Aggradation at bridges

Aggradation at bridges causes the bridge waterway opening to be reduced, po ssibly resulting in upstream flooding and increased contraction scour. Aggr adation results when the sediment load supplied to a reach of river from up stream exceeds its capacity to transport sediment. Solutions to aggradation al problems at bridges are often complex and expensive. Solutions include i ncreasing sediment transport through the bridge by modifying the channel, c onstructing an upstream sediment trap, redesigning the bridge, dredging, an d treating the cause of the aggradation. At many bridges, aggradation probl ems can be severe. As an example, aggradation at a bridge in northern Penns ylvania is described. The benefits, disadvantages, and costs for various po ssible solutions to the example problem are compared and the most cost-effe ctive solution is presented.