Concentrations and Loads of Suspended Sediment 

and Nutrients in Surface Water of the Yakima River 

Basin, Washington, 1999-2000 – With an Analysis of 

Trends in Concentrations

By James C. Ebbert, Sandra S. Embrey, and Janet A. Kelley

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

Portland, Oregon

2003

Water-Resources Investigations Report 03-4026

U.S. GEOLOGICAL SURVEY
For additional information write to:

District Chief

U.S. Geological Survey

10615 S.E. Cherry Blossom Drive

Portland, Oregon 97216-3159

Email: info-or@usgs.gov

Internet: http://oregon.usgs.gov

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does 

not imply endorsement by the U.S. Government.

Copies of this report can be purchased from:

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Information Services

Building 810

Box 25286, Federal Center

Denver, CO 80225-0286

U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director
Foreword iii

National Water-Quality Assessment Program

In 1991, the U.S. Congress began to appropriate funds to the USGS to conduct the National Water-Quality 

Assessment (NAWQA) Program. Since that time, NAWQA has evaluated the quality of streams, ground water, 

and aquatic ecosystems in more than 50 major river basins and aquifer systems across the Nation, referred to as 

"Study Units." As indicated on the map, timing of the assessments varies within the Program's rotational design: 

about one-third of all Study Units are intensively investigated for 3 to 4 years, which is followed by 6 to 7 years of 

low-level monitoring. 

1991–95

1994–98

1997–2001

Not yet scheduled

High Plains Regional

Ground Water Study, 

1999-2004

NAWQA Study Units— 

Assessment schedule

Yakima River Basin

1999–2001

In 2001, the NAWQA Program entered its second decade of investigations and an intensive reassessment of 

water conditions was begun to determine trends, based on 10 years of comparable monitoring data collected at 

selected streams and ground-water sites. The next 10 years of study also will fill critical gaps in characterizing 

water-quality conditions, and increase understanding of processes that control water-quality conditions, which will 

better establish critical links among sources of contaminants, their transport through the hydrologic system, and the 

potential effects of contaminants on ecological health and on the quality of drinking water.

The Yakima River Basin assessment is one of two special studies activated in 1999 for the purpose of piloting 

study techniques for use in NAWQA's second decade of investigations. Specifically, the Yakima River Basin 

assessment piloted techniques to (1) monitor trends in surface water, (2) evaluate transport of agricultural 

chemicals to streams, and (3) assess the possible effects of agricultural chemicals from irrigated farmland on stream 

ecosystems. The Yakima River Basin assessment builds upon monitoring data that the NAWQA Program collected 

previously in the basin from 1987 through 1991, as part of pilot studies conducted before full Program 

implementation in 1991. These data provided a baseline characterization of pesticides, nutrients, trace elements, 

suspended solids, and aquatic life in streams. 
iv Foreword

What kind of water-quality information does the NAWQA Program provide?

The NAWQA Program assesses the quality of the Nation's water resources, which is integrally linked to the 

long-term availability of water that is clean and safe for drinking and recreation and also suitable for industry, 

irrigation, and habitat for fish and wildlife. Assessments in the major river basins and aquifer systems include water 

resources available to more than 60 percent of the population and cover about one-half of the land area of the 

conterminous United States. Scientists in the NAWQA Program work with partners in government, research, and 

public-interest groups to assess the spatial extent of water-quality conditions, the way water quality changes with 

time, and the effects of human activities and natural factors on water quality. This information is useful for guiding 

water-management and protection strategies, research, and monitoring in different hydrologic and land-use settings 

across the Nation.

Water-quality assessments by a single program cannot possibly address all of the Nation's water-resources 

needs and issues. Therefore, it is necessary to define the most pertinent context for NAWQA information. 

• Total resource assessment—NAWQA assessments are long-term and interdisciplinary, and include 

information on water chemistry, hydrology, land use, stream habitat, and aquatic life. Assessments are not 

limited to a specific geographic area or water-resource problem at a specific time. Therefore, the findings 

describe the general health of the total water resource, as well as emerging water issues, thereby helping 

managers and decision makers to set priorities.

