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Publications—Scientific Investigations Report

Prepared in cooperation with New York State Department of Environmental Conservation

Use of an ADCP to Compute Suspended–Sediment Discharge in the Tidal Hudson River, New York

By Gary R. Wall, Elizabeth A. Nystrom, and Simon Litten

U.S. Geological Survey Scientific Investigations Report 2006-5055

The body of the report is available in PDF Format ( 1,186 KB)

Revised 2008


Abstract

Acoustic Doppler current profilers (ADCPs) can provide data needed for computation of suspended-sediment discharge in complex river systems, such as tidal rivers, in which conventional methods of collecting time-series data on suspended-sediment concentration (SSC) and water discharge are not feasible. Although ADCPs are not designed to measure SSC, ADCP data can be used as a surrogate under certain environmental conditions. However, the software for such computation is limited, and considerable post-processing is needed to correct and normalize ADCP data for this use. This report documents the sampling design and computational procedure used to calibrate ADCP measures of echo intensity to SSC and water velocity to discharge in the computation of suspended-sediment discharge at the study site on the Hudson River near Poughkeepsie, New York. The methods and procedures described may prove useful to others doing similar work in different locations; however, they are specific to this study site and may have limited applicability elsewhere.

TABLE OF CONTENTS

Abstract

Introduction

Limitations of an Acoustic Surrogate for Suspended-Sediment Concentration

Purpose and Scope

Study Area

Site Selection

Instrumentation

Procedure for Computation of Suspended-Sediment Discharge

Computation of Suspended-Sediment Concentration

Echo-Intensity Conversion to Decibels

Transmit-Power and Transmit-Length Normalization

Beam Normalization

Acoustic Beam Spreading

Acoustic Absorption by Water

Acoustic Absorption by Sediment

Computation of Acoustic Backscatter

Relating Acoustic Backscatter to Suspended-Sediment Concentration

Cross-Sectional Average Suspended-Sediment Concentration

Computation of Water Discharge

Computation of Suspended-Sediment Discharge

Summary

Acknowledgments

References Cited

Appendix

 

Figures

 

  1.
Map showing principal geographic features of the Hudson River Basin and location of the study site near Poughkeepsie, N.Y.
  2.
Cross section showing river-bottom profile at study site near Poughkeepsie, N.Y.
  3.
Schematic diagram of upward-looking acoustic Doppler current profiler (ADCP).
  4-5. Graphs showing:

4.    Relation between echo intensity recorded in bins 5, 10, 15, 20, 25, and
       30 of beams 1 and 2 of ADCP1.

5.   Attenuation curves of a 614-kilohertz acoustic signal for four
      suspended sediment concentrations as a function of grain size.

6.
Schematic diagram showing position of (ADCP) and water sampler for ADCP calibration.
7.
Graph showing relation between the base-10 logarithm of suspended-sediment concentration and the predicted base-10 logarithm of suspended-sediment concentration derived from acoustic backscatter and water-temperature data measured at the same depth and time.
8.
Schematic vertical section of river showing location of zone in which acoustic Doppler current profiler (ADCP) data were obtained for suspended-sediment concentration (SSC) computation, and zones in which ADCP data were unavailable and SSC estimated.
9-11. Graphs showing:
9.
Relation between estimates of suspended-sediment concentration based on upward-looking acoustic Doppler current profiler (ADCP) measurements and those based on boat-mounted cross-sectional ADCP measurements.
10.
Relation between discharge predicted by equation 14a and 14b and that measured by boat-mounted acoustic Doppler current profiler
11.
A. Daily suspended-sediment discharge computed with tidal-filtered and unfiltered data. B. Daily difference between filtered and unfiltered values computed in A. C. Percent difference between cumulative filtered and unfiltered data over time

 

Tables

 

  1. Scale factors used for conversion of ADCP counts to decibels.
  2. Regression statistics relating echo intensity recorded in each instrument beam to those in ADCP1 Beam 1.
  3. Percent error resulting from omission of corrections and normalizations to data collected during a 208-day acoustic Doppler current profiler (ADCP) deployment in the Hudson River near Poughkeepsie, N.Y.

If you have Adobe® Acrobat® or Adobe® Acrobat® Reader® installed on your computer, you may view and print the PDF version of this report. Acrobat Reader, is a free download from Adobe Systems, Inc. Users with disabilities can view information concerning accessibility at access.Adobe.com .


For further information, contact:

 

Rafael W. Rodriquez, Director
U.S. Geological Survey
New York Water Science Center
425 Jordan Road
Troy, NY 12080

dc_ny@usgs.gov

(518) 285-5600

 

or visit our Web site at: http://ny.water.usgs.gov



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