Spillway Stilling Basins for Maxwell and Opekiska Locks and Dams Monongahela River, Pennsylvania and West Virginia

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SPILLWAY STILLING BASINS FOR MAXWELL AND OPEKISKA LOCKS AND DAMS MONONGAHELA RIVER, PENNSYLVANIA AND WEST VIRGINIA

Hydraulic Model Investigation

TECHNICAL REPORT NO. 2-579

October 1961

:4 , SPILLWAY STILLING BASINS FOR MAXWELL AND OPEKISKA LOCKS AND DAMS MONONGAHELA RIVER, PENNSYLVANIA AND WEST VIRGINIA

Hydraulic Model Investigation

TECHNICAL REPORT NO. 2-579

October 1961

U. S. Army Engineer Waterways Experiment Station CORPS OF ENGINEERS Vicksburg, Mississippi ARMY-MRC VICKSBURG, MISS. PREFACE

The model study reported herein was authorized by the Division Engi- neer, U. S. Army Engineer Division, Ohio River, 19 March 1959, at the re- quest of the U. S. Army Engineer District, Pittsburgh, and was accomplished in the Hydraulics Division of the U. S. Army Engineer Waterways Experiment Station during the period May to July 1959. The investigation was conducted under the general supervision of Mr. E. P. Fortson, Jr., Chief of the Hydraulics Division, and Mr. F. R. Brown, Chief of the Hydrodynamics Branch, and under the direct supervision of Mr. T. E. Murphy, Chief of the Structures Section. The engineer in immediate charge of the model was Mr. E. S. Melsheimer, assisted by Mr. N. V. Cowan. This report was pre- pared by Messrs. Melsheimer and Murphy. Col. Edmund H. Lang, CE, and Col. Alex G. Sutton, Jr., CE, were Directors of the Waterways Experiment Station during the conduct of this study, and preparation and publication of this report. Mr. J. B. Tiffany was Technical Director.

iii CONTENTS

PART I: INTRODUCTION a...... " . . ".. f.. ". f. . .. 2

The Prototype s .. f ., . ." .. f . ." ...... 21 Purpose ofMoLTests " "...... "f. . 2

PART II: TEST RESULT1S ... " ...... 4

Gate Calibration ...... "...... f., f . * f* *14

Tailwater Limits Curves . * . , ,..." .. + Stilingginn eetsts...... f... ""."f,. . f 4

PART III: DISCUSSION ...... ". . $ PHOTOGRAPHS 1-5 PLATES 1-12.

V SUMMARY

Model investigations of the spillway stilling basins for Maxwell and Opekiska Locks and Dams were conducted in a 1:25-scale section model. Tests involved determination of types of basin action and maximum bottom velocities in the exit channel for five stilling basin designs. A suffi- cient range of tailwater conditions was tested to make the resulting data applicable to each project. Natural tailwater at Maxwell Dam is adequate for formation of a hydraulic jump under assumed minimum conditions, and satisfactory performance was obtained in all of the stilling basins tested. Most favorable bottom velocities of 6.5 and 4.5 fps at minimum and maximum tailwater, respectively, resulted with the type 2 basin, which consisted of a 26-ft- long horizontal apron surmounted by a single row of 4-ft-high baffle piers and terminated by a 4-ft-high dentated end sill. At Opekiska Dam natural tailwater is inadequate for formation of a hydraulic jump under assumed minimum conditions. It was found that a 16.8- ft-long horizontal apron terminated by a 4-ft-high dentated end sill (the type 4 basin) will perform adequately with all four gates operating in 1-ft increments, and will result in maximum bottom velocities of 8.3 and 7.0 fps at minimum and maximum tailwater, respectively. However, if one gate is inoperative (assumed minimum tailwater conditions), the other three gates must be operated in increments of not more than 0.5 ft.

vii PITTSBURGH -IA

LEGEND

LOCK &DAM EXISTING LOCKTYG & DAM RT IVEFUTURE

Clarksburg SRESERVOIR

SCALE IN MILES

S 0 5 10 as 20

Fig. 1. Vicinity map SPILLWAY STILLING BASINS FOR MAXWELL AND OPEKISKA LOCKS AND DAMS MONONGAHELA RIVER, PENNSYLVANIA AND WEST VIRGINIA