• Source-water characterization—Assessments focus on the quality of the available, untreated resource 

and thereby complement (rather than duplicate) Federal, State, and local programs that monitor drinking 

water. Findings are compared to drinking-water standards and health advisories, if available, as a way to 

characterize the resource. 

• Compounds studied—Assessments focus on chemical compounds that have well-established methods 

of investigation. It is not financially or technically feasible to assess all the contaminants in our Nation's 

waters. In general, the NAWQA Program investigates those pesticides, nutrients, volatile organic 

compounds, and metals that have been or are currently used commonly in agricultural and urban areas 

across the Nation. A complete list of compounds studied is on the NAWQA Web site at 

http://water.usgs.gov/nawqa.

• Detection versus risk—Compounds are measured at very low concentrations, often 10 to 100 times 

lower than Federal or State standards and health advisories. Detection of compounds, therefore, does not 

necessarily translate to risks to human health or aquatic life. However, these analyses are useful for 

identifying and evaluating emerging issues, such as the presence of new contaminants or the occurrence 

of mixtures, as well as for tracking contaminant levels over time.

• Consistent approach—Assessments are guided by a nationally consistent study design and uniform 

methods of sampling and analysis. Findings thereby pertain not only to water quality of a particular 

stream or aquifer, but also contribute to the larger picture of how and why water quality varies regionally 

and nationally. This consistent approach helps to determine if a water-quality issue is isolated or 

pervasive. It also allows direct comparisons of how human activities and natural processes affect water 

quality in the Nation's diverse environmental settings. 
Foreword v

Introduction to this report

This report contains the major findings of a 1999-2001 assessment of water quality in streams in the Yakima 

River Basin. It is one of a series of reports by the NAWQA Program that present major findings on water resources 

in 51 major river basins and aquifer systems across the Nation. 

In these reports, water quality is assessed at many scales-from large rivers that drain many land uses to small 

agricultural catchments, and is discussed in terms of local, State, and regional issues. Conditions in the Yakima 

River Basin are compared to conditions found elsewhere and to selected national benchmarks, such as those for 

drinking-water quality and the protection of aquatic organisms. 

This report is intended for individuals working with water-resource issues in Federal, State, or local agencies, 

universities, public interest groups, or the private sector. The information will be useful in addressing a number of 

current issues, such as source-water protection, pesticide registration, human health, drinking water, hypoxia and 

excessive growth of algae and plants, the effects of agricultural land use on water quality, and monitoring and 

sampling strategies. This report is also for individuals who wish to know more about the quality of water resources 

in areas near where they live, and how that water quality compares to other areas across the Nation.

Other products describing water-quality conditions in the Yakima River Basin are available. Detailed 

technical information, data and analyses, methodology, models, graphs, and maps that support the findings 

presented in this report can be accessed from http://oregon.usgs.gov/yakima. Other reports in this series and data 

collected from other basins can be accessed from the national NAWQA Web site (http://water.usgs.gov/nawqa). 

.

USGS hydrologists collect samples from a cableway 

across the Yakima River at Kiona
vi Contents

CONTENTS

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

Introduction .......................................................................................................................................................... 3

Purpose and Scope ...................................................................................................................................... 4

Availability of Data Used in This Report ................................................................................................... 4

Acknowledgments....................................................................................................................................... 4

Description of Basin............................................................................................................................................. 5

Land Use and Water Quality....................................................................................................................... 7

Use of Agricultural Best Management Practices ........................................................................................ 9

Methods................................................................................................................................................................ 15

Sample Collection, Field Procedures, and Sample Preparation.................................................................. 15

Field Measurements .................................................................................................................................... 18

Laboratory Procedures ................................................................................................................................ 18

Quality Assurance ....................................................................................................................................... 18

Methods Used to Compute Concentrations and Estimate Loads................................................................ 19

Methods Used to Test for Trends................................................................................................................ 20

Sources of Streamflow and Precipitation Data ........................................................................................... 22

Concentrations and Loads .................................................................................................................................... 23

Results of Basinwide Sampling, August 1999 and July 1988 .................................................................... 27

Loads During 1999–2000 Water Years and Comparisons With Historical Load Estimates ...................... 34

