20160692 Ver 1_Approval Letter_20220202

DocuSign Envelope ID: 2BD7D4BA-30E8-43C8-89E5-64C5334B660D
R.OY COOPER.
Governor
ELIZABETH S. BISER
Secretary
S. DANIEL SMITH
Director
NORTH CAROLINA
Environmental Quality
SENT VIA ELECTRONIC MAIL ONLY: NO HARD COPY WILL BE MAILED.
February 2, 2022
DWR # 16-0692 V2
Buncombe County
City of Asheville
Attn: Leslie Carreiro
Email: [e-mail]
Subject: ADDENDUM TO 401 WATER QUALITY CERTIFICATION
North Fork Spillway and Embankment Improvement Project
Dear Ms. Carreiro:
On October 9, 2018, the Division of Water Resources (Division) issued a 401 Water Quality Certification
approval for the subject project. The October 9, 2018 approval replaced a previously issued approval
dated July 11, 2017. Additional Condition 11 of the October 9, 2018 approval required a follow-up
meeting to finalize the minimum release pipe stage/discharge rating curve and allowable minimum
release cutback triggers based on updated reservoir modeling and drought triggers.
On January 31, 2022, representatives from the City of Asheville (City), the Division, and the North
Carolina Wildlife Resources Commission (NCWRC) met to discuss the Revised Technical Detail
Supplement to City of Asheville's 2022 Water Shortage Response Plan Addressing Minimum Flow Release
Requirements for the North Fork Dam at Burnett Reservoir dated January 2022 (Supplement), which
among other things, describes updates to the City's Water Shortage Response Plan reflecting recent
modifications to the North Fork Dam including the minimum release pipe. The Supplement did not
contain, nor has the Division been provided, a stage/discharge rating curve for the minimum release
pipe as the Division understands the reservoir level has not varied adequately over the full range of
reservoir levels above the minimum release pipe inlet since the pipe was installed to create the rating
curve. However, a record of flow releases for October 2021 was provided and included in the
Supplement. The Division understands from the Supplement that the minimum release valve will not be
manually throttled except to periodically clear debris from the pipe. Therefore, there are no proposed
minimum release cutback triggers, with the exception of the natural decrease in discharge due to
reductions in head pressure as the reservoir level drops.
The Division has determined Condition 11 of the 401 Water Quality Certification approval has been
substantively met. The drought triggers specified in the Supplement are hereby incorporated into the
approval. If the City proposes to modify the drought triggers and/or modify in any way the minimum
release pipe, you must consult with the Division and NCWRC. Depending on the extent of modifications,
a revised 401 Water Quality Certification may be required.
nJoCAROLINA
D_E
o.aemmeni or E,Mr nneev!rnaI
North Carolina Department of Environmental Quality I Division of Water Resources
Asheville Regional Office 12090 U.S. Highway 70 I Swannanoa, North Carolina 28778
828.296.4500

DocuSign Envelope ID: 2BD7D4BA-30E8-43C8-89E5-64C5334B660D
North Fork Spillway and Embankment Improvement Project
DWR # 16-0692 V2
Addendum to 401 Certification
Page 2 of 2
This approval and its conditions are final and binding unless contested. [G.S. 143-215.5]
Statutes by filing a Petition for a Contested Case Hearing (Petition) with the North Carolina Office of
Administrative Hearings (OAH) within sixty (60) calendar days. Requirements for filing a Petition are set
forth in Chapter 150B of the North Carolina General Statutes and Title 26 of the North Carolina
Administrative Code. Additional information regarding requirements for filing a Petition and Petition
forms may be accessed at http://www.ncoah.com/ or by calling the OAH Clerk's Office at [phone].
One (1) copy of the Petition must also be served to the North Carolina Department of Environmental
Quality:
William F. Lane, General Counsel
Department of Environmental Quality
1601 Mail Service Center
Raleigh, NC 27699-1601
This letter completes the review of the Division under section 401 of the Clean Water Act and 15A NCAC
02H .0500. Please contact Andrew Moore at 828-296-4684 or [e-mail] if you
have any questions or concerns.
Sincerely,
�DocuSigned by:
"-7E617A38285848C...
G. Landon Davidson, P.G.
Regional Supervisor
Water Quality Regional Operations Section
Division of Water Resources, NCDEQ—ARO
Enclosures: Revised Technical Detail Supplement to City of Asheville's 2022 Water Shortage
Response Plan Addressing Minimum Flow Release Requirements for the North Fork Dam
at Burnette Reservoir
ec: Jim Borawa, Equinox Environmental
Keith Webb, McGill Associates
Steve Kichefski, USACE Asheville Regulatory Field Office
Fred Tarver, Division of Water Resources
Chris Goudreau, North Carolina Wildlife Resources Commission
Andrea Leslie, North Carolina Wildlife Resources Commission
DWR 401 & Buffer Permitting Unit file

