Improving Estimates of Suspended Sediment concentration and flux in the little bear river
description
Transcript of Improving Estimates of Suspended Sediment concentration and flux in the little bear river
IMPROVING ESTIMATES OF SUSPENDED SEDIMENT CONCENTRATION AND FLUX
IN THE LITTLE BEAR RIVER
Brant Whiting, Jeffery S. Horsburgh and Amber S. Jones
Utah Water Research LaboratoryUtah State University
Introduction• Suspended sediment is cited as the most
common impairment to water quality in the U.S.• 51% of stream miles on Utah’s 303(d) list are for
sediment related impairments
Introduction
• Sediment-related problems cause physical, chemical and biological degradation to water quality including:o Drinking water treatment processeso Recreational uses o Reservoir storage and operationo Fate and transport of heavy metals and other contaminantso Light suppression effects on stream bed vegetationo Ecological function of aquatic habitat, food webs and
spawning bedso And more…
Introduction
• Traditional monitoring approaches involve infrequent grab samples of TSS and periodic or continuous discharge measurement
• Infrequent grab samples do not characterize the temporal variability that we have observed in TSS concentrations
• Many are now using turbidity, which can be measured in-situ with high frequency, as a surrogate for TSS
Node 2 - Lower South Fork Site, Year 2008
Mar Apr May Jun Jul Aug
010
020
030
040
050
0
010
020
030
040
050
0
Turb
idity
, NTU
Tota
l Sus
pend
ed S
olid
s, m
g/L
Turbidity, NTUTSS, mg/L
010
020
030
040
050
060
0
Mon 12:00 Mon 22:00 Tue 08:00
020
040
060
080
010
00
Turb
idity
, NTU
Tota
l Sus
pend
ed S
olid
s, m
g/L
Day/Hour
Turbidity, NTUTSS, mg/L
Research Objective• Test the generality of using turbidity as a surrogate for
suspended sediment and identify potential confounding factors.
Question 1: How and why do relationships between turbidity and suspended sediment differ from site to site in the Little Bear River watershed?
Question 2: Can point measurements of turbidity from a single sensor be coupled with grab samples of suspended sediment concentrations to create high frequency estimates of suspended sediment concentrations that are representative of the entire stream cross section?
Study Site – Little Bear River
Ideal location for this research because:• Existing infrastructure and data (
http://littlebearriver.usu.edu)
• Strong anthropogenic influence: • Surrounding agricultural land uses• Impoundments (e.g., Hyrum, porcupine
reservoirs)• Canal diversions
• TMDL - excess nutrient loading and sediment-related impairments
Study Site
Methods• Instrumentation
– Forest Technologies DTS-12 turbidity sensor• Light source: Laser diode (near infrared wavelength)• Range: 0-1600 NTU (temperature corrected)
• NTU geometry detects forward and backscatter at 900 to incident beam
• Continuous measurement (half hourly) from [Oct 2008- Sept. 2008]
Methods• Suspended Sediment Analysis
– Total suspended solids (TSS) - USEPA Method 340.2 and 160.2
– Grab sample at point of in-situ sensor– Stored at 40C– Filtered through 0.45um glass fiber filter– Dried at 103-1050C and weighed solids to constant weight
• Existing grab samples– Aug. 2005 - Sept. 2008– ~80-170 samples
Methods• Regression Analysis
– Simple linear regression (SLR) techniques• Ordinary least squares (OLS)• y = b0 + b1X and
• y = b0 + b1X + b2Z– Where y is the response or predicted TSS value– b0 , b1 and b2 are parameters estimated by the regression– X is the turbidity value (predictor) and Z is a categorical variable
(1 or 0)– Assumptions of SLR
• Linearity of the independent and dependent variables• Independence of the error terms• Constant variance in the error terms• Normality of the error term’s distribution
Results
Node Condition Reg Eqn1 If Turb < 9 TSS = 0.887 + 0.962*Turb1 If Turb >= 9 and < 40 TSS = 5.739 + 0.467*Turb1 If Turb >= 40 TSS = -48.17 + 1.784*Turb
2 Z1 = 0 where Turb < 40 and Z1 = 1 where Turb >= 40 TSS = -1.717 + 1.924*Turb - 22.45*Z1
4 - TSS = 3.214 + 1.456*Turb 5 - TSS = 3.58 + 1.308*Turb6 - TSS = 2.335 + 1.382*Turb7 - TSS = 0.3406 + 1.413*Turb
0 100 200 300 400 500 600 700 800 900 10000
200
400
600
800
1000
1200
1400
1600
1800
2000
Little Bear River TSS-Turbidity Regression - 2005-2009
Node 1 - USFNode 2 - LSFNode 4 - ConfluenceNode 5 - ParadiseNode 6 - WellsvilleNode 7 - Mendon
Turbidity, NTU
Tota
l Sus
pend
ed S
olid
s, m
g/L
2
4 7 6
1
5
Study Site
Results – Similar Turbidity
– Node 2 • When Turbidity = 161 NTU, TSS = 246 mg/L• Regression equation:
– Predicted TSS = -1.72 + 1.92*161 – 22.45*1 = 286 mg/L– Difference of ~15%
– Node 5 • Turbidity = 163 NTU, TSS = 657 mg/L• Regression equation:
– Predicted TSS = 3.58 + 1.308*163 = 173 mg/L– Difference of ~116%
– Predicted TSS difference of 50% between the two sites with the same measured turbidity
Results – Similar TSS
– Node 2 • When Turbidity = 24 NTU, TSS = 70 mg/L• Regression equation:
– Predicted TSS = -1.72 + 1.92*24 – 22.45*1 = 44.5 mg/L– Difference of ~44%
– Node 5 • Turbidity = 38 NTU, TSS = 70 mg/L• Regression equation:
– Predicted TSS = 3.58 + 1.308*38 = 43 mg/L– Difference of ~48%
– Measured turbidity difference of 45% between the two sites with the same measured TSS
What’s next?– These cases illustrate the site specific nature of turbidity as a
surrogate for TSS in the little bear river– Differences shown in the regression equations (slope, intercept
and range of range of applicable values)– Sources of variability in sediment flux estimates
• Turbidity instrument• TSS analysis• Regression equations• Stage discharge relationship• Turbidity response is affected by particle characteristics such as:
– Size, shape, density (organic, mineral content) and water color• Point vs. cross-section averaged measurements of turbidity and TSS
Continued Research– Research Question 1– Particle size analysis
• Sequoia Scientific LISST-Portable Particle Analyzer– Particle size determined by Laser Diffraction techniques (AWWA Std. No. 2560D)– 1.9 – 381 micron size range
– Organic content analysis at 4 sites• Organic matter determined with Teledyne TOC Analyzer
– Combustion-Infrared Method 5310 B
LISST-PortableTOC Analyzer
Continued Research– Research Question 2– Point vs. Cross section measurements
• Cross section at existing sensor location• Sample at range of hydrological conditions• Vertically integrated turbidity and TSS samples taken across the width of the
channel • Develop a correction factor for conditions
when they are different
Width
Depth
DH-48 Sediment Sampler
TSS
Turbidity
V1 V2 V3 V4 V5 V6 V7 V8
Questions?