lature to make further appropriation, it has been possible, during the biennium, to complete only the first two appendices.

Bulletin No. 13, "Development of the Upper Sacramento River,' contains an analysis of the utility of a dam and reservoir located at Kennett, in connection with development according to the "Coordidated Plan." This bulletin also contains a cooperative report by the United States Bureau of Reclamation on the Iron Canyon Project. The latter dam site located fifty miles below the Kennett site on the Sacramento River controls 2609 square miles of drainage area not tributary to Kennett. Both the Kennett and Iron Canyon reservoir sites lie upstream from the main body of agricultural land on the floor of the Sacramento Valley and are in a physical position to serve any part of these lands with irrigation water. The Kennett site has been chosen, however, as the logical location of a unit in the Coordinated Plan, because of its larger capacity and more favorable foundation conditions.

Bulletin No. 14, "The Control of Floods by Reservoirs," is devoted to investigation of the possibility of coordinating the problems of flood control and conservation through a predetermined method of operating reservoirs. The attempt to use reservoirs for both flood control and conservation seems at first contradictory. To be useful for regulating floods, the thought has been that reservoirs should be held empty during the period of heavy run-off, while for conservation purposes, they should be allowed to fill during this same period. However, a detailed analysis of the time of occurrence and volume of flood flows discloses a procedure for filling reservoirs that will hold in reserve sufficient capacity to absorb floods during the time in which they are likely to occur, and progressively release this space for filling as the end of the flood season approaches.

Heretofore, in looking to the future, the problems of flood control and of conservation have been given separate consideration. Expensive construction programs are known to be necessary in both fields of endeavor to provide habitable conditions for the increasing population. The investigation of the possibility of coordinating these two necessary programs has assumed such large proportions that this entire volume has been given over to the presentation of this phase of the water resources investigation.

GROUNDWATER INVESTIGATION IN SOUTHERN SAN

JOAQUIN VALLEY

Bulletin No. 11, "Ground Water Resources in Southern San Joaquin Valley," which was published by the division during the biennium, contains the results of investigations which have become of increasing importance with the rapid lowering of ground waters in this section of the state in recent years.

Studies were undertaken by this office in 1920 in Kern and Tulare counties, the results of which were published in bulletins *.previously issued. The importance of continuing and extending the records

Bulletin No. 3, "Water Resources of Tulare County and Their Utilization." Bulletin No. 9, "Water Resources of Kern River and Adjacent Streams and Their Utilization."

obtained led to further investigations in 1925 which included areas not previously covered.

The report is the result of an effort to determine the relation of present use to available water supply. The greater portion consists of a detailed discussion of ground water conditions in different parts of the area based on records which cover periods of from one to six years. Practically all of the surface run-off that can be used without storage has been and is being utilized for some type of irrigation. Local sources can never supply the available irrigable area, as the total locally tributary mean annual stream flow is less than one acrefoot per acre of irrigable land.

Ground water supplies, like surface water supplies, have a source and the amount of use that can be maintained permanently is limited to the extent of the supply. If overdraft continues, the resulting lowering causes a gradual decrease in pumping as the less efficient and more expensive plants cease to be profitable.

All areas in the southern San Joaquin Valley need give serious attention to their ground water situation. If records obtained show that the development has not reached a point where the draft exceeds the supply, the advantage of such knowledge will more than repay the effort required for its determination. If it is found that present development has exceeded the available supply, efforts toward limiting further development will extend the time before ground water lowering may result in a decrease in the irrigation development of such localities

CHAPTER VII

SANTA ANA INVESTIGATION

The initial act providing for the Santa Ana Investigation was passed by the legislature in 1925 and provided $25,000 to be expended during the succeeding biennium for a survey of the Santa Ana River watershed and work for control of floods, provided a like sum was appropriated by the three counties of San Bernardino, Riverside and Orange. The supervisors of the three counties in accordance with this act made the required $25,000 available to match the state's appropriation. The money was expended largely in drilling possible dam sites in the mountains for reservoirs and also a dam site in the Lower Santa Ana Canyon. In addition to this some work was done in gathering general hydrographic data, such as fluctuation of water table by means of measurements at existing wells and measurement of run-off.