Revised
Technical Detail Supplement
to
City of Asheville's 2022 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
EQUINOX
Prepared by: Equinox Environmental Consultation & Design, Inc.
November 2021
Revised January 2022

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 2022 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 is 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 Revised January 2022

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 WSRPs (the 2010 plan was updated in 2018 with no
substantive changes; Table 1) were triggered by specific predicted reservoir levels. The probability of
those reservoir levels being reached were used in the modeling effort to set the triggers, but only
elevations were shown for simplicity.
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 Trigger1
Change in Operation
Expected
Frequency
of
Occurrence
I
2,572
29.5
20% chance of
Burnette Reservoir
elevation reaching
2,572 feet in 10
weeks
2% reduction in demand; Mills River
WTP2 production increased by 3
MGD2.
Once per
10 years
II
2,571
30.5
10% chance of
Burnette Reservoir
elevation reaching
2,571 feet in 10
weeks
Additional 2% reduction (cumulative
4%) in demand due to mandatory
conservation measures.
Once per
20 years
III
2,570
31.5
5% chance of
Burnette Reservoir
reaching 2,570 feet
in 8 weeks
Additional 2% reduction (cumulative
6%) in demand due to rate
surcharges.
Once per
25 years
1 Forecast triggers were used in drought modeling but were not shown in the WSRPs.
2 WTP = water treatment plant; MGD = millions of gallons per day.
Note: The forecast trigger elevations listed in Table 1 of the draft document were revised to align
correctly with the reservoir elevation trigger. The elevations listed in the draft report were taken from
those used in developing a flood operations model.
Technical Detail Supplement 3 Water Shortage Response Plan
City of Asheville
Revised January 2022

Concurrent with phased -in reductions in water production, the City's previous WSRPs also called for
reducing customer water usage during the three phases of drought (Table 2). The original usage goals
were intentionally set high to increase the probability that the target demand reductions shown in Table
1 would be achieved.
able 2. Conservation measures implemented to reduce customer water use during drought conditions.
_
Overall Conservation Goals
Based on Average Water Bill
Customer Use Restrictions
2010/2018
2022
Voluntary - water users are encouraged to reduce their
water use and improve water use efficiency; no penalties
applied for noncompliance.
5%
5%
Mandatory — water users must abide by required water use
reduction and efficiency measures; penalties apply for
noncompliance.
10%
III
Emergency Conditions - Rate Surcharges are put into effect;
water users are expected to implement water
conservation measures to ensure remaining water
supplies are sufficient to preserve human health and
environmental integrity.
25%
la
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.
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 (Table 3). During recovery
from drought reservoir elevations had to remain above the target levels for at least 30 days before
moving to the next phase.
Table 3. Changes in operations and water conservation measures during recovery from drought
conditions as described in the 2010/2018 Water Shortage Response Plans.
Phase
Burnette
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.
Technical Detail Supplement
City of Asheville
4
Water Shortage Response Plan
Revised January 2022

