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areas which are not served by canals obtain their entire water supply from the ground-water reservoir. This pumping has resulted in a serious drop in the water table in many areas.

32. As stated in paragraph 29 a portion of Buena Vista Lake Reservoir with a capacity of 23,000 acre-feet has been reserved for storage of water to regulate irrigation supply for the Buena Visus water storage district. Controlled inlet and outlet canals permit regulation of flow. This is the only reservoir regulating irrigation on Kern River. Appendix VIII contains a detailed study of irrigation practice in the Kern River service area.

33. Because of the intermittent nature of the flow of Poso and Caliente Creeks, water from these streams is not a dependable source for direct irrigation. However, both streams discharge into areas adjacent to which irrigation by pumping is practiced extensively

, and they are an important source of ground-water replenishment.

34. Eristing power development and distribution.-- Three hydroelectric plants on the main Kern River and one plant on the North Fork utilize a substantial portion of the available head in the sections of the stream developed for power. All of these plants now operate on unregulated stream flow and feed into an extensive transmission system. Their highly variable power output is supplemented by electric energy produced elsewhere. The two systems of which these plants are a part are owned by the Pacific Gas & Electric Co, and the Southern California Edison Co. The power market of the former company serves northern California, while the latter disposes of most of its power in the Los Angeles distriet

. The entire Kern River area is highly developed for the distribution of electric power. Table 14 shows existing hydroelectric and steam plants in the Kern River area.

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TABLE 14.-Existing hydro and steam electric power plants-Kern River ured

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San Joaquin Light & Power Corporation (subsidiary of Pacific Gas & Electric Co.)

35. The flood-control improvement proposed in this report (par. 61) would not interfere with any existing power plant listed in table lx, except the diversion works and conduit of the existing Borel plant.

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(See enclosure 2.1) The Borel diversion works are located on the North Fork about 5 miles above Isabella. The Borel conduit, consisting of concrete-lined canal and steel flume sections, is approximately 11 miles long.

V. IMPROVEMENTS DESIRED

36. Local interests in the Kern River area desire the construction of a project, primarily for flood control, but including features permitting the more efficient use of stream flow for irrigation. In submitting plans of improvement at the public hearing, they were unanimous in proposing that regulation be effected by detention storage. A summary of desires expressed, and of pertinent data submitted at the hearing is included in appendix I. Specifically, local interests desire:

(a) Flood regulation of Kern River by means of detention storage.

(6) A limited amount of channel improvement in the vicinity of Buena Vista Lake.

(c) The coordination of flood control with the use of water for irrigation. (d) Flood control of Poso Creek.

(e) Check dams and detention basins for flood control and conservation on Caliente Creek.

37. Local interests made the following statements in justification of these desires:

(a) Flood flows of Kern River have inundated and damaged many parts of the affected area. The unregulated river is a serious hazard, particularly to the city of Bakersfield. The business district of this city has been flooded three times in the past 80 years. Growth of this district in recent years has been rapid and damage due to flooding would now be far greater than in the past.

(b) Flood storage on Kern River would provide the only practicable means of keeping flows within the capacity of the present channel even if it were improved.

(c) Diversions from Kern River in its present unregulated condition are inadequate for irrigation requirements. Coordination of food control with water use would result in detention of river flows for release when natural stream flow is deficient.

VI. HYDROLOGY

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38. General.--Hydrological and physiographic conditions in the southern San Joaquin Valley result in floods of two distinct types. Floods of the first type, commonly termed “winter floods," characterized by high peak flows of short duration and small total volume. They result from rainfall, or from rain on snow, and normally occur in the period from December to March, inclusive. The second type, known as late spring floods, or snow-melt floods, occur during the months of April, May, June, and July as a result of the melting of the mountain snow pack. They are characterized by long-sustained flows of moderate stage but result in run-off of large volume. Because of the dissimilar characteristics of these floods and the fact that in general they affect different parts of the valley, they are treated separately in this report.

39. Rainfall.Storms producing rainfall in the area usually come from the northwest, occasionally from the southwest and less frequently from the southeast. Northwest storms produce most of the precipitation in the area, although southwest storms result in greater rainfall intensities and cause the majority of the winter floods on Kern

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River, Southeast storms produce rainfall of the cloudburst" trpe. The latter storms have caused serious damage on the smaller foothill streams, but the probability of a damaging flood on Kern River as a result of one of these storms is very small. Mean annual rainfall on the valley floor is only about 6 inches, and its contribution to stream flow is negligible. Average annual precipitation in the drainage basin ranges from about 10 inches in the foothills to 8 maximum in the mountains of approximately 40 inches, increasing with altitude up to about 7,000 feet elevation and then decreasing to the crest of the range. Precipitation during summer and fal months is negligible. Detailed data relative to precipitation stations and records are given in appendix V.

40. Snoufall.--The storms which bring beavy rainfall in the lower area (par. 39) generally result in snowfall in the higher mountains. At elevation 7,000 feet, which is about the altitude of maximum precipitation, 80 to 90 percent of the precipitation is in the form of snow, most of which is retained until the following spring. The percentage of precipitation retained in the snow pack increases with elevation, Little or no snow falls below 1,000 feet elevation. Snowfall on the watersheds of Poso and Caliente Creeks is negligible.

