Stage-Discharge 

Characteristics of a 

Weir in a Sand-Channel 

Stream

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1898-A
Stage-Discharge 

Characteristics of a 

Weir in a Sand-Channel 

Stream

By D. D. GONZALEZ, C. H. SCOTT, and ]. K. CULBERTSON

STUDIES OF FLOW IN ALLUVIAL CHANNELS

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1898-A

An evaluation of a prototype control 

structure designed on the basis of a 

model study

UNITED STATES GOVERNMENT PRINTING OFFICE, WASFINGTON : 1969
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

For sale by the Superintendent of Documents, U.S. Government Prlntir ft Office 

Washington, D.C. 20402 - Price 25 cents (paper coyer)
CONTENTS

 Page

Abstract- ________________________________________________________ Al

Introduction._ ____________________________________________________ 1

Proposed control structure-____-___________---_-----______________ 5

Construction. ____________________________________________________ 9

Initial construction.___________________________________________ 9

Changes since construction.____---___-_--_____-___-____________ 13

Performance of the controL____-___-------_----__--________________ 17

Stage-discharge relation. _______________________________________ 17

Submergence. ________-__--__----___----_-----_--_-_-_________ 20

Comparsion of model prediction and prototype operation.______________ 21

Effects of control on the channel-___---__-----__--______--__________ 22

Summary and conclusions-_________________________________________ 26

References cited-__-___________-_--_-__--__---_-_-________________ 28

ILLUSTRATIONS

FIGURE 1. Location map of the conveyance channel-_____________ A3

2. Duration curve of daily water discharge from the conveyance channel for 1953-65 water years. ___________ 4

3. Diagram showing details of the control as proposed by

Harris and Richardson (1964, fig. 37) _______________ 8

4. Diagram showing accessories for the control as proposed

by Harris and Richardson (1964, fig. 38) ____________ 10

5. Photographs of sheet piling at the upstream edge of the

controL _________________________________________ 11

6. Photographs of rock base for the controL_____________ 12

7. Diagram showing control on the conveyance channel as

constructed._____________________________________ 14

8. Photograph of drawdown and wave caused by acceleration of flow over the baffles._______________________ 16

9. Photograph of the baffle system installed in July 1966_ __ 17 

10-17. Graphs showing 

10. Stage-discharge relation, gage B, at controL.__________ 18

11. Stage-discharge relation, gage C, at controL ___________ 19

12. Ratio of measured discharge to rated discharge as

a function of percent submergence for the controL _____ 20

13. Water-surface profiles for control K (free-fall

conditions). _ _____________________________________ 23

14. Control sensitivity (gage B)._________________________ 24

15. Stage-discharge relations at the control site.___________ 25

16. Stage-discharge relations for gage A (at bridge).--______ 26

17. Elevations of water surface and of bed at gage A_________ 27

TABLE

TABLE 1. Basic data for the conveyance channel,-________________________ A6

in
STUDIES OF FLOW IN ALLUVIAL CHANNELS

STAGE-DISCHARGE CHARACTERISTICS OF A WEIR 

IN A SAND-CHANNEL STREAM

By D. D. GONZALEZ, C. H. SCOTT, and J. K. CULBEKTSON

ABSTRACT

A unique relation between water-surface elevation and water discharge usually 

does not exist for sand-channel streams. The relation is affected by changes in 

bed roughness and changes in bed elevation because of scour and fill. An artificial 

control on a sand-channel stream must control both the resistance to flow and 

the bed elevation in order to stabilize the relation between water-surface elevation and water discharge.

The weir (control structure) in the Rio Grande conveyance channel near Bernardo, N. Mex., was designed on the basis of a model study and field data (Harris 

and Richardson, 1964). About 72 percent of the measurements used to define 

the base relation between water-surface elevation and water discharge falls 

within plus or minus 5 percent of the mean relation for the prototype. The 

stage-discharge relation is not affected by backwater for values of submergence 

less than 90 percent. There is no consistent relation between the ratio of measured discharge to rated discharge and. submergence for values of submergence 

greater than 90 percent.

The control does not restrict the channel capacity to less than the strted design capacity of 2,000 cubic feet per second. When the control is drowred out, 

or ineffective, the relation of water-surface elevation to water discharge is virtually the same as that prior to construction of the control for discharges greater 

than 1,500 cubic feet per second. When the control is not drowned out that is, 

free-fall conditions exist the water-surface elevation for a discharge of 2,000 

cubic feet per second is greater than the minimum elevation, but is less than the 

maximum elevation that occurred at that discharge prior to construction.

The model study was only partially successful in predicting the operating 

characteristics of the prototype. Some of the differences between prototype 

operation and model predictions may exist because the prototype was not built 

exactly as recommended on the basis of the model study. In general, the prototype has operated somewhat better than the model predicted.

INTRODUCTION

Sand-channel streams often present problems in the determination of 

the total volume of water passing a gaging station because a unique 

relation between water discharge and water-surf ace elevation generally does not exist. The non-cohesive sand beds of the channels,

Al
A2 STUDIES OF FLOW IN ALLUVIAL CHANNELS

which control the stage-discharge relation, are subject to changes in 

roughness and to scour and fill. As a result, the stage-discharge relation often is not well defined, and corrections, based on waterdischarge measurements, must be applied.

Simons and Richardson (1962) have described the effects of changing bed roughness on the stage-discharge relation for several hydraulic 

conditions. Changes in bed roughness in some sand-channel streams 

may be gradual because the bed form consistent with a given discharge 

does not completely develop under unsteady How conditions as a flood 

wave passes. This condition results in a stage-discharge relation in the 

form of a loop. Changes in bed roughness, particularly from dune to 

plane bed, in sand-channel streams sometimes are rather abrupt, resulting in stage-discharge relations that are discontinuous (Colfoy, 1960; 

Dawdy, 1961). For sand-channel streams the change from dune bed 

to plane bed may occur over a wide range of discharges. The cause for 

the change is not easily defined.

The bed elevation of a long reach of sand-channel stream generally 

changes very little owing to scour and fill during the passage of a flood 

wave. Howrever, the change in bed elevation at sections in reaches that 

are narrower than average can be large (Colby, 1964). Gaging stations 

often are located at narrow sections, and the stage-discharge relations 

are subject to the effects of scour and fill.

Natural controls seldom exist on sand-channel streams; however, 

properly designed artificial controls (weirs) can be used to stabilize 

the stage-discharge relation. The elevation of the water surface at 

a given discharge is dependent on depth of flow associated with the 

prevailing bed form and the prevailing elevation of the bed. The structure must, in effect, control two variables, bed elevation anc1 roughness, 

to yield a stable rating.

