The Borel Hydroelectric Project, identified as Project No. 382 by the Federal Energy Regulatory Commission (FERC), is owned and operated by Southern California Edison Company (SCE). The project includes a diversion dam on the North Fork Kern River, settling basin and canal intake, water conveyance system, powerhouse and transmission line. The current FERC license expires on February 28, 2005. SCE is preparing an Application for License with the expectation that it will be filed prior to February 28, 2003. This Application for License, including an Environmental Report, will be prepared by SCE in consultation with the federal and State agencies, and interested members of the public.

The purpose of this investigation is to present impaired and unimpaired streamflow information at locations along the Kern River that are effected by Borel Project operation. This report contains basic streamflow data and a description of streamflow effects due to Borel Project operation. Streamflow in the diverted reach of the Kern River is also effected by the corps lake Isabella Project.

The scope of this work includes investigation of basic streamflow data available from the U.S. Geological Survey (USGS), U.S. Army Corps of Engineers (Corps) and SCE. The results presented here are intended to describe the impaired and unimpaired streamflow conditions of the Kern River which can be used to facilitate understanding the effects of historic Borel Project operation.

The Borel Hydroelectric Project is a 12.0 MW (installed capacity) hydroelectric project located on the Kern River in Kern County, California (see Figure 1), and includes private land owned by SCE and public lands managed by the Corps, the U.S. Forest Service, Sequoia National Forest and the U.S. Bureau of Land Management. The Borel Project was constructed in 1904 and originally diverted water from the North Fork of the Kern River at a point located just east of the town of Wofford Heights. However, when the Corps constructed Isabella Dam in 1953, the Borel Diversion Dam and about 5.0 miles of the Borel flowline were submerged. The original Diversion Dam still exists beneath Lake Isabella, and when reservoir storage is less than about 110,000 acre feet, the Diversion Dam and flowline are exposed and may divert water from the North Fork Kern River. This situation generally occurs only during very dry water years.

FIGURE 1

During normal operation, water for the Borel Project is drawn directly from Lake Isabella at the Isabella Auxiliary Dam and conveyed through about 7.0 miles of Project flowline. The flowline is comprised mainly of a combination of open flumes, siphons, and short tunnels and traverses the hillsides to the south and east of the Lower Kern River below Lake Isabella. Water conveyed through the flowline enters four penstocks, two at 526 and 565 feet long to units 1 and 2, respectively, and two penstocks, both 622 feet long which converge to supply water to Unit 3 turbine. The Borel Powerhouse is located on the east side of the Lower Kern River, approximately seven miles downstream of Lake Isabella. The Corps’ operation of Lake Isabella controls the flow into the Borel flowline.

The Kern River is the southern most river in the Tulare Lake Basin. The basin is located in the Sierra Nevada Mountains and ranges from an elevation of about 2,500 feet near Lake Isabella Dam to about 14,000 feet near Mt. Whitney. About 80 percent of the Kern River watershed is above 5,000 feet in elevation. The Kern River is composed of two principal streams: the main stem of the Kern River (North Fork) and the South Fork. The North Fork makes up about 85 percent of the total flow into Lake Isabella (Corps Regulation Manual).

Normal annual precipitation varies from about 6 inches at the edge of the valley floor to a maximum of 45 inches in the main Kern River area. About 90 percent of the runoff-producing precipitation occurs during the winter months of November through April (Corps Regulation Manual). Typically, precipitation falls as rain at elevations below about 5,000 feet and as snow at higher elevations, but snow can occur on the valley floor and rain at an elevation of 10,000 feet. The snowpack accumulates during the winter months with the peak snowpack occurring about April 1 of each year.

The drainage area of the Kern River at Isabella Dam is 2,074 mi². The average annual runoff of the Kern River at Isabella Dam is about 736,000 acre-feet (1954 – 2000 average). Typically, about two thirds of the annual runoff occurs during the April through July snowmelt period.

The Borel Project diverted reach is the Kern River from the Lake Isabella Main Dam to the Borel Powerhouse (about 7.0 miles). SCE’s Borel Project and the Corps’ Lake Isabella Project affect Streamflow in this section of the Kern River.

