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Show Duty and Measurement Nev? of Water By DON H. BARK, U. 8. Engineer, In Charge of Irrigation Investigations Investi-gations In Idaho. Oregon Short Line Railroad Demonstration Dem-onstration Train Lecture. The greater part of the land In the went would be practically worthless 3 without water with which to Irrigate ' It, yet there la far less attention r given to the ineuHurement of this water than there Is to the measure- ment of the lund. Under the Carey I Act the land Is sold to the settler for r.O cents per acre and would hardly be worth that without the water, while water costs the Bettler all the way from $115 to $100 per acre. Miner's Inch. Water was first used In Idaho and , other western states for mining pur- , poses, the common method of measurement meas-urement being called the miner's Inch method. The miner's Inch was 1 the unit upon which such measure- I went was based, being the amount ' of water that would flow through a j sharp edged orifice one Inch sqimre j under a given pressure. The cuan- , tlty called for by a miner's Inch, however, varied In different states, t duo to the fact that the pressure over i the orifice was not the same. J Cubic Foot Per Second. ' The cubic foot per second, which , represents a definite tangible nmount H that Is easily understood, was adopt- v ed as the legal standard for 1 in t measurement of water by the Idaho t legislature In 1893. It Is commonly v known as the "second foot" and rep- ' resents the flow of water which will 11 exactly fill a vessel containing one cubic foot 'ach second of time for i as long a period us it Is allowed to flow. Hence, a Hut of one cubic ,, foot per second delivers lit) cubic feet per minute, or 3,(;no cubic feet per h hour, or 86,400 cubic feet in a day of a twenty-four hours. tl It Is found that one cubic foot per " second equals a flow of almost exactly a BO Idaho miner's inches, or 4."0 gallons r per minute. A flume one foot wide and one foot deep, if filled with water 0 that is flowing ot tho rate of exactly n one foot per second, will carry one n cubic foot per second, and otner P flumes or ditches in the same propor- ' tioti. The quantity discharged de- pends upon the velocity of the flow and the area of cross election, of the advancing stream ot water. These w two factors are taken Into consider- atlou when determining the flow of t largi streams and canals, It being h only necessary to determine the area P of the cross sectfnij and the average si velocity, whk"i two amounts multiplied multi-plied together gives the discbarge. n The cross section Is found by multl- plying the average depth of the (r stream by the width. The average tl velocity is found by measuring the d rate of tho same either with floats el or with a current meter esjieclally T constructed for the purpose. A close ' approximation of the velocity can be n secured by noting the time that Is ' required for a surface float to ad- " vance through 100 or more lineal ,.i feet of the ditch. This gives the fur- c face velocity, and to find the average velocity one must multiply the surface sur-face velocity by .8, ince the Bver- bl age velocity Is that much slower le than tho surface velocity, owing to " the friction on the sides and bottom ff of the channel. fr Acre Foot. "J Where large volumes of water are to be considered the expression of It the amount In cubic feet would In- di volve the use of such larg'j mimtx-rs " that tho same would be cumbersome. In order to simplify these expressions expres-sions the term "acre foot" Is used, ' which represents enough water to w cover an acre one foot In depth, or JJ,', 43.5(iO cubic feet. The use of this term has the additional advantage of f0 being easily compared with the acre- M age; as for example, a reservoir con- Hi tainlng f.o.woo acre feet of water vt would furnish a depth of two feet In for 2.'.,0oo acres of land. A cubic 1,1 foot of w ater per second flowing con- c tlnuously for twenty four hours furnishes fur-nishes almost exactly two acre feet n of water. ,M Hydraulic Equivalents Which Will be Found Useful to Irrigators. f, 1. Idaho miner's Inch equals an- tt proximately 1 r,o tf a ruble foot ht T second, or nio gallons per minute. 