San Pedro Creek Capistrano Fish Passage Restoration ... Pedro Creek Capistrano Fish Passage Restoration Project Longitudinal Study Brian Crowley Adam Edgell GEOG 642 Fall 2006 12/18/2006

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  • San Pedro Creek Capistrano Fish Passage Restoration Project

    Longitudinal Study

    Brian Crowley Adam Edgell GEOG 642 Fall 2006

    12/18/2006

  • Introduction In the fall of 2005, the City of Pacifica restored approximately 1300 linear feet of

    San Pedro Creek downstream of the Capistrano Bridge. The main objective of the

    project was the removal of a significant obstacle to fish passage while improving habitat

    conditions for migrating steelhead trout. Over the years, severe downcutting by the

    creek, due to the rapid urbanization of the area, had left the bottom entrance to the bridge

    perched approximately nine feet above the downstream channel invert, rendering the

    1960s Denil fish ladder underneath the bridge completely ineffective. This resulted in a

    severe migration barrier to spawning steelhead trout trying to work their way upstream.

    For this project, the City of Pacifica removed the failing fish ladder from beneath

    the bridge, and brought in 12,000 cubic yards of fill to raise and stabilize the streambed at

    its 1950s level and gradient, thus improving fish passage underneath the bridge. A series

    of nineteen rock and log weirs were then placed along the channel, creating a riffle-pool

    and step-pool system that gradually rises in elevation from the downstream gradient up to

    the Capistrano Bridge. This restoration will allow juvenile salmonids to move up the

    channel in a variety of stream flow conditions, while minimizing the height of the jumps

    that they will have to negotiate in order to make it upstream. In addition to enhanced fish

    passage, significant bank reconstruction was done as well. Newly regraded slopes, along

    with the removal of exotic plant species and replacement with natives found throughout

    the watershed, will help to reduce the sediment contribution from bank erosion, to

    increase canopy cover, and to maintain or lower water temperatures. It will also help to

  • create a stable, slightly laid-back bank, with the added benefit of reducing stream

    velocities through the reach (Temple 2006, SPCWC website).

    Our group was given the task of performing a longitudinal and cross-sectional

    study of the reach of San Pedro Creek that was restored in the Capistrano Fish Passage

    Restoration Project. We collected streambed elevation data along the thalweg of the

    creek, beginning at the Capistrano Bridge and working downstream. From this data, we

    were able to construct a longitudinal profile of the stream, from which we could derive

    gradient changes resulting from deposition and/or erosion. We also collected cross-

    sectional elevation data at a number of points along the stream corridor. This data

    allowed us to note any major changes in bank shape and stability, as well as the

    opportunity to document erosional movement along the stream of the originally-placed

    weirs. The main purpose of this study is to compare our data and profile with data

    collected and documented in the as-built plans for the project in November 2005. In this

    way, we hope to provide some initial insight into the ongoing effectiveness of the project

    in preserving and protecting salmonid fish habitat.

    Background on San Pedro Creek Watershed

    San Pedro Creek is a perennial stream that flows northwesterly through San Pedro

    Valley in the city of Pacifica in San Mateo County, California, and empties into the

    Pacific Ocean. It drains a 5,257 acre (8.2 square mile) basin containing the mainstem of

    the creek and five major tributaries (North Fork, Middle Fork, South Fork, Sanchez Fork,

    and one unnamed tributary), and composed of seven major subwatersheds (North Fork,

    Middle Fork, South Fork, Sanchez Fork, Shamrock, Pedro Point, and Hinton) and a

    number of minor subwatersheds. The North, Middle, and South Forks all converge near

  • the eastern end of the San Pedro Valley, and are met downstream to the northwest by the

    Sanchez Fork before reaching the Pacific Ocean. The upper reaches of the creek have

    healthy riparian areas and substantial winter flows that support migrating steelhead trout,

    making it the only creek within 30 miles of San Francisco that offers this type of habitat

    (Collins 2001, McDonald 2004, SPCWC website).

    The area of our study is a roughly 1150-foot reach along the mainstem of the

    creek, extending from the Capistrano Bridge downstream to a bend in the creek near

    where it runs behind the Sanchez Art Center.