Hydraulic Model Investigation

PART I: INTRODUCTION

The Prototypes

1. Maxwell and Opekiska Locks and Dams are proposed navigation structures which will be located 61 and 115 miles, respectively, above the mouth of the Monongahela River at Pittsburgh, Pennsylvania (fig. 1). The locks and dams are units in a general plan for modernization of navigation facilities on the Monongahela River and will replace four outdated locks and dams (numbers 5, 6, 14, and 15). Twin locks will be constructed at both projects. The Maxwell Locks will be 84 by 720 ft, and the Opekiska Locks 84 by 600 ft. The spillway for Maxwell Dam (plate 1) will consist of a concrete gate sill at elevation 737* surmounted by five tainter gates, each 84 ft long by 27 ft high. Concrete piers 10 ft wide will take the gate thrust and support individual gate hoists and a structural steel serv- ice bridge. The Opekiska spillway (plate 1) will consist of a concrete sill at elevation 831 surmounted by four tainter gates, each 84 ft long by 27 ft high. Concrete piers 10 ft wide will support the gates. The end gates at each project will be of the doubleleaf radial type to permit skim- ming of flow from the surface of the pool over the gate. Under normal operating conditions a head of 26 ft over the gate sill will obtain at each of the spillways. 2. Stilling basins consisting of horizontal concrete aprons extend- ing to the ends of the gate piers at elevations 732 and 826 at Maxwell and Opekiska, respectively (5 ft below the elevations of the gate sills), will be provided. The horizontal apron at Maxwell Dam will be 26.0 ft long, whereas the one at Opekiska Dam will be only 16.8 ft long. This difference in apron length resulted from the requirement for a gate radius of 49 ft at

* All elevations are in feet above mean sea level. Maxwell Dam to permit the gate to be raised above maximum expected flood heights, whereas a radius of 39 ft suffices for this purpose at Opekiska Dam.

Purpose of Model Tests

3. Firm rock in the streambeds downstream from each project is of good quality and will resist tendency toward damaging scour from spillway discharges. Thus, stilling basins are not required to provide fully devel- oped hydraulic jumps. However, a limited series of model tests was desired to develop the most efficient stilling basins of the type proposed.

The Model

4. To accomplish the purpose stated above, a section model was constructed to a linear scale ratio of 1:25. It reproduced 200 ft of approach channel, a 25-ft-wide section of the Maxwell gate and gate sill, the stilling basin, and 300 ft of exit area (fig. 2). The model was contained in a glass-sided flume which permitted visual and photographic observations of

Fig. 2. 1:25-scale section model of spillway and stilling basin 3 subsurface basin actions. The approach and exit channels were molded in cement mortar. The gate and gate sill were constructed of sheet metal, and the stilling basin and basin elements were modeled in wood. Water used in operation of the model was supplied by pumps, and discharge was measured by venturi meters. The tailwater elevation in the downstream end of the model was controlled by a vertical-rise tailgate. Water-surface elevations were measured by means of point gages. 4

PART II: TEST RESULTS

5. Tests were conducted in a generalized manner so as to make the resulting data applicable to each of the projects. All data were obtained with the upper pool 26 ft above the gate sill, representing normal pool elevations of 763 and 857 at Maxwell and Opekiska, respectively. Tests consisted of determination of discharges, types of basin action, and maximum bottom velocities in the exit area with the spillway gate at openings of 1 to 10 ft and the tailwater varied over a wide range.

Gate Calibration

6. Calibration curves for gate openings of 1 to 10 ft are plotted in plates 2 and 3. These sets of curves were derived from a single set of data, but discharges are plotted against actual elevations at each project to avoid confusion.

