\.S ��-I"- HYDRAULICS BRANCH

BUREAU OF RECLAMATION HYDRAULIC LABORATORt

OFFICE OFFICIAL FILE COPY ----· FILE COPY

fflN BORROWED RETURN PROMPTLY

CHERRY CREEK.DAM

AND RESERVOIR

CHERRY CREEK AND TRIBUTARIES COLORADO

REPORT OF MODEL STUDIES

• SPILLWAY AND STILLING 'BASIN I

MADE BY T HE HYDRAULIC LABORATORY

U.S. DEPARTMENT OF INTERIOR

BUREAU OF RECLAMATION DENVER,COLORADO

U.S. ENGINEER OFFICE DENVER, COLORADO

JULY 1944

•

September 11, 1944.

FOREWORD

The investigation and the report of model studies of the spill­

way and the stilling basin tor Cherry Creek Dam and Reservoir,

Colorado, were conducted and compiled by the Hydraulic Laboratory,

Engineering and Geological Control and Research Division, Branch of

Design and Construction, Bureau of Reolanation, U. S. Department of

the Interior, Denver, Colorado.

These etudies were oonduoted as requested by the u. s. Engi­

neer Department, Denver Dietriot Office, and by authority of a

direotiT• dated 19 February 1944, from the Office of the Chief of

Engineer,.

The conduct of the work wae under the general euperviaion of

J. E. Warnock. All operation, were direoted by Fred Looher and c.

V. Adkin1.

1

Figure

l 2 3 4 5 6 7 8 9

10 11 12 13 14 15 16 17 18 19

LIST OF FIGURES

Location tnap ••••••••••••••••••••••••••••••••••••••• Original design •••••••••••••••••••••••••••••••••••• Original design A •••••••••••••••••••••••••••••••••• Alternate design •••••••••••••••••••••••••••••••••••

Alternate design A ••••••••••••••••••••••••••••••••• Alternate desi� B ••••••••••••••••••••••••••••••••• Alternate design A ••••••••••••••••••••••••••••••••• Alternate design B ••••••••••••••••••••••••••••••••• Al tern.ate desigri •••••.••••••••••••••••••••••••••••• Alternate design C ••••••••••••••••••••••••••••••••• Scour patterns ••••••••••••••••••••••••••••••••••••• Spillway discharge - Sta. 162+91.83 •••••••••••••••• Original design •••••••••••••••••••••••••••••••••••• Original design A •••••••••••••••••••••••••••••••••• Water surface profile - Alternate design C ••••••••• Second variation of alt.ernate design A ••••••••••••• Variation of alt.ernate design B •••••••••••••••••••• Water surface profile - Original design A •••••••••• Spillway tailwater curves ••••••••••••••••••••••••••

iii

Page No.

19 20 21 22 23 24 25 26 27

28 29 30 31 32 33 34 35 36 37

CONTENTS

Section

Foreword •••••••••••••••••.••••••••••••••.•••.•••••••••••.• Table of Contents ••••••••••••••••••••••••••••••••••••••••• List of Figures •••••••••••••••••••••••••••••••••••••••••••

I - INTRODUCTION AND SUMMARY

Intro duction

1. 2. 3. 4.

Summery

5.

6.

.Purpose and scope of model studies . . . . . . . . . . . . . . . Authority • • • • • • •... • •• •.••. • •..•.•••.•. •.•••• • • • . The definite project plan •••••••••••••••••••••••• General .......................................... .

Undesirable conditions and remedial :measures in the original design ••••••••••••••••••••••••••

Undesirable flow characteristics and remedial

Par;e No.

i

ii

iii

l

2

2

3

4

measures in the alternate design •••••••••••••••• 5

7. 8. 9.

10. 11.

12.

13.

14.

15.

II - MODEL TESTS

Preliminary considerations ••••••••••••••••••••••••••• Initial tests of original design ••••••••••••••••••••• Revisions of o riginal design •••••••••• _ ••••••••••••••• Initial tests of the alternate design •••••••••••••••• Revisions of the alternate design •••••••••••••••••••• Tests leading to the final design •••••••••••••••••••• Final design • . • • . • • ..• • .... • • •...•• • • • .•.••••. • • .. • • .

