BOILING SPRING LAKES, NC Presentation for The Brunswick County - - PowerPoint PPT Presentation

THE NEED FOR AN ADDITIONAL SPILLWAY AT THE SANFORD DAM BOILING SPRING LAKES, NC

Presentation for The Brunswick County Commissioners April 20, 2015

The Sanford Dam

• Earth Dam constructed in 1961
• Drainage area of 6,381 acres (10 sq. miles)
• Length of 1584 feet
• Structural height of 30 feet
• Impounds 285 acres of water
• Maximum storage of 3,600 acre-feet
• Designated as a medium size dam
• Classified as “High Hazard”

What is a High Hazard dam?

• Class C (High Hazard) includes dams located where

failure will likely cause loss of life or serious damage to homes, industrial and commercial buildings, important public utilities, primary highways, or major railroads.

Dam Hazards Classification Hazard Classification Description Quantitative Guidelines Low Interruption of road service, low volume roads Less than 25 vehicles per day Economic damage Less than $30,000 Intermediate Damage to highways, Interruption of service 25 to less than 250 vehicles per day Economic damage $30,000 to less than $200,000 High Loss of human life* Probable loss of 1 or more human lives Economic damage More than $200,000 *Probable loss of human life due to breached roadway or bridge on or below the dam. 250 or more vehicles per day

Statistics from NC Dam Safety “Emergency Action Planning (EAP) Website”

Most dam failure fatalities are not the result of large dams. Most fatalities are the result of small dam failures. Dam failures resulting in fatalities:

• 86% of the fatalities have resulted from dams between 20 and 49 feet

in height

• 47% of the fatalities have resulted from dams with a drainage area

less than 2 square miles

• 75 % of the fatalities have resulted from dams with a drainage area

less than 10 square miles

• 7 dams had less than 300 acre-feet of reservoir storage area

This description fits many of North Carolina's dams

What our dam looks like today

Crest elevation 39.0 ft.

Some definitions

A 100-year flood

 a flood event that has a 1% probability of occurring in

any given year. Probable Maximum Precipitation (PMP)

"...the theoretical maximum precipitation for a given

duration under modern meteorological conditions."

The theoretically greatest depth of precipitation for a

given duration that is physically possible over a particular drainage area at a certain time of year

NORTH CAROLINA DAM SAFETY LAWS AND REGULATIONS

Three main concerns

• 1. Worst case scenario
• The Dam is overtopped at elevation 39.0 ft. and we lose the

impoundment with potential loss of life and property.

• 2. Excessive flooding
• We cannot keep pace with the watershed and flooding damages

roads, property, and eliminates Route 87 as an evacuation route for communities south of BSL.

• 3. Creation of “sink holes”
• Current use of the gates to adjust lake levels in advance of storms

helps to create or accelerate the formation of sink holes. The new spillway will maintain consistent levels during storms, without manual operation. No need to depress water by 2 feet!

What could happen after overtopping

Evacuation Routes – 87, 211 and 133

Users:

Oak Island Caswell Beach Southport St. James Boiling Spring Lakes Military Ocean Terminal Sunny Point Brunswick Nuclear Plant/ Duke Energy

Route 87 – Our hurricane evacuation route!

Road Elevation 34.4 ft 2005, Tropical Storm Tammy 2005, Hurricane Ophelia 1999, Hurricane Floyd 1998, Hurricane Bonnie 1996, Hurricane Bertha 1996, Hurricane Fran

Other key roads flood at this location

• Isolate Residents
• Prevent Emergency

Services Response  EMS facility is located on north side of Rt. 87

• Examples:

 Boiling Spring Rd (SR1539)  Fairway Dr.  South Shore Dr.  Elm Rd

Sinkholes have drained the lake

Impact on our community

How do we operate our existing gates?

• Existing gates in the outlet structure are manually operated to

maintain consistent lake levels (not recommended).

• Repeated manual operation creates future risk of gate failures.
• “Drain down” rates limited to 1 ft./day by NC Dam Safety, to prevent

slope impacts along the lake edge.

• Safety issue - equipment cannot be operated during rainfall due to

lightning shock hazard. So we predict when to lower levels.

• New spillway “open top” will enable consistent water levels without

manual operation!

• Outlet Control

Top of Dam

New Spillway Existing Spillway Discharge Pipes

Four (4) new discharge pipes of 60” Diameter

Endorsements

• Wilmington District, US Army Corps of Engineers

“There is real potential for the dam to be overtopped for storms just

above the 100-year event threatening the integrity of the dam”

• Progress Energy Brunswick Nuclear Plant

“We support and endorse Boiling Spring Lake’s effort to increase

Sanford Dam’s spillway capacity, which is necessary to eliminate the blockage of Highway 87”

• Brunswick County Department of Energy Management
• Brunswick County Commissioners (in 2008)

What have we spent in the past?

Prior Work Year Approximate Expenditures

Install a grout curtain, recoat the inside of original 54" pipes, install pipe couplings, gate modifications and install subdrains 1978 $100,000 (estimated) Re-lining the original pipes with 40" inserts and grouting void spaces between 1989 $92,000 Adding pipe extensions, grouting, and toe drain installation 1991 $75,000 Reconstruction of the downstream face of the dam at the spillway 2001 $124,000 Install four (4) new hydrogates replaced at the existing spillway 2007 $110,000 Engineering Design services for the new Spillway 2013 $130,000

Approximate Total of These Efforts $630,000

Funding This Critical Project

Partnership % Participation Estimated Contributions Boiling Spring Lakes 25% $500,000 (dedicated already) Brunswick County 25% - 50% $500,000 - $1,000,000 State of North Carolina ? ? Federal Agencies ? ? Estimated Project Cost (2013) $2,200,000

How do we proceed with funding?

Spillway Project Schedule

Tasks 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 12th 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 12th

Final Design Review by NC Dam Safety ***** FEMA's CLOMR/LOMR Process ***************************** Advertisement for Construction Bids ****** Pre-Bid Meeting with Contractors ** Bid Review Period *** Contract Award and Notice to Proceed ** Construction Period *********approx. 10 months *********

First year of project schedule in months Second year of project schedule in months

Please partner with us!