Risk Assessment for Jordan Lake Water Supply

DIVISION OF WATER RESOURCES

September 6, 1988

MEMORANDUM

TO: John Morris

THROUGH: John Wray

FROM: David Crawford/Jeanne Csapo

We have performed an assessment on Jordan Lake to determine
the risk of depleting the storage at the lake. As a starting
point we assumed an elevation of 210.2, which corresponds to the
level of the lake at the time the Corps requested a strategy
meeting (August 29, 1988). Since we have had rain, the lake is
now (September 6) at 210.92; therefore, results given here are
conservative.

Two scenarios of conservation have been assumed and compared
with taking no conservation measures. The conservation schemes
are given in Table 1 and model results are plotted in Figures 1
through 6. Tables 2, 3, and 4 give the percent chance of being
at the elevation noted at the end of the various months assuming
the 210.2 starting elevation for no conservation, Scheme 1 and
Scheme 2, respectively. For example, the risks of being below
elevation 208 and 205 at the end of October are:

Risk (%)
Elev. 208 Elev. 205
No conservation - 21.4 4.8
Scheme 1 - 14.3 0
Scheme 2 - 19.1 0

The apparent low risk of depleting the conservation pool (see
Table 2) and the increase in lake level over the past week
indicates that we should not react by reducing flows from the
reservoir, but should plan on knowing what risk level is
acceptable to us and the Corps.

The comparisons between Schemes 1 and 2 are greater for
September and October, but diminish for November onwards.
Therefore, I would suggest that Scheme 2 would be appropriate at
this time.

Attachments

Table 1

LOW FLOW AUGMENTATION (CFS)

Elevation Scheme 1 Scheme 2
>210 600 600
at 210 500 600
at 209 450 500
at 208 350 350

Figure 1

JORDAN LAKE RISK ASSESSMENT
RISK AT END OF SEPTEMBER : CONS1

Figure 2
JORDAN LAKE RISK ASSESSMENT
RISK AT END OF OCTOBER : CONS 1

Figure 3
JORDAN LAKE RISK ASSESSMENT
RISK AT END OF NOVEMBER : CONS 1

Figure 4
JORDAN LAKE RISK ASSESSMENT
RISK AT END OF SEPTEMBER : CONS2

Figure 5
JORDAN LAKE RISK ASSESSMENT
RISK AT END OF OCTOBER : CONS 2

Figure 6
JORDAN LAKE RISK ASSESSMENT
RISK AT END OF NOVEMBER : CONS 2

WITH NO CONSERVATION TABLE 2

AUG SEP OCT NOV DEC JAN FEB MAR APR
199 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%
200 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%
201 0.0% 0.0% 0.0% 0.0% 0.0% 2. 4% 0.0% 0.0% 0.0%
202 0.0% 0.0% 0.0% 2.4% 4.8% 4.8% 0.0%, 0.0% 0.0 '%
203 0.0% 0.0% 0.0% 7.1% 4.8% 4. 8% 0.0% 0.0% 0.0%
204 0.0% 0.0% 2.4% 7.1% 4.8% 4.8% 0.0% 0.0% 0.0%
205 0.0% 0.0% 4.8% 16.7% 4.8% 4.8% 0.0% 0.0% 0.0%
206 0.0% 0.0% 9.5% 16.7% 4.8% 4.8% 0.0% 0.0% 0.0%
207 0.0% 2.4% 14.3% 19.0% 7.1% 4.8% 2.4% 0.0% 0.0%
208 0.0% 9.5% 21.4% 19.0% 7.1% 4.8% 2.4% 0.0% 0.0%
209 0.0% 21.4% 26.2% 23.8% 7.1% 4.8% 2.4% 0. 0% 0.0%
210 7.1% 31.0% 38.1% 28.6% 9.5% 4.8% 2.4% 0.0% 0.0%
211 88.1% 47.6% 40.5% 28.6% 9.5% 4.8% 4.8% 0.0% 0.0%
212 95.2% 54.8% 40.5% 28.6% 16.7% 4.8% 4.8% 0.0% 0.0%
213 100.0% 66.7% 50.0% 35.7% 23.8% 4.8% 4.8% 0.0% 0.0%
214 100.0% 71.4% 54.8% 42.9% 26.2% 4.8%, 4.8% 0.0% 0.0%
215 100.0% 73.8% 59.5% 47.6% 31.0% 4.8% 4.8% 0.0% 0.0%
216 100.0% 83.3% 71.4% 47.6% 33.3% 7.1% 4.8% 0.0% 0.0%
217 100.0% 97.6% 97.6% 90.5% 92.9% 85.7% 85.7% 92.9% 97.6%
218 100.0% 97.6% 97.6'% 95.2% 95.2% 97.6% 90.5% 97.6% 97.6%
219 100.0% 97.6% 97.6% 95.2% 95.2% 100.0% 92.9% 97.6% 97.6%
219 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0%