The Rio Grande conveyance channel near Bernardo, N. Mex. (fig. 

1), is an example of a sand-channel stream that can present a problem 

in determining the discharge and the volume of flow at a gaging station. The conveyance channel has steep banks that are fairly well 

stabilized by native vegetation. In the vicinity of the control, the channel is straight and has a width of approximately 80 feet. Flows greater 

than about 100 cfs (cubic feet per second) occupy the full channel 

width. The banks are of alluvial material and the streambed is composed of fine sand (median diameter, 0.17-0.24 mm). The eH.nnel, constructed in 1954, was designed to convey 2,000 cfs, which is diverted 

from the river through the headworks 5 miles upstream from the 

control. The headworks structure consists of seven gated corrugated 

metal culverts, 7 feet in diameter. Discharges greater than 2,000 cfs 

are carried by the floodway. Median flow in the conveyance channel 

is 315 cfs, and flows exceed 2,000 cfs less than 0.3 percent of the time 

(fig-2).
STAGE, DISCHARGE, WEIR IN SAND-CHANNEL STREAM A3

Control structure 

,and total sediment sampler

FIGURE 1. Rio Grande conveyance channel.
DISCHARGE ^NDICATED TIME OF PERCENTAGE 

EXCEEDED OR EQUALED WAS 

o ro i-- 

oc o m oooo^ho 

JA.O1& KI IVIAflTIV .313XHVHO 
STAGE, DISCHARGE, WEIR IN SAND-CHANNEL STREAM A5

The bed form can be either dune or plane bed over an approximate 

range in discharge of 300 to 1,200 cfs. The depth, on the average, is 

about 35 percent less for plane bed than for dune bed at a given discharge. The channel is also subject to scour and fill, and a change in 

bed elevation of as much as 4 feet could occur at the original gaging 

station on the channel (Harris and Richardson, 1964, fig. 36). Because 

of these changes in bed form and in bed elevation, the stage-discharge 

relation was very unstable and streamflow could not be accurately 

determined without frequent measurements.

In 1961, the U.S. Bureau of Reclamation began a water-salvage 

study in the reach of the Rio Grande between Bernardo and San 

Acacia. An agreement was made between the Bureau of Reclamation 

and the Geological Survey to design and build a control structure at 

Bernardo that would provide a stable stage-discharge relation. The 

structure was designed on the basis of a model study and field data 

(Harris and Richardson, 1964).

The prototype structure was completed in September 1963. Construction was in cooperation with the Bureau of Reclamation under 

the general supervision of W. L. Heckler of the Geological Survey.

The purposes of this paper are (1) to describe the field installr.tion 

and construction, (2) to evaluate the performance of the control, 

including a comparison of the prototype performance with that predicted by the model study, and (3) to evaluate the effect of the 

controlled streambed elevation on channel capacity.

Basic data used in the analysis are given in table 1. Basic datT. include measured water discharge, gage height for gages B, C, and D, 

depth above the crest for gages B, C, and D, and percent submergence 

computed on the basis of depths above the crest for gages B and D.

PROPOSED CONTROL STRUCTURE

The Geological Survey obtained data on water-surface and streambed elevations at the proposed location for the control and also 

conducted model studies at the Colorado State University Hydraulics 

Laboratory. The water-surface and streambed elevations at the proposed site were obtained to determine the proper elevation of the control crest. The crest elevation was to be .such that the channel capacity 

would be as much as 2,000 cfs and the crest would be above mean bed 

elevation and therefore free of sand most of the time. The model 

studies were conducted to determine (1) a control configuration which 

would eliminate, or at least minimize, the effects of changes ir bed 

configuration and changes in bed elevation on the stage-discharge 

relation, (2) the maximum elevation of the control crest which would 

not create sufficient backwater to interfere with the maximum design 

capacity of the channel (2,000 cfs) and the backwater characteristics 

of the control under various degrees of submergence, (3) the design

335-122 O-H69 2
A6 STUDIES OF FLOW IN ALLUVIAL CHANNELS 

TABLE 1. Basic data for the conveyance channel

Date

1964

5-28

6-3

11-16

11-17

11-18

11-20

11-27

12-4

12-11

12-18

12-24

1965

1-5

1-11

1-14

1-20

1-29

2-2

2-3

2-12

2-19

2-26

3-3

3-11

3-19

3-26

3-30

4-8

4-16

4-22

4-29

5-6

5-7

5-8

5-9

5-10

5-12

5-13

5-17

5-26

5-27

5-31

6-2

6-3

6-8

6-22

6-29

7-6

7-13

7-20

7-27

8-3

8-11

9-15

9-29

10-5

10-13

10-20

10-26

11-3

11-10

11-17

11-24

11-29

11-30

Measured 

water 

discharge 

(cfs)

787

806

317

469

721

1,280

328

426

275

215

439

509

1,680

619

582

495

544

562

774

537

692

602

310

362

238

242

1,060

726

1,300

924

835

800

837

784

771

980

894

894

1,210

1,150

1,310

1,180

1,290

1,020

1,040

817

1,070

1,180

1,220

691

1,060

757

350

376

739

304

708

673

906

1,490

1,520

1,240

1,120

1.240

Gage height (ft)

B

5.46

5.36

4.60

4.95

5.29

6.07

4.55

4.78

4.47

4.36

4.86

4.88

6.98

5.20

5.07

4.91

5.01

5.03

5.34

5.01

5.23

5.10

4.63

4.68

4.41

4.41

5.79

5.24

6.51

5.79

5.63

5.96

6.08

5.84

5.80

6.46

6.20

6.18

6.75

6.34

6.76

6.46

6.63

6.40

6.42

5.87

6.12

6.71

6.76

5.43

6.16

5.37

4.68

4.74

5.28

4.50

5.19

5.13

5.44

6.16

6.20

5.93

5.77

5.88

C

5.44

5.30

4.43

4.81

5.12

5.96

4.46

4.64

4.39

4.23

4.67

4.76

6.98

4.98

4.89

4.76

4.84

4.89

5.16

4.84

5.03

4.90

4.47

4.52

4.28

4.35

5.62

5.11

6.49

5.75

5.43

5.79

5.96

5.83

5.65

6.40

6.08

6.08

6.34

6.75

6.46

6.65

6.39

6.40

5.77

6.10

6.62

6.68

5.34

6.15

5.54

4.48

5.04

4.37

5.10

5.40

6.72

6.20

5.96

D

5.32

5.10

3.33

4.12

4.72

5.66

3.57

4.06

3.55

3.35

4.40

4.41

6.84

4.40

4.24

3.95

4.22

4.27

4.88

4.18

4.56

4.36

3.98

4.26

3.82

3.75

5.47

4.72

6.28

5.67

5.49

5.83

5.95

5.69

5.62

6.35

6.02

6.08

6.52

6.19

6.53

6.33

6.50

6.25

6.34

5.70

6.15

6.48

6.59

5.28

5.94

5.34

3.68

3.54

4.66

3.50

4.38

4.61

5.12

5.87

5.84

5.30

4.80

5.00

Depth above crest (ft) "