Lake Isabella has a maximum storage capacity of 570,000 acre-feet and is operated as a multipurpose reservoir. Although its primary function is flood control, the reservoir is also managed to meet water supply demands of downstream users, principally those of agricultural interests and energy companies, and to accommodate reservoir recreation. The reservoir stores spring snowmelt runoff and makes releases from storage during the summer months to irrigate approximately one million acres of Kern County land in the San Joaquin Valley. This operation effects streamflow in the diverted reach of the Kern River by storing Lake Isabella inflow during the spring snowmelt period (about April – July) and releasing storage in the summer and fall.

The Borel Project was constructed as a North form of the "run of the river" project. Prior to the construction of Lake Isabella Dam, the Kern River was diverted up to the maximum capacity of the Borel diversion dam, about 605 cfs, into the Borel Canal. Once Lake Isabella Dam was constructed, the Borel Project began drawing water directly from the reservoir when the Lake level is above the historic Borel diversion dam and intake. However, when the reservoir is drawn down, the original Borel Diversion Dam and intake structure and portions of the flowline are exposed and the Borel Project can no longer operate under reservoir head. When this occurs, water is diverted into the Borel Canal directly from the North Fork of the Kern River at SCE’s historic point of diversion. This is a relatively rare occurrence, typically happening late in the summer, only during particularly dry water years.

The Borel Project diverts water from Lake Isabella (or the North Fork of the Kern River in very dry times) into the Borel Canal and through the powerhouse about 7.0 miles downstream of Lake Isabella Dam. Flow from the Borel Powerhouse returns to the Kern River. The Borel Project effects the streamflow within the diverted reach of the Kern River.

Although the Borel Project was constructed run of the river, at times it does not operated as a typical run of the river project because of its relationship to Lake Isabella. Releases from storage are made from Lake Isabella into the Borel Canal, not the diverted reach of the Kern River, when releases are less than the Borel Canal capacity. Only when the releases from Lake Isabella exceed the capacity of the Borel Canal is water released from the Main Dam into the diverted reach of the Kern River.

The Borel Project is responsible for a FERC mandated minimum bypass requirement in the diverted reach as follows.

Borel Project Minimum Streamflow Requirements from Lake Isabella Main Dam

Rate Period

15.0 cfs October 1 through May 31

50.0 cfs June 1 through September 30

Minimum flow releases are made from the Lake Isabella Main Dam into the diverted reach of the Kern River. Operation to meet this minimum flow started in about 1999. Prior to this, the minimum streamflow was held to about 5 cfs.

Impaired and unimpaired streamflow information is used in this investigation. Impaired streamflow (project flow) is the historical flow in the Kern River with all project impairments. Unimpaired streamflow (natural flow) is flow in the Kern River that would have occurred absent of all upstream project impairments. There were four data sets used in investigating the Borel Project and it’s effects on streamflow in the Kern River.

Unimpaired Flow – The Corps calculates mean daily unimpaired streamflow of the Kern River at Lake Isabella Dam. This information is used as an estimate of flow in the diverted reach of the Kern River that would have been present without Lake Isabella or Borel Project operation. The Corps calculates unimpaired flow as follows.

Lake Isabella total mean daily outflow and change in storage are measured directly. Lake evaporation is estimated using evaporation pan readings and daily average reservoir surface area. Unimpaired flow information was obtained from the Corps and is shown in Appendix A.

Impaired Flow – The Corps records streamflow in the Kern River just below Lake Isabella Dam. This information is used to quantify the flow in the diverted reach of the Kern River from the Main Dam to the outflow of the Borel Powerhouse. Impaired flow information was obtained from the Corps and is shown in Appendix A.

FERC mandated minimum streamflow requirements from Lake Isabella to the diverted reach were imposed in about 1999. Historical streamflow values for this investigation have not been adjusted to reflect the current minimum streamflow release requirements. Where appropriate, the effect of current minimum streamflow requirements from Lake Isabella is considered when determining project effects on streamflow in the Kern River.

