gate, in order that the gate may be lifted. In construction the gate is most simple, any carpenter or farmer

being able to build one. A tightfitting slide over the end of the box or pipe outlet is all that is necessary to shut off the water. The gate may be raised or lowered by a stick of 2x4 bolted to the front of the gate and leading up through slides or guide holes in the end of the walk. Simple means may be provided for fastening the gate either up or down. The pressure of the water against the gate will keep it in position and preserve a tight joint if the sliding surfaces have been properly dressed or surfaced. Grooves should be provided in the sliding supports so as to make sure that the gate will return to its seat when it is desired to lower it. Modifications of detail are many and will suggest themselves to any one as the conditions of the work or the setting may require. One of these is a cast-iron lift gate working in an iron frame with grooves, as seen in Fig

ure 16.

FIG. 16. IRON OUTLET GATE. Evaporation and Seepage. -Evaporation is greatest during warm or windy weather, greater in shallow than in greater in running. than in still water. of a canal during June, July and exceed three to four inches a day.

deep water and The evaporation August will rarely During the remain

ing months the average will be about one inch, making for the year from three to five feet of loss by evaporation. To the loss in this must be added the loss by seepage or filtration either into the earth or through the banks. The amount of seepage through the banks will depend not only upon the character of the soil of which they are made but also upon the solidity with which they are thrown up. So with seepage into the earth. If the soil is of soft loam, sand or gravel the percentage of loss will be greater than if the subsoil be of clay or hardpan. Careful measurements made in a number of cases show that with canals having a good grade and not more than ten to fifteen miles in length, nearly fifty per cent of the water diverted into them at the head is lost before the point of distribution is reached. The matter of filtration or seepage will be dwelt upon more fully later on in this work, as it bears upon irrigation systems other than that of canals.

Cementing Canals.—Seepage loss may be almost obviated by cementing the bottoms and sides of canals, and in very sandy or gravelly soils this measure becomes absolutely imperative. At first most of this work was done by lining the surface with stones, usually cobbles or small bowlders with faces roughly smoothed, and then plastering cement over thera and filling all the interstices. This has been done with very many large canals in the southern part of California, and as may be imagined, it is a very expensive process, especially when the canals are very long and remote from the sources of supply of the stone needed. In California, however, where some of the most expensive stone and cement lining has been done in the past, it has been found that just as good work can be done and effective results obtained without the use of stone and with only a thin crust of cement. The method followed is first to completely saturate the bottom and sides of the canal, which settles the earth thor

oughly in place, and then the coating of Portland or hydraulic cement is put on with a thickness of three-quarters of an inch. It has been found that this layer is durable and abundantly able to withstand all the strain that will be put upon it. The cement is mixed with clean sand in the proportion of one barrel of the former to four barrels of the latter. For a canal carrying 3500 cubic inches of water, with a bottom eight feet wide and sides four feet high, it requires 2000 barrels of cement for seven miles of length. The work of laying the cement is done very rapidly and thoroughly. Along the edge of the canal a small pipe is laid, through which a steam pump forces the water which is used in keeping the earth wet and in mixing the mortar. At regular intervals are placed piles of sand and barrels of cement. A mixing box on wheels with a trough running down into the canal is run on the top of the bank, and the plasterers take from this and cement the sides. This is moved along as fast as needed, thus saving the use of wheelbarrows. Following comes another mixing box on wheels in the bottom of the canal and from this the mortar is taken to cement the bottom. The work should be allowed to stand for a time so as to thoroughly dry before water is turned in.

Building the Laterals.-In constructing the supply laterals leading from the main canal to the farm, the walls should be built up so that the bottom of the lateral may be higher than the surface of the ground. This is vital to the economic use of water. The laterals can be constructed in the loose soil on the farm for the reason that the water is desired to soak into the ground. The laterals may be changed every time water is put on the land, for the reason that always as soon as possible after irrigating, the ground should be cultivated, thus obliterating the lateral and preventing the soil from baking. There is nothing so good in the long run for building

ditch laterals as the common plow and scraper. Make the ditch bottom as wide as the scraper even for the small laterals, if they are to be permanent. The first plowing should be at least three times as wide as the finished ditch, so the earth may be thoroughly broken up and no smooth or grass-covered surface left for the bank to rest upon. On a sidehill the plowing should extend well down the lower side. Under an extensive canal system a water consumer's land may lie a mile or two distant from the main ditch. In a case of this kind the laterals

must be of a permanent character. This work may require as much skill and judgment as the construction of the canal itself, and should be well done. When the ditch is completed let a very little water in for the first few days and shut it off every afternoon. The high embankments will settle and are reasonably sure to crack, and the earth must then be tamped into the cracks. The ends of flumes will need tamping and puddling. The coarse gravel in the banks will leak like a sieve and will require many a shovelful of fine earth to fill up the interstices. In a few weeks, however, all will be settled in place.

CHAPTER VII.

RESERVOIRS AND PONDS.

The fortunate irrigator who has a reservoir of his own has his water supply constantly on tap-the reservoir may also appropriately be called the farmer's savings bank. An irrigation system depending upon storage, when the storage works are judiciously constructed, is the most reliable of all. The reservoirs can hold the waters of a wet year for use in a dry one, and in the possible sequence of several dry years the smaller stored supply gives several months' warning to irrigators, so that water can be husbanded and made to perform a larger duty than usual in order to tide over a period of scarcity.

The problem of water storage for irrigation is a very different one from that for the domestic supply of a city. In the first place it is important that water for domestic use be as nearly as possible free from mud and organic impurities, while for irrigation such impurities are not only no objection to the water but often materially add to its value by enriching the soil to which it is applied. Waters held in reservoirs and intended for irrigation purposes are often rendered much warmer than the flowing waters of streams, and are therefore more beneficial to plant growth when drawn off and applied. The reservoirs must also be credited with having a salutary effect on the atmosphere of the arid region, and countless numbers of them scattered here and there over the lands would greatly increase the humidity, and bring about a marked meteorological change for the better. In Western