Basin Hydrology, Operations and 

2018 Hydrograph

Glen Canyon Technical Work Group

August 30, 2017
95%

98%

62%

78%

80%

1 percent of average based on period 1981-2010.

http://www.usbr.gov/uc/water/basin/index.html

Basin Storage

As of 

8/27/2017

Upper Basin Storage

April to July 2017 Observed Inflow

Reservoir

Apr-Jul 

Observed 

(KAF)

Percent 

of 

Average1

Fontenelle 1,719 237%

Flaming 

Gorge 2,214 226%

Blue Mesa 915 135%

Navajo 775 125%

Powell 8,174 114%
Peak inflow of 60,600 cfs

Max elevation of 3635.8 ft on 

July 11th
0 

Water Year Unregulated lnflowVolume(MAF) 

01 

..... 

0 -01 

I') 

0 

t.) 

01 

1964 t======r---.-i-r~~-i-- --;::::::::=1:::::::::::::::::::~ 1965 

1966 1967 !=======~ 

1968 1========:o!..1-~ 1969 1970 l=========:I=... 

1971 

1972 Fi=::::::::::::::[I1~---1--, 1973 1974i===========r-t----r-' 

1975 i========:::L-1----, 

1976;:::::=======,---,--t-----' 

1977 1978 l====!...-----....l....L. 

1979 !=========:I:!----, 

1980 

)> )> l>~ 

< C ).> C 1111 m11:t,QIQ ... 

~ ~~~ ., OQ m~o""' 

rt, X -• ~ < .. ~,-., ~ ... -Uo,:,I» 

9 8-oa"" 

OJ ··r,- c::T N 

w ._.·· ··o 

3 :-'9'~ ... a, U'1 0 " co -. 000\ 

- 333 ;;' ~ ~~!.""I ...,. co --~V11,gn - " I (J"l(,11C)I» 

[:;, N *#I/I ~ ~-- ... . 9 ·-· 

19821 t~~~~;;;;;;;;;;;;;;;;;;;;;td _ _L_==r 

1983 

1984 

1985 

1986 

1987 

1988 

~ Ill 

... 

1989 r 

1990 ~ 1991 I 

1992 ~ 

1993 "" 1994 ~ 1995 es 1 , 1 

1996 :! 

1997 !I. b>-~-, 1998 .:: I 

1999 ! • 

2000 M 

2001 S 

2002 S! 

2003 - 2004 

2005 

2006 

2007 

2008 

2009 

2010 2011 ~~~~===:::::::~ ::::::::::::;::: i" 

2012 

2013 

2014 

2015 

2016 

Projected 2017 

Min 2018 

Most 2018 

Max 2018 ----------.L...----_J 

"Cl 0 ~ ... 0 ~ 

-· .. (I < ~ .. (I 0.. 

0.. )> 

!I 

NC 

o - ....... 

..... 0 .. ... ... ..... ...... 

• 00 ..... "' ... 3 ..... .. 3 -.. --... _ ...... "' 

~ ... ... -£ 

~. 

-

~ I» ,.. 

-< (I) 

Cl) "ti 

(") ~ 0 

o N =e 3 0 (I) 

"O ..lo, -

Ql (X) -

cii' -n C 

0 0 ::::J 

::, ... :E (I) ""I 

-· (") (I) ::r D,) Ul 

I ~ 5., 

cii' --- I» .- ~ .... 0 Cl) (I) 

'< ls a. 

Q, - ):,, ::::J 

IQ C -- C 0 

~ =e ~ 
1,600 

1,400 

1,200 

cnl 

.:.:: 

~ 1,000 

Q) 

E 

::, 

0 

> 800 

Q) 

(/) 

nl 

Q) 

Q) 

600 

Ct'. 

400 

200 

Potential Lake Powell Monthly Release Volume Distribution 

Release Scenarios for Water Year 2017 

WY 2017 Release Scenarios 

Aug Most Probable: 9.0 maf 

bUl 

<D <D .... .... 

8 15 

z 

898 

<D 

.... 

u 

~ 

880 

,,._ 

.... 

c:: 

nl 

' 

Updated August 2017 

711 

r--

.... 

.Q 

(I) 

LL 

722 

r--

.... 

... 

ro 

2 

r--

.... 

... 

0.. 

