David J. Topping, John C. Sch

and L.E. Vierra, Jr.

Computation and Analysi

Instantaneous Discharge R

the Colorado River at Lee

Arizona - May 8, 1921, th

September 30, 200
http://pubs.water.usg

ftp://ftpext.usgs.gov/pub/wr/az/

Data the t
Objectives

• Evaluation of the natural hydrologic var

Upper Basin as measured in the dischaColorado River at Lees Ferry (42-year pMay 1921 to March 1963; only 10-15% depleted prior to 1963, mostly before 19

• Evaluation of the effects of the operatio

Canyon Dam on the discharge of the Cin Grand Canyon National Park (37-yeaMarch 1963 through September 2000)

• Implications for sediment transport and 

reach between Lees Ferry and the Gragaging station 
Chief analyses

• Flow duration (with sediment transport • Sub-daily discharge variability• Flood frequency
Main problem to overco

• May 8, 1921 through June 12, 1921 

not published

• June 13, 1921, through September 30, 

mean daily

• October 1, 1986, through May 31, 1998

30 minutes

• After June 1, 1998 

15 minutes

Data were of differing precision during differ
Retrieve and compile digitally all raw data c

USGS at the Lees Ferry and Grand Canyon 

4 years of work

Lees Ferry - May 1921 through September 

35 boxes of data in the Federal Records Center

Grand Canyon - November 1922 through S-Construct a continuous record of instantan

-Enter staff gage data from May 8, 1921, through -Digitize strip-chart data from January 19, 1923, t1986-Enter digital-recorder data from February 2, 19630, 1986

-Compute a continuous record of instantaneusing the appropriate rating curves and shif-Quality control 
Check and, if necessary, revise 

discharges of the largest pre-da

Original value 1939 revision 

1921 174,000 ft

3/s 220,000 ft

3/s 

1884 210,000-250,000 ft

3/s 300,000 ft

3/s 

Largest flood within last 4,500 years occurred 

ago (O’Connor et al., 1994) 
0

10203040506070

1920 1930 1940 1950 1960 1970 1980 1990

NUMBER OF DAYS AFFECTED BY ICE

WATER YEAR

CLOSURE OF 

GLEN CANYON DAM

Ice effects
Erro

Examdaily mincorre7.29’ i+6.0% 
-100

-50

0

50

100

1-1-1930

1-1-1940

1-1-1950

1-1-1960

1-1-1970

1-1-1980

DISAGREEMENT BETWEEN THE PUBLISHED AND THE 

COMPUTED DAILY MEAN DISCHARGE TIME SERIES, IN PERCENT CLOSURE OF GLEN CANYON DAM RANGE OF 5-PERCENT DISAGREEMENT

DATE

89 dapumreto exM= 
The continuous record 

instantaneous dischar
0

50,000

100,000150,000200,000250,000

1-1-1880

1-1-1890

1-1-1900

1-1-1910

1-1-1920

1-1-1930

1-1-1940

1-1-1950

1-1-1960

PEAK DISCHARGE OF THE 1884 FLOODMAY 8, 1921 - SEPTEMBER 30, 2000, CONTINUOUS RECORD OF INS

INSTANTANEOUS DISCHARGE, IN CUBIC FEET PER SECOND

NO FLOODS LARGER THAN THE JUNE 1921 FLOOD 

 DURING THIS PERIOD

CLOSURE OF GLEN CANY

EXPLANATION

DATE
0

10,00020,00030,00040,00050,00060,00070,000

1-1-1920

1-1-1930

1-1-1940

1-1-1950

1-1-1960

1-1-1970

DAILY RANGE IN DISCHARGE, IN CUBIC FEET PER SECOND CLOSURE OF GLEN CANYON DAM SEPTEMBER 13, 1927 FLOOD WITH PEAK DISCHARGE OF 125,000 CUBIC FEET PER SECOND 

DATE
Flow duration
0 10 20 30 40 50 60 70 80 9

100

1,000

10,000

100,000

1,000,000

PRE-DAM (May 8, 1921, through March 12, 1963)POST-DAM (March 14, 1963, through September 30

PERCENTAGE OF TIME EQUALED OR EXCEEDED

INSTANTANEOUS DISCHARGE, IN CUBIC FEET PER SECOND SAND CONVEYANCE OR EROSION SAND ACCUMULATION 44.3% 69.0%

EXPLANATION
0 10 20 30 40 50 60 70 80 90 

100

1,000

10,000

100,000

1,000,000

1920s (May 8, 1921, through December 31, 1930) 1930s (January 1, 1931, through December 31, 1940) 1940s (January 1, 1941, through December 31, 1950) 1950s-early 1960s (January 1, 1951, through March 12, POST-DAM (March 14, 1963, through September 30, 20

