Author Description

Debris accumulation at bridge piers has been a significant problem at a number of bridge sites in Indiana, increasing risks of upstream flooding, scour, and stream instability. The current study aimed at identifying factors contributing to debris accumulation in order to formulate guidelines for the design of new bridges that would minimize their occurrence or impact. Three related approaches were taken: i) a systematic study of the available underwater bridge inspections reports, ii) a program of periodic visits and visual examination of bridge sites that were thought to be prone to debris accumulation, and iii) continued video monitoring of three bridge sites, and analysis of video images recorded during debris-transporting events. The available underwater bridge inspection reports spanned a period of 10 years and covered 370 structures. Heavy debris accumulation was observed at ≈20% of these sites, with the heaviest accumulations being concentrated in southwestern Indiana. Almost all of the sites in south-central and southern Indiana experienced at least moderate debris accumulation at one time. Sites with estimated volume of debris accumulation greater than 1000 cubic yards (‘mega’ sites), sites where heavy debris accumulation was observed during more than one inspection (‘chronic’ sites), and sites with at most minor debris accumulation during more than one inspection (‘lite’ sites) were examined in greater detail with regards to their crosssectional geometry and the placement of the piers, and the specific location of debris accumulation. Finally, video monitoring of debris-transporting events was conducted at three sites including one ‘mega’ site. This yielded the most detailed information regarding aspects that were visible above the water surface. This included including the variation of debris ‘discharge’ and amount of debris accumulated with time, typical debris trajectories, and even direct evidence of disaggregation of already accumulated debris. On the