Effect of Calibration Period on Load Computations................................................................................... 39

Trends in Concentrations ..................................................................................................................................... 44

Wilson Creek............................................................................................................................................... 47

Cherry Creek ............................................................................................................................................... 49

Wide Hollow Creek..................................................................................................................................... 50

Moxee Drain................................................................................................................................................ 52

Granger Drain.............................................................................................................................................. 54

Sulphur Creek Wasteway............................................................................................................................ 59

Spring and Snipes Creeks............................................................................................................................ 61

Yakima River at Kiona................................................................................................................................ 66

Summary and Conclusions................................................................................................................................... 69

References Cited .................................................................................................................................................. 72
Contents vii

Appendix A.—Evaluation of quality-control data ............................................................................................... 75

U.S. Geological Survey Data ...................................................................................................................... 75

Table A1. Concentration and precision data for nutrients and suspended sediment in 

replicate surface-water samples, Yakima River Basin, Washington, 1999–2000 ........ 76

Table A2. Concentrations of nutrients and suspended sediment in field blank samples, 

Yakima River Basin, Washington, 1999–2000............................................................. 77

Table A3. Summary of recoveries for laboratory-reagent-spike nutrient analyses for the period 

October 1999 through September 2000 ........................................................................ 77

Roza-Sunnyside Board of Joint Control Data............................................................................................. 75

Table A4. Summary of quality-control data for samples collected by the Water-Quality 

Monitoring Program of the Roza-Sunnyside Board of Joint Control, Yakima 

River Basin, 1997–2000................................................................................................ 79

Bureau of Reclamation Data ....................................................................................................................... 78

Washington State Department of Ecology Data ......................................................................................... 78

Appendix B.—Regression Models Used to Estimate Loads................................................................................ 80

Figure B1. Graphs showing predicted and measured daily loads of suspended sediment and 

nutrients for 1999-2000 water years at Moxee and Granger Drains, Yakima 

River Basin, Washington .............................................................................................. 81

Table B1. Suspended-sediment and nutrient loads transported during calendar year 1999, 

standard deviations, differences between measured and predicted loads, regression 

equations for load estimates, and concentration summary statistics at Moxee Drain, 

Yakima River Basin, Washington................................................................................. 83

Table B2. Suspended-sediment and nutrient loads transported during water years 1999–2000, 

standard deviations, differences between measured and predicted loads, regression 

equations for load estimates, and concentration summary statistics at Granger Drain, 

Yakima River Basin, Washington................................................................................. 84

Table B3. Factors used to assist in selecting calibration periods and regression models for 

loads of total nitrogen, ammonia-plus-organic nitrogen, nitrite-plus-nitrate nitrogen, 

and suspended sediment in the Yakima River at Kiona, Yakima River Basin, 

Washington ................................................................................................................... 86

Figure B2. Graph showing predicted and measured daily loads of total nitrogen, ammonia-plusorganic nitrogen, and nitrite-plus-nitrate nitrogen, and suspended sediment with 

different regression models and calibration periods for the Yakima River at Kiona, 

Yakima River Basin, Washington................................................................................. 87

Figure B3. Graphs showing predicted and measured daily loads of phosphorus for 1999-2000 

water years, Yakima River at Kiona, Yakima River Basin, Washington..................... 92

Table B4. Estimates of average daily loads of suspended sediment and nutrients in the 

Yakima River at Kiona, Yakima River Basin, Washington for the period 

1999–2000, water year 1999, and water year 2000 computed using discharge 

nd concentration data from different calibration periods and different regression 

equations ....................................................................................................................... 93

Table B5. Suspended-sediment and nutrient loads transported during water years 1999–2000, 

standard deviations, differences between measured and predicted loads, regression 

equations, and concentration summary statistics for load estimates at Yakima River at 

Kiona, Washington ....................................................................................................... 95

Appendix C.—Mass-Balance Computations ....................................................................................................... 96

Table C1. Mass-balance analyses for instantaneous streamflows and loads of total nitrogen and 

phosphorus in the reach of the Yakima River extending from river mile 103.7 to 

river mile 55, Yakima River Basin, Washington, August 1999 and July 1988............96
viii Figures

