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WAR DEPARTMENT,
OFFICE OF THE CHIEF OF ENGINEERS,

Washington, December 13, 1943.
Subject: Pajaro River, Calif.
fo: The Secretary of War.

1. I submit for transmission to Congress my report with accomjanying papers and illustrations on preliminary examination and survey of Pajaro River in San Benito County, authorized by the flood Control Act approved June 22, 1936, and Pajaro River, Calif., authorized by the Flood Control Act approved August 28, 1937.

2. Pajaro River drains 1,303 square miles of mountain and valley ands in western California. It rises in San Felipe Lake, flows westerly some 30 miles, its upper section crossing South Santa Clara Valley, and empties into Monterey Bay, about 75 miles south of San Francisco. Tributaries from the north are Corralitos Creek, just above Watsonville, mile 6, and Carnadero and Llagas Creeks which enter upstream from Sargent, mile 23, and drain a portion of South Santa Clara Valley. This valley also extends on the south side of Pajaro River for 10 miles or more to the general vicinity of Hollister on San Benito River. The latter river rises about 70 miles air-line distance south of Pajaro River, drains a long narrow area, and empties into Pajaro River near mile 20 The principal tributary to San Felipe Lake is Tequisquita Slough, which carries waters from the south, east, and northeast. · Agriculture, including the raising of fruits and vegetables, and the processing of agricultural products are the most important occupations. Precipitation varies considerably throughout the basin and has averaged 27 inches per annum at Watsonville and 13 inches at Hollister. Irrigation is extensively practiced with the water largely obtained from wells. About 205,000 acres are under cultivation in the principal valley areas which are along Pajaro River below the mouth of San Benito River, along the lower section of San Benito River and in South Santa Clara Valley. Large areas of bottom lands near San Felipe Lake and in other flood plain sections are poorly drained. Several thousand acres south of the lake contain harmful amounts of alkali and are used only for grazing and forage crops. The basin has a population of 37,500, of which about one-half is urban. The largest towns are Watsonville, with population of 8,940, Hollister, with 3,880, and Gilroy, with 3,620, near mile 8 on Carnadero Creek.

3. No improvement of Pajaro River for flood control has been specifically authorized by Congress. Local interests have constructed small reservoirs for irrigation and provided irrigation wells and canals. In normal years these are inadequate to meet irrigation needs after the month of March. Recently the amount of ground water available has been increased somewhat by the greater precipitation and the infiltration of stored water. This is said to have aggravated

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the drainage problem in the vicinity of the upper Pajaro River and on San Felipe Lake. There is a tendency to resort to dry farming methods in the area south of San Felipe Lake where the ground waters ou are strongly alkaline and in the Hollister area where water suppliesmu are insufficient. Partial protection from floods of areas in the Carma- nidi dero Creek Basin, including Gilroy, has been accomplished by lere sui construction at a cost of $54,340, of which $21,870 was furnished by the Work Projects Administration. Levees constructed on both T banks of Pajaro River for a short section in the vicinity of Watso- ork ville afford partial protection to that city on the north bank and to urban and agricultural areas across the river. The cost to local relie public agencies has been about $181,200 and to the Work Projects Paja Administration $134,790. The work south of the river has been ins suspended. An expenditure of about $99,000 of Work Projects nigh Administration funds is required for completion of the works planned

. done 4. Floods in the basin are essentially limited to the winter months m and result from heavy precipitation. Damages due to floods are aten confined principally to South Santa Clara Valley and to lands along nile Pajaro River. In the San Benito Basin bank erosion constitutes the rate principal flood damage and there is little overbank inundation. Dr. Hould ing flood periods this stream carries large volumes of silt into Pajaro apec River. As a result of this and upstream channel constrictions in mates Pajaro River, flood waters form a large lake along its upper resch

, lutere the lower section of Carnadero and Llagas Creeks, and south of San 135.00 Felipe Lake. Although this accumulation of water causes flood damage to the lands inundated, it is considered beneficial by some as existir it tends to remove alkali from the soil and to increase the amount of ground water available for irrigation. The area, by serving as a Annie natural reservoir, reduces flood flows and flood damages along the The d lower Pajaro River. Tides and the silt at the mouth of the stram ubjec have little effect on floods. Damaging floods occur on Pajaro Rirer ands. below San Benito River with an average frequency of once in claims 2 to 3 years. Watsonville, with its levee protection, is subject to inundation about once in 20 years. Gilroy is at present subject to ribute flood damage about once in 25 years. The agricultural floodplain it ahi along lower Pajaro River is devoted principally to row crops and if this orchards; in the upstream natural reservoir area to pasture, bor

, 6.7 and grain crops; and in the Carnadero and Llagas Creek Basins to conside orchards, vineyards, and row crops. Floods in the basin are not saring

The average annual direct and indo uform rect net flood damages are estimated at $88,900 of which 59 perent prosper occur along Pajaro River below the mouth of San Benito River.it Certain local interests in the basin are interested in irrigation prob by the lems, others in drainage conditions, and still others in flood contml. Since improvements for one of these purposes may injuriously affet certain areas in other respects, local interests do not entirely agree accordir as to what improvements would be advisable. They do, howeter, construc desire flood-control measures and suggest the consideration of respeto Douth voirs, channel improvements, levees, and similar works. They indicate that they would probably be able to furnish suitable local cooper M52.16 ation.

