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PAP-17.

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FILE COPY BUREAU OF RECLAMATION

HYDRAULIC LABORATORY

SUPS 50,N1C KETHUDS SHORT-CM h F B&M-M! SILT _Mf;A6 m-14 l 3

Charlene W. Thomas

Associate iiamber, 4SCE

Engineer, -bureau of keelamation

Denver, Colorado

The entire economy of the samiiarid weatern United States is dependent

upon reservoirs for water storage. Silt-laden rivers carry sediment in

a fi,azing quantities---two billion tons have been deposited in Head Lake

behind Hoover Data since 1.935—and this sediar.ent slowly but permanently

iL-,pairs reservoir ;storage capacity. ~)tudi*s of t-ie location : and extent

of deposits, and the zovem.ent of silt-carrying density currents within

them surely will extend the useful life of storage reservoirs. high-

frequency echo-soundin'; equipment is standard for depth measurevents,

and several electronic instruments are being tried out for coordinati.a}g

quickly the horizontal location of the soundings. After describinx,

conventional silt-survey equipment and procedures before the hydraulic

Division session in Qklahoua City, <r. Thomas cha len~,re enCineers to

develop supersonic sounding equipment further to measure depths of

silt directly as well. as explore the behavior of density curvents.

SUPzRSONIC 143 MODS SHORT-= RES~sYOIR SILT X&AS DMTS

Charles :4. Thomas

Associate ;,!ember, ASCE

Ehgineer, Bureau of Reclamation

Denver, Colorado.

Econoadc life of any water conservation or utilization project,

whether such project be for irrigation, flood control, navigation, power,

domestic water supply, or other use, is directly dependent upon the length

of time that the reservoir continues to fulfill the purpose for which it

was built--namely.. the storage of water. Reservoir sed1mentation must be

studied extensively In order to plan the proper location and operation of

outlets through the dart= and for the reduction of sediment accu ulation.

The Bureau. of LecluAtion has constructed approxirstely 80 storap

reservoirs since its inception as a Federal service. Operation of the

reservoirs is complicated because they r=ust serve multiple parposes by

storing water for irrigation and power and makin:, available additional

capacity for flood control.

After construction of a dani, changes occur in the strear. channel for

a considerable distance both upstreu: and downstrow f Corn the structure.

These changes may be caused by the departure from virgin conditions in

quantities of water released ;into the same channel, by a sirilar change

in the sediagnt content of the water released, by changes of velocities,

by coDbination of these .factors, or by deposition in backwater areas. The

results Of these changes may be to increase drainage difficulties, increase

the head on pua~,ing plants, cause excessive scour around existing structureaw,

excessive deposition around river developments, or other effects due to

changes in strea;~: regimen.

HALE` Of SILT IN UPP h HALF OF RiMRV IR

A study of the reservoir surveys conducted to date has permitted

the deteru:ination of the location of the sediment deposits within

eervoirs. This is important frow rany standpoints, particularly with

r*X*rd to planning aspects. It has been found that W percent of the

sediment its Guernsey Rovervoir, Wyouing, is deposited in the upper

35 percent of the reservoir depth, calculated fro spillway level. This

reservoir is operated so that the reservoir pool is held nearly constant

during the irrigation season, In Eoosevelt Reservoir, Arizona, Mich

operates over wide variations in pool elevation, only 30 percent of the

sediment is deposited in the upper 35 percent of the depth. In contrast

to these two reservoirs is the deposit in Elephant Butte heservoir,

Now Iilexico, where approxix;atel;y %) piresnt of the sedimentss are found in

the upper 25 percent of the reservoir depth. This reservoir also has

considerable variation in the operating levels.

The most important conclusion to be drawn, from these studies is

that i._i all cases so far studied irz the }pest, over 5C percent of the

sediment deposits lie in the upper half of the reservoir. Inasmuch as

allocations for sediment storage in reservoirs have normall3r beep: placed

at the bottom of the reservoirs, it seer=s advisable to question contin—

uation of the practice of allowing relatively large mounts of dread

storage that will not be filled with sediment for many years.

