Artificial recharge in the upper Santa Ana Valley, southern California

Abstract

Artificial recharge has long been an integral part of water-supply management in the upper Santa Ana Valley. About 7,500 acres of unlined channels and 2,590 acres in 60 off-channel recharge facilities are available for water spreading. To estimate potential infiltration rates for the recharge facilities, 63 single-ring infiltrometer tests were conducted at 22 recharge facilities. Tests ranged from 1 to 14 hours and averaged about 14 hours. Measured infiltration rates ranged from about 0.1 foot per day at Patton basin to 106 feet per day at Lynwood basin. Grain-size distribution was determined on 25 soil samples collected at infiltrometer test sites. Regression analysis showed a direct relation between the logarithm of the infiltration rate and the logarithm of the 20th percentile particle diameter, corresponding to 20 percent finer on the grain-size graph. Regression analysis also showed an inverse relation between the logarithm of the infiltration rate and the logarithm of the sorting coefficient. Test sites were grouped into two geologic units--younger alluvium and older alluvium. Logarithmic plots of infiltration rates versus the ratio D20/30 yielded straight-line plots for both geologic units. Silt clogging greatly affects infiltration rates. Some clogging was observed in nearly all facilities, and significant reduction of infiltration rates was measured in seven basins. Drillers' logs, supplemented with data from 11 test holes augered during the investigation, were used to delineate low permeability horizons that might retard downward movement of recharged water. Low permeability zones were found within the upper 50 feet at five basins. Unused storage capacity in underlying ground-water basins ranges from large in Chino basin to minimal in Oak Glen subbasin. Recharge operations in Bunker Hill, Lytle, Etiwanda, and Claremont Heights basins should be carefully monitored to guard against overfilling the aquifers. Recharge capacity, which is the volume rate (cubic feet per second) of water that can be recharged for extended periods at a given site, was estimated for all unlined channels and off-channel recharge facilities. Recharge capacity of all off-channel facilities was estimated to be more than 3,200 cfs (cubic feet per second). Total recharge capacity for major stream systems seems to be adequate to handle floods of 5-year recurrence intervals, and most systems have sufficient capacity to handle 10-year floods. Potential recharge rate, which is the infiltration rate (feet per day) that can be maintained over extended periods under normal operating conditions, was delineated throughout the study area on the basis of controlling geologic and hydrologic factors. Estimated recharge rates range from less than 1 foot per day in areas underlain by older alluvium to 4 feet per day in areas underlain by coarse-grained younger alluvium.