Flood Plain Information Study Nooksack River Washington

Author : Roger G. Bertschi
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (819 download)

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Download or read book Channel Changes and Flood Frequency on the Upper Main Stem of the Nooksack River, Whatcom County, Washington written by Roger G. Bertschi and published by . This book was released on 1992 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This study focuses on three aspects of the hydrology of the lower Nooksack River that are of interest in understanding flooding processes and for planning: (1) a comparison of changes in channel locations and cross-sections at several points along the Nooksack, (2) the determination of distribution of surface sediment in exposed bars and banks, and (3) an estimation of flood frequencies by the Gumbel and Log Pearson methods. These aspects give a useful depiction of recent flooding and channel activity. The Nooksack River channel has remained within a defined thalweg zone from 1906 to 1991, the period of map record. The zone is approximately 1.5 km wide, and roughly centered on the 1987-1991 channel. Channel patterns during the period 1906-1991 have been generally braided, with transition to a single channel at the downstream end of the study reach. Changes in the channel have usually involved temporary reoccupations of previously-used channels. The channels resulting from the major floods of 1945, 1951, 1975, 1989, and 1990 did not significantly depart from the above-defined zone. Cross-section geometry remained approximately constant from 1964 to 1987 throughout the study reach (no pre-1964 data exists). During the 1987 to 1991 period, channels were more active, with episodes of aggradation or degradation at most sections. Sediment appears to have been transported over a few months to a few years in alternating degradation-aggradation cycles. Surface-sediment sampling shows a small decrease in particle sizes downstream and no correlation between grain size and degree of braiding. Comparison of recurrence intervals calculated by the Gumbel Type I and Log Pearson Type III methods for the Deming, Ferndale, and Lynden stream gauges shows that the Gumbel method consistently estimates a higher discharge fora given recurrence interval than the Log-Pearson method.