Sea Level Rise Subcommittee Meeting
Subcommittee of Town of Kiawah Island Environmental Committee
Town Meeting Hall
September 27, 2017
Minutes
Persons attending meeting
John Leffler, Subcommittee Chairman Diana Mezzanotte, Town Council Member
Bob Cheney Jim ChitwoodWill Connor (KICA)David Elliott
Jane EllisMatt Hill (KICA)Jim Jordan (TOKI) Jack Kotz
David Pumphrey Lyn SchroederBruce Spicher
The July 17, 2017 subcommittee meeting minutes were approved on a motion by Ms. Mezzanotte and a second by Mr. Jordan.
Doar and NOAA Meeting Summaries
Ms. Mezzanotte reported on a meeting with Dr. William Doar.
Ms. Schroeder reported on a meeting with Doug Marcy of NOAA.
(Full written summaries of the Doar and NOAA meetings are available separately.)
Union of Concerned Scientists Video Call Summary
Mr. Cheney reported on a video conference with three of the seven authors of the Union of Concerned Scientists (UCS)publications (February 7 and July 7, 2017.) The Post and Courier referred to the UCS studies in the newspaper article which showed Kiawah Island to have the largest percentage of chronically flooded lands in the state of South Carolina.(The article mistakenly excluded Seabrook Island, which was combined with Kiawah in the study.)
The authors summarized the methods used in their study,focusing on information specific to Kiawah Island.
UCS used two methods to study minor coastal flooding: individual tide gauge records and NOAA Digital Elevation Maps (DEMs).
The first method used the National Weather Service definition of nuisance flooding for Charleston: water level 1.25 feet (0.38 m) above mean higher high water (MHHW). This height was exceeded an average of 23 times per year during 2001-2015. This does not necessarily mean 23 days because flooding can happen 2 times per day concurrent with high tides. Each flood counts as an event. When an intermediate rate of SLR scenario is taken into account, this method forecasts that Charleston could see 74 flood events in 2030and 180 flood events in 2040.
In the second method, NOAA DEMs were used to determine the percentage of a community’s area in which nuisance flooding occurs at least 26times per year. The percentage of chronically flooded area on Kiawah/Seabrook is forecasted to be 11% by 2035, and 41% in 2060.
Edisto Island is expected to be the second worst area of chronic flooding in the state.
The UCS analyses used Standard Metropolitan Statistical Area (SMSA) designations to define areas of study. SMSAs are blocks of land defined by the US Census. Kiawah and Seabrook Islands’ percentage of chronic floodingis higher than other areas of the state because Kiawah is a long, narrow, flat island with plenty of wetlands as well as ocean and river frontage. In contrast, Hilton Head has beach front, but also has a large interior land mass with higher elevation. And, Hilton Head is a largerisland than Seabrook and Kiawah. Thus, in 2060, UCS suggests 12% of Hilton Head will flood while in the same time period, 41% of Kiawah/Seabrook floods. However, Hilton Head and Kiawah/Seabrook would each have about 8 square miles of flooded area. Since Hilton Head’s SMSA is a larger area than Kiawah/Seabrook’s SMSA, it’s percentage of flooded land is smaller. Edisto Island’s SMSA includes a good deal of inland area, which may account for its lower percentage of flooded land relative to Kiawah/Seabrook.
Kiawah/Seabrook Islands’ flooding percentages are significant, but not nearly as bad as some other coastal regions. For example, in some communities of Louisiana and Maryland/Chesapeake Bay, flooding predictions exceed 90% by 2060.
It was unclear if the marsh lands and ponds were included as areas subject to chronic flooding. NOAA’s DEM may not be treating low lying areas correctly. Ponds account for 5-7% of Kiawah’s acreage. Most flooding occurs outside the land area of the ponds. UCS used the Fish and Wildlife Service’s National Wetland Inventory maps to locate marshes and wetlands.
Currently Kiawah Island experiences little to no nuisance flooding while Charleston had about 50 flooding events in 2016. Nonetheless, the UCS forecasts still show Kiawah to be subjected to increased nuisance flooding and higher percentages of land flooded than Charleston. UCS posited that there may be two different flooding thresholds. It is possible that the 1.25 ft. above MHHW threshold is too low for Kiawah/Seabrook and that the threshold for the islands maybe be higher, perhaps 2 feet.
A new national climate assessment is expected in 2018. Ice melt is increasingly recognized as a significant contributor to rising sea levels. As more data on ice melt becomes available and accepted, SLR assessments will include a new category called “Extreme.” Extreme scenarios will account for faster rates of SLR driven by melting ice.
Climate Impact Lab Report, University of Chicago
Mr. Pumphrey summarized the Climate Impact Lab’s study. The lab, located at the University of Chicago, attempts to quantify the economic impact of climate change, and to identify areas experiencing positive or negative economic impact. He noted that Kiawah Island is too small an area for this study to produce precise, localized economic impact data. Mr. Kotz, who has also reviewed the Climate Impact Lab’s report, noted that the study identifies the South and Southeast as economic losers while the Midwest and Northwest are expected to see positive economic impact.
