UNITED STATES

DEPARTMENT OF TH[ INTERIOR

BUREAU OF RECLAMATION

HYDRAUL IC MODEL STUDY OF THE MASONVILLE SIPHON

TURNOUT STRUCTURE--HORSETOOTH FEEDER CANAL-­

COLORADO-BIG THOMP SON PROJECT, COLORADO

Hydraulic Laboratory Report No. Hyd.-237

RESEARCH AND GEOLOGY DIVISION

BRANCH OF DESIGN ANO CONSTRUCTION

DENVER, COLORADO

FEBRUARY 1949

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UNITED STATES

DEPAR'.lfflNT OF THE INTERIOR BUREAU OF RECLAMATION

Br-.nch of Design and Construction Research and Geology Division

Denver, Colorado late: February 1949

laboratory Report No Hyd 237 Hydraulic laboratory Cao.piled by: J.C. Schuster

W', P. Simmons Reviewed by: J. w. Ball

Subject: Hydraulic model study of the Masonville Siphon turnout structure--Horsetooth Feeder Canal--Colorado-Big Thompson Project, Colorado.

PURPOSE OF STUDY

The purpose of this study was to develop, by hydraulic model testing, a satisfactory stilling-well and weir basin for a turnout structure which would release supplemental water to the Union Ditch from the Masonville Siphon in the Horsetooth Feeder C"l.nal near Masonville, Colomdo.

CONCLU:3IONS

It � s concluded tM t:

1. The stilling-well design, developed by this model study (Figures 2B end C) will dieei�te satisfactorily the energy in the weter released from the Meeonville Siphon to the Union Ditch.

2. The be.ffle wll between tlle stilling"'Well and weir basin will produce t:ren�uil flow in the weir basin, and permit reasonably acctu'8.te reading of the staff gage indicating the head on the Cipolletti nee.suring•weir.

3. There is a possibility of cavitation occuring in the.pipeline imm.ediat�ly downstream from the valve controlling the turnout flow, since the maximum caJ8ci ty of the valve is 32 cfs and throttling of the valve will be required when the normal discharge of 25 cfs is being rel�sed.

4. If the pipeline immediately downstream from the control valve is vented there will be no cavitation, but air will be drawn into the pipeline· and released in the stilling-well. 'Ihe action will increase the surface, roughness in the well, but should not prove objectionable .

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RECOMMEND.A TIO NS

It w�s recommended that:

1. The flow p,3 ssages of the turnout structure be constructed to conf'orm witii those shown on Figures 2B Qnd C (recommended design) .

2. An e.ir•vent e.t least 2 inches in die.meter with a bel1.mouth entrance to prevent noise, be �l�ced in the top of the supply pipe immediately downstream from the control valve (Figure 2C). Some pro­vision be ms.de to prevent thi� vent being blocked, accidentally or otherwise, by persons or objects covering the entrance.

3. Since the structure is unlike any used previously,' the per­fo!"Il'B.nce of the prototype should be ch�cked by design and labore.tory personnel.

ACKNOWLEDGMENT

The design of the turnout structure for the Masonville Siphon, evolved from the tests described in.this report, was developed through the collaboration of engineers in the Canals Division and Hydraulic I..abor.-tory •.

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INTRODUCTION

General

The Horsetooth Feeder Canal, a :rs,rt of the distribution system of the Colorado-Big Thompson Project, extends from Flatiron Reservoir south­west of Loveland, Colorado, to Horsetooth Reservoir 3 miles du.e west of Fort Collins, Colorado. Its purpose is to convey water north to the Horse­tooth Reservoir for storage and distribution. Approximately 7 miles north of the canal heading, near the smali town of Masonville, a siphon will be provided to cross the valley at Buckhorn Creek {Figure l}. A structure known as t!'.e Masonville Sii-ihon turnout and located near the low point in this si�hon will supply supplemental water to the Union Ditch which crosses it's course at this point. The static head a't the turnout will be about 115 feet mking it necessary to dissipate, or change to nondestructive form., the kinetic energy of the wa. ter taken from the sip._h.on barrel before the water ie released into the Union Ditch. Though the maximum capacity of the strm:-ture is about 32 cfs, its normal release will be about 25 cfs .

The Turnout Structure

The turnout structure evolved from the tests described in subsequent parts of thi� report contained a supply system, stilling-well, weir bas1� and meaeuring-weir (F"lgure 5).. The water s1.,1.pply for this structure was released fro:m the crl .n of the siphon barrel into the stilling-well through a 12-inch :pi:pe containing a 12-inch gate valve for control. This pipe er­tended vertically down into a stilling-well 9 feet wide, 4 feet long, and 16.5 feet cl.ee:-, discharging its flow on to a 2- by 2- by l•foot high ped­estal locater. ·on the floor. The pipe, with its vertical axis l foot from the upstream wall of the well, terminated 1 ·foot above the top surface of the pedestal, The downstream wall of the well contained fifteen 1-foot= square openings arranged in three tiers of five each on 20-inch centers both vertically and horhontally, with the bottom tier 10 feet above the floor of t:r.e well. This wall formed the upstream end of a weir b.asin, 9 feet wide, 12 feet long, and 6 feet 6 inches deep, 'having its floor flush with the bottom of the openings of the ,lower tier. The water JS,Sses from the open:lngs in the wall, through the weir basin, over a 4-foot 6-inch Cipolletti weir, located in the downstream wall, 3 feet 9 inches above the floor, �nd thence into the main ditch.