FIGURES

Figure 1. Map showing the Yakima River Basin, Washington......................................................................... 6

Figure 2. Graph showing streamflow in the Yakima River during irrigation, August 2-6, 1999 ..................... 7

Figure 3. Map showing land use and land cover in the Yakima River Basin, Washington, 1999.................... 8

Figure 4. Map showing conservation districts in the Yakima River Basin, Washington ................................. 13

Figure 5. Map showing status of agricultural best management practices sponsored by the 

Environmental Quality Incentives Program in subbasins of the Yakima River Basin 

through 2000 ...................................................................................................................................... 14

Figure 6. Map showing location of surface-water sites and wastewater treatment plants sampled for 

suspended sediments and nutrients in the Yakima River Basin, Washington, 1999–2000 ............... 16

Figure 7. Graphs showing daily streamflow and concentrations of suspended sediment, total and nitrite-plusnitrate nitrogen, total phosphorus and orthophosphate (as P) in samples collected from selected 

surface-water sites in the Yakima River Basin, Washington, May 1999-January 2000.................... 24

Figure 8. Graphs showing concentrations of suspended sediment, total nitrogen, and total phosphorus in 

the main stem Yakima River, selected major tributaries, and discharges from wastewater treatment 

plants, Yakima River Basin, Washington, July 26-29, 1988, and August 2-6, 1999 ........................ 31

Figure 9. Graphs showing average daily loads of suspended sediment and nutrients in the Yakima River 

at Kiona for selected water years from 1974–2001, Yakima River Basin, Washington ................... 37

Figure 10. Graphs showing monthly total suspended-sediment and nutrient loads, and daily streamflows 

in selected surface-water sites, Yakima River Basin, Washington.................................................... 41

Figure 11. Graphs showing temporal variations in streamflow and variations in concentrations of 

suspended solids and nitrate with streamflow in Wilson Creek above Cherry Creek at Thrall, 

Yakima River Basin, Washington, 1991–2000 water years .............................................................. 47

Figure 12. Graphs showing temporal variations in turbidity and concentrations of suspended solids, 

total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in Wilson Creek above 

Cherry Creek at Thrall, Yakima River Basin, Washington, 1991–2000 water years........................ 48

Figure 13. Graphs showing temporal variations in streamflow and variations in concentrations of 

suspended solids and nitrite-plus-nitrate nitrogen with streamflow in Cherry Creek at 

Southeast 1/4, Section 29, Township 17N, Range 19E, Yakima River Basin, Washington, 

1991–2000 water years ...................................................................................................................... 49

Figure 14. Graphs showing temporal variations in turbidity and concentrations of suspended solids, 

total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in Cherry Creek 

Southeast 1/4, Section 29, Township 17N, Range 19E, Yakima River Basin, Washington, 

1991–2000 water years ...................................................................................................................... 50

Figure 15. Graphs showing temporal variations in turbidity and concentrations of suspended solids, 

total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in Wide Hollow Creek at 

West Washington Avenue, Yakima River Basin, Washington, 1991–2000 water years .................. 51

Figure 16. Graphs showing temporal variations in streamflow and variations in concentrations of 

suspended solids and nitrite-plus-nitrate nitrogen with streamflow in Moxee Drain at 

Birchfield Road near Union Gap, Yakima River Basin, Washington, 1991–2000 water years........ 52

Figure 17. Graphs showing temporal variations in turbidity and concentrations of suspended solids, 

total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in Moxee Drain at 

Birchfield Road near Union Gap, Yakima River Basin, Washington, 1991–2000 water years........ 53

Figure 18. Graphs showing temporal variations in streamflow and variations in concentrations of 

suspended solids and nitrite-plus-nitrate nitrogen with streamflow in Granger Drain at 

Highway 223 near Granger, Yakima River Basin, Washington, 1991–2000 water years................. 55
Figures ix

Figure 19. Graphs showing temporal variations in turbidity and concentrations of suspended solids, 

total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in Granger Drain at 

Highway 223 near Granger, Yakima River Basin, Washington, 1991–2000 water years................. 56

