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Flood Mitigation and Sea Level Rise Adaptation
In the spring of 2017, the Town of Kiawah Island’s Environmental Committee formed a subcommittee to proactively identify steps our community could take to address increased flooding frequency and adapt to future water level changes. This report attempts to identify ways in which Kiawah might be impacted by rising seas and changing weather patterns, to assess potential vulnerabilities to those changes, and to suggest practical actions that Kiawah might take to mitigate those vulnerabilities and ensure a prosperous future. This report does not attempt to sugar-coat the challenges being faced by all southeastern coastal communities. The good news is that there are many practical and useful actions Kiawah property owners and governing bodies can take to preserve our fully functioning and beautiful island.
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
The Flood Mitigation and Sea Level Rise Adaptation report can be found in its entirety here.
The topics below are excerpts from the report.
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
The Flood Mitigation and Sea Level Rise Adaptation report can be found in its entirety here.
The topics below are excerpts from the report.
FAQs
The Sea Level Rise data viewer is a tool that is providing the City of Charleston decision-makers with a preliminary look at sea-level rise. Data depicting the predicted levels of sea-level rise was developed and provided by NOAA Coastal Services Center in Charleston, SC using 2007 and 2009 LiDAR data for Berkeley, Charleston, and Dorchester counties.
Once you open the viewer, you can use the slider bar to see how various levels of sea-level rise will impact this area. Levels represent inundation at high tide.
City of Charleston Sea Level Rise Viewer
The Town is working with the College of Charleston to develop its own higher resolution sea level rise viewer to predict impacts from future flooding events and pinpoint specific areas of concern.
A well planned and executed stormwater management system is critical to handling flooding events on the island. Kiawah is fortunate to have an extensive system of interconnected ponds that can accommodate a rainfall event equivalent to a 100-year flood. Stormwater moves through the ponds and leaves the island through outfalls into the marsh and river. In the future, higher tides will decrease the effectiveness of the pond system by slowing the flow of water from the ponds into the outfalls and out to the estuary. Work to repair clogged and deteriorating pipes are underway and will improve the flow of water into ponds and drainage system.
Recommendations include continued attention to the integrity of the drainage system through reviews of the appropriate size, proactive maintenance and necessary repair and replacement of pipes is critical. The report supports current plans to automate outfall gates and encourages consideration of one or more additional outfalls.
Other recommendations relate to reducing the obstruction of drains, swales, and pipes, investigating the use of physical structures in localized areas to slow nuisance flooding or storm surges, using the best available GIS tools to improve stormwater drainage, working with neighborhoods on location-specific challenges, adopting principles of low impact development, and planning for the resources to support these efforts.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
The bridge at the round-a-bout during Tropical Storm Irma
Roads and bridges that dependably allow vehicular movement are essential for quality of life and for public safety. Island roads and bridges that maintain their reliability during storm events or quickly recover after the event are very valuable assets. It is apparent from Kiawah’s experience with recent storms that some sections of roads will have to be protected from nuisance flooding and storm surge.
Recommendations include an evaluation of the entire road system might identify more areas of the system that will be of concern as Kiawah prepares for 1.5 – 2.5 feet of sea level rise in the coming decades and take actions to ensure main arteries remain passable as long as possible for emergency vehicles to access people on the island who need help, and to assist property owners, guests, and workers in evacuating the island. Planning needs to look several decades into the future, not just at immediate flooding problems. Such planning requires good stormwater management that must address extreme precipitation, tidal nuisance flooding, storm surge, and combinations of these.
Other recommendations include the use of leisure trails for emergency vehicle access, developing a system to warn property owners and guests of specific road sections likely to flood during an approaching or on-going storm, placing water-depth markers along critical sections of roads during a storm to warn motorists of the depth of water on the road, and exploring the possibility of developing temporary auxiliary water storage basins to improve road drainage during major events.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
Native Plant Goldenrod by Pamela Cohen
There are steps property owners can take to adapt their residences and landscapes to more frequent flooding. The Committee met with three local architects, the Town’s Building Official, and the Architectural Review Board’s Director. Committee members reviewed the ARB Guidelines and the Town’s Flood Damage Prevention Ordinance. In addition to the list of recommendations for property owners, additional recommendations were made for how specific regulations of the governing bodies should be modified to assist in flooding mitigation and adaptation.
Examples of recommendations range from adopting low impact development tools like pervious paving and rain gardens, to replacing loose mulch and flood intolerant plants, to increasing freeboard (the required height for the lowest floor of a building) requirements by ordinance, to wet floodproofing the first floor of a residence, to raising one’s entire house above base flood elevation plus freeboard.
Read more in the full report
Coming soon: The Town will kick off the Grow Native Campaign and release a new native plant database during South Carolina Native Plant week, which takes place October 14-20. The campaign will promote the use of native plants on the island and the database is intended to serve as a resource for residents, landscapers, landscape architects, landscape designers, and other entities. The database includes native trees, shrubs, perennials, vines, ferns, and grasses and provides detailed information on growing conditions, size, flowering information, salt tolerance, deer resistance, and the wildlife value for each plant.
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
Kiawah’s east end of the island, where changes to the beach contours occur regularly.