INVESTIG4.TION

Descri�tion of Model

The model used for the study of the Masonville Siphon turnout struc• ture was constructued to a 1 to 6 scale (Figure 3A). It was contained in a wooden box lined with sheet metal. The well with a movable floor was constructed as part of the box . Wooden walls were arranged within the box to represent those of the full-sized structure. The baffle wall between the stilling-well and weir basin was constructed of plywood and held in

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place by screws to facilitate changing its·design. A small Ci:polletti weir of c�lin sheet metal was attached to the downstream. wall of the weir basin to represent the prototype installation. A straight length of 2-inch ID pipe, with a sliding sleev� at the upper end to facilitate placing the discharge end at different elevations, was used to represent the sup­ply conduit . This arra.ngem.ent differed from the prototype in that the model elbow was above the water surface, but this difference has no sig­nificant effect so far as the test results were concerned. A trapezoidal section of concrete-lined channel downstream from the model weir represented the inlet to the Union Ditch. No study was mde of flow conditions in this section of the model since they were assumed to have no influence upon the operation of the turnout structure .

Testing of Model

Nearly all of the tests conducted on the model were of a qualitative nature consisting mainly of visual observations of.the flow conditions in the stilling-well and weir basin for various changes in design. No cali­bration teats were made since a standard Cipolletti weir was to be used in the full-sized structure . Discharges corresponding to 25 and 32 cubic feet per second were used in most cases since these were ·to be the normal and probable ma.ximmn quantities released_ . Specific teats at smaller discharges were notmade since the flow conditions beca:tne more tranquil as the quantity decreased.

Original DesiS71

In the original design (Figure 2A) the elbow exit of the 12-inch line was 10 feet above the floor of the stilling-well and the wall between the well and weir be.sin contained one 2-1/2� by 4-foot opening for conveying the water from the well to the basin. When the end of the 2:-in.Qh line in the model was :placed in -a :position corresponding to the exit of the elbow, the flow in the well was very turbulent as evidenced by large boils and surges at the surface . This turbulence was carried directly into the weir basin through the large opening in the ba:ffle wall ( original design, Figure 2B) . The water flowing through this opening was concentrated in the center of the weir basin and upon striking the downstream wall of the basin was directed upwards causing a turbulent boiling surface at the corners . This action and other undesirable aurface turbulence occurred in the basin (Figure 3B). It was estimated that the length of the basin would have to be increased three or four times to obtain satisfactory flow over the weir with this design. Since this change was considered un• economical and satiafacto::::-y action was questionable, other changes were considered. It was believed that much of the objectionable flow action could be eliminated by altering the ��pply pipe ,and revising the flow pas­sage in the baffle wall. The model tests were continued on this basis.

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Extension of Inlet Pipe and Baffle Moqi/acation

The model was revised by extending the pipe·to within 2 feet (proto­type) of the well floor: The flow conditions were improved, but excessive turbulence still continued through the baffle opening into the weir basin. To suppress this condition and to break up the heavy concentration of fiow through the single opening, the baffle was modified by replacing this open­ing by twelve slot� 6 inches high and 28 inches wide (Design 2, Figure 2B). Supsta.ntial improvement of flow in the weir basin was brought about by the extension of the pipe and the modification of the baffle (Figure 30). How­ever, the velocity through the twelve slots in this design was still of such magnitude that the flow in the weir basin was more turbulent than desired. Moreover, the upper slots in this wall were not submerged adequately, and the water flowing through them had sufficient velocity to cause a surface roller, indicating the need for further alteration.

Modifications Leading to the Recommended Design

A study of flow conditions in the stilling-well of the original design, the design w1 th modifications to the inlet pipe and baffle wall, and a re­view of the results of tests conducted :previously on a similar model, in­dicated that improvement would be obtained by making five changes. These changes includeg: (1) making the stilling-well 2 feet deeper, (2) placing a 2- by 2-foot pedestal 1-foot high on the stilling-well.floor directly beneath the discmrge pipe, (3) lowering the discharge pipe until it was within 1 foot of the pedestal, (4) cmnging the openings through the baf'fle wall f:rom twelve slots to fifteen 1-foot-square openings, and (5) extending the weir basin.downstream 3 feet. It was reasoned that a better distribu­tion of flow within the well would result from increasing the depth of the stilling-well; that additional dissip:3.tion of energy would result from plac­ing a pedestal on the stilling-well floor and placing the end of the inlet pipe near its top surface; that more openings distributed over the area of the baffle wall would improve flow into the weir basin; and that increasing the length of the weir basin vould improve approoch 9onditions to the weir. The more uniform velocity distribution given by these changes would cer­tainly tencl. to give 'the desired improvement.

