LABORATORY INVESTIGATIONS ON THE EFFECTS OF SHORE ICE TO COASTAL GEOMORPHOLOGY

Accurate modeling of coastal evolution in cold climates is hindered by a limited understanding of shore ice processes and their effects on morphology. Winter shore ice alters sediment transport in the nearshore. However, the rates and processes are not well constrained, and how these processes vary from high to low energy beach environments is unknown. To quantify how shore ice on both high and low energy shorelines will mobilize sediment we use a combination of field investigations and laboratory experiments to better understand the processes that lead to sediment entrainment within shore ice.

Thirty-five ice-sediment cores were extracted from two beaches along the Lake Superior shoreline to examine debris content. At a high energy beach, intermittent segments of debris laden ice were found, indicating wave action entrained sediment into the ice. At a low energy beach, no sediment was found in the ice column, but thick sections of sediment were found frozen to the base of the ice core, commonly called “anchor ice”. To examine the mechanics of how these sediments were entrained we built and conducted experiments on two novel devices housed in a large walk in freezer; a large diameter ring shear capable of shearing the anchor ice complex and a wave tank capable of simulating debris inclusion in ice through wave action. The wave tank, 3 m L x 0.6 m W x 1.2 m H, has a plunging wave generator, with variable speed to regulate wave amplitude and period, placed at one end of the wave tank to propagate waves through the flume. At the other end of the wave tank, a sediment bench and ramp were installed to simulate beach, nearshore, and offshore environments. A series of cameras track the motion of neutrally buoyant particles as well as capture wave propagation below the ice cap. The ring shear device shears an annulus of ice, 0.6 m D x 0.2 m W x .3 m H, over a sediment bed and is used to simulate the mobilization of “anchor ice”. A torque sensor records the shear stress needed to mobilize the frozen sediment. Following the completion of each experiment the sediment laden ice is cored and compared to the ice cores collected from the Lake Superior sites. From the correlation of processes active in the wave tank and ring shear with those active in natural sub ice conditions, a better constraint on shore ice sediment entrainment processes has been obtained.