2022 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, a modeling exercise was performed with staff input to guide the 2022
WSRP update. During the exercise safe yield and reservoir level changes were reevaluated to account for
the loss of raw water available for treatment and distribution due to the required release. Consideration
was also given to the impacts poor water quality would have on the treatment process and associated
costs. Staff recognized the concern regarding "sharing the pain" and identified conservation targets that
would reduce demand as minimum releases declined. Multiple scenarios were simulated using 90 years
of weather and hydrological data. Simulation results revealed the effects of various trigger levels. During
this process, staff also considered the frequency of implementing conservation measures; that less
frequent calls for conservation would ensure the public would react positively to the request. Based on
the modeling simulations, the City modified the drought triggers and drought recovery responses as
shown in Tables 4 and 5.
Table 4. Drought triggers for changes in water production and water conservation measures in the 2022
Water Shortage Response Plan.
Phase'
Feet Below
Full Pool
Trigger
Probability
Change in Operation2
Expected
Frequency of
Occurrence at
Current
Demand3
I
16.5
30% chance of
Burnette Reservoir
reaching 2,585 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
Once per 20
years
II
21.5
20% chance of
Burnette Reservoir
reaching 2,580 feet
in 10 weeks
Additional 1% demand
reduction; Mills River
WTP production
increases to 6 MGD;
Wm. DeBruhl WTP
production decreases to
2 MGD
Unce per 100
years
III
26.5
10% chance of
Burnette Reservoir
reaching 2,575 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;
Less than once
per 100 years
'There is a 30-day waiting period before the next drought phase can be implemented.
2 WTP = water treatment plant; cfs = cubic feet per second; MGD = millions of gallons per day.
3 Current demand is 21.5 MGD.
Technical Detail Supplement
City of Asheville
5 Water Shortage Response Plan
Revised January 2022

Table 5. Changes in water production operations under water conservation measures and during
recovery from drought conditions as described in the 2022 Water Shortage Response Plan.
Phases
Burnette
Reservoir
Target
Elevation
(feet)
Feet
Below Full
Pool
Change in Operation
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
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.
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.
'There is a 30-day waiting period before the next drought recovery phase can be implemented.
As described in detail later, the minimum releases are being made through an 8-inch pipe. Releases to
the North Fork Swannanoa River are based on a flow rating curve; maximum discharge is approximately
7 cfs (4.5 MGD) at normal full pool of 2601.5 feet, dropping to zero at the pipe release invert elevation
of 2585.7 feet. A valve was included to throttle the flow as needed to preserve storage in a drought, but
through the modeling exercises, it was determined that throttling will not be needed. Therefore, the
valve will remain fully open under all conditions, both during drawdown and refill of the lake. As the lake
is drawn down during drought conditions, flow will steadily drop until the 2585.7-foot elevation is
reached. As the lake refills as the drought abates, flows will steadily increase until the maximum is
reached at full pool.
The implementation of the drought triggers is based on an in -flow prediction model that is run
frequently during dry periods. The model uses local precipitation data, average water production rates,
and 90 years of historical hydrologic data to predict the probability of the reservoir reaching the target
lake levels over a specific time horizon. Based on the model, the Phase I drought trigger will be
implemented as much as 12 weeks before flow releases reach 0 cfs. By implementing conservation
measures and water production the City "shares the pain" as these measures result in more water being
available for release. These actions will occur at least 2-weeks earlier and at much higher reservoir
elevations than occurred under the 2010/2018 WSRPs.
Concurrent with the new drought trigger reservoir elevations (Table 4), the City's 2022 WSRP also calls
for lowering customer water conservation goals. The lower goals are justified in that regulations put into
effect over the last 15 years now restrict the amount of water used in everyday appliances (toilet,
washing machine, shower head, dishwasher, etc.). Water conservation goals are now overall reductions
of 5%, 10%, and 15% for Phases I, II, and III under drought conditions (Table 2).
Technical Detail Supplement 6 Water Shortage Response Plan
City of Asheville Revised January 2022

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 is required.
To ensure the drought triggers are robust, the triggers were developed to accommodate a future
demand of 24.5 MGD. At that level of demand the trigger frequency of Phases I, II, and III would be six
years, 17 years and 100 years, respectively. The procedures used in developing the triggers are
summarized in the document titled "Summary of Operating Rule Updates_ August_2021 (Appendix A).
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.
This information meets a portion of Condition #9 of the Section 401 Water Quality Certification.
Technical Detail Supplement 7 Water Shortage Response Plan
City of Asheville Revised January 2022

Figure 1. Schematic of North Fork Dam minimum flow release structure with butterfly valve, flow
meter, and outlet extension.
FIELD `.
VERIFY
3/8" STEEL PLATE OVER
OPENING/BOX OUT
1% SLOPE
CONCRETE PIPE
. SUPPORT. DOWEL
INTO CONCRETE
4. D"
SECTION
8" FLG.xPE
PIPE
INVERT: 2585.7
8" FLG.xFLG. 45' BEND
4" SQ. TUBE SUPPORT WITH
BASE BOLT TO CONCRETE
Table 6. Estimated water discharges from Burnette Reservoir to North Fork Swannanoa River.
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 8 Water Shortage Response Plan
City of Asheville
Revised January 2022