II - RESULTS AND CONCLUSIONS

Analysis of the results •••••••••••••••••••••••••••••• Conclusions ••••••••••••••••••••••••••••••••••••••••••

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6

7

8

11

11

12

14

16

18

UNITED STATES DEPARTMENT OF THE INTERIOR

BUREAU OF RECLAMATION

REfORT OF MODEL STUDIES 01" THE SPILLWAY AND STILLING BASIN FOR

CHERRY CREEK DAM AND RESERVOIR, COLORADO

I - INTRODUCTION A!"ID SUMMARY

Introduction

l. Purpose and scope of model studies

The purpose of the model studies of the spillway and stilling

basin, Cherry Creek De.m and Reservoir, Colorado, was to verify the

design and, by adjustment, develop a satisfactory hydraulic struc-

ture.

Two different designs were submitted for tests. For the pur­

pose of this report, the one shown on figure 2 will be designated

as the original design and the successive change will be designated

as original design A, fibure 3. The other design, as shown on fig­

ure 4, is designated as the alternate design and the successive

changes as alternate design A, B, and C.

In order to expedite the testing and have a direct, visual com­

parison between the designs, a la60 hydraulic model of each was con­

structed in the laboratory. From the tests it was necessary to

establish for each of the designs the correct leng;th and the srepe

of crest and size of notch required to produce a predetermined head­

dische.rge curve at the weir; to determine a suitable sh.ape for the

spillway chute; to design a satisfactory stilling basin for the an­

ticipated variation in tailwater; and to determine the difference,

1

if any, in the scour immediately downstream from the stilling basins.

The tailwater elevations at the stilling be.sin, the nax imum

discharge, and the characteristics of the head-discharge curve were

established by the U. s. Engineer Office, Denver, Colorado.

2. Authority

This project was authorized by the Flood Control Act approved

August 18, 1941 (Public No. 228, 77th Congress, 1st Session), which

reads, in part, as follows,

•sEC. 3. That the following works of improvement for the benefit of navigation and the control of destruc­tive floodwaters and ·other purposes are hereby adopted and authorized in the interest of national security and the stabilization of employment, and shall be prosecuted as speedily as may be consistent with budgetary require­ments, under the direction of the Secretary of War and the supervision of the Chief of Engineers in accordance with the plans in the respective reports hereinafter designated and subject to the conditions set forth therein • • • • •"

• * * • * • • • * * • • • • "Missouri River Basin - The comprehensive plan for

the improvement of Cherry Creek and tributaries, Colorado, for flood control and other purposes in accordance with the recommendations of the Chief of Engineers in House Document Numbered 426, Seventy-sixth Congress, first session, is approved and there is hereby authorized $3,000,000 for the initiation and partial accomplishment of the project."

3. The definite project plan

The definite project plan (initial development) provides as

follows,

(a) Complete flood protection for the City of Denver by

the construction of a rolled-earth dam, including an outlet­

control structure through the dam near the right abutmentJ an

2

a

..

overflow-spillway canal to pass the spillway-design flood from

the Cherry c·reek Basin into the Tollg�te Creek Basin and thence

through Sand Creek into the South Platte River at a location

downstream from Denver.

(b) The dam will be oonstruoted in such manner as to pro­

vide for multiple-purpose developmen� (ultimate development),

making available to irrigation and other water-use interests

85,000 acre-feet of storage capacity.

(c) The definite projeot plan will inolude the oonatruo­

tion of the dam to mltiple-purpose height, but it will include

only those features of the outlet oonduits and the spillway

necessary to acooJ1D11odate flood oontrol before irrigation or

other water uses are developed.

4. General

The propoaed multiple-purpose Cherry Creek Dam e.nd Reaervoir

is looated near the site of the existing Kenwood Dam on Cherry Creek

i� Arapahoe County (figure 1), at river mile 11.4 as measured from

the mouth of Cherry Creek at its junotion with the South Platte River

near the center of the business district of Denver. The Cherry Creek

drainage basin is approximately 57 miles in length and contains a

total of approximately 414 square miles. The area upstream from the

proposed Cherry Creek Dam oontains 386 square miles.

