TURBIDITY AND SEDIMENT MONITORING
HY 2002 through HY 2004
Sonoma Creek Watershed, California
Sonoma Ecology Center
205 First Street West
Sonoma, California 95476
707.996.0712
www.sonomaecologycenter.org
October 2004
Report prepared by
Rebecca Lawton, Geologist and Project Manager
Victor Flores, Research and Restoration Assistant
ATTACHMENTS
TABLES
Table 1. Severity Index
Table 2. Monitoring Locations
Table 3. First and Second Flush Storms, Tributary Values
Table 4. Turbidity/SSC Relationships for Station A
Table 5. First Flush Storms, Station A
Table 6. SSC Exposures, Sixteen Storms, Station A, HY 2002
Table 7. SSC Exposures, Nine Storms, Station A, HY 2003
Table 8. SSC Exposures, Twelve Storms, Station A, HY 2004
Table 9. Severity Indices, Sixteen Storms, Station A, HY 2002
Table 10. Severity Indices, Nine Storms, Station A, HY 2003
Table 11. Severity Indices, Twelve Storms, Station A, HY 2004
PLATES
Plate 1. Location Map
Plate 2. Grab Sampling Photographs
Plate 3. Measuring Stream Height
Plate 4. Automated Data Collection Station A and Depth-Integrated Sampler
Plate 5. Grab Turbidity (NTU) versus Suspended Sediment Concentration (mg/L)
Plate 6. SSC/Turbidity (Power Curve), Station A
1.0 Introduction
The Sonoma Ecology Center (SEC) is testing the hypothesis that elevated levels of turbidity and
suspended sediment concentration (SSC) in stream water pose adverse impacts to salmonids
of concern in the Sonoma Creek watershed (chinook salmon [Oncorhynchus tshawytscha] and
steelhead trout [Oncorhynchus mykiss]). Turbidity and SSC are related: water containing SSC
up to approximately 50 milligrams/liter (mg/L) shows a 1:1 ratio with turbidity measured in
nephelometric turbidity units (NTUs); above 50 mg/L, the relationship between SSC and NTU is
no longer 1:1 and becomes variable according to stream location (Fitzgerald, 2004). Water
containing SSC greater than 27 mg/L has been defined as “turbid,” has been characterized as
“not drinkable,” has been observed to effect a 50 percent drop in the catch of fish, and leads to a
10 percent drop in fish production (Anderson, 1975).
Research has correlated elevated turbidity and SSC to observed effects on sample salmonid
populations, such as reduced feeding and growth rates, avoidance of turbid waters, or death.
From their analysis of the published results of 80 separate studies, Newcombe and Jensen
(1996) developed a severity index for ranking and analyzing the effects of excess SSC on
salmonids (Table 1). The various ranks in the index have been examined as thresholds for
salmonid behavior. California Regional Water Quality Control Board (RWQCB) staff have
suggested that a severity index rank of 4 or greater poses significant harm to salmonids and the
cold water fishery by effecting (1) salmonid mortality, (2) reductions of growth in the smolt size,
(3) overall long-term reduction in growth (Fitzgerald, 2004). Trush (2001) proposed that longterm reduction in feeding rates and success (equated with a Newcombe and Jensen severity
ranking of 8) results in smaller salmonids with higher mortality rates.
More information about the Newcombe and Jensen severity index is in Section 4.0, Discussion.
2.0
Methods
To characterize existing levels of turbidity and SSC in Sonoma Creek and selected tributaries,
SEC implemented a program of grab sampling, depth-integrated sampling, and automated data
collection in HY 2002 through HY 2004.
Our study design is explained in the Quality Assurance Project Plan (QAPP) prepared with
technical assistance from California Water Resources Control Board. The QAPP is
appended to the Final Report of Volunteer Monitoring of Suspended Sediment
Concentration and Turbidity prepared for California Regional Water Control Board, San
Francisco Bay Region (Lawton et al., 2002). The report and QAPP are available for
downloading from the SEC website, www.sonomaecologycenter.org, or by calling SEC at
