Proceedings of the Pacific Northwest Floods of February 1996 Water Issues ConferenceOctober 7-8, 1996 — Portland, OR

very high precipitation intensities; a middle zone from 800 - 1200 m where a deeper snowpack firststored then released water, and an upper zone above 1200 m where a very deep snowpack storedmuch of the direct precipitation throughout the storm.

The condition of the vegetation in small (0.1 to 1 km 2) watersheds also influenced peak flows. Peakflows from logged watersheds ranged from 14 to 66% above forested controls, even thoughclearcutting had occurred 20 to 30 years previously. Overall, the 1996 storm had higherstreamflows at lower elevations and smaller flows at higher elevations than the December 1964flood. Delivery of water (and presumably sediment and wood) was more asynchronous in 1996 withless of the total watershed contributing, resulting in less geomorphic disturbance in the most recentstorm.

Co-Authors: Ted Dvrness, Don Henshaw, and Fred Swanson, USDA Forest Service, Pacific NorthwestResearch Station, Corvallis, Oregon: Julia Jones, Department of Geosciences, Oregon State University,Corvallis, Oregon.

GEOMORPHIC RESPONSE TO THE FLOOD OF '96 IN A 5TH-ORDERWATERSHED IN THE OREGON CASCADES

SHERRI JOHNSON, OREGON STATE UNIVERSITY, DEPARTMENT OF GEOSCIENCES

The storm of February 6-8, 1996 produced peak discharges comparable to the December 1964"flood of record" in many Coast Range and Cascade watersheds in Oregon. The February 1996flood offers a rare opportunity to study the geomorphic responses of forested mountain watershedsin the Pacific Northwest to a "formative event" that, due to typically high thresholds of erosion inmountain streams, tends to occur much less frequently than in lowland streams.

As part of a larger regional study, this study focuses on the geomorphic response to the 1996 floodwithin the H.J. Andrews Experimental Forest, a 5th-order watershed in the Blue River basin(tributary to the McKenzie River) of the western Oregon Cascades. This watershed was located onthe southern boundary of the storm track. A wealth of data exists on prior conditions in thewatershed, including detailed maps of channel unit types and valley floor geomorphic andvegetative surfaces for 5+ km of lower Lookout Creek, as well as particle size data, channel crosssections, and detailed maps of (tagged) woody debris at selected sites within the watershed,providing an unusual opportunity for an in-depth assessment of flood effects. The study seeks torelate the structural characteristics of the watershed (e.g., gradient, constrained vs. unconstrainedreaches, becirocEiTs.illuvial channel, valley floor morphology, position relative to tributaryjunctions) and antecedent conditions (e.g., distribution of woody debris and local sediment sources)to the types, intensity, and spatial distribution of geomorphic effects (disturbances) of the 1996flood within the watershed.

Co-Authors: John Faustini, Julia Jones, and Beth Lambert, Department of Geosciences, Oregon StateUniversity, Corvallis, Oregon: Gordon Grant and Frederick Swanson, U.S. Forest Service, PacificNorthwest Research Station, Corvallis, Oregon.

THE NORTHWEST STORM OF FEBRUARY 96: A SOUTHWEST IDAHOHYDROLOGIC PERSPECTIVE

C. W. SLAUGHTER, NORTHWEST WATERSHED RESEARCH CENTER, USDA IDAHO

Understanding extreme hydrologic events can be aided by long-term observation sites. ReynoldsCreek Experimental Watershed (RCEW) in the Owyhee Mountains of southwest Idaho has beenutilized over 35 years for process research and for development of long-term baselinehydrometeorologic records from an upland rangeland watershed. Major winter floods of the

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THE PACIFIC NORTHWEST FLOODSOF FEBRUARY 6-11, 1996

PROCEEDINGS OF THEPACIFIC NORTHWEST WATER ISSUES CONFERENCE

PORTLAND, OREGON, OCTOBER 7-8, 1997

Editor

Antonius Laenen

Assistant to the Editor

James D. Ruff

BARU American

Institute of#111.1162=1•11 EftNABO R! G CI NI HYdrOlOgY

AMERICAN INSTITUTE OF HYDROLOGY

1997

All of the papers in this volume have been reproduced from diskettes or hard copies prepared by theauthors. The Editor and the Organizing Committee wish to make clear that neither they nor thePublisher shall take responsibility for any errors and omissions, or for the opinions stated by theauthors.

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© Copyright 1997 by the American Institute of Hydrology (AIH)

Library of Congress Catalog Card Number is: 97-074852

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