Numerous Challenges Await Kern River Group as Kern River Snowmelt Surges
May 20, 2019
As of midnight, May 19, 2019, Isabella Reservoir storage stands at 338,527 acre-feet, 60% of the full lake capacity of 568,075 acre-feet. The US Army Corps of Engineers, the entity responsible for the operation and maintenance of Isabella Dam, has established a maximum pool level for Isabella Lake for this year of 361,250 acre-feet as part of the Isabella Dam Safety Modification Project first implemented back on 2006. Currently, with a near-record Kern River Basin snowpack in the midst of its spring snowmelt cycle, less than 25,000 acre-feet of Isabella Dam storage space remains before reaching the Corps-imposed storage limit.
On the heels of a bone dry month of April 2019, the month of May has ushered in record breaking precipitation in the Kern River watershed along with unseasonably low temperatures ranging 15-20 degrees below normal. Weather conditions in the Kern River Basin changed dramatically beginning the 9th of May, 2019, as an unusually wet late spring storm moved into the area. On May 10, 2019, 1.29” of precipitation was recorded at the Army Corps of Engineers Isabella Dam headquarters, the single greatest 24-hour rain total on record for May, breaking the previous daily maximum precipitation record of .75” set back on May 19, 1957. A second series of May storms rolled into the Kern River watershed beginning May 16, 2019, bringing a mix of rain and snow to the high mountain regions above Isabella Lake and above normal rainfall to the San Joaquin Valley floor. At Isabella Dam, May 2019 cumulative precipitation for the month to-date has reached 1.87”, already the highest rainfall total for any May since records began in October of 1949. The previous record May rainfall as measured by the Corps was 1.74” in May of 1998.
Kern River Basin Snowpack Conditions
A manual snow survey of the Kern River Basin snowpack was performed by State of California Department of Water Resources and Kern River Ranger District personnel during late March of this year. The annual April 1st measurement of snow depth and snow water content in the Kern has been an ongoing practice since 1948. The Kern River snowpack is typically sampled at 16 long-established snow courses, as well as several snow sensor sites, ranging in elevation from 7,650’ to 11,400’. The April 1, 2019 snow survey reported a Kern River basin-wide average snow water content of 33.5”, 197% of the April 1 average, sixth highest of record. The greatest basin-wide average April 1st snow water content ever registered for the Kern River snow shed was 49.5” in 1969, followed by 44.0” back in 1978. The leanest April 1 average water content ever recorded was 0.4” in 2015, a year that also yielded the lowest April-July snowmelt runoff in Kern River history.
Kern River Basin snowmelt began in earnest around the first of April 2019. Beach Meadow snow sensor (elev. 7,650 ft.), which reported close to 22.0” of snow water content at the end of March 2019, was mostly bare of snowpack by the 20th of April. Based on the latest Kern River snow sensor data, snowmelt is occurring at elevations of up to approximately 8,500 feet.
2019 Water Supply/Operations Outlook
In its final seasonal Bulletin-120 on California Water Supply Conditions as of May 1, 2019, the State DWR predicted the Kern River to flow at 170% of normal during the 2019 April through July snowmelt period, or roughly 780,000 acre-feet. In its very latest streamflow forecast update dated May 14, 2019, the State DWR nudged the expected Kern River snowmelt yield to 790,000 acre-feet, a result of above normal May precipitation in the Kern River watershed.
Kern River inflow to Isabella Lake during April 2019 amounted to 201,092 acre-feet, 219% of the long-term average, the twelfth time in 126 years of record the Kern River natural flow topped 200,000 acre-feet during April. The April 2019 Kern River runoff was bolstered by low elevation snowmelt, most of which accumulated during a series of early March 2019 cold storms that dropped heavy snow down to elevations as low as 1000’. April inflow to Isabella Lake peaked on April 28, 2019, with 5,583 cubic feet per second (“cfs”) during the height of an abnormally warm ten-day episode which saw mountain and valley temperatures soar nearly 20° above normal. A secondary peak inflow occurred on May 10, 2019 at 5,784 cfs, although this particular peak discharge was aided by warm rain in the Kern River watershed that quickly accelerated lower elevation snowmelt. With over 30.0” of snow water content still remaining at Upper Tyndall Creek snow sensor (elev. 11, 450 ft.), it is still possible for Kern River inflow to Isabella Lake to reach a new seasonal high over the next few weeks.
During April 2019, water releases from the Isabella Main Dam into the lower Kern were strong, with a maximum discharge of 3,229 cfs occurring on April 16th. This, in part, allowed the Kern River Interests to evacuate minor quantities of Isabella Reservoir storage, helping to meet local water demands while making additional storage space available for snowmelt runoff yet to come. Depending on near-future precipitation and temperature conditions which are known to have a strong influence in the rate of Kern River Basin snowmelt, water releases at the dam may be pushed even higher in the coming weeks to avoid an excess storage situation at Isabella Lake. Dana Munn, Kern River Watermaster, reminded me that the Kern River Group ordered up to 5,400 cfs during May and June of 2017 to help satisfy irrigation, spreading and incidental domestic water demands within the historic Kern River Service Area, without Corps-induced flood control releases at the dam. Based on these recent short-term water use capabilities of the Kern River Group, there may be sufficient operational flexibility in the days ahead to absorb the Kern River 2019 water supply entirely within Kern County.
May on the Kern: Facts, Notes and Highlights
Over the long-term period of Kern River flow records, the maximum mean natural flow is 2,796 cubic feet per second and falls on the 29th day of May. The maximum median (middle value in a distribution) flow of Kern River is 2,409 cubic feet per second and lands on the 7th day of June.
May 4 – On this date in 1998, Isabella, California received .36” of precipitation in the midst of five consecutive days of measurable rainfall (May 3-7, 1998). Coupled with a second storm period over May 12-13, 1998, total monthly precipitation for May 1998 ended at 1.74”, then maximum of record for May. Since 1949, May of 1957 had been the only May of record to register greater than one inch of precipitation (1.03”) at Isabella Dam headquarters.
May 11 – On this date in 1969, the Kern River was flowing above 10,000 cfs for the first time during May in the river’s storied history. During May of 1969, all-time maximum natural flow records were established for each day between the 9th and 22nd. May 1969 runoff on the Kern River was 617,968 acre-feet, maximum on record and largest known 30-day cumulative flow.
May 29 – The largest Kern River natural flow ever recorded during the spring snowmelt period occurred on May 29, 1983, at 14,038 cfs. At 5:00 a.m. on May 29th, the Kern River North Fork peaked at 10,270 cfs while the mean flow of South Fork Kern River for May 29, 1983 was 2,843 cfs. Snow water content at Upper Tyndall Creek on May 29, 1983 registered an incredible 53.6”.