~ 

Monthly Release Volumes 

900 

850 
Reservoir Operations 

for Water Year 2018
Lake Powell 2018 Operating Tier

Upper Elevation Balancing

• Tier was set in August 2017

– Start with 8.23 maf release

• Use April 24-Month Study 

projections of end of water 

year storage to potentially 

adjust

1. Stay with 8.23 maf

2. Balancing: 8.23 - 9.0 maf

3. Equalization: > 8.23 maf
Water Year 2018 Operating Tier

Operating Tier determined with the August 2017 24-Month Study

Powell Inflow 

Scenario

WY 2018

Release Projection

Probable 

Minimum

Upper Elevation Balancing Tier 

w/ Projected April shift to Balancing

9.0 maf release

Most 

Probable

Upper Elevation Balancing Tier 

w/ Projected April shift to Balancing

9.0 maf release

Probable 

Maximum

Upper Elevation Balancing Tier 

w/ Projected April shift to Equalization

13.8 maf release
April adjustment to 

Balancing releases

April adjustment to 

Equalization releases

No April 

Adjustment
Water Year 2018 projections

Most: 9.0 maf release

Max: 13.8 maf release 

Min: 9.0 maf release 

End of CY 2017 Projection:

3627.34 feet

End of CY 2018 Projection:

3630.17 feet

(Range 3,597 to 3,654 feet)
End of CY 2017 Projection: 

1,083.5 feet (39% full)

Range: 1,083.2 to 1,083.7 feet 

End of CY 2018 Projection: 

1,079.5 feet (38% full)

Range: 1,076 to 1,131 feet
LTEMP Monthly Release Volumes 

1 /i!lfl 

1,10fl 

n uu 

-

~ " 

~ u 1000 

"' 0 

-0 "'

"' C: Rm 

"' ;;, 

0 

,::. 

,_ 

OJ 

V> 

"' bOO 

,!? 

"' "' 

4L\l 

() 

OCT NOV DEC JAN f EB MAR \1AY JUN JU_ AUG SEP 

Monthly J)P.r WYT~rgP.t, Mill iOM ot ~r.rP.-tP.P.t 

. , 8 /.48 • 8.B • Y a Y., 8 10., • 11 a n • B 8 14 
LTEMP Monthly Release Volumes 2018

Month 7.00 7.48 8.23 9.00 9.50 10.50 11.00 12.00 13.00 14.00

OCT 480 480 640 640 640 640 640 640 640 640

NOV 500 500 640 640 640 640 640 640 640 640

DEC 600 600 720 720 720 720 720 720 720 720

JAN 660 720 760 860 920 1040 1100 1230 1350 1470

FEB 590 640 680 750 810 920 970 1080 1190 1300

MAR 620 675 710 800 860 970 1030 1150 1260 1370

APR 550 600 640 710 760 870 920 1020 1120 1220

MAY 550 600 630 710 760 860 910 1020 1120 1220

JUN 580 630 660 750 800 910 960 1060 1170 1280

JUL 650 710 750 850 900 1020 1080 1200 1320 1440

AUG 700 760 800 900 970 1090 1160 1280 1410 1540

SEP 520 565 600 670 720 820 870 960 1060 1160 MIN & MOST

MAX
2018 Hydrograph 

Month LTEMP Release 

Volume, (kaf)

Operational Considerations 

Release Volume, (kaf)*

LTEMP Daily 

Fluctuations (cfs)**

OCT 640 630 5,700

NOV 640 630 5,700

DEC 720 740 6,700

JAN 860 860 7,700

FEB 750 750 6,800

MAR 800 800 7,200

APR 710 700 6,300

MAY 710 700 6,300

JUN 750 760 7,600

JUL 850 860 8,000

AUG 900 900 8,000

SEP 670 670 6,000

• *Modifications of monthly volumes reached between Reclamation and WAPA

• **LTEMP Daily fluctuations determined by, 9 x monthly vol (Sep – May), and 10 x monthly vol (Jun – Aug)

• LTEMP Down ramp rates, 2,500 cfs/hr (all months)

• Up-ramp rates, 4,000 cfs/hr (all months)
1,600 

1,400 

1,200 

<P 

ro 

.:.:: 

~ 1,000 

<I) 

E 

::, 

g 800 

<I) 

rJ) 

ro 

<I) 600 <I) 

0:: 

400 

200 

Potential Lake Powell Monthly Release Volume Distribution 

Release Scenarios for Water Year 2018 

Based on August 2017 modeling 

WY 2018 Release Scenarios 

Aug Probable Min•: 9.0 maf 

Aug Most Probable: 9.0 maf 

Aug Probable Max·: 13.8 maf 

!JOU 

I'- I'- ,._ 00 00 00 00 00 00 00 00 ..- ..- ..- ..- ,- ..- ,- ..- ..- ..- ..-

- ::?- (.) C: ..c ~ ~ >- C: :'i Ol (.) 0 <I) ro Cl) ro Q. ro ::, ::, 0 z 0 -, LL ~ < ~ -, -, 

< 

oAug Probable Min • Aug Most Probable DAug Probable Max 

• Probable Min and Max annual release volume is based on August Min and Max inflow forecasts 

00 

..-

c.. 

