Novato Creek Watershed

The Novato Creek, located at the northwestern extent of San Pablo Bay, is the largest watershed in eastern Marin County.  Its creeks flow eastward through oak and bay forests, grasslands, the City of Novato, and into San Pablo Bay near the mouth of the Petaluma River.  The basin is 45 square miles and the main drainage in the watershed is Novato Creek; Novato Creek joined by six major tributaries along its 17 mile length: Leveroni, Bowman Canyon, Warner, Arroyo Avichi, Arroyo de San Jose, and Simmonds Slough.

Human settlement

Miwok and Pomo people were the earliest residents of the watershed.  Olompali, the site of a significant Miwok village, is located at the southern base of Mt. Burdell.  In 1839 Mexican land grants established Rancho Novato.  Grazing brought a host of invasive annual grassland plants that eventually dominated the deep-rooted native perennial grasses and altered runoff rates.

By 1856 extensive apple orchards occupied the valley floor and many of the creeks had been channelized for irrigation.  The tidal marshlands had also been diked and drained for agriculture (primarily oat-hay production) by the middle of the nineteenth century.  Laurel Collins (1998) notes that at this same time, the marshlands were actually extending into the bay due to massive sedimentation from hydraulic mining in the Sierra Nevada.  In the 1880s the creek was dredged to make way for schooners bound for San Francisco.

The town of Novato covers 49% of the watershed area and occupies former grassland, oak woodland, and savanna areas.  Novato, one of the four townships in existence when Marin County formed in 1850, was incorporated in 1960.  The population grew sharply after the railroad was built.  Ground was broken for Hamilton Air Force Base in 1932 and dedicated in 1935 (the base was decommissioned in 1974, and designated as a historic district in 1988).  Because Novato was one of the last cities in Marin to be developed, it grew rapidly between 1970 and 1990.

 

Changes to Watershed Processes

The Novato Creek watershed’s channel network has been altered from its historic natural conditions.  The channels we see today reflect those alterations and many of the channels are actively in transition to a more stable configuration.  The majority of the channels are narrower than expected for the watershed size and rainfall and urbanization has likely increased the timing and magnitude of peak runoff events such that more water flows to the creek at a quicker rate (Questa, 2007 1).

Extensive bank erosion indicates that the channels are in a widening phase.  Sediment production in the watershed occurs due to upslope processes such as landslides and gully development, as well as channel bed incision and bank erosion.

The mainstem of Novato Creek and its major tributaries are all highly entrenched within the city limits and are constrained by development on the banks.  Channels in the upper watershed are still incising and are expanding headward into hillside swales.

The stream and tide channels in the lower reaches of the watershed are managed for flood conveyance and navigation and no longer function optimally for sediment transport.  Sediment aggradation is occurring in the lower reaches as a natural process to re-establish a natural channel configuration based on hydrology, slope, and sediment supply dynamics.

Habitat Types

Vegetation

The Novato Creek watershed supports a diversity of communities— from mountainous and hilly headwaters to saltwater and brackish-water marsh along the bay.  According to the 1999 Upland Habitat Goals Project, the lower marsh habitats represent some of the largest remaining tidally influenced habitats in the bay region supporting abundant waterfowl populations.  Despite being one of the driest drainages in Marin County, the watershed supports both rearing and spawning habitat for steelhead.  Agricultural baylands within the Novato Creek watershed provide seasonal wetland habitat for migratory waterfowl and shorebirds and this watershed also contains oak woodlands that provide habitat for terrestrial wildlife species.

The watershed is composed primarily annual grasslands interspersed with oak-bay woodland and oak savanna in the upper watershed.  Small patches of northern coastal scrub occur within the woodlands and serpentine outcroppings occur at the upper elevations in the northern watershed.  In the lower watershed, oak woodland and oak savanna become more prevalent.  According to the Novato General Plan, the best developed riparian communities occur in the upper watershed along Novato Creek and Arroyo San Jose.

One of the best examples of an intact riparian community within the watershed is at O’Hare Park at Novato Road and San Marin.  In this area, the riparian plant community is structurally diverse and supports a mixture on native species and large woody debris is left in place by the City of Novato enhancing instream habitat.

The lower reaches of the watershed adjacent to Novato Creek and east of Highway 101 support saltwater marsh and brackish-water marsh; both are subject to tidal action.  Freshwater seasonal wetlands occur in areas that were once historical baylands.  These areas have been diked off to provide agricultural land and now support oat hay production.

Fish and Wildlife

The Novato Creek watershed supports a number of special status plants and animals.  Of particular interest are the occurrences of wetland-adapted species along Rush Creek and lower Novato Creek wetlands.  Noteworthy species include San Pablo song sparrow, California black rail, saltmarsh common yellowthroat, and California clapper rail.  Western pond turtles 2 (Fawcett 2000 3) and naturalized bullfrogs (ESA 2003 4) are known to occur in Novato Creek.

Fish

The Novato Creek watershed is known to support 10 extant fish species (6 native and 4 introduced).  Native species include California roach, Sacramento pikeminnow, Sacramento sucker, steelhead, threespine stickleback, and Prickly sculpin.  Introduced species include rainwater killifish, western mosquitofish, striped bass, and green sunfish.  Historically, the watershed supported native tidewater goby; the last collection occurred in 1945 (Leidy 2007 5).  Fawcett (2000 and 2006 6) also notes the presence of non-native bluegill, largemouth bass, brown bullhead, chameleon goby, and inland silverside.

Salmonids (steelhead and Chinook salmon) are also found within the Novato Creek watershed. According to Supervising Fisheries Biologist with DFG, George Neillands, Chinook salmon are likely strays from the Sacramento River system. A net pen release site for the Sacramento River Chinook is located in Tiburon, which could result in fish moving into Marin streams.

There are no reported occurrences of California red-legged and foothill yellow legged frogs within the watershed (CDFG 2008 7).

Heron and egret nesting colonies have been monitored by Audubon Canyon Ranch since the early 1990s (Kelly, et al., 2006 8; E. Condenso personal communication, May 15, 2008).  There are two active and one inactive heronries within the greater Novato Creek watershed.

Avian surveys were conducted from Diablo Avenue to Grant Avenue during the 2006 nesting season as part of the Novato Flood Control Project (Phase VIII) (ARA 2006).  65 avian species were detected over 1,300 meter reach, 27 confirmed nesting or thought to be nesting on site, and additional 12 suspected.  Noteworthy species include Great blue heron, Cooper’s hawk, Allen’s hummingbird, purple martin, oak titmouse-nesting, Nuttall’s woodpecker – nesting.

Human Habitation and Land Use

Land Use                                        Imperviousness

The development of Novato leveled off between 1990 and 2000 then increased— as a result, Novato was the fastest growing city in Marin in 2005 and is anticipated to continue to grow, reaching a projected population of approximately 63,000 by 2020.  Over the next 20 years the City expects greater growth in jobs than population, lowering the percentage of the population that commutes to other places for work.

Novato is actively engaged in downtown redevelopment with proposed development of commercial and residential uses and supporting infrastructure.  The Marin Countywide Plan identifies Novato as having the greatest growth potential in Marin for commercial and industrial development.

Land protection and restoration efforts in the watershed include the Hamilton Wetland Restoration project, Rush Creek and Bahia restoration projects, and planning by the City of Novato and Marin County Open Space District for preservation and land acquisition for trails.