HYDRAULICS BRANCH OFFICIAL FILE COPY

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U14I TED STA'I"ES *, DEPART M' T Or THE 1 4MLMI0.11

BURT; X OF 3E CLL.;.i~TIOh

Office I'demorandum

PRELI-dI%IARY REPORT 011 MODH.;L TESTS FOR 1''IE * t;ASTE;. AY, CHUTE A10 STILLIIIG POOL OF THE * ALAb10 RIVER CROSSIi4G, ALL-,WRICA.N C"AL, * BOULDER CANYON 2ROJ-t+OT. ~*

by

* J. H. DOU U, JUNIOR E.jGI1 EE'R

Denver, Colorado. * June 9, 1938

Denver, Colorado, June 9, 193.

OFFICE M MORA3(tDLM TO ENGIIMR J. E. WARNOCK. J.H.Douma, Jr. Engineer

Subject: Model tests for the wasteway, chute and stilling pool-;-Alamo River Croasjng--All lmerican Canal.

1, Project, The Alamo River Crossing and wasteway items crassaing are part of the Bou?.&r Dam Projeot--All-American Canal in the vicinity of station.3256. The structure contemplated provides an inlet transition to check and wasteway gate structures. Downstream from the check gate a lined canal section on compacted fill crosses the Alamo ' River, which in turn is carried through the fill in a concrete, double-barrel, box culvert. Below the wasteway gate structure a rectangular chute extends down to the Alamo River bottom and terminates in a stilling pool. A concrete lined transition section J&Jlus the outlet end of the culvert with the stilling pool*

The canal sections above and below the check structure are of 4700 and 4300 second-feet capacity, respectively,. The wasteway is designed to discharge.;approximately 1500 second-feet. The maximum flow through the culvert under the compacted fill is estimated as 1000 second-feet,, with a probable normal flow of 100 to 200 second-feet., The Alamo River has irrigation diversions below this crossing amounting to 175 second-feet, and any deficiency in the discharge through the culvert from Mexico will be made up by diversions through the wasteway chute from the All-American caaalo

2. Flow conditions checked by the model. The model teats included the investigation of flow conditions into the canal inlet transition to check and gate structures, through the wasteway gates, chute and stilling pool, and through the inlet and outlet transitions of the culvert under the compacted fill. There was no concern about flow conditions through the lined canal section below the check.

34, The model. The model of the structure was built to a scale of 1 to 24 and included the canal inlet transition, check gate structure, part of the constricted canal section in compacted fill, the wasteway and the culvert, including its inlet and outlet transitions. The 00mPlete model was made of oil treated, unlined wood. No slope correction was ~'or the chute. Normally, Mannings "n" for the prototype is 0.014 and for the model 0.010. Theoretically, velocities at the pool entrance will be smaller than corresponding prototype velocities, but for this model the difference is small and this difference will probably be more than balanced by reduction of prototype velocities due to entrained air.

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PLAN' ALAMO R/VER CULVERT INLET

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4. Flow conditions in the main canal. Conditions of flow in the inlet transition, check gate structure and constricted section of the, main canal were determined satisfactory by visual observation. Tests_ were made with 4700 second-feet in the canal above the wasteway and 4300 second-feet below the check gate,? 300 second-feet flowing through the wasteway, and with 4700 second-feet in the canal,above and maximum flow through the wasteway for normal canal water-surface elevation '1 39,32 and maximum canal water-surface elevation 40.82..

For all combinations of discharge and water-surface elevation no adverse conditions of flaw were observed. A small loss of head was observed through the check gate structure. There was no observable drawdown of the water surface to the wasteway inlet and except for ocassion.al small eddies the flow into the wasteway was very smooth.

Undoubtedly there is a continuous loss in head as the flow passes through the structures of the main canal, but no attempt was made to.measure the losses in the model, because these modelquantities are so small that factors influenciiig the precision of measurements will not allow reliable data to be obtained.

5. Flow through wasteway gates. The model represented two 6 feet by 7 feet - 6 inches gate openings to the 1:24 scale. bide entrances were rounded as shown in detail "B", figure 1, and the top entrance was roaiided as shown in section B-B, figure 1. These gates were calibrated by measaring their discharge for several heads. .aeasuremeiits were only made for the condition when all of the water is checked acid diverted through, the wasteway. bince canal velocities are very low, the discharge through the gate for any head will be changed very little by passaL;e of some water through the cnecn gate structure.

