DISCLAIMER: Data are verified using a separate air gap technology and undergo continuous quality control; however, users are advised to use these data with appropriate caution. These data include offsets to provide a measurement from lowest bridge steel (at the location indicated on the plots) to the surface of the water. The reported air gap value includes a reduction of the measured clearance to accommodate the estimated uncertainty inherent to the measurement and assure the actual clearance is at least the reported value with 95% confidence.