ATTACHMENT_B_March_2025_Waterway_Debris_Assessment.pdf

Tropical Storm Debby Survey Report of Ashely River Water Trail. 19 March 2025

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I. Background: The US Army Corps of Engineers (USACE) under ESF3 was issued a mission assignment and subsequently deployed a subject matter expert (SME) to assist FEMA. On 17 March 2025, a Debris SME was placed on a tasker for support and forward deployed.

A. Initial Discussion and Expectations: The SME along with the Charleston District (SAC) ESF3 coordinator coordinated with FEMA PA at the Joint Field Office (JFO) in Columbia, South Carolina on safety, areas of assessment, and coordination with state and local points of contact. The directions for the assessment included calculating the waterway debris volume, cataloging types of debris, and to assess the ease or complexity of access to the waterway debris.

B. Methodology: The SME and SAC POC would personally visit the specified area, account for and calculate volume of eligible debris from the Tropical Storm Debby high water event. They would also coordinate with Dorchester County Director of Parks and Recreation to determine specific areas of interest and locations of reported debris. Products to be Provided include; upward reporting of findings, estimates of volume, and a final report and out brief to FEMA and State personnel.

C. Location: The area to be surveyed is the northern section of the Ashley River in Dorchester County.

The river trail begins at Schulz Lake (N 32.972364, W 80.273322) and is over 12 miles long with the upper six miles being the area of interest. The trail does include two public structures (bridges). The Ashley River is a tidal river with a tidal change generally around 3-5 feet. Dorchester County installed multiple kayak launch ramps for the public to access the trail. The northern access ramp (N 32.967851, W 80.249312) was scheduled to open in March of 2025, after completion of the million-dollar project, but opening was postponed due to waterway debris. During Tropical Storm Debby the Ashley River rose to a peak of 25.29 feet which was over eight feet above flood stage surpassing the previous record of 22.7 feet.

II. Field Observations: Debris SME and SAC ESF3 coordinator met with the Parks and Recreation POC and visited portions of the water trail and surveyed waterway debris. Trail was directly surveyed traveling Northwest to Southeast and debris documented.

a. Maintenance – Multiple locations on the river trail showed signs of being maintained (see figure 1 below) but the team was unable to determine frequency of maintenance. Areas surveyed indicated a maintenance width between 10-15 feet for kayak traffic, not the width of the river in its entirety.

Figure 1. Evidence of past maintenance.

b. Area surveyed and Debris Observed - Figure 2 below shows all points where debris was located and documented.

Figure 2. Point 1 is the upper entrance to the trail in green. Point 2 starts at the yellow point on the left and flows sequentially from left to right to point 25.

c. Public Infrastructure – The river trail does pass under two bridges, Sland and Bacon’s Bridge, but no direct hazardous debris was observed at either bridge.

d. Point 2 – Debris observed obstructing waterway.

e. Point 3 – Debris observed near bank hanging in waterway.

f. Point 4 – Debris observed obstructing waterway.

g. Point 5 – Debris observed obstructing waterway.

h. Point 6 – Debris observed obstructing waterway.

i. Point 7 – Debris observed obstructing waterway.

j. Point 8 – Debris observed obstructing waterway.

k. Point 9 – Debris observed obstructing waterway.

l. Point 10 – Debris observed obstructing waterway.

m. Point 11 – Debris observed obstructing waterway.

n. Point 12 – Debris observed obstructing waterway.

o. Point 13 – Debris observed obstructing waterway.

p. Point 14 – Debris observed obstructing waterway.

q. Point 15 – Debris observed obstructing waterway.

r. Point 16 – Debris observed obstructing waterway.

s. Point 17 – Debris observed obstructing waterway.

t. Point 18 – Debris observed obstructing waterway.

u. Point 19 – Debris observed obstructing waterway.

v. Point 20 – Debris observed obstructing waterway.

w. Point 21 – Debris observed near bank hanging in waterway.

x. Point 22 – Debris observed obstructing waterway.

y. Point 23 – Debris observed obstructing waterway.

z. Point 24 – Debris observed obstructing waterway.

aa. Point 25 – Debris observed obstructing waterway.

III. Overall Debris Estimate: The amount of Tropical Storm Debby related vegetative debris in the six miles of Ashley River Trail that was surveyed from bank to bank was estimated at 5,000 CY. No C&D was observed. Several locations were observed having debris one to two feet below the surface, with the river being a tidal river and the survey occurring at high tide some of these would be obstructions at a lower tide. These locations were captured in the overall debris estimate.

IV. Summary of Findings: Overall, the area surveyed included a considerable amount of waterway debris that could be estimated at over 15,000 CY with most of the debris observed not being related to Tropical Storm Debby. Debris across the river forced the surveying team out of the water and to drag the kayaks around obstructions at high tide seven times. All seven of the debris sites that completely blocked the waterway did appear to be from Tropical Storm Debbie.

As stated above, the river showed signs of upkeep, but we were unable to determine the frequency. The observed previous maintenance width was only 10-15 feet wide leaving the rest of the trees in the waterway. The locations that showed signs of trees that had been trimmed to provide access for kayak sized watercrafts where the remaining section of the trees remained, were not considered in the estimate as they were there before the event.

If the debris in the river is to only be trimmed or removed to provide a path as the previous maintenance did the overall estimate could be reduced to 1,000 CY.

Most, if not all the debris would need to be removed from the water as the adjacent properties are either private or not assessable by road. This would require barge(s) and equipment. While a concern, clearing a path for kayaks and leaving the debris where it is in the waterway is certainly an acceptable course of action. Vegetative debris is a natural part of the ecosystem although it can be a hazard to navigation or future flood events, at times it can be less invasive to leave the debris in place if it’s of little or no risk.

It was not known if the surveyed section of the river trail is considered a navigable waterway.

In summary 1,000 – 5,000 CY of debris would need to be removed/moved to restore access to kayaks.