HYDROLOGY AND CHEMISTRY OF FLOODWATERS IN THE YOLO BYPASS, 

SACRAMENTO RIVER SYSTEM, CALIFORNIA, DURING 2000. 

L.E. SCHEMEL, M.H. COX, S.W. HAGER, AND T.R. SOMMER 

U.S.GEOLOGICAL SURVEY 

WATER RESOURCES INVESTIGATIONS REPORT 02-4202 

Prepared in Cooperation with the 

California Department of Water Resources 

SEPTEMBER 2002 
U. S. DEPARTMENT OF THE INTERIOR 

GALE A. NORTON, Secretary 

U. S. GEOLOGICAL SURVEY 

CHARLES GROAT, Director 

For additional information 

write to: 

U.S. Geological Survey, WRD 

345 Middlefield Road 

Menlo Park, California 94025 

ii
CONTENTS 

___________ 

Abstract..................................................1 

Introduction..............................................2 

Hydrology of the Yolo Bypass.........................3 

 Acknowledgments......................................5 

Methods...................................................5 

Results...................................................6 

Results from Fixed-Location Sites....................7 

 Dissolved Metals....................................10 

Samples collected by boat in the Yolo Bypass........11 

Discussion...............................................12 

Summary..................................................17 

References cited.........................................18 

Appendix A 

Filtration and sample preparation methods...........21 

Appendix B: Illustrations 

________________________ 

Fig. 1. Map showing the Sacramento River, Yolo Bypass, 

local streams, and locations of the fixed 

sampling sites.................................24 

Fig. 2. Daily mean discharge in the Yolo Bypass (DAYFLOW 

value) for the 1956-2000 water years...........25 

Fig. 3. Daily total precipitation and mean daily 

irradiance at Davis, California, January through 

May, 2000......................................26 

Fig. 4. Daily mean wind speed and maximum daily air 

temperature at Davis, California, January through 

May, 2000......................................27 

Fig. 5. Daily mean discharge in the Sacramento River at 

Freeport and in the Yolo Bypass (DAYFLOW value), 

January through May, 2000......................28 

Fig. 6. Daily mean discharge in Cache Creek and Putah 

Creek, January through May, 2000...............29 

iii
Fig. 7. Water levels (gauge height) in the Sacramento 

River and Colusa Basin Drain at Knights Landing 

and the Yolo Bypass at HWY5 and in the Lower 

Bypass, January through May, 2000..............30 

Fig. 8. Specific conductance in the local streams (upper 

panel) and at sites in the Yolo Bypass (lower 

panel), January through May, 2000..............31 

Fig. 9. Chloride concentrations at sites in the local 

streams and at sites in the Yolo Bypass, January 

through May, 2000..............................32 

Fig. 10. Sulfate concentrations at sites in the local 

streams and at sites in the Yolo Bypass, January 

through May, 2000..............................33 

Fig. 11. Dissolved inorganic nitrogen concentrations at 

sites in the local streams and at sites in the 

Yolo Bypass, January through May, 2000.........34 

Fig. 12. Ammonium nitrogen concentrations at sites in the 

local streams and at sites in the Yolo Bypass, 

January through May, 2000......................35 

Fig. 13. Dissolved reactive phosphorus concentrations at 

sites in the local streams and at sites in the 

Yolo Bypass, January through May, 2000.........36 

Fig. 14. Dissolved silica concentrations at sites in the 

local streams and at sites in the Yolo Bypass, 

January through May, 2000......................37 

Fig. 15. Dissolved organic carbon concentrations at sites 

in the local streams and at sites in the Yolo 

Bypass, January through May, 2000..............38 

Fig. 16. Specific ultra violet absorbance at 245nm at 

sites in the local streams and at sites in the 

Yolo Bypass, January through May, 2000.........39 

Fig. 17. Suspended particle concentrations at sites in the 

local streams and at sites in the Yolo Bypass, 

January through May, 2000......................40 

iv
Fig. 18. Suspended particle percent carbon at sites in the 

local streams and at sites in the Yolo Bypass, 

January through May, 2000......................41 

Fig. 19. Carbon to Nitrogen ratio by moles at sites in the 

local streams and at sites in the Yolo Bypass, 

January through May, 2000......................42 

Fig. 20. Sodium concentrations at sites in the local 

streams and at sites in the Yolo Bypass, January 

through May, 2000..............................43 

Fig. 21. Calcium concentrations at sites in the local 

streams and at sites in the Yolo Bypass, January 

through May, 2000..............................44 

Fig. 22. Magnesium concentrations at sites in the local 

streams and at sites in the Yolo Bypass, January 

through May, 2000..............................45 

Fig. 23. Strontium concentrations at sites in the local 

streams and at sites in the Yolo Bypass, January 

through May, 2000..............................46 

Fig. 24. Sodium concentrations in Cache Creek and Ridge 

Cut (or Colusa Basin Drain) during the 1996-1998 

NAWQA study and in 2000........................47 

Fig. 25. Sulfate concentrations in Cache Creek and Ridge 

Cut (or Colusa Basin Drain) during the 1996-1998 

NAWQA study and in 2000........................48 

v
Appendix C: Tables 

____________________ 

Table 1. Analytical results from the Sacramento River 

at Fremont Weir................................49 

Table 2. Specific conductance, chloride, and sulfate at 

fixed sites and from boat samples..............50 

Table 3. Nitrite, nitrate plus nitrite, ammonium, 

dissolved reactive phosphorus, and dissolved 

 silica at fixed sites and from boat samples...54 

Table 4. Dissolved organic carbon, specific ultraviolet 

Absorbance, suspended particulate matter, 

Particulate carbon and particulate nitrogen at 

Fixed sites and from boat samples..............58 

Table 5. Analytical results for selected metals at fixed 

sites and from boat samples....................62 

_______________ 

CONVERSION FACTORS 

_______ 

Metric are used in this report. Conversion factors to other 

commonly used units are provided here for the measurements made 

in this study. 

Multiply By To obtain 

________ __ _________ 

μM (micromolar) atomic weight μg/L 

kg (kilogram) 2.205 lb (pound) 

m3

 (cubic meter) 35.3 ft3 (cubic feet) 

 _______________ 

All gauge heights have been adjusted to the National Geodetic 

Vertical Datum of 1929 (NGVD of 1929). 

The use of brand names in this report is for identification 

purposes only and does not constitute endorsement by the U.S. 

Geological Survey. 

vi
Hydrology and Chemistry of Floodwaters in the Yolo Bypass, 

Sacramento River System, California, during 2000. 

Laurence E. Schemel, Marisa H. Cox, Stephen W. Hager and Theodore R. Sommer 

U.S. Geological Survey 

Water Resources Investigations Report 02-4202 

ABSTRACT 

Discharges to and floodwaters in the Yolo Bypass were sampled 

during winter and spring, 2000. The primary purpose of the study was 

to link changes in water quality in the Yolo Bypass to inflows from the 

Sacramento River (over Fremont Weir) and from four local streams that 

discharge to the west side of the floodplain. Specific conductance, 

chloride, sulfate, dissolved inorganic nutrients, dissolved organic 

carbon, particulate carbon and nitrogen, suspended particulate matter 

(mass), and selected dissolved metals were measured in most of the 

samples. When the Sacramento River was spilling over Fremont Weir, the 

water chemistry in the Yolo Bypass was very similar to that in the 

river except along the western margin of the floodplain where 

influences of local stream inflow were evident. When flow over Fremont 

Weir stopped, floodwaters drained from the Yolo Bypass, and the local 

streams were the major discharges as the floodwaters receded eventually 

to the perennial channel along the eastern margin of the floodplain. 

After the initial draining of the floodplain, chemical concentrations 

at sites along the perennial channel showed strong influences of 

inflows from Cache Creek and Ridge Cut, which are sources of nutrients 

and contaminants that are potentially hazardous to wildlife. Runoff 

from spring storms increased flow in the perennial channel and flushed 

accumulated nutrients and organic matter to the tidal river. Releases 

of freshwater to the perennial channel might be beneficial in 

maintaining habitat quality for aquatic species during the dry seasons. 

1
INTRODUCTION 

The Sacramento River is the largest source of fresh water to San 

Francisco Bay Estuary. Studies of this estuary by the U.S. Geological Survey 

(USGS) require increasingly detailed knowledge of the factors that influence 

river discharge and the transport of dissolved and particulate substances to 

the estuary. Over the last century and a half, major modifications of this 

river system have changed the patterns of discharge and constituent transport 

from their natural states (for examples see Nichols and others, 1986). Among 

these modifications are numerous reservoirs and an extensive system of levees 

and bypasses that provide flood protection in the Sacramento Valley. The 

Yolo Bypass is the largest flood-control bypass. It prevents flooding of 

farmlands and municipalities near the city of Sacramento by diverting 

floodwaters at Fremont Weir and routing them directly to the head of the San 

Francisco Bay Estuary near Rio Vista (Fig. 1). In years when floodwaters 

flow to the bypass system, the Yolo Bypass is often a greater discharger to 

the estuary than the main channel of the Sacramento River (see Schemel and 

others, 1995). In addition to the importance of the Yolo Bypass as a source of fresh 

water and riverine substances to the estuary, recent studies by the 

California Department of Water Resources (CDWR) and other agencies have shown 

that periodic flooding of the Yolo Bypass provides numerous ecological 

benefits, and that the Yolo Bypass is a potentially valuable asset for 

restoration of the Sacramento-San Joaquin River-Delta ecosystem. For 

example, the Yolo Bypass has been identified as an important habitat for 

fishes, migratory birds, and other wildlife that inhabit the floodplain 

seasonally or year round (Sommer and others, 2001a). The Yolo Bypass 

Wildlife Area was the largest wetland restoration project in the western 

states when it was dedicated by then-President Clinton in 1997, and it has 

since been enlarged. When inundated by Sacramento River inflow, the amount 

of shallow-water habitat available to aquatic species increases greatly and 

the Yolo Bypass becomes an important migration route for chinook salmon that 

provides better food and shelter than the main river channel (Sommer and 

others, 2001b). In addition to benefits to wildlife, large areas of the Yolo 

Bypass are used for irrigated agriculture when the floodplain is not 

inundated in late spring and summer. Therefore, the Yolo Bypass provides a 

diverse assortment of ecosystem and economic benefits in addition to flood 

protection. 

Until recently, little was known about water quality in the Yolo 

Bypass. A preliminary investigation by USGS and CDWR in 1998 identified large 

changes in water quality with the onset of flooding and while the floodplain 

was draining (Schemel and Cox, 1999). The purpose of the study described in 

this report was primarily to link water quality in the Yolo Bypass to inflows 

from the Sacramento River and local streams that enter the west side of the 

floodplain. This report presents the methods, numerical data, and an 

overview of the results from the study during winter and spring 2000. 

2
Hydrology of the Yolo Bypass 

The Yolo Bypass occupies a small portion of an extensive area that was 

flooded during wet years before reclamation and flood control measures were 

implemented in the early 20th century. Starting in the mid-19th century, 

attempts to establish towns and reclaim marshlands in the Sacramento Valley 

were impeded by frequent episodes of severe flooding from the Sacramento 

River and its tributaries (Kelley, 1989). Accounts of the flood of 1862, the 

greatest flood in the recorded history of California, reported widespread 

inundation throughout the greater Sacramento-San Joaquin (Central) Valley of 

California (Brewer, 1966; Kelley, 1989). Precipitation during 1862 remains 

the highest on record (the longest record dates from about 1850 at Mission 

Dolores in San Francisco), but a recent year, 1998, had the second highest 

precipitation in the 150-year record. Although significant flooding occurred 

in the Sacramento Valley in 1998, as well as 1997, 1986, and other recent 

years, the aerial extent and the level of damage was limited in part because 

of the effectiveness of the Sacramento River bypasses (Teets and Young, 1986; 

Kennedy, 1997). 

The inadequacy of levees alone to contain the Sacramento River during 

major floods of the early 1900’s led to the design of the existing system of 

levees, weirs, and bypasses (Kelley, 1989). Most of the basic features of 

this system were in place by the early 1930’s, but several large reservoirs 

constructed more recently as components of State and Federal water projects 

now provide additional protection from flooding. Even though the design 

capacity of the Yolo Bypass (in the range of approx. 14,000 to 15,000 m3

s-1) 

was exceeded in February 1986, extensive flooding was prevented largely by 

regulation of reservoir discharges (Fig. 2). 

The CDWR DAYFLOW program, an accounting of gauged river and stream 

flows, provides estimates of daily mean discharges in the Yolo Bypass and in 

the major rivers that flow to San Francisco Bay Estuary for water years since 

1956 (a water year is October through September; DAYFLOW program 

documentation and data are available at 

http://www.iep.water.ca.gov/dayflow/). DAYFLOW underestimates discharges 

from the Yolo Bypass when values are in the low range and when the floodplain 

is draining because the estimates are computed from gauged inflows (see 

below). Comparisons of daily mean discharges in the Sacramento River main 

channel at Freeport to DAYFLOW estimates in the Yolo Bypass show that 

discharges at Freeport rarely exceed the range of 2000-3000 m3

s-1, but that the 

Yolo Bypass flows can be nearly five times higher (Fig. 2). Discharge 

through the Yolo Bypass increases rapidly when flow at Freeport reaches about 

2000 m3

s-1, indicating that floodwaters exceed the height of Fremont Weir at 

that level of flow (see Schemel and others, 1996, for details). Major 

inundation of the floodplain is caused primarily by discharge over Fremont 

Weir. Sacramento Weir contributes additional floodwaters from the Sacramento 

River only during the highest flows, and its discharge typically is much 

smaller than that over Fremont Weir. 