It became apparent during the course of the investigation that the money available was not sufficient to complete an investigation of the scope required for such conditions as exist in Santa Ana Basin and the legislature of 1927 made an appropriation of $40,000 which was to be matched by the three counties or by any interested party. One provision of this latter appropriation was that the report should be completed and given to the Governor prior to the first day of December, 1928. The three counties made $40,000 available to the state and this money was used to prosecute the investigation. During the latter period and until completion, the work of the investigation was largely concentrated on more intensive gathering of hydrographic data, extension of stream flow measurements, and analysis of the data already existing. The Jurupa dam site immediately below the Southern Pacific Railroad crossing of Santa Ana River was drilled for a possible reservoir, this being the only additional drilling done during the second biennium of the investigation. The total money expended was $130,000. Advisory Board.

It was felt desirable that men of considerable experience with the local situation should act as an advisory board to the state during the investigation and after starting work under the appropriation made in 1925 each one of the three counties appointed an engineer to serve on such advisory committee. These were Mr. J. B. Lippincott representing Orange County, Mr. A. L. Sonderegger representing Riverside County, and Mr. George S. Hinckley representing San Bernardino County. In October, 1927, Mr. Paul Bailey became engineer for the newly organized Orange County Flood Control District and by appointment of that county he was substituted on the advisory board for Mr. Lippincott.

Santa Ana Basin Physiography and Hydrography.

The watershed of the Santa Ana River comprises 2050 square miles and is 100 miles in length. The stream reaches the Pacific Ocean about 40 miles southeast of Los Angeles. The average run-off from all the hills and mountains to the valley floor is 323,000 acre-feet annually. Rainfall is deficient on the valley floor and practically all of it occurs in the four winter months, December to March. The valley floor is largely utilized for the growing of citrus fruits and other high-grade crops. The assessed valuation of the habitable area is $263,000,000, consisting mainly of land and improvements on the valley floors. There are a total of 640,000 acres on the valley floors, of which 250,000 acres are not yet in use, but the rate of increase of the irrigated area has been approximately 10,000 acres per year for the past sixteen years.

Hydrography of the Basin.

Only at infrequent intervals do the floods from the mountains reach the ocean. During most of the year the streams are dry, sandy washes. The intense rains of the winter falling on the steep granite slopes of the mountains discharge suddenly into the valley and force their way through to the ocean. During all of the remainder of the year the streams as they flow from the mountains are either absorbed into the gravels or are diverted at their point of debouchure into the valley for use in irrigation or domestic supplies. The valley itself consists of a series of basins, mesas and hills. The basins are filled with the detritus brought down from the precipitous mountains by the sudden, violent floods above mentioned. These basins are separated from one another by ranges of hills or by underground barriers which may not be evident on the surface but which are indicated by sudden changes in the elevation of the water plane. As a general division, the Santa Ana Basin separates into five major basins called the Upper Basin, Cucamonga Basin, Jurupa Basin, Temescal Basin and Lower Basin of the coastal plain. In these basins are absorbed the major portion of the stream flow from the mountains and also percolation from rainfall on the valley floor. They form huge reservoirs which have made life in the region as it exists today possible, because they regulate the annual and cyclic flows in the water supply and make it available for use. It is estimated that about 90 per cent of the water supply now in use is derived from the underground water of these basins either by pumps or by diversion of rising water which flows out the lower ends of the basins. These basins constitute a series of reservoirs, one feeding into the other, and thus the water supplying one basin is more or less dependent upon what is taking place in the basin above.

There is now in progress, and has been for sometime past, a gradual lowering of the water plane in almost all of these basins, except in the case of part of the Upper Basin, where by artificial means additional water has been caused to percolate into the basin. In the development of the underground basins as reservoirs, such as is the case in Santa Ana Basin, lowering of the water plane will come about as a natural result of such use, but in the Santa Ana Basin this lowering is going on very rapidly and has caused alarm as to the future of the water supply on the part of those people dependent upon it. The hydrographic investigation was gone into so intensively for this reason, and it was found