    San Pedro Creek Watershed Geology and Geomorphology

    The San Pedro Creek Watershed (SPCW) is located at the northern extent of the

    Santa Cruz Mountains. Montara Mountain, at the southern extent of the watershed, is the

    highest point at 1,989 feet, and, along with San Pedro Mountain and Whiting Ridge,

    forms the southern boundary of the watershed. Sweeney Ridge, peaking at 1,220 feet,

    forms the eastern boundary, and connects to Cattle Hill, which marks the northern extent

    of the watershed. The creek flows towards the northwest where it meets the Pacific

    Ocean.

    The SPCW lies on the western edge of the North American tectonic plate, at its

    junction with the subducting Pacific plate. This leads to significant uplift and faulting in

    the region. The largest fault in the area is the Pilarcitos fault, a strike-slip fault that runs

    through the center of the watershed. The northern side of the fault is called the Pilarcitos

    block, while the southern side is the La Honda block. South of the Pilarcitos fault is the

    smaller San Pedro Mountain fault, which separates the La Honda block from the geologic

    structures to its north and south. This fault moves granitic rocks upward relative to the

  • downward movement of the sedimentary rocks to the north. There are also a number of

    smaller, unnamed faults in the northern half of the valley that run nearly parallel to these

    two faults. The SPCW is characterized by alternating, sheared, northwest-trending beds

    of the Jurassic/Cretaceous Franciscan formation that are faulted against Tertiary

    sedimentary rocks, that are, in turn, faulted against Cretaceous granitic rocks at the

    southernmost ridge top. The bottom of the San Pedro Valley is composed primarily of

    alluvium deposited from runoff from the surrounding highlands. These factors combine

    to make many areas within the SPCW prone to slope failure. (Collins 2001, Sims 2004,

    McDonald 2004).

    SPCW and San Pedro Creek as Steelhead Habitat

    As mentioned earlier, San Pedro Creek is notable in that it is the nearest creek to

    San Francisco that provides habitat to support migrating steelhead trout. In fact, the creek

    even supported a population of Coho salmon up until the 1950s. Although decent habitat

    for spawning is located throughout the mainstem and into the Middle Fork tributary, the

    best spawning habitat appears to be in the upper reaches of the Middle Fork.

    However, the mainstem provides the best conditions for rearing steelhead to smolt size

    (at about two years old) and for stages of development beyond spawning (Davis 2004,

    Hagar Environmental Science 2002, SPCWC website).

    Sediments from upland hillslope sources are a major contributing factor to the

    condition of steelhead habitat. Upland sediments contribute gravels that are important for

    spawning, but also contribute fine sediments that can bury those gravels, thus increasing

    the streams turbidity and disrupting the natural pool and riffle systems that are crucial to

    steelhead spawning and rearing. A growing concern is that, although the San Pedro Creek

  • mainstem is currently supporting steelhead, it is always at risk for elevated

    mobilization of sediment and an increase in fine sediment loads, given the amount of

    development and human activity in the area. Some research suggests that the substrate of

    the mainstem is lower in gravels than what is ideal for supporting steelhead, and that,

    therefore, steelhead using the mainstem are more vulnerable to water quality degradation

    from siltation compared to the Middle Fork tributary. (Hagar Environmental Science,

    2002)

    There are a number of other factors that adversely affect the steelhead

    environment, among them the bridges along the mainstem of San Pedro Creek, which

    serve as obstacles to adult steelhead trying to get to spawning areas, as well as to the free

    movement of the younger steelhead. Also of concern is the destruction of riparian

    corridors due to the regions rapid suburban development, which adversely affects fish

    habitat. This riparian vegetation is vitally important because it provides shade to

    moderate water temperature for the fish, while also providing overhead cover (Hagar

    Environmental Science, 2002).

    Development and Land Use in San Pedro Creek Watershed

    Up until the mid-1800s, what are now the lower reaches of San Pedro Creek were

    comprised of a large seasonal wetland and lagoon. Early maps of the area show a large

    willow thicket in the area east of what is now Linda Mar Shopping Center. West of this

    willow thicket lay a seasonal lagoon. The original stream channel was probably quite

    indistinct through this area, and during the dry season may have dwindled to nothing

    more than a few isolated pools. In all likelihood, the lagoon probably formed during the

    dry se