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Flood Mitigation EFFORTS AND NEW INFRASTRUCTURE

Overview

Water is one of Kiawah’s greatest assets - the ocean, marsh, river and ponds. The island’s natural abundance is a big reason why people are drawn to the island and why they stay, but living with water requires careful stewardship.

In 2019, KICA established the Water Management Task Force to evaluate and refine KICA’s approach to water management, and determine a comprehensive solution to address Kiawah’s commonly recurring flooding issues.

As the first step to any short or long-term flood mitigation efforts, international water resilience experts encourage communities to focus on water removal through drainage optimization. The task force determined that six strategic infrastructure improvement projects would optimize Kiawah’s drainage system, allowing water to more efficiently exit the system. This would eliminate hazardous flooding in significant portions of the island during many heavy rainfall events and position Kiawah to recover more quickly from storm surge.

At present, a severe rainfall at high tide can flood Kiawah’s main roads, limiting access to and from the island. This has occurred five times in the last five years, and is a public safety issue. In the same rainfall scenario, with improvements to Kiawah’s infrastructure, main roads would remain open to traffic and hazardous flooding on common property throughout many neighborhoods would be resolved.

In the spring of 2020 the community voted to approve a special assessment to fund these critical drainage infrastructure improvements. Alleviating hazardous flooding and maintaining passable roads in many heavy rainfall scenarios is an exciting step forward for our barrier island.

KICA board treasurer and task force chair Dave Morley noted that “these projects immediately diminish a threat to property values, quality of life and public safety. There’s nothing higher on the board’s priority list.”

Infrastructure improvements begin in June and reduced flooding may be seen in some areas of Kiawah by the end of the year, with full optimization and the completion of all projects anticipated by the end of 2022.

This flood mitigation effort is supported by the Town of Kiawah Island, the Kiawah Island Golf Resort, Kiawah Partners and the Kiawah Conservancy.

Benefits of Infrastructure Improvements

1. Improved Island Access

Currently, with the highest average annual rainfall at an average high tide (3.8 inch rainfall and 6.16 foot tide), the Kiawah Island Parkway (between West Beach and East Beach) floods with 12 inches of water, the height of some car tailpipes, which could prevent access to most of island. Statistically this happens annually, and it has occurred on Kiawah in all of the last five years.

In the same rainfall scenario, with improvements to Kiawah’s infrastructure, main roads will remain open to traffic and hazardous flooding on common property throughout most of the island will be resolved.

The approved improvements also keep the Kiawah Island Parkway, Governors Drive and Ocean Course Drive open to traffic in more severe rainfall events. In the highest average rainfall within ten years (6.6 inches) Kiawah’s main thoroughfares and side roads remain open with no hazardous flooding. In the highest average rainfall within 25 years (8 inches) Kiawah’s main thoroughfares remain open with some flooding on side roads. In the highest average rainfall within 100 years (10.4 inches) Kiawah's main thoroughfares remain open with some nuisance flooding, and some hazardous flooding on side roads. In a 1000-year storm (approximately 15 inches), like Kiawah experienced in 2015, main thoroughfares will have standing water but would remain passable, with hazardous flooding on many side roads. These engineered solutions will deliver a large reduction in flood risk with corresponding improvements to public safety and island access.

2. Strengthened Property Values

These strategic improvements communicate that Kiawah is a proactive barrier island community that safeguards property values by implementing strong flood mitigation practices. In the short and long-term, property values on Kiawah will be strengthened with this new infrastructure.

3. Reduced Flooding in Kiawah’s Most Susceptible Locations

Along with Kiawah’s main thoroughfares remaining open, many side streets with known flooding issues benefit. Hazardous flooding will be eliminated (in the 3.8 in rainfall at high tide scenario) in the following susceptible locations:

Kiawah Island Parkway, Governors Drive, Vanderhorst Gate, Atlantic Beach Court, Bank Swallow Lane, Bulrush Lane, Fiddlers Reach, Green Dolphin Way, Green Meadow Lane, Kiawah Island Club Drive, Mariners Watch, Marsh Edge Lane, Marsh Hawk Lane, Muirfield Lane, New Settlement Road, River Course Lane, River Marsh Lane, Salthouse Lane, Sanctuary Beach Drive, Sea Forest Drive, Sea Marsh Drive, Summer Duck Way, Sweetgrass Lane, Trumpet Creeper Lane, Turtle Beach Lane

Effectiveness of Infrastructure Solutions

The new infrastructure was developed by Stantec, an international engineering firm that has a successful history working with the association. The projects were selected because they each solve an existing detrimental flooding issue, and they work in tandem to relieve the drainage system and maximize efficiency.