B

2.40

2.30

1.54

1.89

2.23

3.01

1.49

1.72

1.41

1.30

1.80

1.82

3.92

2.14

2.01

1.85

1.95

1.97

2.28

1.95

2.17

2.04

1.57

1.62

1.35

1.35

2.73

2.18

3.45

2.73

2.57

2.90

3.02

2.78

2.74

3.40

3.14

3.12

3.69

3.28

3.70

3.40

3.57

3.34

3.36

2.81

3.06

3.65

3.70

2.37

3.10

2.31

1.62

1.68

2.22

1.44

2.13

2.07

2.38

3.10

3.14

2.87

2.71

2.82

C

2.38

2.24

1.37

1.75

2.06

2.90

1.40

1.58

1.33

1.17

1.61

1.70

3.92

1.92

1.83

1.70

1.78

1.83

2.10

1.78

1.97

1.84

1.41

1.46

1.22

1.29

2.56

2.05

3.43

2.69

2.37

2.73

2.90

2.77

2.59

3.34

3.02

3.02

3.28

3.69

3.40

3.59

3.33

3.34

2.71

3.04

3.56

3.62

2.28

3.09

2.48

1.42

1.98

1.31

2.04

2.34

3.66

3.14

2.90

D

2.26

2.04

.27

1.06

1.66

2.60

.51

1.00

.49

.29

1.34

1.35

3.78

1.34

1.18

.89

1.16

1.21

1.82

1.12

1.50

1.30

.92

1.20

.76

.69

2.41

1.66

3.22

2.61

2.43

2.77

2.89

2.63

2.56

3.29

2.96

3.02

3.46

3.13

3.47

3.27

3.44

3.19

3.28

2.64

3.09

3.42

3.53

2.22

2.88

2.28

.62

.48

1.60

.44

1.32

1.55

2.06

2.81

2.78

2.24

1.74

1.94

Percentage of submergence B-D

94.2

88.7

17.5

56.1

74.4

86.4

34.2

58.1

34.8

22.3

74.5

74.2

96.4

62.6

58.7

48.1

59.5

61.4

79.8

57.4

69.1

63.7

58.6

74.1

56.3

51.1

88.3

76.1

93.3

95.6

94.6

95.5

95.7

94.6

93.4

96.8

94.3

96.8

93.8

95.4

93.8

96.2

96.4

95.5

97.6

94.0

101.0

43.7

95.4

93.7

92.9

98.7

38.3

28.6

72.1

30.6

62.0

74.9

86.6

90.6

88.5

78.0

64.2

68.8
STAGE, DISCHARGE, WEIR IN SAND-CHANNEL STREAM A7 

TABLE 1. Basic data for the conveyance channel Continued

Date

12-3 

12-9 

12-16 

12-22 

12-29

Measured

discharge 

(cfs)

1,230 

1,460 

1,120 

1,360 

1,500

Gage height (ft)

B

5.90 

6.12 

5.86 

6.07 

6.25

C

6.00 

6.32 

5.98 

6.30 

6.28

D

5.07 

5.42 

4.76 

5.09 

5.52

Depth above crest (ft)

B

2.84 

3.06 

2.80 

3.01 

3.19

C

2.94 

3.26 

2.92 

3.24 

3.22

D

2.01 

2.36 

1.70 

2.03 

2.46

Percentage

mergence B-D

70.8 

77.1 

60.7 

67.4 

77.1

1966

1-7

1-13

1-21

2-4

2-10

2-18

2-25

3-4

3-10

3-18

3-24

3-31

4-7

4-13

4-22

4-27

5-5

5-12

5-19

5-26 1

6-2

6-10

6-30

918

926

895

855

920

782

892

714

651

,370

,190

,170

,300

,310

,420

,170

,260

,050

852

,020

,110

380

516

5

5

5

5

5

5

5

5

5

6

5

5

6

6

6

5

6

5

5

5

6

4

5

52

53

51

40

48

30

48

21

16

09

90

91

05

07

13

88

08

82

55

86

06

66

01

5

5

5

5

5

5

5

5

5

6

5

5

6

6

6

5

6

47

56

51

46

50

30

47

18

17

08

82

89

05

00

25

87

04

4

4

4

4

4

4

4

4

4

5

5

5

5

5

5

5

5.

5.

5

5.

5

4

4

03

00

15

19

32

07

52

14

10

25

35

24

41

40

40

01

41

31

26

68

93

03

06

2.46

2.47

2.45

2.34

2.42

2.24

2.42

2.15

2.10

3.03

2.84

2.85

2.99

3.01

3.07

2.82

3.02

2.76

2.49

2.80

3.00

1.60

1.95

2.41

2.50

2.45

2.40

2.44

2.24

2.41

2.12

2.11

3.02

2.76

2.83

2.99

2.94

3.19

2.81

2.98

.97

.94

1.09

1.13

1.26

1.01

1.46

1.08

1.04

2.69

2.29

2.18

2.35

2.34

2.34

1.95

2.35

2.25

2.20

2.62

2.87

.97

1.00

39.4

38.1

44.5 .

48.3

52.1

45.1

60.3

50.2

49.5

88.8

80.6

76.5

78.6

77.7

26.2

69.1

77.8

81.5

88.4

93.6

95.7

60.6

51.3

of an energy dissipator to prevent excessive scour downstream of the 

structure, (4) the location of a section or sections where accurate 

measurements of water discharge and sediment discharge could be 

made, and (5) the position of a total sediment-load sampling sill.

On the basis of the model studies, the following control-structure 

design was recommened (fig. 3). The structure was to have a control 

surface longitudinal slope of 16 to 1 and a transverse slope of 35 to 1. 

The approach apron was to have a slope of 2 to 1, and the downstream 

apron, a slope of 3 to 1. Sheet piling at the upstream end of the control 

was to serve as a cutoff wall and to add to the structural stability of 

the control. The sidewalls were designed to run straight along both 

sides of the control with a side slope of 2 to 1.