Conversely, it has usually been considered that the upper levels of

reservoirs, usually allocated to flood control in multipurpose protects,

would be free Prot. sediment deposits. rata so far collected show that

2

in some cases this "otion of the reservoir may Abe subject to the

greatest amount, of sediment: d*yrovi,tion. These fmats should siter our

planning of mteorvoirs# partica.Urly those intended for multipl -purpoaa

open-OktLon.

5u *ys of sediment deposits -.v-*t~ be ad*Watoly planned its order that

they raj furni*b a as h of Information front which to calculates the lon; th

of 'titers required for the bed;i nt. to raacmulate to the extent of impairing

or ondlog the useful We of the ros,er. ir. The watt location of this

sediment with regard to the dan thus beccv,es important.

For that portion a1 the saws lying atevas the water ourfac* existing

at the tile, L4P survey Vii. ocedu» e Is AW.ar to that followed in the

conduct of * rdinary toMraphic dst+eminationoo Some a i.fi.aection in

a:+ethodA &W +equiprentt used is iwe*ssaary to penetrate share-dine vegetation

and to nogotiats sad flat*.

That portions of the reservoir below the existing water surface is

not resdiily aocessible. The usual prooed.urs in this csse its to explaj,

hydrographic ~u.,vey "t.hodr, ydro~ rsphi.c survey* are thre s disetenaiotae ..

i sourdine. reprosente a vortical dUwnsian downward fm4, the crater surface

to Vie baths;.: of the reservoir, Thias sound3nz ; ausA be located to the

horizontal plans by two coord"too. ne*,, in addition to tba $*=d: g*

there must also be horizontal control of the survey,

In large rss osrvoi.res soundings are rd* along predetsem4ned aodimeenU—

tior: "ranges" or reservoir *room—sectl.on lines. 4h+are practicabl e,e these

ranges are located morns, to the streat, flow and the valley,* and sp*ood

so thRt the ave raga etA areas of adjacent rangers are representativ* of

3

the section b; town them. Ranges are located across the mouths of all

principAl arms of the reservoir, and the range network should extend UqP

these tributaries in a zann*r similar to that on the main stress, The

ends of each range are perrarmntly &ark*d, and all ranges should be tied

together by an active triangulation network expanded Atm a chained and

chocked basso-line. In small reservoirs these rangge zay be spaced

sufficiently close so that bottom contours can be drawn. In some reser-

Mrs when it is desired to develop bottom contours,ranges mis,ht be

dispensed with and independent sounding surveys made.

One of the two major factors inxolvvd in the hydrographic survey

Is obtaining the soundings. These are made in shallow water depth by

means of a sounding pole with a baseplate. The general practice for

measuring greater depths. has beeno until the past few years, to take

soundings by conventional lead-line methods, or by some mechanical

device. A rope, lead line, hold in the hand, or a piano mire on a

rounding wheel have been used, and can still he used to advantage under

certaiR circumstances. However, the more modern supersonic echo-sounding

equipment is now more generally utilized.

Krizontal control of reservoir sedimentation surveys ray be

accomplished by utilizing two ger*ral classes of equipwant: (1) plwai-

metric survey and navigation instruments and (2) electronic equipment.

The first method is now used almost exclusively, while the latter method

has been used in coastal and land surveys and could be adapted to reser-

voirs. The possibility of using photogrammetry has bee- considered, but,

to date, no practical application has teen made.

When range lines are used, the problem resolves itself into

locating the survey craft as it progresses along there. Coordinating

position: and depth determinations is facilitated by the fix button, which

is an integral part of the echo—sounding equipment. Each time- this button

is depressed, a permanent mark is made on the sounding chart. These fix

marks are identified by numbers. The graft is kept on the range line

by the operator, who liners up objects on shore, or by a transitman

stationed at one and of the range line who signals the helmeuAn when

deviations from course occur.

