3.0 Affected Environment - Knik Arm Bridge and Toll Authority

Knik Arm Crossing DraftFinal EIS
Affected Environment
3.8.1.1 The Mat-Su
3.8.1.1.1 Water bodies (lakes, streams, ponds)
Within the Mat-Su, three river systems, the Susitna, Matanuska, and Knik, provide the
majority of the freshwater entering Upper Cook Inlet during spring, summer, and fall
(Mat-Su Borough 2005f) (Figure 3.53). With their headwaters in the mountains, these large
rivers are fed by glaciers. Other water bodies of importance for fisheries include Wasilla
Creek, Cottonwood Creek, Willow Creek, Fish Creek, and Little Susitna River. The average
discharge for these rivers is typically exceeded in the months of May through September,
when rainfall, glacier melt, and snowmelt are at a maximum. Peak flows typically occur in
June, July, and August. As temperatures decrease in October and precipitation turns to snow,
the glacier melt and snowmelt are dramatically reduced.
Lowest flows typically occur in February and March. All streams freeze over, and many of
the smaller ones freeze to their bed. Streams in the Study Area typically begin to freeze over
in late October or early November and do not break up until late April or May (Mat-Su
Borough 2005f).
There are over 22 lakes in the Mat-Su portion of the Study Area. The largest of these include
Big Lake, Wasilla Lake, and Nancy Lake, which are all used for recreation (Mat-Su
Borough 2005f). Most lakes feed small streams and, therefore, contribute to their flow
regulation (Mat-Su Borough 2005f).
Three surface water bodies exist within the immediate Mat-Su portion of the Study Area:
Lake Lorraine, located approximately 1 mile west of Knik Arm and 500 feet north of the
existing Point MacKenzie Road; Twin Island Lake, located approximately 1¾ miles
northwest of Lake Lorraine and 1,000 feet east of Point MacKenzie Road; and Lost Lake,
located approximately 1,000 feet north of Twin Island Lake and 3,500 feet east of Point
MacKenzie Road (Figure 3.53). The three lakes are all partially bordered by wetland areas
with no distinct inflow or outflow channels. The surface area of each of these lakes is
approximately 0.2–0.3 square mile. Numerous smaller, unnamed lakes and ponds exist
between Knik Arm and along Point MacKenzie Road. Two are located just south of Twin
Island Lake and near Point MacKenzie Road, while several smaller lakes are located between
Twin Island Lake and Lake Lorraine. Two additional smaller unnamed lakes are located
northeast of Lake Lorraine.
Existing mapping shows an unnamed stream crossing the Study Area in the vicinity of Twin
Island Lake (Figure 3.53). Field investigations, however, determined that there was no
discernable stream channel present (KABATA 2006q). The area is considered a wetland bog
and is included in the discussion of wetlands in Section 3.8.2.
3-168 12/18/07