The proposed spillway and the stilling basin are located approx­

imately 1.2 miles from the Cherry Creek Reservoir. The floodwaters

will flow from the reservoir via a canal to the spillway whioh will

3

drop the water to a canal discharging into Tollgate Creek. The flow

into Tollgate Creek will discharge into Sand Creek and reach the

Platte River at a point downstream from Denver.

Summary

6. Undesirable conditions and remedial measures in the original design

In the initial teats or the original design (figure 2), it was

discovered that the discharge capacity of both the notch and the

orest exceeded that in the design, thus indicating that this part

of the structure should be decreased in size.

The flow from the notoh spread laterally on the chute and

oaueed a high standing wave that overtopped the walls at the sides

of the ohute. The flow from the stilling basin oaused excessive

soour downstream. As a remedy for these conditions, the notch and

the spillway oapaoities 119re reduced. the training walls downstream

from the notch were raised and lengthened, and a sill and dentates

were placed in the pool.

When the model was tested under these conditions, the desired

flow characteristics were obtainedJ but there was considerable ob­

jection to the standing wave formed in the area between the orest

and the side wall. To eliminate the standing wave the warped aide

walls were replaced by vertical walls which constrioted the open­

i�g• between the longitudinal parts of the crest and the side walls

(figure 3). This submerged the standing wave and improved the flow

in the ohute. There 'W8l"8 no serious objections to the flow pattern

4

in this structure, and the arrantement of figure 3 we.s co�sidered

satisfactory from an hydraulic viewpoint.

6. Undesirable flow characteristics and remedial measures in the alternate design

The first tests with alternate desi�n A (figure 5) indicated

that in addition to decreasing the ca�city, either training walls

or some other device was required to keep the notch flow from spread­

ing laterally and overtopping the side walls. The scour of riprap

along the side walls due to this overtopping is shown in figure 7D.

The discharge capacity of the structure was reduced by shortening

the crest length and varying the notch wid th unti 1 a predetermined

discharge curve similar to the one on figure 12 was obtained. Several

attempts.were made to stop the lateral spread of the notch flow. How­

ever, as none of these was entirely satisfactory, the center notch was

eliminated and half sections of the original notch were placed at the

two ends of the crest (figure 8).

This arrangement caused a high standing wave in the center of

the chute which-gradually leveled until the flow had spread to the

width of the chute at the beginning of the stillins basin (figure 9).

There being little flow along the sides, low walls could be used

along most of the length of the chute (figure 15). Attempts to de­

crease the height of the standing wave, such as using three notches,

bafflas, or a deflecting block were not successful, and in some cases.

they actually made flow conditions in the pool unstable. The design

as shown in figures 6 and 8 was considered satisfactory.

5

The suggestion was made that the height of standing wave might

be reduced by warping the side walls as shown in figures 9 and 10.

This did not improve the flow on the apron. However, the entrance

conditions to the notches were improved and there was considerable

improvement in the appearance of the structure.

This arrangement was selected as the final design. It was

superior to the original design A from both economic and hydraulic

viewpoints. The difference in energy dissipation in the stilling

basins of the two desie;ns is shown clearlJ• in figure 11.

II - MODEL TESTS

7. Preliminary considerations

A thorough study of the original design (figure 2) was Jlflde

in an attempt to anticipate its hydraulic performance before the

model was constructed. Conclusions, based upon previous field and

laboratory experience, were that the stilling basin was too short

for the existing entrance conditions. Following a computation of

the hydraulic characteristics through the spillway chute, the still­

ing basin was lengthened 28 feet to obtain a desirable hydraulic

jump and sufficient energy dissipation in the pool. The crest cross

section was also developed in the laboratory from previous experi­

mental data.

