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|Ice distribution and winter surface circulation patterns, Kachemak Bay, Alaska
|United States. Army. Corps of Engineers. Alaska District.
Gatto, Lawrence W.
|Cold Regions Research and Engineering Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
|CRREL report ; 81-22.
Abstract: Development of the hydropower potential of Bradley Lake, Alaska, would nearly double winter freshwater discharge from the Bradley River into upper Kachemak Bay, and the Corps of Engineers is concerned about possible subsequent increased ice formation and related ice·induced problems. The objectives of this investigation were to describe winter surface circulation in the bay and document ice distribution patterns for predicting where additional ice might be transported if it forms. Fifty-one Landsat MSS band 5 and 7 and RBV images with 70% cloud cover or less, taken between 1 November and 30 April each year, were analyzed for the eight winters from 1972 to 1980 with standard photointerpretation techniques. Results of this analysis showed that glacial sediment discharged into Kachemak Bay acts as a natural tracer in the water. Inner Kachemak Bay circulation in the winter is predominantly counterclockwise, with northeasterly nearshore currents along the south shore and southwesterly nearshore currents along the north shore. Most of the ice in the inner bay forms at its northeast end and is discharged by the Fox, Sheep and Bradley Rivers. Some ice becomes shorefast on the tidal flats at the head of the bay, while some moves southwestward along the north shore pushed by winds and currents. When this ice reaches Coal Bay, it accumulates between Homer Spit and the north shore. This buildup extended out to Coal Point at the tip of Homer Spit in February 1976 and 1979; ice was not observed in the nearshore zone along the south shore of the inner bay. Most of the summer circulation patterns in the outer bay determined by previous drift card and current meter surveys and from temperature and salinity distributions were not observed on the winter imagery. Because the surface water of the outer bay is generally much clearer year-round than that in the inner bay and because ice is usually absent, winter surface circulation patterns cou ld be inferred for only limited areas around the outer bay. No ice was observed anywhere in the entire bay on the November imagery and most of the ice was gone by mid·April. The ice distribution and generalized circulation patterns indicated that any additional ice formed in the inner bay due to future increased winter discharge from Bradley River would be likely to accumulate along Homer Spit and probably be blown into the outer bay by the dominant northerly winter winds.
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