A (perennial) channel along the eastern margin of the Yolo Bypass 

carries discharges from local streams and agricultural irrigation, as well as 

return discharges supplied by a network of canals that cross the floodplain 

(see CALFED, 2001, for details). During the storm season, floodwaters are 

contained in the perennial channel when flows in the Yolo Bypass are less 

than about 100 m3

s-1. At higher discharges, flooding extends toward the levees 

along the western margin. The deepest part of the Yolo Bypass is along the 

eastern margin, but the mean water depth across the floodplain is typically 

only 2-3m. As discharge decreases, shallower areas along the western margin 

become exposed as water drains southward and eastward and eventually is 

confined primarily to the perennial channel. 

3
Weather and climate are highly variable in northern California (Cayan 

and Peterson, 1989; Cayan and others, 1999). Consequently, the timing, 

extent, and duration of flooding in the Yolo Bypass vary greatly from year to 

year. Inundations of the Yolo Bypass have occurred as early as October and 

as late as June, but most major inundations have occurred during the winter 

months. In the 45-year DAYFLOW record, daily mean discharges exceeding about 

two-thirds of the capacity of the Yolo Bypass have occurred only in two 

years, 1986 and 1997 (Fig. 2). Discharges in the Yolo Bypass have exceeded 

those in the lower Sacramento River channel at Freeport in over one-third of 

the years. Daily mean flow exceeded 1000 m3

s-1 in 26 of the years, and the 

average duration of flow at this level or higher among those years was 25 

days. Although the high inter-annual variability makes generalizations 

misleading, daily mean flow for the average year exceeded 100 m3

s-1 for about 

41 days and 1000 m3

s-1 for about 14 days over the 45-year record. Daily mean 

flows of 100 m3

s-1 or greater exceed the capacity of the perennial channel 

along the eastern margin, which can be considered the onset of floodplain 

inundation. In 10 of the 45 years, daily mean flow did not exceed 100 m3

s-1, 

and there was no appreciable flow through the Yolo Bypass during the six 

consecutive years of severe drought following the major flood of 1986 (Fig. 

2). 

Inflows from the local streams that enter the western margin of the 

Yolo Bypass generally are small in comparison to floodwater discharges over 

Fremont Weir. However, local streams are often the greatest sources of 

freshwater to the floodplain in autumn and spring and in dry years when 

Sacramento River water does not spill over the weirs. Localized flooding in 

the Yolo Bypass early in the storm season is often caused by local stream 

discharges. Even though discharges from the local streams are a small 

fraction of the total flow during inundation periods, these inflows can be 

identified in aerial photographs as distinct bands extending to the southern 

outlet along the shallow western margin of the Yolo Bypass during most years 

(Sommer and others, 2001a). 

Cache Creek and Putah Creek are gauged several kilometers upstream of 

the Yolo Bypass (Anderson and others, 2001; Fig. 1). Discharges from both of 

these streams are affected by reservoirs as well as storm runoff. Willow 

Slough, a much smaller discharger that is not gauged, carries storm runoff 

and possibly agricultural and other discharges. Ridge Cut conveys water from 

the Colusa Basin Drain directly to the Yolo Bypass primarily when water 

levels in the Sacramento River at Knights Landing are too high to allow 

gravity flow to the river (CDWR, 1964). The Colusa Basin Drain receives 

inflow from some creeks as well as discharges and runoff from the Colusa 

agricultural basin. Although a gauge on the Colusa Basin Drain measures 

discharge to the Sacramento River near Knights Landing, this gage is not 

rated for discharge to the Yolo Bypass via Ridge Cut. Discharge to the Yolo 

Bypass depends on Sacramento River and Colusa Basin Drain gauge heights and 

other factors such as the condition of the earthen weir at the eastern end of 

Ridge Cut and water elevations in the Yolo Bypass. Aerial observations 

suggest that the inflows from Ridge Cut and Cache Creek are the largest of 

the four local streams. 

4
ACKNOWLEDGMENTS 

We thank the staff of the U.S. Geological Survey and California 

Department of Water Resources for their assistance in collecting samples 

during this study. In particular, we acknowledge assistance from W. Harrell, 

W. Batham, R. Kurth, C. Azevedo, and K. Malchow, and thank them for their 

willingness to participate in this study. Comments by B. Topping and C. 

Lopez also were very helpful. Funding for this study was provided by the 

U.S. Geological Survey National Research Program, the Toxics Substances 

Hydrology Program, and the Interagency Ecological Program for the SacramentoSan Joaquin Estuary. 

METHODS 

Samples were collected primarily at three (fixed-location) sites along 

the eastern margin of the Yolo Bypass (hereafter called HWY5, HWY80, and 

Lower Bypass) and at upstream (fixed-location) sites on four local streams 

that discharge to the western margin of the floodplain (Ridge Cut, Cache 

Creek, Willow Slough, and Putah Creek; Fig. 1). Two of the Yolo Bypass sites 

were located near the major highway causeways of Interstate 5 and 80. Ridge 

Cut was sampled at the road 16 bridge; Cache Creek was sampled near the road 

113 bridge; Willow Slough was sampled near the road 102 bridge; Putah Creek 

was sampled near the Old Davis Road bridge. Additional sites that were not 

sampled on a regular basis included the Sacramento River near the western end 

of Fremont Weir and the Colusa Basin Drain near the road 99E bridge. For 

safety reasons, most samples were collected within a few feet of shore. A 

few additional samples were collected by boat across the flooded area of the 

Yolo Bypass and near its southern outlet during and after inundation by the 

Sacramento River. 

A bulk sample of near-surface water was collected with a plastic bucket 

at each site. Sub-samples were poured into pre-combusted glass bottles for 

dissolved organic carbon and particulate carbon and nitrogen, and into acidcleaned polyethylene bottles for specific conductance, sulfate, chloride, 

selected metals, and dissolved nutrients. Samples were returned to the 

laboratory in ice chests for processing on the following day. In some cases, 

samples from the Lower Bypass site were refrigerated for up to five days and 

then shipped overnight for processing in the laboratory. 

The sample processing details are provided in Appendix A. In brief, 

samples for dissolved organic carbon and particulate carbon and nitrogen were 

filtered with pre-combusted glass fiber filters, whereas samples for 

dissolved nutrients, chloride, sulfate, and dissolved metals were filtered 

with cellulose ester membrane filters. Filtrates for dissolved organic 

carbon (and UV absorption) were stored in pre-combusted brown glass bottles 

with Teflon caps in a refrigerator at 4Co before analysis on a MQ1001 TOC 

analyzer. Absorbance at 254nm was determined on freshly filtered samples 

using a 1-cm quartz cuvette in a Beckman DU spectrophotometer. Glass fiber 

filters containing particulate carbon and nitrogen were dried in a dessicator 

before analysis on a Carlo Erba Instruments Model NA 1500NC analyzer. 

Filtrates for dissolved nutrients (nitrite, nitrate, ammonium, dissolved 

silica, and dissolved reactive phosphate) were stored in acid-cleaned 

polyethylene bottles and frozen. Nutrient samples were thawed overnight 

before analysis on a Technicon AutoAnalyzer II (Hager and Schemel, 1997). 

Samples for sulfate and chloride were refrigerated until analysis on a Dionex 

LC20 ion chromatograph. Samples for dissolved metals (total of 18 metals, 

see below) were acidified with nitric acid and stored at room temperature 

until analysis on a Thermo Jarrell Ash Corp. IRIS Advantage inductively 

5
coupled plasma optical emission spectrophotometer (ICP-OES). Specific 

conductance was measured by electrode in the laboratory at 25C. 

Discharge and water level data for the Sacramento River, local streams, 

and the Yolo Bypass were obtained from the USGS annual report (Anderson and 

others, 2001) or internet sites maintained by USGS (http://water.usgs.gov/ 

nwis/discharge/) and CDWR (http://www.iep.water.ca.gov). The CDWR Northern 

District Office in Sutter, CA, provided gauge height data for the Sacramento 

River and the Colusa Basin Drain at Knights Landing. All gauge heights were 

adjusted to the National Geodetic Vertical Datum of 1929. 

RESULTS 

Results from this study are presented within the context of the weather 

and hydrology during the study period, January-May 2000. The study period 

was preceded by a dry autumn, during which precipitation was less than half 

of the normal amount in northern California. Precipitation was above normal 

in January and February 2000, but precipitation fell to below-normal level 

again in March. Although much lower than the level during a typical winter, 

precipitation in spring 2000 was nearly normal. Among the last 45 years, 

Yolo Bypass discharge for the 2000 water year ranked 19th and was less than 

average. 

Precipitation at Davis, CA, is not representative of the entire 

Sacramento River drainage basin, but it is useful here as an indicator of 

precipitation carried by the local streams that discharge to the western 

margin of the Yolo Bypass and the Colusa Basin Drain (Fig. 3). Daily 

precipitation was highest during the period from late January to early March, 

but the subsequent period from mid-March to mid-April was unusually dry. 

This break in the storm sequence coincided with a large increase in solar 

radiation (irradiance; Fig. 3) and maximum daily air temperature (Fig. 4). 

High-speed winds (Fig. 4) coincided with precipitation in February, but highspeed winds did not coincide with precipitation in mid-March and early April 

2000, the period during which the Yolo Bypass was draining (see below). 

Precipitation increased flow in the Sacramento River in January and 

early February, but the river did not exceed the height of Fremont Weir until 

February 14 (Fig. 5). Discharge over Fremont Weir to the Yolo Bypass 

continued until March 17. Water levels in the Sacramento River remained 

below the height of Fremont Weir for the remainder of the study. Discharges 

in the Yolo Bypass were lower than those in the Sacramento River during the 

single 4-week-long period of inundation by discharge over Fremont Weir (the 

inundation period). There was no discharge over Sacramento Weir during the 

2000 water year. 

Local streams discharged to the Yolo Bypass before, during, and after 

the inundation period (Fig. 6). Storm-driven pulses in discharge are clearly 

apparent in the hydrograph from Cache Creek, whereas only much smaller pulses 

and a continuous release during March are shown for Putah Creek. Discharges 

from both creeks decreased to low levels in early April, but precipitation in 

late April coincided with a distinct flow pulse in Cache Creek that was not 

seen in the gauge data from Putah Creek. Although not gauged, field notes 

taken during sample collection indicated that Willow Slough also exhibited 

storm-driven pulses, but discharges were much lower than those from the other 

creeks. 

Under conditions of low water levels, as in early January 2000, the 

Colusa Basin Drain discharges by gravity directly into the Sacramento River 

at Knights Landing (Fig. 7). When the level of the river exceeds that of the 

Colusa Basin Drain, as in late January through March 2000, Colusa Basin 

6
discharge is diverted to the Ridge Cut canal and flows directly to the Yolo 

Bypass (CDWR, 1964). It is difficult to estimate discharge from Ridge Cut 

because it is the product of runoff from the basin and often rapidly changing 

water levels in the Sacramento River. Observations at the sampling site 

indicated that discharge from Ridge Cut might have been similar in magnitude 

to that from Cache Creek or even greater at times. The short-term variations 

in river level in late April presumably produced a pulse discharge from Ridge 

Cut. Therefore, it appears that gauge height variations at the HWY5 and 

Lower Bypass sites in late April were caused primarily by discharges from 

both Ridge Cut and Cache Creek (Fig. 7). 

The gauge heights from the two locations in the Yolo Bypass show that 

water levels decreased over a near-month-long period beginning about a week 

before the Sacramento River stopped spilling over Fremont Weir to early April 

(Fig. 7). Local Streams continued to discharge after inflow from the river 

stopped and floodwaters were draining from the Yolo Bypass to the Sacramento 

River near Rio Vista. Flow was largely confined to the perennial channel by 

mid-April, although it is likely that canals continued to drain areas of the 

floodplain (see Discussion). Water levels at the Lower Bypass site were 

influenced by tides from the estuary both before the inundation period and 

after the draining period (Fig. 7). 

Results from the Fixed-Location Sites 

Although concentrations of many chemical constituents in Yolo Bypass 

waters might be related directly to supply rates from the river or the local 

streams, concentrations in some cases might be strongly affected by chemical 

and biological processes occurring in the Yolo Bypass. In presentation of 

the chemical data, concentrations in the Yolo Bypass are compared with those 

in the river and local streams to identify potential sources with the 

understanding that processes in addition to simple mixing might be important. 

Results from the fixed-location sites are shown in the following 

figures 8-23(Appendix B), with the exception of values from the Sacramento 

River at Fremont Weir, which are summarized in Table 1. Numerical values for 

all samples are given in Tables 2-5 (Appendix C). 