Tailwater Limits Curves

7. Plotted in plate 4 are a tailwater rating curve and tailwater limits curves for Maxwell Dam. These tailwater limits curves were derived from calibration curves (plate 2) and the tailwater rating curve. It was assumed that the spillway gates would be operated in increments of 1 ft and that operation would be required with all gates operating and with one gate inoperative in a closed position. Thus, the minimum tailwater curve represents the tailwater which will obtain below the first gate moved to a higher position immediately after this gate is raised, four gates assumed operating; and the maximum tailwater curve represents the tailwater below the first gate moved to a lower position immediately after the gate is lowered, five gates assumed operating. Similar curves for Opekiska Dam with three and four gates assumed operating are plotted in plate 5.

Stilling Basin Tests

8. Fig. 3 shows the four types of stilling basin action observed during the test program. Spray action

Forced jump

Hydraulic jump

Submerged jump

Fig. 3. Typical basin actions 6

Type 1 basin 9. The type 1 stilling basin (plate 6) was proposed for use at Maxwell Dam. It consisted of a horizontal apron 26 ft long surmounted by a single row of 6-ft-high baffle piers and terminated by a 3-ft-high vertical-faced end sill.

10. Performance data for the type 1 stilling basin are plotted in plate 7. Minimum tailwater conditions for Maxwell Dam resulted in hydraulic jump action and maximum bottom velocities of about 7 fps, whereas maximum tailwater conditions resulted in submerged jump action and maximum bottom velocities of about 4 fps. 11. Minimum tailwater conditions for Opekiska Dam resulted in forced jump action with maximum bottom velocities of about 9 fps at gate openings of 2, 4, and 6 ft and spray action at gate openings of 8 and 10 ft. Spray action was considered unacceptable in that it resulted in high velocities impinging directly on the bed of the exit channel. 12. Typical examples of stilling action in the type 1 basin are shown in photographs 1 and 2. Type 2 basin 13. In the type 2 stilling basin (plate 6) the baffles were 4 ft high instead of 6 ft high as observations had indicated that the 6-ft-high baffles were creating an excessive obstruction under minimum tailwater conditions. Also, a 4-ft-high dentated end sill was used in lieu of the 3-ft-high vertical-faced end sill. Observations revealed that the dentated end sill resulted in a better distribution of flow entering the exit channel.

14. Performance data for the type 2 stilling basin are plotted in plate 8, and typical examples of stilling action are shown in photograph 3. Under comparable conditions the type 2 stilling basin resulted in velocities slightly lower than those observed with the type 1 basin. Also, tailwater could be lowered an additional 0.5 ft before spray action resulted. 15. Maximum bottom velocities of 6.5 and 4.5 fps were recorded under Maxwell Dam minimum and maximum tailwater conditions, respectively. 16. Minimum tailwater conditions at Opekiska Dam still resulted in spray action at gate openings of 9 and 10 ft and maximum bottom velocities of about 9.5 fps at openings less than 9 ft. 7

Type 3 basin 17. The single row of baffles was moved downstream 4 ft to form the type 3 basin (plate 6). 18. Under Maxwell tailwater conditions bottom velocities were in- creased to a maximum of 7.0 fps by movement of the baffles downstream 4 ft (plate 9). 19. However, under Opekiska tailwater conditions a forced Jump was maintained within the basin for all gate openings, and maximum bottom velocities of 10.5 fps were observed. Type 4 basin 20. The type 4 stilling basin (plate 6) consisted of a 16.8-ft-long apron terminated by a 4-ft-high dentated end sill. This is the basin originally proposed for use at Opekiska Dam except that a 4-ft-high dentated sill was used in place of a 4-ft-high vertical-faced sill. This change was made as a result of observations which revealed that the vertical-faced sill caused spray action at excessively high tailwaters. 21. Typical examples of stilling action in the type 4 basin are shown in photographs 4 and 5, and performance data are plotted in plate 10. 22. Minimum tailwater for Maxwell Dam resulted in maximum bottom velocities of about 7 fps, about the same as observed with the types 1 and 3 basins. However, maximum tailwater resulted in velocities of about 5.5 fps, about 1 fps higher than those observed with the types 1 and 3 basins. 23. Minimum tailwater for Opekiska Dam resulted in spray action at gate openings greater than 7 ft but maximum bottom velocities of only 8 fps at openings less than 7 ft. Maximum tailwater conditions for Opekiska Dam resulted in hydraulic Jump action and maximum bottom velocities of about 7 fps. Type 5 basin 24. The type 5 stilling basin had a 26-ft-long apron terminated by a 4-ft-high dentated end sill (plate 6). 25. In general, bottom velocities downstream from the type 5 stilling basin were slightly higher than those observed with the type 4 basin. However, tailwater could be lowered an additional 0.5 ft before spray action resulted. Performance characteristics for the type 5 stilling basin are plotted in plate 11. 8