Control accessories, including baffles, bubbler-gage orifice mounts, 

total-sediment-load sampling sill, and energy dissipator, were also 

designed on the basis of the model studies. The system of bafles was 

designed to be mounted on the upstream edge of the control surface 

to keep the bubbler-gage orifice and the crest of the control free of 

sand. The model studies indicated that the bubbler-gage orifice could 

be on the centerline of the control 4 or 8 feet upstream from the crest.

The downstream apron was designed to include a sampling sill from 

which total-sediment-load samples could be obtained. The sill was to
A8 STUDIES OF FLOW IN ALLUVIAL CHANNELS

be 1.5 feet lower than the crest at the centerline and to nm the entire 

width of the control. The sill covers a trench which contains pipes 

leading to an automatic-pump sediment sampler. A groove on the 

doAvnstream edge of the sill permits a guide to be positioned so that 

total-sediment-load samples may be obtained using a DH-48 sediment 

sampler.

Cutting surface C

Flow

Cutting surface B

Cutting surface D

Cutting surface A

-40.5'-

Section A

T T

16:1

-40.5'-

Section B

-80'-

Section C

35:1

Section D

FIGURE 3. Details of the control as proposed by Harris and Rid ardson

(1964 fig. 37).
STAGE, DISCHARGE, WEIR IN SAND-CHANNEL STREAM A9

An energy dissipator, 1.5 feet high, was designed to be placed at the 

downstream toe of the control. It was suggested that it might be 

necessary to place riprap on the bed and along the banks for a short 

distance downstream of the toe of the control to prevent ercessive 

scour. Figure 4 shows the positions of the control accessories.

Harris and Eichardson (1964) recommended that the elevs.tion of 

the crest of the control be 4.50 feet below bankfull stage, or 4,723.5 

feet above mean sea level at the proposed control location. At this elevation the crest of the control would be 0.5 foot above the maximum 

bed elevation observed in 1958 and 0.25 foot lower than the maximum 

bed elevation observed in 1957.

CONSTRUCTION

INITIAL CONSTRUCTION

Construction was started in August 1963. Excavation for thQ, structure was 80 by 40 feet, to a depth approximately 3 feet below mean 

bed level. Sheet piling, used as the upstream cutoff wall, was placed 

across the channel and 10 feet into both banks at the upstream edge 

of the control. The top of sheet piling was driven to an elevation of 

4,718.0 feet above mean sea level, 5.5 feet below the crest (fig. 5).

Rock, 0.5 to 1.5 feet in diameter, was placed in the excavation to 

create the approximate shape of the control. The base was then covered 

with finer rock, 2 to 3 inches in diameter (fig. 6). On top of tKs finer 

material a concrete cap was placed to form the surface of the control. 

Six-gage 6 X 6-inch steel-wire reinforcement was used in the concrete 

cap.

The approach apron was constructed to a 2 to 1 slope and the control 

surface to a 16 to 1 slope to the crest. A transverse slope of 35 to 1 was 

used for the crest, converging toward the centerline in order to confine 

low flows. The downstream apron was constructed to a 3 to 1 slope 

from the crest to the sampling sill and to an 8 to 1 slope from the 

sampling sill to the energy-dissipator wall. The energy-dissipator wall, 

constructed of grouted rock, was 1.5 feet high and 1.5 feet thick and 

extended across the width of the control. A 3-inch clay pipe was placed 

across the control near the toe to relieve hydrostatic pressure under the 

downstream apron. One bubbler-gage orifice was recessed into the 

concrete cap 4 feet upstream of the crest at the center line. A vertical 

staff gage was placed 0.8 foot upstream of the orifice.

Sidewalls were constructed along both banks extending from the 

upstream sheet piling to the energy-dissipator wall. They were constructed to a % to 1 slope and converged slightly toward the centerline 

downstream of the crest. Riprap 0.5 to 1.5 feet in diameter was placed 

on the bed of the channel downstream of the energy-dissipator wall 

for a distance of about 20 feet and to a depth of approximately 3 feet.
A10 STUDIES OF FLOW IN ALLUVIAL CHANNELS

Sampling curb

Dissipator wall' 

CROSS SECTION OF DOWNSTREAM APRON

16:1 ^-» 77"/* 1 J

0.2'

Auxiliary orifice mount ' £ Main orifice mount 

CROSS SECTION ON CONTROL CENTERLINE

-Control 

crest

Upstream edge ofcontrol surface BAFFLE POSITION

FIGURE 4. Accessories for the control as proposed by Harris and R'^hardson

(1964, fig. 38).
STAGE, DISCHARGE, WEIR IN SAND-CHANNEL STREAM All

. 1

'^^^^

FIGURE 5. Sheet piling at the upstream edge of the control. Upper, Driving the 

piling. Lower, Piling in place.
A12 STUDIES OF FLOW IN ALLUVIAL CHANNELS

i>4is^?ji'1|!''jr^» if.O'^- *-« »>"' ' «*.'*''" -i"- S'.S&'^'rv *<>"--;w,

**' -v

FIGURE 6. Rock base for the control. Upper, Hand finishing coarse rock to grade. 

Loicer, Fine rock finished to grade.
STAGE, DISCHARGE, WEIR IN SAND-CHANNEL STREAM A13

The footbridge was made from pairs of standard three-bar roof-joist 

assemblies, 30 feet long, spaced 30 inches apart. Two pairs of 4-inch 

pipe piers, imbedded in the downstream apron of the control, were used 

to support the bridge. A concrete-block shelter, 8 X11 feet, was constructed 50 feet from the right bank to house the bubbler-manometer 

unit for recording water-surface elevations at the bubbler orifice and 

to house a pump sediment sampler. A longitudinal cross section along 

the centerline of the completed structure is shown in figure 7.

A tail-water gage was installed 160 feet downstream from the control 

to be used for determining the percentage of submergence on the control. In the model study, the tail-water gage was 60 feet downstream 

of the control.

The sampling sill was constructed of 20-gage galvanized steel and 

covered a 10 X 10-inch trench. The sill extended across the width of 

the control on the downstream apron. Plastic %-inch pipes were run 

from three sampling heads containing orifices through the trench to 

the concrete-block shelter on the right bank. The %-inch lines were 

placed inside of li/^-inch plastic tubing for ease of replacement and 

protection against damage. Three extra plastic lines were installed so 

that three additional intake heads could be installed later if desired. 

The sampling heads were molded of lead and contoured to fit snugly to 

the sill and concrete apron. The intakes were perpendicular to the flow 

and 0.2 foot above the surface of the sill. An automatic-pump sediment sampler was housed in the concrete-block shelter.

