Ventura River

 

The Ventura River and its tributaries comprise the major watershed in Zone 1 in the western portion of Ventura County. The other drainages in Zone 1 are relatively small undeveloped coastal drainages like the San Jon Barranca that drains a portion of the City of San Buenaventura. The Ventura River Watershed comprises an area of approximately 223 square miles with a little less than half of it within the Los Padres National Forest. The Ventura River outlets into the Pacific Ocean and has several major tributaries including Matilija Creek, North Fork Matilija Creek, San Antonio Creek, Coyote Creek and Canada Larga.

The zone boundaries incorporate two of the supervisorial districts for Ventura County, District 1 and District 3. Supervisor District 1 incorporates a majority of the zone. The O&M superintendent for Zone 1 is John Lagomarsino.

The weather extremes are characterized by hot summer daytime highs (often exceeding 100 degrees Fahrenheit) and cool winter. Winds from the ocean have a moderating effect on the climate near the coast. Frosts are rare in the coastal region and common in the inland valleys and mountains. In general, the higher elevations receive more rain. The average annual rainfall for the drainage basin upstream of Matilija Dam is 23.9 inches per year while the average annual rainfall near the mouth of the Ventura River is approximately 16.9 inches per year. The average for the entire watershed is approximately 20 inches per year. There is extreme seasonal variation in the rainfall and over 90 percent of the rainfall occurs between the months of November and April. The peak historic rainfall intensity is approximately 4.04 inches per hour measured during a 15-minute period at the Wheeler Gorge gage in the mountains adjacent to Ojai.

The Ventura Watershed lies within the western Transverse Ranges in California, an active tectonic region that contributes some of the highest sediment yields in the United States. The range is composed almost entirely of highly folded and faulted marine sedimentary rocks. Steep slopes in the upper portion of the watershed produce a large portion of sediment supplied to the Ventura River. Mass wasting from erodible, colluvial soils on hillsides, including slides, slumps, debris flows and earthflows, is a common mechanism by which sediment is transported to the river channels. Sediment production in the area is also impacted by the occurrence of forest fires that clear the normally dense vegetation and greatly increase the erodibility of land surfaces (US Army Corps of Engineers, 2004).

The watershed topography is characterized by rugged mountains in the upper basins transitioning to relatively flat valleys in the lower downstream areas. Over 75 percent of the Ventura River Watershed is classified as rangeland covered with shrub and brush and 20 percent of the basin is classified as forested. In general, the highest sediment-producing parts of the watershed are those covered in shrub and brush and are located in the upper parts of the watershed where slopes are greater and annual rainfall is larger. Nearly 45 percent of the watershed can be classified as mountainous, 40 percent as foothill, and 15 percent as valley area. Two major reservoirs lie within the watershed, Lake Casitas and Matilija Reservoir. Both serve as water supply reservoirs, with Casitas Dam located on Coyote Creek about 2 miles upstream of its confluence with the Ventura River.

There are five debris basins that collect sediment from drainages before they enter the mainstem Ventura River. Live Oak, McDonald and Dent Canyon basins are on direct tributaries of the Ventura River. There is one on Stewart Canyon, a tributary to San Antonio Creek, and another partially destroyed basin on upper San Antonio Creek. Major communities in Zone 1 include the City of Ojai, community of Oak View, and the western part of City of San Buenventura. Total population in these communities in year 2000 was approximately 22,988, excluding the western portion of the City of San Buenaventura and County inhabitants (USACE, 2004).

Ventura River Programs and Projects

Hydrology Reports - Partial Listing