In the initial development, although the spillway and the still­

ing basin will not be constructed, a canal from the reservoir to West

Tollgate Creek will be excavated to elevation 5598.00. In the

6

/I

•

ultinate development the canal will be deepened and widened. The

outlet channel below the stilling be.sin will be excavated to a slope

of 0.0015, be�inning at elevation 5567. It was planned that any

additional depth obtained would result from retrogression. Two tail­

water elevation curves were submitted to the hydraulic laboratory,

representing conditions both before and after retrogression. The

outl$t channel in the model was built to represent conditions indi­

cated to exist after retrogression and with a bottom width such that

the tailwa.ter in the model could be lowered to the required eleva­

tions. Otherwise, the model of the original design was constructed

according to plan.

A sketch of the alternate design as submitted to the hydraulic

laboratory is shown on figure 4. The same design of stilling basin

and outlet channel was used in both models. The crest cross section

was developed from previous laboratory data and is shown on figure

9. A comprehensive study of the sketch and computation of the hy­

draulic characteristics through the chute showed that other changes

could be made that would improve the hydraulic action of the chute

and also make it more economical. The over-all length of the chute

was reduced, and a new floor shape was developed. The bottom width

of the approach canal was reduced from 170 to 75 feet. The model

as it was first constructed is shown on figures 5 and 7A.

8. Initial tests of original design

The model was operated with flows of from 3,000 to.45,000 second-

feet (figure 13). There was a fairly even distribution of flow over

7

the lower part of the apron at all discharges. At the higher dis­

charges, the water passing through the notch spread and climbed the

chute walls just above the stilling basin.

The entire head-discharge curve fell below that shown on figure

12, indicating surplus capacity. The flow over the sections of the

crest parallel to the longitudinal a.xis of the chute was considerably

less than that over the sections normal to the longitudinal axis.

The depth over the crest varied from a minimum of approximately 2.6

feet at the notch to a maximum of approximately 9 feet at the chute

walls for a discharge of 45,000 second-feet. This condition was due

partly to the drawdown in the water surface through the notch and

partly because the flow of the approaching water was not normal to

the axis of the crest. The efficiency of the longitudinal sections

was reduced thereby.

An imperfect hydraulic jump formed in the stilling pool. The

jet of water from the apron was diving under the tailwater and flow­

ing along the bottom. Consequently, there was insufficient energy

dissipation and considerable scour immediately downstream from the

pool.

A very high standing wave was formed in the side channels just

below the crest. The choking action accompanying the wave gave an

impression of insufficient channel capacity for the water passing

over the crest.

9. Revisions of original design

Several changes were sugr,ested in attempting to improve the

8

•

•

hydraulic performance of the structure (figure 3). Since the exten­

sions of the downstream ends of the crest serve as training walls,

it was thought that by raising and lengthening them the tendency of

water to olimb the chute walls could be eliminated. These walls were

extended 20.5 feet down the apron and sloped from the crest elevation

at the notch to a height of 6. 25 feet at a point 105 feet below the

notch. This reduced the lateral flow and minimized the tendency of

the water to climb the chute walls. The flow pattern on the apron

was also improved.

As a means of raising the head-discharge curve, the crest seo­

tions were moved toward the center of the chute to obtain a notoh

bottom width of 12 feet (figure 3). The sections of crest parallel

to the longitudinal axis of the chute were shortened 10 feet. Thia

moved the sections normal to the longitudinal axis downstream 10

feet. The resulting head-discharge curve agreed favorably with the

required curve. The desired discharge curve having been obtained,

the depression in the approach floor was filled with no change in

the discharge curve.

A row of dentates and an end sill were built in the stilling

basin to break up the jet flowing along the bottom (figures 3 and

13). A good hydraulic jump was created, thus dissipating consider­

able energy. Scouring was materially reduced; but the scour pattern

(figure llA) shows that the section immediately below the basin re­

qu ires riprapping. The scour pattern was obtained by replacing the

riprap with fine sand and operating the model with the maximum

9

discharge of 46,000 second-feet until the channel had stabilized.

This required one hour and fifteen minutes.

The belief was expressed that considerable saving could be

effected by making the vertical walls of the stilling basin the same

height as the chute walls, the additional height required to be se­

cured by slope paving from the tops of the basin walls on a 2al

slope. With this arrangement large vortices were formed below and at

the sides of the stilling basin. The result was poor energy dissi­

pation and consequently deep scour below and to the sides of the

stilling basin. No further consideration was given to this type of

design, and the original vertical walls were replaced. The model

was considered to indicate satisfactory hydraulic performance except

for the high standing wave in the side channels below the crest.