707.996.0712. Methods for each aspect of the study are summarized below.
Grab Sampling
SEC staff established turbidity and SSC grab-sampling stations at 21 monitoring locations in the
Sonoma Creek watershed (Plate 1 and Table 2). Sixteen of the 21 locations were sampled
regularly during wet storms; all 21 were sampled only during major storm events and when
staffing allowed (Table 2). Grab sampling, primarily done during and directly following rainfall,
consisted of the simultaneous filling of one 15-milliliter (mL) HACH cell and one 500-mL SSC
sample bottle with stream water (Plate 2). Turbidity cells were analyzed in the field using a
HACH 2100P turbidimeter. SSC sample bottles were delivered under chain-of-custody protocols
to the M.U.D. Laboratory at the Sonoma Valley Watershed Station, Eldridge, California. Methods
used for analyzing the SSC grab samples derive in part from the Redwood Sciences Laboratory
Standard Operating Procedures for SSC Determination and from Standard Methods (2540B—
Total Solids Dried at 103 to 105 degrees Celsius [C]).
When taking grab samples at monitoring locations throughout the watershed, SEC staff used a
staff plate or wire-weight gauge to measure stream height (Plate 3). Once stream height was
established, the cross-sectional area of stream flow was estimated from previously established
measurements of channel cross section at each site (Orme et al., 2004). Staff clocked orangepeel floats on the stream surface and averaged velocity of the floats to complete the calculation
Discharge = Velocity x Area.
Automated Data Collection
The automated data collection system at Station A (STA) at Sonoma Valley Watershed Station,
Eldridge, California (Plates 1, 4), measures stream depth, turbidity, and rainfall. Readings were
taken at 10-minute intervals in HY 2002 and at 15-minute intervals in HY 2003 and HY 2004.
Data was downloaded weekly from STA and uploaded into Excel spreadsheets on computers at
the Sonoma Valley Watershed Station.
Depth-Integrated Sampling
A depth-integrated (DI) sampler was lowered through the water column to the stream bottom to
collect samples at 5-foot intervals across the stream cross section at STB (Plate 4). Samples
were collected only during and directly following wet storms.
Assessing Biological Significance
To arrive at a ranking in the severity index (Table 1), we analyzed automated turbidity data from
STA along with correlated SSC values using methods developed by Newcombe and Jensen
(1996). First we calculated a suspended sediment dose index for STA based on hours of aquatic
exposure to SSC:
Suspended Sediment Dose Index = natural log (SSC x Hours Exposed)
(Examples: Using this equation, exposure to 3.13 mg/L SSC for 24 hours results in a dose index
of 4. Similarly, exposure to 75.19 mg/L SSC for just 1 hour results in a dose index of 4
[Fitzgerald, 2004].)
Next we correlated the calculated SSC dose indices from Sonoma Creek to the Newcombe and
Jensen severity index (1996) based on analyses of salmonid species in the Russian River
watershed (chinook salmon, steelhead trout, and coho salmon [Oncorhynchus kisutch]). Only
coho salmon were studied sufficiently to make a strong correlation between changes in
environment and biological response; for coho salmon, a dose index of 4.55 correlates to a
severity index of 4. However, studies for all three species show that, as the SSC dose index
increases, so do the symptoms observed and ranked in the severity index. For all species
studied, the severity index ranking correlates to the SSC dose index as follows:
Severity Index Ranking = 0.7491(SSC dose index) + 0.7625
Using this relationship, an SSC dose index of 4.55 correlates to a severity index of 4.17.
3.0
Results
Datasets from the study include (1) three seasons (HY 2002 through HY 2004) of grab sampling
data (discharge, turbidity, and suspended sediment concentration [SSC]); (2) three seasons of DI
samples (turbidity, SSC) collected at STB (Sonoma Creek at Harney Road, Plate 1); and (3) three
seasons of automated weather data (stream depth, turbidity, and rainfall) collected at STA.
