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50 WATER RESOURCES OP CALIFORNIA. M P A C IF IC C O A S T D R A IN A G E B A SIN S— S A N T A B A R B A R A C H A N N E L T O M E X IC A N BORDER. Southward from Santa Barbara Channel skirting the coast and on the Pacific slope of the Southern California mountains, lie 2,300,000 acres of fertile soils. These lie in the valleys of streams draining into the Pacific Ocean that are less separated by mountains than the valleys northward from the Santa Barbara Channel and form an almost con­tinuous body o f agricultural land. Although several large streams traverse portions of this area, the total waters are hardly sufficient to cover the arable lands to half a foot in depth in the average year. Their flow is- erratic and would require much storage capacity for their com­plete development for irrigation use. Reservoir sites are few in number and dams expensive. • However, it is found that the water supply can be perfected on a large part of the 759,000 acres now irrigated and perhaps 250,000 additional acres be brought under water. Under the comprehensive plan, surface reservoirs would be con­structed and largely used for the temporary detention of the waters in the streams that they might he released in a more or less uniform flow for spreading over gravel beds. Excepting in the southern areas of this region, there are coarse alluvial fills that have1 a large water-holding capacity and easily yield their contained waters to wells sunk into their depths. Waters spread on the gravel beds of these valley fills would be absorbed to join the subterranean waters of these basins. Severed from contact with the atmosphere, these waters would he held in storage in the porous substrata without loss by evaporation and would be available as needed through pumping from wells. B y combining surface and underground storage in a coordinated plan, the maximum service will be attained from these waters, even a greater service than could be obtained from storage in surface reservoirs, for with complete develop­ment by surface storage, about one-third of all the water would be lost by evaporation. Without some surface storage, however, to partially equalize the flow, large volumes of flood water would rush off into the ocean too quickly for absorption by the gravels in the stream beds or diversion to artificial spreading grounds. The artificial spreading of water is being practiced with success in some of the basins by diverting the clear waters that follow the first turbid flood flows. These spreading operations can be much extended by the use of surface storage works to partially equalize the flood flows ahd the employment of additional spreading areas. These investigations have mapped the location of the absorptive basins in this territory and collected much data on the surface and underground waters.(1) Considerable amounts of water spread on the surface o f these basins in irrigation, are known to sink to join the ground waters and increase the available supply for other areas. The total quantity of water in this region is so limited, however, that there cannot be any great increase in the areas watered unless means are discovered of maturing crops with smaller applications of water than are now customary. It is possible as water- increases in value, that much may be accomplished in reducing losses by evaporation while applying the waters to the soils but at greater expense than is justifiable at the present time. <1!.See. Appendix "O” to this report, Bulletin works, for maps of absorptive areas and undergrouNnod. w7,a tSetra tceo nDtoeuprasr.tment of Publio \ WATER RESOURCES OF CALIFORNIA. 51 G R E A T BASIN D R A I N A G E - S O U T H O F , L A K E T A H O E . souAhalfof “ lie 111 the the range extending southerly from g B i W B B Mountains and in several parcels varying in elev a tio n W ,T i SS' I B are situated or more above. The locfl waters aro H I B B B B to 5000 feet waters collected by the mountains that * m amount, for of all the rest of the state, ? arf S from tlie small part of the entire area could h? IB B 6f terly sloPes- Bu* a Colorado River bringing waters from rlrnin1“ated l1; were not for tiie within reach of 9 3 9 ,0 0 0 ^ 8 of these landsFn S T * tb® State to corner of the state. There are now 500 000 th extreme southeastern natural flow of the C o l o r a d o B B B R aereV mgated from the almost doubled by the construction of^torale^woJk ^ ean be flood waters. These waters would be divertef• ^°r savinS °ver canals, that serve the greatest possible ^ Pan’ by gravit* The local streams in the northerly ?narf n-Ffhic* • productive than in the south. H B B 1 B B B Su Q much more elevations greater than 5000 feet The H 6nt m B B m m lands are at most of these wateS southerlv in H c?“ Preh®sive plan would carry long to areas 4000 feet or lessin elevation^he^ai? eigj1^ miles are sufficient to irrigate 430,000 acres, and'in all B B B i Strea“ S irrigated in these regions. a V 69,000 acres can be G R E A T BASIN D R A I N A G E - N O R T H OF L A K E T A H O E « — ? 1 H H from tain valleys and on tho M H M l B | H g 5 g H B B H b b IH ^ H N O R T H PACIFIC C O A ST DRAINAGE. About half of the agricultural areas of the Pacific Coast drain a™ lie adjacent t° Mount Shasta on the northern and western s ^ ? H H f f lM p h f 00 ,o 40»° H t r ib u t S s a n ^ T B B I Slreams’ P™ cipally the Klamath or its I H H ai?d convey them by gravity to the regions of use The levels BBRl 9 Pacific: Coast drainage basins lie in’lower vafleys or on theSd 5S°, f < a bo v e the sea’ these lands | in the Gravity convevancf ofalti?eatt at0ng tbe -°W6r reacbes f l tlle streams, miles in B H I H H tbe waters requires' one canal over seventv acres cari h f l ” ^ ? m°re K H twenty miles long. In all 699,200 can be irrigated under the comprehensive plan. Onlv 87 300 f f l H I ” ? » B | ? ™ter out of a total area of — — i agricultural lands m this region. 01