20080299 Ver 1_More Info Received_20080822

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August 22,2M8
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Amanda Jones
USACE
Asheville Regulatory Field Offloe
151 Patton Avenue
Room 208
Asheville, NC 28801
Re. Linville Land Harbor Darn Recrostruction Project
USACE Action ID: 2005-0894
NC DM project* 084M
Dear Ms Jones,
643 omy Reed
Suher43
axone, NC 28907
M; M-2844980
Far 82826148890
o*W: lohnoenw-emmm
The purpose of this letter is to Inform you of a design change to the cold water release structure that will
resufl in a reductio6 in the maramum discharge capacity of this structure. This design change vwill not
have any effect on the minimum relem of 6,6 eft specHied in the Issued permits and related
documents.
In previously submitted reports, this structure was indicated to have a maximum capacity of 40 cis. The
original design would cause frequent lake level fluctuations of 6 inches or more. To reduce this
mmessive fluctuation, a design change resulting in a reduction in the maximum capacity to 25 cis was
necessary. Maxdmum Capacity in this instance terers to maximum flow through the stnxture befbm
surface flow begins to pass over the labyrinth weir, As the lake level increases (e.g.: during a storm
event), the increased head will Increase the total flow thnxgh the cold water release structure. The
purpose or this structure'* to provide a minimum ootdwater baseflow, drawn from approxmately 15 feet
below lake surface, in order to maintain cooler instregm water temperatures downstream of the darn
and to protect trout habitat. Flows in excess of the mzdmum capacity of this Wuat a will flow over the
top of the labyrinth weir. The original rr aodmum capacity of this structure was set to allow all but high
wintertime baseflow to pass. Our analysis of baseflow for the land Harbor Darn site Indicates that 25
ci{5 is still sulflctent to pass all but above average mwdmum wintertime baseflow.
The baseflow ans" performed for this site oonsisted of a review of the pubished data for the UreA1e
River near Nebo (USG5 gage 0 02138500). This site is downstream of the Land Harbor site, jog
above Lake .tames, and is the same gape that was used to determine the 7040 discharge for the land
Harbor Dam. Baseflow for the NOW gage was determined by extrapolating a line alrg the bottom of
the hydrograph for the period I M to 2008. Seasonal high and low basefloow vatues were taken from
the hydrograph for each year and entered into a spreadsheet. These values were adjusted by a factor
of 0.285, which is the ratio of drainage area between the Nebo sfle (88.T sq.mi.) and the Land Harbor
site (19 sq.mi.), to give estimated .baseflow at the Land Harbor site. for the period 1980 to 2008 the
average summer or low ba8wflow was approxmately 8 cis, For the same period the average winter or
high baseflowrwas approximately 25 cis.
The proposed cold water release structure. with maximum capacity of 25 cis. will pass the majority of
baseflow in any given year. The data suggests that elevated baseflow, exceeding 25 efs for adended
periods, will generally oocut during the winter months when maintaining downstream water temperature
below 68 degrees F will not be significant concern. DerirV the summer months, when lore flows and
elevated temperatures pose the greatest threm to downstream trout habits;,, the 25 cfs flow capacity of
the cold water release structure will be amore than sciftent
Lard HerWDam DeApCf Ne LeW
• Page 2
August 22, 2048
Based on this analysis it is our opinion that the design change to the cold water release structure on the
Land Harbor Darn will have no signficwt effect on downstream water temperatures in the Linville River
while at the same time reduce the potential for pool fAtduations in the lake and associated afteds to the
lake rim aquatic life. This design change will not affect the minimum release of 6.8 cis required in ftte
pwnk. With this letter we request concurrence that this design change complies V ft all conditions of
the referenced permits.
If you have any questions or require additional Wonnation please call me at 82&264-8880, thank you.
Sincerely,
Joyc.vlas
President, ENV ErFAronmental Consulting Services Inc.
CC: Kevin Bamett, NCMM
Ron Linville, NCWRC
Mike Simpson, Linville Land Harbor
Mark Landis, Schnabel Engineering
Land Harbor Dam Design Change Letter