Total-sediment load passes over the control in suspension and may 

be sampled by means of a US-DH-^t8 hand sampler. A guide rod 

placed in the lip on the downstream edge of the sill is used to guide the 

DH-48 sampler, which samples total sediment concentration when 

lowered to the sill.

CHANGES SINCE CONSTRUCTION

Several changes have been made since the control structure was 

completed. Some of the changes resulted because of a partial failure of 

the structure and other changes were made because of difficulties in 

measurement of stage on the structure.

Early in January 1966, the banks of the channel just downstream 

from the control began eroding rapidly and the scour hole downstream 

of the control deepened. This damage occurred at the end of an extended period of high flow. The mean discharge for the months of 

November and December 1965 was nearly 1,350 cfs.

The energy-dissipator wall apparently operated as predicted from 

the model study and created a reverse roller which caused the scour 

hole to be well downstream of the toe of the control. However, the 

scour hole became so large during the high flow that the banks began 

to fail and riprap placed just downstream of the control settled. The

335-122 O-^69 8
A14 STUDIES OF FLOW IN ALLUVIAL CHANNELS

rockfill under the downstream apron also settled, and as a result the 

energy-dissipator wall and part of the apron failed. The convergence 

of the sidewalls downstream of the crest caused a strong eddy and 

backflow on either side of the channel, and this contributed to the 

failure.

Bubbler orifice-

^Crest

Upstream edge of 

control surface 2.0'

\ \

2.7'

BAFFLE SYSTEM, PLAN VIEW

I "'-I

n n n n n n'

^ p 

BAFFLE SYSTEM, DOWNSTREAM VIEW

Baffles

Sampling

sill Energy 

dissipator 

8:1

£5i?{itt£

-8-foot sheet piling

CENTERLINE CROSS SECTION

FIGURE 7. Control on the conveyance channel as constructed.
STAGE, DISCHARGE, WEIR IN SAND-CHANNEL STREAM A15

Approximately 400 cubic yards of rock 0.5 to 1.5 feet in diameter 

was placed immediately downstream of the apron. Inspection of the 

rock when the channel was dry showed that the rock was well settled 

in place. The riprap now serves as the energy dissipator.

In July 1966, the convergent sidewalls were straightened. This reduced the side eddies and backflow considerably. It is not anticipated 

that more than minor maintenance will be required in the future.

Difficulties with the measurement of stage have required that some 

changes be made. The vertical staff gage which was used as a reference 

for gage C (bubbler gage) collected trash which made reading the 

staff difficult and also caused drawdown over the bubbler orifice. The 

vertical staff was cut off at the base on March 5, 1964, and a horizontal chain gage was installed on the footbridge as a reference on 

April 24, 1964. The chain gage was installed on the right pier which 

is about 15 feet to the right of the centerliiie of the control where the 

orifice is located. The chain gage measured the water surface the same 

distance upstream as the distance of the orifice from the footbridge. 

The baffles caused a standing wave over the bubbler orifice; however 

the chain gage wras outside the influence of the standing wave. Different flow conditions and trash on the baffles caused the standing wave 

over the orifice to vary and the chain gage \vould not check the bubblergage reading with any consistency. Differences in water-surface elevation between the chain-gage reading and the bubbler-gage reading of 

0.1 foot were not uncommon. Because of the inconsistency in the readings between the gages, the chain gage wras moved to the centerline 

of the control on August 10,1966. The chain gage, now measures water 

surface directly over the bubbler-gage orifice.

Because the chain-gage and bubbler-gage readings woud not agree, 

a gage well, designated gage B, was installed on the right bank 28 feet 

upstream of the control crest on May 8, 1964. The float-actuated recorder was housed in a shelter mounted on a 36-inch corrugated-metal 

pipe well. Gage B was designated as the primary gage and gage C was 

continued in operation as an auxiliary gage.

During a period of a few days in May 1964, the control was covered 

with about 1 foot of sand at the centerline of the control. It was not 

known whether the sand was deposited on the control because the 

baffles did not create sufficient turbulence to keep the control clear or 

whether sand accumulation in the channel downstream caused deposition on the control. Extensions of 0.5 foot were added to each of the 

baffle plates to increase turbulence to aid in keeping the control clear 

of sand. The baffle system caused a large standing wave 011 the control crest over the bubbler orifice (fig. 8), and trash tended to collect 

on the baffles; for these reasons this baffle system wT as removed and a 

newr system was installed during July 18-20,1966.
A16 STUDIES OF FLOW IN ALLUVIAL CHANNELS

The new system of baffles consists of plates in three rows that are 2 

feet apart. The plates are each 2 feet long and. their centers are spaced 6 

feet apart. The baffle plates are bent to form an angle of about 50° 

with the control surface in a downstream direction. The effective height 

of the baffles is approximately 1.2 feet. The new baffle system is the 

same as one described by Harris and Richardson (1964, top of p. 150), 

except that the baffles are angled from the vertical in a downstream 

direction. No data obtained after the baffle system was changed are 

included in this report, but observations indicate that the new baffle 

system is effective in keeping the control free of sand, does not collect 

trash, and does not create a large standing wave. Figure 9 shows the 

new baffle system as it appeared after a runoff event. The material 

on either side of the control is fine material deposited on the falling 

stage. Sand did not deposit on the control beyond the first row of 

baffles and no trash has been observed on the baffle plates. The water 

surface downstream of the baffles is rougher than it was with the old 

system but is not so rough as to preclude measurement of stage with 

the chain gage.

I

FIGURE 8. Drawdown and wave caused by acceleration of flow over the baffles

(right center).
STAGE, DISCHARGE, WEIR IN SAND-CHANNEL STREAM A17

FIGUBE 9. The baffle system installed in July 1966.

PERFORMANCE OF THE CONTROL

STAGE-DISCHARGE RELATION

In this report, the data used to define the stage-discharge relation for 

the control were obtained from late May 1964 to July 1966. The baffle 

system in use during this period was that originally installed on the 

control. During this period, gage B was used as the primary gage and 

gage D, 160 feet downstream of the control, w^as used to measure the 

tail-water stage. The location of gage D so far downstream of the 

control led to two noteworthy conditions with respect to analysis of 

the effect of submergence. First, the stage at gage D was subject to 

fluctuations due to scour and fill and to bed-roughness changes. This 

would present no particular problem in the analysis of effect of submergence on the stage-discharge relation provided the stage at gage 

D maintained a constant difference from the stage immediately below 

the control. It is not known if a constant difference was maintained. 