Borel Canal Flow –The USGS reviews and publishes SCE measurements of the flow diverted into the Borel Canal. This information is used to quantify the flow from Lake Isabella that bypasses the diverted reach of the Kern River and returns below the Borel Powerhouse. Borel Canal flow information was obtained from the USGS database and is shown in Appendix A.

Impaired Flow Without Borel – This information represents the flow in the diverted reach without Borel Project operation. Impaired flow without Borel is the total overflow from Lake Isabella or the summation of the Kern River impaired flow below Lake Isabella Main Dam and the Borel Canal flow. This information was calculated for the study period and is shown in Appendix A.

The Borel Project was constructed in 1904 and operated as a true run of river project until the construction of the Lake Isabella Project. Major facilities of the Lake Isabella Project were completed in 1953 and brought a change in Kern River and Borel Project operation. Although the Borel Project remains a run of the river project, releases from Lake Isabella storage are made into the Borel Canal. The first 605 cfs of releases from Lake Isabella are made via the Borel Canal, not including the minimum streamflow maintenance requirement. As such, only years after Lake Isabella construction are included in this investigation. The first full year of Lake Isabella Project operation was 1954. The study period for this analysis is water years 1954 through 2000 (October 1, 1953 - September 30, 2000).

Hourly streamflow information is also used to describe release characteristics from Lake Isabella into the Kern River. Hourly streamflow information is investigated for the period of available record, January 1995 to February 2001. This information was obtained from the Corps. Hourly streamflow basic data files are quite large and not presented in this investigation. A summary of hourly streamflow fluctuations in the diverted reach is presented.

The Borel Project is run of the river with no major storage facilities. The quantity of water diverted into the Borel Canal is dependant on the natural flow of the North Fork Kern River. The Borel Project is entitled to divert flows originating from the North Fork Kern River up to 605 cfs (the capacity of the Borel Canal). SCE and the Borel Project facilities have no control of Kern River flow in excess of 605 cfs. Streamflow in excess of 605 cfs is stored in Lake Isabella and/or released through the main dam into the Kern River. A 1953 agreement between SCE, the Corps and the downstream water users provides that releases from Lake Isabella, regardless of natural flow of the North Fork Kern, are made via the Borel Canal even when those releases are made from reservoir storage. Releasing stored water from Lake Isabella via the Borel Canal, up to it’s capacity, results in additional water through the Borel facilities in excess of that available from the natural flow of the North Fork Kern River. This water bypasses the diverted reach and is returned to the Kern River below the Borel Powerhouse.

It is convenient to consider streamflow effects for different time periods independently. This section considers streamflow effects in the diverted reach of the Kern River in terms of annual, monthly, daily and hourly time periods.

The average annual unimpaired flow of the Kern River at Lake Isabella Dam is about 736,000 acre-feet (range of 175,000 – 2,312,000 acre-feet). The average annual impaired flow of the Kern River in the diverted reach is about 398,000 acre-feet (range of 46,000 – 1,821,000 acre-feet). The reduction in annual streamflow (about 46% reduction on average) is primarily a result of the operation of the Borel Project. The average annual flow diverted into the Borel Canal is about 296,000 acre-feet (range of 77,000 – 425,000). Flow diverted into the Borel Canal bypasses the diverted reach of the Kern River. Further reduction in Kern River annual streamflow results from Lake Isabella losses. Annual evaporation of Lake Isabella can be about 40,000 acre-feet or more. The primary annual effect on streamflow in the diverted reach from operation of Lake Isabella is seasonal timing of flow.

Lake Isabella stores inflow during the spring snowmelt period for water supply and flood control and releases water in the summer and fall to meet downstream irrigation demands. The Lake Isabella Project alters monthly timing of flow in the diverted reach. A monthly summary of the Kern River impaired, impaired without Borel, unimpaired and Borel Canal flow are shown in Table 1.

Operation of the Borel Project reduces flow in the diverted reach by up to 605 cfs, the capacity of the canal. The combined effect of the Corps’ Lake Isabella Project and SCE’s Borel Project compound the effect on unimpaired streamflow alteration during the winter and spring when operation of both projects tend to reduce flows in the diverted reach. In the summer months when Lake Isabella is releasing water from storage, the Borel Project tends to counter act the effects on streamflow alteration in the diverted reach by bypassing up to 605 cfs.

