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Table of Contents:

OF 2004-1014

Disc Contents

Geologic
    Discussion

• Introduction

• Field Program

• Field Equipment

• Interpretation

• Discussion

• Summary

• Acknowledgments

Data/GIS

Metadata/Data
    Catalog

References Cited

Contacts

Introduction

The John Day Reservoir, also known as Lake Umatilla, occupies a 123 km long section of the Columbia River, and was formed after completion of the John Day Dam in 1968 (Fig. 1).

Figure 1.

Recently, concerns about declining stocks of endangered anadromous salmonids in the Columbia River basin raised the issue of restoration of riverine functions in this and other Columbia and Snake River reservoirs (ISG, 2000; Dauble and others, 2003). One option for restoration of riverine functions includes lowering water levels within selected reservoirs such as the John Day Reservoir. Questions about how much sediment has been trapped by this dam warranted a detailed study of the floor of the reservoir to assess changes that had occurred since impoundment. High-resolution geophysical mapping techniques were employed to provide, to our knowledge, the first detailed view of the floor of the reservoir since its formation. This geophysical "road map" in concert with bottom video images, some sediment samples, and historical data collected prior to creation of the reservoir were incorporated into a GIS. The subsequent text summarizes the techniques used in this study. It also provides a preliminary analysis of the results and a background for the GIS that accompanies this report.