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Measurement of Long-Term Channel Change Through Repeated Cross-Section Surveys at Bridge Crossings in Alaska

Open-File Report 2019-1028
Prepared in cooperation with the Alaska Department of Transportation and Public Facilities
By:  and 
https://doi.org/10.3133/ofr20191028

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Abstract

The U.S. Geological Survey (USGS) has been working with Alaska Department of Transportation and Public Facilities (ADOT&PF) since 1993 to provide hydraulic assessments of scour for bridges throughout Alaska. The purpose of the program is to evaluate, monitor, and study streambed scour at bridges in Alaska; this includes surveying streambed elevations at regular intervals and monitoring real-time bed elevation changes. Over the duration of the scour program (1994–2017), repeated cross sections have been surveyed along the lengths of 76 bridges. Channel soundings are depth-from-bridge measurements on either the upstream or downstream side of a bridge. Flow, depth, and velocity dictated whether streambed elevations were measured using either USGS sounding weights on cable reels, weighted measuring tapes, or acoustic Doppler current profilers. The soundings were done on an annual basis at most sites. In addition to annual soundings, channel soundings were made during floods or periods of scour. Results show that general scour can be uniform or non-uniform across the channel. The magnitude and distribution of scour across the channel are influenced by several factors that include streambed sediment type, degree of channel contraction at the bridge crossing, influence of instream structures, and bridge pier location and alignment. The data collected from the repeat soundings can be used to identify long-term aggradation or degradation of the streambed, as well as seasonal changes in streambed elevations.

Suggested Citation

Dworsky, K.L., and Conaway, J.S., 2019, Measurement of long-term channel change through repeated cross-section surveys at bridge crossings in Alaska: U.S. Geological Survey Open-File Report 2019-1028, 118 p., https://doi.org/10.3133/ofr20191028.

ISSN: 2331-1258 (online)

Table of Contents

  • Abstract
  • Introduction
  • Purpose and Scope
  • Cross-Section Surveys
  • Summary
  • References Cited
  • Appendixes 1–2
Publication type Report
Publication Subtype USGS Numbered Series
Title Measurement of long-term channel change through repeated cross-section surveys at bridge crossings in Alaska
Series title Open-File Report
Series number 2019-1028
DOI 10.3133/ofr20191028
Year Published 2019
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Alaska Science Center Water
Description Report: vii, 118 p.; 2 Appendices
Country United States
State Alaska
Online Only (Y/N) Y
Additional Online Files (Y/N) Y
Google Analytic Metrics Metrics page
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