Mr. Chitwood noted that it is likely that for the next 50 years the island will need to rely upon its own resources to manage problems. Later we may be able to count on federal or other outside sources to provide resources. The problems will take decades to manage.
Professor Norman Levine, Geographic Information Systems, College of Charleston Meeting
Mr. Jordan reported on a meeting with Profession Norman Levine. Professor Levine works with local governments on hazard planning. Currently Professor Levine is working on a federally funded study assessing all things related to flooding. Kiawah Island is included in the study, and we can get access to the information for free.
His study models different SLR scenarios using 1 x 1 meter DEMs. The study assesses SLR, rainfall, drainage,upstate rain affecting down state land, storm surge, and flooding from upstream. His models consider how all these different water events might interact with one another. Part of his work considers the impact of water damage and flooding. For example, cars begin floating when flood depths reach 8-12 inches.
Professor Levine noted NOAA and UCS use connectivity models, but these models do not account for storm drains which allow water to flow into an area even if the area is protected by other barriers. If storm drains flow water into an area, connectivity models underestimate the flooding risk.
He expects more detailed topography maps to become available in winter 2017-18. These maps will have 3-4 pixels/ inch and will be sufficiently detailed to show curbs, stop signs, 1st floor home elevations, locations of pipes, storm drains, drain elevations and more. Levine has a survey grade unit available to collect data. The survey data can be collected by someone riding a bike.
Professor Levine expects his study to be completed in spring 2018. He is willing to come out and show the SLR subcommittee his work.
Mr. Connor’s Presentation on Ponds
Connor heads KICA’s Major Repairs and Replacements Department. He has worked there for 5 years. His responsibilities exclude water and sewer which are managed by Kiawah Island Utility.
Drainage System: Kiawah Island’s 125 ponds are mostly interconnected. There are two major drainage basins and several smaller ones. The major western most main drainage basin flows out at Inlet Cove. The other major basin, largely serving the area behind the V-gate to Canvasback Pond, drains at Canvas Back Pond, near Flyway & Governor’s Drive by the fire station.
Other drainage basins include Rhett’s Bluff, Egret Pond, The Preserve, and Ocean Park. Sparrow Pond drainage basin includes The Timbers.
Most of Kiawah Island’s ponds are at the same elevation. Our ponds work on head pressure so flow rates vary depending on the height of water in a pond.
Mr. Connor believes utilities and sewage facilities are high enough to avoid being flooded.
The drainage system can accommodate 6 inches or more of rainfall within 24 hours. Kiawah’s drainage system has twice the capacity of typical storm system ponds. Storm surge fills the ponds immediately, and produces washouts (due to rushing water) and flooding. During Hurricane Irma, the storm surge came over the roads and filled the ponds.
Mr. Connor noted that 2015’s historic rainfall and Hurricane Irma’s storm surge happened at, or during high tides. High tides make it harder to drain the ponds as the outfalls allow water to flow into the island from the ocean and river. KICA could have drained the island in October 2015 better had they been able to open and close the gates every six hours, but with the manual spinning wheel gates they cannot open and close all the gates in time.
If rain falls at the V-gate, is has three miles to travel before flowing out to the river through outlets.
KICA received suggestions from consultants to add more outlets to the system in order to reduce the distance water must travel to flow out of the system. One new outlet for the main western drainage basin has been identified. KICA put this new outlet into the 2018 budget for consideration and may build it in 2019.
Gates: Drainage gates are opened and closed by manually operated spinning wheels. KICA is designing an automatic control which will operate remotely and can be programmed to open and close with the tides. The control unit will have its own generator allowing it to operate when the power goes out. The remote control is being designed this year (2017), and expected to be built and installed in 2018. The device will be mounted on the Beachwalker/Inlet Cove outlet. The Canvasback drainage basin is slated to be the next automatic control installation. Once installed, the Lakes department will be in charge of operating the gates.
Drainage Pipes & Pond Flushing: Pipes are placed to sit 1 foot below the water’s surface when ponds are at normal levels. The top of drainage pipes are 1.2 to 3.2 feet above mean sea level. High tides flow about 2-3 inches of water into the ponds, effectively flushing pond water. The amount of water the actually flowing into the ponds depends upon individual tide heights. During spring tides KICA personnel close the gates to prevent too much in flowing water. Rain can produce flooding during high tide periods.
The largest pipes are 54 inches in diameter, so the bottom of the pipe is below sea level.
Pipes are about 40 years old (installed by the Kuwaitis.) Ocean Park has concrete pipes. Concrete pipes have a 100 year life. Corrugated metal pipes, (the old drainage system) and PVC pipes can be drilled through, often without the knowledge of the driller.
