REAL-TIME RESPONSE OF STREAMFLOW AND SPRING DISCHARGE TO PRECIPITATION RECHARGE EVENTS IN ICEHOUSE CANYON WATERSHED, EASTERN SAN GABRIEL MOUNTAINS, CALIFORNIA

Icehouse Canyon watershed lies in the eastern San Gabriel Mountains of Southern California within a pristine region of Angeles National Forest. Icehouse Creek is an important tributary of the San Antonio watershed that provides drinking water supplies to residents of Mount Baldy Village and the city of Upland. Flow during dry periods is controlled by discharge from landslide and alluvial deposits in addition to deep-seated fractures and fault zones in crystalline rock. We utilized a velocity flow probe, V-notch weirs, and pressure transducers to measure streamflow in Icehouse Creek and discharge from associated perennial springs at approximately bi-weekly intervals between July 2014 and December 2015. Pressure transducers were installed at selected gauging stations in order to obtain a continuous record of surface-flow over long periods of time. Coincident with the discharge study, we have monitored precipitation at 5 rain gauges located between 4600 and 6200 ft elevation beginning December 2014. Our general objective is to record the watershed’s response to precipitation recharge events.

Hydrographs comparing precipitation data with discharge over the observation period yield interesting preliminary results that provide an important baseline for documenting hydrology during the end of an extended 4-year drought period. Precipitation totals for individual storm events varied from 0.1 to 1.9 inches, which appear to be low compared to typical storm events occurring in Icehouse Canyon. An orographic relationship is only observed in precipitation records for 4 of the 8 largest storm events, perhaps due to the sporadic, showery nature of thunderstorms or other geographic controls. Comparison of two springs discharging from Cedar landslide along Icehouse Trail suggest that Spring 1 is more responsive to rain events while Spring 2 discharge remains relatively constant during minor storm events. It’s possible that Spring 1 is dominated by near-surface drainage from landslide material while Spring 2 may be fed by deeper bedrock fractures. We are eager to continue these measurements during heavy rain events from the forthcoming El Nino season which is finally occurring. Significant recharge events following four years of extended drought conditions are expected, which should provide a contrasting data set.