 Bennett Valley is drained by Matanzas Creek which is incised into the valley floor; an unnamed stream and Spring Creek drain into Matanzas Creek from the east side of Bennett Valley below the Matanzas Creek Reservoir.A flood-control reservoir on Matanzas Creek in the central portion of the valley collects water from the drainage of the upper portion of the valley.Precipitation in the valley varies from approximately 35 to 40 inches (90 to 100 cm) per year.