U.S. Department of the Interior

U.S. Geological Survey

Update on Water Quality Powell and Glen Canyon ReleasesBill VernieuSouthwest Biological Science CenterGrand Canyon Monitoring and Research Centerbvernieu@usgs.gov

Technical Work Group MeetingNovember 8, 2006
2005 Glen Canyon Dam Rel

Two Unusual Events Highest Release Temperature Sin

 16°C (61°F) on October 8, 2005

 Lowest Dissolved Oxygen on Rec

 3.3 mg/L on October 8, 2005 from draf

 (Data since 1990 – no evidence of prior 
Lake Powell Water Quality 

Monitoring Locations

•Monthly forebay surveys•Quarterly reservoir-wide surveys•25-30 stations

•Profiles•Major Ions - Nutrients•Chlorophyll - Plankton
Lake Powell History

• Glen Canyon Dam completed in 1963•Full pool in 1980•Droughts in late 1970s, early 1990s, and 2000-2004

Full Pool Elev. 3700 ftPenstock Elev. 3470 ft

Elevation - ft

34003450350035503600365037003750

Year

1960 1964 1968 1972 1976 1980 1984 19
Recent Drought

 1999 – 97% capacity - 3695 ft – 25.5 MAF Five consecutive years of low inflow

 2000 – 62% 2001 – 59% 2002 – 25% 2003 – 51% 2004 – 49%

 2005 – 38% capacity – 3555 ft – 9.9 MAF

 2005 – 105% 2006 – 73%

 Currently – 55% capacity - 3608 ft – 14.4 MAF

Glen Canyon Dam Release T

Low reservoir brings warmer surface water closer to penstocksWarmest releases since 197116°C (61°F) on October 8, 20056°C above 12-yr average (1990-2002)2006 showing similar pattern to 2003

200

2

2006 
Glen Canyon Dam Release Te

•Temperature fluctuations confined at higher reservoir levels•Warmest temperature in winter from reservoir mixing•Recent release temperatures highest since 1971•Current 2005 temperature 60 °F
Lake Powell Hydrology - 20

 Pre-Runoff Conditions

 Surface elevation - 3555 ft on April 8 Lowest elevation since May 1969 38 % of total capacity

 2005 Runoff

 Apr-Jul 2005 unreg. inflow - 111% of  Surface elevation - 3608 ft on July 1 Runoff increased elevation by 53 ft i 55% total capacity
2005 Inflow to Lake Powell

 Above average inflows 

caused head cutting of exposed deltaic sediments

 Resuspension of large 

amount of sediment from inflow areas

 Resulted in low dissolved 

oxygen levels in inflow plume as it traveled through reservoir
Effects of Reservoir Dra

Lake Powell Dissolved Oxygen – S
NOTE: Specific Conductance in mS * 10

T (deg C) - D.O. (mg/L)

 2 3 4 5 6 7 8 9

101112131415161718

01JAN05 01APR05 01JUL05 

Temperat

Dissolved Oxygen

Lowest dissolved oxygen on record (since 1990)3.3 mg/L on October 8, 2005 from draft tubesHypoxia dissipated by reservoir surface mixingData since 1992 –no evidence of prior hypoxia

Specific Conducta

pH

3

Glen Canyon Dam Releas

Mean daily values
NOTE: Specific Conductance in mS * 10

T (deg C) - D.O. (mg/L)

 2 3 4 5 6 7 8 9

101112131415161718

01JAN06 01APR06 01JUL06 0

Temperature

Dissolved Oxygen

Lower temperature, higher dissolved oxygen from higher reservoir levels6.3 mg/L on October 1, 2006 from draft tubesShows effect of localized inflows from October precipitation event

Specific Conductance

pH

6.3 mg

12.2

Glen Canyon Dam Releas

Mean daily values
Reaeration of Dam Release

 Past monitoring data has shown 

dissolved oxygen levels in GCD tduring nighttime hours (~11 pm t

 These spikes appear to be assoc

low discharge levels from individ

 Reclamation experimented with v

operational regimes during recenexperimental flow period (9/3/06 tto achieve optimal balance 
Nighttime Reaeration Spik
5 @ 1600 cfs 3 @ 2670 cfs 2 @ 2800 cfs

2 @ 1200 cfs

3 @ 2670 cfs 

Day: 3 @ 3000 cNight:2 @ 2600 c1 @ 1300 c

Reaeration Experim

Long-term monitoring at three locations:CRDT (red) GCD Draft TubeCRBD (blue) GCD tailwaterCRLF (green) Lees Ferry
Dissolved Oxygen Patterns 

CRBD reaeration (blue line) reduced with cessation of experimental flows (10/31/06)Displaying nighttime D.O. spikesIncrease in draft tube D.O. (red line) indicates reservoir mixingNo CRBD data available Nov 8-28
Conclusions from Reaeration 

D.O. in tailwater affected by 

GCD release concentrationsturbine operationsatmospheric equilibrationphotosynthetic productivity

Certain aspects of dam operations can significant aeration in the GCD tailwaterConcerns remain about low operating edamage to powerplant machinery
Winter Underflows in Lake P

 2005 – Seventh consecutive year 

underflows, no underflow in 2006

 Winter underflows displace hypo

water upward to be entrained in d

 Hypolimnion contains lower diss

oxygen, higher nutrient concentr

 Winter underflows appear in fore

April

Recent inputs to Lake Powe

 Extraordinary precipitation in Oct

 October precipitation - 235% of norm October inflows 1.02 MAF – 184% of 

 Does not include localized inflow (~0.35 

 Basinwide and localized inflows Storms raised Lake Powell elevat

 0.644 MAF Similar event in October 1972 - 5.7 ft 

 Effects seen in Glen Canyon Dam 

Dirty Devil River Oct
Dirty Devil River Octobe