Figure 20. Graphs showing temporal variations in streamflow and variations in concentrations of 

suspended solids and nitrite-plus-nitrate nitrogen with streamflow in Granger Drain at 

Granger, Yakima River Basin, Washington, 1997–2001 .................................................................. 57

Figure 21. Graphs showing temporal variations in turbidity and concentrations of suspended solids, 

total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in Granger Drain at 

Granger, Yakima River Basin, Washington, 1997–2001 .................................................................. 58

Figure 22. Graphs showing temporal variations in streamflow and variations in concentrations of 

suspended solids and nitrite-plus-nitrate nitrogen with streamflow in Sulphur Creek Wasteway 

near Sunnyside, Yakima River Basin, Washington, 1997–2001....................................................... 59

Figure 23. Graphs showing temporal variations in turbidity and concentrations of suspended solids, 

total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in Sulphur Creek Wasteway 

near Sunnyside, Yakima River Basin, Washington, 1997–2001....................................................... 60

Figure 24. Graphs showing temporal variations in streamflow and variations in concentrations of 

suspended solids and nitrite-plus-nitrate nitrogen with streamflow in selected surface-water 

sites in Yakima River Basin, Washington, 1997–2001 ..................................................................... 61

Figure 25. Graphs showing temporal variations in turbidity and concentrations of suspended solids, 

total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus, in Spring Creek at mouth 

at Whitstran, Yakima River Basin, Washington 1997–2001............................................................. 63

Figure 26. Graphs showing temporal variations in streamflow and variations in concentrations of 

suspended solids and nitrite-plus-nitrate nitrogen with streamflow in Yakima River at Kiona, 

Yakima River Basin, Washington, 1991–2000 water years .............................................................. 67

Figure 27. Graphs showing temporal variations in turbidity and concentrations of suspended solids, 

total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in Yakima River at Kiona, 

Yakima River Basin, Washington, 1991–2000 water years .............................................................. 68
x Tables

TABLES

Table 1. Chronology of implementation of best management practices sponsored by the Environmental 

Quality Incentives Program in the Yakima River Basin, Washington, 1996–2001 .......................... 11

Table 2. Surface-water sites and wastewater treatment plants sampled for suspended sediment and 

nutrients in the Yakima River Basin, Washington, 1999–2000 ........................................................ 17

Table 3. Laboratory methods used to determine concentrations of nutrient compounds in samples 

collected by the U.S. Geological Survey in the Yakima River Basin, Washington, 1999–2000 ...... 19

Table 4. Comparison of concentrations of suspended sediment, total nitrogen, and total phosphorus 

in surface water of the Yakima River Basin, Washington, during basinwide sampling, 

July 26–29, 1988, and August 2–6, 1999 .......................................................................................... 28

Table 5. Results of mass-balance computations comparing streamflow and loads of total nitrogen and

phosphorus in the reach of the Yakima River extending from river mile 103.7 to river mile 55, 

Yakima River Basin, Washington ..................................................................................................... 34

Table 6. Suspended-sediment and nutrient loads transported during water years 1999–2000 in 

Granger Drain and Yakima River at Kiona, Yakima River Basin, Washington ............................... 35

Table 7. Annual and seasonal average suspended-sediment and nutrient loads transported during 

calendar year 1999 in Moxee Drain, Granger Drain, and Yakima River at Kiona, Yakima 

River Basin, Washington ................................................................................................................... 38

Table 8. Spring (March through June) suspended-sediment and nutrient loads and their fraction 

of the annual loads transported in the Yakima River at Kiona, Yakima River Basin, 

Washington ........................................................................................................................................ 39

Table 9. Estimates of average daily loads of suspended sediment and nutrients in the Yakima River 

at Kiona, computed using streamflow and concentration data from three different periods 

to calibrate the load models, Yakima River Basin, Washington, water years 1999–2000................ 40

Table 10. Proximity of surface-water sites sampled during 1999–2000 by the U.S. Geological Survey 

to sites sampled by the Bureau of Reclamation, Roza-Sunnyside Board of Joint Control, and 

Washington State Department of Ecology in the Yakima River Basin, Washington........................ 44

