The URL can be used to link to this page

Home My Public Portal AboutTybee Dune Restoration_SPA Presentation Packet_11x17_2-15-18.pdfTYBEE ISLAND DUNE RESTORATION 2018 15 FEBRUARY 2018 PRESENTED BY: THOMAS ANGELL, ASLA - VERDANT ENTERPRISES, LLC - AGENT ALAN ROBERTSON - CITY OF TYBEE ISLAND BEACH TASK FORCE - CITY OF TYBEE ISLAND PAGE 2 - PROPOSAL FOR IMPROVED SHORELINE PROTECTION PAGE 3 - DEFINITION OF SCOPE, IMPACT AREA & JUSTIFICATION PAGE 4 - EXISTING CONDITIONS - HURRICANE DAMAGE PAGE 5 - EXISTING CONDITIONS - 16TH STREET WASHOUT PAGE 6 - EXISTING CONDITIONS - VEHICULAR ACCESS PAGE 7 - EXISTING CONDITIONS - PEDESTRIAN PROMENADE PAGE 8 - DESIGN SOLUTION - DUNE RESTORATION PLAN PAGE 9 - DESIGN SOLUTION - BEACH - BERM - PEDESTRIAN PROMENADE INTERFACE PAGE 10 - DESIGN SOLUTION - VEHICULAR ACCESS PAGE 11 - DESIGN SOLUTION - SAND RETENTION STRUCTURES PAGE 12 - DESIGN SOLUTION - PEDESTRIAN PROMENADE PAGE 13 - DESIGN SOLUTION- PEDESTRIAN PROMENADE STORMWATER PAGE 14 - SUMMARY TABLE OF CONTENTS: PAGE 2 OF 14TYBEE ISLAND DUNE RESTORATION 2018PROPOSAL FOR IMPROVED SHORELINE PROTECTION We are requesting authorization to restore the dune field from immediately south of 15 ½ Street extending approximately 1800 linear feet to immediately south of 19th Street, including closing vehicular access at 18th Street, adding subsurface stabilization at 19th Street to support access of Public Safety and Department of Public Works vehicles, and enhance the landscaping on the landward side of the impact area. In its duty to promote beach preservation and the prevention of shoreline erosion, the Beach Task Force examined each of the City’s 27 public beach access points. As part of the assessment, the access points were evaluated based on Type of crossover (Pedestrian or Vehicular), Condition of the crossover, whether it was Critical to emergency access or heavy pedestrian traffic during season, its Flooding potential, and if we could readily Dam the access point in the event of a major weather event. Private crossovers were not evaluated at this time but should be included at a future date. In summary, the condition of our dune system is good but has been seriously weakened by both Hurricanes Matthew and Irma. There are several points at which dunes should be improved. Most importantly, there are five vehicle access points that weaken the dune system dramatically because they are relatively large and “at grade”. During Hurricanes Matthew and Irma the City realized significant flood events at these vehicle access points, specifically 19th, 18th, Center, 3rd, and 2nd Streets. For purposes of this request for a Letter of Permission, we are limiting the impact area to the South end of the shoreline. As we consider our recommendation we are mindful of City emergency vehicle access (fire,police, lifeguard), adequate public access (number and locations), ADA access (height, degree of slope, and wheelchair accessibility) requirements, GADNR Shoreline Protection and Coastal Marshlands Protection requirements, and Public Works access. We also considered our recommendation in the context of the broader City Public Works Plan for appropriate storm water management, the City Emergency Management Plan for evacuation during a major storm event, and the City budget. This recommendation from the Beach Task Force was approved by the City Council at their September 28, 2017 meeting. PAGE 3 OF 14TYBEE ISLAND DUNE RESTORATION 2018DEFINITION OF SCOPE, IMPACT AREA & JUSTIFICATION 0 100 200 400 SCALE: 1"=200' We propose to use the current 18th Street crossover to bring sand onto the beach, placing it from approximately just south of the 15 ½ Street crossover to 19th Street. We estimate using dump trucks and front end loaders to place the sand along the length