CHANNEL GEOMETRY AND MORPHOLOGY OF THE DRY CIMARRON RIVER OF NEW MEXICO AND OKLAHOMA

This study is part of a project comparing the geometry, morphology, and erosional and depositional history of two river basins, the Canadian River of Texas and New Mexico and the Dry Cimarron.

The upper segment of the Dry Cimarron in the volcanic highlands of the Raton-Clayton Volcanic Field decreases in elevation from about 2500 to 1700 meters above sea level and has an average gradient of 17.5 m/km. The width of the river valley is generally 1-2 km wide in this segment.

The middle segment of the river valley is carved into Mesozoic shales, sandstones, and siltstones, and channel elevation decreases from 1700 m to 1220 m above sea level with an average channel gradient of 4 m/km. The lower segment studied, upstream from the Kansas/Oklahoma line, lies within the High Plains Province, underlain by the late Tertiary Ogallala Formation. In this segment the channel elevation decreases from 1220 m to 1130 m above sea level with an average channel gradient of 1.9 m/km.

Although width of the valley generally increases downstream, the greatest valley widths are achieved in the Mesozoic section segment where width may exceed 3 km. The width of the active channel, at bank full discharge, increases downstream from 2 to 4 m wide in the volcanic highlands segment; to 6 to 15 m in the middle segment; to 15 to 60 m wide in the High Plains segment. Moderately sinuous reaches alternate with relatively straight reaches in all three segments studied. In the more sinuous reaches, sinuosity ranges from 1.5 to 1.7 in all segments. Within a relatively short stretch within the Mesozoic segment sinuosity exceeds 2.1. Radius of curvature of meanders generally increases downstream correlative with increase in channel width. Radius of curvature in the upper, volcanic highlands segment, ranges from 20 to 60 m, increases to 60-150 m in the middle segment, and dramatically increases to 600 to 900 m in the High Plains segment and in the transition zone between the Mesozoic and High Plains segments. Valley sinuosity ranges from 1.0 to 1.1 along the segments studied except for a small reach at the transition zone between the middle and lower segments where the sinuosity is approximately 1.8.

Although bedrock canyons are most abundant in the upper segment, all segments of the Dry Cimarron River Valley contain moderate amounts of alluvial fill. Dating of terrace material is underway to decipher the history of erosion and infilling.