Kiawah is fortunate in that it has a beach that accretes sand and that building construction has not generally been permitted to encroach on it or the dunes. As long as a plentiful supply of sand continues to move down the coast and as long as no anthropogenic structures create a barrier to dune building, natural processes should be able to maintain the beach and dune system despite rising sea levels. In most places on the island, experts recommend allowing the Kiawah beach and dune system to recover from storm erosion naturally rather than using artificial means such as sand fencing which can create other problems. Challenges may arise as the dune system moves landward with higher sea levels and encroaches on residences and public buildings. Such a barrier to beach movement may, in the future, lead to beach loss and require beach renourishment.
Recommendations include advanced planning for access to beach compatible sand for if and when a beach renourishment is needed, monitoring the beach and its wildlife populations and to manage the beach as is currently done. All entities should discourage or prohibit the construction of buildings or recreational facilities seaward into the dune system. Construction into the dune system ensures not only infrastructure damage should a breach in the remaining dunes occur, but provides a highway for ocean water to flow onto other land-based properties and perhaps weaken the integrity of a considerable area.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
Salt Marsh preservation and restoration of Kiawah’s salt marshes is critical. Kiawah Island has more acres of salt marsh than dry land and five times more marsh front than beach. The salt marsh protects the land from erosion by reducing wave action and provides abundant wildlife, recreational, and aesthetic amenities. With rising sea levels, the marsh can grow vertically if it can accumulate sediments at a sufficient rate, it can migrate landward if paths are not obstructed by anthropogenic barriers, or it will drown and be converted to open water and mud flats. Experts fear that a large proportion of South Carolina marshes will be lost to sea level rise.
Recommendations include working with neighborhoods and developing policies to protect migration routes for marshes and possibly supplying supplemental sediment for vertical growth. Living shoreline construction may be appropriate in some locations to protect marshes from sea level rise induced erosion.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
Kiawah’s terrestrial ecosystems depend on freshwater provided by precipitation. The groundwater reservoir for this water is the freshwater lens that floats on salt water underlying the island. Drought can reduce the recharge of this freshwater lens, reducing its volume and ability to hold back seawater. Sea level rise will also contract this lens by creating more pressure for saltwater infiltration. This could lead to changes in the island’s vegetation assemblages. Kiawah’s extensive irrigation supplements precipitation as a source of freshwater.
Recommendations include a hydrology study to map the freshwater lens and to monitor the groundwater table through the coming decades. As changes are detected, considerations should be given to a variety of actions for retaining freshwater on the island, such as low impact development practices and modifications to pond management.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
A one-foot increase in sea level over the last 100 years has been documented for the Charleston area. Over the next 100 years the consensus of almost all scientific studies projects both a substantial increase in the rate of sea level rise (SLR) as well as increasing periods of drought broken by periods of intense rainfall.
Sea levels are definitely rising as measured by NOAA tide gauges and satellite altimetry, and the Southeast coast has recently been particularly vulnerable due to effects of the Gulf Stream, the El Nino Oscillation, and the North Atlantic Oscillation. While the exact rate of future sea level rise is uncertain, nearly all modeled scenarios indicate that it will accelerate during the coming decades. While many areas are already experiencing flooding challenges, recent research by multiple sources suggests that Kiawah Island, as well as the rest of the South Carolina coast, will face significant flooding challenges during the next 30 years.
In studying actual and potential flooding on Kiawah, our Committee has focused on the following four phenomena all of which can also occur simultaneously:
Tidal flooding
According to the National Weather Service in Charleston, tidal flooding occurs when unusually high tides exceed Mean Higher High Water (MHHW) by 1.25 feet causing flooding even in the absence of any rainfall or storm event. In 2016, Charleston experienced 50 days of tidal flooding.
Storm Surge
As the name implies, Storm Surge is an abnormal rise in seawater level during a storm, measured as the height of the water above the normal predicted astronomical tide. The surge is caused primarily by a storm’s winds pushing water onshore. The amplitude of the storm surge at any given location depends on the orientation of the coastline with the storm track, the intensity, size, and speed of the storm, and the local bathymetry. The rise due to the low atmospheric pressure of the storm is generally minimal.
Since wind-generated waves ride on top of the storm surge, the total instantaneous elevation may greatly exceed the predicted storm surge plus astronomic tide. It is potentially catastrophic, especially on low lying coasts with gently sloping offshore topography. In addition, extreme precipitation can add to the height of the water, especially in estuaries receiving floodwaters from rivers or the surrounding land. A Storm Tide is the total observed seawater level during a storm, resulting from the combination of the astronomical tide, the storm surge, wind-blown waves, and precipitation (Figure below)
Figure Total seawater height = Astronomical tide + Storm surge + Wind generated waves + Rainfall. (National Hurricane Center, 2018)
Extreme precipitation events
These events can be associated with tropical storms or may occur when other meteorological fronts come together and often stall or move slowly over an area. Warmer air masses, as are predicted in the coming decades, increase evapotranspiration and can hold greater volumes of water. Although droughts of various severity may result, when rain does come it is projected to more frequently be in the form of downpours, sometimes extreme. We experienced flooding from such an event in 2015.
