20160692 Ver 1_Technical Report-Final_20211108

Technical Detail Supplement
to
City of Asheville's 2021 Water Shortage Response Plan
Addressing Minimum Flow Release Requirements for the
North Fork Dam at Burnette Reservoir
Prepared for: City of Asheville, Department of Water Resources
E:.
EQUINOX
Prepared by: Equinox Environmental Consultation & Design, Inc.
November 2021

Objective
The purpose of this document is to provide the technical details for the implementation of minimum
flow releases for the North Fork Dam Spillway and Embankment Improvements Project. It excerpts
operations under both normal water production operations and during times of drought as described in
the City of Asheville's (City) updated 2021 Water Shortage Response Plan (WSRP). It also addresses the
conditions of the North Carolina Division of Water Resources (NCDWR) Section 401 Water Quality
Certification #16-0692 for the project. The information in this document will be used by NCDWR to
prepare an amendment to the 401 Water Quality Certification.
Background
In 2012 the City of Asheville initiated a project to meet current North Carolina Dam Safety Program
requirements for the North Fork Dam, a high hazard dam that impounds the North Fork Swannanoa
River as Burnette Reservoir and Asheville's main water supply. The objectives of the project were to
improve the seismic stability of the main and saddle dams, increase maximum reservoir flood water
storage, and to allow for controlled discharges of flows associated with predicted maximum
precipitation (flood) events via a new auxiliary spillway. As a part of permitting for the project, the
NCDWR and resource agencies required a continuous minimum water release from the reservoir.
Following meetings with the NCDWR and the North Carolina Wildlife Resources Commission (NCWRC),
the City of Asheville agreed to install an 8-inch diameter pipe that would allow for the passive release of
a minimum flow to the North Fork Swannanoa River. The mechanism was to be installed during
renovation of the existing spillway gates. The minimum flow system was designed to provide
consistency in downstream aquatic habitat enhancements under normal conditions while giving the City
some relief from those requirements under drought conditions.
On October 9, 2018, NCDWR approved the City's request seeking a Water Quality Certification (permit)
as required by Section 401 of the Clean Water Act. As a condition of certification #16-0692 the City is to
update its water shortage response plan (WSRP) to incorporate changes in reservoir operations that
take into account the effects that the new minimum flow release has on water production. Because the
WSRP is only a part (Section X) of the City's Department of Water Resources Water Policies document
intended for public consumption, the details of how the flow release requirement will be met are
presented in this technical document. It describes the water release mechanism as well as water
production operations and water releases occurring under both normal rainfall and drought conditions.
This document will be a supplement to the WSRP.
For reference, operations under the 2010/2018 WSRPs are included. Minimum release volumes
presented take into account updated modeling of estimated safe yield under new drought triggers,
increased efficiency in water usage fixtures, and the implementation of the minimum flow release
requirements. Safe yield is the maximum quantity of water that is available for use during a critical dry
period.
Technical Detail Supplement 2 Water Shortage Response Plan
City of Asheville November 2021

2010/2018 Water Shortage Response Plans
The City's primary water source consists of two reservoirs, Bee Tree Reservoir and Burnette Reservoir,
with Burnette being the major source, providing 70% of all water for the system. The City also has a
water treatment plant (WTP) on Mills River in Henderson County. It draws water mainly from the Mills
River; water is drawn from the French Broad River to supplement water production when necessary.
Burnette Reservoir has a nominal full pool elevation of 2,601.5 feet (actual 2601.49); the three phases of
drought operations as described in the 2010/2018 WSRP (the 2010 plan was updated in 2018 with no
substantive changes; Table 1) were triggered by specific reservoir levels. The probability of those
reservoir levels being reached were used in the modeling effort to determine changes in water
production but were not included in the WSRPs.
Table 1. Changes in water production operations as related to Burnett Reservoir water levels as
described in the 2010/2018 Water Shortage Response Plans. Demand was assumed to be 24.5
MGD.
Phase
Reservoir
Elevation
(feet)
Trigger
Feet
Below
Full
Pool
Forecast Trigger'
Change in Operation
Expected
Frequency
of
Occurrence
(years)
I
2,572
30.5
20% chance of
Burnette Reservoir
elevation reaching
2,570 feet in 10
weeks
2% reduction in demand; Mills River
WTP2 production increased by 3
MGD2.
10
II
2,571
30.5
10% chance of
Burnette Reservoir
elevation reaching
2,569 feet in 10
weeks
Additional 2% reduction (cumulative
4%) in demand due to mandatory
conservation measures.
20
III
2,570
31.5
5% chance of
Burnette Reservoir
reaching 2,568 feet
in 8 weeks
Additional 2% reduction (cumulative
6%) in demand due to rate
surcharges.
25
1 Forecast triggers were used in drought modeling but were not included in the 2018 WSRP.
2 WTP = water treatment plant; MGD = millions of gallons per day.
Concurrent with phased -in changes in water production, the City's previous WSRPs also called for
reducing customer water usage during the three phases of drought (Table 2).
Technical Detail Supplement 3 Water Shortage Response Plan
City of Asheville
November 2021