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 every evening; the data are then entered into a spreadsheet (Table 7; Figure 2).
Reservoir levels are similarly automatically measured, displayed on the operator's terminal, and
recorded.
An alarm has been set to notify staff in the operator's control room should the pipe become clogged.
The warning is activated if releases drop below 6.68 cubic feet per second (cfs; 2,500 gallons/minute
[gpm]) and remain there for more than 12 hours or if the release goes below 4.01 cfs (1,500 gpm) and
remains there for more than 1 hour. Upon receiving the warning 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. Also, standard operating procedures now include
exercising the valve once every other week.
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 9 Water Shortage Response Plan
City of Asheville Revised January 2022

Table 7. Example spreadsheet for the October 2021 record of flow releases from Burnette Reservoir.
PRIMARY SPILLWAY RELEASE
NORTH FORK DAM / BURNETT RESERVOIR
Example
Convrts Elev to cfs
YEAR 2021
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
Technical Detail Supplement
City of Asheville
10
123,528,950
768.67
Water Shortage Response Plan
Revised January 2022
*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 flow remains between 2,500 - 1,500 gpm for more than 12 hours or below 1,500 gpm for >1 hour, operators will notify watershed crews to operate the butterfly valve.
If a period of 48 hours has passed without improvement, notify the Division of Water Resources at 828-296-4500 or [e-mail].

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.CCC
S.000
7.000
r
15
to
- 6.000
an
iv
5.000
4.000
3.000
2.000
Red Line indicates day when butterfly
valve closed/reopened to clear debris.
61N'
,��1 ,�❑1 ,��1
Date
Meter Discharge
—4— Lake Elevation (ft}
2606
2605
2604
2603
2602
2601
2600
2599
Lake Elevation (feet)
Technical Detail Supplement 11 Water Shortage Response Plan
City of Asheville Revised January 2022

Appendix A
Hazen
Hazen arid Sawyer
4011 1 We:4Wuse BP .,, Slrte 500.
Raleigh, N0276Q7
To: Leslie DarreirolBill Hart, Asheville Water Department
From: Steven Nebiker, Hazen
Re: Operating Rule Updates
Date: August 5; 2021
The City ofAsheville is preparing to activate the new auxiliary and upgraded spillways at North Fork
Reservoir but is first required to submit to the North Carolina Department of Environmental Quality
DEQ) any planned updates to its drought triggers in its Water Shortage Response Plan (WSRP)_ These
updates would incorporate the impacts of the new minirmrrn release requirenment ;at North Fork associated
with the spillway upgrade.
To determine what updates were needed, Hazen conducted a drought exercise with Water Department
staff on December 15, 2020_ Staff included treatment plant operators; production supervisors: department
managers_ and laboratory technicians. In the exercise, staff were introduced to a -virtual" historical
drought event and asked to make operating decisions as the drought intensified and then eased. At the
end, the drought event was revealed and results compared with how the drought would have been
managed under the previously eloped rules_ This memo captures the key observations from the
lexercise and how that information was used to update the drought triggers. Details of the exercise are
captured in the attached Powerpoint slide deck.
Hazen spent the early part of the exercise familiari2ing staff with the OASIS model that has been used
since the mid-2000s to evaluate the reliability of Asheville's raw water supplies_ The review covered key
inputs to the OASIS model, including inflows: production levels; and reservoir and treatment capacity
limits. HydroLogics (now Hazen) used this information in the mid-2000s to develop the triggers that are
reflected in the WSRP, with periodic review of the triggers to factor in changing operations (namely
bringing Bee Tree back into operation). These tuggers are summarized below, along with the actions:
• Trigger 1 (voluntary): 20% chance of North Fork hitting 2 572 feet (9 feet down) in 10
weeks (action = 2% demandredutton, with increases in production at Mills and Bee
Tree)
• Tri er 2 (mandatory): 10% chance ofNorth Fork hitting 2571 feet (30 feet down) in 10
weeks (action = an additional 2% demand reduction)
• Trigger 3 (surcharge): 5% chance of North Fork hitting 2570 feet (31 feet down) in
weeks (action = an additional 6% demand reduction)
For the game, these triggers were not shown to the group. Instead; the participants were left to decide
when to take coireclive action_ These actions are a function of risk tolerance_ concerns over production
and pumping cost whichvary widely depending on reservoir or river supply; and other concerns like
water quality. As the exercise unfolded, Hazen presented information in real-time during the drought
event, including stream gaging flows and OASIS projections of reservoir storage over the coming year
based on historical data.
The results of the exercise demonstrated a greater concern for reservoir drawdown than was reflected in
the existing triggers_ It also demonstrated a preference for preserving Bee Tree supply as the drought
intensified, as manifested by curtailproduction rather than increasing it as North Fork. the primary
source; drew down_ Under the existing triggers, when the first trigger is reached_ Bee Tree is assumed to
increase production to relieve pressure on North Fork. However, during the game, participants decided to
hazena ndsawyer.corn
Technical Detail Supplement 12 Water Shortage Response Plan
City of Asheville Revised January 2022

