Sep

26

2024

From The Blog

The Role that Stormwater Management Plays During Hurricane Season

Above: water ponding on a roadway during Tropical Storm Debby.

The island’s pond drainage system and the infrastructure that supports it are some of KICA’s primary responsibilities. As a barrier island, it’s essential to ensure that water is efficiently moved into Kiawah’s gravity-based drainage system and out into the watershed. While this need is even more apparent during a storm event, there is little the drainage system can do to impact the severity of a storm’s tidal surge effects. Below, we’ll cover how preparation before a storm and responsiveness after are the key pieces of the drainage puzzle.

 

How Island Drainage Works

Kiawah’s ponds were constructed to serve as stormwater detention and retention ponds. They were designed to receive water, hold it to prevent flooding, and then pass it through KICA’s drainage system and off the island efficiently. The ponds are intended to receive roadway and golf course runoff in addition to rainwater and tidal flow. Kiawah’s lakes and ponds are connected to 10 outfall structures which allow surface water to drain through the island into the Kiawah River and then to the Atlantic Ocean for several hours before and after low tides. 

 

Projects Making Drainage More Efficient

For many years, KICA has been engaged in working to optimize the island’s drainage system. For example, the association annually budgets for the repair and replacement of drainage pipes on the island. For many years, KICA has been cleaning out, taking video, and lining many of the older metal pipes on the island to optimize drainage. In addition, six problem areas were identified through the Flood Mitigation projects, approved by the members in 2020. With the projects nearly all completed (the second phase of Project 6 at Trumpet Creeper is outstanding), water is able to move more efficiently off the island, and improvements have been evident in the areas of impact.

Other smaller optimization projects take place throughout the year. For example, before and during hurricane season, the island’s storm drains are cleaned out to help ensure they are functioning properly.

 

Before A Storm – Preparing the System

With several days’ notice, these connected lakes and pond water levels can be lowered in order to accommodate excess surface water. KICA manages 10 outfalls where gates allow water to flow into or away from the island. The two largest drainage basin outfalls can be operated remotely by KICA staff, enabling staff to be more responsive to severe weather events regardless of where they are. The team may also proactively lower water levels in the system to allow additional capacity for rainfall. However, pond lowering is not a one-size-fits-all solution, and it can come with detrimental side effects for pond health, so it requires expertise and a strategic approach. 

As a storm approaches, KICA will test and equip staff with mobile pumps that can be deployed should the need arise, and critical stormwater drains will be cleared to ensure proper functioning. Finally, the Lakes team will close the island’s outfall gates before a storm, preventing tidal in-flow to the ponds in order to reserve pond capacity for rainfall.

 

During A Storm 

Some of a storm’s most potent impacts can be from storm surge, especially if a surge coincides with a high tide. During a storm surge, winds from a storm push water up onto the island on the ocean side, but also from the Kiawah River and surrounding marshland. Unlike a rainfall event, this type of flow can’t be addressed by the drainage system. Simply put, the island’s pond network can’t hold the ocean. While proactive planning may create additional capacity for heavy rainfall, a storm surge is an insurmountable amount of water.

 

How to Stay Safe During a Storm

KICA and other island entities encourage members to leave if an evacuation is issued, or if you simply don’t wish to stay through severe weather. If you decide to leave, give yourself time to do so safely. Once the storm impacts have begun, the window to leave the island has closed. 

If no evacuation is issued, the safest course of action is always to remain at home throughout the duration of the storm. By venturing out onto roadways during a storm, you put yourself and potentially island security or first responders at risk. KICA’s security does stay on the island if no evacuation has been ordered, and will conduct patrols if conditions allow. As during Tropical Storm Debby earlier this year, Security will place cones or close roadways as needed in the event of flooding. 

 

After a Storm Event

After a storm, staff will assess island pond levels and the integrity of drainage infrastructure, and respond. If needed, outfall gates will be opened before low tide so that water can drain away from the island as the tide lowers and pulls it out. For the two largest drainage basins, staff can open storm gates remotely with electronic outfalls, but for the other eight, staff must be on the island to open the gates manually. Storm surge must first recede and then the drainage system will begin to move water from the island once tides are below 6 feet.

In remaining areas of standing water on roadways, staff will deploy the mobile pumps to help speed up water flow off the island. Like the stormwater system, pumps can only combat floodwaters that remain after tidal flooding has subsided.

Following larger storms, KICA’s MR&R department typically has a contractor suction out storm drains to remove debris that can clog drains and cause larger problems in the wider system if not removed. At the Trumpet Creeper inlet, Flood Mitigation drainage improvements are scheduled for later in 2024. Road drainage from Governors Drive will be redirected into a drainage basin with greater stormwater capacity, and an outfall structure at Trumpet Creeper Inlet will be reconstructed. The outfall construction will take place late September to early November. KICA’s civil engineer Ryan Ellmers believes that, while this project won’t impact storm surge, “post-storm efforts will be more effective once the area is able to drain efficiently.”

 

Resilience

Although stormwater management is something most members only consider when a storm is imminent, or flooding is occurring, it’s one of the most critical priorities of the association. Maintenance and preparation are key, but as importantly, it takes experienced staff to navigate the unique variables that each storm brings. Every day, KICA’s teams are proactively working to ensure Kiawah’s long-term resilience.