Table 11. Trend statistics for streamflow, turbidity, and concentrations of suspended solids, 

total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus for data collected 

during the 1991–2000 water years at surface-water sites in the Yakima River Basin, Washington . 46

Table 12. Comparison of trend statistics for turbidity and concentrations of total nitrogen and total 

phosphorus in samples collected from the Yakima River at Kiona, Yakima River Basin, 

Washington ........................................................................................................................................ 66
Conversion Factors, Datum, Abbreviations, and Definitions xi

CONVERSION FACTORS, DATUM, ABBREVIATIONS, AND DEFINITIONS

CONVERSION FACTORS

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) or 

micrograms per liter (μg/L).

DATUM

Vertical datum: Vertical coordinate information is referenced to the North American Vertical Datum 

of 1929 (NAVD 29).

Horizontal datum: Horizontal coordinate information is referenced to the North American Datum of 

1983 (NAD 83).

Altitude, as used in this report, refers to distance above or below sea level.

Multiply By To obtain

Length

inch (in) 2.54 centimeter

inch (in) 25.4 millimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

Area

acre 0.004047 square kilometer

square mile (mi2) 2.590 square kilometer 

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second 

Mass

pound, avoirdupois (lb) 0.4536 kilogram 

pound per day, avoirdupois (lb/d) 0.4536 kilogram per day

ton per day (ton/d) 0.9072 metric ton per day

ton per day (ton/d) 0.9072 megagram per day
xii Conversion Factors, Datum, Abbreviations, and Definitions

ABBREVIATIONS

BMP Best management practice

BOR Bureau of Reclamation

Ecology Washington State Department of Ecology

EQIP Environmental Quality Incentives Program

LRL Laboratory reporting level

NAWQA National Water-Quality Assessment Program

NWQL National Water Quality Laboratory

PAM Polyacrylamide

RM River mile

RSBOJC Roza-Sunnyside Board of Joint Control

USGS U.S. Geological Survey

WWTP Wastewater treatment plant

DEFINITIONS

Agricultural return flows include 1) canal water; 2) irrigation water, rain, and snowmelt transported from agricultural fields to streams and surface drains via overland flow; and 3) shallow 

ground water discharged to surface drains and streams, either directly or from subsurface tile drains.

Canal water (in the context of this report) is irrigation water diverted from the Yakima or Naches 

River for delivery via canals, laterals, and pipes to farm land. During irrigation season, canal water in 

excess of the amount needed to irrigate crops in a particular area or drainage basin is returned 

through drains and streams to the rivers. Concentrations of suspended sediment and nutrients in 

canal water usually are lower than concentrations in shallow ground water beneath agricultural fields 

and in irrigation water that runs off of agricultural fields and flows to drains and streams.

Water year in U.S. Geological Survey reports is the 12-month period October 1 through September 

30. The water year is designated by the calendar year in which it ends and which includes 9 of the 12 

months. Thus, the year ending September 30, 1999, is called the "1999 water year."
Abstract 1

Concentrations and Loads of Suspended Sediment and 

Nutrients in Surface Water of the Yakima River Basin, 

Washington, 1999–2000—With an Analysis of Trends in 

Concentrations

By James C. Ebbert, Sandra S. Embrey, and Janet A. Kelley

ABSTRACT

Spatial and temporal variations in 

concentrations and loads of suspended sediment 

and nutrients in surface water of the Yakima River 

Basin were assessed using data collected during 

1999–2000 as part of the U.S. Geological Survey 

(USGS) National Water-Quality Assessment 

(NAWQA) Program. Samples were collected at 34 

sites located throughout the Basin in August 1999 

using a Lagrangian sampling design, and also 

were collected weekly and monthly from May 

1999 through January 2000 at three of the sites. 

Nutrient and sediment data collected at various 

time intervals from 1973 through 2001 by the 

USGS, Bureau of Reclamation, Washington State 

Department of Ecology, and Roza-Sunnyside 

Board of Joint Control were used to assess trends 

in concentrations.