Specific conductance (SPC) is a property of natural waters that is 

related to the abundance of dissolved ions, and therefore can be an indicator 

of overall changes in water chemistry. All three sites in the Yolo Bypass 

showed similar variations in SPC over this study (Fig. 8). SPC was high 

until mid-February, when values decreased to levels consistent with those in 

the Sacramento River discharge over Fremont Weir (Table 1). In mid-March, 

SPC began to increase sharply, reaching pre-inundation levels by early April. 

During this period, SPC typically was highest at the HWY5 site and lowest at 

the Lower Bypass site. Precipitation and runoff from the small storm in 

late-April coincided with a decrease in SPC values. 

Local streams were more important to water quality in the Yolo Bypass 

when there was little or no discharge over Fremont Weir. During the 

inundation period, SPC in the Yolo Bypass was much lower than values in the 

four local streams. In general, SPC values in the local streams increased 

from mid-March to mid-April; however, SPC remained low in Putah Creek during 

the short period when its discharge was substantial in late March. SPC 

values in Ridge Cut were among the highest in the local streams. SPC values 

in late March were highest in Willow Slough. Field notes indicated that 

discharge was very low in Willow Slough in late March, but discharge had 

increased in April and May when SPC values were lower. 

Chloride, a major anion, exhibited variations in concentrations in the 

Yolo Bypass and in the local streams that were very similar to SPC (Fig. 9). 

Chloride concentrations showed a near-linear increase with respect to 

7
increasing SPC at all of the sites, although the data were scattered in a few 

cases. The correlation was good, in part, because concentrations of chloride 

were high and chloride is transported conservatively through many freshwater 

systems. This was also the case for some dissolved metals (see below), but 

correlation with nutrients, for example, was poor presumably because of their 

high biological reactivity. 

Concentrations of sulfate were lowest during the inundation period, 

which was consistent with values in the Sacramento River (Fig. 10; Table 1). 

Concentrations increased from mid-March to mid-April at all three Yolo Bypass 

sites, but then dropped to levels that were lower than those before the 

inundation period. With few exceptions, sulfate was much more concentrated 

in Ridge Cut than in the other local streams. From mid-March to mid-April, 

concentrations of sulfate in the Yolo Bypass exceeded concentrations in the 

local streams except for Ridge Cut, indicating that Ridge Cut was a major 

discharger to the Yolo Bypass. The decrease in sulfate concentrations in the 

Yolo Bypass in late April was consistent with reduced concentrations in Ridge 

Cut and discharge pulses from Cache Creek and Ridge Cut. 

Dissolved inorganic nitrogen (DIN), the total concentration of nitrite, 

nitrate, and ammonium, was relatively low in the Yolo Bypass and in the river 

during the inundation period (Fig. 11; Table 1). DIN concentrations in the 

Yolo Bypass increased from late March to mid-April, but decreased at the 

Lower Bypass site following late-April precipitation and runoff. DIN 

concentrations in the local streams also were lowest during the inundation 

period, but increased substantially in all but Ridge Cut from late March 

through May. The two highest values for DIN in the Yolo Bypass were at HWY5 

in April (270 μM) and May (226 μM), and these values appeared more likely 

related to inflow from Cache Creek than from Ridge Cut. Most of the DIN was 

nitrate at all sites throughout this study (see Table 3). 

Although ammonium is often applied as a fertilizer and can be present 

in agricultural runoff and other wastewaters, it also can be an indicator of 

organic matter degradation and nutrient regeneration processes. During the 

inundation period, ammonium concentrations were low at the Yolo Bypass sites 

and in the river (Fig. 12; Table 1). Increases after mid-March were greatest 

at the HWY80 and Lower Bypass sites. Ammonium concentrations in Ridge Cut 

were typically higher than in the other local streams with the exception of 

Willow Slough in mid-April. Cache Creek and Putah Creek typically were 

lowest in ammonium, often less than half the concentration in Ridge Cut. 

Concentrations of ammonium were greater than nitrite but much lower than 

nitrate at all sites during this study. 

Dissolved reactive phosphate (DRP) concentrations at the Yolo Bypass 

sites and in the river were also low during the inundation period, but values 

increased sharply in the Yolo Bypass after mid-March (Fig. 13; Table 1). DRP 

concentrations decreased at the Lower Bypass site during the late-April 

precipitation and runoff, but increased again in May. Although DRP 

concentrations in Putah Creek were higher than in the other local streams in 

April and May, inflow from Putah Creek was probably minimal after earlyApril, and Putah Creek inflow could not have affected concentrations at the 

HWY5 and HWY80 sites (Fig. 13). Concentrations at the Yolo Bypass sites in 

mid-April and May were generally higher than would be expected if Cache Creek 

and Ridge Cut were the major sources of DRP. 

Dissolved silica is a nutrient that is particularly important for the 

growth of diatoms, which are a highly nutritious energy source to primary 

consumers. In contrast to most of the dissolved constituents presented thus 

far, the highest concentrations of dissolved silica at all three Yolo Bypass 

sites occurred during the inundation period (Fig. 14). These concentrations 

were consistent with high concentrations in the Sacramento River (Table 1). 

Concentrations decreased after mid-March to a minimum in early-April, which 

8
was followed by an increase and finally a decrease near the end of the study. 

Dissolved silica did not show a large change during the late-April 

precipitation and runoff, as has been shown for many of the other analytes. 

Concentrations of dissolved silica in Cache Creek and Ridge Cut were 

typically less than those in Putah Creek. Concentrations were highly 

variable in Willow Slough, and the values in late March were the lowest in 

this study (see Discussion). 

 Most of the organic carbon that is transported by rivers is usually in 

dissolved form (DOC). DOC at the Yolo Bypass sites was lowest during the 

inundation period, and then increased in late March to values that were 

relatively stable for the remainder of the study (Fig. 15; Table 1). Of the 

local streams, DOC was generally highest in Ridge Cut and lowest in Cache 

Creek. Although there were a few exceptions, DOC concentrations in Putah 

Creek and Willow Slough were similar to Cache Creek. Specific ultra-violet 

absorbance at 254nm (SUVA) was computed by dividing the absorbance value by 

the DOC concentration. All of the local stream and Yolo Bypass sites showed 

the same general pattern in that the SUVA values were highest during the 

inundation period (Fig. 16; Table 1). Generally, the high values indicated 

that the DOC consisted of more complex organic molecules during the 

inundation period than during the late winter and spring when DOC might 

contain more recently produced organic matter. Low SUVA values for recently 

produced organic matter indicate that it can be more easily utilized as an 

energy source. 

The Sacramento River is the major riverine source of suspended 

particles to San Francisco Bay (see Schemel and others, 1995). Samples 

collected from the Yolo Bypass during this study are not representative of 

the concentrations of suspended sediments through the water column or across 

the floodplain, and in some cases samples from the streams might not be 

representative of their mean values as well. The Yolo Bypass is a relatively 

shallow floodplain, and resuspension of particles might be an important 

factor regulating concentrations. The highest concentrations in mid-February 

and late March were associated with periods of high winds(Figs. 17 and 4). 

Discharges from Cache Creek were high during the inundation period, and 

concentrations of suspended particles there were the highest among the local 

streams. However, Cache Creek discharges into a settling basin, and it was 

unlikely that all of the sediment reached the Yolo Bypass. 

Composition of the suspended particles, particularly the organic matter 

content, was more important than concentrations to this study. Percent 

carbon of the suspended particles ranged from about 1 to 4 percent in most of 

the samples (Fig. 18). The percent carbon was unusually high (>10 percent) 

in Willow Slough in late March. Field notes indicated a high abundance of 

filamentous algae in the water and very low flow in the stream at that time. 

The carbon to nitrogen ratio (C:N) is higher in detrital organic 

material compared to phytoplankton and other aquatic plants. In general, C:N 

ratios in the Yolo Bypass and in the local streams were high during the 

inundation period then decreased sharply in late March (Fig. 19). This is 

consistent with measurements made in the Yolo Bypass in 1998 (Schemel and 

Cox, 1999) and with chlorophyll samples collected in the Yolo Bypass and the 

local streams in 2000, which indicated an increase in algal biomass 

immediately following the inundation period and extending into the spring 

(Mueller-Solger, personal communication). 

9
Dissolved Metals 

Filtered samples were scanned for 18 metals using a radial-view (ICPOES) method appropriate for parts-per-million-level concentrations. Seven of 

the metals, Cadmium, Cobalt, Copper, Manganese, Nickel, Vanadium, and Zinc, 

were not detected in concentrations significantly higher than the blank (less 

than 0.01 mg/L). In addition to these 7 elements, concentrations of 

Aluminum, Iron, and Lithium were mostly below 0.1 mg/L, and will not be 

reported here. Concentrations of Boron (B), Barium (Ba), Calcium (Ca), 

Potassium (K), Magnesium (Mg), Silicon (Si), Sodium (Na), and Strontium (Sr) 

generally exceeded 0.1 mg/L, and their values are reported in Table 5. Si 

also was measured as dissolved silica by a colorimetric method, and the ICPOES results were very similar. Si by ICP-OES values averaged 13% higher than 

those by colorimetry, which could be explained by the dissolution of 

colloidal particles in the strong acid used to preserve the metals samples. 

In general, concentrations were lowest (less than 4 mg/L) for B, Ba, K, 

and Sr. Concentrations exceeded 5 mg/L for Ca, Mg, and Na in all of the 

samples, including those from the Sacramento River, where concentrations were 

typically lowest among the fixed sites (Tables 1 and 5). Concentrations of 

these three most-concentrated metals increased in a near-linear manner with 

increasing specific conductance at most of the sampling sites, although 

scatter in the data was substantial in some cases. Among the lessconcentrated metals, Sr concentrations exhibited good linearity with respect 

to specific conductance, while the others typically exhibited poor 

correlation. Results for Ca, Mg, Na, and Sr are described below. 

All four metals showed a distinct drop in concentration in the Yolo 

Bypass upon inundation by the Sacramento River, an increase from mid-March to 

mid-April, and lower concentrations following the late-April runoff (Figs. 

20-23). In some cases, large differences in concentrations among the local 

streams possibly could be used to identify major sources of waters in the 

Yolo Bypass. During most of the study, Na was much more concentrated in 

Ridge Cut than in Cache Creek or Putah Creek (Fig. 20). In the weeks 

following the inundation period, concentrations of Na were high at HWY5 and 

HWY80 relative to the Lower Bypass, where Sacramento River water was still 

draining from the floodplain. Low concentrations of Na in Putah Creek also 

could have influenced levels at the Lower Bypass site. Even though 

concentrations of Na were high in Willow Slough in late March, discharge was 

very low. Concentrations of Na at all three sites in the Yolo Bypass in midApril were higher than levels in all of the local streams except Ridge Cut, 

which (as in the case of sulfate) indicated the importance of this inflow as 

waters became confined to the perennial channel. 

Concentrations of Ca showed a pattern similar to Na in the Yolo Bypass, 

but the differences in concentrations among the local streams were not as 

great (Fig. 21). The differences in concentrations among the local streams 

were much less for Mg (Fig. 22). From mid-March to mid-April, little 

difference was seen in concentrations of Mg among the three sites in the Yolo 

Bypass. Differences between concentrations at HWY5 and HWY80 and 

concentrations at the Lower Bypass site were greater for Ca and greatest for 

Na. This pattern was also apparent for Sr, even though its concentrations 

were low compared to Na, Ca, and Mg (Fig. 23). 

10
Samples collected by boat in the Yolo Bypass 

Even though discharges over Fremont Weir are typically much greater 

than inflows from local streams during periods of inundation, discharge 

plumes from the local streams are often identifiable in aerial photographs. 

In some cases these inflows are prominent bands extending from their sources 

all the way to the southern outlet of the Yolo Bypass (Sommer and others, 

2001a). In an attempt to locate discharge plumes from the local streams and 

to determine the extent of water from the Sacramento River, near-surface 

waters were sampled on four days (February 17-20) by boat shortly after the 

onset of major flooding. The samples were collected across the flooded 

bypass about half way between highway 80 and the southern outlet. Specific 

conductance and concentrations of nutrients and metals were consistent among 

three of the four sites on all four days, and only the site nearest the 

western margin of the floodplain had significantly higher concentrations, 

indicating the presence of discharge from local streams (see data tables). A 

local stream source could be identified on only two days. Concentrations of 

Na on February 18 and 20 were at levels consistent with discharge from Ridge 

Cut, the local stream with the highest Na values. Values for most of the 

analytes on most days were within the ranges for all four local streams, but 

these values were still significantly different (mostly higher) than 

concentrations in the Sacramento River discharge. Since Ridge Cut is the 

most upstream inflow, it is likely that plumes from the other local streams 

were confined to very shallow water along the western margin at that time. 

Samples were collected by boat at locations near the southern outlet of 

the Yolo Bypass while the floodplain was draining after inundation (March 23) 

and after the floodplain had drained to the level of the perennial channel 

(April 11). Specific conductance, nutrients, and metal concentrations on 

March 23 were consistent with values at the Lower Bypass site, indicating 

discharge from the Yolo Bypass to the river. On April 11, however, values 

near the southern outlet were lower than those at the Lower Bypass site, 

indicating substantial dilution by tidal mixing with water from the 

Sacramento River. 

