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5.7 Biological Resources

sources. Large and small mammal tracks were observed along the sandy banks and within
both wet and dry washes of many of the drainages on the site. Coyotes, including two pups,
were observed using the Baltic rushes in moist to seasonally dry drainage channels at den
sites (Impact Sciences 2003).

The opportunity for plant diversity in the riverine, palustrine, and small lacustrine
environments appears to be limited, likely due to water stress during dry periods and
scouring flows during the rainy season. All wetland and drainage communities on the site
exhibit generally low species diversity, except for Oso Creek in the northwestern portion of
the site and the drainage north of SR-138 and east of the National Cement Plant Road.
Limiting factors for diversity may be livestock grazing and the presence of invasive,
non-native plants.

Stream Shoreline Stabilization/Sediment Retention, Storm Water Attenuation, and
Groundwater Recharge
Stream shoreline stabilization is occurring where sufficient vegetation is present along the
drainages to control stream bank erosion. Most of the sparsely vegetated stream banks are
eroding and contribute to the quantity of sediment moving downstream. The translocation
of sediments is evident in the size of the alluvial fans and by direct observation of sediment
movement, even during periods with low stream flows. Storm water attenuation is limited
in the systems because the on-site sandy soils do not retain significant water and stream
gradients encourage water to move through the site rapidly. The wetlands associated with
the loam soils retain some of the peak runoff and release the water into the drainages at a
slower rate than do the adjacent sandy soils (see Table 5.7-1, Soil Types and their
Hydrological Characteristics, for permeability and runoff rates of each soil type).

Groundwater recharge has a high degree of opportunity to occur and a high degree of
effectiveness since all the water flowing through the site infiltrates in the alluvial fans at the
downstream ends of each in the watershed. All of the water from the drainages assist in
recharging groundwater, as discussed in greater detail in Section 5.2, Hydrology and Flood,
which apparently moves in a subterranean manner toward the east, where a large quantity
is extracted for agricultural irrigation.

Jurisdictional Resources

Wetlands and permanent and intermittent drainages, creeks, and streams are generally
subject to the jurisdiction of the U.S. Army Corps of Engineers (USACE) under Section 404 of
the Federal Clean Water Act (CWA) (U.S. Congress 2008). By USACE definition, all aquatic or
riverine habitats between the ordinary high water mark (OHWM) of rivers, creeks, and
streams, are considered “waters of the U.S.” and may fall under USACE jurisdiction. If
adjacent wetlands occur, the jurisdictional limits extend beyond the ordinary high water
mark to the outer edge of the wetlands. The USACE defines wetlands as “those areas that are
inundated or saturated by surface or groundwater at a frequency or duration to support, and
under normal circumstances do support, a prevalence of vegetation typically adapted for life
in saturated soil conditions” (Environmental Laboratory 1987). The presence and extent of
wetland areas are normally determined by examination of the vegetation, soils, and

R:\Projects\PAS\CEN\000306\Draft EIR\5.7 Bio_051117.docx 5.7-132 Centennial Project
Draft EIR