Sea Level Rise
A documented phenomenon that physical laws project will accelerate in the coming decades. Not only is it a challenge in its own right, but it will exacerbate all of the other phenomena. Normal tides and storm surges will start from a higher baseline. Higher water levels in the Kiawah River and the ocean means that precipitation stormwater will drain more slowly as the time period of daily lower tidal water decreases.
Sea levels are definitely rising as measured by NOAA tide gauges and satellite altimetry, and the Southeast coast has recently been particularly vulnerable due to effects of the Gulf Stream, the El Nino Oscillation, and the North Atlantic Oscillation. While the exact rate of future sea level rise is uncertain, nearly all modeled scenarios indicate that it will accelerate during the coming decades. While many areas are already experiencing flooding challenges, recent research by multiple sources suggests that Kiawah Island, as well as the rest of the South Carolina coast, will face significant flooding challenges during the next 30 years.
In studying actual and potential flooding on Kiawah, our Committee has focused on the following four phenomena all of which can also occur simultaneously:
Tidal flooding
According to the National Weather Service in Charleston, tidal flooding occurs when unusually high tides exceed Mean Higher High Water (MHHW) by 1.25 feet causing flooding even in the absence of any rainfall or storm event. In 2016, Charleston experienced 50 days of tidal flooding.
Storm Surge
As the name implies, Storm Surge is an abnormal rise in seawater level during a storm, measured as the height of the water above the normal predicted astronomical tide. The surge is caused primarily by a storm’s winds pushing water onshore. The amplitude of the storm surge at any given location depends on the orientation of the coastline with the storm track, the intensity, size, and speed of the storm, and the local bathymetry. The rise due to the low atmospheric pressure of the storm is generally minimal.
Since wind-generated waves ride on top of the storm surge, the total instantaneous elevation may greatly exceed the predicted storm surge plus astronomic tide. It is potentially catastrophic, especially on low lying coasts with gently sloping offshore topography. In addition, extreme precipitation can add to the height of the water, especially in estuaries receiving floodwaters from rivers or the surrounding land. A Storm Tide is the total observed seawater level during a storm, resulting from the combination of the astronomical tide, the storm surge, wind-blown waves, and precipitation (Figure below)
Figure Total seawater height = Astronomical tide + Storm surge + Wind generated waves + Rainfall. (National Hurricane Center, 2018)
Extreme precipitation events
These events can be associated with tropical storms or may occur when other meteorological fronts come together and often stall or move slowly over an area. Warmer air masses, as are predicted in the coming decades, increase evapotranspiration and can hold greater volumes of water. Although droughts of various severity may result, when rain does come it is projected to more frequently be in the form of downpours, sometimes extreme. We experienced flooding from such an event in 2015.
Sea Level Rise
A documented phenomenon that physical laws project will accelerate in the coming decades. Not only is it a challenge in its own right, but it will exacerbate all of the other phenomena. Normal tides and storm surges will start from a higher baseline. Higher water levels in the Kiawah River and the ocean means that precipitation stormwater will drain more slowly as the time period of daily lower tidal water decreases.
Historical Record
Throughout the history of the Earth, sea levels have risen and fallen by hundreds of feet. At the end of the last glacial maximum 20,000 years ago, the surface of the world ocean was about 350 feet below its present level because so much water was trapped in continental ice sheets. As the Earth warmed and the ice melted, sea level rose, sometimes as rapidly as several feet per century. Of course, during those times, human populations and permanent coastal developments were not an issue as they are today. During the 20th century, global sea level rose at an average rate of 6 inches per 100 years according to tide gauge data (Church and White, 2011). This value provides a modern benchmark for determining whether global sea level rise is currently accelerating as the Earth continues to warm.
Recent Observations
During the last 25 years, there has been an explosion of new, highly accurate observations that document what is happening now. These include satellite altimeter measurements of sea level, sub-surface ocean measurements of temperature and salinity, and satellite monitoring of glaciers and polar ice sheets. The combination of these new data has revealed not only the current rate of sea level rise, but also the relative contribution of ocean warming versus ice melt.
Kiawah Island Sea Level
There is no tide gauge on Kiawah, but if there were, it would be virtually the same as Charleston’s for monthly means and longer. This is because the tide, land subsidence, and sea level rise are all large-scale phenomena. Evidence of this is provided by the tide gauge record at Fort Pulaski, GA, maintained since 1935, which is virtually the same as Charleston’s. But even though Kiawah is subject to the same sea level as nearby areas, the impact of sea level rise must be assessed separately for each coastal community based on its own unique beach dynamics, river/marsh conditions, and upland topography.
Charleston has experienced 1 foot of rising seas over the past century based on trends from 1921 to 2013 (see figure below). Mean Sea Level always varies between months, but the recent trend in Charleston is a rise of about 1/8 of an inch each year. One hundred years ago, the mean monthly sea level in Charleston was about 1 foot lower than it is today. This rise has contributed to the frequency and the severity of King Tide flooding.
Monthly mean sea level measured by the NOAA tide gauge at Charleston, SC. The trend is 13 inches per century (NOAA-Tides and Currents, 2017)
Throughout the history of the Earth, sea levels have risen and fallen by hundreds of feet. At the end of the last glacial maximum 20,000 years ago, the surface of the world ocean was about 350 feet below its present level because so much water was trapped in continental ice sheets. As the Earth warmed and the ice melted, sea level rose, sometimes as rapidly as several feet per century. Of course, during those times, human populations and permanent coastal developments were not an issue as they are today. During the 20th century, global sea level rose at an average rate of 6 inches per 100 years according to tide gauge data (Church and White, 2011). This value provides a modern benchmark for determining whether global sea level rise is currently accelerating as the Earth continues to warm.