 During irrigation season (mid-March to 

mid-October), concentrations of suspended 

sediment and nutrients in the Yakima River 

increase as relatively pristine water from the 

forested headwaters moves downstream and mixes 

with discharges from streams, agricultural drains, 

and wastewater treatment plants. Concentrations 

of nutrients also depend partly on the proportions 

of mixing between river water and discharges: in 

years of ample water supply in headwater 

reservoirs, more water is released during irrigation 

season and there is more dilution of nutrients 

discharged to the river downstream. For example, 

streamflow from river mile (RM) 103.7 to RM 72 

in August 1999 exceeded streamflow in July 1988 

by a factor of almost 2.5, but loads of total 

nitrogen and phosphorus discharged to the reach 

from streams, drains, and wastewater treatment 

plants were only 1.2 and 1.1 times larger.

In years of ample water supply, canal water, 

which is diverted from either the Yakima or 

Naches River, makes up more of the flow in drains 

and streams carrying agricultural return flows. The 

canal water dilutes nutrients (especially nitrate) 

transported to the drains and streams in runoff 

from fields and in discharges from subsurface field 

drains and the shallow ground-water system. The 

average concentration of total nitrogen in drains 

and streams discharging to the Yakima River from 

RM 103.7 to RM 72 in August 1999 was 2.63 

mg/L, and in July 1988 was 3.16 mg/L; average 

concentrations of total phosphorus were 0.20 and 

0.26 mg/L.

After irrigation season, streamflow in 

agricultural drains decreases because irrigation 

water is no longer diverted from the Yakima and 

Naches Rivers. As a result, concentrations of total 

nitrogen in drains increase because nitrate, which 

constitutes much of total nitrogen, continues to 

enter the drains from subsurface drains and 

shallow ground water. Concentrations of total 
2 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

phosphorus and suspended sediment often 

decrease, because they are transported to the 

drains in runoff of irrigation water from fields. In 

Granger Drain, concentrations of total nitrogen 

ranged from 2-4 mg/L during irrigation season and 

increased to about 6 mg/L after irrigation season, 

and concentrations of total phosphorus, as high as 

1 mg/L, decreased to about 0.2 mg/L.

In calendar year 1999, Moxee Drain 

transported an average of 28,000 lb/d (pounds per 

day) of suspended sediment, 380 lb/d of total 

nitrogen, and 46 lb/d of total phosphorus to the 

Yakima River. These loads were about half the 

average loads transported by Granger Drain during 

the same period. Average streamflows were 

similar for the two drains, so the difference in 

loads was due to differences in constituent 

concentrations: those in Moxee Drain were about 

40-60 percent less than those in Granger Drain.

 Loads of suspended sediment and total 

phosphorus in Moxee and Granger Drains were 

nearly four times higher during irrigation season 

than during the non-irrigation season because with 

increased flow during irrigation season, 

concentrations of suspended sediment and total 

phosphorus are usually higher. Loads of nitrate in 

the drains were about the same in both seasons 

because nitrate concentrations are higher during 

the non-irrigation season. 

Loads of nutrients in the Yakima River at 

Kiona were similar during irrigation and nonirrigation season, generally differing by less than 

20 percent. This is because average streamflows 

and concentrations of nutrients were similar 

between the two seasons. Average streamflow 

during the irrigation season was within about 6 

percent of the average streamflow during the nonirrigation season and average nutrient 

concentrations differed by less than 13 percent. 

Loads of suspended sediment were about 60 

percent larger during irrigation season. Large 

fractions of the total annual loads were transported 

during the first half of the irrigation season. For 

example, 38 percent or more of the annual loads of 

suspended sediment, total nitrogen, ammoniaplus-organic nitrogen, total phosphorus, and 

orthophosphate were transported from March 

through June.

Departure from relations between average 

daily loads and annual mean streamflow suggests 

some reduction in loads of suspended sediment, 

ammonia-plus-organic nitrogen, and total nitrogen 

in the Yakima River at Kiona in water years 1999 

and 2000. The relation between loads and 

streamflow was established using loads previously 

estimated for water years 1974, 1977, 1980, 1988, 

and 1989 and loads estimated by this study for 

other water years from 1974 through 1994. 

