Smooth Sheet Bathymetry of Cook Inlet, Alaska
February 25, 2014
The bathymetry of Cook Inlet is unusually well-described for an Alaskan area, with a majority of the relevant surveys conducted since 1964, and the entire area well-surveyed except for some of the northern mud flats. Part of the reason for this wealth of information is that Cook Inlet is home to Alaska's largest city, Anchorage, which includes significant shipping routes and several active oil rigs. Approximately 11% of the area has also been mapped with multibeam acoustic methods in six sections, providing modern, higher resolution data. Still, there have been a number of obstacles for surveyors of all eras to overcome as noted in the Descriptive Reports for earlier National Ocean Service (NOS) hydrographic surveys, including rough weather (H03431/H03432), winter ice in the north end (H03431/H03432), "steep banks breaking off and falling into the water sounding like small explosions of dynamite" (H03431/H03432), large tidal range (H03431/H03432), a tidal bore 3 to 6 ft high (H03431/H03432), strong currents up to 8 knots (H03203), shifting channels (H03431/H03432), dangerous shoals (H03044), extensive mud flats (H03431/H03432), and atmospheric refraction causing superior mirages of landmarks on clear days (H03203). Later surveys also noted the difficulties caused by areas of sand waves
Cook Inlet is a large, semi-enclosed body of water extending north off of the central Gulf of Alaska, between the Kenai Peninsula and the base of the Alaska Peninsula, with the Barren Islands lying just south of the 90 km wide opening (Fig. 1). Just inside the Inlet are the indentations of Kamishak Bay on the west and Kachemak Bay on the east, creating an expanse about 200 km across. There is a narrowing about 190 km from the mouth of Cook Inlet at two capes called the East and West Forelands, constricting the width of Cook Inlet to about 16 km. In the north end are two 70 km long arms with extensive mudflats: Knik Arm on the west side, which has the Matanuska and Knik rivers entering at its terminus, and Turnagain Arm on the east side which has Twentymile River, Portage Creek, and the Placer River entering near its terminus. The largest river in Cook Inlet, the Susitna, and its neighbor the Little Susitna, enter on the west side just below Knik Arm near Fire Island. Cook Inlet is about 320 km in length from its mouth to the tip of Knik Arm. There are four large islands within Cook Inlet: Augustine in Kamishak Bay, Kalgin and Chisik just south of the Forelands, and Fire Island at the division between Knik and Turnagain arms - there are over 500 other islands smaller than 5 km2 in size. At 20,000 km2 in size, Cook Inlet is larger than several other partially enclosed marine bodies of water in the lower 48 United States, including Chesapeake Bay, Long Island Sound, San Francisco Bay, and Puget Sound.