Second, submergence as computed from stage readings at gage B and 

gage D should always be less than 100 percent because of the distance 

between gage B and gage D. Gage C was operated during most of the 

period but only as an auxiliary gage.
A18 STUDIES OF FLOW IN ALLUVIAL CHANNELS

The period of record used in this report can be divided into three 

fairly distinct subperiods. For the subperiod May 22,1964, to April 29, 

1965, the measurements of discharge generally were less than 800 cfs, 

and most of the measurements plot on the base rating for gages B and 

C. For the subperiod April 29-October 20, 1965, the measurements of 

discharge generally were between 700 and 1,300 cfs, and nearly all 

measurements plotted off the base rating. For the subperiod October 20, 

1965, to July 1-i, 1966, the measurements of discharge generally were 

between 800 and 1,500 cfs, and nearly all measurements plotted on the 

base rating for both gages. (See figs. 10 and 11.) There were very few 

measurements with which to define the ratings below 200 cfs.

The base rating for gage B plots as a straight line through the range 

of discharge from 200 to 1,500 cfs. However, the base rating for gage 

C shows a definite break for discharges greater than 600 cfs. This break 

is probably clue to the baffle system, which causes a standing wave 

whose crest is near the orifice of gage 0. The amplitude of the wave 

tends to increase with discharge. As a result, the water-surface eleva9

7

6

5

4

3

1

1

-

1 1 1

FXPi ANATION

 n May 22, 1964, to April 29, 1965

April 29, 1965- Oct. 20, 1965 -

- A Oct. 20. 1965, to July 14, 1966

Ra<s*» ratinp

1

nmrttf

1

<

1 ^

1

« 

* t

1

1

M 

>*-

» 0

? 

I

1

&

\

D

/

1

1

-

-

_

-

^ 

-

1

200 400 600 800 1000 1200 1600 20

WATER DISCHARGE, IN CUBIC FEET PER SECOND

FIGURE 10. Stage-discharge relation for conveyance channel, gage B, at control.
STAGE, DISCHARGE, WEIR IN SAND-CHANNEL STREAM A19

tion at gage C is higher than at gage B for discharges greater than 

about 1,100 cfs.

Deviations of discharge measurements from the base rating of the 

control are caused by variation of the gage height at a given discharge 

or by errors in water-discharge measurements. The variation of the 

gage height at a given discharge can be caused by scour and fill at the 

gage location, changes in bed roughness at the gage location, backwater 

on the control, or burial of the control.

For those measurements made when free-fall conditions existed 

that is, the stage-discharge relation was not affected by backwater 

72 percent is within plus or minus 5 percent and all are within plus or 

minus 10 percent of the base rating for gage B. The errors in discharge 

measurements are likely to be from 2 to 5 percent and perhapr even 

larger for some conditions at the measuring sections in this channel. 

Therefore, it is likely that most of the scatter from the rating is caused 

by errors in discharge measurements for free-fall conditions.

9 

8

7 

6

5

4

3

2

1 

2C

1

-

 

A

-

-

_ Cl^^^

^^ego<» D

'D ^^^

1 1

EXPLANATION 

May 22, 1964, to April 29,1 

April 29, 1965- Oct. 20,196 

Oct.20,1965,toJuly 14, 19

1

365 

)5 

66

 Predicted by model (Harris and 

Richardson, 1964, fig. 43)

D ^^

^

\

\ 

A Jg D

>-V

A

r*Jf

1

A

D

^

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» D

M*&

^

A

^A

/

'

D

^

\

'-

-

-

-

-

0 400 600 800 1000 1200 1600 20

WATER DISCHARGE. IN CUBIC FEET PER SECOND

FIGURE 11. Stage-discharge relation for conveyance channel, gage C, at control.
A20 STUDIES OF FLOW IN ALLUVIAL CHANNELS

SUBMERGENCE

Backwater causes submergence of the control if the elevation of the 

tail water becomes greater than the elevation of the lowest point on 

the crest of the control. Submergence is the ratio of the depth above 

the crest of the tail water to the depth above the crest of the upstream 

head on the control, and experiment has shown that the discharge is 

a function of submergence as well as gage height (Eisenlohr, 1964). 

Most of the measurements during the subperiod April 29-October 20, 

1965, plotted off the base rating and, therefore, a study of submergence 

was made to determine the effect on the stage-discharge relation. The 

ratio of the measured discharge to the rated discharge was plotted as 

a function of submergence computed from depths above the crest for 

gages B and D (fig. 12). From figure 12, it is obvious that backwater 

has no effect on the stage-discharge relation for values of submergence 

less than 90 percent. For values of submergence greater than 90 percent, the stage-discharge relation is affected by backwater, but no 

consistent relation exists between the ratio of the measured discharge 

to the rated discharge and the percent submergence.

It should be noted that, as the control approaches complete submergence, the submergence ratio approaches a maximurr value which

1.5

1.0

0.9

0.8 

0.7 

0.6 

0.5

_

^ D

On

u

D

A 0

ao°°an * 

J? A A

A n

0

D

f o D D

A CP A :

A ^

AAA

A

_ EXPLANATION

a May 22, 1964, to Apr. 29, 1965

o Apr. 29 -Oct. 20, 1965

__ A Oct. 20, 1965, to July 14, 1966

A

A

A

a\

A CD

A

D

A

0 A

O

^&0 °n

0 0

0°

°0 0 0

oo 0

8 °tf"

__

o

50 60 70 80 90

PERCENTAGE OF SUBMERGENCE (GAGES B AND D)

100

FIGURE 12. Ratio of measured discharge to rated discharge SLF a function of 

peix-entage of submergence for the control.
STAGE, DISCHARGE, WEIR IN SAND-CHANNEL STREAM A21

is less than 100 percent for this structure because of the distance between gages used to measure the headwater and tail-water stages. 

A further increase in the tail-water stage affects the stage-discharge 

relation, but the submergence ratio tends to remain constant. Therefore, at complete submergence of the control, the submergence ratio 

cannot be used as a correction for backwater on the control. Because 

backwater affects the stage-discharge relation for this structure only 

for values of submergence approaching a maximum, it is apparent 

that some other method, such as the shifting-control method, should 

be used to correct for the effect of backwater on the stage-discharge 

relation. In other words, the control should be considered as completely ineffective, or droAvned out, for values of submergence greater than 

90 percent.

The stage-discharge relation at the control, for free-fall conditions, 

is much improved over the rating prior to the control. However, for 

those periods of time during which the control can be considered to 

be drowned out that is, the submergence ratio is greater than 90 percent the presence of the control structure does not improve- the 

stage-discharge relation compared to that which would exist if the 

structure were not in place.

