River bed sediments are generally characterized as gravelly sands with some silts. Gravel mining continues to be active within the river corridor with gravel pits reclaimed for water storage purposes. The 1977 FHAD hydraulic model, which is the basis for the regulatory floodplain, was updated based on new topography, channel cross-sections, vertical datum adjustments, and model refinements to improve water surface elevation predictions at bridge crossings and other structures. Because of these changes, the existing 100-year water surface profile is predicted to be less than or equal to the regulatory profile. Natural vegetation in the Phase II corridor consists of shortgrass prairie.
Wetlands occur primarily along the river's edge, in backwater areas and along bars.
Wetlands of regulatory interest are located on the west bank between 88th Avenue and Cooley Drop 2, approximately 2,500 feet downstream of 88th Avenue, along Bull Seep, eastern tributary to the South Platte that runs along the floodplain terrace, between McKay Road and the Fulton Ditch, and below 104th Avenue on the east bank at the north end of the first bar. No suitable Preble's habitat was found due to the riparian corridor being disrupted by anthropogenic activities. Potential Spiranthes habitat was identified in the Bull Seep wetlands between McKay Road and the Fulton Ditch. Alternatives considered various combinations of reaeration structure locations and weir heights, and modifications to the Fulton Ditch Diversion structure. Efforts to move RS3 closer to the diversion structure would cause submergence of the weir, impacting reaeration performance.