The lOal slope at the upper end of the chute floor was extended

up through the side channels to the foot of the crest sections lying

normal to the longitudinal axis of the chute, to alleviate the high

standing wave. As this change was of little value, the level floor

was replaced.

The warped walls of the chute were replaced by straight, vertical

walls set in such positions that they constricted the side channels

(figures 3 and 14). This change resulted in submergence of the stand­

ing wave. A smoother and a more even distribution of flow along the

apron was also obtained. It could be seen that the chute walls would

have to be raised considerably to provide sufficient freeboard. Fig­

ure 18 is a water-surface profile along the chute walls for a

10

'

discharie of 46,000 second-feet. Due to the diffioulty and the cost

of constructing this design in the field, it was considered best to

abandon it in favor of the alternate design shown on figure.9.

10. Initial tests of the alternate design

The model of the so-called alternate design was not constructed

according to the original sketch of figure 4 but according to the

revised laboratory design of figuJO 5. The first tests with the de­

sign on figure 5 showed that at all flows the discharge from the

center notch spread laterally until it impinged on the walls and de­

flected down the chute {figure 7). At the higher discharges, the

lateral component of velocity was sufficient to carry the flow over

the walls, thus resulting in scour of the adjoining riprap. Thia is

evident from a close inspection of figure 7.

It was also found that the head-discharge curve was consider­

ably lower than that anticipated in the design. This indicated that

the area over the notch passed more water than was originally

assumed. As a result, it was necessary to decrease gradually the

crest length until the desired conditions were obtained. This was

accomplished by moving the side walls toward the center and alter­

ing the approach channel to satisfy the new requirements. The shape,

the curvature, and the location of the crest remained unchanged.

11. Revisions of the alternate design

To reduce the lateral flow and thus eliminate the undesirable

flow over the chute walls, two schemes were tried. In the first

one, training walls of various heights were placed at each side of

11

the notch and extended approximately 120 feet downstream. The walls

produced the desired results at low flow, but at higher discharges

the radial flow from the crest was deflected by-the training walls

to the chute walls where it fonned a high fin and intermittently

splashed over onto the riprapped banks.

The second attempt was more successful. It consisted of rais­

ing the apron to within five feet of the top of the crest and extend­

ing the notch through the apron as shown on figure 16. This produced

a fairly even distribution of flow across the lower part of the apron

at all discharges. However, there was still a tendency for same of

the water passing through the notch to spread laterally and climb the

walls near the stilling basin. The apron could have been raised

still more and the notch extended to the stilling pool, thus elimi­

nating the side-wall fin entirely. However, in the initial develop­

ment of the project, the canal from the reservoir will be excavated

to elevation 5598.00. With part of the apron at this elevation or

higher, a considerable portion of the structure would have to be

built on backfill. As there was considerable objection to this fea­

ture, the original apron was replaced and no further tests were made

in that direction.

12. Tests leading to the final design

From the results of the previous tests, it appeared that the

design could be made workable if the notch was div ided and half sec­

tions placed at the ends of the crest with the channel wall forming

one side of each notch. Accordingly, the center opening was plugged,

12

'

and new notohes were cut at eaoh end of the crest. Their combined

area was slightly more than that of the original oenter notoh. The

tests with this arrangement revealed that at low disoharges there

was a pronounced concentration of flow in the center of the apron

which continued into the stilling basin. As the discharge increased,

a standing wave formed in the center of the apron just below the

crest and spread gradually as it approached the pool. When the dis­

charge reached the maximum of 45, 000 second-feet, the lateral dis­

plaoement of the flow from the standing wa.v.e approximately equalled

the chute width as it reaohed the end of the apron. The result was

a sheet of water of uniform depth as it entered the stilling basin.

This phenomenon produced a very satisfactory hydraulio jump, with

the result that there was little movement of the erodible material

downstream from the stilling basin. There was very little depth of

flow along the ohute walls except in the immediate vicinity of the

notch·. This was a distinct.advantage as it was now possible to use

walls of considerably less height than in any of the previous de­

signs.

