■■iiii■iiii■i■i■■i� '�iGiiiii►`iiiiiiii■iiii■iii■ 1 ■■■■■■i��i!■■i■■■!■i■iiii �■■■■■■■i\i■■i■■ice■■■iiii■ iiiiii■ ii■i■ii■i ■i■ii■i■ ■i ■iiiiiiii��iiiiiiiiii■iii■ ■■■■■■■■■■!■■■■■■!■■■■!■■■■■■■■■■■■■■iii■■i■■■■■■■■■ iiii■iiii■iiii■i ■i■ii■i■ ■iiiiiiiiiiiiii►iiiiii■iii■ iiiiii■iiiiiiiii ■iiiiii■ ■iliiiiiiiiiiiiii�iiiii■iii■ iiiiii■ ii■i■i■■i ■iiiiii■ ■i ■iii iiiii iiiiiii���ii■i■i■ iiimmIIIMMmMmMMmM ■ i■■■■■■■Ii ■i■iiii am am 1 ■■■■� ■■■■■i■■■■ 11 I If 11 11 11 of .11 11 :11 •11 III so II 1 • ' - • ■ • ■ - . Figure 1— Representative profile depicting construction template of dune and pad An analysis was also performed to compare the amount of 'recreational' beach, which was defined as the width from elevation +7 ft NAVD88 to MHW (+1.8 ft NAVD88)), to determine how the construction of the proposed renourishment template would affect the amount of recreational beach available. The widths of recreational beach were determined for the 2016 profiles (pre -Hurricane Matthew), pre -construction profiles (June 2019 survey), the proposed construction template profiles, and representative SBEACH 2- yr return period storm equilibrated profiles of the construction template, see Table 2. One important caveat to mention in this analysis is that the 2019 pre -construction profile represents the beach in a state of erosion, as many profiles are currently without a dune. Therefore, these profiles will have more recreational beach available since the beach face is on a shallower slope and the +7 ft NAVD88 contour has been pushed landward due to dune erosion. When comparing the width of recreational beach available in the 2019 pre -construction profiles to the SBEACH equilibrated profiles the majority of the profiles show a reduction in the recreational beach width. A more representative comparison would be the recreational beach width that was present in 2016 when a dune existed with the SBEACH equilibrated profiles. This 2016 survey was taken before Hurricane Matthew at a time when a dune was present along a majority of the profiles. When comparing 2016 profiles to the SBEACH equilibration profiles the majority of profiles show maintaining or increasing the recreational beach width. Plots are provided to show how the construction template compares with the historical profiles. It is important to note that the construction template is designed for a 25-year return period storm level of protection, this did not exist across much of the island in 2014 (date of earliest survey). The construction template in many cases will restore what was there in 2016 (before Matthew), however in many cases it will add to what was there before Matthew. This is the intent of the design so that the Town will be in a better position to recover from future storm events. Please also recall that the Town's plans involve the construction of a dune repair/recreational berm project in the future that should greatly enhance the recreational beach. Even if this project were to never materialize, we could expect that the same behavior that has happened recently would occur, and the recreational beach would be fed by the dune during larger storm events. Table 2 — Recreational Beach Width Values Recreational Beach Width from +7' NAVD88 to MHW Station Pre -Matthew 2016 Pre -Construction June 2019 Construction Template SBEACH 2-yr Storm Construction Equilibration 300+00 67 93 63 310+00 51 82 104 320+00 59 86 104 330+00 59 77 104 66 340+00 53 78 104 350+00 56 67 104 360+00 47 66 104 370+00 48 71 104 53 380+00 53 171 104 390+00 62 70 104 400+00 74 81 104 410+00 59 74 104 67 420+00 79 66 104 430+00 98 49 104 440+00 90 86 104 450+00 90 86 104 61 460+00 71 85 104 470+00 58 75 104 480+00 71 80 104 66 490+00 64 81 104 500+00 77 72 104 Average 66 81 102 63 Minimum 47 49 63 53 Recreational Beach Width from +7' NAVD88 to MHW Pre -Construction Construction SBEACH 2-yr Storm Station Pre -Matthew 2016 June 2019 Template Construction Equilibration Maximum 98 171 104 67