It was expected that the flow from the pipe would strike the pedestal where it would be deflected horizontally and spread radially toward the walls of the stilling-well. The jet u:pon leaving the pedestal would be ex­posed both on the top and bottom to the relatively slow moving water in the stilling-well, and it was reasoned that additional dissip:i.tion of energy would take place because of this condition. It was expected also that placing the inlet pipe near the pedestal would aid the deflection and radial spreading of the jet .

Because there was inadequate time to determine the individual merits of each of these changes in decreasing the turbulent action in the stilling-

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well and weir basin, the changes were all incorporated in the model for the final series of tests (Figure 2, recommended design).

It is to be inferred that the pedestal functioned as :planned for the water surface in the stilling-well was very smooth, a..TJ.d tliat the end

·of the pipe being nearer the su.rface of the pedestal gave a better dis­'tribution of velocity in the well. The fifteen 1-foot-squa.re openings

in the baffle provided more area tllan the slots of Design 2, thus water· flowed f'rcm the well to the weir basin at lower velocities. In thi-s design the openings were arranged to obtain cc:mplete submergence of the top row. This change gave a lower entrance velocity and with an extension of the wier basin, ·provided a greater distance in which the dissipation of energy could take place. Even with thece modifications, some surface roughness was observed in the basin directly downstream f'ram the baffle wall. Since this appeared to be caused by flow through the upper·openings, a horizontal sill extending outwards 1 foot and the full width of the basin .was placed above these openings to suppress the upward movement of flow (Figure 2C). This modification resulted in a marked improvement in surface conditions. The sill was inclined at various slopes to determine optimum position, but it appeared to function beat when set horizontally.

In the design of the prototype stilling-well to allow clearance for the bolts in the flanged elbow leading down into the well, the pipe center .. line was set 1 foot 6 inches out from the. upstream waLl. This changed the pedestal from a 2-foot square to a rectangle 2 feet by 2 feet- 6 inches (Figure 5), This change was not tested but there should be no adverse flow conditions resulting from this alteration.

A final change in the model was ma.de when it was learned that the model weir was 9 inches (prototype) below the elevation.required to give the designed weir-basin depth. Th:i.s change gave further improvement in flow conditions within the structure and additional teats were considered unnecessary. Flow conditions for the final design, including the 9-inch rise in weir elevation but not the 6-inch change in the supply pipe loca­tion, are shown in Figure 4.

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--·· CONCRETE SIPHON---­

STA 265+55

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1'-HORSETOOTH

SUPPLY CONDUIT

FLATIRON •• R£5£RVO/R·'

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SCALE OF MILES

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R. 70 W. R. 69 W.

UNITED STATES

DEPARTMENT OF THE INTERIOR

BUREAU OF RECLAMATION

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SCALE OF MILES

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KEY MAP

COLORADO-BIG THOMPSON PROJECT-COLO.

HORSE TOOTH FEEDER CANAL

LOCATION MAP

FIGURE

TO MASONVILL SIPHON',

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ORIG INAL DESIGN

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A. ORIGINAL DESIGN

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RECOMMENDED DESIGN

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SECTION A-A

G. RECOMMENDED DESIGN

COLORADO BIG THOMPSON PROJECT

HORSE TOOTH FEEDER CANAL

MASONVILLE SIPHON TURNOUT

A. Original Design-Flow of O cfs

B. Original Design-Flow of 3 2 cfs

C. Design 2-Flow of 32 cfs

Flow Conditions in Weir Ba:sin MASONVILLE SIPHON TURNOUT

1:6 Model

FIGURE 3

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A . Recommended Design-Flow of 3 2 cfs

B. Recommended Design-Flow of 25 cfs

Flow Conditions in Weir Basin-Recommended Design MASONVILLE SIPHON TURNOUT

1:6 Model

FIGURE 4

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PL A N OF I N L E T

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L O N G I TU D I N A L S E C T I O N OF I N L E T

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P L A N OF O U TL E T

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S E C T I O N OF OUTL E T

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S E C T I O N A - A H A L F S E C _ D - O

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N O R M A L S E C T I O N B - B

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S E C T I O N K - K

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S E C T I O N

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S E C T I O N M - M

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,,-Provide earth transition and protection as direcfed

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stem extension with wheel and stem quides as required. Extend 2" standard pipe fa ouflet as direcfed _

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L - L

N O T E

For general notes, estimated quantifies and hydraulic properties see Dwg. zi,s -D -381,7

U N f 1 ED STATES

DEPA R TMENT OF THE IN TERIOR

B U R E A U OF R E CL A M A TION

CO LORAO O - B I G THO M P SON P � O J EC T - COLO.

H O R SE TOOTH FEEDER C A NA L - S TA. 3 3 6 1- 97

MA SON V I L L E S I P H O N

TRA NSITIO NS - TURN O U T

::::;D'.· - -�-:��--�- -- - - ' · · :�:::�:::- ;�:��: :

CHECKED: - - � - - APPROVEO : _ _ _ �CH�- f.JG-iiic'i:R -

-·· DENVER c.soH���A:"o; :er. !t, 1941

48