This site is operated in cooperation with the

U.S. Army Corps of Engineers
Chicago District - Chicago, Illinois



Air Gap Disclaimer:
Estimation of "air gap" (also commonly referred to as "air draft" or "clearance") is provided as the difference in measured low-steel elevation and stream stage (elevation) obtained either directly or indirectly, from USGS streamgaging stations. This air gap data is provided as a planning tool only and users of this data must exercise due diligence while underway and assume full responsibility for ensuring safe transit through all bridge openings. Although USGS intends to make this data available through the USGS server 24 hours a day, 7 days a week, timely delivery of data and products from this server through the Internet is not guaranteed. The USGS provides this data "as-is" for a quick reference planning tool but assumes no legal liability or responsibility resulting from the use of this information.