Figure 2 shows the experi)iental wasteway discharge rating curve converted to -prototype quantities. j,roia this curve, the waste-way will carry 1660 second-f<:..et for the normal canal water-surface elevation 39.32 and 1790 second_ feet for t;ie maximum canal water surface elevation 40.82. The discharge curve may be used to determine the canal water surface elevatioi when any kiiown flow is checked and diverted by means of the wasteway. -'his elevation rria,r be useful in determining the operation of u_stream structures should they exist.

ieasurements were also Made for a s.ivare ton entrance to determine the influence of rounding this part of the entrance. The dashed curve of fi~_,ure 2 is for the square eatranice. itou.iidiiig the entraiice increases the discharge about 15 'oerceiit over the discriarxge for the s,,I,-are entraiice for the maxi _:um oPerating head.

irhe size of gate oneiiiii~ s are ai:iple since the desib i discharge for the wasteway was 1500 second.-feet for the normal canal water surface elevation 39.32. ;the 6;ate size may be sai'ely reduced to 6 feet 'by 7 feet for which the disci-rge at normal water surface elevation is estimated as 1550 second-feet.

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6. Coefficients of contraction and discharge for rectangular undershot gates. hccordiii: to Torricelli•s theorem, water dischar6iiL Lrom an orifice under a head, H, has a theoretical velocity equal to the velocity acquired by a body fiallim~ freely "in vacuo" throuLji a vertical distance, H; that is

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the The expression Vt2r 2 g is termed ss velocity head.

Beca,_tse of the effects of _rictioii and viscosity, the mean velocity of ti:e jet is always less than the theoretical velocity. Expressed by symbols:

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Therefore from (1) Vo ' Cv 2 g g ( 4 )

If At is the cross-sectional area of the jet at vena contracta and A is the area of the gate opening, the coefficient of contraction is

Cc = At/ A (5)

Cc ddcreases as contraction is reduced and approaches unity for an opening with well rounded corners.

The discharge from any gate opening; is equal to the product of the cross-sectional area of the jet at the versa contract a the mean velocity at the sad=ie section a,id a coefficient, C;, which represents the influence of velocity of ap`;roach; that is

4 _ Ca Vo At = Ca cc Cv A Vt

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where C = as Ce Cy

The values of Ca and Cv are difficult to obtain experiment-ally and these coefficients are of theoretical rather than practical value. `.'he value of Cc may be readily obtained by r,,,easarine, the discharge from an openii.L6 of known dimensions and the governiiig pressure head.

The coe..'ficient C, as given by formula (6), includes the effect of velocity of apr,roach, contraction and loss of head due to friction and viscosity. The knowledge of the coefficient is not sufficient to justify the use of a formula which c intains separate terms to correct for each of the above factors.

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The use of rectangular gates on wasteways are almost without exception with conditions for vinich the flow is terned ,partially submerged. ether investigatbaa have found that it appears, for gates o this type, conditions influencing side and bottom contractions have very little effect on C.

For partially submerged floss, a me- surernent of the upper water surface at the versa coiitracta theoretically ~Jves the pro_)er H to use in formula (4). The distance CCD (see figure 3) was measured in the model for several values of Ho. The proper o?.eratinL head is these given by

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The contraction and discharge coefficients, Cc and C, are plotted agaijist canal water.-surface elevation in figure 4 for the rounded and square top entrances. The water surface at the versa contracta was considerably smoother f:z the sharp-edged square entrance, and there was a more uniform change4 in thickness of vena cr,,ntrac'-~a with head, as shown by the curves. The coefficients are considerably higher for the rounded entrt;nce, evert though the conditions of flow aro not as good. It is not kn_;wn whether the type of rounded entrance herein tested is the most efficient. general tests should. be conducted to determine the most efficient rounded entrance.

The curve of gig-ire 5 was drawn to show the percent increase in discharge of the rounded entrance over the square entrance. The percent increase is plotted against D/Ho so the curve is applicable to other Late sizes, asing the same entrance conditions. For values of DIHo greater than 0.6 the head is insufficient to prevent the formation of vortices and the entrance of air through the gates. The change in percent increase in discharge is rapid for values of D/Ho greater than 0.6 when vortices exist, but for values of D/i.o less than 0.6 with no vortices the _;percent increase remains nearly constant at about 15 percent.

