A survey of the groundwater and surface-water interactions within drainages of Camp Pendleton was conducted. Stream flow was measured at several locations within the Santa Margarita, Las Flores and San Onofre Rivers. Stream flow, precipitation and groundwater levels from other sources were collected for the same time period. Stream flow and groundwater levels rose in response to precipitation events. Stream discharge increased by 2.7 - 38.7cfs and 0.4 - 2.4cfs for the Santa Margarita and Las Flores gaging locations, respectively. Groundwater levels rose 0.01 - 0.4ft and 0.01 - 0.1ft for the Santa Margarita and Las Flores, respectively. Differences in response could be explained by distance from river or size of drainage basin. Base flow or the stream flow contributed by groundwater was measured during fall 1998. Base flow ranged from 13.66- 28.12cfs, 0.67 - 1.24cfs, and 0.7 - 1.02cfs for the Santa Margarita, Las Flores and San Onofre drainages respectively. Calculation of net loss or gain of flow along a stream stretch indicated regions of gaining and losing streams. A possible relationship of regions of gaining streams within areas of narrowing stream channels was observed.
