PAJARO RIVER, CALIF. WAR DEPARTMENT, Subject: Pajaro River, Calif. 96893-44- -2 1. I submit for transmission to Congress my report with accomanying 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 cier the drainage problem in the vicinity of the upper Pajaro River and San Felipe Lake. There is a tendency to resort to dry farming meth-all ods in the area south of San Felipe Lake where the ground waters are strongly alkaline and in the Hollister area where water supplies ou are insufficient. Partial protection from floods of areas in the Cama-ch dero Creek Basin, including Gilroy, has been accomplished by levee 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 Watson-or ville afford partial protection to that city on the north bank and to mpr urban and agricultural areas across the river. The cost to local relief public agencies has been about $181,200 and to the Work Projects Paja Administration $134,790. The work south of the river has been r suspended. An expenditure of about $99,000 of Work Projects nigh Administration funds is required for completion of the works planned. long to m 4. Floods in the basin are essentially limited to the winter months and result from heavy precipitation. Damages due to floods are exten confined principally to South Santa Clara Valley and to lands along mile Pajaro River. In the San Benito Basin bank erosion constitutes the Tay principal flood damage and there is little overbank inundation. Dur-ould ing flood periods this stream carries large volumes of silt into Pajaro pect River. As a result of this and upstream channel constrictions in ates Pajaro River, flood waters form a large lake along its upper reach, tere the lower section of Carnadero and Llagas Creeks, and south of San $35.00 Felipe Lake. Although this accumulation of water causes flood damage to the lands inundated, it is considered beneficial by some as existin it tends to remove alkali from the soil and to increase the amount of fost t ground water available for irrigation. The area, by serving Annus natural reservoir, reduces flood flows and flood damages along the The d lower Pajaro River. Tides and the silt at the mouth of the stream subjec have little effect on floods. Damaging floods occur on Pajaro River 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 tribute flood damage about once in 25 years. The agricultural flood plain at a hi along lower Pajaro River is devoted principally to row crops, orchards; in the upstream natural reservoir area to pasture, hay, 6. and grain crops; and in the Carnadero and Llagas Creek Basins to conside orchards, vineyards, and row crops. Floods in the basin are not having particularly hazardous to life. The average annual direct and indinforma rect net flood damages are estimated at $88,900 of which 59 percent prospec 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 control. Since improvements for one of these purposes may injuriously affect certain areas in other respects, local interests do not entirely agree accordin as to what improvements would be advisable. They do, however, construc desire flood-control measures and suggest the consideration of reser mouth voirs, channel improvements, levees, and similar works. They indi-tection cate that they would probably be able to furnish suitable local cooper ation. and 5. The district engineer finds that the only site in the basin at which an effective flood control reservoir could be constructed is o mpro recol bridge 7. A $452,160 Gilroy levee at States 0 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 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 th with the plans of the district engineer as shown on the accompany E. REYBOLD, The REPORT OF THE BOARD OF ENGINEERS FOR RIVERS AND Subject: Pajaro River and tributaries, Calif. [Second endorsement] $35.000 THE BOARD OF ENGINEERS FOR RIVERS AND HARBORS, 1. Local interests were advised of the nature of the division engi neer's report and invited to submit additional information to the Board. No communications have been received. Cear G onnal ated s The Basemen Respectiv Lents f 2. The Board concurs in the views of the reporting officers that the will: Watson Stimat $497.70 local lands Camade Fore Fe rajaro L thi Pr Car (e Paspecial e Vienlare and main g Gir And opera Tim and in and c |