Benito River receives an average of nearly 20 inches of rainfall annually. Snow in measurable quantities is rare in the watershed and of no consequence in flood problems. Reference is made to the VI in which the map numbers of the above stations, among others, may be found. The map referred to is figure 1 of appendix III. end 13. Published maps and charts.-The area in which the drainage basin lies has been completely mapped by the United States Geologial Survey at scales of 1 to 62,500 and 1 to 125,000. These quadrangle maps are listed in appendix II,' together with other published maps of the region. A general index map of the watershed is presented as inclosure 1. A map of the areas subject to flooding is presented as inclosure 2.1 the v TABL 1 14. Population. The population of the Pajaro River drainage basin is divided about equally between urban and rural groups. In the Watsonville area where truck farming is extensive, most of the agricaltural workers are Filipinos. A considerable number of Chinese, Japanese, and Mexicans live in the rest of the basin. In 1935, the Department of Agriculture made a population survey of California and presented the findings in a map entitled "Population, 1935." The portion of this map which covers the basin is presented in figure of appendix II. By using this population distribution map and United States Census Bureau figures for the juridical townships lying entirely or partly within the Pajaro River drainage basin, it is estimated that the population of the basin was 20,000 in 1910, 24,000 in 1920, 34,000 in 1930, and 37,500 in 1940. Table IV presents Census Bureau figures for the populations of the incorporated towns of the basin breas the four most recent census dates. crops, TABLE IV.-Census figures for population of incorporated places in the Pajaro Riser drainage basin Morgan Hill. Gilroy.. Hollister. San Juan Bautista. 1910 607 2, 437 4, 446 1920 646 2,862 2,781 501 5,013 creamery, and bakery operations, canning, drying, and packing fruit, 17. he w and v acres crops. orchar area, t Lack o siderat 908 3,757 laimed 772 8,344 plies ca Lake, here Creek. 15. Occupations, industries, and products.-Agriculture and processing of agricultural products are commercially the most inportant occupations in the Pajaro River Basin and represent its mest valuable resources. The products manufactured in the basin in the year 1939 had a value of approximately $8,000,000, half of which was added by manufacture. The manufacturing consists of wine $500 or 19. 7 18. callers than $ Bautist from as ville to 16. The principal agricultural crops are deciduous fruits, grap basin. vegetables, and fodder. Prunes, apricots, pears, and apples are gro in large quantities, especially in south Santa Clara and San Benito 1 Not printed. Valleys. Lettuce, artichokes, peas, tomatoes, and sugar beets are produced in greatest quantity in Pajaro Valley, and these crops are now supplanting some of the older orchards along lower Llagas Creek and elsewhere in south Santa Clara Valley. There are several seed farms in the drainage basin. Dairy cattle are raised generally in the valleys, and beef cattle and sheep are raised on the higher grasscovered woodlands. The average values of the Pajaro River drainage basin agriculture products for the years 1937-40 are presented in table V. The figures are derived from farm prices and do not include the value of processing or canning. TABLE V.-Average value of Pajaro River drainage basin agricultural products for 1937-40 Orchard crops.. Truck crops.. Field crops.. Livestock and dairy products... Product All agricultural products (farm values). Value $6,500,000 500,000 1,500,000 13, 000, 000 17. Land use and development.-The approximate percentages of the watershed area represented by various broad types of land use and vegetative cover are given in table III. A total of some 205,000 acres is under cultivation in the principal valley areas. Of this acreage, 36 percent is in orchards and vineyards, 21 percent in truck crops, and the remainder in alfalfa, hay, grain, and miscellaneous crops. Nearly all of the truck crops and about two-thirds of the orchards are irrigated. With the possible exception of the Hollister area, the present land use may be considered generally stabilized. Lack of ample water supplies in the Hollister area may result in considerable reversion to dry farming, unless supplementary water supplies can be made available. Extensive bottom lands near San Felipe Lake, poorly drained and excessively alkaline, may ultimately be reclaimed and converted from pasture to cultivated land. Currently, there is a trend from orchards to truck farming along lower Llagas Creek. 18. Within the limits of the historical flood plains in the principal valleys (enclosure 2), the value of privately owned property is more than $10,000,000. The total assessed value of the five incorporated towns in the watershed (Morgan Hill, Gilroy, Hollister, San Juan Bautista, and Watsonville) is more than $13,000,000. Values vary from as little as $2 per acre for inaccessible mountain woodland to $500 or more per acre for good bearing orchard and row-crop land. 19. Transportation facilities. Communications in the Pajaro River drainage basin are good. The coast railroad line of the Southern Pacific Co. passes through South Santa Clara Valley from Morgan Hill to south of Gilroy, thence through Chittenden Pass to Watsonville Junction, which lies across Pajaro River from Watsonville, and thence southward to Salinas and other points south of the drainage basin. Also, from this junction a branch line runs through Watsonville to Santa Cruz. Another branch line extends from Gilroy through 1 Not printed. Hollister to Tres Pinos. Eighty miles of State and Federal-al highways traverse the region and are fed by 300 miles of surfaced and 100 miles of unsurfaced county roads which cover the valley areas. The index map of this report (enclosure 1) shows the railroads and the main highways. 