THE IRRIGATION AGE. 



349 



mountain earthen dams were insufficient 

 to hold back the water, when the soil be. 

 came thoroughly soaked. The mountain 

 reservoirs constructed in natural draws or 

 basins seldom leak, and the evaporation is 

 not so great as in the valleys, but they 

 should be puddled with clay to insure an 

 impervious bottom. 



The reservoir should be so located as to 

 be filled and emptied easily and cheaply, 

 and if on the farm, ought to be at the high- 

 est point obtainable. Under ordinary cir- 

 cumstances, where less than 1,000 acres 

 are to be irrigated, the reservoir should be 

 round or elliptical, to prevent cutting the 

 banks and filling with earth from erosion, 

 and occupy a space of two to ten acres. 



to prevent an overflow from the tides of 

 the ocean. 



A wooden flume, pipe or culvert built in 

 the wall at the proper height, makes the 

 best outlet for a reservoir, while a similar 

 device may be used for an overflow. The 

 gate can be made of iron or wood and so 

 constructed as to be quickly lifted or put 

 down by a handle extending above the 

 water. The mains for conveying water to 

 the fields may be mere open ditches, cut or 

 plowed on a line admitting of a fall of four 

 feet or more per mile. This should vary 

 with the nature of the soil, the gravelly 

 surface having greater and the sandy less 

 fall per rod, depending on the extent the 

 surface will wash. Water may be con- 



RESERVOIR WITH FURROW, FLOODING AND SEEPAGE IRRIGATION. 



The greater the depth of water the less 

 evaporation, and the smaller the space the 

 less destruction from waves, but deep 

 reservoirs require strong, well constructed 

 dams, and are more dangerous than the 

 shallow enclosures. A bank seven feet 

 high should be about thirty feet on the 

 bottom, with a slope of two feet on the in- 

 side, one foot on the outside and four feet 

 or more in width at the top. The banks 

 should be covered with trees, willows or 

 grass to prevent washing, and the reser- 

 voir fenced to keep away cattle and sheep. 

 One of the best soil retainers and some- 

 thing that ought to be planted on every 

 reservoir and ditch bank is the marram 

 grass used on the sand dunes of the coast 



veyed in wooden boxes, V shaped flumes 

 or clay pipes, from the reservoir to the 

 field of distribution with greater economy 

 than by using open ditches, if the farmer 

 has sufficient capital to put in these im- 

 proved conveniences. If a swale must be 

 crossed with the main, a good plan is to 

 throw up a grade, similar to a roadbed, 

 and when thoroughly settled cut a ditch 

 through the center. An elevated flume is 

 frequently better and cheaper than throw- 

 ing up a grade, and is the only plan for 

 crossing a canyon or ditch, except con- 

 structing a gravity canal for some distance 

 up and down the mountain slope. 



Laterals are made to run parallel with 

 the main, and each cut in the canal draws 