11
DISCUSSION 

Floodwaters from Fremont Weir were responsible for the major inundation 

of the floodplain from mid-February to mid-March, 2000. Even though 2000 was 

not a particularly wet winter, Sacramento River discharge to the floodplain 

was substantially greater than the total inflow from the local streams. 

Results from the samples collected by boat during the inundation period 

confirmed that surface waters were dominated by Sacramento River water and 

that local streams only affected the western margin. This is consistent with 

aerial photographs from previous years, although discharge plumes from local 

streams are probably more extensive in winters with higher discharges than 

2000. 

Discharge over Fremont Weir began to decrease in early March, and water 

levels in the Sacramento River dropped below the height of Fremont Weir in 

mid-March. Draining of the floodplain was rapid after mid-March, reaching 

the level of the perennial channel by early April. Observations made at the 

sites in the Yolo Bypass indicated that open water areas drained relatively 

quickly, followed by ponds and canals that cross the floodplain. Rapid 

draining of the open water areas is also indicated by the gauge height data 

from the Lower Bypass (Fig. 7). We expect that the numerous canals continued 

to drain shallow groundwaters from the floodplain for weeks after the 

inundation period. 

During and after the draining period, the paths of discharges from the 

local streams to the perennial channel are not always clear and probably 

change as the floodplain is utilized for agriculture. An overview of water 

sources (including local streams and wells) and channels in the Yolo Bypass 

can be found in a recent management strategy report prepared for the CALFED 

Bay-Delta Program (CALFED, 2001). When water levels are still high in the 

Sacramento River relative to the Colusa Basin Drain, discharge from Ridge Cut 

can flow down a channel directly to the perennial channel upstream of our 

HWY5 site. Later in spring and in summer, gates in the Ridge Cut weir near 

the western levee of the Yolo Bypass supply water to irrigation water canals, 

and drainage canals route the return flow to the perennial channel. It 

appeared that some discharge from Ridge Cut was flowing directly to the 

perennial channel in mid-April, but that most of the flow from the Colusa 

Basin Drain was discharging to the Sacramento River at Knights Landing in May 

2000. 

Cache Creek also can flow directly to the perennial channel near our 

HWY5 site, but part of its flow can be diverted to an irrigation canal along 

the western levee of the Yolo Bypass. The primary flow of Cache Creek 

appeared to be runoff from precipitation during this study, and discharge 

directly to the perennial channel was evident as late as mid-April. 

Willow Slough did carry runoff from storms during winter, but low-tomoderate discharges also were observed in April and even in May at times when 

storm runoff could not have been the source. During the three samplings from 

mid- to late-March, discharge was very low in Willow Slough, and 

concentrations of many dissolved analytes were high. Constituent transports 

to the Yolo Bypass in mid- to late-March were probably insignificant because 

of the low flows. At low water levels in the Yolo Bypass, Willow Slough 

discharge flows southward along the western levee to the basin at the end of 

Putah Creek. Water from this basin is used for agriculture and the return 

flows are routed to the perennial channel. 

We noted that Putah Creek carried some runoff from the winter storms 

even though this was not evident in the gauge data. However, the major 

discharge during this study appeared related to reservoir releases extending 

to early April. Some of this water and discharge from Willow Slough could 

have been impounded in a basin on the floodplain, although a channel can 

12
carry overflow directly to the perennial channel. It is likely that neither 

Willow Slough nor Putah Creek discharged directly to the perennial channel 

after early April 2000. Discharge from Willow Slough and Putah Creek that 

reached the perennial channel could have influenced water chemistry at the 

Lower Bypass site, but not at HWY5 or HWY80. Discharges from numerous canals 

that carry agricultural return flows were probably more significant late in 

this study at the Lower Bypass site. 

Although direct observations were lacking in some cases, it is likely 

that Cache Creek and Ridge Cut were the major direct sources of local stream 

flow to the perennial channel from mid-March to mid-April. This was 

indicated by the chemical data at both HWY5 and HWY80 in many cases. 

Groundwater, agricultural return flows, and perhaps other sources could have 

been significant in late April and May, when local streams probably did not 

flow directly to the perennial channel. These other sources could explain 

why some results from the Yolo Bypass sites were not consistent with the 

assumption that the local streams were the major sources, particularly at the 

Lower Bypass site. 

The sharp increases in concentrations of many dissolved analytes in the 

Yolo Bypass immediately after the inundation period indicated a rapid 

transition from domination by Sacramento River water to increasing influence 

of waters from the local streams as floodwaters receded to the perennial 

channel. Generally higher concentrations at the HWY5 and HWY80 sites 

compared to those at the Lower Bypass site also suggest that Sacramento River 

water was draining southward in the floodplain and being replaced by water 

primarily from the two major local stream inflows, Cache Creek and Ridge Cut. 

Mass balance calculations cannot be used to verify that Cache Creek and 

Ridge Cut are the major sources to the perennial channel because flows were 

not measured in Ridge Cut. However, the chemical data do suggest that the 

HWY5 and HWY80 sites were affected by discharge from Ridge Cut. 

Concentrations of Na and sulfate were much higher in Ridge Cut relative to 

the other local streams, including Cache Creek. In late March and early 

April, concentrations of Na and sulfate at HWY5 and HWY80 were between the 

values in Cache Creek and Ridge Cut, indicating that waters in the perennial 

channel were primarily a mixture of these two sources. 

It is expected that concentrations of dissolved constituents vary 

greatly with discharge in both Cache Creek and Ridge Cut. Specific 

conductance (SPC) was used as a surrogate for discharge variability in order 

to examine fundamental differences in the chemical variability in these two 

streams. We pooled the data from our study with data collected at two-week 

or monthly intervals in the Colusa Basin Drain and in Cache Creek from 

February 1996 through April 1998 to see if different patterns emerged for Na 

and sulfate (Figs. 24 and 25; Domalgalski and Deleanis, 2000). Discharges 

were available for Cache Creek over this earlier study, and, generally 

speaking, the highest SPC values represented low discharges and the lowest 

SPC values corresponded to discharges that were higher than those in 2000. 

The relationships between Na and SPC were similar for the two local streams, 

but most of the values in the Colusa Basin Drain were grouped higher than 

those in Cache Creek. Consequently, Na can be a tracer for mixing when 

differences in concentration between the two streams are relatively large. 

The relationships between sulfate and SPC were clearly different for the two 

streams (Fig. 25). Most concentrations of sulfate in the Colusa Basin Drain 

were substantially higher than those in Cache Creek over a wide range of SPC 

values. Therefore, sulfate might be a good tracer of discharge from Ridge 

Cut at the Yolo Bypass sites over a wide range of hydrologic conditions. The 

extent to which sulfate can be altered by bacterial processes in the 

perennial channel is unknown, so we estimated the fraction of the total 

13
inflow that came from Ridge Cut at the HWY5 and HWY80 sites using 

concentrations of both Na and sulfate. 

If we assume that the chemical concentrations were largely determined 

by two-component mixing, estimates can be based on the following 

relationship: 

The receiving water concentration in the perennial channel [TD] = (the 

fraction of the total inflow contributed by Ridge Cut, QRC, times the 

concentration in Ridge Cut, [RC]) + (the fraction of total inflow contributed 

by Cache Creek, 1-QRC, times the concentration in Cache Creek, [CC]). 

Rearranging the expression gives: QRC = ([TD] – [CC])/([RC] – [CC]) 

Simple two-component mixing models such as this have been useful in 

identifying sources of water to floodplain lakes (Forsberg and others, 1988; 

Carignan and Neiff, 1992). 

Calculations for March 17, immediately after flow over Fremont Weir had 

stopped, gave very low QRC values because most of the water was from the 

Sacramento River. Calculations for March 23 gave comparable results for Na 

and sulfate at HWY5, 0.63 and 0.78, respectively, and HWY80, 0.78 and 0.72, 

respectively. Similarly, results for March 28 for Na and sulfate were: 

HWY5, 0.54 and 0.57, respectively, and HWY80, 0.39 and 0.40, respectively. 

The calculations for HWY5 suggest that the inflow from Ridge Cut was similar 

to or perhaps even greater than the inflow from Cache Creek over the two 

weeks following inundation by the Sacramento River. It is likely that 

channels draining the floodplain had a greater effect at HWY80, and that the 

Lower Bypass site also was affected by flow primarily from Putah Creek. 

Assuming the other local stream inflows had concentrations of Na and sulfate 

similar to Cache Creek, the calculations indicate that from 10 (Na value) to 

29 (sulfate value) percent of the water in the Lower Bypass was from Ridge 

Cut on March 28. 

Concentrations of dissolved inorganic N and P nutrients increased at 

the Yolo Bypass sites while the floodplain was draining and continued to 

increase in the perennial channel until the small flow pulse in mid-April. 

Depletion of these nutrients by biogeochemical processes, such as 

phytoplankton production, was not observed, indicating that the rate of 

supply by local streams and other sources and processes outweighed removal 

mechanisms. Over-enrichment of N and P nutrients can lead to nuisance algal 

blooms, particularly if depletion of dissolved Si occurs (see reviews by 

Conley and others, 1993, and Cloern, 2001). Dissolved Si was most 

concentrated in the Sacramento River inflow, but concentrations in the Yolo 

Bypass were reduced to about half that in the river by the end of March. 

Inflow from the local streams could account for at least some of this decline 

in dissolved Si, but removal by phytoplankton production probably was a 

factor as well (see below). It is most important to note that dissolved Si 

was never reduced to sub-micromolar concentrations indicative of Si 

limitation. However, the abundance of dissolved Si relative to the other 

nutrients was reduced to a level such that an intense diatom bloom would 

deplete dissolved Si from the water column before the other nutrients. 

A recent USGS assessment of water and sediment quality in the 

Sacramento River Basin identified many sources of contaminants that can 

degrade habitats and pose risks to aquatic and other species, including human 

beings (Domalgalski and Deleanis, 2000). Some of these contaminants are 

derived from natural sources, such as mercury (Hg) deposits in the coastal 

range watershed, whereas other contaminants are products of human activities, 

such as pesticides from agricultural applications and urban runoff. During 

winter, a large fraction of the runoff from the Sacramento River Basin can 

14
flow through the Yolo Bypass carrying dissolved and particulate contaminants 

to the Delta and San Francisco Bay (for example; Domagalski and Kuivila, 

1993; Bergamaschi and others, 2001). Undoubtedly, some contaminants from the 

Sacramento River can be trapped in the Yolo Bypass as the floodplain begins 

to drain. In addition, local stream inflows, irrigation return flows, and 

discharges from the local urban areas are potential sources of contaminants 

to the Yolo Bypass. The Yolo Bypass provides habitat for a wide range of 

aquatic organisms, migratory birds, and many other species, which could be 

affected by contaminated waters and sediments. 

Ridge Cut and Cache Creek were identified above as major sources of 

discharge to the Yolo Bypass for weeks after the inundation of the floodplain 

by Sacramento River discharge. The Colusa Basin Drain is the source of water 

for Ridge Cut. Irrigation return flow is typically a large fraction of the 

water in the Colusa Basin Drain, and this water can be substantially enriched 

in dissolved salts, sediments, and chemicals derived from agricultural 

activities in the Basin (for example see Schemel and others, 1989, and 

references therein). The Colusa Basin Drain is a major source of pesticides 

and their degradation products particularly during spring (Domagalski, 1996 

and 2000). Similarly, many canals carry return flows to the perennial 

channel from agricultural areas in the Yolo Bypass floodplain from spring 

through summer. Pesticides and their degradation products that have been 

detected in the Yolo Bypass appear to be related to runoff events during 

winter and agricultural return flows later in the year (Domagalski, 2000). 

The Sacramento River Basin has many natural and man-made sources of Hg 

(Domagalski, 1998). The highest loading of Hg to San Francisco Bay has been 

attributed to sources in the Cache Creek watershed. Highest transport rates 

for Hg coincide with the highest discharges, and most of the Hg from the 

Sacramento River system entered the Estuary via the Yolo Bypass during the 

1997 and 1998 water years (Domagalski, 2001). Although levels of total Hg 

were lower than those in Cache Creek, significant concentrations of methyl 

mercury, which is particularly hazardous to aquatic organisms, have been 

measured in the Colusa Basin Drain. Conditions that could produce methyl 

mercury include stagnant waters and marshes with an abundance of sulfate and 

organic carbon, which are conditions similar to those in the Yolo Bypass 

during spring of our study. 

Plans to develop habitat in the Yolo Bypass might need to consider 

water sources, contaminants, and biogeochemical processes in order to 

optimize conditions for wildlife. Runoff from local streams during April of 

our study increased flow and reduced concentrations of many substances that 

had accumulated in the perennial channel of the Yolo Bypass. Habitat 

conditions in the perennial channel also might be enhanced by periodic 

flushing by water from the Sacramento River, releases from reservoirs on 

Cache or Putah creeks, or other suitable freshwater sources during the 

irrigation season. 

Discharge from the Yolo Bypass is a source of many dissolved and 

particulate substances to the tidal Sacramento River. Transports of 

dissolved and particulate substances from the Yolo Bypass are often greater 

than those from the upstream Sacramento River channel during winter floods, 

but inputs from the draining of the floodplain channels after the inundation 

period and runoff from spring storms also might be important to the river. 