The following methods employing optical and mechanical equipment

have been used successfully to a scamplish the horizontal cor-troll, but

are dependent upon visibility frorr, shore to survey drafts

One or more transits are set up on share, at suitably situated

and accurately located triangulation stations, and the an;,~les from

known geographic loeGati.ons to the survey craft are read at the instru—

ment or instruments. The angle or angles Brea read periodically, and

a voice, radio, or flag signal is transruitted to the survey craft at

the exact inst-nt that the 'Measurerce►nt is made so the fix may be

recorded on the sounder chart. This method gives quite accurate results

but necessitates trained instrumentmen and sme means of boat-to-shore,

coz u nication. Notes must be kept both on the craft and on shore and

these must be coordinated frequently.

Another method of usin ~ intersection to deterai.ine the position

of the survey craft on the range line is to :mare use oil' the alidade

and planetable. One or more planetablexas are located on shore at

carefully located points, and the angle botween aso known point on shore

and the survey craft is determined graphically. This method gives

results slightly lease accurate than the use of transits.

A method of resectio.- is used to determine the position of the

craft on the range line by reading,the angle betwo*n two points on

shore with a sextant located can they surrey craft. The: monuments, or

m ints or shore, mst be acou:rate:l.y located. This is a seimrl.+e, accurate

Liethod and does not necessitate cozwani.cati b*t^r en the beat aid the

share except to keep the survey boat on the range line. Since the

angles are read at or near the sounder, notes may be wade directly

on the recording.(he man on the boat can operate a sextant with

a sl+ all, a-mount of' qpecial training,

Piano wires on a calibrated reel, is used to reaMsuree the distance

fro=g: the boat to a known paint on land as the b*at proceeds aloe

the range line &*rose the reservoir. This method, which requires

only a calibrated reel, for the wire, has the advantage of being; used

and read: on. the craft. The silt range roc rent and the shore anchor

for the wire must be accurately located. The brat is kept or, the silt

range line by range Darkens or by instrumentswi. Floats attached to

the wire at intervals keep it on the mater surface wA hanese in a

horizontal. position. Distances up to one mile j~iy be measured in this

manner without appreciable error.

A calibraated, price-tom current Beater is used to weasure distance

along the range line. The meter is suspended In the water and the

MV

revolutions of the bucket wheel counted electrically as the moat

proceeds. From data read on the calibration curves for the meter,

the distar. ;e traveled rna., be calculated.

Where: it is desired to study the deposition of material brought

in by tributaries :and deposited an a delta, or to determd.n;e accurate

bottom m contours, a piano wire in fastened to an anchor on share and

the stmt is coved in arcs about this point as a Rauh. ~rces of 25 or

50 feet in radius are ordinarily used. The locations of the boat or

the are is deter _i..ed b.-r the trarxsit or al.idade and planetables.

There are a iiumber of n:etho?ds of horizontal control that employ

electronic equipment. Some of this equipr ent ha-- bew used In raking

hydrogrraphic surveys, and the=_ra is other equipment that, may 00 applicable

to hydrographic surveys o re-ervoir sediresntatioy. surveys. Z-% brief

description of the= eq iphient and the sa.ethod o:' operationn, of a few of these

electronic devices follows: :

the: Shoran n,eethod wa,s develoFed for precision control of air-

borne aircraft on boubing rkiescions duriAg the war. Two laird stations

could control a number of air-borne stations aboard the bombers. The

Coast and Geodetic Survey has successfully used this egaxipaae>at in

conducting off-shore surveys In both the Atlantic and the Pacific

Ueeans. Two accuratel.;. located shore stations and one station on the

craft are needed. The; station on the craft radiates pulses i, alternate

groups at two different carrier frequencies nciees of very short wave lengAh.

7

One of the share stations is tuned to one carrier frequency and

the ether station to the reuaainina frequency.

reception of the pulse from the aircraft causes a yround

station to act as a transponder and relay a pulse ore a different

frequency back to the craft where it Is received and displayed and

the distaanc* to the station recorded. The equipment consists of very

compact and tall-built components, and the accuracy is very good for

long; distances, but the percentage of error is greater .for short

distances. This is due to equipwent errors. ~atimated probable

error with =modified Shoran equipment is +50 feet rsga,rdl.e s* ry e

distance.

