BATHYMETRIC AND HYDRAULIC SURVEYS OF THE MISSOURI RIVER AT THE U.S. HIGHWAY 59 BRIDGE AT ATCHISON, KANSAS

Bathymetric and hydraulic surveys of the sand-bed channel documenting flow characteristics were conducted on the Missouri River in the vicinity of the Amelia Earhart Bridge on U.S. Highway 59 at Atchison, Kansas. A multibeam echo sounder mapping system and an Acoustic Doppler Current Profiler were used to obtain channel bed elevations and vertically-averaged and near-bed velocities for a 2,300-foot long reach of the Missouri River, encompassing an active railway bridge, the Earhart Bridge on U.S. Highway 59, and the location of a new bridge being constructed on U.S. Highway 59. Survey information was used to determine the conditions of the streambed in the vicinity of the bridges prior to and during construction of the replacement bridge main channel pier. Data collected in July 2009 are being used as the base conditions of the channel bed prior to the construction of the new bridge on U.S. Highway 59. Subsequent surveys of the area during and after construction of the main channel pier and cofferdam of the new U.S. 59 Bridge will be used to monitor the streambed and document the effects of the construction on the streambed.

The pre-construction streambed in the vicinity of the bridges displays a classic sand-bed dune and ripple pattern, with high-frequency, low-amplitude ripples in the higher velocity thalweg of the channel near the Kansas (right descending) bank, and lower-frequency, higher-amplitude dunes in the more turbulent middle of the channel and toward the Missouri (left descending) bank. Larger dunes were more prominent in the area of turbulent flow near the piers of the railway bridge and the Amelia Earhart Bridge, and near the ends of wing dikes on the inside of the bend of the river on the Missouri bank. Substantial scour holes were observed at both of the railway bridge piers, with the scouring effect of one of the railway bridge piers extending to the Amelia Earhart bridge pier. The pre-construction streambed elevations will be compared to the streambed elevations during construction.