5. The district engineer finds that the only site in the basin at which an effective flood control reservoir could be constructed is on

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Gilroy!

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San Benito River near mile 15, and that even this site is not geologically favorable. He estimates that the resulting flood-control benefits would justify an expenditure of only $1,400,000, whereas the reservoir would cost $3,000,000. To secure water conservation benefits in addition would require a larger, more expensive reservoir and irrigation benefits would have to be charged with the $1,600,000 deficiency, plus the increased cost.

The district engineer concludes that it would not be advantageous for local irrigation interests to join with the United States in such an -improvement. He has considered various other measures for flood relief and finds that levees with bank protection works along lower Pajaro River and on Carnadero Creek at Gilroy would constitute the only effective and economically justified flood-control measures which might be undertaken in the basin at this time. He proposes a levee

along Pajaro River extending from the mouth along the right bank i to mile 11.8, making use of the existing levee at Watsonville and extending about 1 mile up Corralitos Creek and along the left bank to mile 10.6, incorporating the short section of the existing levee. Highway and railway bridge changes are a part of the plan. The levees would afford a freeboard of about 2 feet above the largest flood to be expected with an average frequency of once in 100 years. He estimates the first cost to the United States at $497,700 and to local interests at $243,300 and the average annual costs and benefits at $35,000 and $40,600, respectively. He proposes to provide the same degree of protection at Gilroy by raising and strengthening the existing levee and extending it a short distance. The estimated first cost to the United States is $59,000 and to local interests $6,000. Annual costs are estimated at $2,570 and annual benefits at $3,100. The district and division engineers recommend these improvements subject to the conditions that local interests furnish the necessary lands, agree to maintain the works, hold the United States free from claims for damages resulting from them; and for the Pajaro River improvement, modify a highway bridge near the mouth and contribute $46,000 to the United States for special channel construction at a highway bridge at Watsonville as an alternate to the modification of this bridge at their own expense.

6. The Board of Engineers for Rivers and Harbors, having fully considered the reports of the district and division engineers and having afforded local interests an opportunity to present additional information, concludes that the plans presented are suitable and that prospective benefits economically justify the expenditures required. It recommends the work, subject to the local cooperation proposed by the district engineer, and also the cost of raising the railroad bridge at Watsonville and related changes.

7. After due consideration, I concur in the views of the Board and accordingly recommend improvement of Pajaro River, Calif., by the construction of levees on the right and left banks from near the mouth to miles 11.8 and 10.6, respectively, with suitable bank protection, at an estimated construction cost to the United States of $452,160, and improvement of its tributary, Carnadero Creek, at Gilroy by raising, enlarging in section, and lengthening the existing levee at that place at an estimated construction cost to the United States of $59,000, both improvements to be in general accordance

with the plans of the district engineer as shown on the accomparing drawings; subject to the condition that responsible local agencis en give assurances satisfactory to the Secretary of War that they will be (1) provide, without cost to the United States, all lands, easemente

, na and rights-of-way necessary for the construction of the project; and make at their expense all necessary changes in existing improvements

, il including utilities and highway and railway bridges, with the privilege of contributing $46,000 to the United States for special channel onstruction work at the Watsonville highway bridge in lieu of bearing the expense of altering that structure; (3) hold and save the United States free from damages resulting from construction of the works

; and (4) maintain and operate all works after completion in accordance with regulations prescribed by the Secretary of War.

E. REYBOLD,

Major General,
Chief of Engineer

The

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(Second endorsement)
THE BOARD OF ENGINEERS FOR RIVERS AND HARBORS,

Washington, D. C., August 23, 1943.
Subject: Pajaro River and tributaries, Calif.
To: The Chief of Engineers, United States Army.

1. Local interests were advised of the nature of the division engineer's report and invited to submit additional information to the Board. No communications have been received.

2. The Board concurs in the views of the reporting officers that the proposed levee improvements are economically justified. In that the sand benefits from the work would be largely local in character, it is of the opinion that Federal participation in the cost and construction should be limited to the levee and channel work and that local interests should be required to furnish lands and make all necessary changes in existing 4. M improvements, including the raising of the railroad bridge at Watsup ville and related changes, the cost of which has been included in the recommended Federal expenditure by the reporting officers. The car Board accordingly recommends improvement of Pajaro River, Calif

. by the construction of levees on the right and left banks from near the mouth to miles 11.8 and 10.6, respectively, with suitable back Thurma protection, at an estimated construction cost to the United States of post 89 AM $452,160, and improvement of its tributary, Carnadero Creek, at Gilroy by raising, enlarging in section and lengthening the existing levee at that place at an estimated construction cost to the United States of $59,000, both improvements to be in general accordance with the plans of the district engineer as shown on the accompanying drawings; subject to the condition that responsible local agences give assurances satisfactory to the Secretary of War that they (1) provide, without cost to the United States, all lands, easements and rights-of-way necessary for the construction of the project

; !) make at their expense all necessary changes in existing improvements, including utilities and highway and railway bridges, with the privilege

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