Our results show a large change in the quality of dissolved and particulate 

organic matter in the Yolo Bypass after the inundation period. SUVA values 

and C:N ratios decreased, which was a strong indication that recently produce 

organic matter was more abundant. Chlorophyll a measurements have confirmed 

that increased primary production by diatoms and other phytoplankton was a 

major feature of the draining period through mid-April (W. Sobczak and A. 

Mueller-Solger, personal communications). In addition, chlorophyll a

15
monitors at Rio Vista have shown for many years that concentrations in the 

Sacramento River increase during the draining of the Yolo Bypass and often 

following late-season storms that flush materials from the perennial channel 

(Sommer and others, 2001). These results suggest that the Yolo Bypass not 

only is a producer of highly nutritious organic matter for its inhabitants, 

but that it exports organic matter to the river-delta-estuary system, where 

supplies of phytoplankton organic carbon have become increasingly scarce in 

recent years (Jassby and others, 2002). Recommendations for rehabilitation 

of the Delta include better utilization of potentially productive areas 

including the Yolo Bypass, other floodplains, and marshlands (Jassby and 

Cloern, 2000). 

Floodplains of large river systems are critically important components 

of their ecosystems (Junk and others, 1989; Tockner and others, 2000). Large 

expanses of the Sacramento River valley were floodplains and wetlands before 

the California gold rush. Serious ecological damage to the Sacramento River 

might be expected from the huge reduction in floodplain and wetland areas by 

reclamation for agriculture alone. The Yolo Bypass is a remnant of a once 

extensive floodplain that has been engineered and leveed to provide flood 

protection. In recent years, we have learned that this floodplain also 

provides many benefits to the river ecosystem and the San Francisco Bay (see 

Sommer and others, 2001, and references therein). Actions that could 

preserve and enhance ecological benefits of the Yolo Bypass recently have 

been proposed as part of the Bay-Delta Ecosystem Restoration Program (see 

CALFED, 2001). This study in 2000 and our previous study in 1998 provide 

knowledge of water quality conditions in the Yolo Bypass and local streams 

that should prove useful in the implementation of proposed management 

actions. 

16
SUMMARY 

Results from this study during winter and early spring 2000 link 

variations in water quality in the Yolo Bypass to discharges from the 

Sacramento River and local streams that enter the western margin of the 

floodplain. When floodwaters were flowing over Fremont Weir, the water 

chemistry in the Yolo Bypass was very similar to that in the Sacramento River 

except along the western margin where the influences of local stream inflows 

were evident. When flow over Fremont Weir stopped, the floodplain 

subsequently drained, and discharges from local streams became major sources 

of water and waterborne constituents. As waters were confined to the 

perennial channel along the eastern margin of the floodplain, chemical 

concentrations indicated strong influences of discharges from Cache Creek and 

Ridge Cut. Both of these streams are sources of contaminants that are 

potentially hazardous to wildlife. Sources of some constituents were not 

clearly identified during early spring, which might be expected as canals 

drain shallow groundwaters from the floodplain and agricultural activities 

commence in the area. The perennial channel provides habitat for aquatic 

species throughout the year. Water chemistry in the perennial channel of the 

floodplain was influenced by runoff from storms during spring, which flushed 

accumulated nutrients and organic matter from the channel. Such freshwater 

inflows could reduce the risk of over enrichment of inorganic nitrogen and 

phosphorus nutrients, nutrients that promote algal blooms that could degrade 

habitat quality. Habitat conditions during the dry irrigation season might 

be enhanced by periodic releases of suitable freshwater to the perennial 

channel. 

17
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_____________, _______________, and Cole, B.E., 2002, Annual primary 

production: Patterns and mechanisms of change in a nutrient-rich tidal 

ecosystem: Limnology and Oceanography v.47, p.698-712. 

Junk, W.J., Bayley, P.B., and Sparks, R.E., 1989, The Flood Pulse Concept in 

River-Floodplain Systems: in Dodge, D.P., (ed.), Proceedings of the 

International Large River Symposium, Canadian Special Publication of 

Fisheries and Aquatic Sciences 106, p.110-127. 

 

Kelley, Robert, 1989, Battling the Inland Sea: University of California 

Press, Berkeley, CA. 

Kennedy, D.N., 1997, Forward to the 1997 edition of Battling the Inland Sea: 

University of California Press, Berkeley, CA. 

Nichols, F.H., Cloern J.E., Luoma, S.N., and Peterson, D.H., 1986, The 

modification of an estuary: Science v.231, p.567-573. 

Schemel, L.E., Ota, A.Y., Hager, S.W., and Swithenbank, A.M., 1989, Sources 

of dissolved and particulate substances to the Sacramento River near 

Sacramento, California, Summer, 1985: U.S. Geological Survey Open-File 

Report 89-45. 

_____________ , Childers, D, and Hager, S.W., 1995, The supply and carbon 

content of suspended sediment from the Sacramento River to San Francisco Bay, 

in San Francisco Bay, The Ecosystem, Hollibaugh JT (ed.): Pacific Division, 

American association for the Advancement of Science, San Francisco, CA p.237-

260. 

______________ and Cox, M.H., 1999, Overview of Chemical Analyses for the 

Yolo Bypass, in Results and Recommendations from 1997-1998 Yolo Bypass 

Studies: California Department of Water Resources, Sacramento, CA. 

Sommer, T.R., Harrell, W.C., Nobriga, M.L., Brown, R., Moyle, P., Kimmerer, 

W.J., and Schemel, L.E., 2001a, California’s Yolo Bypass: Evidence that 

flood control can be compatible with fisheries, wetlands, wildlife and 

agriculture: Fisheries v.26, p.6-16. 

19
______________, Nobriga, M.L, Harrell, W.C., Batham, W., and Kimmerer, W.J., 

2001b, Floodplain rearing of juvenile chinook salmon: evidence of enhanced 

growth and survival: Canadian Journal of Fisheries and Aquatic Sciences 

v.58, p.325-333. 

Teets, B, and Young, S., 1986, Rivers of Fear: The Great California Flood of 

1986: C.R. Publications, Inc., WV. 

Tockner, K., Malard, F., and Ward, J.V., 2000, An extension of the flood 

pulse concept: Hydrological Processes, v.14, p.2861-2883. 

20
Appendix A: FILTRATION AND SAMPLE PREPARATION METHODS 

FOR THE YOLO BYPASS STUDY IN 2000 

DISSOLVED INORGANIC CONSTITUENTS: 

Cellulose ester filters (47mm-diameter, 0.45um-pore-size; Millipore 

type HA or equivalent with tare weights in the range of 90-100 mg) were used 

to filter samples for ICP, IC, and nutrient analyses. The polycarbonate 

filter apparatus (Sartorius 16510, or equivalent) was cleaned with dilute HCl 

between batches of samples and rinsed with acid-distilled water between 

samples. After processing the sample, each filter was dried in a desiccator 

for a month and weighed to provide an estimate of the suspended particulate 

matter concentration in the sample. The procedure was as follows: 

1) Rinse filtration apparatus by filling the upper reservoir to the 200ml 

mark with acid-distilled water and swirling the liquid as it drains through 

to the lower reservoir. The liquid in the lower reservoir is shaken before 

being discarded. This is repeated for a total of two rinses. 

2) Install filter, making sure that it is centered properly. 

3) Weigh sample bottle on the pan balance and record value. 

4) Shake sample, then pour approximately 50ml into filtration apparatus. 

Swirl contents to rinse sample reservoir, then apply vacuum. Place the 

plastic cap loosely onto the sample reservoir. After aliquot has been 

filtered, turn off vacuum and disconnect vacuum line. Holding the entire 

assembly, gently swirl the liquid so that the lower reservoir is rinsed to 

the level of the "O" ring. Remove filtrate reservoir and pour off the 

filtrate over the graduated side of the reservoir (use this same side for all 

pouring). Reassemble apparatus. 

5) Repeat step 4. 

6) Shake sample, then pour between 150 and 200ml of sample into sample 

reservoir and apply vacuum. Place the plastic cap loosely onto the sample 

reservoir while the sample is being filtered. Weigh the sample bottle and 

record the difference in weight on the petri dish that will be used to store 

the filter. After the sample has filtered, turn off the vacuum and 

disconnect the vacuum line. 

7) Remove the sample reservoir-filter assembly from the filtrate reservoir 

and pour the samples in the following manner. Fill the 60ml poly ICP bottle 

to the shoulder. Pour out the artificial river water from the 30ml nutrient 

bottle. Rinse the nutrient bottle and cap three times with a small amount of 

filtrate, then fill the bottle to the shoulder. Fill the 60ml IC bottle to 

the shoulder with the remaining filtrate. 

8) Remove the sample reservoir and remove the filter. Place the filter in 

the petri dish and label the dish with the sample location, date, and time. 

9) Repeat procedure from step 1 for the next sample. After all samples are 

filtered, soak the filtration apparatus in dilute HCl overnight, rinse with 

distilled water, and allow to dry. 

10) Place nutrient bottles in freezer, IC bottle in refrigerator, and store 

the ICP bottle at room temperature after acidification with concentrated 

nitric acid to 1% final concentration. 

21
Appendix A: continued. 

DISSOLVED ORGANIC CARBON: 

 

Stainless steel pressure filtration funnels (Gelman, 47-mm, or equivalent) 

with glass fiber filters were used to process the dissolved organic carbon 

(DOC) samples. The filtration funnels were cleaned initially in a boiling 

low-DOC MilliQ water bath. Between samples the apparatus was rinsed once 

with room temperature low-DOC MilliQ water and then placed in a boiling lowDOC MilliQ water bath. Glass fiber filters (47 mm type A/E, or equivalent) 

were cleaned by baking in a muffle furnace at 450o

C for 12 hours. Sample 

bottles (amber glass) were rinsed with distilled water, air dried, covered 

with Al foil, and then baked at 450o

C for 12 hours. The teflon-lined caps 

were (Qorpak, or equivalent) were rinsed with distilled water, soaked in 2% 

HCL for 2 hours, rinsed with distilled water, and then air dried. Samples 

were prepared as follows: 

1) Rinse the inside of the filtration funnel with an aliquot of sample by 

swirling the liquid as it drains and discard the sample. 

2)Rinse the funnel again and let the sample drain into a sample bottle. 

Rinse the collection bottle and cap with filtered sample. 

3) Fill the funnel again. Take the first part of the filtered sample and 

rinse the sample bottle and cap again. The remainder of the filtered sample 

is kept. Once the sample bottle is filled, take two caps full of sample from 

the bottle to rinse the cap. 

4) Store sample in refrigerator until analysis. 

PARTICULATE CARBON AND NITROGEN: 

Stainless steel vacuum filter holders were used to collect particles onto 

13mm glass fiber filters for carbon and nitrogen analysis. The filter 

holders were cleaned initially in a boiling low-DOC MilliQ water bath. 

Between samples, the apparatus was rinsed once with room temperature low-DOC 

MilliQ water, and then cleaned in a boiling low DOC MilliQ water bath. 

Filters were baked at 450o

C for 6 hours. 

1) Rinse a glass cylinder with sample, and then measure 20-ml of sample. 

Pour sample into vacuum filter and apply vacuum without letting the sample 

settle in the cylinder. Keep adding known volumes of sample to the vacuum 

filter until the rate of filtering decreases. Record volume of sample 

filtered. 

2) Once the filter is dry, turn off vacuum. Disassemble filter funnel and 

remove filter. 

3) Place filter on petri dish. Store sample in desiccator until analysis. 

 

22
Appendix B: ILLUSTRATIONS 

23
Figure 1. Map showing the Sacramento River, Yolo Bypass, local 

streams, and locations of the fixed sampling sites. 

24
Figure 2. Daily mean discharge in the Yolo Bypass (DAYFLOW 

value) for the 1956-2000 water years. 

25
Figure 3. Daily total precipitation and mean daily irradiance 

at Davis, California, January through May, 2000. 

26
Figure 4. Daily mean wind speed and maximum daily air 

temperature at Davis, California, January through May, 2000. 

27
Figure 5. Daily mean discharge in the Sacramento River at 

Freeport and in the Yolo Bypass (DAYFLOW value), January through 

May, 2000. 

28
Figure 6. Daily mean discharge in Cache Creek and Putah Creek, 

January through May, 2000. 

29
Figure 7. Water levels (gauge height) in the Sacramento River 

and Colusa Basin Drain at Knights Landing and the Yolo Bypass at 

HWY5 and in the Lower Bypass, January through May, 2000. 

30
Figure 8. Specific conductance in the local streams (upper 

panel) and at sites in the Yolo Bypass (lower panel), January 

through May, 2000. 

31
Figure 9. Chloride concentrations at sites in the local streams 

and at sites in the Yolo Bypass, January through May, 2000. 

32
Figure 10. Sulfate concentrations at sites in the local streams 

and at sites in the Yolo Bypass, January through May, 2000. 

33
Figure 11. Dissolved inorganic nitrogen concentrations at sites 

in the local streams and at sites in the Yolo Bypass, January 

through May, 2000. 

34
Figure 12. Ammonium nitrogen concentrations at sites in the 

local streams and at sites in the Yolo Bypass, January through 

May, 2000. 