PART III: DISCUSSION

26. Under assumed minimum tailwater conditions at Maxwell Dam (see paragraph 7), depths on the stilling basin apron were equal to about 113 per cent of the theoretical depth required for a hydraulic jump. Thus, stilling basin elements were not required to force the jump. Reasonably satisfactory performance was obtained in all of the stilling basins tested, but most favorable bottom velocities of 6.5 and 4.5 fps at minimum and maximum tailwater, respectively, resulted with the type 2 basin. However, performance of the type 4 basin with a 16.8-ft-long apron rather than a 26.0-ft-long apron also was considered adequate as bottom velocities did not exceed 7.1 fps. 27. Under assumed minimum tailwater conditions at Opekiska Dam (see paragraph 7), depths on the stilling basin apron were equal to only about 87 per cent of the theoretical depth required for a hydraulic jump. Thus, formation of the jump was dependent upon the effect of the baffles or sills. The jump was held in the basin under assumed minimum tailwater conditions only in the type 3 basin. However, with all four gates operating in 1-ft increments, minimum tailwater would be adequate to maintain a forced jump in the type 4 basin (that originally proposed for Opekiska Dam) and maximum bottom velocities in the exit channel would be about 8.3 and 7.0 fps at minimum and maximum tailwater, respectively. Thus, it is suggested that the type 4 basin be adopted for Opekiska Dam. If operation with one gate inoperative is required, the remaining three gates should be operated in increments of not more than 0.5 ft. Tailwater Maxwell 746.0 Opekiska 840.0

Tailwater Maxwell 750.0 Opekiska 844.0

Photograph 1. Type 1 stilling basin, gate open 4 f't Tailwater Maxwell 754.0 Opekiska 848.0

Tailwater Maxwell 756.0 Opekiska 850.0

Photograph 2. Type 1 stilling basin, gate open 10 ft Tailwater Maxwell 750.5 Opekiska 8144.5

Tailwater Maxwell 753.0 Opekiska 847.0

Tailwater Maxwell 755.5 Opekiska 849.5

Photograph 3. Type 2 stilling basin, gate open 8 ft Talwater Maxwell 743.5 Opekiska 837.5

Tailwater Maxwell 746.8 Opekiska 840.8

Tailwater Maxwell 748.2 Opekiska 842.2

Photograph 4. Type 4 stilling basin, gate open 4 ft Tailwater Maxwell 751.0 Opekiska 845.0

Tailwater Maxwell 752.7 Opekiska 846.7

Tailwater Maxwell 756.0 Opekiska 850.0

Photograph 5. Type 4 stilling basin, gate open 10 ft MAXWELL DAM OPEKISKA DAM

SPILLWAY SECTIONS r 01 0 10 20 30 40 FT m1 fitm 7t5

R PE Ol, EL 763.0

767

77550

z z

745 c1-

740

7 35 0 2 4 6 8 10 12 14 16 18202 DISCHARGE IN 1000 CFS

NOTE., DISCHARGE BASED ON FLOW THROUGH 29.7 PER CENT OF A GATE BAY AND MULTIPLIED BY 3.36 TO OBTAIN DISCHARGE FOR ONE GATE BAY. GAT MAXELSLLA r860----- ~ 6

855 5

F z

4 45

4[\4

6300 1- 2 -4---6 16 832 I DISCHRGECF N 100

NOTE. DISCHARGE BASED ON FLOW THROUGH 29.7 PER CENT OF A GATE BAY AND MULTIPLIED BY 3.36 TO OBTAIN DISCHARGE FOR ONE GATE BAY. 13 GATE CALIBRATION r1 OPEKISKA SPILLWAY n1 7?0