For example, in May unimpaired flow in the diverted reach of the Kern River averages about 155,000 acre-feet. The Borel Project diverts an average of about 32,000 acre-feet in May. The remaining flow, about 123,000 acre-feet, would remain in the diverted reach of the Kern River if Lake Isabella where not operated. However, the streamflow in the diverted reach is reduced further to about 52,000 acre-feet by Lake Isabella operation. The Borel Project and the Lake Isabella Project reduce the unimpaired flow in May by about 66%, combined. In the summer months, releases from storage are made at Lake Isabella.

In August, average unimpaired flow in the diverted reach of the Kern River is about 34,000 acre-feet. Lake Isabella releases about 50,000 acre-feet on average in August into the diverted reach. The Borel Project diverts an average of about 28,000 acre-feet in August. The net result is an increase in August flow of 66% above unimpaired conditions.

Unimpaired and impaired streamflow for dry, normal and wet year types are shown in Figure 2. The figures illustrate the Borel Project and Lake Isabella Project effect on streamflow in the diverted reach of the Kern River. For this analysis, water year types are defined as follows.

The average inflow to Lake Isabella for the study period is 736,000 acre-feet. Dry years are; 1955, 1959, 1960, 1961, 1964, 1972, 1976, 1977, 1988, 1990, 1992 and 1994. Normal years are; 1954, 1956, 1957, 1962, 1963, 1965, 1966, 1968, 1970, 1971, 1974, 1975, 1979, 1981, 1984, 1985, 1987, 1989, 1991, 1993, 1999 and 2000. Wet years are; 1958, 1967, 1969, 1973, 1978, 1980, 1982, 1983, 1986, 1995, 1996, 1997 and 1998.

In dry years, flow in the diverted reach of the Kern River is typically low during September through April. During this time, flow in the diverted reach of the Kern River is commonly at the minimum maintenance flow requirement. Greater releases into the diverted reach occur from about May through August with average flow ranging from about 100 to 450 average monthly cfs. Impaired flow is less than unimpaired flow in the diverted reach in all months except July and August on average in dry years.

In normal years, flow in the diverted reach of the Kern River is typically low during September April. During this time, it is not uncommon for flow in the Kern River to be at the minimum maintenance flow requirement. Greater releases into the diverted reach of the Kern River occur from about May through August with flow ranging from about 300 to 950 average monthly cfs. On average, impaired flow is less than unimpaired flow in the diverted reach from about November through June on average in normal years.

In wet years, flow in the diverted reach of the Kern River is typically low during October through February. During this time, releases from Lake Isabella can be at the minimum maintenance flow requirement in some years. Releases into the diverted reach of the Kern River occur from about March through September with average flows ranging from about 800 to 3,000 average monthly cfs. During wet years it is sometimes necessary to operate Lake Isabella to control flood flows and releases are made in anticipation of spill. On average, impaired flow is less than unimpaired flow in the diverted reach from about October through June on average in wet years.

The average flow in the diverted reach of the Kern River during the month of October is not largely affected by Lake Isabella and Borel Project operation. The average monthly unimpaired and impaired flow in the diverted reach is 17,506 and 17,653 acre-feet, respectively. This corresponds to an average daily flow of 285 and 287 cfs respectively. During October, unimpaired flow in the diverted reach of the Kern River is usually steady and quite low as snowmelt runoff has typically concluded. In very wet years, snowmelt runoff can continue or rainfall events occur in to October, producing higher flows.

Greater ranges of flows are experienced in the diverted reach under impaired conditions as compared to unimpaired conditions. In about 57% of years, the minimum streamflow maintenance requirement is maintained in the diverted reach at sometime during the month of October (currently 15 cfs, previously about 5 cfs). The minimum daily unimpaired flow for the month of October is 69 cfs for the study period. Typical minimum flows during October are about 150 cfs. Releases from storage sometimes occur in October, especially in years following a year with high snowpack year and late season runoff.

