20011729 Ver 1_More Info Received_20040712

Actions by the Town of Siler City to Improve Water Quality
in the Rocky River and Tributaries
July 12, 2004
(Brian McCrodden)
The following are the primary measures that Siler City has already taken or has committed to
take to mitigate the water quality impacts of its proposed reservoir expansion and to protect surface
water quality in the area. In my professional opinion these measures, in combination, will ensure that
the proposed expansion will not result in the degradation of water quality in the Rocky River and its
tributaries, but instead should improve it.
• The minimum release regime for the new reservoir provides for significantly higher flows than
the current minimum release regime. In many cases the flows will be higher than would have
occurred absent the dams.
o The minimum release for the new reservoir is significantly higher in the months that are
most important for the health of the aquatic environment.
o The minimum releases are higher in 15 of 36 conditions (one for each month for each of
3 tiers [defined below]) and are never lower than the present regime. At build-out
(water supply withdrawal of 6 million gallons per day [mgd], which is not projected to
occur until well after the year 2025), for days when the current reservoir is below full
(and minimum releases are made), flows from the new reservoir will be higher than
those from the current reservoir about 60 percent of the time. At no time will the
release be less than that which would occur from the current reservoir.
o During the worst two-three weeks of major droughts, flows from the new reservoir will
be higher than those that would have occurred if there were no dams on the River.
• The Town has agreed to re-design the outlet works of the new reservoir to allow releases of up
to 20 cubic feet per second (cfs) to allow for pulse releases.
o Estimated cost $150,000.
Y

o Requiring that new developments limit impervious surfaces by limiting/discouraging
the use of curb and gutter and requiring grassed swales where the slope is less than 5%.
o Requiring stormwater controls for any new development exceeding 7 percent
impervious surface area.
o Prohibiting the direct discharge of stormwater via ditches or pipes in or through buffer
areas. Alternate stormwater discharge methods, such as infiltration practices, will be
encouraged over the use of detention ponds.
• A fenced 100-foot vegetative buffer (117.3 acres) will be maintained around the expanded
reservoir. All wetlands (0.31 acres) and stream channels (773 linear feet) within this buffer
will be preserved, enhanced or restored, as appropriate. Additionally, 34 other wetlands (17.89
acres) will be created.
5.53 acres of wetlands in the headwaters of the Rocky River in Randolph County will be
enhanced and preserved.
• The Town will participate with other parties to remove the Carbonton Dam on the Deep River.
This project will restore approximately 50,000 linear feet of the Deep River to free flowing
status.
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Actions by the Town of Siler City to Improve Water Quality
in the Rocky River and Tributaries
July 12, 2004
(Brian McCrodden)
The following are the primary measures that Siler City has already taken or has committed to
take to mitigate the water quality impacts of its proposed reservoir expansion and to protect surface
water quality in the area. In my professional opinion these measures, in combination, will ensure that
the proposed expansion will not result in the degradation of water quality in the Rocky River and its
tributaries, but instead should improve it.
• The minimum release regime for the new reservoir provides for significantly higher flows than
the current minimum release regime. In many cases the flows will be higher than would have
occurred absent the dams.
o The minimum release for the new reservoir is significantly higher in the months that are
most important for the health of the aquatic environment.
o The minimum releases are higher in 15 of 36 conditions (one for each month for each of
3 tiers [defined below]) and are never lower than the present regime. At build-out
(water supply withdrawal of 6 million gallons per day [mgd], which is not projected to
occur until well after the year 2025), for days when the current reservoir is below full
(and minimum releases are made), flows from the new reservoir will be higher than
those from the current reservoir about 60 percent of the time. At no time will the
release be less than that which would occur from the current reservoir.
o During the worst two-three weeks of major droughts, flows from the new reservoir will
be higher than those that would have occurred if there were no dams on the River.
• The Town has agreed to re-design the outlet works of the new reservoir to allow releases of up
to 20 cubic feet per second (cfs) to allow for pulse releases.
o Estimated cost $150,000.
• The Town will ensure there is a pulse release of 20 cfs for 12 hours every 30 days whenever
the aggregate storage remaining in the two reservoirs greater than 40 percent (Tiers 1 and 2.)
o Tier 1 is less than full but more than 70 percent storage remaining; Tier 2 is less than 70
percent but more than 40 percent storage remaining; Tier 3 is less than 40 percent
storage remaining. Even at build-out, the reservoir will be in Tier 3 only 5 percent of
the time. Note that even without pulse events, the new minimum release regime calls
for higher Tier 3 flows than are currently required in 3 of 12 months. During drought
years, the pulse release regime will provide twice as many pulses during the critical
months of July through September as the current reservoir and 25 percent more than
would occur if there were no reservoirs.
The Town expanded its Extra Territorial Jurisdiction (ETJ), which gives the Town control of
both sides of the Rocky River for a distance totaling approximately 18.26 miles. This allows
the Town to utilize and expand existing ordinances to manage and direct growth and to control
its environmental impacts.
o Prior to the ETJ expansion, the Town had jurisdiction of only 6.28 miles along only one
side of the Rocky River.
• The Town modified its Unified Development Ordinance (UDO) as suggested by the North
Carolina Wildlife Resources Commission. The most important modifications relating to water
quality include:
o Increasing the minimum buffer requirements along the Rocky River, perennial
tributaries and intermittent tributaries within the Town's ETJ to between 50 and 200
feet. A 200-foot buffer will be imposed along the entire reach of the Rocky River
within the Town's planning area and along all perennial and intermittent streams within
2,500 feet of the Rocky River. Beyond 2,500 feet, the buffer requirement will be 100
feet for perennial streams and 50 feet for intermittent streams within the Town's
jurisdiction. (Areas within the Town's jurisdiction but outside of the Rocky River
subbasin are required to have 100-foot buffers on perennial streams and 50-foot buffers
on intermittent streams.)
2
o Requiring that new developments limit impervious surfaces by limiting/discouraging
the use of curb and gutter and requiring grassed swales where the slope is less than 5%.
o Requiring stormwater controls for any new development exceeding 7 percent
impervious surface area.
o Prohibiting the direct discharge of stormwater via ditches or pipes in or through buffer
areas. Alternate stormwater discharge methods, such as infiltration practices, will be
encouraged over the use of detention ponds.
• A fenced 100-foot vegetative buffer (117.3 acres) will be maintained around the expanded
reservoir. All wetlands (0.31 acres) and stream channels (773 linear feet) within this buffer
will be preserved, enhanced or restored, as appropriate. Additionally, 34 other wetlands (17.89
acres) will be created.
• 5.53 acres of wetlands in the headwaters of the Rocky River in Randolph County will be
enhanced and preserved.
• The Town will participate with other parties to remove the Carbonton Dam on the Deep River.
This project will restore approximately 50,000 linear feet of the Deep River to free flowing
status.
3