As part of Glen Canyon

Environmental Studies, an experimental flood release from Glen 

Canyon Dam of discharges up to 

45,000 cubic feet per second (cfs) is

planned for spring 1996. To aid in

preparation for this release and to 

help researchers and boaters who 

will be working and traveling on the 

Colorado River during that time, this 

Fact Sheet presents estimates of the 

progression and evolution of the step 

waves that will result from the 

transitions between high and low

flow.

The experimental release will consist 

of a low steady flow, a rapid increase to 

the steady high flow, and a decrease back 

down to a steady low flow (Wegner and 

others, 1996). After a steady flow of 

8,000 cfs lasting 96 hours, the discharge 

at the dam will be increased to 45,000 cfs 

over 10 hours. After 167 hours at 45,000 

cfs, the discharge at the dam will be 

decreased over 46 hours until 8,000 cfs 

is reached, and held at 8,000 cfs for 88 

hours (fig. 1). For the calculations 

described below, a steady 15,000 cfs flow 

was added to the beginning and end of 

the experimental flow to approximate the 

the transitions between regular dam 

operation and the experimental flow. 

The rising and falling limbs of the dam 

release travel downstream as waves that 

move faster than the speed of the water. 

The higher discharge part of the wave 

moves faster than the lower discharge 

part, and this, along with smoothing of 

the sharp transitions between steady 

discharge and decreasing discharge, 

causes the wave to change shape as it 

travels downstream. The rising limb of 

the wave will steepen and the trailing 

limb will be stretched out.

 The calculations of wave propagation 

were made with a one-dimensional model 

developed for the Colorado River 

between Glen Canyon Dam and Lake 

Mead (Wiele and Smith, in press). It has 

been shown to be accurate for discharges 

up to about 30,000 cfs, the highest 

discharge for which measurements of 

flow velocities, used to obtain channel 

roughness, and channel shape are 

available. For the calculations presented 

here, channel shape and roughness above 

30,000 cfs were extrapolated using 

functions developed from data obtained 

below 30,000 cfs. The extrapolated 

channel shape and roughness affect the 

shape of the entire wave, including that 

part of the wave below 30,000 cfs, so the 

Figure 1. Hydrograph of proposed experimental flow release and calcula ted hydrographs for gaging stations.

accuracy of the predicted hydrographs 

is degraded because of the uncertainty 

of the channel properties above 30,000 

cfs. Tests of model accuracy during

development showed that the average

error in predicted travel time at 

Diamond Creek (240 miles downstream 

from the dam) ranged from 1.8 to 4.6 

percent for daily waves with peaks less 

than 30,000 cfs.

Model-calculated hydrographs at the 

locations of USGS streamflow-gaging 

stations show the changes in wave 

shape, approximate wave travel times, 

and the approximate times at which the 

flow will be at the high and low 

discharges (fig. 1). On the rising limb, 

the wave steepens (fig. 2 A) and the 

increase from 10,000 cfs to 40,000 cfs 

that takes 7.5 hours at the dam will take 

only about 2 hours at National Canyon, 

181 miles downstream. The rising limb 

of the wave will reach a stable shape 

around National Canyon that will 

propagate with little change as it moves 

downstream. The falling limb will 

stretch out over the entire study reach 

(fig. 2B), taking about 39 hours to fall 

from 40,000 cfs to 10,000 cfs at the 

dam and about 63 hours to fall the same 

amount at Diamond Creek, 240 miles 

below the dam.

U.S. Department of the Interior

U.S. Geological Survey

Grand Canyon Monitoring and Research Program

Calculated Hydrographs for the Colorado River

Downstream from Glen Canyon Dam during the

Experimental Release, March 22–April 8, 1996 

0

22 23 24 25 26 27

March April

28 29 30 31 1 2 3 4 5 6 7 8 9 10

DISCHARGE, IN CUBIC FEET

PER SECOND

10,000

20,000

30,000

40,000

50,000

Fact Sheet printed

on recycled paper

Dam release

Colorado River gaging stations:

