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Scientific Investigations Report 2008-5083

In cooperation with the Edwards Aquifer Authority

Evaluation of Acoustic Doppler Velocity Meters to Quantify Flow From Comal Springs and San Marcos Springs, Texas

By Marcus O. Gary, Robin H. Gary, and William H. Asquith

Abstract

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Comal Springs and San Marcos Springs are the two largest springs in Texas, are major discharge points for the San Antonio segment of the Edwards aquifer, and provide habitat for several Federally listed endangered species that depend on adequate springflows for survival. It is therefore imperative that the Edwards Aquifer Authority have accurate and timely springflow data to guide resource management. Discharge points for Comal Springs and San Marcos Springs are submerged in Landa Lake and in Spring Lake, respectively. Flows from the springs currently (2008) are estimated by the U.S Geological Survey in real time as surface-water discharge from conventional stage-discharge ratings at sites downstream from each spring. Recent technological advances and availability of acoustic Doppler velocity meters (ADVMs) now provide tools to collect data (stream velocity) related to springflow that could increase accuracy of real-time estimates of the springflows. The U.S. Geological Survey, in cooperation with the Edwards Aquifer Authority, did a study during May 2006 through September 2007 to evaluate ADVMs to quantify flow from Comal and San Marcos Springs. The evaluation was based on two monitoring approaches: (1) placement of ADVMs in important spring orifices—spring run 3 and spring 7 at Comal Springs, and diversion spring at San Marcos Springs; and (2) placement of ADVMs at the nearest flowing streams—Comal River new and old channels for Comal Springs, Spring Lake west and east outflow channels and current (2008) San Marcos River streamflow-gaging site for San Marcos Springs. For Comal Springs, ADVM application at spring run 3 and spring 7 was intended to indicate whether the flows of spring run 3 and spring 7 can be related to total springflow. The findings indicate that velocity data from both discharge features, while reflecting changes in flow, do not reliably show a direct relation to measured streamflow and thus to total Comal Springs flow. ADVMs at the Comal River new channel and old channel sites provide data that potentially could yield more accurate real-time estimates of total Comal Springs flow than streamflow measured at the downstream Comal River site. For San Marcos Springs, the findings indicate shortcomings with ADVM installations at diversion spring and in the west and east outflow channels. However, the accuracy of streamflow measured at the San Marcos River gage as an estimate of real-time San Marcos Springs flow could potentially be increased through use of ADVM data from that site.

Version 1.0

Posted August 2008

Report PDF (49.3 MB)

Appendix 1 files


Suggested citation:

Gary, M.O., Gary, R.H., and Asquith, W.H., 2008, Evaluation of acoustic Doppler velocity meters to quantify flow from Comal Springs and San Marcos Springs, Texas: U.S. Geological Survey Scientific Investigations Report 2008–5083, 37 p.



Contents

Abstract

Introduction

Purpose and Scope

Previous Acoustic Doppler Velocity Meter Applications

Physical Setting

Comal Springs

San Marcos Springs

Acoustic Doppler Velocity Meters

Principles of Operation

Description of Models Used

Methods of Study

Monitoring Approaches

Description of Monitoring Sites and Instrumentation

Comal Springs—Spring Run 3

Comal Springs—Spring 7

Comal Springs—New Channel

Comal Springs—Old Channel

San Marcos Springs—Diversion Spring

San Marcos Springs—West Outflow

San Marcos Springs—East Outflow

San Marcos Springs—San Marcos River Streamflow Gage

Data Quality Assurance and Archival

Evaluation of Acoustic Doppler Velocity Meters to Quantify Flow

Comal Springs—Spring Run 3

Comal Springs—Spring 7

Comal Springs—New Channel

Comal Springs—Old Channel

San Marcos Springs—Diversion Spring

San Marcos Springs—West Outflow

San Marcos Springs—East Outflow

San Marcos Springs—San Marcos River Streamflow Gage

Implications of Findings Pertaining to Improving Real-Time Springflow Estimates

Comal Springs

San Marcos Springs

Summary

References

Appendix 1—Acoustic Doppler Velocity Meter Data



For additional information contact:
Director, Texas Water Science Center
U.S. Geological Survey
8027 Exchange Drive
Austin, Texas 78754-4733

World Wide Web: http://tx.usgs.gov/
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