Table 2. Restrictions implemented to reduce customer water use during drought conditions.
Phase
Customer Use Restrictions
I
Voluntary actions to achieve a 5% reduction in customer water use from their previous
water bill; water users are encouraged to reduce their water use and improve water use
efficiency; however, no penalties apply for noncompliance.
II
Mandatory actions to achieve a 10% reduction in customer water use from their previous
water bill; water users must abide by required water use reduction and efficiency
measures; penalties apply for noncompliance.
III
Emergency Conditions - Rate Surcharges; customers are expected to reduce their water use
by 25% from their previous water bill; implemented to ensure remaining water supplies
are sufficient to preserve human health and environmental integrity.
Under the 2010/2018 WSRPs, water was released following a Flood Operations Plan; no minimum flow
release was required. Under that plan, water was released following a rule curve designed to protect the
dam and to attenuate downstream flooding preceding predicted high rainfall events. Water was also
released following high rainfall events when reservoir levels exceeded full pool, and, when necessary, to
conduct maintenance operations. The 2010/2018 WSRPs assumed system production of 24.5 million
gallons per day (MGD).
As drought conditions abate, the 2010/2018 WSRPs described how the City would ease customer
restrictions and modify water production operations as reservoir levels rose. During recovery from
drought lake levels had to remain above the target levels for at least 30 days (Table 3) before moving to
the next phase.
Table 3. Changes in operations and customer restrictions during recovery from drought conditions as
described in the 2010/2018 Water Shortage Response Plans.
Phase
Reservoir
Elevation
(feet)
Target
Feet
Below Full
Pool
Change in Operation and Customer Restrictions
III to II
2,571
30.5
When reservoir level reaches 2,571, move from Phase III to
Phase II customer use restrictions.
II to I
2,572
29.5
When reservoir level reaches 2,572, move from Phase II to
Phase I customer use restrictions.
I to
None
2,601.5
0
When reservoir level reaches full pool (2,601.5 feet), remove
water use restrictions.
2021 Water Shortage Response Plan
Because the City has been required to provide a minimum flow release from Burnette Reservoir to the
North Fork Swannanoa River, safe yield and reservoir level changes were reevaluated to account for the
loss of raw water available for treatment and distribution. As a result, the City modified the drought
triggers and drought recovery responses (Tables 4 and 5). The modeling for this plan assumed a current
water production rate of 21.5 MGD.
Technical Detail Supplement 4 Water Shortage Response Plan
City of Asheville
November 2021

Concurrent with the new drought trigger reservoir elevations (Table 4), the City's 2021 WSRP also calls
for implementing the same phased actions to reduce customer water usage as under the previous WSRP
(Table 2). As water levels return to normal, restrictions on customer usage are eased in a similar reverse
order (Table 3) but with the new reservoir target elevations. The same 30-day waiting period between
implementation phases was required.
Table 4. Phases of drought and Burnett Reservoir water elevation triggers for changes in water
production operations in the 2021 Water Shortage Response Plan.
Phase'
Reservoir
Elevation
(feet)
Target
Feet
Below
Full Pool
Trigger'
Change in
Operation
Minimum Flow
Release
Expected
Frequency
of
Occurrence
(years)
2,585
16.5
30% chance of
Burnette
Reservoir
reaching 2,570
feet in 12
weeks
2% reduction in
total demand;
Mills River WTP3
production
increases from 4
to 5 MGD3;
William DeBruhl
WTP reduces
production to 2.5
MGD
Flow based on
reservoir level; 0
cfs' when
reservoir level
reaches 2,585.7
feet, the invert
elevation of the
release pipe;
valve closed at
that elevation
20
II
2,580
21.5
20% chance of
Burnette
Reservoir
reaching 2,569
feet in 10
weeks
Additional 1%
demand
reduction; Mills
River WTP
production
increases to 6
MGD; Wm.
DeBruhl WTP
production
decreases to 2
MGD
0 cfs; reservoir
level below
release pipe
invert elevation of
2,585.7 feet; valve
remains closed
100
III
2,575
26.5
10% chance of
Burnette
Reservoir
reaching 2,568
feet in 8
weeks
Additional 1%
reduction in
demand; Mills
River WTP
production
increases to 7
MGD; Wm.
DeBruhl plant
production
remains at 2
MGD;
0 cfs; reservoir
level below
release pipe
invert elevation of
2585.7 feet; valve
remains closed
>100
'There is a 30-day waiting period before the next drought phase can be implemented.
2Forecast triggers were used in drought modeling but are not included in the 2021 WSRP.
3 WTP = water treatment plant; cfs = cubic feet per second; MGD = millions of gallons per day.
Technical Detail Supplement
City of Asheville
5
Water Shortage Response Plan
November 2021