35
Figure 13. Dissolved reactive phosphorus concentrations at 

sites in the local streams and at sites in the Yolo Bypass, 

January through May, 2000. 

36
Figure 14. Dissolved silica concentrations at sites in the 

local streams and at sites in the Yolo Bypass, January through 

May, 2000. 

37
Figure 15. Dissolved organic carbon concentrations at sites in 

the local streams and at sites in the Yolo Bypass, January 

through May, 2000. 

38
Figure 16. Specific ultra violet absorbance at 245nm at sites 

in the local streams and at sites in the Yolo Bypass, January 

through May, 2000. 

39
Figure 17. Suspended particle concentrations at sites in the 

local streams and at sites in the Yolo Bypass, January through 

May, 2000. 

40
Figure 18. Suspended particle percent carbon at sites in the 

local streams and at sites in the Yolo Bypass, January through 

May, 2000. 

41
Figure 19. Carbon to Nitrogen ratio by moles at sites in the 

local streams and at sites in the Yolo Bypass, January through 

May, 2000. 

42
Figure 20. Sodium concentrations at sites in the local streams 

and at sites in the Yolo Bypass, January through May, 2000. 

43
Figure 21. Calcium concentrations at sites in the local streams 

and at sites in the Yolo Bypass, January through May, 2000. 

44
Figure 22. Magnesium concentrations at sites in the local 

streams and at sites in the Yolo Bypass, January through May, 

2000. 

45
Figure 23. Strontium concentrations at sites in the local 

streams and at sites in the Yolo Bypass, January through May, 

2000. 

46
Figure 24. Sodium concentrations in Cache Creek and Ridge Cut 

(or Colusa Basin Drain) during the 1996-1998 NAWQA study and in 

2000. 

47
Figure 25. Sulfate concentrations in Cache Creek and Ridge Cut 

(or Colusa Basin Drain) during the 1996-1998 NAWQA study and in 

2000. 

48
Appendix C: TABLES 

Table 1. Specific Conductance in μS cm-1, chloride, sulfate, 

dissolved organic carbon, suspended particles, particulate 

carbon and nitrogen, and dissolved metals in mg/L, and dissolved 

nutrients in μM in the Sacramento River at Fremont Weir during 

the inundation period, March 2000. 

Analyte March 7 March 17

Specific Conductance 121 147 

Chloride 3.5 4.0 

Sulfate 9.2 10.4

Dissolved organic carbon 2.9 1.3 

Specific UV absorbance 0.079 -- 

Suspended particles 145 68 

Particulate carbon -- 0.82 

Particulate nitrogen -- 0.09 

Dissolved metals: 

Boron 0.04 0.04

Barium 0.02 0.02

Calcium 10 13 

Potassium 1.3 1.2 

Magnesium 5.1 6.4 

Sodium 6.3 7.2

Silicon 9.4 10.6

Strontium 0.06 0.09 

Dissolved nutrients: 

Nitrate 10.9 14.0

Nitrite 0.1 0.1

Ammonium 0.9 0.3 

Dissolved reactive phosphate 1.1 0.7 

Dissolved silica 308 339 

49
Table 2. Specific conductance (uS/cm) and concentrations of 

chloride and sulfate (mg/L). 

 Specific 

Sample ID Date Conductance Chloride Sulfate

Fremont Weir (FRW) 

FRW 7-Mar-00 121 3 9 

FRW 17-Mar-00 147 4 10 

Lower Bypass (STTD) 

STTD 26-Jan-00 790 49 104 

STTD 28-Jan-00 712 43 100 

STTD 31-Jan-00 728 41 90 

STTD 2-Feb-00 747 42 87 

STTD 3-Feb-00 753 49 90 

STTD 7-Feb-00 769 48 90 

STTD 9-Feb-00 823 52 100 

STTD 11-Feb-00 810 51 98 

STTD 14-Feb-00 570 35 68 

STTD 16-Feb-00 201 10 16 

STTD 25-Feb-00 169 7 11 

STTD 28-Feb-00 146 5 10 

STTD 6-Mar-00 146 5 10 

STTD 20-Mar-00 476 23 44 

STTD 22-Mar-00 534 27 51 

STTD 23-Mar-00 574 30 57 

STTD 24-Mar-00 559 30 54 

STTD 27-Mar-00 568 31 50 

STTD 31-Mar-00 640 37 61 

STTD 10-Apr-00 824 53 92 

STTD 17-Apr-00 921 77 71 

STTD 24-Apr-00 464 25 40 

STTD 1-May-00 654 45 55 

STTD 8-May-00 763 62 55 

STTD 15-May-00 604 44 45 

STTD 22-May-00 642 49 48 

50
Table 2 continued. 

 Specific 

Sample ID Date Conductance Chloride Sulfate

Toe Drain at I-80 (TD80) 

TD80 26-Jan-00 832 51 118 

TD80 16-Feb-00 163 7 13 

TD80 28-Feb-00 160 6 11 

TD80 7-Mar-00 153 5 11 

TD80 17-Mar-00 262 11 23 

TD80 23-Mar-00 715 42 87 

TD80 28-Mar-00 705 45 71 

TD80 3-Apr-00 833 54 93 

TD80 17-Apr-00 911 75 84 

TD80 21-May-00 678 52 60 

Toe Drain at I-5 (TD5) 

TD5 26-Jan-00 783 41 124 

TD5 16-Feb-00 128 5 10 

TD5 28-Feb-00 138 4 9 

TD5 7-Mar-00 157 7 10 

TD5 17-Mar-00 363 16 39 

TD5 23-Mar-00 731 42 92 

TD5 28-Mar-00 741 44 88 

TD5 3-Apr-00 837 52 107 

TD5 17-Apr-00 805 66 50 

TD5 21-May-00 778 75 61 

Ridge Cut Canal West Side at Road 16 (RCW16) 

RCW16 26-Jan-00 744 38 115 

RCW16 16-Feb-00 442 24 62 

RCW16 7-Mar-00 554 28 69 

Ridge Cut Canal East Side at Road 16 (RCE16) 

RCE16 26-Jan-00 725 35 112 

RCE16 16-Feb-00 442 24 63 

RCE16 20-Feb-00 600 30 83 

RCE16 28-Feb-00 588 30 79 

RCE16 7-Mar-00 571 29 72 

RCE-16 17-Mar-00 780 41 102 

RCE-16 23-Mar-00 784 42 108 

RCE-16 28-Mar-00 891 51 129 

RCE-16 3-Apr-00 842 46 113 

RCE-16 17-Apr-00 895 76 87 

51
Table 2 continued. 

 Specific 

Sample ID Date Conductance Chloride Sulfate

Colusa Basin Drain at Road 99E (CBD99) 

CBD99E 20-Feb-00 613 31 85 

CBD99E 28-Feb-00 612 31 84 

CBD99E 21-May-00 515 23 83 

Cache Creek at Road 113 (CC113) 

CC113 26-Jan-00 702 78 52 

CC113 16-Feb-00 389 26 29 

CC113 28-Feb-00 334 14 26 

CC113 7-Mar-00 359 14 25 

CC113 17-Mar-00 416 20 25 

CC113 23-Mar-00 544 35 34 

CC113 28-Mar-00 550 35 33 

CC113 3-Apr-00 747 49 41 

CC113 17-Apr-00 498 30 26 

CC113 21-May-00 728 46 37 

Willow Slough at Road 102(WS102) 

WS102 26-Jan-00 441 26 54 

WS102 16-Feb-00 323 17 36 

WS102 28-Feb-00 421 22 40 

WS102 7-Mar-00 423 21 37 

WS102 17-Mar-00 870 26 28 

WS102 23-Mar-00 851 60 81 

WS102 28-Mar-00 1181 68 78 

WS102 3-Apr-00 659 44 45 

WS102 17-Apr-00 457 26 28 

WS102 21-May-00 551 31 30 

Putah Creek at Old Davis Road (PCD) 

PCD 26-Jan-00 471 

PCD 16-Feb-00 336 14 30 

PCD 28-Feb-00 430 17 45 

PCD 7-Mar-00 358 8 30 

PCD 17-Mar-00 352 7 26 

PCD 23-Mar-00 351 7 25 

PCD 28-Mar-00 354 7 25 

PCD 3-Apr-00 434 15 29 

PCD 17-Apr-00 573 27 33 

PCD 21-May-00 567 24 34 

52
Table 2 continued. 

 Specific 

Sample ID Date Conductance Chloride Sulfate

Boat Samples from Yolo Bypass: Band A =East Side; Band D = West 

Side 

BAND A 17-Feb-00 133 5 10 

BAND B 17-Feb-00 109 4 9 

BAND C 17-Feb-00 118 4 10 

BAND D 17-Feb-00 220 9 23 

BAND A 18-Feb-00 119 4 9 

BAND B 18-Feb-00 117 4 9 

BAND C 18-Feb-00 114 4 10 

BAND D 18-Feb-00 368 20 47 

BAND B 19-Feb-00 132 4 10 

BAND C 19-Feb-00 127 4 10 

BAND D 19-Feb-00 288 13 33 

BAND A 20-Feb-00 147 6 10 

BAND B 20-Feb-00 140 4 10 

BAND C 20-Feb-00 145 4 11 

BAND D 20-Feb-00 416 16 42 

Boat Samples from Southern Outlet of Yolo Bypass 

LH-1 11-Apr 527 33 51 

PS-1 23-Mar 558 28 54 

PS-1 11-Apr 341 20 29 

PS-2 23-Mar 536 26 51 

PS-2 11-Apr 322 19 27 

PS-3 23-Mar 551 27 54 

YB-1 11-Apr 221 11 18 

53
Table 3. Concentrations of nitrite (NO2), Nitrate plus Nitrite 

(N+N), Ammonium (NH4), dissolved inorganic nitrogen (DIN), 

dissolved reactive phosphorus (DRP), and dissolved silica 

(DiSi). 

Station ID Date NO2 N+N NH4 DIN DRP DiSi

Fremont Weir (FRW) 

FRW 7-Mar-00 0.14 11.1 0.89 12 1.09 308 

FRW 17-Mar-00 0.08 14.1 0.33 14.4 0.68 339 

Lower Bypass (STTD) 

STTD 26-Jan-00 3.59 73.5 9.16 82.7 5.41 243 

STTD 28-Jan-00 2.87 76.2 14.7 90.9 4.62 273 

STTD 14-Feb-00 1.63 58.6 12.08 70.7 4.08 205 

STTD 16-Feb-00 0.53 22.1 4.43 26.5 1.88 271 

STTD 25-Feb-00 0.17 15.6 0.89 16.5 1.25 352 

STTD 28-Feb-00 0.17 12.5 0.9 13.4 0.99 321 

STTD 6-Mar-00 0.15 10.5 0.77 11.3 0.84 327 

STTD 20-Mar-00 0.2 6.8 2.03 8.8 1.22 221 

STTD 22-Mar-00 0.35 16.1 2.8 18.9 1.36 200 

STTD 23-Mar-00 0.4 19.3 2.19 21.5 1.6 206 

STTD 24-Mar-00 0.61 20.7 5.49 26.2 1.62 194 

STTD 27-Mar-00 0.81 25.2 6.26 31.4 1.64 188 

STTD 31-Mar-00 1.3 36.6 11.63 48.3 2.05 161 

STTD 10-Apr-00 3.18 101.4 6.15 107.5 5.03 203 

STTD 17-Apr-00 4.62 136 6.85 143 7.52 256 

STTD 24-Apr-00 1.67 45 4.63 49.6 2.27 188 

STTD 1-May-00 3.27 84.1 11.29 95.4 4.98 222 

STTD 8-May-00 5.31 154 9.4 163 8.46 227 

STTD 15-May-00 2.05 95.1 2.5 97.6 4.45 142 

STTD 22-May-00 2.24 94.8 5.82 100.6 5.26 128 

Toe Drain at I-80 (TD80) 

TD80 26-Jan-00 2.13 71.5 23.2 94.7 4.72 264 

TD80 16-Feb-00 0.46 19.7 3.62 23.3 1.54 255 

TD80 28-Feb-00 0.26 15.2 1 16.2 1.19 308 

TD80 7-Mar-00 0.2 12.8 0.66 13.4 0.97 309 

TD80 17-Mar-00 0.27 14.7 0.45 15.1 1.08 304 

TD80 23-Mar-00 0.72 33.8 2.65 36.4 1.69 186 

TD80 28-Mar-00 0.84 37 4.04 41 1.15 159 

TD80 3-Apr-00 1.6 68.2 11.29 79.5 3.44 188 

TD80 17-Apr-00 2.95 82.5 10.31 92.8 6.17 290 

TD80 21-May-00 2.68 71.4 15.5 86.9 7.6 174 

54
Table 3 continued. 

Station ID Date NO2 N+N NH4 DIN DRP DiSi

Toe Drain at I-5 (TD5) 