Grab Sampling
Results of grab sampling for turbidity and SSC are shown on Plate 5. The number of grab
samples taken at each location ranges from 11 samples collected on Graham Creek at the Emery
Restoration Site to 150 samples collected at STA. Our confidence in the data (shown by Rsquared values) range from 0.6111 at Nathanson Creek at Nathanson Creek Park to 0.9234 at
Asbury Creek at Arnold Drive. SSC:turbidity ratios estimated from the trendline equations vary
with location. Lower SSC:turbidity ratios were observed at Carriger Creek at Arnold Drive (27
mg/L:52 NTU) and Calabazas Creek at Dunbar Road (27 mg/L:49 NTU). Higher SSC:turbidity
ratios were observed at Sonoma Creek above the Yulupa Creek confluence (27 mg/L:23 NTU)
and Mill Creek at Redwood Street (27 mg/L:29 NTU). These latter correlations more closely
approximate the previously cited 1:1 rule of thumb for SSC < 50 mg/L and turbidity < 50 NTU
(Fitzgerald, 2004).
Grab sampling during first- and second-flush storms showed peak SSC values exceeding those
of storms later in the season. Example first- and second-flush values are in Table 3. Maximum
SSC values on tributaries exceeded 4,000 mg/L on Asbury Creek and 1,100 mg/L on Mill Creek,
with values at other locations ranging from approximately 50 to 500 mg/L (Table 3).
Depth-Integrated Sampling
Results of DI sampling for turbidity and SSC at STB are shown on Plate 5. Forty-five samples
collected at peak-flow times indicated a SSC:turbidity ratio at STB (27 mg/L:37 NTU) similar to
that of STA directly upstream (27 mg/L:35 NTU).
Automated Data Collection
Results of automated data collection at STA are shown on Plate 6. Summaries from sixteen wet
storms in HY 2002, nine wet storms in HY 2003, and twelve wet storms in HY 2004 indicate SSC
(in grab samples from STA) related to turbidity (in automated readings at STA) in a natural log
relationship that fits a power curve (Plate 6):
SSC (mg/L) = 0.0116*(turbidity in NTU)1.9902
Example SSC/turbidity relationships derived from the power curve equation are listed in Table 4.
Turbidity was measured in first flush storms at STA at the automated station’s maximum reading
of 2,000 NTU, indicating peak SSC values on the mainstem on the order of 1,000 mg/L (Table 5).
However, SSC values in grab samples were measured at STA in first flush storms as high as
4,043.4 mg/L (February 16, 2004). A new probe installed at STA with the capacity to measure to
4,000 NTU will help capture higher-end readings.
Turbidity/SSC levels dropped at STA after storms such that 90 percent of maximum values were
generally reached within 0.25 hour (15 minutes), 50 percent in less than 3 hours, and 0 percent
(total clearing) in less than 30 hours (Lawton et al., 2002). Total clearing occurred in an average
of 15.5 hours in HY 2002, 7.1 hours in HY 2003, and 29.7 hours in HY 2004.
Assessing Biological Significance
Turbidity/SSC exposures for aquatic organisms at STA are shown in Tables 6 through 8. Values
are sorted in bins according to thresholds used by Newcombe and Jensen (1996). Duration of
exposure at each automated turbidity value incorporates duration in lower-value bins; therefore,
duration times are cumulative as turbidity/SSC values increase.
The longest turbidity/SSC exposures observed at STA were 305.83 hours for HY 2002, in the
season’s longest and wettest storm (HY 02 Storm 11, December 30, 2001, to January 6, 2002;
Table 6); 166 hours for HY 2003, in the first major, longest, and wettest storm of the season (HY
03 Storm 1, December 16 to 23, 2002; Table 7); and 75 hours for HY 2004 (HY 04 Storm 9,
February 16 to 19, 2004; Table 8). The maximum severity index observed at STA was 8.94 for
HY 2002 (HY 02 Storm 11; Table 9); 9.04 for HY 2003 (HY 03 Storm 1; Table 10); and 8.20 for
HY 2004 (HY 04 Storm 9; Table 11). Severity indices were above 4 in most storms and
occasionally above 8 (Tables 9 through 11).
4.0
Discussion
As stated previously, Trush (2001) proposed that long-term reduction in feeding rates and
success (equated with a Newcombe and Jensen severity ranking of 8) directly results in smaller
salmonids with higher mortality rates. Therefore, salmonids exposed to situations with ranking 8
or higher on the Newcombe and Jensen severity index are subject to major physiological stress.
Other observers (Ligon, 2004) have noted that the severity index rankings are most significant
when resulting in major effects (e.g., at a Newcombe and Jensen severity index of 10 or above,
resulting in direct mortality).