COMPARISON OF MODEL PREDICTION AND 

PROTOTYPE OPERATION

The Bernardo control model was only partially successful in predicting the operation of the prototype, and there are differences in 

practically every detail of operation of the prototype from that predicted by the model. Some of the differences may exist because the prototoype was not built exactly as specified on the basis of the rrodel 

study.

The base rating predicted by the model study (fig. 11) shows that 

about 15 to 20 percent more depth above the crest at a given discharge 

is required for the prototype than was predicted by the model study. 

The transverse slope of the crest was 40 to 1 in the model but was 35 to 

1 in the prototype, and this probably accounts for the greater dQ<pth 

on the prototype than on the model.

On the basis of the model study and field data, free-fall conditions 

for the Bernardo control would occur for discharges of less than 300 

cfs if the control crest was established 4.5 feet below bankfull s^age. 

The crest of the prototype was actually set at elevation 4,723.0% or 

0.44 foot lower than was recommended; for the conditions experienced, 

the prototype has had free-fall conditions for discharges less than 

about 700 cfs. Also, the model predicted an effect of backwater on the 

stage-discharge relation for submergences greater than about 60 percent (Harris and Richardson, 1964, fig. 42). The prototype shoAved
A22 STUDIES OF FLOW IN ALLUVIAL CHANNELS

an effect of backwater on the stage-discharge relation only for submergences greater than 90 percent.

The model study showed that the baffles caused no detectable surface 

wave at the bubbler orifice 4 feet upstream of the control crest (fig. 13), 

but a large surface wave was observed in the prototype. The baffles on 

the prototype were 0.5 foot higher than the model baffles, and this may 

have contributed to the formation of the surface wave on the prototype but not on the model. The baffle system now in use on the prototype was rejected on the basis of the model study as not b^ing effective 

in keeping the control clear of sand and for causing a rough water 

surface (Harris and Kichardson, 1964, p. 150, position 1). The present baffle system appears to be more effective in keeping the control 

clear of sand than the system selected from the model study. The 

present system does create a somewhat rough water surface, but the 

wave caused by the baffles has been virtually eliminated.

The sensitivity of the rating of the model was based on a vee notch 

with a 40 to 1 lateral slope; however a lateral slope of 35 to 1 was 

recommended and used in the prototype. The model discharge, given 

in terms of prototype discharge, changed 1.5 percent or less for a 0.01- 

f oot change in stage at 400 cf s or more and changed 7 percent at 30 cf s. 

The prototype discharge changed 1.5 percent or less fc~ a 0.01-foot 

change in stage at 300 cfs or more and changed slightly more than 

4 percent at 30 cfs (fig. 14). The prototype is more sensitive than the 

model because of the slightly greater lateral slope of the prototype 

notch.

EFFECTS OF CONTROL ON THE CHANNEL

One main purpose of the model study was to determine the proper 

crest elevation so that the control would not restrict th°, capacity of 

the channel to less than 2,000 cfs. From the model study it was determined that with 100 percent submergence at 2,000 cfs, the water surface 

would be 4 feet above the crest of the control (Harris anc1 Richardson, 

J.964, fig. 42). Allowing 0.5 foot for freeboard, the control crest would 

be placed 4.5 feet below the bankfull stage or at an elevation of 4,723.5 

feet above mean sea level. The control was actually set approximately 

0.5 foot lower than recommended to insure that the channel capacity 

would not be restricted.

A staff gage established just upstream of the control site prior to 

construction of the control indicated that the range of discharge for 

a given gage height was about the same at the control site as at the 

cable upstream (fig. 15). The limits of the range of water-surface elevation at a given discharge were estimated from the rating for gage A 

at the bridge upstream of the control. The base rating for gage B 

(from fig. 10) shows that the water-surface elevation at 2,000 cfs is 

slightly higher than the minimum possible before the control but is 

well below the maximum possible before the control.
DISTANCE, IN FEET

FIGURE 13. Water-surface profiles for control K (free-fall conditions). Ha
A24 STUDIES OF FLOW IN ALLUVIAL CHANNELS

The maximum water-surface elevation, on the basis of gage B, for 

a given discharge when the control is drowned out is almost identical 

with the maximum water-surface elevations prior to the control for 

discharges greater than about 1,500 cfs. In other words, for discharges 

greater than 1,500 cfs with the control drowned out, the control has no 

effect on the stage-discharge relation and the channel controls the 

stage-discharge relation as it did prior to construction of the control.

The stage-discharge relation at the cable section upstream of the 

control has also been improved by the control structure (fig. 16). Gage 

A at the bridge, on which this relation is based, was not in operation 

during the period that the bed was in dunes, and the rating after the 

control structure was completed is for a plane-bed condition only. For 

this reason the rating for gage A has less scatter than it would if dunebed data were included. The form of the rating has much the same 

appearance as the base rating for gage B at the control structure. The 

somewhat greater scatter for the gage A rating than for the base 

rating for the control results from minor adjustments in bed elevation 

and bed roughness at gage A site. Extending the rating, based on 

measurements after the control structure was completed, to 2,000 cfs 

shows that the structure does not limit the discharge for the, plane-bed 

condition at gage A. It seems reasonable that when the control structure is drowned out and the channel is definitely controlling, the same 

situation prevails at gage A as at the control structure and, on the 

basis of the available data, the channel at gage A is not restricted in 

any way by the control for discharges greater than 1,500 cfs.

I

CO £5 

Q< 

cc co

zl 

~ <

UJ I

CJO Ife

°

-

-

\

\ \

\

\

-

-

^

^^

. -

-

-

-

-

-

k~*~-

0 100 1000- 10,

WATER DISCHARGE, IN CUBIC FEET PER SECOND

FIGURE 14. Control sensitivity (gage B).
STAGE, DISCHARGE, WEIR IN SAND-CHANNEL STREAM A25

The bed elevation is controlled at the structure location at an elevation higher than average prior to construction. Water-surface elevations were obtained at the control site prior to construction, but no 

cross sections were obtained; therefore, the average bed elevation at 

that point was not established. The mean bed elevation at gage A for 

the 3 years prior to construction of the control structure was about 

4,722.9 feet (fig. 17). The average fall between the cable and the control site is about 0.7 foot; therefore, the average bed elevation at the 

control site was about 4,722.2 feet prior to construction of the control 

structure. The control crest elevation is 4,723.06 feet or about 0.9 foot 

above the mean bed elevation at the control site prior to construction. 

The mean bed elevation at the cable since construction of the control is 

about 4,723.8 feet or about 0.9 foot above the mean prior to the control. 