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Finall;;.,to make the experiments of this one gate size universally applicable to other sizes. curves of filcure 6 were drawn for both the rounded and square entrances, giving the experi..iental vslae of Cc and the computed value of C against the ratio of gate openin,,, p, and head on the gate sill, tio. From this figure, Cc can be determined for any D/Ho ratio, which allows the effective heb.d to be computed by formula (7). Using the proper value of C as determined from the fig'are the discharge from any known gate opening and head of water above the gate sill may now be computed by formula (6).

Some question remains regarding extrapolation of the experimental data for the one gate size to other gate sizes. Velccity of approach, v entrance loss and contraction are probably all affected same by gate size and shape. However, xinE, has found that the combined influence of these factors on the discharge from an orifice is not more than about 5 percent of the total discharge, so any variation in discharge for several gate sizes due to these factors will probably be no more than one or two percent of the discharge for the experimental gate opening. Ifests should be conducted on gate openings of several sizes and shalpes to determine the correctness of this statement.

7. ?low through Alamo River Oulvert. As stated before, tic Alamo fiver flow is carried under the maul canal by means of a culvert with two 7- by 9-foot rectangular openings. A series of tests were made in which the discharge and tailwater elevations were varied and the corres,),)nd- ing head water elevation was measured. The curves of gigure 7 were _plotted from this data.

With the wasteway operatir4-; at maximum discharge and the culvert at its rnaximwra discharge of 1000 second-feet, the tailwater elev tion in the river do„nstr~-am before much scouring occurs may be expected to be around 21.0. From the curve the maximum head-water elevation above the culvert inlet for the 1000 second-feet discharge sill be about 22.2. ~Wor these conditions the culvert flow is submerged and the operating head is 1.2 feet. Solution of Q,=C A 2 g H gives a value of C equal to 0.90. 'Tile high value of C is due to the fact that the velocities are small, resulting in small losses.

8. Flow in the Wasteway Chute. 1'o check the flow in the wasteway chute with the theoretical co:rsiderations given to the design of the chute, depth measurements in transverse secti..rrs at seven stations along the chute were taken. v'iEure 8 shows the water cross-section at each of the stations and the experimental mean water surface curve through the chute. Yhile the water surface in a transverse section is somewhat rough at the upper stations, the depth distribution is very uniform at the entrance to the pool. 'Phis condition insures a uniform and more efficient hydraulic jump. 6ince the depth distribution is uniform at the pool entrance, the angle of flare of the chute side walls is not excessive.

In figure 9, a comparison is made for the experimental and theoretical velocities through the chute. velocity is plotted against

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chute bottom elevation. The full line curve is the experimental curve computed from experimental depth and di--harL-e measurements. The dotted curve is for the theoretical velocity neglectinL the friction loss. bince it would be difficult to properly alra txr.#z evaluate losses through the wasteway entrance so that a reliable theoretical velocity could be had at the chute entrance. and to determine the difference between experimental and theoretical velocity due to chute friction alone, the theoretical velocity at the beginninE of trie chute was assumed the same as the experimental velocity. pith this starting velocity, the velocity at any other point in the chute was computed from the gain in velocity head, determined from the difference in water surface elevations.

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where the nomenclatiu.re is the same as that used by King.

As is to be expected the experimental velocities are sensibly smaller than the theoretical velocity for which friction has been neglected. The experimental values agree ver, well with the theoretical velocities computed by includinE friction loss.

9. The wasteway stilling basin. The wasteway and Alamo river stilling basics are combined to form a "twin" stilling basin. This basin has been designed so that any combination and amount of flow throu~l-s either or both the wasteway and culvert does not produce objectionable scour conditions below the structure.

The tailwater of the Alamo river is not definitely known but the water surface for normal flows is ap?roximrately at elevation 14.0 aad it is estim,,ted by the project engineers that the water surface will build up to elevation 19.5 for a sustained flow of 1500 second-feet. However, it is believed desirable that the stilling basin be designed, to produce a satisfactory hydraulic jump with the tailwater surface at elevation 18.0 even for the unusual case of concurrent discharges of 1500 second-feet from the wasteway and 1000 sec nd-feet from the -ulvert.

A number of tests were run to determine the best size, spacing and location of blocks and sills in the basin. The best arrangement was determ-- ned by visual observ,,tion of the hydraulic jump and resalting scour. Data was recorded only for a basin without blocks or sills and for tn.e recommended design.