Recent Observations
During the last 25 years, there has been an explosion of new, highly accurate observations that document what is happening now. These include satellite altimeter measurements of sea level, sub-surface ocean measurements of temperature and salinity, and satellite monitoring of glaciers and polar ice sheets. The combination of these new data has revealed not only the current rate of sea level rise, but also the relative contribution of ocean warming versus ice melt.
Kiawah Island Sea Level
There is no tide gauge on Kiawah, but if there were, it would be virtually the same as Charleston’s for monthly means and longer. This is because the tide, land subsidence, and sea level rise are all large-scale phenomena. Evidence of this is provided by the tide gauge record at Fort Pulaski, GA, maintained since 1935, which is virtually the same as Charleston’s. But even though Kiawah is subject to the same sea level as nearby areas, the impact of sea level rise must be assessed separately for each coastal community based on its own unique beach dynamics, river/marsh conditions, and upland topography.
Charleston has experienced 1 foot of rising seas over the past century based on trends from 1921 to 2013 (see figure below). Mean Sea Level always varies between months, but the recent trend in Charleston is a rise of about 1/8 of an inch each year. One hundred years ago, the mean monthly sea level in Charleston was about 1 foot lower than it is today. This rise has contributed to the frequency and the severity of King Tide flooding.
Monthly mean sea level measured by the NOAA tide gauge at Charleston, SC. The trend is 13 inches per century (NOAA-Tides and Currents, 2017)
In the past three years, Kiawah has experienced island-wide flooding from extreme precipitation events and from storm surges. These episodes are likely to become more frequent.
2015
In early October 2015, the movement of very moist air over a stalled frontal boundary near the SC coast caused an extraordinary amount of rainfall in the state. The outer circulation of Hurricane Joaquin, situated well off the coast, added additional tropical moisture to the system. Kiawah experienced 16”-20” inches of rainfall over a four-day period (Di Liberto, 2015; National Weather Service, 2016). Runoff-swelled rivers, onshore winds, a perigee spring tide, and possibly Joaquin’s slowing of the Gulf Stream created tides that exceeded Mean Higher High Water (MHHW) by 2.5 feet (Morrison, 2018; Murphy, 2016; NOAA-Tides and Currents, 2017). Widespread nuisance flooding occurred across Kiawah with approximately 42% of its land surface covered by water at some point
2016
Hurricane Matthew was a Category 5 storm in the Caribbean but had dropped to Category 1 when it made landfall briefly on October 8th just south of McClellanville. Severe damage from winds and storm surge occurred just south of us on Hilton Head and Edisto islands. The storm tide at 3.5 feet above MHHW in Charleston was the highest since Hugo in 1989 and severe flooding was extensive (National Weather Service, 2017; NOAA-Tides and Currents, 2017). Rainfall on Kiawah was approximately 10 inches over a two-day period. Kiawah also experienced widespread flooding with approximately 65% of the island covered with some water and erosion to its dunes.
2017
The record storm surge of Matthew was exceeded the next year by Tropical Storm Irma, the third highest recorded for Charleston. Once a Category 4 storm when it hit southern Florida, it was a tropical storm and 200 miles inland when it damaged the South Carolina coast. Hilton Head, Edisto, and Folly Beach islands were again severely damaged by storm surge with major beach erosion (National Weather Service, 2018). Kiawah also suffered some beach erosion, but for the most part, its sand dunes stayed intact. The storm tide arrived at high tide and peaked at 4.15 feet above MHHW in Charleston. Kiawah’s rainfall was approximately 6 inches over a two-day period. Flooding covered at least 73% of the island, prevented travel, and damaged some garages and first floor spaces.
2015
In early October 2015, the movement of very moist air over a stalled frontal boundary near the SC coast caused an extraordinary amount of rainfall in the state. The outer circulation of Hurricane Joaquin, situated well off the coast, added additional tropical moisture to the system. Kiawah experienced 16”-20” inches of rainfall over a four-day period (Di Liberto, 2015; National Weather Service, 2016). Runoff-swelled rivers, onshore winds, a perigee spring tide, and possibly Joaquin’s slowing of the Gulf Stream created tides that exceeded Mean Higher High Water (MHHW) by 2.5 feet (Morrison, 2018; Murphy, 2016; NOAA-Tides and Currents, 2017). Widespread nuisance flooding occurred across Kiawah with approximately 42% of its land surface covered by water at some point
2016
Hurricane Matthew was a Category 5 storm in the Caribbean but had dropped to Category 1 when it made landfall briefly on October 8th just south of McClellanville. Severe damage from winds and storm surge occurred just south of us on Hilton Head and Edisto islands. The storm tide at 3.5 feet above MHHW in Charleston was the highest since Hugo in 1989 and severe flooding was extensive (National Weather Service, 2017; NOAA-Tides and Currents, 2017). Rainfall on Kiawah was approximately 10 inches over a two-day period. Kiawah also experienced widespread flooding with approximately 65% of the island covered with some water and erosion to its dunes.