It was suggested that three notohes, one at eaoh end of the

crest and one in the oenter, be tested in an attempt to reduce the

height of the standing wave and obtain a better distribution of the

flow on the apron at low discharges. With this arrangement a stand­

ing wave of the same height as before was fonned on each side of the

oenter line, in the area between adjacent notches. As these waves

spread on the apron, part of the flow returned to the center line of

13

the struature to form another standing wave and the remainder traveled

to the side of the structure and overtopped the walls. With some

experimenting and adjusting of the size and the an�les of the notches,

satisfactory flow conditions could have been obtained. However, it

was obvious that in order to accomplish this the center notch would

have to be considerably smaller than the side notches. The possibi­

lity of clogging by debris caused abandonment of the plan.

At this time it as suggested that there might be an improvement

in the flow pattern if the notches were moved away from the channel

walls. The sections between the notches and the channel walls would

form buttresses, thus affecting favorably the economy of the design.

The notches were moved 10 feet toward the center line (figure 17).

The standing wave was not affected materially, but another fin of

water was formed between the notches and the chute walls which ex­

tended well above the top of the wall. The scheme was abandoned,

and the notches were returned to their former positions.

At this point the alternate design, with notches at the ends of

the crests, was accepted as the final design, and the laboratory

proceeded to make refinements to improve the appearance and to curve

the chute walls to conform more nearly to the flow pattern (figure 6).

13. Final design

In the arrangement shown on figure 6, the ourvature of the chute

walls was easedr the entrances to the notches were streamlined, and

the transition above the crest consisted of plane surfaces. This

change did not affect the flow pattern (figure 8} or the head-discharge

14

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I

,

curve. Therefore, the design was considered satisfactory. However,

two more attempts were ma.de to reduce the height of the standing

wave. In the first trial, four rows of half-elliptical baffles were

placed on the apron, extending from the foot of the crest to a point

75 feet downstream. Two rows were placed in line with the inside

faces of the notches and the others were placed parallel to them and

10 feet nearer the oenter line of the structure. The major axes of

the baffles 119re placed in the direction of flow through the notches,

and companion rows were spaced such that the openings were staggered.

This scheme accomplished the purpose to some extent, wt the improve­

ment was not sufficient to warrant their use.

In the second trial, a triangular blook 12 feet high was placed

on the center line of the apron with the apex against the crest to

deflect the flow from the crest into that from the notches. Thia

reduced the height of the standing wave considerably. Howaver, the

resulting flow into the stilling basin did not produce a stable jump.

So the plan was abandoned.

It was suggested that an improvement in the flow pattern could

be obtained by warping the walls from a point in the canal to some

point downstream from the crest. The model was revised as shown on

figure 9. There was no improvement in the flow pattern on the apron

(figure 10). However, the entrance conditions to the notches were

improved to the extent that their bottom widths were reduced from 10

to 9 feet.

This structure presented a more pleasing appearance than the

15

previous arrangement, and it was selected as the final design. The

head-discharge curve is shown on figure 12. The resulting soour

pattern, after an equivalent prototype flow of 45, 000 seoond-teet

tor 1.26 hours in the model, is .shown on figure 13A. The scour test

was not continued for a greater period of time because the channel

bed in the model had stabilized.

III - RESULTS AND CONCLUSIONS

14 • .Analysis of the results

The hydraulic performance of ori@;i.na1 design A was satisfactory.

However, from an economic viewpoint it did not compare favorably

with the final design. The depth of water on the chute at the walls

of the first design was considerably deeper than that at the walls

of the final design, necessitating higher walls over a greater length

(figures 16 and 18).

Original design A also required a greater length of crest than

was necessary on the final design, due to the unfavorable entrance.