The Carps of 4ngineer, Department of the Army, has experiweentead

with the use of XR-584 radar systeea in Galveston harbor. Positioning

of soundings in this harbor had been accomyl.i:sheed, previously, by

means of two saxtant angles read aboard the survey boat between

prominent landn,,arkee on the shore. An effort to spsad up this meathod

by means of a sextant angle grid was a definite i:..provert*nt, but the

fact, that the work could be delayed by bf#A weather and poor visibility

was ax.other difficulty that had to be overcome. The mobile radar unit

SC.-584 consists of a large truck-mounted steel van with all equipment

and controls inside. The antenna, located on the roof of the van,

will automatically position on a ship and track it. .eadings for

range and azimuth are obtained from dials. A small telescope is

mounted or., the antenna and may be used to assist in the initial

orientation of the unit. The operating power is furnished by a portable

generator. M.

For the Galveston surveys a responder was mounted on the survey

craft to assist the antenna in tracking the survey boat. Ship-to-shore

radio contact was z-tintainod for supervision of the vvrk. The results

of the experiment showed that a greater error -existed in the data from

the-measureu4nt of the angle than ir, the distance measurezent. The

distance zeasurements were obtained with an error of +6 fe*t for the

best results.

A system known as Raydist,, developed by the Hastings Instrwhent

Company, Hampton, Virginia, for wartime use, has since undergone inter.-

sive developr:ent as a means of surveying over water or, mouth terrair,

and as a precise tavigaticni and tracking system. In these applications

the i-aydist systevt results in high accuracy with the use of light and

simple apparatus. Raydist is a continuous wave system and depends o:,,

the reln-tivo phase relationship betweer-, continuous wave radio

transmitters.

Prob4bln the beat application of thir equipment for sedimentation

surveys is to use it as a pure range. system. Orly two instriments are

- . required,, and a continuous indication of the distance betw-ee-.: the two

sets is obtained. If one instriment were located at the end of the

range line and a recording instru",nt carried in the survey O"afti, cars -

tinuous indication of distance aloni- the line could be bad, "'Squiprent

of this type built for the Navy has been put in operatioi., and consis-uently

repeated measurev*nts within 2 feet on 'the indiwAor-e and 5 feet on the

recorders have boor. obtained. These errors were obtained In distances

of approximately 6 rdles. The eTc zip ment rray be coij;,letely housed in

W

suitcas*-type cabinets, the heaviest single unit weighing approxizately

32 pounds. Equipikent, necessary for the horisontal control of a **(U-

atentation survey would probably cost in the neighborhood of 420,,OW

at the present time, but this amount should be sonowhat reduced after

*.%et needs are known and production of the equipment increases,

Lora*.. or "long-range accuracy,* developed by the ismor graph

Service Corporation) to amother radio suryeying systm-r., operating on

iredium frequencies and mwdium wsve lengths. The uso of medim. frRquencles

and low voltages eauswp the equipment to be loss susceptible to ooraon

electrical problems that give trouble In high-frequomy, high-voltage

systems and does not tonfine its use to line-of-sight operation. In

this oyster three short stations and one boat installation are required.

The boat installation is quite small., and the for rvrtion may be

aounted in an out-of-the-way position.

The three lend statiorto are bulk-y and presently used squip,4snt

is not easily moved. This characteristic would be a disadvantase in

sedimentation surveys in that when. the Purvey moved froir one portion

of a la"s lake to anothor., it would probably be necessary to move

the shore equipment. The average repentaVility error in distance$

up to 9-1/2 miles has been found to be about 2-1/2 to 3 feet.