of the project, extending approximately 75’ seaward from the most seaward point of the DNR jurisdiction line. The outlined area denotes the approximate loss of the seaward dune field from Oct. 2016 (date of Google Earth image). The length is approximately 1800 linear feet extending from just south of the Pier at 16th Street to approximately 30 yards south of 19th Street and varying from 30’ to 50’ in width. The height of the dunes varies from approximately 1’ to 6’. APPROXIMATE SPA JURISDICTION LINE APPROXIMATE PROJECT LIMIT: +/- 492,285 SF (≈11 ACRES) APPROXIMATE PERVIOUS SURFACE (BEACH & DUNES): 340,930 SF (≈7.5 ACRES, 68% OF TOTAL AREA) APPROXIMATE IMPERVIOUS SURFACE (PARKING LOT & PAVILION): 151,355 SF (≈3.5 ACRES, 32% OF TOTAL AREA) 15TH 1/2 STREET CROSSOVER18TH STREET19TH STREET18TH PLACE17TH STREET17TH PLACETs CHU TERRACESILVER AVENUEIZLAR AVENUE16TH STREETATLANTIC AVENUE15TH STREET0 100 200 400 SCALE: 1"=200'N PAGE 4 OF 14TYBEE ISLAND DUNE RESTORATION 2018EXISTING CONDITIONS - HURRICANE DAMAGE SAND WASHOUT AT 18TH STREET VEHICULAR ACCESS HURRICANE IRMA STORM SURGE STORM SURGE BREACHING UNSTABILIZED DUNES STORM SURGE AT TYBRISA CIRCLE (16TH STREET WASHOUT HURRICANE IRMA STORM SURGE UNSTABILIZED DUNE STORM SURGE DEGRADATION PAGE 5 OF 14TYBEE ISLAND DUNE RESTORATION 2018EXISTING CONDITIONS - 16TH STREET WASHOUT The section between the Marine Science Center and 18th Street represent the most oft used and populous area of Tybee Island. During Hurricanes Matthew and Irma, this area experienced a massive washout and complete destruction of the constructed dune system, exposing and damaging local businesses crucial to Tybee Island’s tourist economy. N500’17TH STREETSILVER AVENUEIZLAR AVENUE16TH STREETTs CHU TERRACE17TH PLACE PAGE 6 OF 14TYBEE ISLAND DUNE RESTORATION 2018EXISTING CONDITIONS - VEHICULAR ACCESS The 18th Street access is currently used by emergency vehicle access but in doing so, they are going against traffic on the Strand to reach the Beach Emergency Station on the Tybrisa Circle, creating a difficult and dangerous situation. This access also begins at a choke point for traffic as vehicles come off the Strand going out 18th and vehicles also come in 18th. The dune field has been severely eroded from Hurricanes Matthew and Irma. By closing 18th we remove one of the three most critical flooding points realized during Storms Matthew and Irma and provide adequate and more effective emergency vehicle and DPW vehicle access to and from the beach. Of particular note is that sand is most effective in preventing storm surge flooding when part of an entrenched dune system. It is vital that we build an integral dune system, with a combination of engineered dunes, restoring dunes, and adding improved dune fencing.N500’18TH STREET18TH PLACE17TH STREET17TH PLACETs CHU TERRACESTRAND PAGE 7 OF 14TYBEE ISLAND DUNE RESTORATION 2018EXISTING CONDITIONS - PEDESTRIAN PROMENADE CLUTTERED SIDEWALK - UNSIGHTLY BACK OF DUNES - POOR SIGNAGE - NO SHOWER OR FOOT WASH The existing concrete collector walk from the parking area to the beach access points is lacking in aes- thetics and functionality. The street furnishing such as benches, waste receptacles, lights and parking meters are randomly placed and in conflict with the pedestrian use of the promenade. The continuous sand-fence is unsightly and the quality of the back dune vegetation is variable. The 10’-30’ swathe of bare sand between the back of existing dunes and the walk is bare and under utilized. There is a great opportunity to upgrade both the usability and aesthetics of this area with hardscape and planting im- provements. Storm water infiltration can also be improved. The use, enjoyment, services and orientation of both visitors and residents can also be enhanced by