Table 5. Changes in water production operations and flow releases from Burnette Reservoir to North
Fork Swannanoa River during recovery from drought conditions as described in the 2021
Water Shortage Response Plan.
Phases
Reservoir
Elevation
(feet)
Target
Feet
Below
Full Pool
Change in Operation
Minimum Flow
Release
III to II
2,580
21.5
Move from Phase III to Phase II operations
when the reservoir level reaches 2,580. Wm.
DeBruhl WTP production remains at 2 MGD;
Mills River WTP production decreases to 6 MGD
0 cfs; reservoir
level below
release pipe
invert elevation of
2,585.7 feet;
release valve
closed
II to I
2,585
16.5
Move from Phase II to Phase I operations when
the reservoir level reaches 2,585; Wm. DeBruhl
WTP production increases to 2.5 MGD; Mills
River WTP production decreases to 5 MGD.
0 cfs; release
valve closed
I to
Normal
2,601.5
Full Pool
0
Resume normal operations when reservoir
reaches full pool; Wm. DeBruhl WTP production
increases to 3 MGD; Mills River WTP production
decreases to 4 MGD or to meet demand.
Release valve fully
opened when
reservoir reaches
full pool
elevation, 2,601.5
feet
'There is a 30-day waiting period before the next drought recovery phase can be implemented.
This information meets Condition #8 of the Section 401 Water Quality Certification.
Minimum Flow Releases
Minimum flow releases to the North Fork Swannanoa River are made using an approximately 20 foot
long, 8-inch inside diameter pipe with an inlet invert elevation of 2,583.5 feet. It runs through one of the
fixed gate weirs on the principal spillway. The pipe is fitted with a Mueller butterfly valve to control flow
and a McCrometer Model UM06 electromagnetic flow meter to monitor release volumes. The meter has
an accuracy of ±0.5% of actual flow in waters with conductivities >5 mS/cm. The sensor sleeve has an
inside diameter of 7.782 inches. This configuration required the installation of 45° elbow at the original
outlet and a 2.5-foot extension to maintain the "full pipe" condition required for proper operation of the
flow meter (Figure 1). Invert elevation of the extension outlet is 2,585.7 feet. Estimated discharges from
this structure will vary from about 7 cfs at full pool (2,601.5 feet) elevation to 0 cfs when the reservoir
level reaches the flow release pipe invert elevation of 2,585.7 feet (Table 6).
In developing the minimum flow release plan under drought conditions, the City considered both the
environmental impacts and water production needs. Under the new WSRP the City sacrifices water
production capacity to maintain a flow release to the North Fork Swannanoa during the onset of
drought conditions and as long as the reservoir level is above the invert of the release pipe. Doing so
even during the onset of drought conditions will minimize the effects of drought on downstream aquatic
habitat. If drought conditions persist and the reservoir level drops below the release pipe invert the
valve will be closed. The valve will remain closed until the lake returns to full pool (elevation 2,601.5
Technical Detail Supplement 6 Water Shortage Response Plan
City of Asheville November 2021

