Ice jam mitigation using setback dykes: Coldwater River at Merritt, BC

Merritt, B.C. has a history of suffering damages from ice-jam and open-water floods. The most damaging flood on record happened in the city in 1991 due to an ice jam on the Coldwater River. A numerical ice-jam model is calibrated using the field data collected during the 1991 flood event, and the resulting model coefficient values ate shown to be comparable to what has been found in previous applications. With the ''calibrated'' input, hit model is then applied to different dyking scenarios as a means of protecting the city from future ice-jam events. It is shown that the common approach of placing dykes at the river's edge is not a satisfactory solution because it can aggravate winter floods by enhancing peak water levels, and augmenting ice-jam surge severity. This difficulty can be addressed by setting the dykes back for suitable distances, thus providing for adequate ice storage, and reducing the length of ice jams.