KWIMAM FOR VMAAL SILT-WRVEY PARTY

The equipment now employed by the Bureau of i4eclawation is designed

to provide omplete moVility, since the reservoirs are separated geograph-

ically. This separation distance may be a few miles or several hundred

miles. The prime mover consists of as 1-1/2-ton,, 4-whoel drive, Dodge

10

power wagon equipped with racks and hitches for carrying the survey

equipment and towing the survey boat and trailer. This vehicle has

adequate power to traverse rough terrain and will develop satisfactory

speed for movin . frou, one lake to another without undue delay. A station

wagon is also wr pl dyed to carry instruxonts and p< rs o nnel. and to serve as

a utility vehicle on the job.

Are 18-foot boat with a 6-Moot -inch beau: is used for t.:* underwater

survey. This craft is of the open type, has a; plywood hull., and is

powered by a 52.--horsepower Inboard gasoline engine. The, boat has ample

space for a fives arena. O s set of asst>illators -f-Ortive supersonic

echo-sounding equipment is permanently installed i^ the hull of the

craft, and brackets are provided for outboard mounting of a separate

pair of oscillators. t small boat equipped with a--. outboard .motor is

used for obtainin;;,he soundings in shallow water.

A two eel trailer capable of caM-ing the brut at reasonable

speed on the highway is provided. This trailer is backed into the water

for loading; and unloading.

The supersonic echo-sounding equipment being used is a Submarine

Signal Cospany Model 808-J. As previously mentioned,, both inboard and

outboard oscillators have been provided with this wounding scluipment.

xperienoi has shown that the outboard oscillators Eive a better-definod

record than the oscillators installed in the hull of the: boat. This may

be due to the .Pact that the, hull is not of iiodel dimensions. The sounding

equipment is of the portable type and 33 not installed perrmnentlj in

11

the survey craft. An NK-2 adodel sounder aseanufactur•ed by Bloodworth

Marine Cookpany is rraintained in the laboratory in working order as

standby equipxent.

A very ussful piece of equipaeteent for the party has provod to be

walky-talky radios. This means of comunio tion enables the boat party

and the ins33tru►eaentmen on shore to maintain conversational. contact with

one another, thereby reducing hand signals and idisunderstanding. The:

equipuaeent used is forwor Army Signatl. Corps radio receivers and trans-

mitters and is operated on the frequencies assi.c-need to the Dureau of

«ecl.azation. - These radios are used to supplement the--wi alv sent and

received betws,*N, the beat and shore parties and to check they data as

taken.

The hydrographic party for the seedirw.ntation investigations consists

of frc»: three to rive: men specially trained for their duties in this

particular kind of work. Sine* the boat crew also does the above-crater

surveys, it is neceessaRry in r,o:kt inFUncess to suprIeveent the crews with

personnel obtained locally or borrowed froz Nearby pro jscts. It is

desirable for the recorder operator, or Some: other .,:art ir: the party, to

have son>e kn Pledgee of radio and electronic circaits in order to mAi.ntair:

the supersonic echo-solmdini: eaui rent, the radios, and r th..r slectri.c&I

devices used by the party.

In a3 number of the suz•veys the water sxi- face of they lake Varied

considerably during, the tire tote surveys were being m adc. In these

instances it was necessary to supplant th(-; so;md!nn- charts at oach end

of the ranges by land surveying. "his surveyir , * was done In the aonventicnal

12

method by use; transit, rod, and level, or alidade and rod. 1~o

significant differences were noted between the profiles obtained by the

conventional methods and those obtained by the use of the echo sounder

where they overlapped. In many instances profiles =mere intentionally

overlapped to provide a check. Since the lake stage usually fluctuates

during the period in which the survey is in progress, nurBrous check

readings may be nade using both methods on the saves portion of the reser-

voir cross-sections.

NAVY ODOMATIS IN LAZE MEAD SMVEY

A silt survey is now being conducted on Lake Read above: ,ioaver Slam.

`11iis survey, is being esarried out under a cooperative agreement by the

navy, the Bureau of ILeclamaticn, and the Geological :xurvey. Preliminary

reports indicate that in the 13 years since completion of Hoover Dam,

sedimentation deposits ranging, in depth frov; as little as 4 feet in the

Virgin iver arm of the lake to as much as 260 feet in the Colorado river

am have accumulated in the lake. With the rate of Colorado River deposits

averaging 400.,000 tons per day, a total of about two billion tons have

been deposited in the lake to date.