feet) at which time the valve will be fully opened. Keeping the valve closed will help shorten the time to
restore the minimum flow releases and allow the City to return to normal water production operations.
This information meets a portion of Condition #9 of the Section 401 Water Quality Certification.
Figure 1. Schematic of North Fork Dam minimum flow release structure with butterfly valve, flow
meter, and outlet extension.
FIELD•
VERIFY ' r
3/8" STEEL PLATE OVER
OPENING/BOX OUT
1% SLOPE -.-
:CONCRETE PIPE
SUPPORT. DOWEL
INTO CONCRETE
4' 0"
SECTION
8" FLG.xPE
PIPE
INVERT:2585.7
2'-6"
8" FLG.xFLG. 45' BEND
4" SO. TUBE SUPPORT WITH
BASE BOLT TO CONCRETE
INVERT 2583.1
Table 6. Estimated water discharges from Burnette Reservoir to North Fork Swannanoa River under
normal water production.
Reservoir
Elevation
(feet)
Operational
Notes
Feet Below Full Pool
Estimated Discharge from
Minimum Release Pipe
(cfs)
2,601.5
Full Pool
0.0
7.11
2,600.0
1.5
6.99
2,598.0
3.5
6.21
2,596.0
5.5
5.68
2,594.0
7.5
5.09
2,592.0
9.5
4.42
2,590.0
11.5
3.64
2,588.0
13.5
2.64
2,586.0
15.5
0.87
52585.7
Invert of discharge
pipe opening
15.8
0.00
Technical Detail Supplement
City of Asheville
7
Water Shortage Response Plan
November 2021

Data Collection and Archiving
The flow meter has a digital readout that displays a 200-second moving average of the discharge in
gallons per minute. A logic controller converts the readings to a format that can be recorded in the City's
database system. The data is also displayed on the WTP operator's terminal; the discharge is read
manually at 10:00 pm and then entered into a spreadsheet (Table 7; Figure 2). Reservoir levels are
similarly automatically measured, displayed on the operator's terminal, and recorded.
To avoid loss of flow, a system of alarms has been set to appear on the WTP's operator terminal. The
first alarm is activated if releases drop below 6.68 cubic feet per second (cfs; 2,500 gallons/minute
[gpm]) for a period of >12 hours. A secondary alarm will sound should the minimum flow release flow go
below 4.01 cfs (1,500 gpm) within the initial 12 hours. When either alarm is activated, staff will operate
the butterfly valve as soon as possible to clear debris and restore normal flow. If the low flow lasts for
more than 48 hours, the Division of Water Resources will be notified.
Flow records will be maintained by the City for not less than 10 years and will be available for review by
the Division of Water Resources upon request. Should observations or plots of the data (Figure 2)
indicate a malfunction of the flow release structure or meter, repairs or replacement will be made as
quickly as is practicable so as to restore flows and minimize the loss of data.
This information meets a portion of Condition #9 of the Section 401 Water Quality Certification.
Agency Coordination Meeting
Condition 10 of the Section 401 Water Quality Certification requires the City to meet with the NCDWR
and NCWRC upon completion of the project. The purpose of the meeting will be to finalize the minimum
release pipe stage/discharge rating curve and minimum releases triggers based on updated reservoir
modeling and drought/drought recovery triggers. Those items will be included in an addendum to the
Water Quality Certification to be prepared by NCDWR. That meeting will occur upon a mutually agreed
upon date, time, and place after the NCDWR and NCWRC have reviewed the contents of this report.
Technical Detail Supplement 8 Water Shortage Response Plan
City of Asheville November 2021

