Low-Cost Ice-Control Structure

Communities located on small, northern rivers can experience severe breakup ice jams. While flood damages may be significant locally, they are often insufficient to justify the cost of conventional flood-control structures. Environmental concerns also tend to render these structures unattractive. A new, low-cost structure appears to be well suited to control breakup ice jams on small rivers. It consists of massive sloped blocks, partially buried in riprap, placed across the river adjacent to a natural floodplain. The blocks will arrest a breakup ice run and form a stable, partially grounded ice jam. Trees or boulders on the floodplain retain ice pieces in the river channel while allowing flow to bypass the structure. Large gaps between blocks allow easy fish and canoe passage. Refrigerated hydraulic model tests indicate that the structure should perform well even during severe breakup events. A prototype built in Hardwick, Vt., has performed well during the four mild breakup events experienced to date. Its cost of $3,600/m of river width represents about an order-of-magnitude reduction compared with previous ice-control structures.