Phreatic Water Surface Profiles along Ice Jams – An Experimental Study

Abstract

In Northern Regions, the formation of ice jams along many rivers is a common phenomena. These ice jams may occur during the freeze-up and more importantly during the spring break-up period. Ice jams in general have considerable effects on the water levels because they alter the water surface profile for stretches of tens of kilometers along the rivers. As a consequence, water levels increase significantly upstream of the ice jam and result in the flooding of towns situated along the river banks. Knowledge of the water levels within an ice jam can be used to estimate many parameters that are difficult to measure and observe. Examples of such parameters are the local and global ice jam resistance to the flow, and forces acting within an ice jam. While ice jams are notorious causes of serious problems in hydraulic engineering, very little engineering methodology exists to deal with such problems. In this paper, the results of a laboratory study aimed at investigating the development of the water surface profile along an ice jam that is lodged in place, are analyzed and presented. A rectangular flume with a horizontal bed was used for the experiments. Twelve experiments carried out under different geometrical, hydrodynamic and ice conditions, were analysed. A simulated floating ice cover was used to arrest the downstream transport of the ice floes, forming the ice jams. The experiments indicate two types of ice jams, those that are floating and others that are lodged at one or more locations along their length. The phreatic water level along a floating ice jam is up to 0.92 the ice jam thickness. This is not true when an ice jam is lodged in place. Different experiments have shown that the water surface profile along a lodged ice jam follows similar tendencies regardless of the geometry, ice floe size distribution and hydrodynamic conditions. It was found that the phreatic water level varies linearly from the trailing edge of the ice jam up to approximately 90% of its length downstream. Towards the remaining part of the jam's length the water level follows a cubic polynomial line.