PERCENTAGE OF TIME EQUALED OR EXCEEDED

INSTANTANEOUS DISCHARGE, IN CUBIC FEET PER SECOND SAND CONVEYANC

OR EROSION SAND ACCUMULATI

POST-DAM 69.0% 1920s 57.7% 1930s 36.5% 1940s 47.5% 1950s-early 1960s 37.6%

EXPLANATION
0 10 20 30 40 50 60 70 80 

100

1,000

10,000

100,000

1,000,000

1960s (March 14, 1963, through December 31, 1970s (January 1, 1971, through December 31, 1980s (January 1, 1981, through December 31, 1990s (January 1, 1991, through September 30PRE-DAM (May 8, 1921, through March 12, 196

PERCENTAGE OF TIME EQUALED OR EXCEED

INSTANTANEOUS DISCHARGE, IN CUBIC FEET PER SECOND SAND CONVEYANCE OR EROSION SAND ACCUMULATION PRE-DAM 44.3% 1960s 52.7% 1980s 75.5% 1970s 62.2% 199

82.

EXPLANATION
100

1,000

10,000

100,000

1,000,000

Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. 

PRE-DAM MONTHLY MEDIAN DISCHARGPRE-DAM MONTHLY MINIMUM DISCHARGPRE-DAM MONTHLY MAXIMUM DISCHAR

INSTANTANEOUS DISCHARGE, IN CUBIC FEET PER SECOND

EXPLANATION

MONTH
100

1,000

10,000

100,000

1,000,000

Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. 

PRE-DAM POST-D

INSTANTANEOUS DISCHARGE, IN CUBIC FEET PER SECOND

MONTHLY MEDIAN DISCHARGE

EXPLANATION

MONTH
0 10 20 30 40 50 60 70 80 90 100

100

1,000

10,000

100,000

1,000,000

PRE-DAM POST-DAM 

PERCENTAGE OF TIME EQUALED OR EXCEEDED

INSTANTANEOUS DISCHARGE, IN CUBIC FEET PER SECOND SAND CONVEYANCE OR EROSION SAND ACCUMULATION 1.1% 75.2% JANUARY

0 10 20 

100

1,000

10,000

100,000

1,000,000

PRE-DAPOST-D

PERCENTA

INSTANTANEOUS DISCHARGE, IN CUBIC FEET PER SECOND 

27.7% 
Sub-daily discharge var
0 10 20 30 40 50 60 70 80 90 

10

100

1,000

10,000

100,000

PRE-DAM (May 8, 1921, through March 12, 1963)POST-DAM (March 14, 1963, through September 30, 2000

PERCENTAGE OF TIME EQUALED OR EXCEEDED

DAILY RANGE IN DISCHARGE, IN CUBIC FEET PER SECOND

EXPLANATION
0 10 20 30 40 50 60 70 80 9

10

100

1,000

10,000

100,000

1920s (May 8, 1921, through December 31, 1930) 1930s (January 1, 1931, through December 31, 191940s (January 1, 1941, through December 31, 191950s-early 1960s (January 1, 1951, through MarcPOST-DAM (March 14, 1963, through September 3

PERCENTAGE OF TIME EQUALED OR EXCEEDED

DAILY RANGE IN DISCHARGE, IN CUBIC FEET PER SECOND

EXPLANATION
0 10 20 30 40 50 60 70 80 

10

100

1,000

10,000

100,000

1960s (March 14, 1963, through December 311970s (January 1, 1971, through December 311980s (January 1, 1981, through December 311990s (January 1, 1991, through September 30PRE-DAM (May 8, 1921, through March 12, 19

PERCENTAGE OF TIME EQUALED OR EXCEED

DAILY RANGE IN DISCHARGE, IN CUBIC FEET PER SECOND

EXPLANATION
1

10

100

1,000

10,000

100,000

Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. 

PRE-DAM MONTHLY MEDIAN DAILY RANGE IN DISPRE-DAM MONTHLY MINIMUM DAILY RANGE IN DPRE-DAM MONTHLY MAXIMUM DAILY RANGE IN D

DAILY RANGE IN DISCHARGE, IN CUBIC FEET PER SECOND

EXPLANATION

MONTH
1

10

100

1,000

10,000

100,000

Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. 

PRE-DAM POST-D

DAILY RANGE IN DISCHARGE, IN CUBIC FEET PER SECOND

MONTHLY MEDIAN DAILY RANGE IN DISCHARG

EXPLANATION

MONTH
0

10,00020,00030,00040,00050,00060,00070,000

0.001

0.01

0.1

1

5

10

20

30

50

70

80

90

95

99

PRE-DAM (May 9, 1921, through March 12, 1963)POST-DAM (March 14, 1963, through September 30, 2000

DAILY RANGE IN DISCHARGE, IN CUBIC FEET PER SECOND

PERCENTAGE OF DAYS WITH RANGE IN DISCHA

LESS THAN VALUE SHOWN
0

10,00020,00030,00040,00050,00060,00070,000

.001

.01

.1

1

5

10

20

30

50

70

80

90

95

99

PRE-DAM ALL (May 9, 1921, through March 12, 1963)PRE-DAM JULY THROUGH OCTOBER (summer thundePRE-DAM NOVEMBER THROUGH JUNE

