THE EFFECTS OF ICE ON COASTAL EROSION

Winter shore ice, whether continuous or variable, alters sediment transport in the nearshore but the rates and processes are not well constrained. Accurate modeling of coastal evolution in cold climates is hindered by a limited understanding of these processes and their effects on morphology. Consistent ice cover likely buffers the beach and upper shoreface from the erosive impacts of winter storm waves, while shorelines with ice subject to multiple breakup events likely enhances erosion and sediment transport; however, there is a lack of quantitative observations describing how variable ice cover influences coastal morphology. To quantify how cold climate shorelines will respond to reduced and variable winter ice cover associated with climate change we use a combination of laboratory experiments and field investigations to quantify the processes that lead to sediment entrainment within shore ice.

A large flume, 3m L x 0.6m W x 1.2m H, was constructed within the UW-Madison Surface Processes’ walk-in freezer to simulate the effect of wave motion on sediment entrainment in shore ice. The freezer is set to -6°C to initiate ice formation at the water surface while a heating element in the bottom of the tank keeps the lower region of the flume ice free. A plunging wave generator placed at one end of the flume, that is kept ice free, propagates waves through the sample chamber. After surface ice has formed, the wave generator will produce waves similar to those we have recorded beneath the ice-capped surface of Lake Superior. The wave generator can also extend the range of wave properties beyond those observed at our study site to investigate other possible conditions. Sand from the study site is placed in the flume and the passing waves entrain the material in the freezing ice cap. A series of cameras mounted along the perimeter of the wave tank will track the motion of neutrally buoyant particles as well as capture wave propagation below the ice cap. Following the completion of each flume experiment the sediment laden ice is cored, thin sectioned, and compared against a series of ice cores collected from the Lake Superior site. Correlating processes active in the flume with those active in natural sub ice conditions will give us a better understanding of the constrain on sediment entrainment processes.