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of contributing $46,000 to the United States for special channel con-
JOHN J. KINGMAN,
SURVEY OF PAJARO RIVER, CALIF.
The district engineer finds that neither the construction of works to provide complete flood protection in the Pajaro River Basin nor of reservoirs to provide partial flood control with or without water conservation or drainage features is economically justified by the prospective benefits at this time. He further finds that damages from excess water in the lowland area between Gilroy, Sargent, and San Felipe Lake are caused partly by poor drainage and in some alkaline areas are offset by substantial benefits from flooding. He finds, however, that recon. struction and extension of the existing levee system in the vicinity of Watsonville could be accomplished at an estimated first cost of $741,000 and an annual cost of $35,000, which would afford additional flood-control benefits evaluated at $40,600 annually. He also finds that reconstruction and extension of the existing levee near Gilroy could be accomplished at an estimated first cost of $65,000 and a total annual cost of $2,570, which would afford additional flood-control benefits eval. uated at $3,100 annually.
The district engineer recommends that the existing levees in the vicinities of Watsonville and Gilroy be reconstructed and extended by the United States at an estimated first cost of $741,000 for the Pajaro Valley levee (plan A), of wbich $497,700 would be made available from Federal funds and $243,300 is allocated to local interests as the cost of lands and casements and relocated improvements to lands and bridge modifications; and at an estimated first cost of $65,000 for the Carnadero Creek levee near Gilroy, of which $59,000 would be made available from Federal funds and $6,000 is allocated to local interests as the cost of land and easements provided that prior to construction, local interests in each of their respective areas:
(a) Provide, without cost to the United States, the required lands and easements for construction and maintenance, estimated to cost $125,000 for the Pajaro Valley project and $4,000 for the Carnadero Creek project.
(6) Provide, at their own expense, flowage rights for flooding adjoining lands on the Carnadero Creek project, estimated to cost $2,000.
(c) Relocate, at their own expense, all existing improvements to lands in the levee right-of-way on the Pajaro Valley project, estimated to cost $63,300.
(d) Agree to accomplish, at their own expense, all required modifications in the Thurwachter bridge and approaches on the Pajaro Valley project, estimated to cost $9,000.
(e) Pay to the United States the sum of $46,000 as the estimated cost of paving special channel transitions and other works required on the Pajaro Valley project to enlarge the inadequate clearance under the present highway bridge at Watsonville, or, as an alternate, adequately increase the channel capacity at their own expense by means of suitable bridge modifications.
(9) Establish satisfactory arrangements for cooperation with the United States and maintenance of the project through city, county, or other suitable authorities.
(g) Give assurances satisfactory to the Secretary of War that they will maintain and operate the project works in accordance with regulations to be prescribed by him and hold and save the United States free from damages due to the construction and operation of all the project works.
San Francisco, Calif., October 5, 1948
engineer, South Pacific Division).
AUTHORIZATION AND SCOPE OF SURVEY 1. Section 6 of the Flood Control Act approved June 22, 1936, 41thorized and directed a preliminary examination and survey for find a control at
Section 5 of the Flood Control Act approved August 28, 1937, amended far section 6 of the above previous act by adding to the list of localities at rinit which preliminary examinations and surveys were authorized
2. A single preliminary examination report for flood control of Pajaro River, covering the scope of both of the two above authoristions, was submitted by the district engineer May 20, 1928. The report was reviewed by the Board of Engineers for Rivers and Harbers and a survey of the locality was ordered by the Chief of Engineers July 6, 1938.
3. There have been no prior War Department reports on Pajaro River for flood control. A report on the survey of the Part of Watsonville and Santa Cruz Harbor for the improvement of navigation, authorized by the River and Harbor Act approred March 4, 1915, was submitted by the Chief of Engineers on February 14, 1918, and published in House Document No. 947, Sixty-fith Congress, second session. This report and two subsequent reviti thereof were unfavorable.
DESCRIPTION 4. General features of the drainage basin.-The Pajaro River and it's tributaries drain some 1,303 square miles of mountain and valles land situated in the Coast Range of California easterly from Monterey selerat Bay into which the river empties. The center of the drainage besin is about 100 miles southeasterly from San Francisco. The Diablo Range separates the Pajaro River Basin from that of the San Joaquale River to the east; the northern tributaries of the Pajaro River Isle Morgan in the Santa Cruz Mountains which form the general boundary of the watershed on the north. The Gabilan Range separates the drainge vile 12 of the San Benito River, principal southern tributary of the Pajaro
mv River, from that of the Salinas River to the west. The principal a ir valley areas are Pajaro Valley around Watsonville, that portion of a santa Clara Valley extending from Morgan Hill to the vicinity of Hollister, termed South Santa Clara Valley in this report, and San Benito Valley extending from Hollister to the mouth of the San Benito River near Sargent.
5. The source of the Pajaro River is in San Felipe Lake, from which the stream follows a southwesterly course to a confluence with the San Benito River near Sargent. From this confluence the Pajaro River meanders in a westerly direction to Watsonville, and thence southwestward to its mouth in Monterey Bay. The principal tributary to San Felipe Lake is Tequisquita Slough, through which Pacheco and Santa Ana Creeks contribute to the lake waters which are now drained ' more by the bypass, Miller's Canal, than by the old upper channel of
the Pajaro River. Three important tributaries drain the area north
of the Pajaro River. These are Llagas, Carnadero, and Corralitos · Creeks. The largest tributary is the San Benito River, whose source is far to the south of the Pajaro River in the Diablo Range in the vicinity of Hernandez. The San Benito River has an important tributary known as Tres Pinos Creek. The general course of the San Benito Řiver is northwesterly from the headwaters to its confluence with the Pajaro River near Sargent. The principal tributaries and several subtributaries of the Pajaro River, with their drainage areas, are presented in table I.
