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Show Duty and Measurement of Water y DON M. BARK. U. S. Engineer, In Charge of Irrigation Inveitl-gatlona Inveitl-gatlona In Idaho. Orecon Short I.lne Itallroad IVm-natratlon IVm-natratlon Train lxvture. The rreater part of the land In the iri'.t would he prnetlriilly wnrihlea. wlthoul water with whl.h to Irritate It. yei Ihere la far leaa atienilon given to thn ineaa.irement of tin. water than there I. lo the .m anure tnent of the land. I'mler Hie fi.rey Aet the land I. anM to Hie aeiiler for r,i ienl per iurp and would hardly lie worth thai without the water, while water roata the aettler I all the way from .T, in $no ,, r ajTe. Miner'a Inch. Wnlnr wna Ural uaiil In Idaho mid other wealern atalea for mining pur poaee, the common method of men. urp.np.it being railed Hip miner'a Inch method. The miner a Inch waa the unit upon which audi niPiK.ire Dienl waa baaed, l.iiK the umouiit of water thai would flow through a ahnrp edged orifice one Inch aipiare under a given preaaure. The quantity quan-tity railed for by a mlnpra Inch, however, varied In different aiatea due to the fact thnt tho preaaure over tho orifice waa not the aaine. Cubic Foot Per Second. The cubic- foot ppr aecond, which repreaenta a definite tangible atnounl that la eaally underatnod, waa adopt-ed adopt-ed aa the legal atnudard for the meaaureinent of water by the Idaho leglalature In lM. It la commonly known aa the) "aecond foul" and rep reaenta the flow of water which will eiactly ml a veaael romnlnliiK one cubic foot each aecond of time for aa long a period na It la allowed to I flow. Hence, a flow of one ruble fool per aecond deliver CO ruble feet per minute, or 3 ".'") cubic feet per hour, or mi.ttio cubic feet In a day of twenty. four hour.. It la found thnt one ruble foot per econd equal, a flow of nlmoat exactly KO Idaho miner'a Inchea, or 4",0 gallon, per minute. A flume one fool wide and one foot deep. If filled with water that la flowing at tho rule of exactly one foot per econd, will rnrry one I cubic foot per aecoinl, nml otner fluniea or dlichea In the nine proportion. propor-tion. Tho quantity discharged do-penda do-penda upon the velocity of the flow and the area of croaa aectlon of the advancing atrenin vt water. Thc.e two fartora are taken Into conalder-atlon conalder-atlon when determining the flow of large atreama and ranala, It being only neceaaiiry to determine the area of the croaa sect Ion and Hie average velocity, whlc'j two amount mtilil-PIIimI mtilil-PIIimI together give the discharge. The croaa section la found by multiplying multi-plying the average depth of the stream by the width. The average velocity la found by mcaaurliig the rale of the same either with floats or with a current meter especially constructed for the purpose. A close approximation of the velocity can be "cured by noting tho time that Is required for a surface float to advance ad-vance through lot) or more lineal feet of the ditch. This gives tho sur face veloclly, and to find the average velocity one must multiply the ur-lace ur-lace velocity by .8, alnce tho average aver-age veloclly la that much slower than the aurfaco velocity, owing lo tho friction on Hie sides and button, of the channel. Acre Foot. Where lurge volumes of water are to be considered the expression of the amount In ruhlo feet would Involve In-volve the use of such law; numbers that the same would be cumboreome. In order to simplify those exprea Ion the term acre-foot" la uaini, which representa enough water to cover an aero one foot In depth, or 4:i.r,60 cubic feet. The use of thla term has tho addltloi.nl advanluge of being easily compared with thn acreage; acre-age; aa for example, a reaervnlr containing con-taining (io.oiiO acre feet of water would furnish depth of two feel for 2.-I.0UU acre of land A cubic foot of water per second flowing continuously con-tinuously for twenty-four hours fur-nlahes fur-nlahes utmost exactly two acre feet of wuter. Hydraulic Equivalent Which Will b Found Useful to Irrigators. 1. Idaho miller's Inrh equals approximately ap-proximately i.Rti or a cubic foot per secu.nl, or nine gallona per minute. 2. The flow of a cubic, foot per econd rquula approximately Ml miner'a min-er'a Inchea, or 4."0 gallons per minute. min-ute. 3. One cuhlc foot per rocond for 24 hours iquuls approximately 2 acre feet. 4. One ncre foot equals enough water to cover un acre exactly foot In dopth, or 43.r,iiO cubic feel. r,. One miner'a Inrh pet acre for 100 duya equals 3 97 feet deep on the land. ! .. 