The average flow diverted into the Borel Canal during October is 17,431 acre-feet. This corresponds to an average daily flow of 283 cfs or 47% of capacity. This flow bypasses the diverted reach of the Kern River. Releases from storage are made from Lake Isabella during October when the previous water year was wet maintaining available storage into October. This release to the diverted reach on average is equivalent to the flow diverted to the Borel Project. This maintains about the same streamflow in the diverted reach as under unimpaired conditions.

Without the Borel Project influence, the streamflow in the diverted reach would tend to be higher than under unimpaired conditions. Flow from the Borel Project and releases from Lake Isabella combine to total about 35,000 acre-feet on average in October. Without the Borel Project influence, streamflow in the diverted reach of the Kern River would be about double that of unimpaired conditions on average assuming that Lake Isabella would not store additional water when it is available in October.

The average flow in the diverted reach of the Kern River during the month of November is not largely affected by Lake Isabella and Borel Project operation. The average monthly unimpaired and impaired flow in the diverted reach is 19,521 and 12,826 acre-feet, respectively. This corresponds to an average daily flow of 328 and 216 cfs respectively. During November, unimpaired flow in the diverted reach of the Kern River is usually steady and quite low as snowmelt runoff has typically concluded. Precipitation, typically falling as rain, can occur in November increasing runoff.

The range of flows experienced in the diverted reach under impaired conditions is similar to unimpaired conditions. Under impaired conditions flow can be less than unimpaired conditions especially in dry years. In about 77% of years, the minimum streamflow maintenance requirement is maintained in the diverted reach at sometime during the month of November (currently 15 cfs, previously about 5 cfs). The minimum mean daily unimpaired flow for the month of November is 81 cfs for the study period. Typical minimum flows during November are about 150–200 cfs. Releases from Lake Isabella storage occur rarely in November and only following an unusually high snowpack year and late season runoff.

The average flow diverted into the Borel Canal during October is 15,352 acre-feet. This corresponds to an average daily flow of 258 cfs or 43% of capacity. This flow bypasses the diverted reach of the Kern River.

Without the Borel Project influence, the streamflow in the diverted reach would tend to be higher than under unimpaired conditions. Flow from the Borel Project and releases from Lake Isabella combine to total about 28,000 acre-feet on average in November. Without the Borel Project influence, streamflow in the diverted reach of the Kern River would be about 50% greater than unimpaired conditions on average assuming that Lake Isabella would not store additional water when it is available in November.

The flow in the diverted reach of the Kern River during the month of December is reduced with Lake Isabella and Borel Project operation. The average monthly unimpaired and impaired flow in the diverted reach is 31,450 and 6,555 acre-feet, respectively. This corresponds to an average daily flow of 511 and 107 cfs respectively. During December, unimpaired flow in the diverted reach of the Kern River rises with rainfall.

The range of flows experienced in the diverted reach under impaired conditions is less than unimpaired conditions. Unimpaired flow is commonly 200-400 cfs, or more, with impaired flow at the minimum streamflow maintenance requirement (currently 15 cfs, previously about 5 cfs) about 85% of the years sometime during the month of December. The minimum mean daily unimpaired flow for the month of December is 81 cfs for the study period. Lake Isabella is typically storing water in December for water supply and flood control.

The average flow diverted into the Borel Canal during December is 17,144 acre-feet. This corresponds to an average daily flow of 279 cfs or 46% of capacity. This flow bypasses the diverted reach of the Kern River.

If the Borel Project were not operating, the streamflow in the diverted reach would tend to be higher than currently expected under impaired conditions. Water rights associated with the Kern 1 Project (downstream of Borel) call the natural flow of the Kern River up to 412 cfs must not be stored in Lake Isabella. Without operation of Borel, this flow would remain in the diverted reach of the Kern River.

The flow in the diverted reach of the Kern River during the month of January is effected similarly as streamflow during December. The average monthly unimpaired and impaired flow in the diverted reach is 39,532 and 7,450 acre-feet, respectively. This corresponds to an average daily flow of 643 and 121 cfs respectively. During January, unimpaired flow in the diverted reach of the Kern River rises with rainfall.