TD5 17-Jan-00 1.21 363 7.83 370.8 29.2 270 

TD5 26-Jan-00 2.28 77.1 16 93.1 4.17 276 

TD5 16-Feb-00 0.26 19.3 2.11 21.4 1.13 287 

TD5 28-Feb-00 0.12 11.5 0.45 12 0.86 342 

TD5 7-Mar-00 0.16 15.5 0.79 16.3 1.03 337 

TD5 17-Mar-00 0.46 21.2 1.53 22.7 1.63 293 

TD5 23-Mar-00 1.05 45.1 4.7 49.8 1.94 192 

TD5 28-Mar-00 1.1 46.6 3.39 50 1.05 144 

TD5 3-Apr-00 1.5 79.2 3.51 82.7 2.78 171 

TD5 17-Apr-00 2.26 268 2.31 270 5.99 202 

TD5 21-May-00 1.76 224 2.16 226 9.59 218 

Ridge Cut Canal West Side at Road 16 (RCW16) 

RCW16 17-Jan-00 3.37 85.9 5.15 91.1 1.4 323 

RCW16 26-Jan-00 2.57 81.7 14.5 96.2 4.31 275 

RCW16 16-Feb-00 1.95 55.3 11.83 67.1 3.75 212 

RCW16 7-Mar-00 1.24 45.4 4.57 50 2.88 227 

Ridge Cut Canal East Side at Road 16 (RCE16) 

RCE16 26-Jan-00 2.59 81.2 14.1 95.3 3.91 277 

RCE16 16-Feb-00 2.03 56.9 11.76 68.7 3.55 215 

RCE16 20-Feb-00 1.37 34.1 7.98 42.1 2.77 274 

RCE16 28-Feb-00 1.52 44.7 6.3 51 3.59 255 

RCE16 7-Mar-00 1.19 46.7 4.7 51.4 2.76 225 

RCE-16 17-Mar-00 1.23 43.6 5.46 49 2.9 224 

RCE-16 23-Mar-00 1.35 50.4 6.91 57.3 2.18 210 

RCE-16 28-Mar-00 1.66 58.9 7.73 66.7 2.02 166 

RCE-16 3-Apr-00 2.27 65.5 14.27 79.8 2.93 176 

RCE-16 17-Apr-00 4.41 94.5 8.95 103.5 2.37 245 

Colusa Basin Drain at Road 99E (CBD99E) 

CBD99E 20-Feb-00 1.33 32.4 8.14 40.6 2.58 273 

CBD99E 28-Feb-00 1.52 40.6 6.52 47.1 3.52 254 

CBD99E 21-May-00 1.18 21.8 6.07 27.9 2.28 209 

55
Table 3 continued. 

Station ID Date NO2 N+N NH4 DIN DRP DiSi

Cache Creek at Road 113 (CC113) 

CC113 17-Jan-00 1.52 309 0.55 309.6 0.05 143 

CC113 26-Jan-00 0.81 79.8 4.86 84.7 0.13 240 

CC113 16-Feb-00 0.28 28.4 2.7 31.1 0.66 230 

CC113 28-Feb-00 0.16 12.7 0.71 13.4 0.59 216 

CC113 7-Mar-00 0.18 14.3 0.71 15 0.4 201 

CC113 17-Mar-00 0.15 30.3 0.24 30.5 0.12 150 

CC113 23-Mar-00 0.19 58.4 0.12 58.6 0.08 174 

CC113 28-Mar-00 0.22 62.2 0.22 62.4 0.08 127 

CC113 3-Apr-00 1.31 335 1.89 337 0.08 183 

CC113 17-Apr-00 0.81 119 0.34 119 0.18 163 

CC113 21-May-00 2.6 375 4.22 379 0.13 199 

Willow Slough at Road 102 (WS102) 

WS102 26-Jan-00 6.06 380 11.8 391.8 4.94 170 

WS102 16-Feb-00 1.56 96 7.65 103.7 3.58 209 

WS102 28-Feb-00 1.18 103.7 3.95 107.6 3.29 219 

WS102 7-Mar-00 1.46 126.3 5.09 131.4 2.67 225 

WS102 17-Mar-00 0.27 52.8 0.16 53 0.07 32 

WS102 23-Mar-00 3.28 304 0.43 304 0.08 36 

WS102 28-Mar-00 10.86 458 0.4 458 1.29 265 

WS102 3-Apr-00 1.04 74.1 2.8 76.9 0.68 136 

WS102 17-Apr-00 5.72 109 21.63 130.6 4.6 174 

WS102 21-May-00 5.15 211 2.75 214 1.57 158 

Putah Creek at Old Davis Road (PCD) 

PCD 17-Jan-00 1.02 183 2.36 185.4 0.76 251 

PCD 26-Jan-00 1.05 133 7.24 140.2 1.93 254 

PCD 16-Feb-00 0.77 84 21.98 105.9 5.97 244 

PCD 28-Feb-00 0.22 51.3 2.5 53.8 2.95 268 

PCD rerun 28-Feb-00 0.22 51 2.32 53.3 2.92 266 

PCD 7-Mar-00 0.3 18.6 2.4 21 1.66 273 

PCD rerun 7-Mar-00 0.3 18.4 2.46 20.9 1.63 272 

PCD 17-Mar-00 0.06 14.3 0.34 14.6 1.21 270 

PCD 23-Mar-00 0.29 12.2 0.38 12.6 1.01 245 

PCD 28-Mar-00 0.08 14.8 0.18 15 0.2 250 

PCD 3-Apr-00 0.36 87 0.71 87.7 5.24 268 

PCD 17-Apr-00 1.18 248 3.13 251 9.92 295 

PCD 21-May-00 1.35 201 2.5 204 5 303 

56
Table 3 continued. 

Station ID Date NO2 N+N NH4 DIN DRP DiSi

Boat Samples from Yolo Bypass: Band A = East Side; Band D = 

West Side 

BAND A 17-Feb-00 0.28 15.2 2.56 17.8 1.27 281 

BAND B 17-Feb-00 0.22 15.8 3.12 18.9 1.15 268 

BAND B 17-Feb-00 0.21 15.3 2.64 17.9 1.16 270 

BAND C 17-Feb-00 0.25 15.6 3.1 18.7 1.46 279 

BAND D 17-Feb-00 0.55 24.8 4.6 29.4 2 269 

BAND D 17-Feb-00 0.55 25.1 4.55 29.7 1.96 268 

BAND A 18-Feb-00 0.23 13.2 2.49 15.7 1.11 274 

BAND B 18-Feb-00 0.15 11.5 0.72 12.2 0.92 272 

BAND C 18-Feb-00 0.2 11.7 1.05 12.7 1.2 267 

BAND D 18-Feb-00 1.59 39.7 5.75 45.4 3.17 220 

BAND B 19-Feb-00 0.12 11.6 1.57 13.1 0.83 302 

BAND C 19-Feb-00 0.17 10.6 2.16 12.8 1.06 283 

BAND D 19-Feb-00 0.98 27.4 5.99 33.4 2.2 246 

BAND A 20-Feb-00 0.15 12.2 1.27 13.5 0.93 308 

BAND B 20-Feb-00 0.11 10.4 0.97 11.4 0.82 329 

BAND C 20-Feb-00 0.16 9.3 1.26 10.5 1 316 

BAND D 20-Feb-00 1.15 27 5.71 32.7 2.42 256 

Boat Samples from Southern Outlet of Yolo Bypass 

PS-1 23-Mar-00 0.35 17.7 1.68 19.4 1.46 194 

PS-2 23-Mar-00 0.31 15.1 1.72 16.9 1.32 204 

PS-3 23-Mar-00 0.35 17.6 1.76 19.4 1.52 208 

PS-1 11-Apr-00 0.8 30 6.23 36.2 1.89 236 

PS-2 11-Apr-00 0.75 27.6 6.49 34.1 1.81 228 

LH-1 11-Apr-00 1.16 50.9 4.18 55.1 2.91 212 

YB-1 11-Apr-00 0.58 18.8 9.29 28.1 1.42 242 

57
Table 4. Dissolved organic carbon (DOC mg/L), specific 

ultraviolet absorbance of the DOC (SUVA), suspended particulate 

matter (SPM mg/L), particulate matter (SPM), particulate carbon 

(PC mg/L) and particulate nitrogen (PN mg/L). 

Site Date DOC SUVA SPM PC PN

Fremont Weir (FRW) 

FRW 3/7/2000 2.9 0.079 145 

FRW 3/17/2000 1.3 68 0.82 0.09 

Lower Bypass (STTD) 

STTD 1/26/2000 6.8 0.026 235 5.15 0.72 

STTD 1/28/2000 7.9 0.03 123 4.95 0.69 

STTD 2/14/2000 7.1 0.033 167 3.64 0.59 

STTD 2/16/2000 4.4 0.104 173 2.55 0.36 

STTD 2/28/2000 2.6 0.072 55 1.08 0.11 

STTD 3/6/2000 1.8 0.061 36 

STTD 3/20/2000 4.4 0.026 489 9.58 1.37 

STTD 3/22/2000 4.7 0.027 114 1.94 0.32 

STTD 3/23/2000 4.8 0.026 147 2.81 0.47 

STTD 3/24/2000 4.6 0.026 124 3.12 0.55 

STTD 3/31/2000 3.9 0.025 49 1.23 0.17 

STTD 4/10/2000 5 0.025 36 1.6 0.32 

STTD 4/17/2000 3.9 0.026 63 2.3 0.46 

STTD 4/24/2000 4.1 0.029 76 1.7 0.29 

STTD 5/1/2000 4.5 0.027 68 1.55 0.29 

STTD 5/8/2000 3.9 0.026 65 1.45 0.28 

STTD 5/15/2000 5.2 0.024 68 2.7 0.58 

STTD 5/22/2000 5.1 0.026 83 2.67 0.58 

Toe Drain at I-80 (TD80) 

TD80 1/26/2000 6.9 0.027 232 4.22 0.55 

TD80 2/16/2000 4.7 0.06 62 1.24 0.17 

TD80 2/28/2000 2.8 0.064 42 1.08 0.1 

TD80 3/7/2000 2 0.057 26 

TD80 3/17/2000 2.4 0.034 56 0.89 0.14 

TD80 3/23/2000 4.9 0.025 92 1.8 0.28 

TD80 3/28/2000 4.1 0.024 77 1.79 0.34 

TD80 4/3/2000 5.1 0.026 103 2.2 0.37 

TD80 4/17/2000 3.9 0.026 139 2.79 0.5 

TD80 5/21/2000 5.9 0.025 116 3.84 0.71 

58
Table 4 continued. 

Site Date DOC SUVA SPM PC PN

Toe Drain at I-5 (TD5) 

TD5 1/26/2000 7.8 0.031 363 3.97 0.59 

TD5 2/16/2000 3.8 0.075 107 1.97 0.29 

TD5 2/28/2000 2 0.059 49 1.14 0.14 

TD5 3/7/2000 2 0.061 60 

TD5 3/17/2000 3.5 0.032 131 2.27 0.33 

TD5 3/23/2000 5.4 0.026 78 1.56 0.26 

TD5 3/28/2000 4.5 0.024 68 1.59 0.34 

TD5 4/3/2000 5.8 0.026 94 2.48 0.5 

TD5 4/17/2000 2.2 0.024 80 1.61 0.28 

TD5 5/21/2000 4.4 0.023 46 2.51 0.52 

Ridge Cut Canal at road 16 (RCE16) 

RCE16 1/26/2000 8.3 0.029 135 3.04 0.42 

RCE16 2/16/2000 8.3 0.071 88 3.1 0.46 

RCE16 2/28/2000 7.9 0.041 78 1.48 0.19 

RCE16 3/7/2000 8.1 0.044 103 

RCE16 3/17/2000 7.4 0.027 87 2.1 0.29 

RCE16 3/23/2000 5.9 0.026 99 2.04 0.3 

RCE16 3/28/2000 5.3 0.025 102 2.05 0.4 

RCE16 4/3/2000 6.5 0.026 110 2.1 0.34 

RCE16 4/17/2000 4.2 0.024 54 1.95 0.42 

Colusa Basin Drain at road 99E (CBD99E) 

CBD99E 2/28/2000 7.9 0.051 79 1.41 0.17 

CBD99E 5/21/2000 6.1 0.024 67 1.96 0.36 

Cache Creek at road 113 (CC113) 

CC113 1/26/2000 5 0.031 151 3.31 0.48 

CC113 2/16/2000 4.1 0.049 271 3.04 0.39 

CC113 2/28/2000 3.5 0.05 401 3.99 0.44 

CC113 3/7/2000 2.8 0.04 382 

CC113 3/17/2000 2.3 0.02 87 1.35 0.14 

CC113 3/23/2000 2 0.02 38 0.59 0.07 

CC113 3/28/2000 2.3 0.02 15 0.52 0.1 

CC113 4/3/2000 1.3 0.023 25 0.49 0.08 

CC113 4/17/2000 1.7 0.023 32 0.73 0.12 

CC113 5/21/2000 1.8 0.02 28 0.7 0.12 

59
Table 4 continued. 

Site Date DOC SUVA SPM PC PN

Willow Slough at road 102 (WS102) 