In two independent digital hydrologic models of Kiawah Island, simulations confirm that the proposed new infrastructure successfully eliminates hazardous flood waters, in the scenario of the highest average annual rainfall at an average high tide, with no unintended water displacement or erosion issues.

An Explanation of Funding

The community association does not have a funding source for building new infrastructure. KICA’s reserve budget funds the repair and replacement of existing infrastructure as it ages, but typically infrastructure is built by a developer and then conveyed to the community association to maintain. The robust drainage system conveyed to KICA was sufficient at the time it was built. However, in recent years, the frequency of rain events has increased, more often challenging the drainage system. The new infrastructure will relieve the system and maximize the efficiency of water removal from Kiawah.

The total cost of the infrastructure projects, with endowed maintenance, is $2.9 million. This equates to a special assessment of $130 per improved property or $65 per unimproved property annually for five years. The Kiawah Island Golf Resort and Kiawah Partners (the developer) are members of the association and will be responsible for the combined amount of approximately $400,000. The first annual payment is due July 1, 2020.

The terms of this special assessment restrict funds to be used for water management efforts only. The special assessment cannot be extended past 2024 and the amount cannot be increased. Any debt used to finance these projects will be paid back over the five-year term. No changes may be made to these terms without another vote of the membership.

Back

Questions?

Submit your questions about this flood mitigation effort and vote to flood@kica.us. View the answers to frequently asked questions at the link below.

VIDEO RESOURCES

Full Presentation to the Community (start at minute 33:00) - from March 13

Q&A Webinar - from March 31

Overview of New Infrastructure

Project 1

Project One is in the area of the Kiawah Island Parkway and Sea Marsh Drive near the west end of the island. Sea Marsh Drive floods in this location. Water from the road is designed to shed into Pond 21, but the water level in this pond stays too high due to insufficient capacity to drain, so there is no place for water to be displaced. The solution is to add another pipe from Pond 21 to its neighboring pond, to increase its capacity to flow through the pond system and out through the drainage system. This will significantly reduce rainfall flooding on Sea Marsh Drive.

Project 2

Project Two is in the area of the Kiawah Island Parkway and Sea Forest Drive near the fire station. On at least an annual basis, the Kiawah Island Parkway floods in this location with 12 inches of water, the height of some car tailpipes, which could prevent access to most of island. There is no possible detour in this area, so it is critical to maintain access here. Overall drainage capacity issues also contribute to significant flooding (up to 26 inches) on Sea Forest Drive and many side streets.

The solution is add a new outfall to the marsh at an existing inlet and raise an existing berm at that inlet to prevent tidal water from flooding the parkway. Currently, one outfall at Inlet Cove drains all of the ponds on the west end of the island up to the V-gate, 37 ponds and over three miles of drainage. A new outfall will drain The Settlement neighborhood on the north side of the parkway, relieving the Inlet Cove outfall from draining this one-mile section. The additional outfall helps keep the Kiawah Island Parkway clear, and alleviates hazardous flooding in The Settlement neighborhood and throughout West and East Beach areas. This is a critical and impactful project.

In two independent digital hydrologic models of Kiawah Island, simulations confirm the new outfall will effectively relieve the Beachwalker Drainage Basin with no negative impact to the existing inlet and surrounding properties. As a precaution, KICA has surveyed this inlet, and will continue to survey and analyze it annually to monitor any impact of the new outfall.

Beachwalker Drainage Basin - Current
Beachwalker Drainage Basin - New Proposed Outfall

Project 3

Project Three is in the area of the Kiawah Island Parkway and Green Dolphin Way. At this location, the Kiawah Island Parkway’s elevation dips, creating a bowl, and it floods with several inches of water. The solution is to raise 450 feet of the parkway to eliminate the bowl so that water does not collect in this area. There is no possible detour in this location, so maintaining a passable road is imperative.

Project 4

Project Four is in the area of the Vanderhorst Gate (V-gate). This area is also low and can hold water from rainfall. In some cases, a nearby pond can push excess water onto the road through curb drainage, compounding flooding. There is no possible detour in this area, so it is a priority to maintain traffic flow in this location. The solution is to add a flap gate to the pipe from the nearby pond, so that water cannot be pushed up into the intersection, and install a pump so that water can be pumped out from the V-gate area, keeping it passable for cars. The pump can also alleviate Governors Drive flooding in the Project Five area.

