Historical channel adjustments of the lower Big Blue River below Tuttle Creek Reservoir, Manhattan, Kansas, 1857-1991

Abstract

The complex channel adjustments identified below Tuttle Creek Reservoir along the lower Big Blue River occur as channel degradation, bank erosion, and isolated zones of channel deposition or widening. As a result of the impoundment of the Big Blue River, the regulated clear water discharge from Tuttle Creek Reservoir frequently exceeds the critical -power threshold for stream power. Channel bank erosion and steepening have been the principal changes resulting from river regulation below the Tuttle Creek Dam. The lower Big Blue River is additionally impacted by Rocky Ford Dam. At this spillwater dam, which is located 1.4 miles (2.3 km) downstream of Tuttle Creek Dam, river velocity is increased because of a steeper slope. Excess stream power below Rocky Ford is dispersed through channel bank erosion and channel widening. Channel degradation below Rocky Ford is impeded by extensive channel bed armoring. Channel bed armoring below Rocky Ford has protected a small channel island from scour since 1937. At Casement Road bridge, which is located 2.5 miles (4.0 km) downstream from Tuttle Creek Dam, 12.1 feet (3.69 m) of degradation have occurred in the last 40 years. Sand dredging operations along the lower Big Blue River have severely impacted the channel morphology along the reach of river approximately 6 miles (9.7 km) downstream of Tuttle Creek Reservoir. Channel widening has occurred in both of the channel bends in which sand dredging activities occurred. Significant channel adjustments along the lower Big Blue River are primarily a result of the 1951 flood, the construction of Tuttle Creek Reservoir, and sand dredging activities.