In the longitudinal section of the crest the water flowed diagonally

to the crest axis, causing an appreciable reduction in the coeffi­

cient of discharge. In addition, the downstream portion suffered a

reduction in head due to a drawdown in water surface in the area be­

tween the crests which also contributed toward reducing the over-all

coefficient. The width of the notch required to pass 10,000 second­

feet at elevation 6623.00 was much less for original design A than·

for the final design. Thia was due to more favorable approach con-

16

t

ditions above the notch, more slope in the downstream apron, and the

fact that critical flow occurred downstream from the notch. In the

final design the control section of the notch was at the upstream

edge of the crest and cri tica.l flow oc_curred before the water reached

the apron.

With both designs, a suitable hydraulic jump was formed in the

stilling basins and visual observations did not indicate any differ­

ence in performance. However, a scour test revealed that original

design A 1coured much more severely near the pool walls than did the

final design (figure 11). This might have been caused by the converg­

ing chute walls of the original design which concentrated the flow and

reduced the effective width of. the pool at maximum discharge.

At the early stages of retrogression in the downstream channel

leading into Tollgate Creek, the water surfaoe will be thirty to

forty feet above the stilling-pool walls at maximum discharge. Thia

condition will not produce any unfavorable conditions at the struc­

tur, if sufficient bank protection is provided against wave aotion in

the vicinity of the structure. Aa retrogression progresses and the

tailwater approaches the top of the stilling basin walls, a vortex

will form on each side of the pool and there will be considerable

return flow into the stilling basin. The velocity of this return flow

is sufficient to cause scour and sloughing of the banks. If this ia

to be prevented, protection must be provided for velocities of approx­

imately 12 feet per second.

17

15. Conclusions

(a) The stilling pool for the final design. as shown on figure

9. is satisfactory for discharges up to 45.000 second-feet in combi­

nation with the corresponding tailwater elevations as shown on figure

19.

(b) The final design (figure 9) is superior to that shown on

figure 6. from an aesthetic viewpoint. There is no appreciable dif­

ference in their hydraulic properties.

(c) For the final design. the bottom velocitiea downatream from

the pool are less conducive to scour than those of the original de­

sign A. Any decrease in the channel area immediately downstream from

the pool will have a tendency to increase the scour.

(d) The variation in the alternate design. as shown on figure

16. could be ma.de workable. It was not considered practical tor

structural reasons.

(e) The three-notch arrangement could have been made satisfac­

tory. and the height of the standing wave could have been reduoedJ

but the narrowness of the center notch would have presented a clogging

hazard.

-18

,

R 68 W

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T 4 S

TSS

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T 8 S

N

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DOUGLAS COUNTY-·­-- ELPAs·o couNfY �

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CHERRY CREEK_

AND TRIBUTARIES

LOCATION MAP

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C H E R R Y C R EEK D A M

S P I L L W � Y - U L T I M A T E D E V E L O P M E N T

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SPI L L W A Y - U L TI M A T E D E VEL O P M E N T N EA T L I NES O F WA TER PA S S A G ES

A L TE R NA TE D E S I G N 8 S E C T I O N A - A

A · ---.-� ..J A

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11'

FIGURE 7

A. Model arrangement B. Discharge 10 , 000 C.F. S.

'· C. Dis chfil'ge 25 , 000 C. F. S. D. Discharge 45 , 000 C.F. s.

ALTERNATE DESIGN A

A. Model arrangement.

c.. Dis charge 25 , 000 C.F .. S •

FIGURE 8

B .. Discharge 10 , 000 C.F. S.

D. Discharge 45 , 000 C .F. S.

.ALTERNATE �SIGN B

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S E C T I O N A - A

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C H E R R Y C R E E K D A M

S P I L L W A Y - U L T I M A T E D E V E L O P M E N T

N E A T L I NES O F WA TER PA S S A G ES

A L T E R N A T E D E S I G N C

[FI N A L D E S I G N]

LJ·i / 25' �-!