'I,0

H 760

750

DAM NO..4 POOL

70 20 40 60 80 100 120 140 10 I80 zoo DISCHARGE IN 1000 CFS

NOTE: SILL ELEVATION 737.0. TAILWATER CURVES MAXWELL DAM

PLATES I-850

2 4

840

NIL DE8RANO DAM POOL______

8301C 0 20 40 60 80 100 120 140 160 160 200 DISCHARGE IN 1000 CFS

NOTE: SILL ELEVTION 831.0. TAILWATER CURVES OPEKISKA DAM

PL ATE5 EL 770 4__

:e e' EL 826.0 . '.4"'A ~ '' .~' ' . .' ELT 0

®' 'ta. 8'. "' - 12'

TYPE I (ORIGINAL MAXWELL)

EL s31.0* XKIOCY '2

77 - .. .4'EL 826.0* 4 m

4'a. .

TYPE 2

EL 831.0a* X '400oY

EL d3 EL,826.* 4' '. 22 '

* . A. 2

EL 831.0LX/OOY 2 ELE737.0

TYP 760rI I I5

LEGEND TAILWATER < A SPRAY ACTION 852 7361 TAILWATER ®-O FORCED JUMP TAILWATER 0-0 HYDRAULIC JUMP TAILWATER > 0 SUBMERGED JUMP ----- MAXWELL TAILWATER LIMITS 850 -- OPEKISKA TAILWATER LIMITS -J U

U- - 5 I2 z IL z 0 752 z 0 w w 750 w w J- t

J748 I- 4 0 I-

748

7421

13 14 15 r PERFORMANCE CHARACTERISTICS TYPE I STILLING BASIN MAXIMUM BOTTOM VELOCITY IN FPS -i LEGEND m TAILWATER < A SPRAY ACTION TAILWATER £-O FORCED JUMP TAILWATER 0-0I HYDRAULIC JUMP TAILWATER > 0 SUBMERGED JUMP MAXWELL TAILWATER LIMITS -- -- OPEKISKA TAILWATER LIMITS -J d?

348 I- z-

I-. z 0 z 844 O 84w

842 1N {

0 - 2 4

4 838

._.I_1 I___ L IL 1 834 11 12 13 14 15 16

PERFORMANCE CHARACTERISTICS TYPE 2 STILLING BASIN MAXIMUM BOTTOM VELOCITY IN FPS 7 601rr r ri

-J

-J 3 LL U.. z z z 0 z 4 w -J w' W -J ti i J U 4 W 4 IL

0 J U' 'C 34

r PERFORMANCE CHARACTERISTICS

MAXIMUM BOTTOM VELOCITY IN FPS r 760

-4 LEGEND TAILWATER < A SPRAY ACTION 758 TAILWATER A-O FORCED JUMP TAILWATER 0-0 HYDRAULIC JUMP TAILWATER > 0 SUBMERGED JUMP -- -- MAXWELL TAILWATER LIMITS - --- OPEKISKA TAILWATER LIMITS J

4 0) 848 I- 2 2 }" 2 z 0 z 848 . 0

w w 842 w

3 4 844

0 0 4 4 w

2 838

838

2 13 14 15

PERFORMANCE CHARACTERISTICS 4 5 6 8 9 10 TYPE 4 STILLING BASIN MAXIMUM BOTTOM VELOCITY IN FPS 760

LEGEND TAILWATER < A SPRAY ACTION 758 TAILWATER A-O FORCED JUMP 852 TAILWATER 0-0 HYDRAULIC JUMP TAILWATER > 0 SUBMERGED JUMP ----- MAXWELL TAILWATER LIMITS 850 ----- OPEKISKA TAILWATER LIMITS

;754

I- z .. 752 z 0

750

748

J46

748

I I I______1 i____'1534 i 12 13 14 15 16 IU r PERFORMANCE CHARACTERISTICS mI TYPE 5 STILLING BASIN MAXIMUM BOTTOM IN FPS