Low-Water Stream Crossings: The Iowa Experience

Replacement of old, unsafe bridges on low-volume roads is an increasing concern in rural America. Counties and local jurisdictions with inadequate bridges on secondary roads are faced with large capital expenditures for replacement structures or possible road closings. Low-water stream crossings (LWSCs) can provide a low-cost and reasonably safe alternative. Three types of LWSC are unvented fords, vented fords, and low-water bridges. A study was conducted to develop design guidelines for all three types of LWSC. Although the study focused on Iowa, the results are thought to be applicable to a wider geographic region. The salient features of this design process, including site selection, selection of most effective LWSC type, and geometric and material selection design, are described for the three types of structures. Although potential legal liability associated with LWSCs is a concern, the Iowa experience indicates that, with adequate warning signs, accidents and subsequent tort claims may actually be less with LWSCs than with deficient and obsolete bridges. On the basis of this history, it appears that potential liability from the use of prudently designed LWSCs is not a high risk. However, each state and local agency should thoroughly study code and local ordinance restrictions when considering LWSC options.