2017
The record storm surge of Matthew was exceeded the next year by Tropical Storm Irma, the third highest recorded for Charleston. Once a Category 4 storm when it hit southern Florida, it was a tropical storm and 200 miles inland when it damaged the South Carolina coast. Hilton Head, Edisto, and Folly Beach islands were again severely damaged by storm surge with major beach erosion (National Weather Service, 2018). Kiawah also suffered some beach erosion, but for the most part, its sand dunes stayed intact. The storm tide arrived at high tide and peaked at 4.15 feet above MHHW in Charleston. Kiawah’s rainfall was approximately 6 inches over a two-day period. Flooding covered at least 73% of the island, prevented travel, and damaged some garages and first floor spaces.
There is no tide gauge on Kiawah, but if there were, it would be virtually the same as Charleston’s for monthly means and longer. This is because the tide, land subsidence, and sea level rise are all large-scale phenomena. Evidence of this is provided by the tide gauge record at Fort Pulaski, GA, maintained since 1935, which is virtually the same as Charleston’s. Click here for more info on how scientists measure the sea level
There is so much evidence that sea levels are rising, and will almost certainly accelerate in the coming decades, that the questions become, “how fast will oceans rise?”, and by “how much?” Many factors come into play when trying to predict the future, how can one begin planning?
The widely accepted approach is to consider a variety of scenarios and select ones to act upon by the amount of risk a community is willing to accept. The committee reviewed several scenarios developed by different groups and decided to work from similar scenarios being used by the City of Charleston.
The committee chose to base its report on NOAA’s Intermediate High scenario shown below. Notice that there is a box around the point approximately 50 years out along the Intermediate High scenario. This brackets a sea level rise at that time of about 1.5-2.5 feet.
The figure above depicts several global sea level rise scenarios derived from work of the U.S. Corps of Engineers and the National Oceanic and Atmospheric Administration and adopted by the City of Charleston (City of Charleston, 2015; Marcy and Jackson, 2016; Williams and Cabiness, 2017).
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
There is so much evidence that sea levels are rising, and will almost certainly accelerate in the coming decades, that the questions become, “how fast will oceans rise?”, and by “how much?” Many factors come into play when trying to predict the future, how can one begin planning?
The widely accepted approach is to consider a variety of scenarios and select ones to act upon by the amount of risk a community is willing to accept. The committee reviewed several scenarios developed by different groups and decided to work from similar scenarios being used by the City of Charleston.
The committee chose to base its report on NOAA’s Intermediate High scenario shown below. Notice that there is a box around the point approximately 50 years out along the Intermediate High scenario. This brackets a sea level rise at that time of about 1.5-2.5 feet.
The figure above depicts several global sea level rise scenarios derived from work of the U.S. Corps of Engineers and the National Oceanic and Atmospheric Administration and adopted by the City of Charleston (City of Charleston, 2015; Marcy and Jackson, 2016; Williams and Cabiness, 2017).
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
The Sea Level Rise data viewer is a tool that is providing the City of Charleston decision-makers with a preliminary look at sea-level rise. Data depicting the predicted levels of sea-level rise was developed and provided by NOAA Coastal Services Center in Charleston, SC using 2007 and 2009 LiDAR data for Berkeley, Charleston, and Dorchester counties.
Once you open the viewer, you can use the slider bar to see how various levels of sea-level rise will impact this area. Levels represent inundation at high tide.
City of Charleston Sea Level Rise Viewer
The Town is working with the College of Charleston to develop its own higher resolution sea level rise viewer to predict impacts from future flooding events and pinpoint specific areas of concern.
A well planned and executed stormwater management system is critical to handling flooding events on the island. Kiawah is fortunate to have an extensive system of interconnected ponds that can accommodate a rainfall event equivalent to a 100-year flood. Stormwater moves through the ponds and leaves the island through outfalls into the marsh and river. In the future, higher tides will decrease the effectiveness of the pond system by slowing the flow of water from the ponds into the outfalls and out to the estuary. Work to repair clogged and deteriorating pipes are underway and will improve the flow of water into ponds and drainage system.
Recommendations include continued attention to the integrity of the drainage system through reviews of the appropriate size, proactive maintenance and necessary repair and replacement of pipes is critical. The report supports current plans to automate outfall gates and encourages consideration of one or more additional outfalls.
Other recommendations relate to reducing the obstruction of drains, swales, and pipes, investigating the use of physical structures in localized areas to slow nuisance flooding or storm surges, using the best available GIS tools to improve stormwater drainage, working with neighborhoods on location-specific challenges, adopting principles of low impact development, and planning for the resources to support these efforts.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
The bridge at the round-a-bout during Tropical Storm Irma
Roads and bridges that dependably allow vehicular movement are essential for quality of life and for public safety. Island roads and bridges that maintain their reliability during storm events or quickly recover after the event are very valuable assets. It is apparent from Kiawah’s experience with recent storms that some sections of roads will have to be protected from nuisance flooding and storm surge.