KICA sends in a Go Pro camera to see what is in the pipes and assess the condition of the pipes.
SLR could impair drainage pipes’ ability to convey stormwater.
ARB will not approve visible pipes in the ponds. A decision to raise the pipes would be a substantial project requiring digging up golf courses, roads and yards. (Recall, the system is gravity operated.)
Slip Lines: Many of Kiawah Island’s drainage pipes have slip lines. A slip line is a new pipe of slightly smaller diameter slipped into the old pipe of larger diameter. It is possible that the slip lines could impair KI’s drainage capacity because the slip lines are slightly smaller in circumference than the original drainage lines.
Smaller diameter pipes (18-24 inch diameter) are repaired by sliding resin liners in place. Liners are made of resin which must be kept cold. Once the resin heats up it begins to set, so installers have a short time to slide it into place. The liner is cured with steam once it’s inserted into the pipeline. The liner cures and cools for a few days. Once the liner cures, you effectively have a new PVC pipeline.
Larger pipes are repaired using a cement spinning process. Near the 12th tee box of Cougar, KICA cleaned out a 54 inch circumference pipe and repaired it. To repair large diameter pipes KICA spins a cement and adhesive mixture at 9,000 psi inside the existing metal pipe. The mixture adheres to the old pipe, and once it dries, produces the equivalent of a new cement pipe within the old metal pipe.
Problems: Sea Marsh is a major failure. Hurricane Irma’s tidal storm surgeovertopped the road, and water ran down the right of way eroding the bank. The pipes were loose. KIU’s water main blew out. On the other end of Sea Marsh there is a pipe off the roadway which was clogged with pinestraw. The drain pipe on the golf course collapsed. They plan to run a liner in from the street, about 400 feet, into the golf course. This worked is expected to begin in October, 2017.
Clogged pipes can be vacuumed however they must be structurally strong enough. Old, crumbling pipes must be washed with a hose. Many pipes are clogged with pine straw which washes into the drainage system.
Many of the old and often failed, metal pipes are impeded by sediment sandbars at the head of the pipe. Frequently the sandbar is so large it stands above the top of the pipe. Removing sand from the ponds requires an OCRM permit because ponds contain brackish water; OCRM requires permits for digging in areas of salt and brackish water. Permits take about 6 months to process, so KICA has proactively applied for permits to dig 1/3 of the ponds on the island.
Near Trumpet Creeper sand and marsh mud is above the top of the pipes. In the area of 1 Governor’s and Flyway all the pipes are failing.
In the last few years a number of failures have been prompted by degraded pipe materials becoming destabilized when rushing water from floods due to rain or high storm surge flows through the pipes.
Connor estimates KICA will continue to replace metal pipes for the next 15 years. All of the pipes under Turtle Point need to be replaced.
Cougar Golf Course repair: A sinkhole developed off the cart path on the 11th fairway at Cougar Point near Low Oak Wood. KICA injected hydroactive grout which expands 8x. In attempting the repair, they discovered there was no pipe left in a section about 20 feet long.
On the 12th tee area, a Go Pro camera inserted into the pipe found a large belly in the pipe. 2/3 of the metal pipe was gone and it was filled with sand. There was a large sandbar in front of the 12 tee box drainage pipe. KICA dug up part of Cougar Point to find the box. KICA needed to dewater ponds to replace the collapsed pipe. Ponds are dewatered by floating out bladders which are then filled with pond water. Once they located the box, KICA facilitated the repair and installed a riser. KICA will replace vegetation damaged by digging if property owners request repair.
SLR and infrastructure: KICAcontacted an engineering firm with SLR expertise. This firm consults with NYC where they have considered building a berm around lower Manhattan which has storm surge gates to protect the roads.
Action Points and Other Discussion
Committee members discussed freeboard allowances, base flood levels and new flood map designations. Mr. Spicher noted new flood maps may identify low wave action areas from Rhett’s Bluff to Ocean Park. Base flood level plus one foot of freeboard may lead to a requirement that first floors of buildings be 15 feet high. He noted Isle of Palms required elevations of 15 feet (plus or minus.)
Mr. Elliott noted homeowners risk vitiating their flood insurance policies if they build into the sub levels of their homes. Mr. Spicher believes that some policies allow entrance rooms on lower levels
Planning Parameters: Mr. Leffler noted 30-50 year time framesfor planning is a common time period from study to study. He also noted that many organizations adopt forecasts of 1.5 to 2 feet of SLR rise for planning purposes. Folly Beach uses 3 feet. Mr. Chitwood noted that Folly Beach’s choice may reflect their risk tolerance; infrastructure flooding is usually assessed differently than flooding of residential neighborhoods.
Mr. Pumphrey notes the UCS authors made it clear that they didn’t like to tell communities what to do since action plans are all related to the level of risk a community was willing to take on.
Mr. Leffler notes there are two types of flood events to plan around: surges which might be protected by a structure and rain fall flooding.