The average flow diverted into the Borel Canal during January is 19,846 acre-feet. This corresponds to an average daily flow of 323 cfs or 53% of capacity. This flow bypasses the diverted reach of the Kern River.

If the Borel Project were not operating, the streamflow in the diverted reach would tend to be higher than currently expected under impaired conditions. Water rights associated with the Kern 1 Project (downstream of Borel) call the natural flow of the Kern River up to 412 cfs must not be stored in Lake Isabella. Without operation of Borel, this flow would remain in the diverted reach of the Kern River.

The flow in the diverted reach of the Kern River during the month of February is effected similarly as streamflow during December and January. The average monthly unimpaired and impaired flow in the diverted reach is 45,053 and 10,553 acre-feet, respectively. This corresponds to an average daily flow of 811 and 190 cfs respectively. During February, unimpaired flow in the diverted reach of the Kern River rises with rainfall.

The average flow diverted into the Borel Canal during February is 22,218 acre-feet. This corresponds to an average daily flow of 400 cfs or 66% of capacity. This flow bypasses the diverted reach of the Kern River.

If the Borel Project were not operating, the streamflow in the diverted reach would tend to be higher than currently expected under impaired conditions. Water rights associated with the Kern 1 Project (downstream of Borel) call the natural flow of the Kern River up to 412 cfs must not be stored in Lake Isabella. Without operation of Borel, this flow would remain in the diverted reach of the Kern River.

The flow in the diverted reach of the Kern River during the month of March is effected similarly as streamflow during December, January and February. The average monthly unimpaired and impaired flow in the diverted reach is 63,562 and 19,917 acre-feet, respectively. This corresponds to an average daily flow of 1,034 and 324 cfs respectively. During March, unimpaired flow in the diverted reach of the Kern River rises with rainfall or early season snowmelt.

The average flow diverted into the Borel Canal during March is 29,248 acre-feet. This corresponds to an average daily flow of 476 cfs or 79% of capacity. This flow bypasses the diverted reach of the Kern River.

If the Borel Project were not operating, the streamflow in the diverted reach would tend to be higher than currently expected under impaired conditions. Water rights associated with the Kern 1 Project (downstream of Borel) call the natural flow of the Kern River up to 412 cfs must not be stored in Lake Isabella. Without operation of Borel, this flow would remain in the diverted reach of the Kern River.

The flow in the diverted reach of the Kern River during the month of April is affected similarly as streamflow during December, January, February and March. April 1 typically marks the beginning of the spring snowmelt season. Lake Isabella begins to store inflow. The average April unimpaired and impaired flow in the diverted reach is 93,903 and 33,205 acre-feet, respectively. This corresponds to an average daily flow of 1,578 and 558 cfs respectively. During April, unimpaired flow in the diverted reach of the Kern River rises with rainfall and snowmelt.

The average flow diverted into the Borel Canal during April is 30,339 acre-feet. This corresponds to an average daily flow of 510 cfs or 84% of capacity. This flow bypasses the diverted reach of the Kern River.

If the Borel Project were not operating, the streamflow in the diverted reach would tend to be higher than currently expected under impaired conditions. Water rights associated with the Kern 1 Project (downstream of Borel) call the natural flow of the Kern River up to 412 cfs must not be stored in Lake Isabella. Without operation of Borel, this flow would remain in the diverted reach of the Kern River.

The Lake Isabella Project operates to reduce flows in the diverted reach by storing inflow during the spring snowmelt season.

Streamflow in the diverted reach of the Kern River during the month of May is affected similarly as streamflow during April. Flows are reduced in the diverted reach as Spring snowmelt runoff is stored in Lake Isabella during May. The average May unimpaired and impaired flow in the diverted reach is 155,395 and 51,713 acre-feet, respectively. This corresponds to an average daily flow of 2,527 and 841 cfs respectively. During May, unimpaired flow in the diverted reach of the Kern River rises as temperatures rise and snowmelt increases.