an integrated design.N500’18TH STREET17TH STREET17TH PLACETs CHU TERSILVER AVEIZLAR AVE16TH STREETWEAK AND DAMAGED SIGNAGE WITH INADEQUATE WASHING FACILITIES WEAK LANDSCAPE/SAND STABILIZATION AT PAVILION ENTRANCE OBSTRUCTED AND DATED PROMENADE PAGE 8 OF 14TYBEE ISLAND DUNE RESTORATION 2018DESIGN SOLUTION - DUNE RESTORATION PLAN 0 100 200 400 SCALE: 1"=200' 0 100 200 400 SCALE: 1"=200'18TH STREET18TH PLACE17TH STREET17TH PLACETs CHU TERRACESILVER AVENUEIZLAR AVENUE16TH STREETATLANTIC AVENUE19TH STREET12 3 DUNE RESTORATION & MAINTENANCE: DUNE 1: 43,475 SF @ 8’ AVERAGE HEIGHT = +/- 22,000 TONS (+/-11,000 CUYDS) OF SAND DUNE 2: 27,870 SF @ 6’ AVERAGE HEIGHT = +/- 10,000 TONS (+/- 5,000 CUYDS) OF SAND DUNE 3: 1,500 SF @ 4’ AVERAGE HEIGHT = +/- 8,000 TONS (+/- 4,000 CUYDS) OF SAND SAND RETENTION SYSTEM: +/- 3,800 LF PLANTING AND IRRIGATION (SAND STABILIZATION): +/- 190,000 SF SUBSURFACE STABILIZATION (VEHICULAR ACCESS): (1) PERMASHIELD SYSTEM - 6’ HT x 70 LF CROSSOVER DUNE: 84’ DEEP x 70’ WIDE @ 7’ MAX HEIGHT = 158 TONS (78 CUYDS) OF SAND EQUIPMENT: - BULLDOZERS - DUMP TRUCKS - BACKHOE LOADER - SKID-STEER LOADER - CEMENT TRUCKS (CROSSOVER) - HAND SHOVELS - RUBBER TIRE LOADERS - VIBRATORY SMOOTH DRUM ROLLER 1 2 3 PAGE 9 OF 14TYBEE ISLAND DUNE RESTORATION 2018DESIGN SOLUTION - BEACH - BERM - PEDESTRIAN PROMENADE INTERFACE RESTORED DUNE - 50’-75’ WIDTHAVERAGE ANGLE OF REPOSE: 30°-34°STABILIZED WITH NATIVE, XEROPHYTIC, SALT TOLERANT SPECIES *NEW PEDESTRIAN LOUNGE PADS- +/-10’x10’ EXISTING SIDEWALK EXISTING PARKING LOTEXISTING BEACH ANGLE OF REPOSE: 30°-34° ≈ 1.5:1 RESTORED DUNE - 6’ - 8’ HT* BUFFER ZONE: PROTECTIVE PLANTING & SAND RETENTION STRUCTURES *HEIGHTS & LOCATIONS VARY http://travel.home.sndimg.com/content/dam/images/travel/fullset/2014/05/06/dd/top-10-southern-california-beaches-venice-beach.rend.hgtvcom.1280.720.suffix/1491584248480.jpeg PAGE 10 OF 14TYBEE ISLAND DUNE RESTORATION 2018DESIGN SOLUTION - VEHICULAR ACCESS 0 100 200 400 SCALE: 1"=200'NAt 19th Street we propose to build a dune crossover that can provide effective access to Police, Fire, Lifeguard, and Department of Public Works vehicles. We will also use this crossover for beach access to movie productions. The crossover will be positioned on the landward side of the existing dune field. Guardian Retention Systems uses a steel welded proprietary installation sled to assist with the erection of sand field 6’ PermaShield™ system. Rubber Tire loaders will access the system from pavement and pour beach quality sand into the system utilizing the installation sled’s hoppers. After filling the system, the Rubber Tire loaders will construct the remainder of the crossover. A vibratory smooth drum roller will compact the crossover dune. After compaction, Geofrabric will be installed over the entire access, followed by Bipod85 Geogrid. The Geogrid will then be filled and covered with an additional 6” of sand, with that 6” of sand extending throughout the entire crossover. The entire crossover will then have a final pass of vibratory compaction. *Graphics & text courtesy of Guardian Retention Systems 18TH STREET19TH STREET18TH PLACE0 100 200 400 SCALE: 1"=200' APPROX. SUBSURFACE STABILIZATION PAGE 11 OF 14TYBEE ISLAND DUNE RESTORATION 2018DESIGN SOLUTION - SAND RETENTION STRUCTURES EXISTING SAND RETENTION STRUCTURES: +/- 1,303 LF PROPOSED DUNE FOOTPRINT PROPOSED VEHICULAR ACCESS STRUCTURE PROPOSED SAND RETENTION STRUCTURES: SINGLE LINE STRUCTURE: +/- 1,975 LF OPEN LINE STRUCTURE (TURTLE FENCE) +/- 1,780 LF N500’17TH STREETSILVER AVENUEIZLAR AVENUE16TH STREETTs CHU TERRACE17TH PLACE18TH STREETTYBEE ISLAND WIND ROSE EXISTING SAND FENCE OPEN LINE FENCING STRUCTURE (TURTLE FENCE) 0 100 200 400 SCALE: 1"=200' 0 100 200 400 SCALE: 1"=200'NPREVAILING WIND 18TH STREET19TH