Project 5

Project Five is in the area of Governors Drive and Halona Lane (across from the Turtle Point maintenance facility). A tidal inlet at the end of Halona Lane can cause flooding on Governors Drive. A weir, a low barrier to reduce the infiltration of minor tides, and flap gate on the end of the pipe will reduce flooding in Indigo Park and on Governors Drive. A new dry detention area next to Governors Drive will collect excess rainwater. The pump at the V-gate could also be connected to this section of Governors Drive to relieve road flooding, as there is no detour in this area.

Project 6

Project Six is in the area of Governors Drive, between the Vanderhorst Mansion (across from Flyway Drive) and Persimmon Court. Blocked pipes and an inefficient drainage configuration cause flooding on Governors Drive. The solution involves adding pipes, reconfiguring pipes and raising the level of pipes so that water efficiently drains from the road and area ponds into the inlet. The inlet will also be dredged, to remove several decades of deposited sediment, and flap gates on pipes will prevent water from coming in with tides. A weir will be added to the end of Pond 56, to prevent tidal water from infiltrating and overflowing the pond.

Projects Timeline

In June, the association commenced work on Project Two and Six. Project Two will result in the most significant overall improvement to Kiawah’s drainage system. It adds a critical new outfall to Kiawah’s drainage system, relieving many of the flooding issues (with a heavy rainfall at high tide) throughout the west half of the island. Project Six involves dredging the inlet at Trumpet Creeper, a large project which must occur before pipe work in the area. Project Two and a portion of Project Six are in permitting. If approved by the membership, Project Two is scheduled for completion by the end of 2020.

The remaining projects (1, 3, 4, 5) are scheduled for 2021 and 2022. According to standard approval timelines, all projects will be complete by the end of 2022. In just two years, KICA could accomplish drainage optimization, the essential foundation for barrier island water management.

Flood Mitigation is an Ongoing Community Effort

These infrastructure improvement projects are a significant and exciting step toward effectively managing water on our barrier island, but water management doesn’t stop with drainage optimization. It is an ongoing effort.

Currently, Kiawah entities are working together to build a comprehensive understanding of Kiawah’s water environment: the ocean (the town’s 2018 Sea Level Rise and Adaptation Study and 2020 Kiawah River tide gauge installation), the marsh (the conservancy’s 2020 marsh vulnerability study) and groundwater (the conservancy’s 2020 groundwater table study). These studies and tools will provide Kiawah leaders with an arsenal of data to inform decisions and adaptive strategies.

Water Management Task Force

Dave Morley: Task Force Chair, KICA Board Treasurer, Community Member

In 2018, before joining the KICA board in 2019, Dave was a member of the Finance Committee. KICA staff had presented an infrastructure improvement project to the Finance Committee in a draft of the 2019 Budget, which spurred the committee to grapple with the question of funding such a project, since KICA does not have a funding source for new infrastructure. The committee and staff also discussed the potential for several other new infrastructure projects where known flood susceptibilities exist. It was determined these new infrastructure projects should be presented to the board in a comprehensive plan, so Dave was asked to lead a new Water Management Task Force.

Rajan Govindan: Finance Committee Member, Former Board Member, Community Member

Chris Widuch: Town of Kiawah Island Mayor Pro-Tem, Community Member

Barry Abrams: Engineer, Lawyer, Community Member

Justin Tye, PE: Stantec Consulting

Justin is a traffic engineer with project emphasis in site development, stormwater modeling and utility coordination.

Jimmy Bailey: KICA Chief Operating Officer

Jimmy oversees all association operations and executes the directives of the board.

Shannon White: KICA Director of Operations

Shannon oversees all maintenance, security, livability and recreation operations of the association.

Will Connor, PE: KICA Director of Major Repairs, Town Sea Level Rise Committee Member

Will is a civil engineer and oversees all repairs and replacements to island infrastructure, including drainage, roads, bridges, leisure trails and boardwalks.

Lucas Hernandez: KICA Resilience Specialist

Lucas executes all research and planning for association resilience projects, with a primary focus on water resilience. Lucas developed a digital hydrologic model of Kiawah Island, that demonstrates how water moves throughout the island, considering precise topographic details down to 2.5 square feet, like elevation, soil type, ground cover and water levels. The model was created with National Oceanic and Atmospheric Administration (NOAA) and SC Department of Natural Resources (DNR) data, and also incorporates flood reports from community members.

Questions?

Submit your questions about this flood mitigation effort and vote to flood@kica.us. View the answers to frequently asked questions at the link below.