<I) 

(/) 
Unit 

Number

Oct 

2017

Nov 

2017

Dec 

2017

Jan 

2018

Feb 

2018

Mar 

2018

Apr 

2018

May 

2018

Jun 

2018

Jul 

2018

Aug 

2018

Sep 

2018

1

2

3

4

5

6

7

8

Units 

Available 5 5 7 5 5 5 5 6/8 8 8 8 7

Capacity 

(cfs) 17,200 17,200 17,200 17,200 17,200 17,200 17,200 21,600 28,700 28.700 30,300 24,800

Capacity 

(kaf/month) 1,270 1,140 1,410 1,240 1,120 1,060 1,010 1,610 1,710 1,760 1,760 1,560

Max (kaf) 1 630 630 740 1,450 1,280 1,350 1,200 1,200 1,260 1,420 1,520 1,141

Most (kaf) 2 630 630 740 860 750 800 700 700 760 860 900 670

Min (kaf) 1 630 630 740 860 750 800 700 700 760 860 900 670

Glen Canyon Power Plant Planned Unit Outage Schedule for Water Year 2018

1 Projected release, based on Aug 2017 Min and Max Probable 

Inflow Projections and 24-Month Study model runs

2 Projected release, based on Aug 2017 Most Probable Inflow 

Projections and 24-Month Study model runs

9.0

9.0

13.80

(updated 8-14-2017)
Sand Budget Model Results

• As of 8-24-2017, not enough sediment input to trigger a 

fall 2017 HFE 

• Still early in the season
Percent of Traces with Event or System Condition 

Results from August 2017 CRSS1,2,3,4 (values in percent)

Event or System Condition 2018 2019 2020 2021 2022

Upper

Basin 

–

Lake 

Powell

Equalization Tier 20 29 27 29 31

Equalization – annual release > 8.23 maf 20 29 27 28 30

Equalization – annual release = 8.23 maf 0 0 0 1 1

Upper Elevation Balancing Tier 80 68 55 52 52

Upper Elevation Balancing – annual release > 8.23 maf 75 52 41 35 37

Upper Elevation Balancing – annual release = 8.23 maf 5 15 15 17 14

Upper Elevation Balancing – annual release < 8.23 maf 0 1 0 0 1

Mid-Elevation Release Tier 0 3 17 15 12

Mid-Elevation Release – annual release = 8.23 maf 0 0 0 0 2

Mid-Elevation Release – annual release = 7.48 maf 0 3 17 15 10

Lower Elevation Balancing Tier 0 0 0 4 5

Lower

Basin 

–

Lake 

Mead

Shortage Condition – any amount (Mead ≤ 1,075 ft) 0 15 42 45 52

Shortage – 1st level (Mead ≤ 1,075 and ≥ 1,050) 0 15 40 35 33

Shortage – 2nd level (Mead < 1,050 and ≥ 1,025) 0 0 2 10 15

Shortage – 3rd level (Mead < 1,025) 0 0 0 1 5

Surplus Condition – any amount (Mead ≥ 1,145 ft) 0 0 7 12 17

Surplus – Flood Control 0 0 1 2 3

Normal or ICS Surplus Condition 100 85 51 43 31

1 Reservoir initial conditions based on results from the August 2017 most-probable 24-Month Study.

2 Percentages computed from 110 hydrologic inflow sequences based on resampling of the observed natural flow record from 1906-2015 for a total of

110 traces analyzed.

3 Percentages shown may not sum to 100% due to rounding to the nearest percent.

4 Percentages shown may not be representative of the full range of future 18 possibilities that could occur with different modeling assumptions.
Questions?

Paul Davidson

801-524-3642

PDavidson@usbr.gov

Hydraulic Engineer, Glen Canyon

Reclamation, Upper Colorado Region

Resource Management Division

Water Resources Group