I-10 Twin Peaks Traffic Interchange, Environmental Assessment

Affected Environment and Environmental Impacts October 2005
AGFD records indicate that no Gila chub surveys have been conducted within the
study area; however, no native fish species have been documented within the
effluent dominated reaches within the study area. Gila chub were not observed
during a pedestrian survey of the study area. The study area is more than 40 miles
from the nearest population of Gila chub in the Tucson Basin. Connectivity from
the study area to these known populations is restricted because the Pantano and
Rillito River systems no longer have perennial flows and are dry washes with the
exception of flows during storm events.
Gila Topminnow
The Gila topminnow is listed as endangered without critical habitat. The basic
habitat requirement for the Gila topminnow is water that is permanent and free
from nonindigenous and invasive predators. Beyond that, habitat requirements of
Gila topminnows are broad. The species historically occupied headwater springs
and vegetated margins and backwater areas of intermittent and perennial streams
and rivers. Topminnows can withstand water temperatures from near freezing to
90-100 degrees Fahrenheit. Gila topminnows can live in a fairly wide range of
water chemistry conditions, from acidic water to water with low levels of
dissolved oxygen. Preferred habitats contain dense mats of algae and debris,
usually along stream margins or below riffles, with sandy substrates sometimes
covered with organic muds and debris.
AGFD records indicate that no Gila topminnow surveys have been conducted
within the study area; however, no native fish species have been documented
within the effluent dominated reaches within the study area. Gila topminnows
were not observed during a pedestrian survey of the study area. The study area is
more than 40 miles from the nearest population of Gila topminnow in the Tucson
Basin. These drainages are not connected to the study area by perennial water
flows.
Southwestern Willow Flycatcher
The southwestern willow flycatcher is listed endangered with proposed critical
habitat. The southwestern willow flycatcher breeds in dense riparian habitats along
rivers, streams, or other wetlands. The vegetation can be dominated by dense
growths of willows, seep willow, or other shrubs and medium-sized trees. There
may be an overstory of cottonwood, tamarisk, or other large trees, but this is not
always the case. In some areas, the flycatcher will nest in habitats dominated by
tamarisk and Russian olive. One of the most important characteristics of the
habitat appears to be the presence of dense vegetation, usually throughout all
vegetation layers present. Almost all southwestern willow flycatcher breeding
habitats are within close proximity (less than 20 yards) of water or very saturated
soil. This water may be in the form of large rivers, smaller streams, springs, or
marshes. At some sites, surface water is present early in the nesting season, but
gradually dries up as the season progresses. Ultimately, the breeding site must
have a water table high enough to support riparian vegetation
Interstate 10 Traffic Interchange at
Twin Peaks/Linda Vista
4-29
Project No.: NH-010-D (AIW)
TRACS No.: 10 PM 236 H5838 01D