counties): At Nigger Canyon reservoir site and at Temecula Canyon near Fallbrook.
San Luis Rey River (San Diego County): At the mouth and also at Bonsall about 15 miles upstream.
San Dieguito River (San Diego County): Discharge will be calculated from Lake Hodges reservoir records.
Tia Juana River tributaries are to be measured at international boundary as follows: Campo, Tecate and Cottonwood creeks.
SANTA ANA RIVER INVESTIGATIONS IN ORANGE, RIVERSIDE AND SAN BERNARDINO COUNTIES
An intensive investigation along several lines is being made in the Santa Ana River Basin. Conservation in the Upper Santa Ana Basin can be best accomplished by "spreading," which consists of diverting the flood waters, which would otherwise flow to the ocean unused, onto the gravel cones extending into the valley and sinking this flood water into the underground reservoir, from which it is later drawn by pumps. Much work along this line has already been done by the Tri-Counties Water Conservation Association, but it is planned to increase the facilities for spreading by means of a permanent weir or dam across the mouth of the canyon and larger spreading works. The state is making a detailed survey of the Santa Ana Cone, and the topographical survey of possible diversion works at the mouth of the canyon is almost completed. This is to be used as a basis for preliminary plans for diversion works which will function during high water periods and allow the diversion during floods of 1000 second-feet for spreading which will cause it to percolate into the cone on the north side of Santa Ana River. Diversions of this magnitude under conditions of violent floods found in southern California rivers are unprecedented and the problem presents many new and extremely difficult features.
AERIAL SURVEYS; OTHER STUDIES
Arrangements have been made for an aerial survey of the entire area in the Cucamonga Plain from San Antonio Creek eastward to Day Creek and from the mountains southward to Foothill Boulevard in the western part of the area and to Base Line road in the eastern part of the area. This will cover the cones of all the streams of any magnitude issuing from San Gabriel Mountains onto the Cucamonga Plain and will provide a basis whereby systematic plans for spreading these waters on the cones can be worked out and also will provide a basis for plan for a channel to carry the surplus waters of extremely excessive floods safely to the Santa Ana River. Recent studies made by the state have indicated that there is a very material accretion to the groundwater supplies from rainfall on the valley floor itself and from return water from irrigation. Also, there is a considerable loss from evaporation from swamps and waterlogged land. In addition to the stream gaging program mentioned, a comprehensive study is being made of rainfall percolation, evaporation from waterlogged lands and allied subjects. This work is being done in conjunction with the United States Geological Survey and Department of Agriculture; also with the three counties.
MOJAVE RIVER, SAN BERNARDINO COUNTY
A program for a thorough investigation of the Mojave River Basin has been laid out, consisting of stream gaging, measurements of depth to water plane at wells, together with mapping of irrigated and other areas more or less swampy which are dissipating water. The results of this investigation will show what further agricultural development can be made with the water supplies available in the Mojave River.
An aerial survey of the entire valley has been completed which will yield the needed information as to extent of irrigated lands and also areas dissipating water through evaporation. A close estimate showed that this work could be performed more cheaply by aerial survey and a great deal more quickly than by other standard surveying methods.
VENTURA COUNTY
An intensive water resources investigation is being made of the watersheds of Ventura River, Santa Clara River and Calleguas and Conejo creeks, lying southward in the Oxnard section of Ventura County. In short it is an investigation of the entire water resources of Ventura County, looking toward plans for as complete conservation by surface and underground reservoirs as is possible to make together with the determination of the areas in which the water can be best used. Work under way during the month consisted of measuring percolation, determining capacity of underground reservoirs and assembling and analyzing data gathered in the field. Ventura County cooperates in this work.
GENERAL
A general underground water investigation of the entire Pacific slope of southern California is nearly completed. Well records over several years on 968 wells have been obtained by the state itself or furnished from other sources, and all these data are being compiled into a report, which together with maps will be published at an early date.
