20070721 Ver 2_Design/Maps/Site Plans Revised_20231102

STANDARD OPERATING PROCEDURE
WATER AND SEWER DEPARTMENT
Water Treatment Division
Title: North Fork Reservoir Bottom Release Valve
Author: Ricky Levi, Water Treatment Facility Manger
Verified By: � // � Tj Date:
Water Treatment Facility Manager Az!V
Approved By: U464" a. Date: OCt 23, 2023
Utilities Director
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Oct 23, 2023
Purpose: To establish guidelines for operation of a bottom coldwater release valve at
the North Fork Mills River Reservoir to ensure compliance with permit conditions for
minimum flow through the bottom valve opening while achieving de minimus sediment
impacts downstream.
Section I — Operation of the Bottom Release Valve
1) Continuous Bottom Release During Normal Baseflow Conditions
During baseflow conditions, keep the bottom release valve open 5.2 inches,
corresponding to 15'/z turns counterclockwise, to discharge at least 8 cubic feet per
second (cfs).
2) Storm Event Flushing Release
Periodically during rainfall events greater than one-half inch during a running 24-hour
period, open the outlet pipe gate fully to maximize the discharge, correlating to 28 cfs, of
bottom water and sediment.
Water Treatment — North Fork Reservoir Bottom Release Valve
Water & Sewer Department

After the storm event when flow over the dam weir is heavily reduced or ceases,
partially close the gate valve to the baseflow condition of 5.2 inches corresponding to 15
�/2 turns counterclockwise.
3) Drought Conditions
During drought conditions and in accordance with Operational Guidelines for Raw
Water Withdraws within Table 1 and when the USGS Mills River gauge drops below 55
cfs, the bottom release valve shall be closely monitored and adjusted as needed to
maintain a minimum downstream flowrate of 8 cfs:
— ; 1 11 %-+
- When the inflow to the reservoir exceeds 8 cfs, the bottom release valve shall
remain at baseflow condition (15'/z turns counterclockwise with a discharge of 8
cfs). Excess inflow will spill over the top of the dam downstream.
- When the inflow is less than the 8 cfs minimum, the bottom release valve shall be
adjusted to match the upstream incoming flow into the reservoir by maintaining
normal pool elevation at or near the top of the dam. --k - y
At the same time, when the USGS Mills River gauge drops below 55 cfs, flow from the
reservoir to the water treatment facility shall be reduced to no more than 0.8 cfs (0.5
million gallons per day) as the rate required to maintain flow through the system for
maintenance/operational purposes and to ensure adverse effects to water quality within
the non -potable pipeline do not occur. The flow reduction is achieved by throttling the
rate setter (Bailey Sleeve Valve) located at the water treatment facility.
.01 —.2111
Table 1. O erational Guidelines or Raw Water Withdrawals*
Operation Conditions
Minimum
Maximum
Minimum
Mitigation
Withdrawal
Withdrawal
Downstream
Strategy
Rate*
Rate**
Flow Rate
Bradley
Reduce
Creek
0.5 MGD
2.5 MGD
8 cfs
withdrawal rate to
Reservoir
minimum
North Fork
Reduce
Mills River
0.5 MGD
2.0 MGD
8 cfs
withdrawal rate to
Reservoir
minimum
Reduce
Mills River
withdrawal rate to
Intake
2 MGD
12 MGD
42 cfs
minimum,
transition to
withdrawal from
the French Broad
Intake
Water Treatment — North Fork Reservoir Bottom Release Valve
Water & Sewer Department

Proposed
French
0.5 MGD
15 MGD
N/A
N/A
Broad Intake
*Minimum Withdrawal Rate is the rate required to maintain flow through the system for
maintenance/operational purposes
** The total combined withdrawal from all sources is limited to the permitted capacity of the WTP
Section II — Monitoring and Reporting
1) Continuous Bottom Release During Normal Baseflow Conditions
During baseflow conditions, visual inspection of the bottom release valve shall occur on
a monthly basis.
ARIL VIA
2) Storm Event Flushing Release
Or"-V' A, . �
During a storm event flushing release, visual inspection of the bottom release valve
shall occur every three days.
After a storm event flushing release, visually inspect the outlet pipe to ensure no
blockage and inspect the stream bed within 1,000 ft downstream of the dam to observe
any sediment accumulation conditions.
3) Drought Conditions
During drought conditions, visual inspection of the bottom release valve shall occur
weekly.
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4) ReportinT* J,
Maintain records of the position of the bottom release valve as it pertains to the different
operational settings, i.e. normal baseflow condition, storm event flushing condition and
drought conditions, as well as records of on -site monitoring events.
Water Treatment — North Fork Reservoir Bottom Release Valve
Water & Sewer Department

North Fork Reservoir - Bottom Release Valve Discharge Schedule
# Turns CCW
Flow (cfs)
3
1.0
4
1.3
5
1.8
6
2.2
7
2.7
8
3.3
9
3.8
10
4.4
11
4.9
12
5.8
13
6.4
14
7.1
15
7.7
16
8.6
17
9.3
18
10.0
19
10.7
20
11.4
21
12.1
22
12.8
23
13.5
24
14.5
25
15.2
26
15.9
27
16.6
28
17.6
29
18.3
30
18.9
31
19.6
32
20.3
33
20.9
34
21.6
35
22.2
36
23.1
37
23.7
38
24.3
39
24.8
40
25.6
41
26.1

30.0
25.0
20.0
U
3 15.0
0
10.0
5.0
0.0
42
26.5
43
27.0
44
27.4
45
27.7
46
28.0
47
28.3
48
28.4
50
28.4
North Fork Bottom Release Valve
10 20 30 40 50 60
# Turns CCW