208 IRRIGATION IN THE SOUTHWEST. 



THE SWEETWATER DAM. 



In 1887-88 the Sweetwater dam was constructed, on the Sweetwater 

 river, twelve miles southeast of San Diego, on a stream from which 

 no irrigation was possible prior to the erection of the dam, because 

 of the fact that it was generally dry every year after June 1st. The 

 dam is built of masonry, founded on porphyry bedrock, at a point seven 

 miles inland from the bay of San Diego, at an elevation of 140 feet 

 above tide. The height is nearly 100 feet; length, 150 feet at base, 350 

 feet at top; arched up stream similarly to the Bear Valley dam, but of 

 much heavier section, being 46 feet thick at bottom and 12 feet at top. 



The reservoir had an original capacity of 18,000 acre-feet, en- 

 larged in 1896 to 22,866 acre-feet, and is fed from the run-off of 186 

 square miles of watershed, whose extreme elevation is about 6,500 feet. 

 The mean annual run-off from 1888 to 1896 ranged from 1,007 to 70,625 

 acre-feet, averaging 18,708 acre-feet. The drought of the past two 

 years has failed to replenish the reservoir, and its supply in the sum- 

 • mer of 1899 is quite exhausted, and reliance is had upon water pumped 

 from wells. 



From the dam water is conveyed and distributed through iron 

 pipes, over an area exceeding 5,000 acres, planted chiefly to lemon 

 orchards. The cost of the dam and distribution system has exceeded 

 ?1, 000, 000, but it has added many millions to the wealth of the county. 

 Ir is a striking illustration of pure development of water from a 

 stream that had been useless and valueless without the reservoir. 



THE CUYAMACA RESERVOIR. 



A similar case of the conversion of a useless stream into one of 

 usefulness and value is that of the Cuyamaca reservoir, built in 1887 

 by the San Diego Flume Company, for the irrigation of mesa lands 

 lying east of San Diego, and the supply of the city of San Diego. 

 This reservoir is located in the Cuyamaca mountains, at an elevation 

 of 4,500 feet above sea level. It is formed by an earth dam, 41.5 feet 

 high, and has a maximum capacity of 11,410 acre-feet, covering 959 

 acres of surface. It has a tributary watershed of but 11 square miles, 

 which greatly restricts the usefulness of what would otherwise be a 

 very valuable reservoir. Up to 1896 the minimum annual catchment 

 was 1,158 acre-feet, the maximum 11,464 acre-feet, and the mean 5,397 

 acre-feet. The evaporation loss was a mean annual depth of 4.73 feet, 

 amounting to 25.5 per cent, of all the catchment entering the reservoir. 



The area irrigated by the reservoir prior to 1898 is given at 5,700 