20. Navigation improvements.-There are no navigation improve ments in Pajaro River or its tributaries. Map 21. Storm and seasonal hydrology of the Pajaro River basin is treated in detail in appendix III, and the information presented 23 herein is condensed from that appendix. The rainfall data, upr which the hydrology is based, were obtained from the records of precipitation stations in and near the Pajaro Basin. The more inportant stations are listed in table VI, which includes the average annual rainfall at stations having comparatively long periods of record. For additional station references, as well as further details on hydrologic subjects generally, reference is made to appendix III: TABLE VI.-Principal precipitation stations in and near Pajaro River Basis Station Lonoak Idria Priest Valley. San Jose Upper Tres Pinos. Morgan Hill.. Gilroy San Benito Uvas Creek Stayton Mine Hernandez (near). Los Banos. Lick Observatory. Enos Highland. PRECIPITATION Ives Williams Reservoir. Button Ranch do 1 Map numbers refer to fig. 1, appendix III. (Appendix III is not printed.) * Recorder since 1928. 27 1880-91, 1899-192 13: 1874 1873 12 1923 16 1918 189814 1874 1911-28, 1928-1 1940 20 1924 20 1894 27 1940190719391935 8 187329 1884 27 13 19 1935 1937193737 1912-39. 14 1924 14 1925 1940 1916 1911 1940 only. Records 1885-1915. 14 1926 22. Notable storms in or adjacent to the area. Due to scarcity of records, it has not been practicable to analyze storms which occurr prior to 1906. The daily records of precipitation at Priest Valley Hollister, and Uvas Creek, during 14 characteristic flood-producing storms since that year, are presented in table II of appendix III 1 Not printed. Each of these storms included at least 1 day of heavy rainfall, usually preceded by several days of lighter rainfall, which reduced the rate of infiltration on the day of maximum rainfall. The greatest daily precipitation recorded at any of these three stations in this series of storms was 7.99 inches, which occurred at Uvas Creek on December 11, 1937. All great storms are general in extent over the basin, but rainfall intensity varies markedly throughout the area. The time of most intense rainfall is generally the same in the northern and southern tributaries. 23. River-stage and stream-gaging stations. The longest record of stream flow in the Pajaro River Basin is that on Uvas Creek, a headwater tributary of Carnadero Creek, for which the United States. Geological Survey has kept continuous records since 1930. In the early part of the 1939-40 season, staff and wire weight gages and water stage recorders were installed on the main stream and various tributaries. A summary of hydrologic data pertaining to the more important of these stations is presented in table VII. TABLE VII.-High and low water records of representative stream-gaging stations RUN-OFF 1,188 250 210 1 Estimates of February 1938 flood from high water marks. Gaging stations have shifting controls. 24. Adequacy of stream flow for all purposes.-The normal stream flow in the Pajaro River and its tribu aries is not adequate for navigation or the generation of power. It is also inadequate during dry cycles for maintaining the underground waters which are relied upon for both domestic and irrigation supplies. In Technical Bulletin No. 746 entitled "Quality of Irrigation Waters of the Hollister Area of California," published by the United States Department of Agriculture in March 1941, it is estimated that the average recession in well levels in the lower part of South Santa Clara Valley and in San Benito Valley between January 1924 and December 1935 varied from 2.8 to 4.0 feet per year. In that report, is is also estimated that of the replenishing watersheds for these areas, the San Benito yields about 1 inch of run-off annually and Pacheco Creek about 3 inches annually. During the seasons from 1935 to date, above normal annual rainfall has prevailed, and from the observations of ground water levels for this period, it is found that the average rise in water levels in the lower part of South Santa Clara Valley and San Benito Valley var from 2.2 to 8 feet per year. Ground water recovery is further con sidered in appendix V. The construction of a 6,000 acre-foot storg: reservoir on Pacheco Creek in 1939 has improved the gound water supply materially in the valley area to which Pacheco Creek is tribetary. Serious ground water recession has also occurred in the past in the vicinity of Gilroy, where considerable recovery has been observad during the last few years of heavy rainfall. 25. Worst probable flood. The worst probable flood in the river was determined by combining the rainfall accompanying the worst probable meteorological condition over the basin, as determined by the rainfall depth-duration envelope curve method, with the minimum loss rates. The resulting computed flood heights, peak dischargs, and total run-off are presented in table VIII. The method of esi mating the worst probable flood is explained in detail in appendix Ill.' TABLE VIII.-Maximum stages, peak discharges, and total run-off for worst proble flood onsider 26. Measured flood discharges.-The discharges gaged at fire principal stations during the floods of February 1940, February 1941, March 1941, and April 1941, are given in table IX. The data presented in the table include the average depths of run-off for the tribtary areas and the duration of the flood flows by dates. The flood of April 1941 was the largest during the period of record of the Chittendend gage (1939 to date), although it is estimated that the flood of February 1938 was considerably greater. The largest flood of record at the Uns Creek gage occurred in December 1937. It has been found that little reliance can be placed on reported records of high-water marks, espe cially those for the large floods of 30 to 60 years ago, as a basis for estimating flood discharges in the drainage basin. Not printed. nd was ajaro Priod a nito |