TABLE I.–Tributaries of the Pajaro River
Drainage area in square
San Benito River...
Tres Pinos Creek.. San Juan Creek.. Carnadero Creek.
Uvas Creek Llagas Creek Tequisquita Slough.
Santa Ana Creek and tributaries.
Total drainage basin...
6. Topography -The ridges of the Diablo Range bounding the drainage basin on the east vary from 2,000 to 4,000 feet above sea level in elevation with several higher peaks. The ridges of the Santa Cruz Mountains and the Gabilan Range are generally from 1,500 to 3,000 feet, with peaks nearly 4,000 feet in elevation. The South Santa Clara Valley floor slopes gently from elevations of about 350 feet near Morgan Hill and Hollister to 150 feet in the vicinity of San Felipe Lake. The Pajaro Valley slopes from elevations of 75 feet near river mile 12 to about 10 feet near the mouth. The distribution of the drainage basin area as to elevation is presented in table II.
TABLE II.--Elevation distribution of the Pajaro River drainage basin
7. Vegetative cover.—The mountainous country drained by the northern tributaries receives a greater seasonal rainfall and consequently has a heavier timber cover than other portions of the drainage basin. The eastern and southern tributaries drain mountainous areas covered with grass and brush with only a sparse tree growth. The forest trees are principally oak, pine, and redwood. The vegetaire cover and land use of the drainage basin have been classified bř the Soil Conservation Service, United States Department of Agriculture. The principal classifications are presented in table III.
TABLE III.- Land use and vegetative cover, Pajaro River watershed, California
8. Soils in South Santa Clara, San Benito, and Pajaro Valleys 12.1 range in texture from gravelly loam through sandy and fine sands og loam to clay adobe. Some of the dense soils along part of Santa Ana Creek and south of the Pajaro River westerly from San Felipe lakes contain alkali, and are suitable only for grazing or the production of birta iz forage crops.' The soils of the Gilroy, Hollister, and Pajaro Valley wine areas have been surveyed by the United States Department of Agriculture in conjunction with the University of California. Os total of about 295,000 acres of tillable valley and upland, 24.2 percent were graded for agricultural purposes as 'excellent, 10.3 percent as good, and 52.4 percent as fair. Improvements and waste land en prise the balance.
9. General geology of the basin.—The Coast Range, in which the party drainage basin is situated, comprises a system of folding and faulting dominated by the great San Andreas rift which extends from Paint Arena north of San Francisco some 600 miles southeasterly to Gulf of California. This active fault closely parallels, and for a shor distance follows, the bed of the San Benito River. The Diablo Range, forming the eastern boundary, and the Santa Cruz Mountains
in the northwest of the watershed are characterized by sedimentary ind metamorphic rock formations, including soft sandstones, limestones, cherts, and serpentines classified as the Franciscan group, with occasional ultra-basic intrusives, such as peridotite and volcanics Huch as andesite and basalt. The geologic formations of the Gabilan Range, forming the western boundary of the drainage basin from San Juan Bautista to the vicinity of San Benito, are granitic rocks jf crystalline structure, including granite, quartz, and diorite. The Falleys are all characterized by deposits of recent alluvium. In most of the stream beds, this alluvium is composed principally of sand and ravel through which the ground water of the basin percolates. This eature is pronounced in the lower San Benito River.
10. Stream slopes.- The slope of ühe Pajaro River bod varies from 2.7 feet per milo below Watsonville to 8.0 feet per mile in the vicinity of the mouth of the San Benito River. The slope of the latter stream ncreases from 15.5 feet per mile near its mouth to 29.6 feet per
mile hear the town of San Benito. Carnadero and Llagas Creoks havo nadients increasing from about 12 feet per mile neai cheir mouths to about 30 feet per mile near their headwaters. Stream slopes of the
nore important tributaries are presented in tabular form in appendix II.
11. Channel dimensions and capacities.— The Pajaro River channel werages 210 feet in width and 13 feet in depth from the mouth to Chittenden and has a bank-full capacity in this reach of about 10,000 cubic feet per second. Local lovce works havo increased this capacity in the immediate vicini y of Watsonville. From Chittenden to Sargent, the average channel is 270 feet wide and 17 feet deep and has a bank-full capacity of about 16,000 cubic feet per second. The northern tributaries tend to diminish in cross-sectional area and carrying capacity as they approach the Pajaro River. The San Benito River channes is a wide, sandy wash from its mouth to mile 26, a short distance below the mouch of Tres Pinos Creek. The banks from the mouth to mile 13 are about 4 feet high and the channel is about 650 feet wide; the estimated bank-full capacity in this reach is 10,000 cubic feet per second. More detailed channel dimension and capacity data are piesented in tabular form in appendix II.'
12. Climate.- The climate of the Pajaro River Basin is equable throughout the year, without extremes of temperature, but with occasional killing frosts. It is characterized by the comparatively rainless summer season from May through October of each year, which is common to all of central California. The seasonal rainfall , concentra ied in the months from November through April, varies markedly with clevation and location in the drainage basin. The mean seasonal precipitation recorded at Gilroy (elevation 200 feet) is slightly more than 20 inches, whereas chat recorded at nearby Lick Observatory (elevation 4,209 feet) is nearly 29 inches. The mean annual precipitation at Watsonville (elevation 23 feet) near the coast is more than 27 inches, whereas Hollister (elevation 284 feet) at the southern end of south Santa Clara Valley receives an average of slightly less than 13 inches of rainfall annually. Priest Valley (elevation 2,400 feet) in Monterey County near the headwaters of the San
* Not printed.