Recommendations include an evaluation of the entire road system might identify more areas of the system that will be of concern as Kiawah prepares for 1.5 – 2.5 feet of sea level rise in the coming decades and take actions to ensure main arteries remain passable as long as possible for emergency vehicles to access people on the island who need help, and to assist property owners, guests, and workers in evacuating the island. Planning needs to look several decades into the future, not just at immediate flooding problems. Such planning requires good stormwater management that must address extreme precipitation, tidal nuisance flooding, storm surge, and combinations of these.
Other recommendations include the use of leisure trails for emergency vehicle access, developing a system to warn property owners and guests of specific road sections likely to flood during an approaching or on-going storm, placing water-depth markers along critical sections of roads during a storm to warn motorists of the depth of water on the road, and exploring the possibility of developing temporary auxiliary water storage basins to improve road drainage during major events.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
Reliable supplies of services of high-quality potable water (drinking water), handling of wastewater and electrical services are essential for any community. If the systems that handle any of the essential services are damaged or contaminated by floods or regular inundation from sea level rise, it would severely reduce the community’s ability to recover quickly following the event or even to persist into the future.
Both water services are provided by the Kiawah Island Utility and electrical service is provided by Berkeley Electric Cooperative. The report indicates that both services appear to be well-managed and relatively prepared to withstand most expected flooding events. Susceptible stations for both systems can be raised incrementally and adaptively over time as dictated by flooding as it develops.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
Both water services are provided by the Kiawah Island Utility and electrical service is provided by Berkeley Electric Cooperative. The report indicates that both services appear to be well-managed and relatively prepared to withstand most expected flooding events. Susceptible stations for both systems can be raised incrementally and adaptively over time as dictated by flooding as it develops.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
Native Plant Goldenrod by Pamela Cohen
There are steps property owners can take to adapt their residences and landscapes to more frequent flooding. The Committee met with three local architects, the Town’s Building Official, and the Architectural Review Board’s Director. Committee members reviewed the ARB Guidelines and the Town’s Flood Damage Prevention Ordinance. In addition to the list of recommendations for property owners, additional recommendations were made for how specific regulations of the governing bodies should be modified to assist in flooding mitigation and adaptation.
Examples of recommendations range from adopting low impact development tools like pervious paving and rain gardens, to replacing loose mulch and flood intolerant plants, to increasing freeboard (the required height for the lowest floor of a building) requirements by ordinance, to wet floodproofing the first floor of a residence, to raising one’s entire house above base flood elevation plus freeboard.
Read more in the full report
Coming soon: The Town will kick off the Grow Native Campaign and release a new native plant database during South Carolina Native Plant week, which takes place October 14-20. The campaign will promote the use of native plants on the island and the database is intended to serve as a resource for residents, landscapers, landscape architects, landscape designers, and other entities. The database includes native trees, shrubs, perennials, vines, ferns, and grasses and provides detailed information on growing conditions, size, flowering information, salt tolerance, deer resistance, and the wildlife value for each plant.
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
Kiawah’s east end of the island, where changes to the beach contours occur regularly.
Kiawah is fortunate in that it has a beach that accretes sand and that building construction has not generally been permitted to encroach on it or the dunes. As long as a plentiful supply of sand continues to move down the coast and as long as no anthropogenic structures create a barrier to dune building, natural processes should be able to maintain the beach and dune system despite rising sea levels. In most places on the island, experts recommend allowing the Kiawah beach and dune system to recover from storm erosion naturally rather than using artificial means such as sand fencing which can create other problems. Challenges may arise as the dune system moves landward with higher sea levels and encroaches on residences and public buildings. Such a barrier to beach movement may, in the future, lead to beach loss and require beach renourishment.
Recommendations include advanced planning for access to beach compatible sand for if and when a beach renourishment is needed, monitoring the beach and its wildlife populations and to manage the beach as is currently done. All entities should discourage or prohibit the construction of buildings or recreational facilities seaward into the dune system. Construction into the dune system ensures not only infrastructure damage should a breach in the remaining dunes occur, but provides a highway for ocean water to flow onto other land-based properties and perhaps weaken the integrity of a considerable area.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
Salt Marsh preservation and restoration of Kiawah’s salt marshes is critical. Kiawah Island has more acres of salt marsh than dry land and five times more marsh front than beach. The salt marsh protects the land from erosion by reducing wave action and provides abundant wildlife, recreational, and aesthetic amenities. With rising sea levels, the marsh can grow vertically if it can accumulate sediments at a sufficient rate, it can migrate landward if paths are not obstructed by anthropogenic barriers, or it will drown and be converted to open water and mud flats. Experts fear that a large proportion of South Carolina marshes will be lost to sea level rise.
Recommendations include working with neighborhoods and developing policies to protect migration routes for marshes and possibly supplying supplemental sediment for vertical growth. Living shoreline construction may be appropriate in some locations to protect marshes from sea level rise induced erosion.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
Kiawah’s terrestrial ecosystems depend on freshwater provided by precipitation. The groundwater reservoir for this water is the freshwater lens that floats on salt water underlying the island. Drought can reduce the recharge of this freshwater lens, reducing its volume and ability to hold back seawater. Sea level rise will also contract this lens by creating more pressure for saltwater infiltration. This could lead to changes in the island’s vegetation assemblages. Kiawah’s extensive irrigation supplements precipitation as a source of freshwater.
