Abstract

In late winter and early spring, ice covers become weak in strength and break-up. The passage of the resulting ice floes may be arrested at a downstream location and create an ice jam. The increase in ice and water pressures may eventually cause the break-up of the blockage. The sudden release of the jam can result in violent ice runs and surges. Ice jam related floods can cause substantial damage to property, erode river beds, endanger hydraulic structures and affect safety at river crossings. The current understanding of the breakup ice jam phenomena is insufficient and therefore the state-of-the-art is not well advanced. There is an urgent need to improve it. The primary objective of this study is to identify and determine through laboratory as well as numerical modeling, the processes involved during the collapse of an ice jam and the formation, development and propagation of the resulting surges and ice run. The research work was carried out in three parts, namely the investigation of the phreatic water levels along an ice jam, the transport of accumulation ice covers, and the characteristics of surges and ice runs caused by the jam release. From this study, five different types of release mechanisms related to the break-up of ice jams were identified. It was evident that the surge characteristics depend primarily on the type of release mechanism and the prevailing initial hydrodynamic conditions prevailing immediately before release. Observations showed that during the collapse of the jam, its thickness profile at the toe of the ice jam undergoes redistribution for a short period of time and subsequently the ice mass moves downstream in a relatively single layer scenario, A two-dimensional two-layer model is formulated for the simulation of an ice jam release event. The model is capable of simulating the phreatic water surface profile along an ice jam, the formation, development and propagation of the surge and ice run after the release and the redistribution of ice jam thickness after release. The numerical model was validated by the experimental data of the present and post studies.