Downstream Changes in Stream Power in the Henry Mountains, Utah

Total stream power does not necessarily increase systematically in the downstream direction because of the conflicting influences of channel slope, width, and depth. Historical records and field data for arroyo systems of the northern Henry Mountains, south-central Utah, show that total stream power decreased in the downstream direction during a deposition period before 1896 and increased downstream during an erosion period thereafter. When total stream power declined in the downstream direction, channels were small and meandering, and the ten-year flood exceeded channel capacity, resulting in overbank deposition of sediment. After an especially erosive flood in 1896, total stream power increased in the downstream direction because channels were in the bottoms of arroyos that confined discharges, resulting in channel erosion and through-put of sediment. In 1980 deposition was occurring in the headward portions of the continuous arroyo system and in the large master stream, but not in mid-basin areas. Channels in the arid and semi-arid Henry Mountains do not exhibit mutual adjustment between form and process. Rather, at times of catastrophic system-wide events, fluvial processes control channel forms, whereas at other times channel forms control fluvial processes. Comparison of historical and modern conditions shows that mutual adjustment is unlikely to occur in the discontinuous operation of semi-arid fluvial systems.