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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007–5216

Estimating Water Fluxes Across the Sediment–Water Interface in the Lower Merced River, California

National Water-Quality Assessment Program

By Celia Zamora

Table of Contents

FOREWORD

Abbreviations and Acronyms

Abstract

Introduction

Seepage Measurements

Estimates of Streambed Hydraulic Conductivity

Estimating Seepage Using Heat as a Tracer

Conclusions

References

Figures

Figure 1. Study area and locations of fixed transect 1 and transect 2 in the lower Merced Basin. Arrow indicates direction of streamflow.

Figure 2. Location of monitoring wells and monitoring equipment at fixed transects 1 and 2 in the lower Merced Basin.

Figure 3. Mean annual streamflow, Merced River near Stevinson, California, water years 1941–2005.

Figure 4. Seepage meter arrays at transects 1 and 2.

Figure 5. Seepage meters.

Figure 6. Field deployment of paired seepage meters.

Figure 7. Scouring of streambed around seepage meter typically encountered 48 hours after deployment.

Figure 8. Measured vertical flux rates over consecutive 24-hour measurement periods for seepage meter pairs A-1 and B-2.

Figure 9. Measured vertical flux rates over consecutive 24-hour measurement periods for seepage meters pairs C-3 and D-4. A.

Figure 10. Measured vertical flux rates over consecutive 24-hour measurement periods for seepage meter pairs E-5 and F-6.

Figure 11. Laboratory test tank setup used for testing of different types of collection bags attached to seepage meters.

Figure 12. Seepage meter collection bag types.

Figure 13. Boxplots of relative percent difference between measured and known seepage rates.

Figure 14. Boxplots of relative percent difference of bag compliance under various test scenarios.

Figure 15. Cross-sectional schematic of monitoring well name and location for the upstream and downstream transects.

Figure 16. Grain-size distribution curves for sediment cores collected at the upstream and downstream transects.

Figure 17. Example of typical recovery time and fit of data for estimating hydraulic conductivity by slug test.

Figure 18. Streamflow and temperature histories for gaining and losing reaches of a stream coupled to the local ground-water system.

Figure 19. Bank and in-stream monitoring well pair at downstream transect.

Figure 20. Cross-sectional view of instrumented transect.

Figure 21. Measurement of spacing for temperature loggers placed in in-stream well and placement of temperature loggers in riparian bank well.

Figure 22. Head differences (delta H) between deep and shallow well pairs.

Figure 23. Temperature profiles collected at instrumented in-stream monitoring wells at the downstream transect (transect 1) during the study period.

Figure 24. Diurnal scale of temperature profile for monitoring well BW-017 during June 2004.

Figure 25. Cross-section of downstream transect (transect 1) showing measurement locations and model domain.

Figure 26. Plots of observed and simulated temperatures for monitoring well RW-044. A.

Figure 27. Plots of observed and simulated temperatures for monitoring well RW-035.

Figure 28. Results of simulated temperatures with an increase in hydraulic conductivity beginning at departure for monitoring well RW-035.

Tables

Table 1. Description of monitoring equipment in monitoring wells used in this study that corresponds with depictions in figure 2.

Table 2. Objective and description of field measurements using seepage meters.

Table 3. Results of measured and known vertical flux rates, including relative percent difference, for collection bag types.

Table 4. Comparison of test tank flux rate at beginning and end of each test run.

Table 5. Results of test scenarios using thin-walled packaging collection bags.

Table 6. Estimated hydraulic conductivity by slug test and (or) grain-size analysis at upstream transect (transect 2).

Table 7. Estimated hydraulic conductivity by slug test and (or) grain-size analysis at downstream transect (transect 1).

Table 8. Monitoring well identification number, depth, location, and type of data collected.

Table 9. Modeling input values of listed parameters for modeling periods listed.

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Send questions or comments about this report to the author, Celia Zamora, (919) 278-3293.