The average flow diverted into the Borel Canal during May is 31,962 acre-feet. This corresponds to an average daily flow of 520 cfs or 86% of capacity. This flow bypasses the diverted reach of the Kern River.

If the Borel Project were not operating, the streamflow in the diverted reach would tend to be higher than currently expected under impaired conditions. Water rights associated with the Kern 1 Project (downstream of Borel) call the natural flow of the Kern River up to 412 cfs must not be stored in Lake Isabella. Without operation of Borel, this flow would remain in the diverted reach of the Kern River.

Streamflow in the diverted reach of the Kern River during the month of June is affected similarly as streamflow during March and April. Flows are reduced in the diverted reach, as spring snowmelt runoff is stored in Lake Isabella during June. The average June unimpaired and impaired flow in the diverted reach is 140,343 and 80,678 acre-feet, respectively. This corresponds to an average daily flow of 2,359 and 1,356 cfs respectively. During June, unimpaired flow in the diverted reach of the Kern River typically recedes as snowmelt decreases.

The average flow diverted into the Borel Canal during June is 32,135 acre-feet. This corresponds to an average daily flow of 540 cfs or 89% of capacity. This flow bypasses the diverted reach of the Kern River.

If the Borel Project were not operating, the streamflow in the diverted reach would tend to be higher than currently expected under impaired conditions. Water rights associated with the Kern 1 Project (downstream of Borel) call the natural flow of the Kern River up to 412 cfs must not be stored in Lake Isabella. Without operation of Borel, this flow would remain in the diverted reach of the Kern River.

Impaired streamflow in the diverted reach of the Kern River during the month of July is higher on average than under unimpaired conditions. Flows are increased in the diverted reach, as spring snowmelt runoff recedes and releases from Lake Isabella storage are made to meet downstream irrigations demands. The average July unimpaired and impaired flow in the diverted reach is 75,143 and 80,080 acre-feet, respectively. This corresponds to an average daily flow of 1,222 cfs and 1,302 cfs respectively.

The average flow diverted into the Borel Canal during July is 30,682 acre-feet. This corresponds to an average daily flow of 499 cfs or 82% of capacity. This flow bypasses the diverted reach of the Kern River.

If the Borel Project were not operating, the streamflow in the diverted reach would be higher than currently expected under impaired conditions. The Borel Project bypasses the diverted reach of the Kern River up to 605 cfs. Without Borel operation, this additional flow would remain in the diverted reach.

Impaired streamflow in the diverted reach of the Kern River during the month of August is higher on average than under unimpaired conditions. Flows are increased in the diverted reach, as spring snowmelt runoff continues to recede and releases from Lake Isabella storage are sometimes at maximum for the year to meet downstream irrigations demands. The average August unimpaired and impaired flow in the diverted reach is 33,710 and 55,991 acre-feet, respectively. This corresponds to an average daily flow of 548 and 911 cfs respectively.

The average flow diverted into the Borel Canal during August is 27,612 acre-feet. This corresponds to an average daily flow of 449 cfs or 74% of capacity. This flow bypasses the diverted reach of the Kern River.

If the Borel Project were not operating, the streamflow in the diverted reach would be higher than currently expected under impaired conditions. The Borel Project bypasses the diverted reach of the Kern River up to 605 cfs. Without Borel operation, this additional flow would remain in the diverted reach.

The average flow in the diverted reach of the Kern River during the month of September can be affected by the Lake Isabella and Borel Project operation in some years. The average monthly unimpaired and impaired flow in the diverted reach is 21,744 and 20,453 acre-feet, respectively. This corresponds to an average daily flow of 365 and 344 cfs respectively. During September, unimpaired flow in the diverted reach of the Kern River is typically steady and low as snowmelt runoff has typically concluded. In very wet years, snowmelt runoff can continue into September or rainfall events occur producing higher flows.

The average flow diverted into the Borel Canal during September is 21,511 acre-feet. This corresponds to an average daily flow of 362 cfs or 60% of capacity. This flow bypasses the diverted reach of the Kern River. Releases from available storage are made from Lake Isabella during September.

