20180705 Ver 1_Project Narrative_20180522

Lumbee Tribe of North Carolina
Cultural Center Lake Dam Repairs

Project Narrative
May 2018

JEWELL Engineering Consultants was contracted by the Lumbee Tribe of North Carolina to assess
the hydraulic adequacy of the Lumbee Cultural Center Dam and design repairs and improvements.
The dam system consists of a roughly 6,000-foot-long earth embankment that runs generally
northwest - southeast (north-south for the purposes of this work). There is a primary riser/barrel
outlet at the south end, a secondary riser/barrel outlet about 800 feet from the north end, and a
concrete overflow spillway at the north end. The lake is approximately 93 acres in size, based on
a delineation using aerial photography. The attached Figure 1 shows the locations of the dam
structures on an aerial of Cultural Center Lake.

The dam was overtopped during Hurricane Matthew in October 2016 and experienced damage
due to overtopping and the extended period of high water levels in the lake. In areas where
overtopping occurred, there is scouring and erosion on the top and downstream slope of the dam.
There is a linear sinkhole along the northern segment of the dam where it appears piping has
occurred. This is likely due to the forces exerted on the dam from the extended period of high
water levels. Approximately 2700 linear feet of the dam has a band of concrete for erosion
protection at the normal water level range of the lake. During major rain events, like Hurricane
Matthew, the water level rises above the concrete slab. In numerous places, the slab has been
undercut by water forces and the upstream face of the dam now has areas of significant erosion.

This project will repair the damaged embankment, raise the crest elevation to 169.5 along the
whole length of the dam, repair the existing concrete spillway with a gabion structure, stabilize the
headcut/channel area, add an emergency spillway, install articulated concrete block where wave
protection is needed, and replace the slide gates & lower trash racks at the primary riser/barrel
structure. The lake has been drained since October 2017 to allow the embankment work to be
done in dry conditions. Access to the lake side of the dam will be established at shallow areas of
the dam at two locations: near the boat ramp at the south end of the dam and from an area where
the dam turns to the north away from Terry Sanford Drive.

Headcut / Channel Repair

We are proposing to permit the stabilization of the eroded channel and headcut area under a NWP
13 – Bank Stabilization. Over time, overland flows have formed a headcut and channel from a
low area north of the dam. This channel flows into the discharge pool just downstream of the
concrete spillway. In significant precipitation events, this area provides some discharge capacity
from the lake and needs to be addressed as part of the overall dam repair. The pictures below
show the existing headcut and channel. This project will stabilize the channel with a reno
mattress channel bottom and gabion basket wall. See Sheet 7.0 of the construction drawings for
the repair plan and cross sections.

Concrete Spillway Repair

We are proposing to permit the spillway repair and stabilization of the discharge pool under a
NWP 3 – Maintenance. The repair of this existing structure will sawcut and remove the
damaged portion of the concrete spillway and replace it with a stepped gabion structure. A
concrete section will be poured at the top of the gabion structure to provide a seal between the
gabion structure and existing concrete spillway.

The discharge pool appears to have some riprap just downstream of the spillway structure, but it
does not appear to be adequate for energy dissipation and erosion protection in larger storm
events. This project will add Class 1 riprap approximately 60 feet beyond the spillway structure.
The pictures below show the downstream portion of the spillway taken in the fall when the lake
had been lowered. See Sheet 6.0 of the construction drawings for the repair plan and cross
sections.

Emergency Spillway Outlet Protection

We are proposing to permit the outlet protection of the proposed emergency spillway under a
NWP 3 – Maintenance. The existing secondary riser discharges through a concrete pipe to a
stream that flows across Tribe property to the Lumber River. In order to increase outlet capacity
for the dam, this secondary riser/barrel will be removed and an emergency spillway will be
constructed in this location. An 8” DIP lake drain will be installed through the spillway and
discharge at the same location as the existing riser/barrel. Because this channel will receive
significantly higher flows during large storm events, it will be lined with Class 1 riprap for energy
dissipation and erosion protection.

Embankment Repairs

The crest elevation of the dam embankment varies across the length and will be raised to a
consistent 169.5. The left picture below shows the deteriorated condition of the existing concrete
wave protection apron across approximately 2700 linear feet of the embankment. It will be
replaced with articulated block as part of this project. Additionally, the slide gates and lower trash
racks at the primary riser structure will be replaced. The right picture below, taken while the lake
is drained, shows the primary riser.

NCCGIA
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L
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RIVERGUM LITTLEJUNIPERBRANCHCultural Center DamLumbee Tribe of NC
Figure 1: Cultural Center LakeSWAMPPrimaryRiser/ Barrel
Seconda ryRiser / Barrel
ConcreteSpillway
Cultural Center Lake
Linear sinkhole
0 500 1,000250 Feet
Headcut/ErodedChannel