STREET18TH PLACE17TH STREET17TH PLACETs CHU TERRACESILVER AVENUEIZLAR AVENUE16TH STREETPROPOSED SAND RETENTION STRUCTURES PAGE 12 OF 14TYBEE ISLAND DUNE RESTORATION 2018DESIGN SOLUTION - PEDESTRIAN PROMENADE http://seaturtlelighting.net/wp-content/uploads/2012/02/sea-turtle-lighting-banner-4.png NEW SEATING NODES @ ABOUT 100’ O.C. = +/-11 NEW NODES EACH NODE = +/- 10’x15’ = 150 SF EACH = ADDITIONAL 1,650 SF OF IMPERVIOUS SURFACE MATERIAL Stormwater infiltration can be enhanced by the creation of interdunal swales and rain gardens created to handle shower run-off as part of a nuanced grading plan. Proposed improvements will meld with existing as selective fill and plantings will be done in gaps within the existing dune system such that the entire area is well-stabilized. Great opportunity exists to utilize a more diverse palette of appropriate native dune species to respond to slope aspect, moisture gradient and aesthetic considerations. Defensive plantings such as opuntia and yucca may be used to dissuade unauthorized access in combination with the selective use of sand-fencing. Migration of nuisance sand may be diminished with a sand-retention system, more thorough revegetation and the creative disposition of the dune fencing. Possible streetscape furnishing changes will consider greater emphasis on community interaction, pedestrian comfort and environmental education. In combination with an integrated signage package, this area can be the pride of the island and an exemplar for other projects in the region. PAGE 13 OF 14TYBEE ISLAND DUNE RESTORATION 2018DESIGN SOLUTION - PEDESTRIAN PROMENADE STORMWATER Outdoor showers, rain garden & shallow well may be located near the existing lavatory facilities. Shower/foot washing stations may be placed on an elevated wood or composite wood platform. Possible use of multiple shower heads to allow more than one user to access this facility. A new shallow well could serve first to supply water to the temporary irrigation system and later to be repurposed to supply the new outdoor showers. The area below the bathing platform will be graded to collect & direct shower runoff to a newly created rain (bog) garden. The rain garden with be creatively shaped & planted with native plants for interest & stabilization. This bog garden will also serve to demonstrate creative and beautiful water runoff management with additional education signage. APPROXIMATE SHOWER/WELL/RAIN GARDEN LOCATION COLLECTED SHOWER WATER NATIVE BOG PLANTS AMENDED SOIL DRAINAGE MEDIA WATER PERCOLATES18TH ST17TH ST17TH PLTs CHU TERSILVER AVEIZLAR AVE16TH ST PAGE 14 OF 14TYBEE ISLAND DUNE RESTORATION 2018SUMMARY APPROXIMATE PROJECT LIMIT: +/- 492,285 SF (≈11 ACRES) APPROXIMATE PERVIOUS SURFACE (BEACH & DUNES): 340,930 SF (≈7.5 ACRES, 68% OF TOTAL AREA) APPROXIMATE IMPERVIOUS SURFACE (PARKING LOT & PAVILION): 151,355 SF (≈3.5 ACRES, 32% OF TOTAL AREA) DUNE RESTORATION & MAINTENANCE: DUNE 1: 43,475 SF @ 8’ AVERAGE HEIGHT = +/- 22,000 TONS (+/-11,000 CUYDS) OF SAND DUNE 2: 27,870 SF @ 6’ AVERAGE HEIGHT = +/- 10,000 TONS (+/- 5,000 CUYDS) OF SAND DUNE 3: 1,500 SF @ 4’ AVERAGE HEIGHT = +/- 8,000 TONS (+/- 4,000 CUYDS) OF SAND SAND RETENTION SYSTEM: EXISTING SAND RETENTION STRUCTURES: +/- 1,303 LF PROPOSED SAND RETENTION STRUCTURES: SINGLE LINE STRUCTURE: +/- 1,975 LF OPEN LINE STRUCTURE (TURTLE FENCE): +/- 1,780 LF PLANTING AND IRRIGATION (SAND STABILIZATION): +/- 190,000 SF SUBSURFACE STABILIZATION (VEHICULAR ACCESS): (1) PERMASHIELD SYSTEM - 6’ HT x 70 LF CROSSOVER DUNE: 84’ DEEP x 70’ WIDE @ 7’ MAX HEIGHT = 158 TONS (78 CUYDS) OF SAND NEW SEATING NODES: EACH NODE = +/- 10’x15’ = 150 SF EACH (@ ABOUT 100’ O.C. = +/-11 NEW NODES) ADDITIONAL 1,650 SF OF IMPERVIOUS SURFACE MATERIAL = ADDITIONAL 1% OF IMPERVIOUS SURFACE AREA