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The recommended design is shown in figure 10. Six 24-inch high chute blocks spaced as shown in the figure, seven four feet high chute blocks 0 12 feet 8 inches from the end oi' stilling basin an 18-inch high solid sill at the end of the basin and a 12-inch hig solid sill at the end of the transition floor ate recomended. The sills may be made of any cross-section since their height is of most importance. reetangalar shapes as shown are probably the most economical. Likewise the height of apron blocks is of faost importance so the top width and back slope can be made according to the best economy. The top width however, should probably be not less than 8 inches. Since the vertical upstreau:i faces of these blocks are subject to c;nsiderable impact, it is recoi'.,ended that 12-inch iron plates be anchored to the top of the blocks. The 24-inch block width and spacing is the most effective and economical.

Comparison of the jump and scour for the stilling basin with n blocks or sills and for the reco,:Lruended blocks and sills is shown in figure 10-B. Maximixii scour is 2.5 feet for no blocks and sills and is reduced to 1.5 feet for the recoriiiended design. The 12-inch sill at the end of the transition floor is effective in reducing the scour. The crest of the jump is about 15 feet beyond the end of the stilling basin with no blocks or sills, but is well within the stilling basin for the blocks and sills. The blocks and sills are effective in pzshiiig the jump upstream sip that a shorter stilling basin may be employed.

A further advantage of the recommended basin is that the ,lump regains in the basin no matter how low the river tailwater down-stream (see elate 12-B). AVithout blocks or sills the jump sweeas out of the basic for tailwater elevation 16.0, resulting; in excessive scour dow-stream (See plate 12-A). '

ThiLt the recommended basin is a more effective energy dissipator is determined by comparing the velocity distributions at the end of transition floor shown in figure 11. Generally, the velocities are lower and the stream has a better spread over the transverse section for the recommended design.

:when the wasteway operates alone a whirl with reverse direction along the left river bank exists for both the original and recommended wasteway and culvert stilling basins (plate 7). Thb whirl is smaller and velocities less for the recommended design, however. s+ith the wasteway operating alone at maximum capacity, the maximum reverse prototype velocity along the left bank about 25 feet from the end of the culvert basin is 4.2 feet per second and the maxiaum forward velocity where the maid stream strikes the left bank about 200 feet from the end of the culvert basin is 2.8 feet per second for no blocks and sills. With blocks and sills the corresponding velocities are 3.3 and 2.3 feet per second,respectively.

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Since the bank velocities are ;robably scouring velocities for the fine material of the locality, some riprap protection should be provided along the left bank. The extent of this protection can best be determined from the results of initial operation.

10. The Alamo hiver uulvert stilling basin. The original design of the culvert stilling; basin is shown in figure 12-A. The basin was made unsyminetrical about the extended culvert center line so that the basin side walls woald conform more nearly to the river bank on the left and the main canal emiankment on the right. uperation of this basin with the maximum ca;,oacity of 1000 second-feet and a minimum tailwater elevation 16.0 immediately showed poor conditions. because of the wide unsy.,inetrical basin the entire forward flow exists in the left portion of the basin with considerable flow in the upstream direction on the right side tfigure 13-A) resulting in a large whirl in the basi=i, xhe excessively high velocities along the left bank results in excessive bank and bottom scour downstream.

Several arrangements of dividing wall and blocks were tried at the culvert exit i-a an attempt to spread the forward flow over the entire basin width. These were helpful but it was necessary to make the basin symmetrical about the culvert center line and reduce its width before satisfactory spreading; of the stream was obtained. With the smaller symmetrical basin the dividing wall and blocks were still required so the recommended design, figure 12-3, incorporates a 9-foot high dividing; wall extending 20 feet beyond the culvert exit and five 4-foot high blocks, 28 feet from the culvert exit. The 12-inch high solid sill at the end of the basin reduces bottom scour to a minimum.

Vigure 13-b shows the velocity distribution at the end of the basin for the recommended design, maximum capacity and minimum tailwater elevation. For the recommended design; the culvert flow is spread over the entire width of the basin, no whirl exists, bank velocities on the left side are reduced about'100 percent and scour on the bottom and left bank is reduced to a minimum.

ror the wasteway operating alone, the whirl still exists in the culvert pool, but its volume and velocities are greatly reduced as can be seen by comparing; figures 13-v and 13-D. Yor the original design the reverse bank velocities were sufficiently high to erode the left bank and deposit considerable material in the culvert basin as shown in figure 13-v. ;rith the reeoanended design there was no such scouring; and depositing.