Hazen
August 5, 2021
scale back production starting with the first trigger to preserve supply in the reservoir_ These decisions
mostly reflected concerns over the ability to treat the water and provide distribution. system pressure. To
ease the pressure on North Fork; two actions were identified: curtail the minimum release by 50% and
increase production from Mills River. The latter was increased incrementally on activation of each
trigger to account for con.cerns about the relatively high cost of production.
As for minimum release; the group recogpized the concern about "sharing the pain" and identified
conservation targets that wouldrednce demand at the same time as reducing mininaama release Minimum
release is to be provided through an 8-inch pipe with a valve to throttle back the normal hydraulic
discharge (based on a rating curve)_ When the lake elevation reaches 2584 feet; or the invert of the pipe,
the flow drops to zero.
As a result, the game produced much lower drawdown in Bee Tree than raider eaasting pules. At the same
time; triggers would be enacted far sooner to help conserve storage in North Fork.
Hazen updated the triggers based on the results of the game and are simmmarized in the attached
spreadsheet along with the new actions. They are probability -based for drawdown, tied to when there is a
high enough chance of drawing down North Fork to certain levels over different forecast horizons. For
refill_ they are elevation -based, triggered on elevation alone, and reflect the preference for keeping actions
in place for as long as possible to accelerate reservoir refill. Actions related to demand management
result in much lower demand reductions than assumed in the past, reflecting the increased efficiency of
customer's normal water use.
The triggers were later updated to reflect the actual release through the minimim, release pipe, which is
approximately 50 percent of the initial rating curve amount_ Due to the lower actual minimum release,
the tuggers no longer incorporate a further reduction (through valve throttling) when the tuggers are
activated. This reflects the fact that the lower normal minimum release reduces the impact on reservoir
drawdown_
The triggers are tested over the historic inflow record to make sure they work for all drought events; not
just the one in the exercise that capturedthe 1998 drought_ The goal is to ensure drawdown triggers
detect the droughts in time while nunimiiina false alerts (i.e., droughts which end up not requiring
significant corrective actions). The triggers are also tested over a range of system demands to ensure they
are robust over a givenplanning horizon. This horizon is approximately 15 years based on future demand
projections_ Given there is production loss in the treatment process, the demands were increased by the
amount of the production loss (assumed to be 2 percent) to reflect the raw watervuithdrawn. The loss
from North Fork is returned to the river downstream of the dam combining with the assumed dam
leakage of 0.25 cfs and any minimum release from the dam_
Frequency of activating the drawdown triggers at today s lei'e1 of demand (21.5 mgd) and raw water
withdrawal (22.0 mgd) is as follows: 5: 1: and 0 for triggers 1: 2, and 3; respectively_ Over the 100 year
inflow record, tugger 1 for example ouldbe activated on average once every 20 years (5 events in 100
years).
Frequency of activating the triggers at year 2030 1eve1 of demand (24.5 mgd) and raw water withdrawal
(25.0 mgd) is as follows: 16, 6, and 1 for triggers 1, 2, and 3, respectively. Over the 100 year inflow
record, trigger 1 would be activated on average once every six years, trigger 2 once every 17 years; and
tugger 3 once every 100 years.
Coy of Atect1]
Operating Rule L"pdates
Technical Detail Supplement 13 Water Shortage Response Plan
City of Asheville Revised January 2022