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;; ' -Top of crest

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El .5598.o- ·, • \

R, 10.25' r,50•-41 ·

:- - - - - -- - 2 7. oo'-- -- -----...!6. oo' k -

TA B LE O F COORDINATES FOR O G EE SEC T I O N X I N FEET J 1 /V FEET

0.000 0.000 +0. 1 1 5 +o. 1 65

0.230 0. 3 1 0 0.344 0.439 0.459 0.539 , 0.574 0.633 0.689 0. 7 1 2 0.9 1 8 0. 844 1 . 1 5 0 0. 950 1 .607 1 . 1 02 2.066 1 . 1 85 2.527 1 . 2 1 3 3.2 1 4 1 . 2 1 0 3 . 9 1 0 1 . / 60 4.590 1 .036 5 .740 0. 735 6 .890 + 0.299 8.040 - 0.2 76 9. / 80 0.9 1 8

1 0.340 1 . 676 1 1 .480 2.526 1 7.230 8.380

+22.960 - 1 6. 740

FIGURE 10

A. Model arrangement B. Discharge 10 , 000 C.F. S.

c. Di scharge 25 , 000 C.F. s •. D. Dis charge 45 , 000 C.F . S •

.ALTERNATE DESIGN C

FIGURE 11

A. Scour after flow 45 , 000 C .. F. S. Original Design A.

B. Scour after flow 45 , 000 C . F. S. Alternate Design C .

SCOUR PATTERNS.

5640

en -z

5630 0

I-ct

w _J w .... �

.1, ..... w u ',, ct

a:: I/

5620

0:: I w ., ct /

I/

I

56 1 0 I

I -,

j .I

0 1 0

-

---� ----� -_Lo,.--

i-..... _i,.,,,o' -

C H E R RY CREEK AND TR IBUTARIES - COLO R A DO CHER R Y CREEK D A M

SPI L L WA '( D I SCHA RGE - STA. l62 t 91. 83

ULT I M A TE DE:VELOPMENT F I NA L DES IGN

20 30 40

D I S C HARGE - T H O U SANDS C. F. S. 50

.,, GI C

;D r, "'

FIGURE 13

A. Model arrangement

B. Discharge 45 , 000 C.F. S.

ORIGIN.AL DESIGN

FIGURE 14

A. Model arrangement

B. Flow conditions with discharge of 45 , 000 C.F. S.

ORIGINAL DESIGN A

µ End of canal

5638. 00 I-

... / . 5632. 24 - -I ,

w w lJ...

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a a C H E RRY CREEK AND TRI BUTA RIES - C O LO RA D O cri

C H ER R Y CREEK D AM I()

WATER SURFA CE PROFILE ALONG WALL � I OF SPILLWAY- DISCHARGE 45,000 C.F.5.

..... , ...... :-.... - .7' r-.. " ' ..... I'-.:

F E E T

ULTI M A TE D E VELOPMEN T ALTER/I/ATE DESIGN C

F I N A L DES IGN

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FIGURE l6

. A. Mo del arrangement �.. Discharge 10·, 000 C.F . S •

C. Discharge 25 , 000 C.F .• S. D .. Discharge 45 , 000 c.F. S.

SECOND VARIATION OF .ALTERNATE DESIGN A.

FIGURE 17

A. Model arrangement

B.. Discharge 45 . 000 C.F. S.

VARIATION OF ALTERNATE DESIGN B.

� -

5 6 3 8.00 ,,

I-w w LL

z 5 6 1 8 .00 -(/) z 0 -I- 5 5 9 8.00 <[ > w _j w w

5 5 78 .0 0 (.) <[ LL a:: ::> (/)

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�End o f cana l I I I I I I I I I I I I I I -

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C H E R R Y C R E E K D A M -- (X) t >--.._ -.- :1 --U L T I M A T E D E V E L O P M E N T - CX) --

WA TER S U R FA C E PRO FI L E A L ONG WA L L O F -.- � T --

-'- o r >-->--S P I LL WA Y - D I S C H A R G E 45,000 C. F. S. -f- ...... 1

O R I G I N A L D ES I G N A Cf) -,_ I 1

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S. A. M. 2-5-44

F I G U R E 1 9

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10 20 30 40

D I S C H A R G E I N THOUSAN DS OF S ECON D - F E E T

CH ER RY. C R EEK, COLO .

C H E R R Y C R E E K D A M

U L T I M A T E D E V E L O P M E N T S PI L LWA Y TA I L WA TER

CU R V ES FOR STA TIO N 1 7 1 + 90

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