The maximum bed elevation observed at the cable since construction of 

the control was about 4,723.3 feet, which is slightly lower than the 

maximum of 4,723.5 feet observed in 1957 (Harris and Kichardson,

iU

9 

8

7 

6

5 

4

3 

2

1

_ 1

-

-

-

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-

-

I

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^

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EXPL

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to

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dr

1 1

1

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9

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.ANATIC

j rating for

oximate lir 

a given ga 

constructs

er limit of 

Dwned out

1

1

^

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+ 

t ^

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control

nits of d 

ge heigh 

Dn of the

rating fo

1

1

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contr

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1

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,

^

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1

1

^'

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^

-

-^

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-

-

-

I 200 400 600 800 1000 1200 

WATER DISCHARGE, IN CUBIC FEET PER SECOND

1600 2000

FIGTJBE 15. Stage-discharge relations at the control site before and af'^r the

control.
A26 STUDIES OF FLOW IN ALLUVIAL CHANNELS

1964). No dune-bed data are included after construction of the control because gage A was not in operation during the period when the 

bed was in dunes.

SUMMARY AND CONCLUSIONS

A control structure, based on model and field studies, \^as installed 

in the Eio Grande conveyance channel near Bemardo, N. Mex. Some 

changes have been made on the control structure since construction 

because of problems in measurement of stage and because of a partial 

failure of the structure during a period of high flow. The major 

changes were the installation of a gage at the upstream edge of the 

control, the installation of a new baffle system, and the straightening 

of the sidewalls.

The stage-discharge relation is much improved over the relation 

prior to construction of the control except when the centre 1 is drowned 

out. Approximately 72 percent of the measurements falls within plus

10

9 

8

7

6 

5

4 

3

2

1 

20

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^ <

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EXPLANATION 

o 1961-63 water years (before control) 

 1964-66 water years (after control) 

_ _ Limits of discharge at a given gage height

1

^

m

O 

%n

^

o

0 ' 400 600 800 1000 1200 1600 20C

WATER DISCHARGE, IN CUBIC FEET PER SECOND

FIGUBE 16. Stage-discharge relations for gage A (at bridge).
STAGE, DISCHARGE, WEIR IN SAND-CHANNEL STREAM A27

or minus 5 percent of the base rating for free-fall conditions. The 

stage-discharge relation shows no influence of backwater for submergences up to 90 percent. For submergences greater than 90 percent, 

backwater affects the stage-discharge relation, but submergence cannot be used as a correction for backwater because there is no consistent 

relation between the ratio of measured discharge to rated discharge 

and percentage submergence.

The stage-discharge relation of the prototype compared with the 

stage-discharge relation of the model showed .that 15 to 20 percent 

more depth at a given discharge was required on the prototype than 

on the model. The prototype showed a backwater effect on the stagedischarge relation for submergences greater than 90 percent, whereas 

the model predicted a backwater effect for submergences greater than 

60 percent. Also, the prototype structure was set 5 feet below bankfull 

stage, and free-fall conditions have occurred for discharges less than 

700 cfs. The model predicted free-fall conditions for discharge? less 

than 300 cfs if the control crest were set 4.5 feet below bankfull stage.

One main purpose of the model study was to determine a crest elevation so that the control would not restrict the capacity of the channel to less than 2,000 cfs. Comparison of the stage-discharge relation 

on the basis of staff-gage readings at the control site prior to conELEVATION FEET) MINUS 4,720.0 0<N> OJ .p*<Ji CJ >*j* 

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FIGURE 17. Elevations of water surface and of bed at gage A.
A28 STUDIES OF FLOW IN ALLUVIAL CHANNELS

struction and the stage-discharge relation at the control site after construction shows that the water-surface elevation at 2,000 cfs is slightly 

higher than the minimum possible before the control but is well below 

the maximum possible before the control. When the control is drowned 

out, the maximum water-surface elevations for discharges' greater than 

1,500 cfs are almost identical with the maximum water-surface elevations that existed for discharges greater than 1,500 cfs prior to construction of the control. The stage-discharge relation on the basis of 

measurements at gage B at the control and at gage A upstream of the 

control shows that the control does not restrict the channel to a maximum discharge of less than 2,000 cfs at either location, although the bed 

elevation is now controlled.

The following conclusions are based on experience with the control 

on the Bernardo conveyance channel:

1. Controls on sand-channel stream require at least some maintenance.

2. The control improved the stage-discharge relation for free-fall conditions. Submergence cannot be used as a correction when the 

stage-discharge relation is affected by backwater.

8. The model study was useful in predicting the main operating characteristics of the prototype. However, in the following respects 

the model did not correctly predict the behavior of the prototype.

(a) The depth above the crest, at a given discharge, was 

greater on the prototype than predicted by the model.

(b) The baffle system now in use is effective in keeping the 

control clear of sand deposits, whereas the model indicated this system would not be effective. The present system does create a rough water surface, which was predicted by the model, but the surface wave caused by the 

baffles has been virtually eliminated.

(c) The model study predicted a backwater effect on the stagedischarge relation for submergences greater than 60 percent. However, the data from the prototype showed 

backwater effect for submergences greater than 90 

percent.

4. The available data show that the control structure doe? not restrict 

the channel capacity to a maximum discharge of less than 2,000 

cfs.

REFERENCES CITED

Colby, B. R., 1960, Discontinuous rating curves for Pigeon Rocs': and Cuffawa 

Greeks in northern Mississippi: U.S. Dept. Agriculture, Agr. Research 

Service pub. ARS 41-56, 31 p.

 1964, Scour and fill in sand-bed streams: U.S. Geol. Survey Prof. Paper 

462-D, 32 p., 19 figs.

Dawdy, D. R., 1961, Depth-discharge relation of alluvial chann°ls; discontinuous rating curves: U.S. Geol. Survey Water-Supply Paper 1498-C, 16 p.. 11
STAGE, DISCHARGE, WEIR IN SAND-CHANNEL STREAM A29

Eisenlohr, W. S., Jr., 1964, Discharge ratings for streams at submerged section 

controls: U.S. Geol. Survey Water-Supply Paper 1779-L, 32 p., 6 figs., 1 pi.

Harris, D. D., and Richardson, E. V., 1964, Stream gaging control structure for 

the Rio Grande conveyance channel near Bernardo, New Mexico: U.S. Geol. 

Survey Water-Supply Paper 1369-E, 123-154, figs. 29-54.

Simons, D. B., and Richardson, E. Y., 1962, The effect of bed roughness on depthdischarge relations in alluvial channels: U.S. Geol. Survey Water-Supply 

Paper 1498-E, 28 p., 9 figs.

U.S. GOVERN MENT PRINTING OFFICE: 1969 O 335-122