June 20, 2019

Shortly after my May 2019 Kern River water report for the Valley Ag Voice was circulated, the full impact of May storm activity in the Kern River watershed became clear. The State of California Department of Water Resources in its initial June 2019 water supply bulletin posted a nearly unprecedented 120,000 acre-foot increase in anticipated Kern River snow melt runoff above the first of May 2019 forecast volume of 780,000 acre-feet. In order to accommodate this 11th hour boost in Kern River water supply and because of the limited storage space available at Isabella Reservoir due to dam construction work, the Kern River Watermaster, acting on behalf of the Kern River Interests, began a steady increase in Isabella Dam outflow, reaching a then-seasonal high discharge of 4,500 cubic feet per second (“cfs”) by the end of May.

Due to the highly unusual May 2019 weather conditions, which brought cooler temperatures and precipitation, the Kern River Basin had an increase of four times than normal. Snowpack at the very highest elevations in Kern remained virtually frozen. This combined with the advent of higher than normal temperatures in early June 2019 caused rapidly melting snow to rush down the southern Sierra Nevada mountain slopes, which finally unleashed the near record Kern River snowpack. At Lake Isabella, maximum Kern River inflow for the year was registered on June 14, 2019 at 6,713 cfs. Based on 126 years of the Kern River April to July stream flow records, this year’s timing of peak snow melt flow was one of the ten latest ever to occur. Not since 2011 when the river peaked on June 16th has the date of Kern River maximum daily April through July yield been pushed back so late in the season. Over the long-term record, the latest peak snow melt discharge as verified at First Point of Measurement near Bakersfield occurred on June 22nd, 1906. By comparison, the earliest known date of peak April to July runoff was April 8th, which happened in both 1902 and 2018.

In reaction to the early June 2019 sudden rise in snow melt runoff to Lake Isabella, water orders were again sharply boosted by the Kern River Group, resulting in a mean discharge from the dam of 5,400 cfs as of June 11, 2019, the maximum water release out of Isabella Reservoir for the year to-date.

 The immediate goal of the Kern River water users over the next few weeks is to gradually fill Isabella Reservoir to no more than 361,250 acre-feet, the temporary capacity of Lake Isabella. Once the storage mission is achieved, expect dam outflow to                 be curtailed to around 3,500 cfs sometime after the 4th of July. The most current water operation outlook places the flow of Kern River below Isabella Dam at or above 2,000 cfs through late August of 2019.

In order to meet winter flood control measures required by the US Army Corps of Engineers for operation of Isabella Dam and Reservoir, Lake Isabella storage is likely to be drawn down to no more than 170,000 acre-feet by November 1, 2019.

June on the Kern – Hydrographic Notes and Highlights 

June 8 – On this date in 1972, a heavy downpour dumped 0.50” at the Corps of Engineers Isabella Dam headquarters, the maximum 24-hour precipitation amount to be registered during June since records began in 1949. For the entire month of June 1972, a total of 0.80” of precipitation was measured at the dam, the greatest on record for the month.

June 13 – On this date in 1983, water began to flow over the Isabella Dam spillway for only the 3rd time (1969, 1980) since dam operations began in 1954. Spillway mean discharge peaked on July 6, 1983 at 5,721 cfs. Water would continue to flow over the spillway through July 20, 1983, constituting a record 38 consecutive days of spillway operation.

June 15 – On this date in 1969, total flow at Second Point of Measurement near Enos Lane was 3,748 cfs. During the month of June 1969, maximum 2nd     Point flow fell on June 8th with 4,475 cfs. Total flow passing 2nd Point during the month was 203,484 acre-feet. The total annual flow at Second Point of Measurement during 1969 was 1,088,892 acre-feet, surpassing the 1916 annual 2nd Point flow of 1,052,100 acre-feet to become maximum of record.

June 16 – On this date in 1924, the mean natural flow of Kern River at First Point of Measurement was 179.82 cfs, the lowest amount of discharge ever recorded for any June 16th. Total Kern River natural flow for June of 1924 was 14,069 acre-feet, which stood as the lowest volume of June runoff ever measured until June of 2015 when Kern River managed only 13,813 acre-feet of natural flow, becoming the driest of record.

June 19 – On this date in 1961, Isabella Reservoir reached its peak storage level for the spring snow melt season with 53,096 acre-feet. The lake surface covered 2,725 acres; mean inflow to the reservoir was 427 cfs while total outflow from the dam was 355 cfs. On November 19, 1961, lake storage bottomed out for the 1961 calendar year at 17,410 acre-feet. This extremely low lake level prompted discussions between the County of Kern and the Kern River Interests that would ultimately result in formation of the Kern County Recreational Pool Agreement of 1963 that permanently established a 30,000-acre-foot minimum recreation storage pool at Lake Isabella. 

June 21 – Computations of Isabella Reservoir daily mean storage for the period of 1954 to 2017 reflect that maximum annual lake storage falls on the 21st of June at 291,359 acre-feet. Minimum annual storage falls on December 2nd at 142,296 acre-feet.

SOURCEBy Steve Lafond, Valley Ag Voice
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