41. Run-off. The flow of Kern River is generally similar in seasonal distribution to that of other major streams flowing from the Sierra Nevada into the San Joaquin Valley. However, the volume of run-off of this stream is subject to wider variations than that of the more northerly streams. The seasonal run-off (water-year, October I to September 30) during the period of record has ranged from a minimum of 181,600 acre-feet in 1930-31 to a maximum of 2,459.000 acre-feet in 1915-16. These extremes represent 26 and 350 percent, respectively, of the 45-year average run-off of 701,800 acre-feet. The variation in annual run-off and the characteristics of flow of Kern River for the 45-year period of record (from 1893 to 1938) are clearly indicated by hydrographs, appendix II-B and C'.

42. The run-off of Poso and Caliente Creeks is intermittent and follows rainstorms in the drainage basins, snow melt not being a factor in the flow of these creeks. Flow measurements have been made on Poso Creek at infrequent intervals in the past, but no stream gaging bas been done on Caliente Creek.

43. Snow surveys.-In recent years annual snow surveys conducted by several cooperating agencies and coordinated by the State of California have made possible a reasonably accurate determination of the water content of the snow pack and a close estimate of the rate and total volume of run-off to be expected. State reports indicating snow conditions are issued in February, March, April, and Vay. Predictions of run-off for the April to July period are made in the month of April and are adjusted in the month of May for departure of April precipitation from the mean. Table 15 indicates the accuracy with which these determinations have been made on Kern River. Methods and equipment used in conducting snow surveys are adequately described in the 1938 Transactions of the American Geophysical Union. A copy of the March 1939 State

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bulletin, and related data are shown in appendix V. These surveys would be the basis for reservoir operation as they insure an accurate predetermination of the releases necessary to provide adequate storage space for control of late spring floods.

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44. Winter floods.--Maximum peak flows on Kern River occur during winter floods. These floods are flashy, seldom exceed 3 days in duration, and are of relatively small total volume. The flood of December 1867 is considered to have been the greatest since the area was settled. From field investigations of high-water marks and other data (appendix XII-B)," it is estimated that the peak discharge of this flood was about 104,000 cubic feet per second in the vicinity of Isabella. Channel storage in the intervening fifty-odd miles of river reduced this peak to approximately 51,000 cubic feet per second in the vicinity of Bakersfield. Great floods occurred during the winters of 1862 and 1893, but no estimates of discharge are possible because high-water marks for these floods were not found. Table 16 lists the known maximum winter floods on Kern River.

TABLE 16.-Winter floods, Kern River at first point of measurement ?

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1 "First point of measurement” is the principal irrigation measuring station on Kern River located 6. miles above Bakersfield.

· During period in which discharge exceeded 4,000 cubic feet per second. * Estimated.

45. Table 17 gives an estimate of probable frequencies of winter floods at “first point of measurement. The frequency curve from which these values were derived is included in appendix V.1

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TABLE 17.-Estimated frequency of winter foods, Kern River, at first point of

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1 Figures shown are independent and would not necessarily occur in the same floods. 2 During period in which discharge exceeds 4,000 cubic feet per second.

46. Winter floods primarily affect areas along the upper delta sections of the river. Channel storage and losses materially reduce such flows before they arrive in the lower valley area. The most critical section of the river during winter flash floods is the channel in the vicinity of Bakersfield which has a safe capacity of about 15,000 cubic feet per second. However, fows of this magnitude would probably cause inundation of Fairhaven and Fruitvale, small communities a few miles westerly of Bakersfield. The effect of winter floods is not noticeable below the upper end of Goose Lake Slough, and the volume of such floods is insufficient to cause damage in the trough of the valley. Very little water reaches Buena Vista Lake and no water has ever been known to reach Tulare Lake as a result of this type of flood.

47. Late spring floods.-Late spring floods result from the melting of the snow pack accumulated in the mountains during the winter months. Their magnitude is governed by the volume and water content of the snow and they normally comprise 60 to 70 percent of the total seasonal run-off. They are of long duration, frequently extending over 3 or 4 months. Peak flows seldom exceed 9,500 cubie feet per second which does not seriously tax the channel capacity on the upper delta. Overbank flow frequently occurs on the flood channels in the valley trough with consequent inundation of large areas therein.

48. Since Kern River discharges into a closed basin, inundation caused by late spring floods is roughly proportional to the volume of run-off rather than the rate of flow. The dispersion of the total flow of these floods tends to follow certain more or less definite trends. About 650,000 acre-feet are diverted for irrigation use. Channel losses account for about 100,000 acre-feet, and another 100,000 acrefeet are dissipated in Goose Lake Slough and other channels. Flows reaching the inlet channel of Buena Vista Lake are divided, a portion thereof being diverted to Buena Vista Lake Reservoir for storage. Except in years of large late spring floods, not more than about 23,000 acre-feet are so diverted (see par. 29), a condition which permits the farming of the remaining leveed area in the reservoir. In seasons of large flow, diversions have been made up to the full reservoir capacity of 230,000 acre-feet. The remaining flow at Buena Vista

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