Extended times of elevated SSC exposures that result in severity indices of 4 and above also
pose concern for salmonids. Newcombe and Jensen observed that a severity index of 4 results
in short-term reduction in feeding rates and/or feeding success (Newcombe and Jensen, 1996).
The RWQCB has suggested 4 as a potential severity index target for the protection of salmonids
in the cold-water fishery (especially with regard to coho salmon; Fitzgerald, 2004).
Winter storms in Sonoma Creek in HY 2002, 2003, and 2004 were observed to sustain SSC
exposures that cause minor to major physiological stress in salmonids, moderate habitat
degradation, possible impaired homing, and poor condition. Severity indices for STA on
mainstem Sonoma Creek have not been observed to exceed 9. Therefore SSC alone probably
does not account for reduced growth rate, delayed hatching, reduced fish density, severe habitat
degradation, and direct mortality. SSC exposures do, however, appear to be contributing
intermittent salmonid stressors, potentially significant when severity indices are highest, i.e., in
first and second flush events (long, early [usually December] storms). Between storms, SSC
exposures on the mainstem generally drop within 30 hours to less significant levels.
5.0
Recommendations
Future water-quality sampling should focus on better understanding human impacts on sediment
delivery to waterways. We specifically recommend that future turbidity and SSC monitoring
should include the following:
 Increased sample collection in major tributaries to Sonoma Creek to estimate severity indices
in these contributing waterways
 Increased sample collection at STB (e.g., DI sampling on at least falling limb of four to five
storms across STB cross section) to correlate to grab and automated samples at Eldridge
sampling locations
 Continued use of the automated station to monitor all previously measured parameters at
STA
 Analysis of data from an additional turbidity probe installed in November 2004 at STA to back
up the existing probe
 Correlation of sample results to a RUSLE-style model of sediment production for Sonoma
Valley that includes land-use map coverage from the SEC GIS database
 Correlation of SSC results at each location to stream discharge.
References
Anderson, H.W., 1975. Sedimentation and Turbidity in Wildlands. Reprinted by permission in
Watershed Management, ASCE-1975, Prox. Watershed Management Symposium, Division of
Irrigation and Drainage, American Society of Civil Engineers, Logan, Utah. August 11-13.
Fitzgerald, R., 2004. Salmonid Freshwater Habitat Targets for Sediment-Related Parameters.
Draft. Prepared for State Water Resources Control Board, North Coast Region. October.
Lawton, R., R. Hunter, and J. Menze, 2002. Final Report, Volunteer Monitoring of Suspended
Sediment Concentration and Turbidity and Watershed Monitoring of Road Remediation in
Annadel State Park, Sonoma Creek Watershed, Sonoma County, California. Prepared for the
Sonoma Ecology Center and Regional Water Quality Control Board, San Francisco Bay Region.
September.
Ligon, F., 2004. Stillwater Sciences. Personal communication with Lisa Micheli, Sonoma
Ecology Center. June 28.
Newcombe, C.P. and J.O.T. Jensen, 1996. Channel Suspended Sediment and Fisheries: A
Synthesis for Quantitative Assessment of Risk and Impact. North American Journal of Fisheries
Management. 16(4):693-727.
Orme, M., Lawton, R., and Micheli, L., 2004. Stream Stewards Project: A Five-Year Report of
Volunteer Monitoring. Prepared for the Sonoma Ecology Center. October.
Trush, W.J., 2001. Testimony of W.J. Trush before the State Water Resources Control Board.
June 25 and 26, 2001.