11. Si=.iultaneous operation of rtaste.ay and uulvert at maximum capacities. Mhen both the wasteway and culvert aVe operating at maximum capacity the two basins o-,I)erate very satisfactorily as a "twin" stilling basin. There is a `;ood junction of the two streams about 100 feet doulistrean frori the ends of the basins. There is very little difference in the velocity distributions at he ends of the basins than for se_oarate operation. For combined operation the high left bank velocities for wasteway only operating; are eliminated and no whirl exists anywhere in the basins.

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PLATE 1

A. LOOKING INTO THE AdAIN CANAL CHEQ{GATE AND WASTEWAY ENTi3ANCE.

t ' J B. LOOKIiZ ACROSS THE iiAlii ^ANAL INLET TRAiuSITION TO THE 'NASTEWAY GATES.

PF

PLATE 2

A. FLOW I3TO WASTEWAY. WASTEWAY DISCHARGE 1790 SECOND-FEET. MAIN CANAL DISCHARGE 4700 SECOND-r+ T. ClUiAL WATER SURFACE EL. 40.82.

B. FLOW IiM WASTE'NAY. WASTEWAY DISCHARGE 1790 SECOiiD-FEET. . MAIN CA14AL DISCHARGE 4700 S-,",001,11)- FEET. CANAL WATER SU_-tFACE ELEVATION 40.82.

PLATE 3

A. ALAKO RIVER CULVERT IivLET.

B. FLOW IiVTO ALAMO RIVER CULVERT INLET. DISCHARGE 1000 SECOND-FEET.

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PLATE 4

A. ORIGIiUL DESIGiti OF STILLING BASIIJS.

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PLATE 5

A. ORIGIVAL DESIGN. CULVERT DISCHARGE 1000 SECOND—FEET. TAILoVATER ELEVATION 16.0.

B. RECOi4MEWDED DESIGN. CULVERT DISCHARGE 1000 SECOND—MET. TAILiATER SLEVATION 16.0.

I

PLATE 7

A. ORIGINA! DESIGN. JASTWAY DISCHARGE 1790 SECOND—FEET. TAMATrR ELEVATION 18.0.

B. RECOMIbIENDED DESIGN. WASTEWAY DISCHARGE 1790 SECOAM—FEET. TAILeVATER ELEVATION 18.0.

PLATE 9

A. ORIGINAL DESIGN. WASTE'tuAY DISCHARGE 1790 SECOND-vEET. CULVERT DISCHARGE 1000 SECOND-rEET. TAILiNATM ELEV. 18.0.

B. .RECO1~1~lMQED DESIGN. WASTEUAY DISCHARGE 1790 SECOND-b'EET.- CULVERT DISCHARGE 1000 SECOND- F {ET. TAILkLTER ELEVATION 18.0..

PLM 10

RECOMIENDED DESIGN. WASTEWAY DISCHARGE 1790 SE001dD-1+FEET, CULVERT DISCHARGE 1000 SECOND—FEET. TAILWATER ELEVATION 18.0.

R

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PLATE 11

A. ORIGIiiAL D:.SIGi~. SCUJtt dFT&( 0,,E-HOUR RUli FOR :4 ASTEWAY DISCHARGE OF 1790 SF.CORD-FEET, CULVERT DISO—HARGE 1000 SECOAD-FEET. TAIL,VATut3 F.Z. 18.0.

B. RECOMMMED DESIGN. SCOUR AFT,,M 0.114E-HOUR RTJ i FOR WASTEWAY DISCHARGE OF 1790 SECOND-FEET, CULVEaT DISCHARGE 1000 SECOND-FEET AND TAILWATER EL. 18.0.

PLATE 12

A. ORIGINAL DESIGN. WASTEWAY DISCHARGE 1790 SECOND-FEET. JUMP SWEEPS OUT AT ELEVATION 16.0.

B. RECC MENDED DESIGN. IVASTEuti'AY DISCHARGE 1790 SECOAD-FEET. .NM' REMAINS IN BASIN NO IMMER HOW LOW THE TAILWATER BECOIAE9.