Page 22 - Yucaipa Sustainable Groundwater Management Agency - Yucaipa SGMA

hydrogeologic conditions, including the geologic structure of the basin, vadose zone and
aquifer characteristics, location and hydraulic effect of geologic faults, groundwater level
trends, and groundwater quality distribution (Geoscience, 2014b; USGS, 2001 and 2016).
Additionally, estimates of groundwater storage, usable storage, and safe yield (Geoscience,
2014a and 2015) have revealed the need to manage the groundwater basin conjunctively.

Yucaipa Valley Water District has been recharging in the Yucaipa Basin for the past decade.
However, only two studies have directly tested the infiltration capacity of surficial
sediments, findings from which are useful for interpreting infiltration test results for this
investigation. In 1969, the USGS performed a 26‐day pilot‐scale infiltration test at the
Wilson Creek Basins (Mooreland, 1970). The test involved creating a 100‐feet square test pit
by scraping the upper 1‐foot of basin sediment into a 4‐foot high berm. A total of 27 acre‐
2
feet of water over a wetted area ranging from 3,000 to 5,125 ft was infiltrated. Ponded
water levels in the test pit ranged up to 3 feet and averaged less than 1 foot. Results
indicated an infiltration rate of approximately 16 feet/day (after initial adsorptive forces and
air entrainment influences were removed), with a gradual decline to approximately 12
feet/day after 14 days, and 9 feet/day after 26 days. Declines were attributed to the
development of a shallow perching condition about 30 feet below ground surface caused by
apparent fine‐grained sediments and observed in a shallow piezometer during testing.

From December 2017 through January 2018, the City of Yucaipa, Yucaipa Valley Water
District (YVWD), Valley District, and San Bernardino County Flood Control District (SBCFCD)
performed full‐scale infiltration testing at the three basins (two detention basins to the west
and easterly debris basin) comprising the Oak Glen Creek Basins (City of Yucaipa, et al.,
2018). SWP water was used to pre‐wet all three basins for eleven days prior to testing.
Testing consisted of isolating each basin sequentially until a steady‐state recharge rate was
achieved in all three basins. Results revealed steady‐state infiltration rates of 4.3 feet/day in
the upper, eastern debris basin, 3.3 feet/day in the middle basin (the same basin tested for
this investigation), and 1.8 feet/day in the lower, western basin. It is noted that the full‐scale
infiltration testing was conducted on the undisturbed basin bottoms (with no removal of
historically accumulated fine‐grained clogging materials).

In addition to local investigations, foundational research in clogging dynamics in surface
spreading basins (Phipps, D.W., Lyon, S., and Hutchinson, A., 2007; see Appendix A) and
discussions with Orange County Water District (OCWD) (Adam Hutchinson, Recharge
Planning Manager, personal communication, November 7, 2018) were used to predict initial
and long‐term infiltration rates for full‐scale recharge basins at each investigation site.
Descriptions are provided in the site‐specific results of the assumptions used to account for
unknown variables, including the dimensions of a full‐scale recharge facility, site recharge
goals and active spreading period, and approach/frequency of basin maintenance.

Infiltration Testing at Eleven
Investigation Sites in the Yucaipa
Basin, Yucaipa Valley, CA 3 TODD GROUNDWATER

Yucaipa Sustainable Groundwater Management Agency - January 23, 2019 - Page 22 of 137