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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 talle VI in which the map numbers of the above siations, among others
, may be found. The map referred to is figure 1 of appendix III.
13. Published maps and charts.-The area in which the drainage basin lies has been completely mapped by the United States Geologia Survey at scales of 1 to 62,500 and 1 to 125,000. These quadrangle
table 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
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 agricultural workers are Filipinos. A considerable number of Chinse, Japanese, and Mexicans live in the rest of the basin. In 1935, the Department of Agriculture made a population survey of California and direkte presented the findings in a map entitled "Population, 1935." The portion of this map which covers the basin is presented in figure 1 of appendix II. By using this population distribution map and C'nited States Census Bureau figures for the juridical townships lying entinly 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, 34,00 alle in 1930, and 37,500 in 1940. Table IV presents Census Bursu figures for the populations of the incorporated towns of the basin for the four most recent census dates.
Table IV.--Census figures for population of incorporated places in the Pajaro Kiser
Lake, claimei there is
15. Occupations, industries, and products. --Agriculture and the processing of agricultural products are commercially the most important 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 50 or creamery, and bakery operations, canning, drying, and packing fruit, and canning vegetables. The mineral production of the basin was $1,412,000 in 1940 and is expected to increase in 1941 due to the recent reopening of a large cement plant near San Juan Bautista which has an estimated annual capacity of 750,000 barrels of cement, the manyfactured value of which will be about $1,250,000.
16. The principal agricultural crops are deciduous fruits, grapes vegetables, and fodder. Prunes, apricots, pears, and apples are growi 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
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 Hollister to Tres Pinos. Eighty miles of State and Federal-il 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 railroeds and the main highways.
1 Not printed.
20. Navigation improvements.--There are no navigation improve 1.1 ments in Pajaro River or its tributaries.
21. Storm and seasonal hydrology of the Pajaro River basin i treated in detail in appendix III, and the information presented herein is condensed from that appendix. The rainfall data, upe which the hydrology is based, were obtained from the records of a
tator precipitation stations in and near the Pajaro Basin. The more sportant stations are listed in table VI, which includes the average iris annual rainfall at stations having comparatively long periods of record. For additional station references, as well as further detais tibur on hydrologic subjects generally, reference is made to appendix III:
TABLE VI.-Principal precipitation stations in and near Pajaro River Basta
22. Notable storms in or adjacent to the area.--Due to scarcity a records, it has not been practicable to analyze storms which occurri 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 * 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.
RUN-OFF 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
· 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 mainiaining 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 Benico Valley between January 1924 and December 1935 varied from 2.8
In chat 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
to 4.0 feet per year.
has prevailed, and from the observations of ground water lerds 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 vara from 2.2 to 8 fe. í per year. Ground water recovery is further cosidered in appendix V?? The construction of a 6,000 acr--foot stories reservoir on Pacheco Creek in 1939 bas improved the gound wak supply materially in the valley area to which Pacheco Crock is tritatary. Serious ground water recession has also occurred in the på: 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 rive was determined by combining the rainfall accompanying he wont probable meteorological condition over the basin, as determined by the rainfall depth-duration envlope curve method, with the minimum loss rates. The resulting compuiid flood heights, peak discharus and total run-off are presented in table VIII. The method of esmating the worst probable flood is explained in detail in appendix II! Table VIII.—Maximum stages, peak discharges, and total run-off for u'orst probele
26. Measured flood discharges.—The discharges gaged at fire de principal stations during the floods of February 1940, February 1941, March 1941, and April 1941, are given in table IX. The data pre sented in the table include the average depths of run-off for the tribunod a tary areas and the duration of the flood flows by dates. The flood of to April 1941 was the largest during the period of record of the Chittenden NT gage (1939 to date), although it is estimated that the flood of Februar 1938 was considerably greater. The largest flood of record at the l'is Creek gage occurred in December 1937. It has been found that lite reliance can be placed on reported records of high-water marks, este cially those for the large foods of 30 to 60 years ago, as a basis for estimating flood discharges in the drainage basin.
1 Not prinled.