Jordan Lake Operation - Alternative Operating Methods

DC 1-29-87

Jordan Lake Operation ----- Alternative Operating Methods

The CORPS has expressed an interest in being able to have
some flexibility in meeting the 600 cfs target flow at
Lillington. This flexibility would consist of allowing some
deviation from the 600 cfs target.

To assess the impact of such an operation mode, we have
performed an analysis of several alternatives using last summers
flows (April 1 to September 30)

Gross assumptions include:

. Flows on the Deep remain unchanged from that recorded at
Moncur. Thus giving a maximum amount of uncertainty in
estimates and assumes no change from present hydro
operation.

. Flow at Lillington known from previous day.

. Release from dam can be adjusted by 50 cfs increments.
Operation tests:

. Dam release based on previous day flow at Lillington.

. If flow at Lillington was between 550 and 650 cfs then no
adjustment to dam release.

. If flow at Lillington in excess of 650 cfs then dam
release reduced by 50 cfs, subject to a minimum flow
constraint.

. If flow at Lillington is less than 550 cfs then release
increased by 50 cfs.

Tests:

1. 50 cfs minimum.
2. 400 cfs minimum.
3. 300 cfs minimum.

COPY JW
JM

Results:

Figure 1 shows recorded flows for the Deep, dam release (at
gage) and at Lillington. From April 1 through September 30,
93553 cfs-days of water was released from the dam.

Figures 2 through 4 illustrates the results of the three test
cases. For each test the volume of water released was computed
and was always less than actual release. These volumes are:

Case Minimum Volume Percent
Flow Reduction
cfs cfs-days

Actual -- 93553 0
Test 1 50 74800 20
Test 2 400 84500 9.7
Test 3 300 78900 15.6

Figure 2 shows that a minimum release of 50 cfs was unable to
correct for flow variations in the Deep. Frequent recurrence of
flows much less than 500 cfs would result. For a 400 cfs minimum
however (Figure 3) flows less than 500 cfs occurred on 2 days,
the lowest flow at Lillington being 488 cfs on June 8.

Conclusion:

Based on this cursory analysis it would appear that some
flexibility in meeting the 600 cfs flow at Lillington is
warranted The setting of a minimum dam release from the dam
assures against serious flow reductions due to hydro operations
on the Deep. However improved reliablity in knowing what will
occur on the Deep could allow lower minimum releases.

The combination of coordinated hydro operation and minimum
flow targets would allow conservation of storage within Jordan,
therby preventing serious drawdowns, and allow maximum economic
benefits to be gained from the hydro operations.

CAPE FEAR DAILY FLOWS
MAY THROUGH JULY 1986

Figure 1 - Actual Operation

FIGURE 2
TEST 1 50 min + 50

FIGURE 3 TEST2 400 min + 50

FIGURE 4 TEST3 300 min + 50

TEST2 400 min + 50
3-DAY MOVING MEAN FLOW