The experiences of the Bureau of Reclamation have shown that echo-

sounding equipment provides a rapid and accurate meads of conducting the

underwater portion of the reservoir sedimentation surveys. Caution gust

be exercised it the use of the equipment near the faces of` dams, against

steep cliffs, in swiftly flowing water, and in grater containing air in any

noticeable quantity. Frequent bar checks of the equipment will insure

that the necessary constants have been correctly applied.

13

DE =P SUPcxR IG &UIPMMT FLMTHER

Although the results of the sedimentation surveys conducted to date

have been quite satisfactory, engineers should not be satisfied that the

ultimate has been reached, but should be always on the alert for possibil-

ities of further advances either by way of electronics or by extended

application of the present equipment. Thinking along* these limes, it

appears possible that the supersonic echo-sounding equipment now used to

obtain the top of the sediment deposit in the reservoir may also be used

to measure the depth of the deposit in the reservoir directly.

It is also possible that this echo-sounding equipment may be used

for detecting and measuring depth and extent of density cuxxenta in a

reservoir such a Locke mead. If so, it would provide a rapid and, economi-

cal means: of measuring and plotting these currents. Once the behavior

of this phenop enon is understood, selected operation of gate$ and sluices

might permit passaage of considerable sediment through the eves. These

potential uses of the instrmeent in question have bee=., considered, and a

limited amount of work has beer. done to determine their adequacy for

such surveys.

In Elephant Butte Reservoir a reecurding was made on one range, and

a series of spot tests was made to coordinate the nvl.tiple echoes of the

echo sounder Ifith the results shown by sampling of the sediment with a

spud. The spud is a rod equipped with cups designed for taking samples

at different levels in the sediment. The spud used was only 10 feet long

and did not penetrate the old button, in all cases. Inspection of the

spud samples showeed layers of silt that corresponded to the reflection

14

surfaces in the recording. However, in one area of the reservoir, only

one surface was recorded by the echo sounder, and the spud teat showed

about & Peet of sediment above the old original bottor. It was assumed

from this that there was no penetration of the sound energy into the

sediment. This may have beer due to baking of the surface during the

low water period in the past. The results of the meager experimentation

are not conclusive, but some indications have been found fro, the serzall

amount or data taken. Fvidence from these and associated studies shown

that a different frequency of the supersonic wave will have a different

penetration into the soil or milt layer. The €08-J Submarine Signal

Company echo-sounding equipment operates at approximately 21 kilocycles

per second. The NK 2 Bloodworth 4arine equipment operates at approximately

14 kilocycles. The Bendix aviation Corporation is now building equipment

that operates at about 40 kilocycles per second. It appears that the

nigher Frequency equipment has a s13.-;htly better definition in the study

of either silt layers or density currents. It is proposed to use the

equipment having; the 'three different frequencies to obtain comparatives

recordings, from which the optimua frecuency for probing the sediment

deposits might be indicated., or an instrument developed for the purpose

whenever a conwehensive study of deposits might be initiated.

The overall s agnitude of reservoir sedimentation determinations, is

such that it merits the concerted cooperative efforts of all concerned,

even to the Joint purchase and developfi:ent of equipment. There is a

definite need for an accurate, continuous mews of position finding as

well as a wider adaptation for the use of the present sounding equipment.

15

SPILLWAY ELEVATION OR -•~ 1 90

BOTTOM OF FLOOD STORAGE

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f / /. LOCATION OF SEDIMENT DEPOSITS

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IMPULSE FROM MOBILE STATION RELAYED BACK TO SHIP FROM SHORE STATION ----------

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AND RECORDING

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HORIZONTAL , DISTANCE TO TARGET

REFERENCE I~II (SLANT RANGE)

LINE I ~l i ,-ANGLE OF ELEVATION

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AZIMUTH ANGLE

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