Recommendations include a hydrology study to map the freshwater lens and to monitor the groundwater table through the coming decades. As changes are detected, considerations should be given to a variety of actions for retaining freshwater on the island, such as low impact development practices and modifications to pond management.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
While emergency management is a broad topic, the Committee focused on the challenges raised by current levels of flooding and the expectation of more frequent events as sea level rise occurs.
Successful emergency management is the coordinated effort of KICA, the Town, the Resort, and the Developer during the kind of flooding events that Kiawah has experienced and that will likely increase in the future. Legally, only the Town can coordinate with County and State entities for pre-event planning and post-event recovery operations. KICA’s Security Department provides also extensive experience and expertise in dealing with emergencies and is an important partner with the Town.
Recommendations include expanded communications efforts, development of an expected flooding model for public use, and distributing water-level-marking stakes along the Parkway and Governor’s Drive in advance of a major storm event so that drivers can read the water depth.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
Successful emergency management is the coordinated effort of KICA, the Town, the Resort, and the Developer during the kind of flooding events that Kiawah has experienced and that will likely increase in the future. Legally, only the Town can coordinate with County and State entities for pre-event planning and post-event recovery operations. KICA’s Security Department provides also extensive experience and expertise in dealing with emergencies and is an important partner with the Town.
Recommendations include expanded communications efforts, development of an expected flooding model for public use, and distributing water-level-marking stakes along the Parkway and Governor’s Drive in advance of a major storm event so that drivers can read the water depth.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
Property owners need and deserve timely, understandable, and accurate information on sea level rise, the consequences of that change, and the current status of storm and flooding preparation. To plan their lives, they also need information on plans for changes to be made in the next 3-5 years and over the next few decades. They also need to know the communication channels, trust those sources, and how to access them in the event of an emergency or to access relevant information.
Recommendations include bringing a series of speakers to the island on the issues surrounding sea level rise and its consequences, inform residents of exact locations where the island is most vulnerable to street flooding, educate residents on what the Town and KICA do to prepare for a storm or large rain event so residents better understand how the island systems function.
Read more and view the list of recommended readings in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
Recommendations include bringing a series of speakers to the island on the issues surrounding sea level rise and its consequences, inform residents of exact locations where the island is most vulnerable to street flooding, educate residents on what the Town and KICA do to prepare for a storm or large rain event so residents better understand how the island systems function.
Read more and view the list of recommended readings in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
Kiawah Island developed with an emphasis on living with nature and respecting the island’s environment. The rules, regulations and guidelines that govern development protect the natural environment, influence what the island looks like and govern how property owners develop and maintain their homes, yards, businesses, golf courses and the like. It’s important for the islands’ various regulatory regimes to encourage practices which protect and adapt the island to rising water levels.
Recommendations include Kiawah’s regulating entities, property owners, and developers review Low Impact Development in Coastal South Carolina: A Planning and Design Guide to identify and adopt new practices to improve stormwater management on existing and new developments; ARB guidelines should be modified to strongly encourage the use of pervious surfaces; and implementation of neighborhood property drainage and grading reviews, beyond initial lot construction reviews, to proactively address issues before they cause flooding.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
Recommendations include Kiawah’s regulating entities, property owners, and developers review Low Impact Development in Coastal South Carolina: A Planning and Design Guide to identify and adopt new practices to improve stormwater management on existing and new developments; ARB guidelines should be modified to strongly encourage the use of pervious surfaces; and implementation of neighborhood property drainage and grading reviews, beyond initial lot construction reviews, to proactively address issues before they cause flooding.
Read more in the full report
Disclaimer: This report and recommendations made within have not been considered and adopted by the Kiawah Town Council. In the coming months, the Town Council, with the involvement of other community entities, will review the recommendations in the full report and develop a strategy to meet the challenges.
In order to successfully address issues of flooding and sea level rise, it is essential that the Town, KICA, other governing bodies, as well as property owners work together to address the issues identified in the report that will confront the island.
In the coming months, meetings will be taking place with all the major entities to review the recommendations in the full report and develop a strategy to meet the challenges.
The Committee recommended:
In the coming months, meetings will be taking place with all the major entities to review the recommendations in the full report and develop a strategy to meet the challenges.
The Committee recommended:
- The long-term challenges posed for a barrier island by sea level rise are serious and Kiawah’s decision-makers should embrace the opportunity to develop policies and actions that will permit Kiawah to adapt and remain a resilient and vibrant community.
- The Town and KICA, and perhaps the other major interests, should appoint a small group of professionals such as the Town’s Wildlife Biologist, KICA’s Director of Major Repairs, and a few others with relevant expertise to recommend a range of “trigger points” for action. This will be essential to the decision-makers for long-term adaptation and resilience planning.
- In order to ensure that the flooding and sea level rise issues receive the necessary planning and implementation attention, the Town and KICA need some structure:
-to assist in policy and planning development,
-to provide GIS analysis, data and technical support,
-to provide educational and problem-solving, technical support for the community at large,
-to foster communication and cooperation among the major decision-making entities,
-to coordinate research and monitoring studies related to sea level rise on the island and disseminate the results,
-to monitor trigger points, project progress, and new data as it appears in the literature,
-to represent Kiawah in county, state, and regional groups such as the Charleston Resilience Network and SCDHEC-OCRM’s Coastal South Carolina Community Ratings System Users Group.
