Spatial variation in the power of mountain streams in the Sangre de Cristo Mountains, New Mexico

The principle indicator of river energy expenditure, stream power, has a significant influence on many forms and process attributes of the fluvial system, yet few basin-wide analyses of stream power variations have ever been conducted. Recent studies hypothesize a peak in the mean stream power distribution in small (10 km2)- to intermediate (100 km2)-sized basins. To test hypothetical stream power profiles in a high mountain setting, 129 cross-sections of stream networks within the Costilla basin of northern New Mexico and southern Colorado were measured for channel form, local sediment conditions, and basin characteristics. Geomorphic and hydrologic analysis of these river sites throughout the Costilla basin yielded evidence of abundant local control over fluvial processes and forms. Within the basin, the spatial deviations of stream power from the hypothetical patterns derived from hydraulic geometry, in some cases >200% deviation, match areas of specific geologic and hydrogeologic control. As an alternative to traditional hydraulic descriptions of downstream channel form, a probabilistic process–response model can incorporate local and basin-scale variables and allow more realistic feedback mechanisms than in traditional regime theory. The probabilistic nature of this type of model also allows prediction of multiple modes of channel adjustment, an ever-present challenge to extremal and physically based simulations.