CMUD_Drought-Management-Plan

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SECTION 5
Drought Management Plan
Lake Norman and Mountain Island Lake are part of the Catawba River Basin and are part of
eleven hydropower impoundments in the Catawba-Wateree Project. The impoundments
are owned and managed by Duke Power under license from the FERC. Lake levels are
managed to provide for power generation, flood control, water supply (for CMUD), and
secondarily to provide recreational opportunities. Duke Power manages the lake levels
according to the “target levels” in Table 5-1, which are presented as a percentage of the
normal (full) pool elevation. The normal pool elevation for Lake Norman is 760 feet msl and
its maximum drawdown is 15 feet. The normal pool elevation for Mountain Island Lake is
647.5 feet msl and its maximum drawdown is 10 feet. The maximum drawdown for each
lake represents the minimum lake level required by Duke Power for power generation.
TABLE 5-1
Target Level for Lake Norman and Mountain Island Lake1
Month Target Operating Range for
Lake Norman
Target Operating Range for
Mountain Island Lake
January 94 - 96% 96%
February 92 - 94% 96%
March 92 - 94% 96%
April 94 - 96% 96%
May 96 - 98% 96%
June 98% 96%
July 98% 96%
August 98% 96%
September – November 97 - 98% 96%
December 96 - 97% 96%
Note:
1 Target operating range is presented as a percentage of normal (full) pool.
Duke Power owns and manages four surface water impoundments upstream of Lake
Norman and Mountain Island Lake including Lake James, Lake Rhodhiss, Lake Hickory,
and Lookout Shoals Lake.
During drought conditions, Duke Power can release some storage in these upstream
impoundments to ensure adequate water supply in Lake Norman and Mountain Island
Lake and to maintain minimum downstream flows. This was the case during the severe
drought of 1999 and 2000 when flows in the Catawba River exceeded the minimum release
from Lake Wylie of 411 cfs required by Duke’s FERC license. The minimum downstream
flows for the impoundments in the Duke Catawba-Wateree Project are presented in Table 5-
2.
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TABLE 5-2
Minimum Flow Requirements for Duke’s Catawba Wateree Project
Development
(Reservoir)
Minimum
Continuous Flow
(cfs)
Minimum
Average Daily Flow
(cfs)
Lake James 25 66
Lake Rhodhiss 40 225
Lake Hickory 40 261
Lookout Shoals Lake 60 278
Lake Norman 80 311
Mountain Island Lake 80 314
Lake Wylie - 411
Fishing Creek Lake - 440
Great Falls Lake - 444
Rocky Creek Lake - 445
Lake Wateree - 446
Currently, CMUD does not have an adopted drought management plan. CMUD is in the
process of completing a Water Conservation Plan. Development of a drought management
plan would require the cooperation of Duke Power since CMUD’s water supplies are only
two of eleven impoundments managed by Duke Power. Due to the complexity of the
Catawba-Wateree system, Duke Power uses a reservoir operations model, a proprietary
version of the commercially available CHEOPS (Computer Hydro-Electric Operations and
Planning Model Software) model, to manage the lakes.
The model was calibrated specifically for the Catawba-Wateree Hydroelectric Project by
Duke using detailed engineering and operations data for the project and historical flow
records from available flow gauges in the basin. The Catawba-Wateree operations model
accounts for inflows (streamflows) and outflows (withdrawals, generation, and indirectly,
evaporation) for each reservoir in the project. The model contains detailed data for storage-
area-volume relationships, reservoir elevation constraints, operating rules, turbine and
generator efficiency curves, travel times and paths.
The complexity of the operation and management of the Catawba-Wateree Project do not
allow for a simple monitoring of CMUD’s available raw water supply capacity.
Cooperation by Duke Power would be needed in order to implement an effective drought
management plan.
However, CMUD has developed the Water Watch Index to provide customers with a
measure of the water supply capacity. The Water Watch Index is updated daily based on
water demands and the delivery capacity of the distribution system. Therefore, the index
was developed to primarily to keep customers informed about water demands and the
utility’s capacity to deliver finished water throughout the distribution system without
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adverse impacts to system pressures rather than a measure of raw water supply capacity.
The Water Watch Index includes the following alert levels:
• STABLE: Demand for water is manageable. Thanks for your conservation
• SERIOUS: Water use is very high. Please minimize nonessential water use
• CRITICAL: Water use is too high. Eliminate nonessential water use
• MANDATORY: Mandatory water restrictions are in effect and will be enforced.
Water Watch Index for Friday June 22, 2001
Mandatory conservation measures could be instituted if the water supply situation becomes
critical. Depending on the severity of the problem, mandatory restrictions could limit or
forbid lawn watering, car washing, filling swimming pools or other specified non-essential
outdoor use during certain days and times. Those who violate a City water conservation
ordinance would receive a fine for each recorded event/offense. Depending on the severity
of the problem, landscapers and some other businesses that rely on water may be allowed to
continue operation under certain circumstances. The first and only time that mandatory
conservation restrictions ever issued was in 1986.