Snowmelt hydrology, paleohydrology, and landslide dams in the Deschutes River Basin, Oregon

The magnitude and frequency of stream runoff determines water supply and floodplain hazards on a human timescale, and the evolution of river channels on a geologic timescale. The studies constituting this dissertation employ statistical, geomorphic, and hydraulic methods to analyze (1) climatic controls on the magnitude and frequency of runoff and floods in high-elevation tributaries over the past century, and (2) geomorphic controls on channel morphology in the lower Deschutes River canyon over the past several thousand years.; Hydrology east of the Cascade mountain range in Oregon is dominated by snowmelt runoff from high-elevation drainage basins. Lower elevations in the Deschutes River Basin are arid and surface water is regulated by numerous dams. Snowmelt runoff is statistically related to circulation anomalies in the Pacific Ocean (Pacific Decadal Oscillation, or PDO, and El Nino Southern Oscillation, or ENSO) that determine coastal temperature and the path of the polar and subtropical jet streams. Higher mean annual and peak discharge events occur during PDO and ENSO cool phases, when the jet streams converge on the Pacific Northwest, and the persistence of these phases affects flood distribution on a decadal time scale.; The lower Deschutes River channel has been unusually stable under the historical hydrologic regime, reflecting the armoring of the channel by high magnitude, exceptionally rare events. The largest Holocene flood occurred 4000–5000 years ago, and had a discharge 2 to 5 times the largest historical flood. This paleoflood created or significantly reworked many alluvial surfaces bounding the lower 160 km of the channel. Runoff patterns were similar to those of historical rain-on-snow events centered over the Cascade Range, suggesting the flood was of meteorological origin. Breached Pleistocene landslide dams have created yet more enduring channel features such as constrictions, rapids armored with large boulders, and outburst flood deposits. Analysis of four landslide dams along the lower Deschutes River indicates that channel configuration through these reaches is stable under the full range of reconstructed Holocene meteorological floods, suggesting that the position of landslide debris controls canyon incision on millennial timescales.; This dissertation includes my coauthored and my published coauthored materials.