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Show Duty and Measurement of Water By DON H. BARK, U. 8. Engineer,; In Charge of Irrigation Investigations Investi-gations In Idaho. j Oregon Fbort Line Railroad Demonstration Dem-onstration Train Lecture. I (Continued from latt week) 4. The Issuing utream of water must have full contraction; that la, it must be sharp and clear cut. This is brought about by making the upstream up-stream edge of the weir board as nearly a knife edge as pontile, ami by keeping the sides and bottom of the box below the weir at a good distance dis-tance from the falling stream so that the air may puss freely clear around and In under the lsulng stream. The water below the weir should never l allowed to back up to the level of the crest so as to exclude the air from tinder the Issuing stream, elm , complete contraction will not be re-cured re-cured and the discharge will be affect i ed. If air can pass freely underneath the Issuing atreara the level of the water below the weir has no Influence j on the discharge. An observance of i the following rules will usually In-1 1 ure complete contraction. j a. The opening of the weir or the weir notch must be made In a plane;1 surface perpendicular to the direction 1 of the flow of water. ( b. The opening Itself must have a , sharp edge on the upstream side and t the walls should be beveled away on i the downetream side. i c. The dlstanre of the crest of the f weir from the bottom of ihe box or J basin should be at least three times the depth" of the water on the crest. d. The distance of the aides of the ( weir notch from the sides of the box or channel should be at leant twice as great as the depth of the water , flowing over the crest. s e. tn order that the lateral con- I traction should not be disturbed the ' length of the weir crest should be " aroxlmntely three times that of the depth of water flowing over It. I, r . The depth of water flowing over j, UlC we,r should not bo less than two nr-hes, nor more than onelhird, of the v lenijih of the cTrest, and it should be measured where It will not be affect ed by waves, wind or eddies, and far s ' enough up stream so that It will not be influenced by the curvature In 1 duced by the falling water. Thi run ' hot be done by measuring it exactly i'; over the crest. The distance above ' the crest which Is usually found suffl- dent. Is up stream from the crest a " distance equal to the length of the t crest. a-. ' he Cff frequent cause of rrj ( weir measurements is exewes ty of approach and this must be c guarded against by providing a good ( lied pool above the weirs which t must be kept clean and free from c sediment , c "Don'ts" In Regard to Weirs. ' 1. I)o not set a weir Immediately below a curve in the ditch, for the " curve will cause the water to flow to the side of Ihe crest 2. IV) not set It Immediately below or too close to a head gate where the water has high velocity, as by so do- , ing. It will cause too high a veUxlty ( ef approach. 3. lon't allow the water below the f weir to back up even with the rrent , as It will not allow complete contrac , toln and will cut down the disc harge. 4. IH not set the weir any other way than perpendicular and at rlsht angles to the flow of the stream. 5. Do not attempt to use too small a weir. Put In a larger weir where ' the water to be nvanureri exceed a K depth on the crest f 1 3 the crest !' length. " 6. Do not allow the ikI above the J weir to fill up with sediment, a the ' resulting decrease In the cross see- " tion will increase the velocity of ap- proach. v 1. The weir box should be set with ' Its floor even with the bottom of the " Duty of Water. j To know the proper amount of lr- s ligation water that should be applied p to the different soils and crops In or- w der to make the greatest possible p yield, ha always been, a serlotm prob- n lent to all Irrigator. It ha always a been known that in order to secure A the biggest poaHlhle crop it I neces tl ary to apply different amounts to r different crops and to different soil n with the same crop, but Just how -murh thi amount should be has never d been known only tn an Indefinite way. a The IrritHtlnn Investigations d- I. partment, which I represent In the tl state of Idaho, has. In cooperation j al with the state engineer's office, been oi carrying on a series of experiment , lr for the pat two year by means of! pi which it Is hoped to determine thlsjtl very Important factor, and we have1 secured a vast amount of data eon-itl cernlng It. Theae experiments havejh; all been carried out on comparatively I a: large areae and In a prartlcHl way. If, It does not give any Indication of ni how much water I necegary for t maximum crop production on any o soil to merely measure the amount p that some farmer applies for the rea rl son that the same or a larger crop ti miKht have been produced wilh either , more or less water than that which i was really used, so we have been try Ing to woik out this feature by select ling a large number of tract on typl caJ farms In different parts of Idahc 'and then divide each tract Into three different parts and apply different amouats of water to each one. Water I was