Without the Borel Project influence, the streamflow in the diverted reach would be higher than under unimpaired conditions. Average monthly flow in the diverted reach of the Kern River is about 6% greater than under unimpaired conditions. Without the Borel Project influence the flow in the diverted reach of the Ken River would be about 113% greater that under unimpaired conditions, on average.

The Borel Project alters flows in the diverted reach as discussed in Section 3.2. The Corps, through Lake Isabella operation, controls daily fluctuations of streamflow in the diverted reach. Lake Isabella operation can reduce natural daily fluctuations by storing peak inflow and releasing a more consistent flow pattern into the diverted reach. Alternatively, especially during times of steady reservoir inflow (summer, fall and early winter) downstream irrigation demands can dictate releases more variable than would occur naturally.

Annual mean daily hydrographs for the study period illustrating the impaired and unimpaired streamflow of the diverted reach of the Kern River are shown in Appendix B.

The Corps, through Lake Isabella operation, controls hourly fluctuations in streamflow in the diverted reach of the Kern River. A measure of ramping rate is used to illustrate the hourly variability of streamflow in the diverted reach of the Kern River. Table 2 lists the maximum one hour positive (increasing flow) and negative (decreasing flow) flow variation for each month for the period of available hourly data. It is typical to see hourly ramping rates in the 200 to 300 cfs/hour range and not unusual for ramping rates to be over 500 cfs/hour. The maximum values of 1,196 and -2,303 cfs/hour occurred in June of 1995. Figure 3 illustrates hourly hydrographs for select historical months.

Hourly streamflow information indicate releases from Lake Isabella into the diverted reach tend to be higher during the weekdays than weekends. Releases tend to be scaled back on Friday afternoon and ramped back up on Sunday afternoon (see Figures 3 and 4). This is presumably due to downstream irrigation demands being higher during weekdays than on weekends.

Channel configuration is important when examining streamflow, especially changes in streamflow. A rating table for the streamflow gage on the Kern River below Lake Isabella is used to understand water level changes that occur with fluctuations in flow (see Appendix C). This rating table was developed in 1989, it should provide guidance to water level alteration with a given flow. Table 3 is a summary of the rating table.

Fluctuations in streamflow have a larger effect on river stage when flows are low. Referring to the rating table in Appendix C, at the minimum fish flow of 15 cfs, a 200 cfs rise in flow changes the Kern River stage from 3.5 feet to 5.5 feet, a 2.0 foot increase. A 500 cfs rise in flow increases the Kern River stage from 3.5 feet to 6.7 feet, a 3.2 foot increase. At a flow of 500 cfs, a 200 cfs rise in flow changes the Kern River stage from 6.6 feet to 7.1, or about a 0.5 feet increase. A 500 cfs rise in flow increases the Kern River stage from 6.6 feet to 7.6 feet, a 1.0 foot increase.

The Corps and operation of the Lake Isabella Project control flows in the Kern River below the Borel Powerhouse. Operation of Lake Isabella can cause a significant change to the unimpaired hydrology, by storing snowmelt runoff in the spring and making releases from storage in the summer, fall and early winter to correspond with irrigation demands. Borel Project operation has an insignificant effect on the Kern River streamflow below the Powerhouse.

Kern River impaired and unimpaired streamflow is investigated in the diverted reach and below the Borel Powerhouse. Streamflow information is tabulated in Appendix A. Annual mean daily hydrographs for the study period illustrating the unimpaired and impaired streamflow of the Kern River in the diverted reach with and without the Borel Project are shown in Appendix B.

Both the Lake Isabella and Borel Projects affect Streamflow in the diverted reach of the Kern River. The Borel Project bypasses up to 605 cfs around the diverted reach year around. Lake Isabella stores spring snowmelt runoff and makes releases from storage during the summer and fall to meet downstream irrigation demands. Operation of the Borel Project has an insignificant effect on the Kern River streamflow below the Powerhouse.

Department of the Army Sacramento District, Corps of Engineers Sacramento, California. Isabella Lake Kern River, California Reservoir Regulation Manual. June 1953, Revised January 1978.

U.S. Geological Survey. 2001. Database at World Wide Web site: http://www.usgs.gov/

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