1. I . One miner's Inch per re fn 1 1'.,) days equals ! .". feet deep on land. 7. Klve eighths miner'. Inrh f ncrx fur 10 i days equals 2 4S it deep on the land. S I'lte-elgliths miner's Inch ) acre for l.'iO day. equals 172 Irs deep on the lnnd I One half miner's Inch per sjf for leu days equal 1 IIH feet iIitih tlm land. I 10 Onehslf miners Inch per it' for l.,0 days equals 2 MS feet deeu 4 the laud. i Weirs and Weir Measurements Tho moat nccu.a'e. practical i I economical method of water tiuvv ureme.it that liua 1 n deviaed If ! the meaBurcment or coinparatifcf Mm, II heaila of water I. the (Ve ; menaiirenieiit. The wetr cnnalat .aetitlally of a Ihlu notch of a ap.-ci' ahnp... which the water la caiiBi i flow o.-r The nninunl of Howl" pcud iiM,n the depth of water m UK over the cteal, as the In, tlm ' the notch la called. Thn weir lb Iteen used fur Hie ii.eaureme.ill ' water for hundred, of years and.a method of Its inalallnllim'. and i diachargn of water can bo meaHfal over It with an error of leaa tinniest per cent. If care la used. f Thprn nm several form, of . Hi" inline of each dealfirV lug the shape of the notch. ( Ip lettl, n Italian engineer. ev4a and perfected the weir which isprs hi. name, many ypara ago, this In the weir that la now most g!" ally liaed In the wet. i Weir lint -lii order to nialan the weir In a proper nnd rotitt position nnd to prevent leij' around and under It. and In MT that nil water that I. In bp meak"' abouM be conducted over It, Ills uaua.ly neceaaiiry to ron.tnict efln sort of box or frame to hold I n weir In place. A common fornf type of this box which la rsjrari'1 mended for a one foot Clpiay"1 weir la nine feet long, two and iuu.lt feet deep nnd three feet wide I sat, measurement, nnd with ft one 'sot weir will menstire with ae, rvy nmotints rnnglng from ten to H'J Idaho miner' Inches. Where a weir box Is built. It Id tec enaury that II In made of euftlrtenl site and depth In comparison tU't aire of tho weir notch to elliiliaH nil excess velocity of approach II the box la built too narrow of toe ahallow ll will add to the vcloi h of appronch to such an extent that cor reel meaaiirettient rnn not bo e cured. It Is but n mere matter i convenience, however, to have g not of the exact length prescribed, fnf that part of the box libove thn well may lie omitted If a settling bnsla or laiol of the same slrn Is const rtrl.a In Hi" ditch nlxivn the weir. 1 Tin weir lioxes nnd pools which ahouM lw ennatrneted for weirs of b,r sixes should be In Hip same iiropor Hon with rosppcl to the sire al Ha weir aa for the one foot. Tlif sin of weir box that la required In orde lo eliminate velocity of nppron)t( been found, by exppriuipnt, to be proximately seven times the trost section of the weir notch. Dlschnrge. The discharge of erj has linen acciirntely calculated by varloua engineers who have rirrlial on hundreds of exiiprlmenls, rover log ypara of time, nnd It Is lout thai under like conditions the lamt depth alwnya produces the same die ehurge over the aame slr.o of a well The conditions given for th rot-al rot-al ruction and Installation of vein must be rigidly adhered to, however. If Bcctirnin measurement Is to ke made. The formula which has been evolved and which gives the discharge dis-charge of accurately ronatnrted Clppolpltl wnlra la Q equal. 3.3I-.7 I. II 3 2. Where Q equals the number at ruble ru-ble feet per aecond, I. equals the length or crest In feet and II etuals the depth or water on the crett In feet, provided I ho same ! meuured from a point level with the crest and up stream from It nt a distance Mual to the length of the rrest 1. The wen Ikk should be eel wit j Its floor even with thn bottom ot the dlteh and should bo level In all 4lroe. Hon a. The wolr Haelf should at eg. actly level and perpendicular. 2. Thn channel lending to thswelr should be of uniform croae si'etkn, or what la atlll bettor, should gradually enlarge aa thn weir la a, profiled. The axla or the at renin should pasa through the weir and pprpendlrular lo It; or, In other words, the lr should bn located at right anelts to thn middle or the stream. Tbe advancing ad-vancing stream shosjd be free front Intprnal cross ri.rre.i.a or eddlei, aa these huvo on Influence iiam tin die-charge. die-charge. II. Tho wnler should be hrouxht aa nearly a possible to a stale of rest beore ll enters the weir. An eieeea velocity of approach due to tbe velocity ve-locity of the advancing current will affect af-fect tlncrcntte) tho discharge mora than almost any other one thing. Thla velocity can be reduced by wld piling nnd deepening the box or pool uIkivo Hip weir. It la calculated that weir Hi roe feel long with a depth of water of twelve Hirliea, should not havo a greater velocity of approach than six inches per second, which amount may be allowed to Increase very slightly where greater depths over wider weir are used. 11 constructing con-structing the box or ko nhov the weir with a cross section at least seven times that of the weir notch, a sufficiently low velocity of aproacb la usually secured. (To Imj Continued) |