2. The flow of a ruble foot per al second equals approximately M mln- er's Inches, or 4.'0 gallons per mln- , ute. ,' 3. One cubic foot per second for j al 24 hours equals approximately 2 acre!v feet. jo' 4. One acre foot equals enough's! water to cover an acre exactly a w foot in depth, or 43.r.t.o cubic feet. ( .1. One miner inch per acre for j si 100 days equals 3 97 feet deep on the lis land. I I L 6. One miner's Inch per ar fon 110 days equals 5 91 feet doep ou the land. 7. Hve-elghths miner's Inch pel ncre fur 100 days equals 2,48 feet deep on the land. 8. Five-eighths miner's Inch per acre for 1.10 days equals 372 feet deep on the land. 9. One-half miner's Inch per acre for 100 days equals 1 88 feet deep on the land. 10. One-half miner's Inch per acre for 1.10 days equals 2M feet deep on the land. Weirs and Weir Measurements. Tho most accurate, practical and economical method of water meas ureuient thut bag been devised for the measurement of comparatively small heads of water Is the weir measurement. The weir consists es sentially of a thin notch of a specltio shape, which the water Is caused to flow over. Tho amount of flow depends de-pends upon the depth of water llow ng over the crest, as the bottom off the notch Is called. The weir ba been used for the measurement of water for hundreds of years and thu method of its Installation and th illscharge of water can be measured owr It with an error of less than onu per cent, if care is used. -t There are several forms of welrs, the came of each designing designi-ng the shape of the notch. Cippo ettl, an Italian engineer, evolved, md perfected the weir which beavra lis name, many years ago, this Ai ng tho weir that Is now most gener-illy gener-illy used In the west. Weir Ilox. In order to maintain he weir In a proper nnd constant losltlon and to prevent leakage iround nnd under It, and In order hat all water that Is to be measured liou'd be conducted over It. It Is isuaily necessary to construct some tort of box or frame to hold tho I'clr In place. A common form ot' ypo of this box which Is reenm-nended reenm-nended for a one foot Cippoletti lelr Is nine feet long, two and a half eet deep and three feet wide Inside, iieasurement, and with a one foot relr will mensure with accuracy mounts ranging from ten to fifcy. ilaho miner's) Inches. Where a weir box Is built. It Is nee-sMary nee-sMary that It bo made of suffarlent ize and depth In comparison to the i,e of the weir notch to eliminate 11 excess velocity of Approach. If he box Is built too niirrow or too hallow It will add to the velocity of ppmach to such an extent that cored cor-ed measurement can not be se-ured. se-ured. It Is but a mere matter of onvenlence, however, to have a box f the exact length prescribed, for tiat part of the box above the weir iay be omitted If a settling basin or ool of the same size Is constructed, i the ditch above the weir. Tho elr boxes and pools which should e constructed for weirs of larger les should be In the same .propor-on .propor-on with respect to the size of the 'elr as for the one foot. The rh.a f weir box that Is required In w-h. eliminate v .! - jr .soproiynouldef. een fotid, fr i truer. 'E, to t went, j roxlmately seven times the Yii-Xi, pet Ion of the weir notch. , Illscharge. The discharge of weirs as been accurately calculated by j arlous engineers who have carried n hundreds of experiments, cover-ig cover-ig years of time, and It Is found j int under like conditions the same ' epth always produces the same dls- I liarge over the same size of a weir. I he conditions given for the con- 1 ruction and Installation of weirs tust be rigidly adhered to, however. accurate measurement Is to be iade. The formula which has been solved and which gives the dts-large dts-large of accurately constructed ' Ippolettl weirs Is 1 Q equals 3,307 L II 3 2. 1 Where Q equals the number of eu- c ft per second. L equals the ' ngth of crest In feet and II equals ie depth of water on the crest In 4 ct, provided the same hi measured t otii a K)lnt level with the crest and t i stream from It at a distance euual ; ' the length of the crest. r 1. The weir box should be set wltij a n floor even with the iKittom of the tch and should be level In all dlrec-mis. dlrec-mis. The weir Itself should be ex-tly ex-tly level and perpendicular. 2. The channel leading to the weir J1 lould be of uniform eros section, or hat Is still better, should gradually ilargo as the weir Is approached, t he axis of the stream should pass t rough the welr and perpendicular t i it: or. In other words, the welr lould be located at right angles to p i middle of the stream. The ad-inclng ad-inclng stream should be free front ternal cross currents or eddiew, as iese have an Influence upon the dis- 11 large. 3. The water should lie brought as II 'iirly as possible to a state of rest n ore It enters the welr. An excess a locity of approach due to the ve- city of the advancing current will af- t, ct (Increase) the discharge more i.'in almost any other one thing. . his velocity can be reduced by wid ilng and deepening the box or pool ove the weir. It is calculated that e eirs thre" feet long with a depth of n ater of twelve Incbe. should not ive a greater velocity of approach 1 tl ian six inches r second, which s mount nny be allowed to Increaw ry slightly where greater depths rer wider weirs are used. I!y ron- c ru'ting the Ux or jxsd aboVe the 0 eir with a cross section at least ven times that of the welr notch, a P ifflcietitly low velocity of approach usually secured. n (To lw Continued ) P tl |