hydroacoustic sediment surrogates and methods —test results for a small urban river—

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Hydroacoustic Hydroacoustic Sediment Surrogates Sediment Surrogates

and Methodsand Methods—test results for a —test results for a small urban river—small urban river—

Mark N Landers, [email protected] Interagency Sedimentation Project Chief

January 10, 2012USGS, Reston, VA, and WEB-EX

water.usgs.gov/fisp

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Yellow River at Gees Mill Road near Metro Atlanta, Yellow River at Gees Mill Road near Metro Atlanta, GA, 02207335GA, 02207335

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Yellow River at Gees Mill Road near Metro Atlanta, Yellow River at Gees Mill Road near Metro Atlanta, GAGA

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Acoustic Doppler Current Profilers (A) 1.2MHz (B) 1.5MHz (C) 3.0MHz

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Acoustic Doppler Current Profiler Acoustic Doppler Current Profiler ConfigurationConfiguration

Urick’s Method:SSC = 10(A+B ( RL + 2TL))

2TL=20log10(ψr) + 2r(αs+ αw)

αw = 8.686 f 2 (55.9−2.37T+0.0477T 2−0.000348T 3) 10−15

Measured Backscatter

Computed WaterAttenuation

Acoustic Surrogates of SSCAcoustic Surrogates of SSC

Urick’s Method:


SSC = 10(A+B ( RL + 2TL))

2TL=20log10(ψr) + 2r(αs+ αw)Measured Backscatter

Computed WaterAttenuation

2.3)/5.2()/35.1(11)(

nn rrrrr

Near Field for 3.0 MHz SW (27mm dia) is 1.16m; for 1.5MHz SL (50mm dia) is 1.98m; for 1.2MH RDI ChanMaster (70mm dia) is 3.11. Correction at 1m for each is about 4%, 20%, and 70%, respectively.

Hybrid Urick-Sheng-Hay Method:

Acoustic Attenuation by Sediment:Acoustic Attenuation by Sediment:

34.4)24.03.11(5)(

)1( 4422

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222

akakak

ss

kSSCVS

aas

11

49

2

a

495.0

Backcatter Amplitude Profiles: Measured & Normalized

Acoustic Attenuation by Sediment:Acoustic Attenuation by Sediment:

)2)(log20(21

10 ws rrRLdrd

Slope = 2TL

Slope = 2r(αw + αs)

Slope = 2r(αs )

Relative Backscatter

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Urick’s Method:


SSC = 10(A+B ( RL + 2TL))

2TL=20log10(ψr) + 2r(αs+ αw)Measured Backscatter

Computed WaterAttenuationMeasured Sediment Attenuation

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Conclusions re: Acoustic Conclusions re: Acoustic Backscatter and Attenuation as Backscatter and Attenuation as Surrogates of Suspended Sediment Surrogates of Suspended Sediment ConcentrationConcentration

The methods proposed by Topping et al. (2007) to empirically The methods proposed by Topping et al. (2007) to empirically measure acoustic attenuation from profiling ADCP measurements measure acoustic attenuation from profiling ADCP measurements do apply for a stream in the southeastern USA. do apply for a stream in the southeastern USA.

Using both relative acoustic backscatter (Using both relative acoustic backscatter (RBRB) and acoustic ) and acoustic attenuation as explanatory variables results in a significantly attenuation as explanatory variables results in a significantly improved model of improved model of SSCSSCxsxs, compared with traditional sonar , compared with traditional sonar equations using only equations using only RBRB. .

Fluvial suspended sediment concentration can be determined by Fluvial suspended sediment concentration can be determined by high-resolution acoustic measurements with much greater high-resolution acoustic measurements with much greater accuracy than using traditional SSC ~ streamflow discharge accuracy than using traditional SSC ~ streamflow discharge ratings. Rratings. R22 improved from 0.57 to (0.79 to 0.80); and model improved from 0.57 to (0.79 to 0.80); and model residual standard error improved from 73% to (34% to 40%).residual standard error improved from 73% to (34% to 40%).

Sediment Size from Acoustic Sediment Size from Acoustic AttenuationAttenuation

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Representative particle sizes cannot be determined Representative particle sizes cannot be determined from these data by optimizing the theoretical from these data by optimizing the theoretical acoustic attenuation equation using measured acoustic attenuation equation using measured acoustic attenuation for single acoustic frequencies acoustic attenuation for single acoustic frequencies nor for ratios of multiple acoustic frequencies. nor for ratios of multiple acoustic frequencies.

Suspended sediment PSD is significantly correlated Suspended sediment PSD is significantly correlated with ratios of measured acoustic attenuation at with ratios of measured acoustic attenuation at different frequencies.different frequencies.

Conclusions re: Acoustic Attenuation Conclusions re: Acoustic Attenuation Surrogates of Sediment SizeSurrogates of Sediment Size

This study has identified the following needs for further research:This study has identified the following needs for further research: Evaluate measured and theoretical acoustic attenuation for Evaluate measured and theoretical acoustic attenuation for

characterization of suspended sediment size. The data needed for this characterization of suspended sediment size. The data needed for this research includes concurrent measurements of SSC, full PSD, and multi-research includes concurrent measurements of SSC, full PSD, and multi-frequency profiles of acoustic backscatter and attenuation on different frequency profiles of acoustic backscatter and attenuation on different streams having diverse sediment characteristics.streams having diverse sediment characteristics.

Test, validate, and develop generalized methods for use of acoustic Test, validate, and develop generalized methods for use of acoustic backscatter and attenuation for estimation of suspended backscatter and attenuation for estimation of suspended sediment concentration and load.sediment concentration and load.

Recommendations for Further Recommendations for Further ResearchResearch

hydroacoustic sediment surrogates and methods —test results for a small urban river—

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