Table 7. Example spreadsheet for the October 2021 record of flow releases from Burnette Reservoir.
PRIMARY SPILLWAY RELEASE
NORTH FORK DAM I BURNETT RESERVOIR
Example
YEAR 2021
Convrts Elev to cfs
MONTH October
Convrts 8" pipe Daily flow fom Weir outflo + 8" Weir outflo + 8"
gpm to cfs Totalzed Flow
pipe cfs pipe MGD
Day
Time
SCADA
Reservoir
Elevation (ft)
Gate
Concrete Weirs
8" Orifice
Approximate
Total Daily
Flow (cfs)
Approximate
Total Daily
Flow (MGD)
Exercise 8"
Minimal Flow
Valve
Reservoir
Level (ft)
Raised /
Lowered
Outflow (cfs)
Totalized _Flow
(gallons)
Gallons Per
Minute (gpm)
(cfs)
Daily Flow Total
(gallons)
1
10:00 PM
-0.43
2,601.06
R
0
3,593,280
2,670.00
5.93
3,916,000 1
5.9
3.83
2
10:00 PM
-0.53
2,600.96
R
0
7,389,610
2,712.00
6.03
3,796,330
6.0
3.89
3
10:00 PM
-0.65
2,600.84
R
0
11,125,760
2,574.00
5.72
3,736,150
5.7
3.70
4
10:00 PM
-0.65
2,600.84
R
0
14,761,530
2,553.00
5.67
3,635,770
5.7
3.67
5
10:00 PM
-0.65
2,600.84
R
0
18,315,450
2,490.71
5.53
3,553,920
5.5
3.58
6
10:00 PM
0.26
2,601.75
R
17
22,214,300
2,583.00
5.74
3,898,850
22.9
14.82
7
10:00 PM
1.8
2,603.29
R
390
25,938,000
2,724.00
6.05
3,723,700
395.9
255.87
8
10:00 PM
1.31
2,602.80
R
239
29,959,420
2,648.00
5.88
4,021,420
244.7
158.11
close/reopen
9
10:00 PM
0.95
2,602.44
R
145
33,765,910
2,714.00
6.03
3,806,490
150.7
97.39
10
10:00 PM
0.67
2,602.16
R
83
37,496,770
2,664.00
5.92
3,730,860
89.1
57.61
11
10:00 PM
0.48
2,601.97
R
49
41,204,640
2,657.00
5.90
3,707,870
54.4
35.17
12
10:00 PM
0.4
2,601.89
R
36
44,792,220
2,532.00
5.63
3,587,580
41.5
26.83
13
10:00 PM
0.25
2,601.74
R
16
48,524,490
2,543.00
5.65
3,732,270
21.7
14.02
14
10:00 PM
0.23
2,601.72
R
14
52,219,450
2,573.00
5.72
3,694,960
19.6
12.64
15
10:00 PM
0.13
2,601.62
R
5
56,060,430
2,915.00
6.48
3,840,980
11.3
7.29
16
10:00 PM
0.11
2,601.60
R
4
60,590,210
3,051.00
6.78
4,529,780
10.3
6.66
17
10:00 PM
0.05
2,601.54
R
1
64,953,120
2,985.00
6.63
4,362,910
7.5
4.86
18
10:00 PM
0.01
2,601.50
R
0
69,248,240
3,123.00
6.94
4,295,120
6.9
4.49
19
10:00 PM
-0.02
2,601.47
R
0
73,783,690
3,026.00
6.72
4,535,450
6.7
4.35
20
10:00 PM
-0.08
2,601.41
R
0
77,994,680
3,117.00
6.93
4,210,990
6.9
4.48
21
10:00 PM
-0.12
2,601.37
R
0
82,372,650
2,993.00
6.65
4,377,970
6.7
4.30
22
10:00 PM
-0.11
2,601.38
R
0
87,051,350
3,054.00
6.79
4,678,700
6.8
4.39
close/reopen
23
10:00 PM
-0.22
2,601.27
R
0
91,113,430
3,021.00
6.71
4,062,080
6.7
4.34
24
10:00 PM
-0.2
2,601.29
R
0
94,905,830
2,907.00
6.46
3,792,400
6.5
4.17
25
10:00 PM
-0.23
2,601.26
R
0
99,046,750
2,938.00
6.53
4,140,920
6.5
4.22
26
10:00 PM
-0.29
2,601.20
R
0
103,121,610
2,905.49
6.46
4,074,860
6.5
4.17
27
10:00 PM
-0.33
2,601.16
R
0
107,331,030
2,851.00
6.34
4,209,420
6.3
4.09
28
10:00 PM
-0.37
2,601.12
R
0
111,392,970
2,739.00
6.09
4,061,940
6.1
3.93
29
10:00 PM
-0.31
2,601.18
R
0
115,333,010
2,785.04
6.19
3,940,040
6.2
4.00
30
10:00 PM
-0.28
2,601.21
R
0
119,306,770
2,705.00
6.01
3,973,760
6.0
3.88
31
10:00 PM
-0.2
2,601.29
R
0
123,206,230
2,722.00
6.05
3,899,460
6.0
3.91
*In the event the flow drops to 2,500 gpm or to the low of 1,500 gpm an alarm is displayed through SCADA.
If the levels remains between 2.500 - 1.500 UM for more than 12 hours. Operators will notify watershed crews to operate the
123,528,950
768.67
butterfly valve.
If a period of 48 hours has passed without improvement. notify the Division of Water Resources at 828-296-4500 or Andrew.W.Moore@ncdenr,gov.
9

Figure 2. Plot of October 2021 North Fork Dam minimum flow release and reservoir elevation including dates on which the release valve was closed and
reopened to clear suspected debris accumulations.
9.a00
8..000
7.000
a� 5.000
tm
L
5.000
vt
4.000
3.000
2.000
Red Line indicates day when butterfly
valve closed/reopened to clear debris.
I
6
Date
. M ete r !Discharge +Lake Elevation (ft)
10
2606
2605
2604
2603
2602
2601
2600
2599
Lake Elevation (feet)