WITH CONSERVATION 1 TABLE 3

AUG SEP OCT NOV DEC JAN FEB MAR APR
199 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%.
200 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%
201 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%
202 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%,
203 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%
204 0.0% 0.0%, 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%
205 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%
206 0.0% 0.0% 0.0% 4.8% 2.4% 0.0% 0.0% 0.0% 0.0%
207 0.0% 0.0% 7.1% 11.9% 4.8% 2.4% 0.0% 0.0% 0.0%
208 0.0% 4.8% 14.3% 16.7% 4.8% 4.8% 0.0% 0.0% 0.0%
209 0.0% 19.0% 23.8% 21.4% 4.8% 4.8% 0.0% 0.0% 0.0%
210 7.1% 26.2% 35.77 23.8% 7.1% 4.8% 0.0% 0.0% 0.0%
211 88.1% 47.6% 40.5% 28.6% 7.1% 4.8% 0.0% 0.0% 0.0%
212 95.2% 54.8% 40.5% 28.6% 11.9% 4.8% 2.4% 0.0% 0.0%
213 100.0% 64.3% 50.0% 35.7% 16.7% 4.8% 2.4% 0.0% 0.0%
214 100.0% 71.4% 54.8% 42.9% 19.0% 4.8% 2.4% 0.0% 0.0%
215 100.0% 73.8% 59.5% 47.6% 28.6% 4.8% 2.4% 0.0% 0.0%
216 100.0% 83.3% 71.4% 47.6% 31.0% 4.8% 4.8% 0.0% 0.0%
217 100.0% 97.6% 97.6% 90.5% 90.5% 85.7% 85.7% 92.9% 97.6%
218 100.0% 97.6% 97.6% 95.2% 95.2%, 97.6% 90.5% 97.6% 97.6%
219 100.0% 97.6% 97.6% 95.2% 95.2% 100.0% 92.9% 97.6% 97.6%
219 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0%

TABLE 4

ELEV CONS2 RUN 600 CFS 500 CFS @ 350 CFS @208
AUG SEPT OCT NOV DEC JAN FEB MAR APR
199 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
200 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
201 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
202 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
203 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
204 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
205 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
206 0.00 0.00 2.38 7.14 2.38 0.00 0.00 0.00 0.00
207 0.00 0.00 7.14 14.29 4.76 2.38 0.00 0.00 0.00
208 0.00 7.14 19.05 19.05 4.76 4.76 0.00 0.00 0.00
209 0.00 21.43 23.81 21.43 4.76 4.76 0.00 0.00 0.00
210 7.14 28.57 38.10 26.19 7.14 4.76 0.00 0.00 0.00
211 88.10 47.62 40.48 28.57 7.14 4.76 0.00 0.00 0.00
212 95.24 54.76 40.48 28.57 14.29 4.76 2.38 0.00 0.00
213 100.00 66.67 50.00 35.71 16.67 4.76 2.38 0.00 0.00
214 100.00 71.43 54.76 42.86 19.05 4.76 2.38 0.00 0.00
215 100.00 73.81 59.52 47.62 28.57 4.76 4.76 0.00 0.00
216 100.00 83.33 71.43 47.62 30.95 7.14 4.76 0.00 0.00
217 100.00 97.62 97.62 90.48 90.48 85.71 85.71 92.86 97.62
218 100.00 97.62 97.62 95.24 95.24 97.62 90.48 97.62 97.62
219 100.00 97.62 97.62 95.24 95.24 100.00 92.86 97.62 97.62
100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00