I-10 Twin Peaks Traffic Interchange, Environmental Assessment

Affected Environment and Environmental Impacts October 2005
Desertscrub vegetation is found in the light industrial area west of I-10 to the Santa
Cruz River and east of I-10 to Linda Vista Boulevard.
Riparian Scrub is associated with dry ephemeral washes that occur throughout the
study area, but occur in the highest density and most natural condition east of El
Camino de Mañana along Linda Vista Boulevard. Riparian Scrub vegetation is
characterized by plant species found in adjacent desertscrub habitat, such as
foothill palo verde and velvet mesquite, although riparian plants are typically
larger and often occur at higher densities than those in upland areas. Plants in this
association grow in rows along the margins of the watercourses and are clearly set
apart from the intervening vegetation of the uplands. Plant species present include
foothills paloverde and velvet mesquite. Most of the washes have been stabilized
within Continental Ranch and within the residential housing areas along Linda
Vista Boulevard. Stabilized washes in these areas have straightened stream
channels, improved bank protection (often using soil cement), and are cleared of
most vegetation.
Cottonwood/Willow Riparian Forest occurs along the Santa Cruz River. This
vegetation association is characterized by a narrow band of small to moderatesized
(10 to 30 feet in height) Freemont cottonwood and Goodding willow.
Additional plant species in the area include seep willow, cattail, bulrush, tamarisk,
and velvet mesquite. Along this reach of the Santa Cruz River, Riparian Forest is
restricted to small, scattered stands separated by areas of low shrubs such as
desertbroom and seep willow. The Riparian Forest is restricted to the low-flow
channel where the influence of perennial effluent water flow from Pima County's
Roger and Ina Road Treatment Plants allows this vegetation to survive in an
otherwise dry river. Vegetation outside the low-flow channel, in the high-flow
channel, is characteristic of disturbed areas. This vegetation consists of
desertbroom, shrub-like velvet mesquite, four-wing saltbush, and grasses. In
addition, large areas of bare soil characterize the high-flow channel.
Riparian habitat includes the trees, other vegetation, and physical features
normally found on the banks and floodplains of rivers, streams, and other bodies of
water. Although riparian areas occupy a small area, they support a diversity of fish
and wildlife species. In addition, riparian areas can help reduce flood flows and
flood damage, improve groundwater recharge, reduce the damaging chemicals and
other compounds that reach open water, and reduce wind erosion on adjacent
lands. Riparian areas also provide important open space and recreational
opportunities. Riparian areas approximate the jurisdictional waters presented in
Figure 4-3.
Wetlands are low-lying areas typically saturated with moisture that typically
provide habitat for a variety of plant and animal species, including many
endangered species. The state of Arizona has no wetland protection program, but
wetlands are regulated by the Corps under Section 404 of the CWA. A regulated
wetland is one that meets 3 criteria: 1) hydrophytic vegetation; 2) hydric soils; and,
3) wetland hydrology (the presence of water).
Interstate 10 Traffic Interchange at
Twin Peaks/Linda Vista
4-37
Project No.: NH-010-D (AIW)
TRACS No.: 10 PM 236 H5838 01D