measured and varied In this manner man-ner on sixty different farms durlnif 1 1910 and on as many more during the !past season. Several factors In regard to the use of water have been very strongly emphasized, the principal ones being that the amount or water ! required depend uon: (II The Character of the soil and subsoil. The texture of the soil as regards poro-eity poro-eity hits more to do with the amount of water used than any other one thing and It has been found that adobe doIIm may be Irrigated with a total application of but two or three acre Inches while in some Instance from one to two acre feet are re quired to spread over and thoroughly Irrigate an acre of very gravelly soil. At IcHHt 2 3 of this latter amount la almost invariably wasted as It either passes Into the ground water or percolates per-colates beyond the reach of the plant roof. If coarse soil Is underlaid with an Impervious stratum, the amount of water necessary I ma terlally cut down, while if the imper vlous stratum la lacking, some lrriga Hon system must be used which will flood the ground quickly before the water has time to penetrate too deeply deep-ly If a high duty I to be secured. (2) Climatic Condition. The annual an-nual precipitation and Its seasonal distribution, together with the temper ture, humidity and wind movement, ill have a very evident effect upon :he amount of water required. (3i Diversification of Knrm Tops. Where a farm I all devoted o one crop sifh a grain, hay or po-atoeK, po-atoeK, the greatest need for water lstiiilly falls within a comparatively ihort time, and there Is but lltMf use or It during the rest of the season, hlle by diversifying his crop, the 'armer'a need for water will be more or.Htant and be I better ablu to nake good we of a continuous flow f the ditch throughout the season. (4) I'se of Rotation It Is well mown to most irrigator that little an be accomplished by Irlgating with inall Jicads 0f water, and a much arger and U-fter use Is secured from he water where larger head can be ised. Rotation systems, by mean of thich a farmer can exchange water vlt h his neighbor and use larger leads for shorter periods, are now clng used with success In many l iOitie and the saving of water is ery material. (5) Preparation of the Land .laxlmutn crop production can rtof be 1 ecured without a uniform wetting of he soil and this I impossible If the and is not properly prepared and eveled for Irrigation. Hough, uneven and, It Is plain to see. requires more vater than smooth land, for it ha to e held on the land long enough to oak up the high pots. Careful prep-irution prep-irution of the land Is an abaolute lecessity If the best uo Is to be se-uid se-uid from the water. (61 Kind of crop grown whether 'tiltivated or non cultivated and length f season that it need water have a 'ery direct bearing upon the amount if water that will be required by the rop. Spring grain, on account of heir short season of growth, requires onslderably less water than a'Jalfa, t-hlch grows from early eprlng until ate fall. Winter grains, all other blngs being equal, require les Irrl allon water than spring grain, be ause of their ability to utilize more f the moisture !eKited In the soil torn winter precipitation. A cop bat can be cultivated will need con Iderably lens water than a non-cult! ated one, because of the great waving hat can be marit by the reduction ol lie evaporation through cultivation. It Is as easy to apply too much rater as It Is to apply too tittle, and ; very bit harmful. The expert-tent expert-tent carried on this year at C.ood ig show up the results of over-lrri ation very clearly. We had twenty-tie twenty-tie different plot of wheat cotiBlHt-ig cotiBlHt-ig of three varieties of seven ptoU ach. These were planted and hand-d hand-d In exactly the same manner ex ' ept that different amount of watei ere applied to each plot, all thre arietles being handled alike as a heek one upon another. The watei pplled to each of the three serlca ol lot was varied all the way from of lil tit? upon the first plot of estcb crhtt, to an average depth of ap roxlmat'iy two and a half feet here the greatest amount was spiled. sp-iled. With the dry farming where 0 water was appried. the yield wa 1 proximately I .boo iKxmd per acre the amount of water was Increased lie yield a I ho Increased until the plot , iM'ciiinr an application of approxl- ( lately 1.7 feet made a yield of 1.800 i mind per acre, after which the yield ecreased rapidly until the plot re , flvlng an application of from 1 6 to I 7 feet yielded lewi on the average , isn that which reived no water at i tl. This show strikingly the eff-ct f over Irrigation on wheat and show J 1 (1 (I it Ion. as do all of the other ex i erlments that we have carried on. ' tat sprinir grain do r.ot rerulr inch water. Alfalfa and clover i irountiout all of the experimentf ' ave responded to the use of larger mount of water and have been mnd to require fully f.O per cent lore than grain. The one thing that ' a been emphaslxed throughout all I f the ex perlment I that careful reparation of the ground for the lr-gation, lr-gation, at the outset, pay la rite re-irns re-irns upon the amount of money In-ested. |