SBCT Final EIS - Govsupport.us

Chapter 3 ⎯ Affected EnvironmentThe northwest corner of DTA is at the edge of the 200-mile-wide Salcha seismic zone that extendsfrom Fairbanks southward through Prince William Sound. The Fort Greely (DTA) installation liesimmediately north of the active Denali Fault, which runs roughly west-northwest near the southernboundary of the West Training Area and the northern edge of the Alaska Range (USARAK 1999a).Slip on this fault is less than 0.5 inch per year (USARAK 2007).Prior to the November 3, 2002 earthquake, only three earthquakes larger than magnitude 4 have beenrecorded in or immediately adjacent to the installation since 1973. Recent deposits of sand, gravel,and silt mask faults can be found on DTA. Damage from the November 3, 2002 earthquake is still beingassessed and repaired. Continuing research into this most recent and strong earthquake may revealmore information about the potential hazards along the Denali Fault and associated seismic zones tothe north.3.2.2 WATER RESOURCESThe ROI for surface water resources includes portions of watersheds containing FRA and DTA. Morespecifically, the areas from the upstream military boundary to the downstream watershed boundary ofTanana and Cook Inlet watersheds. The ROI for surface water is not necessarily the same as the ROIfor groundwater. Because groundwater often crosses topographic (watershed) boundaries, the ROI forsurface water is expanded to include the aquifers underlying these watersheds and any aquifersdowngradient (in the direction of groundwater flow) from these areas.3.2.2.1 Fort RichardsonSurface Water OccurrenceFRA is located within the Cook Inlet watershed. Two major waterways on FRA include Eagle Riverand Ship Creek. Eagle River is a glacial waterway that originates at the base of the Eagle Glacier inthe Chugach Mountains, and then meanders across FRA west towards the Knik Arm. Ship Creek, anon-glacial stream, originates at Ship Lake in the Chugach Mountains and flows 25 miles to the KnikArm. The stream is diverted by a water supply diversion dam located at the base of the ChugachMountains on FRA, approximately 10 miles from the mouth of the river for U.S. army base use(USARAK 2004).Other perennial streams at FRA include Chester Creek and North Fork Campbell Creek flowingthrough the southwestern portion, McVeigh Creek and Snowhawk Creek (tributary to Ship Creek)draining the central portion, and Otter Creek (tributary to Eagle River) draining the northwestern portionof FRA. Numerous seasonal tributaries and drainage ditches also exist at FRA. A portion ofNorth Fork Campbell Creek from Long Lake in the Chugach Mountains to the southwestern corner ofFRA is an important source of recharge for the groundwater aquifer (Cederstrom et al. 1964).FRA also has 12 named lakes and ponds and several unnamed water bodies. The combined area forthe named lakes and ponds is 359 acres. Five relatively large lakes managed for recreational fishinginclude Clunie, Otter, Gwen, Thompson, and Waldon. The other seven lakes and ponds on FRA includeChain Pond, Web Pond, Lake Kiowa, Dishno Pond, Cochise Lake, Diablo Pond, and TanainaLake (USARAK 2004).No ice bridges are constructed on FRA, and no permits exist for creating ice bridges. Permanentbridges exist as necessary at all maneuver trail crossing points over Eagle River, Ship Creek, and thesmaller waterways on FRA (USARAK 2004).February 2008 3–100 2/25th SBCT Final EIS