Table 1. Severity Index (Newcombe and Jensen, 1996)
Rank
Description of Effect due to Excess Turbidity or SSC
0
No effect
1
Alarm reaction
2
Abandonment of Cover
3
Avoidance response
4
Short-term reduction in feeding rates and/or feeding success
5
Minor physiological stress, increased coughing rate, and/or increased
respiration rate
6
Moderate physiological stress
7
Moderate habitat degradation and/or impaired homing
8
Major physiological stress, poor condition, and/or long-term reduction in
feeding rates and/or feeding success
9
Reduced growth rate, delayed hatching, and/or reduced fish density
10
0 to 20% mortality, increased predation, and/or moderate to severe habitat
degradation
11
>20 to 40% mortality
12
>40 to 60% mortality
13
>60 to 80% mortality
14
>80 to 100% mortality
Table 2. Monitoring Locations, Sonoma Ck Watershed, HY 2002-HY 2004
Site
Site Name
What
Years
Grab Location
Code
Sampled
STA*
Sonoma Creek at Station A Grab, Q
HY 2002,
Right bank, bottom step of
2003, 2004 old damsite staircase, SDC
STB*
Sonoma Creek at Station B Q, DI
HY 2002,
From downstream side of
2003, 2004 bridge, Harney Drive, SDC
ACG*
Asbury Creek at Glen Ellen Grab, Q
HY 2002,
Left bank, downstream of
(Jack London Village)
2003, 2004 bridge and parking lot
CCA*
Carriger Creek at Arnold
Grab
HY 2002,
Right bank above Arnold
Drive
2003, 2004 Drive bridge
CCD*
Calabazas Creek at Dunbar Grab, Q
HY 2002,
Left bank downstream of
Road
2003, 2004 bridge guardrail
CCG
Calabazas Creek in Glen
Grab
HY 2002,
Left bank downstream of
Ellen
2003
O’Donnell Ln bridge
CCL
Carriger Creek at Leveroni
Grab
HY 2002,
Right bank above bridge
Road
2003
FCL
Frey Creek (Annella) at
Grab
HY 2002,
Mid upstream side of bridge
Lawndale Avenue
2003
MCR*
Mill Creek at Redwood
Grab, Q
HY 2002,
Right or left bank upstream
Road
2003, 2004 of bridge
NCP*
Nathanson Creek at
Grab, Q
HY 2002,
Left bank
Nathanson Creek Park
2003, 2004
RCV*
Rodgers Creek at Via
Grab, Q
HY 2002,
Right bank, upstream of
Colombard
2003, 2004 bridge
SCA*
Stuart Creek at Arnold
Grab, Q
HY 2003,
Left bank upstream of bridge
Drive
2004
SCC*
Schell Creek at Eighth
Grab, Q
HY 2003
Left bank upstream of bridge
Street East
SCD
Sonoma Creek at Larson
Grab
HY 2002,
Right bank above dam at
Dam
2003
Larson Park
SCG*
Sonoma Creek at Agua
Grab
HY 2002,
Right bank downstream of
Caliente Road
2003, 2004 bridge (USGS gauge)
SCH*
Sonoma Creek at Hwy 12
Grab
HY 2002,
Left bank above Highway 12
2003, 2004 bridge in Kenwood
SCL*
Sonoma Creek at Leveroni
Grab
HY 2003
Left bank downstream of
Road
bridge
SCS*
Sonoma Creek in Sugarloaf Grab, Q
HY 2002,
Left bank above Goodspeed
Ridge State Park
2003, 2004 Bridge
SCW
Sonoma Creek at 986
Grab
HY 2002,
Left bank, from boulder bar
Warm Springs Road
2003
upstream of marsh outlet
SCY*
Sonoma Creek at Yulupa
Grab
HY 2002,
Right bank upstream of
Creek
2003, 2004 confluence
SCZ
Sonoma Creek at Hwy 121
Grab
HY 2002,
Right bank, under Highway
2003
121 bridge in Schellville
YCC*
Yulupa Creek at Warm
Grab
HY 2002,
Left bank upstream of
Springs Road
2003, 2004 Sonoma Ck confluence
Grab location description looking
Q = discharge estimate
downstream.
* = ongoing monitoring location
Grab = surface grab sample
DI = depth-integrated sample
Table 4. SSC/Turbidity Relationships for Station A,
Sonoma Creek, HY2002 to HY2004
(SSC [mg/L] = 0.0116*[turbidity in NTU] 1.9902)
Turbidity (NTU) from automated
station
8
15
25
42
70
116
191
316
523
864
1428
2360
SSC *bins after Newcombe & Jensen 1996
Predicted SSC (mg/L)
1
3
7
20
55
148
403
1097
2981
8103
22026
59847
INSERT TABLEs 3 and 5
first flush
INSERT Tables 6, 7, 8
Ssc exposures for HY 2002, 2003, and 2004
INSERT Tables 9, 10, 11
Severity Indices for HY 2002, 2003, and 2004