OBSERVATIONS OF SUB-ICE CURRENTS IN FOUR NEW YORK LAKES USING ADCP

Few studies have been made on sub-ice currents and seiches in ice-covered lakes. Research was conducted during the winter of 2010-2011 to investigate shallow currents within four seasonally ice-covered lakes in upstate New York. An Acoustic Doppler Current Profiler (ADCP) was inverted and fixed in place in an ice hole above the deepest portion of each lake. The ADCP measured three-dimensional currents within the first five meters below the ice surface every 10 seconds for 3.00 to 6.75 hours. The lakes investigated had high surface-area-to-depth ratios expressed as relative depth (%). The theoretical first-mode surface seiche of each lake was calculated using the length and maximum depth of each lake. Arnold Lake in Central NY had a relative depth of 3.6 %, a length of 0.93 km, and a theoretical seiche period of 2.3 minutes. ADCP data show Arnold Lake had a mean horizontal speed of 19.0 cm/s, a maximum horizontal speed of 21.8 cm/s, and an average current direction of N 188¢ª E. Canada Lake in the southern Adirondacks had a relative depth of 2.4 %, a length of 2.8 km, and a theoretical seiche period of 4.8 minutes. It had a mean horizontal speed of 21.8 cm/s, a maximum horizontal speed of 74.1 cm/s, and an average current direction of N 176¢ª E. Lake Canadice in the western Finger Lakes had a relative depth of 1.4 %, a length of 5.1 km, and a theoretical seiche period of 10.8 minutes. It had a mean horizontal speed of 19.7 cm/s, a maximum horizontal speed of 70.2 cm/s, and an average current direction of N 178¢ª E. Otsego Lake in Central NY had a relative depth of 1.1 %, a length of 14.5 km, and a theoretical seiche period of 21.8 minutes. It had a mean horizontal speed of 41.1 cm/s, a maximum horizontal speed of 200 cm/s, and an average current direction of N 188¢ª E. In each lake, horizontal current speed, the vertical component of velocity, and the current direction oscillate over time. One possible explanation for these changes includes surface seiches caused by wind acting upon the ice-cover. As wind applies pressure to the ice, the water beneath it is forced to move up and down, causing the seiche. This is the first application of ADCP equipment to measure sub-ice currents within ice covered lakes in New York.