| Show I L HOW TO CONSTRUCT RESERVOIRS 1 ne Reservoirs built in the beds of I streams or other depressions are used mainly for Irrigation purposes The dam may be of e earth rth loose rock timber concrete or masonry or combinations combinations combinations com com- of two or or more of these I However since on the large majority of at I sites earth Is the most abundant and cheapest material available Q It has I been used chiefly The perc percentage of failure of dams lImns of this tn type e has been large The main causes have ha been 1 faulty and an inadequate quate waste ys 2 porous earthen embankments not properly compacted and 3 insecure foundations Examination for Foundation When the tile location for fOI the dam has been decided upon a careful examination examination examina examina- tion of the time foundation should be made malle I Test pits should be sunk at Intervals across the stream bed bell or depression and If rock or other Impervious material material material ma ma- is found near the surface the themore themore themore more porous top covering should be removed removed re re- re moved movell and foundation laid on the Impervious impervious Im hn im- im pervious substratum In any event all aU shrubbery sod and decayed vegetable matter should be bo cleared away b before before be be- fore the dam Is begun In the time better better bet bet- ter class s of such dams a a n narrow tre trench ch chI I L most part In the beds of at streams Breams and andIn andin In the time direct line of flood fl flow flow V nrc are subjected subjected sub sub- at times to high water which may carry floating driftwood Or other debris The overflow dam is designed ned to withstand such severe severo tests lint hut the dam dum considered here Is not of this this type trpe It Is intended elI only to Impound water to a n certain safe height and to pass by-pass all surplus waters through the This throws a heavy burden burden bur hur den upon this structure In times of or flood and It should be of such strength and capacity as ns to perform Its part purt without danger to the dam In making ranking rank milk ing provision for a should it-should be borne In mind that a n. flood may mar occur occur oc oc- oc cur when the reservoir Is full fuJI so that the entire flow of the stream must pass through the Consideration Consideration Consider Consider- aU on also should be given to obstructions obstructions to the flow of water caused by driftwood and clogging by fish screens Such features of ot this type of reservoir reservoir reservoir reser reser- voir as inlet and outlet pipes slope protection and the time like mec have o been dis cussed in Farmers Farmers' Bulletin No 8 8 Commonly Used Method In Tn the early days of mining mining-in In Ca California Cali l. l fornia someone evolved the Idea o of ot washing down the gold gold bearing sand t i I r I Ir r r so Shaped V-Shaped Flume Used in Sluicing Is dug beneath the time center of the embankment em em- down n to bedrock or other I good material and a wall of concrete known as a n rim core wall Is built ther therein ln This wall projects above the I surface and serves a purpose similar to a tongue In grooved and nue lumber Joints A clay puddle may may- maybe be I substituted where a concrete core wall around the rim would prove to ex- ex I pensive In this case a n much wider trench should be dug ug filled with the best material available and carefully and rammed Packing Materials In building n a reservoir embankment I of ot earth many farmers and not a few fw engineers fall to un understand the time difference difference differ differ- I ence between an embankment capa capa- bJ of at withstanding a load lond such as i is I placed upon It by the passage of a locomotive c and one compact and stable stahl enough to hold water In highway amt ami railroad fills little If any on attention I Is paid to packing materials hut but In the time case of at earth fills to retain water is necessary Experience has I shown that one of at the best to pack ordinary dirt which does not con con- con I i I 2 Recta g lar- lar Flume lain tain too much clay Is to dump It Into I water and let nature do the packing When this method meth d Is not feasible the j I earth should be placed on the embankment em em- In thin layers and ea each l lay layer er moistened moistened- r or other compacted In In some cases the earth can be mol moistened before It Is removed remo trout from Its natural site Cause of of r Failure As has hns been stated a frequent cause of or failure of or such dams is faulty waste waste- ways Time The dams being h built fa for the b. b by means of ot powerful streams of water water wa wa- tva- tva ter directed against the banks and hillside hill hill- sl side side This pra practice has been Improved Im lit- proved pro and extended and now is Isa a come used method of building e earthen n embankments and of loosening and trans transferring earthy material for fOl other purposes In making making- use of at this method an nn ample supply of water Is necessary What Is called the cutting stream Is under high pressure from Cram GO CO to pounds per pel square Inch The The pressure may be obtained by gravity fall CaU or by hy pumping and the water Is conveyed to the material to be excavated rated In a n pressure pipe of suitable diameter The end of the pressure pipe terminates In a n giant from which a n stream Is directed against the bank of dirt A large stream of ot water water wa wa- ter tel but under minder little or no pressure then Is added to the former stream to carry the material loosened by hy the giant Into a n flume or pipe In which ItIs It ItIs Itis Is transported transporte to the dam lIam Figs 1 and 2 show two forms of wooden flume used for this purpose The gla grade e on which they thy are laid should be as os steep as practicable and never no less than about five per cent Under Under- favorable conditions material can I be be- e placed In a dam by this process at a t lower cost per cubic yard ar than by hy the use of at teams and scrapers or teams and wagons Such embankments are also more compact and watertight water ht th than those ordinary or n y methods |