 At Lees Ferry

 Above Little Colorado River

 Near Grand Canyon

 Above National Canyon

 Above Diamond Creek
The length of time the flows will be at 

their steady high and low discharges will 

decrease downstream from the dam as a 

result of the stretching of the falling limb 

and the smoothing of the initial wave 

shape (fig. 3 ). The first low flow, 

scheduled to last 96 hours at the dam, will 

will last only about 74 hours at Diamond 

Creek. The high flow, which will be held 

steady for 167 hours at the dam, will last 

160 hours at Diamond Creek. The second 

low flow, lasting 88 hours at the dam, 

will last about 76 hours at Diamond 

Creek. Approximate times for the 

beginning and ending of the steady flows 

at the streamflow-gaging stations are 

listed in the table 1 below. Because the 

smoothing of the initial wave causes the 

transitions to the steady flows to be 

gradual, discharges 2 percent above the 

low steady discharge (8,160 cfs) and 2 

percent below the high steady discharge 

(44,100 cfs) were used to define the 

points of transition.

The length of time the entire length of 

the study reach will simultaneously be at 

the steady low flow depends on the dam 

release and the wave travel time. The 

flow will be at a steady 8,000 cfs, plus 

tributary inflow, through the entire length 

of the study reach simultaneously for 

about 1 day before (March 24 at about 

1500 hours to March 26 at about 0100 

hours) and after (April 6 at about 2000 

hours to April 8 at about 0000 hours) the 

high flow (figs. 1 and 3; table 1). 

Figure 3. Periods of low and high steady flows separated by periods of rising and 

declining flows as functions of river mile.

Figure 2. Hydrographs of rising (A) and falling (B) limbs of the dam releases and calculated hydrographs showing the wave steepening 

on the rising limb and stretching out on the falling limb as it moves downstream. Sites are as defined in figure 1. Hydrographs have 

been shifted in time so that they are centered about the discharge midpoint to show the differences in rates at which the discharge 

changes.

Sites

 Steady low flow

Start End

 Steady high flow

Start End

 Steady low flow

Start End

Table 1. Beginning and ending times [month– day/hour, in military time] of the steady 

flows at the dam and at the streamflow -gaging stations

[River mile measured upstream (–) or downstream (+) from Lees Ferry]

0

– 6

DISCHARGE, IN CUBIC FEET

PER SECOND

10,000

20,000

30,000

40,000

50,000

 9

7

April 5

A B

3

1

30

28

March 26

24

22

– 4 –2 0

–15 0 25 50 75 100

Steady high flow

Declining flow

Steady low flow

Rising flow

Steady low flow

125 150 175 200 225

References

March 1996 (revised) FS-083-96

2 4 6

Glen Canyon Dam,

 river mile –15

Streamflow-gaging stations:

 At Lees Ferry,

 river mile 0

 Above Little Colorado

 River, river mile 62

 Near Grand Canyon

 river mile 88

 National Canyon,

 river mile 166

 Diamond Creek,

 river mile 225

03–22

0100

03–26

0100

03–26

1100

04–02

1000

04–04

0800

04–08

0000

03–22

0600

03–22

2200

03–23

0500

03–24

0000

03–24

1500

03–26

0300

03–26

1400

03–26

1900

03–27

0800

03–27

1700

03–26

1200

03–26

2000

03–27

0000

03–27

1100

03–27

2000

04–02

1200

04–02

1900

04–02

2100

04–03

0600

04–03

1200

04–04

1200

04–05

0400

04–05

1000

04–06

0600

04–06

2000

04–08

0300

04–08

1500

04–08

2000

04–09

1200

04–10

0000

TIME, IN HOURS

– 40 –20 0 20 40

RIVER MILE

Wegner, D.L. Stevens, L., and Melis, T., 1996, 

Controlled flood studies, Glen Canyon Dam, 

Spring, 1996: Glen Canyon Environmental 

Studies Office, Bureau of Reclamation, Flagstaff, 

Arizona.

Wiele, S.M. and Smith, J.D., in press, A reachaveraged model of diurnal discharge wave 

propagation down the Colorado River through the 

Grand Canyon: Water Resources Research.

—S.M. Wiele

For more information contact:

S.M. Wiele

U.S. Geological Survey

3215 Marine Street

Boulder, CO 80303

(303) 541-3001

NOTE: The lines for site 

above National Canyon and 

Diamond Creek coincide