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3. INFILTRATION TEST RESULTS

Infiltration testing was conducted over an uninterrupted 12‐week period from July 9 to
October 1, 2018. A synopsis of each infiltration test is presented on Figures 2 through 13
and depict calculated infiltration rates, cumulative water volume added, and pond water
levels over time, along with selected field photographs. Key conclusions, remaining
knowledge gaps, and recommendations for additional investigation work are included in the
bottom right text box of each figure.

Table 2 summarizes the results of all twelve infiltration tests, including the test period, basin
dimensions, infiltrating area, total volume of infiltrated water, and calculated one‐
dimensional vertical infiltration rates. Investigation sites are arranged in the order that tests
were completed. Infiltration rates from the main constant‐head tests were calculated based
on data near the end of each test after flow rates had stabilized and become effectively
asymptotic (discussions of infiltration rate trends are discussed further in respective site‐
specific discussions later in this section). As shown in the table, infiltration rates were
calculated based on an infiltrating area equal to the basin bottom footprint only (high
infiltration rate) as well as based on an infiltrating area equal to the basin bottom footprint
and saturated sidewall area (low infiltration rate). An average rate from the constant‐head
test based on calculated high and low infiltration rates is also presented.

All infiltration tests were concluded by shutting off the water source to the test basin and
tracking the rate of pond level decline (herein referred to as a falling‐head test). In one test
basin with a low infiltration rate (Wildwood Creek at California Street), two falling‐head
tests were conducted. Differences in pond water levels recorded every hour during draining
were used to calculate infiltration rates in units of feet/day based on an infiltrating area of
the basin bottom footprint only. For test basins with very high infiltration rates, only one or
two hourly measurements were recorded. In contrast, for test basins with low infiltration
rates, up to 10 or more hourly measurements were recorded. The high and low infiltration
rates calculated from the falling‐head test are presented in Table 2. Infiltration rates
calculated from the falling‐head test are not considered as reliable as those calculated from
constant‐head tests due to the change in driving head when the basin is draining, but they
do provide a good confirmation of the accuracy of metered flows during the constant‐head
test.

Infiltration Testing at Eleven
Investigation Sites in the Yucaipa
Basin, Yucaipa Valley, CA 9 TODD GROUNDWATER

Yucaipa Sustainable Groundwater Management Agency - January 23, 2019 - Page 28 of 137