WS102 2/16/2000 7.8 0.071 186 3.58 0.51 

WS102 2/28/2000 8.9 0.053 187 1.69 0.21 

WS102 3/7/2000 7.6 0.048 193 

WS102 3/17/2000 2.3 0.04 96 1.67 0.28 

WS102 3/23/2000 2.3 0.023 22 0.96 0.16 

WS102 3/28/2000 1.9 0.023 39 4.3 0.78 

WS102 4/3/2000 3 0.023 83 1.45 0.27 

WS102 4/17/2000 3.8 0.034 193 2.79 0.46 

WS102 5/21/2000 4.1 0.024 52 1.32 0.25 

Putah Creek at Old Davis Road (PCD) 

PCD 2/16/2000 6.4 0.058 135 1.91 0.26 

PCD 2/28/2000 4.1 0.037 105 1.84 0.21 

PCD 3/7/2000 3 0.032 57 

PCD 3/17/2000 2.4 0.021 18 0.46 0.07 

PCD 3/23/2000 2.5 0.02 15 0.42 0.05 

PCD 3/28/2000 2.5 0.02 10 0.25 0.04 

PCD 4/3/2000 2.7 0.02 17 0.39 0.06 

PCD 4/17/2000 2.8 0.023 21 0.84 0.15 

PCD 5/21/2000 2.4 0.021 15 0.47 0.07 

Boat Samples from Yolo Bypass: Band A = East Side; Band D = 

West Side 

BAND A 2/17/2000 47 

BAND B 2/17/2000 102 

BAND C 2/17/2000 3.9 0.07 74 1.26 0.14 

BAND D 2/17/2000 4.8 0.084 73 1.37 0.18 

BAND A 2/18/2000 78 

BAND B 2/18/2000 104 

BAND C 2/18/2000 82 

BAND B 2/19/2000 57 

BAND C 2/19/2000 58 

BAND D 2/19/2000 72 

BAND A 2/20/2000 2.5 0.076 47 0.74 0.1 

BAND B 2/20/2000 2.2 0.064 37 0.54 0.07 

BAND C 2/20/2000 2.6 0.072 33 0.59 0.06 

BAND D 2/20/2000 7 0.051 47 1.26 0.17 

60
Table 4 continued. 

Site Date DOC SUVA SPM PC PN

Boat Samples from stations near the southern outlet of the Yolo 

Bypass 

PS = Prospect Slough; LH = Little Holland Tract; YB = Yolo 

Bypass 

PS 1 3/23/2000 130 

PS 2 3/23/2000 98 

PS 3 3/23/2000 77 

PS 1 4/11/2000 79 

PS 2 4/11/2000 84 

LH 1 4/11/2000 98 

YB 1 4/11/2000 40 

61
Table 5. Analytical results for selected metals by ICP-OES (see 

text). Concentrations in mg/L. 

SITE & DATE 

month/day B Ba Ca K Mg Na S Sr

Fremont Weir (FRW) 

FRW3/7 0.04 0.02 10 1.3 5 6 9.4 0.06 

FRW3/17 0.04 0.02 13 1.2 6 7 10.6 0.09 

Lower Bypass (STTD) 

STTD 1/26 0.53 0.09 39 3.9 34 95 8.1 0.51 

STTD 1/28 0.46 0.08 35 5 30 83 8.5 0.46 

STTD 1/31 0.37 0.08 36 4.8 33 94 9.2 0.48 

STTD 2/2 0.43 0.09 38 4.1 33 84 8.9 0.5 

STTD 2/3 0.62 0.09 37 3.9 32 85 8.3 0.49 

STTD 2/7 0.58 0.09 39 4 34 86 9.1 0.5 

STTD 2/9 0.66 0.1 41 4 36 93 8.9 0.53 

STTD 2/11 0.61 0.1 40 4 36 91 8.8 0.52 

STTD 2/14 0.43 0.07 28 3.5 21 58 6.4 0.34 

STTD 2/16 0.11 0.03 13 2.1 9 13 8.5 0.12 

STTD 2/25 0.07 0.02 13 1.5 7 10 10.8 0.1 

STTD 2/28 0.05 0.02 12 1.4 6 8 9.8 0.09 

STTD 3/6 0.04 0.02 12 1.3 6 8 10.2 0.09 

STTD 3/20 0.42 0.06 28 2.4 20 34 7 0.3 

STTD 3/22 0.5 0.07 32 2.5 29 46 6.5 0.35 

STTD 3/23 0.5 0.08 33 2.5 31 50 6.3 0.37 

STTD 3/24 0.51 0.08 33 2.6 31 49 6.1 0.36 

STTD 3/27 0.6 0.08 33 2.6 33 49 6 0.37 

STTD 3/31 0.68 0.09 34 2.5 35 56 4.8 0.41 

STTD 4/10 0.6 0.11 43 3.1 40 86 6.2 0.54 

STTD 4/17 1.46 0.13 47 3.5 49 87 7.7 0.55 

STTD 4/24 0.6 0.07 28 2.5 23 40 5.8 0.33 

STTD 5/1 0.85 0.1 35 2.9 33 62 6.8 0.42 

STTD 5/8 1.22 0.11 40 3.5 40 71 6.8 0.49 

STTD 5/15 1.09 0.09 32 3.3 33 53 4.2 0.38 

STTD 5/22 1.17 0.09 34 3.4 34 56 4.1 0.4 

62
Table 5 continued. 

SITE & DATE 

month/day B Ba Ca K Mg Na S Sr

Toe Drain at I-80 (TD80) 

TD80 1/26 0.48 0.08 39 4 30 98 8.1 0.54 

TD80 2/16 0.03 0.02 11 2.3 8 12 8.4 0.09 

TD80 2/28 0.03 0.02 12 1.5 7 10 9.5 0.09 

TD80 3/7 0.03 0.02 11 1.7 8 11 10.4 0.09 

TD80 3/17 0.11 0.03 17 1.9 13 18 10 0.16 

TD80 3/23 0.63 0.09 38 3.1 35 90 6.1 0.48 

TD80 3/28 0.93 0.09 38 3 39 76 5.3 0.48 

TD80 4/3 0.8 0.1 44 3.5 43 114 6.3 0.54 

TD80 4/17 1.47 0.09 41 3.3 52 98 8.8 0.48 

TD80 5/21 1.06 0.09 34 3.7 32 69 5.4 0.41 

Toe Drain at I-5 (TD5) 

TD5 1/26 0.23 0.08 38 4.7 31 108 8.9 0.52 

TD5 2/16 -0.01 0.02 9 1.6 6 9 9.4 0.08 

TD5 2/28 -0.01 0.02 11 1.5 7 8 11 0.09 

TD5 3/7 -0.01 0.02 12 1.5 7 10 11.1 0.09 

TD5 3/17 0.08 0.04 22 1.9 15 20 9.3 0.23 

TD5 3/23 0.44 0.08 40 2.7 31 80 5.9 0.5 

TD5 3/28 0.72 0.09 40 3.1 39 90 4.8 0.52 

TD5 4/3 0.54 0.1 45 2.9 36 106 5.6 0.57 

TD5 4/17 1.8 0.14 49 3.9 49 81 6.7 0.55 

TD5 5/21 1.16 0.11 41 4 34 79 6.6 0.49 

Ridge Cut Canal West Side at Road 16 (RCW16) 

RCW 1/26 0.2 0.08 36 5.1 30 105 10.4 0.49 

RCW 2/16 0.11 0.06 22 4 15 44 6.6 0.28 

RCW 3/7 0.12 0.06 29 3.2 21 68 7.4 0.38 

Ridge Cut Canal East Side at Road 16 (RCE16) 

RCE16 1/26 0.18 0.08 32 5 27 100 9.1 0.47 

RCE16 2/16 0.1 0.05 22 4 15 46 6.5 0.28 

RCE16 2/20 0.12 0.07 29 3.9 22 65 8.4 0.4 

RCE16 2/28 0.14 0.07 31 4 24 75 8.2 0.41 

RCE16 3/7 0.13 0.06 29 3 22 68 7.3 0.39 

RCE16 3/17 0.28 0.09 44 3.6 34 106 7.8 0.53 

RCE16 3/23 0.25 0.08 41 3 33 105 6.8 0.55 

RCE16 3/28 0.33 0.1 48 3.3 41 133 5.7 0.62 

RCE16 4/3 0.28 0.09 40 2.9 30 106 5.6 0.58 

RCE16 4/17 1.1 0.11 55 3.6 44 84 7.6 0.67 

63
Table 5 continued. 

SITE & DATE 

month/day B Ba Ca K Mg Na S Sr

Colusa Basin Drain at Road 99E (CBD99E) 

CBD99E 2/20 0.2 0.07 30 4 22 70 8.4 0.4 

CBD99E 2/28 0.2 0.08 32 3.6 22 69 7.8 0.41 

CBD99E 5/21 0.21 0.07 26 2.1 18 58 6.3 0.33 

Cache Creek at Road 113 (CC113) 

CC113 1/26 1.86 0.11 32 3.6 42 68 7.7 0.45 

CC113 2/16 0.65 0.06 21 1.9 22 18 7.1 0.27 

CC113 2/28 0.44 0.04 19 1.6 22 16 7 0.24 

CC113 3/7 0.56 0.05 21 1.6 22 16 6 0.26 

CC113 3/17 0.89 0.07 26 2 25 18 4.8 0.31 

CC113 3/23 1.13 0.09 33 2.4 33 37 5.6 0.41 

CC113 3/28 1.26 0.1 34 2.6 35 40 4.1 0.41 

CC113 4/3 1.83 0.15 51 3 46 56 5.8 0.55 

CC113 4/17 1.08 0.1 32 2.2 30 36 5.2 0.38 

CC113 5/21 1.89 0.16 53 3.1 43 54 6 0.56 

Willow Slough at Road 102 (WS102) 

WS102 1/26 0.99 0.1 29 6.4 24 43 6.4 0.34 

WS102 2/16 0.68 0.07 18 4.5 14 17 8.1 0.2 

WS102 2/28 0.69 0.08 26 3.8 18 35 6.7 0.29 

WS102 3/7 0.68 0.08 27 3.4 18 33 6.9 0.29 

WS102 3/17 1.75 0.16 57 3.1 44 85 6 0.62 

WS102 3/23 2.09 0.12 42 2.6 49 95 1 0.58 

WS102 3/28 2 0.13 37 2 86 130 8.6 0.6 

WS102 4/3 1.41 0.11 40 2.9 39 52 4.1 0.46 

WS102 4/17 0.88 0.08 27 3 24 23 5.2 0.32 

WS102 5/21 1.15 0.1 32 3.3 32 39 4.8 0.4 

Putah Creek at Old Davis Road (PCD) 

PCD 2/16 0.18 0.05 20 3 19 18 8.1 0.22 

PCD 2/28 0.21 0.06 27 2.5 24 19 8.5 0.27 

PCD 3/7 0.13 0.05 21 1.8 26 14 8.9 0.19 

PCD 3/17 0.11 0.05 19 1.6 30 14 8.7 0.18 

PCD 3/23 0.12 0.05 19 1.7 28 13 8.4 0.17 

PCD 3/28 0.11 0.05 20 1.5 31 13 8 0.19 

PCD 4/3 0.19 0.06 22 2.2 35 27 9 0.24 

PCD 4/17 0.35 0.09 30 3.3 42 38 9.4 0.39 

PCD 5/21 0.38 0.1 32 1.9 44 32 9.4 0.43 

64
Table 5 continued. 

SITE & DATE 

month/day B Ba Ca K Mg Na S Sr

Boat Samples from Yolo Bypass: Band A = East Side; Band D = 

West Side 

BANDD 2/17 0.12 0.03 13 2.3 9 13 8.2 0.14 

BANDC 2/17 0.06 0.02 9 1.5 5 7 8.6 0.07 

BANDB 2/17 0.04 0.02 9 1.4 5 6 8.2 0.07 

BANDA 2/17 0.04 0.02 10 1.6 6 7 9 0.08 

BANDB 2/18 0.04 0.02 10 1.4 5 6 8.2 0.07 

BANDC 2/18 0.04 0.02 9 1.4 5 6 8.1 0.07 

BANDD 2/18 0.16 0.06 20 3.5 13 34 8.8 0.22 

BANDB 2/19 0.04 0.02 11 1.4 6 7 9.6 0.09 

BANDC 2/19 0.04 0.02 11 1.4 6 6 8.8 0.09 

BANDD 2/19 0.12 0.04 17 2.8 11 16 7.5 0.18 

BANDA 2/20 0.05 0.02 12 1.5 6 8 9.6 0.1 

BANDB 2/20 0.05 0.02 12 1.4 6 7 10.1 0.09 

BANDC 2/20 0.06 0.02 12 1.5 6 8 9.6 0.09 

BANDD 2/20 0.13 0.06 21 3.5 14 32 8.1 0.24 

Boat Samples from Southern Outlet of Yolo Bypass 

PS1 3/23 0.5 0.07 33 2.6 30 47 6.3 0.36 

PS2 3/23 0.5 0.07 32 2.6 28 47 6.4 0.34 

PS3 3/23 0.52 0.07 32 2.7 29 51 6.6 0.35 

PS1 4/11 0.22 0.04 21 1.8 15 20 7.3 0.2 

PS2 4/11 0.21 0.04 19 1.9 16 19 7.8 0.18 

LH1 4/11 0.42 0.06 28 2.8 26 53 7.1 0.32 

YB1 4/11 0.11 0.03 15 1.4 10 12 7.6 0.12 

65