The Town and other Kiawah entities should work together to hire a Resilience Specialist, or to develop a Resilience Committee consisting of appointed representatives from the major decision-making bodies, but at least the KICA and the Town. This will likely require new resources rather than just expanding the job description of a current employee. If a Resilience Specialist position is created, joint funding could be considered.
- The Town and KICA should establish a procedure whereby every four years (maybe following the publication of the new National Climate Assessment) a small appointed “external” group reviews the recent literature, the progress made regarding projects on Kiawah, and any monitored changes on the island relevant to sea level rise issues. The group would then modify the recommendations in this report, make new ones as appropriate, and present its findings to the decision-making bodies.
- The Town should recognize the importance of sea level rise planning by incorporating it into the next revision of the Town’s Comprehensive Plan.
- Similarly, KICA should recognize the importance of sea level rise planning by incorporating it into its Strategic Plan.
The Town’s water level monitoring station, located at the Kiawah River Bridge, provides real-time water level information that is now available to residents and the general public at https://public.eagle.io/public/dash/hqunq45zw5jobf8
In addition to the water level data, the webpage also provides real-time weather information from a weather station recently installed by the Town on the roof of The Timbers oceanfront residences. The water level monitoring station is solar-powered and collects water level data every 15 minutes with an accuracy of 2 mm or less. Data is transmitted in real-time via the cellular network, and the station will also transmit data via satellite if the cellular network goes down during a storm event. Historically, tidal data predictions for the Kiawah River Bridge were extrapolated from nearby stations in the Charleston area. This new station will collect current and historical water level data specific to Kiawah and allow for monitoring the long-term effects of sea-level rise. The weather station is also solar-powered and collects and transmits weather data every minute. It will provide critical data during storm events, and in conjunction with water level data, will assist in the emergency management decision-making process.
Understanding the Public Webpage
The current water level can be seen at the top of the page. The chart underneath provides current and historical data for the previous seven days. The blue line represents the current output from the Town station, and the black line represents the NOAA (National Oceanic and Atmospheric Administration) tide prediction for the same time period as well as the following three days. Below the chart are two additional tables that provide historical data from the station as well as a listing of King Tide events by date. If you have questions, email Jim Jordan at jjordan@kiawahisland.org.
In addition to the water level data, the webpage also provides real-time weather information from a weather station recently installed by the Town on the roof of The Timbers oceanfront residences. The water level monitoring station is solar-powered and collects water level data every 15 minutes with an accuracy of 2 mm or less. Data is transmitted in real-time via the cellular network, and the station will also transmit data via satellite if the cellular network goes down during a storm event. Historically, tidal data predictions for the Kiawah River Bridge were extrapolated from nearby stations in the Charleston area. This new station will collect current and historical water level data specific to Kiawah and allow for monitoring the long-term effects of sea-level rise. The weather station is also solar-powered and collects and transmits weather data every minute. It will provide critical data during storm events, and in conjunction with water level data, will assist in the emergency management decision-making process.
Understanding the Public Webpage
The current water level can be seen at the top of the page. The chart underneath provides current and historical data for the previous seven days. The blue line represents the current output from the Town station, and the black line represents the NOAA (National Oceanic and Atmospheric Administration) tide prediction for the same time period as well as the following three days. Below the chart are two additional tables that provide historical data from the station as well as a listing of King Tide events by date. If you have questions, email Jim Jordan at jjordan@kiawahisland.org.
Interested parties can view the supporting material and data resources used in the development of the Flood Mitigation and Sea Level Rise Adaptation Report provided via the link below.
Data & Resources Drive
Flood Mitigation and Sea Level Rise Adaptation for Kiawah Island: A Report by Jack Kotz (published in Naturally Kiawah magazine Volume 40, Summer/Fall 2018)
Data & Resources Drive
Flood Mitigation and Sea Level Rise Adaptation for Kiawah Island: A Report by Jack Kotz (published in Naturally Kiawah magazine Volume 40, Summer/Fall 2018)
- Robert Cheney – MS in Physical Oceanography
- Jim Chitwood – Ph.D. in Chemistry (University of California – Berkeley) and Advanced Management Program (Harvard)
- William Connor – Bachelor’s and Master’s degrees in Civil Engineering from Clemson University
- Jane Ellis – Ph.D. in Plant Physiology, Clemson University
- Jim Jordan – BS in Biology, Furman University; MS in Wildlife Ecology and Management, University of Georgia
- Jack Kotz – Ph.D. in chemistry, Cornell University
- John Leffler – Ph.D. in Zoology/Ecology, University of Georgia
- Diana Mezzanotte (Town Councilmember) Bachelor of Business Administration – Accounting, St. Mary’s College, Notre Dame, IN. CPA Emeritus, South Carolina.
- David Pumphrey – B.A. in Economics, Duke University; M.A. in Economics from George Mason University
- Lynette Schroeder – MBA, University of Virginia, A.B. University of Chicago
- James V. Sullivan – B.S. in Chemical Engineering from Northeastern University
- Ex-Officio: Matt Hill -KICA and Sara Senst- ARB