DAILY RANGE IN DISCHARGE, IN CUBIC FEET PER SECOND

PERCENTAGE OF DAYS WITH RANGE IN DISCHA

LESS THAN VALUE SHOWN

EXPLANATION
0 10 20 30 40 50 60 70 80 90 100

10

100

1,000

10,000

100,000

PRE-DAMPOST-DAM 

PERCENTAGE OF TIME EQUALED OR EXCEEDED

DAILY RANGE IN DISCHARGE, IN CUBIC FEET PER SECOND JANUARY

0 10 20 

10

100

1,000

10,000

100,000

PRE-POST

PERCENTA

DAILY RANGE IN DISCHARGE, IN CUBIC FEET PER SECOND 
Flood frequency
10,000

100,000

0.001 0.01 0.1 1 10 100 1,000 10,000

PRE-DAM PARTIAL-DURATION FLOOD SERIES 

POST-DAM PARTIAL-DURATION FLOOD SERIES 

PEAK DISCHARGE, IN CUBIC FEET PER SECOND

RETURN PERIOD, IN YEARS

500,000

50,000

200,000

20,000

UPWARD EXTENSION OF PRE-DAM PARTIAL-DURATION FLOOD SERIES BASED ON THE PALEOFLOOD DATACOMPUTED FROM THE REVISED DISCHARGES AND ADJUSTED RETURN PERIODS FROM THIS STUDY

EXPLANATION

PRE1 yr 

2 yr

6 yrPOS1 yr 

2 yr

6 yrPRE20,0POS20,0
Duration of sustained hig
0

50

100150200250

1-1-1920

1-1-1930

1-1-1940

1-1-1950

1-1-1960

1-1-1970

1-1-1980

1-1-1990

1-1-2000

DURATION OF SUSTAINED DISCHARGE OVER 

18,500 CUBIC FEET PER SECOND, IN DAYS 1983

1984

1985

1997

CLOSURE OF 

GLEN CANYON DAM

1929

DATE

4 LPESUHIGOCAFOF 
Conclusions --- pre-

• Substantial natural variability existed in discharge an

in discharge over decadal timescales prior to constru

• Median discharge = 7,980 ft

3/s 

• Median daily range in discharge 542 = ft

3/s 

• Wettest decade---1920s---median discharge 10,700 

range in discharge 808 ft

3/s 

• Driest decade---1930s---median discharge 6,720 ft

3/

range in discharge 516 ft

3/s 

• Flows conducive to sand accumulation occurred 55.7

between 1921 and 1963, with the 1930s likely being dominated by sand accumulation

• Discharges in excess of 18,500 ft

3/s occurred only 2

dam

• Daily ranges in discharge exceeded 10,000 ft

3/s only 

pre-dam days and exceeded 30,000 ft

3/s during 1 da

• On average, floods with peak discharges of 50,000 f

year, floods with peak discharges of 85,000 ft

3/s occ

years, and floods with peak discharges of 120,000 ft

6 years 
Conclusions --- post

• Changes imposed on the hydrology by dam operations exc

quasi-natural pre-dam period of record; seasonality removedischarge and the daily range in discharge 

• Median discharge -- 1960s = 9,490 ft

3/s --- 1990s = 13,500 

• Dam operations have largely eliminated base flows; pre-da

discharge = 483 ft

3/s; pre-dam discharges < 5,000 ft

3/s 32.

• Median daily range in discharge has increased by a factor 

dam; post-dam median daily range (8,580 ft

3/s ) exceeds p

discharge (7,980 ft

3/s ) 

• Post-dam daily range in discharge exceeds pre-dam daily r

except during 0.1% of all pre-dam days

• Flows conducive to sand accumulation have progressively 

discharge exceeded 9,000 ft

3/s --in 1960s, 52.7% of the tim

the time--in 1980s, 75.5% of the time--in 1990s, 82.6% of t

• Dam operations have maintained the frequency of floods w

of 29,000 ft3/s, have decreased the frequency of floods witdischarges, and have greatly increased the frequency of “s

• Pre-dam 2-year flood = 85,000 ft

3/s ; post-dam 2-year flood 

• Recurrence interval of 20,000 ft

3/s flood -----97 days pre-da

dam (factor of 27 increase)

• Longest 4 periods of sustained high discharge all post-date 

1997, 1983, 1985 
More that could be d

• Analyses of quasi-daily temperatu

the Lees Ferry and Grand Canyon stations; not all data from Lees Febeen analyzed; none from Grand (pre-dam river at these 2 sites wawith respect to temperature)

• Analyses of decadal, annual, sea

daily variability in turbidity (1925 t1972 at the Grand Canyon gaging note HBC were listed in 1967