The summary of trend statistics for 

concentration data collected from 1991–2000 

indicates that some of the factors affecting 

constituent transport to surface water may be 

common to many agricultural subbasins in the 

Yakima Basin. For example, concentrations of 

nitrate and total nitrogen increased in five of six 

streams and drains while concentrations of 

suspended solids and total phosphorus either did 

not change or decreased. This difference is 

consistent with no change, or a decrease, in 

amounts of suspended solids and phosphorus 

transported to surface water in runoff and an 

increase in the amount of nitrate transported to 

streams and drains from ground-water discharges 

and subsurface drains. Decreased transport of 

sediment and associated phosphorus to streams 

and drains likely results from increased use of 

agricultural best management practices that reduce 

runoff from cropland. Nitrate is less affected 

because much of it enters from subsurface drains 

and shallow ground water. Increasing 

concentrations of nitrate in some drains over the 

period 1991–2000 suggest that concentrations of 

nitrate in ground water are increasing.
Introduction 3

Data collected from 1997–2001 also 

indicate a decrease in concentrations in suspended 

solids and total phosphorus in some drains and 

streams receiving agricultural return flows. 

Turbidity has decreased in drains where 

concentrations of suspended solids have 

decreased. The data also indicate that 

concentrations of nitrate in some streams and 

drains have leveled off and may be decreasing. 

This observation does not conflict with the trend 

statistics for 1991–2000, but suggests that a slow 

increase over a decade may be leveling off.

Trend statistics computed using both 

unadjusted and flow-adjusted data indicate small, 

but significant, increases in turbidity and 

concentrations of total phosphorus in the Yakima 

River at Kiona from 1991 through 2000. There 

also was an increase in flow-adjusted 

concentrations of nitrate, which is consistent with 

increasing concentrations of nitrate in some 

streams and drains flowing to the Yakima River. 

Although nitrogen discharged from streams and 

drains is a large fraction of the nitrogen load in the 

river, a relation between increasing concentrations 

of nitrate in streams and drains and increasing 

concentrations in the Yakima River at Kiona was 

not established. The trend test using flow-adjusted 

concentrations showed no trend in the 

concentration of suspended solids. This seems 

reasonable because concentrations of suspended 

solids correlated with streamflow, and higher 

values of both were observed after 1995.

INTRODUCTION

In 1986, the U.S. Geological Survey (USGS) 

implemented a pilot program to test and refine the 

concepts for what was to become the National WaterQuality Assessment (NAWQA) Program. The Yakima 

River Basin was included in the pilot program as one of 

four river basins selected for the study of surface-water 

quality. Using pilot-study data collected from 1987 to 

1991, along with data collected earlier by the USGS 

and other agencies, the study significantly advanced the 

understanding of the effects of land use on the quality 

of surface water in the Yakima River Basin. The study 

showed that agricultural practices in the Basin can 

greatly increase concentrations of suspended sediment, 

nutrients, trace metals, pesticides, and fecal-indicator 

bacteria in streams that receive agricultural return 

flows. In examining the effects of agricultural practices 

on water resources, the pilot study provided some 

information about the effectiveness of various best 

management practices in reducing erosion of soil, 

nutrients, and pesticides from agricultural fields, 

thereby improving the quality of surface water draining 

agricultural land (Morace and others, 1999).

In 1991, the NAWQA Program was fully 

implemented, and by 2001 the Program had assessed 

the quality of streams and ground water in more than 

50 study units throughout the Nation (U.S. Geological 

Survey, 2001). The NAWQA Program in the Yakima 

River Basin began its second cycle (cycle II) in 1999, 

when surface water throughout the Basin was sampled 

for concentrations of suspended sediment, nutrients, 

pesticides, and other constituents. Cycle II has 

provided an opportunity to reassess water quality and 

study the effectiveness of best management and other 

land-use practices on the quality of surface water. Part 

of the reassessment included determining spatial and 

temporal variations in concentrations and loads of 

suspended sediment and nutrients in surface water in 

the Yakima River Basin and assessing trends in 

concentrations.

Manure, from animal feeding operations, is commonly spread on crops 

including corn, asparagus, and hops. 
4 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Purpose and Scope

This report describes (1) spatial and temporal 

changes in concentrations and loads of suspended 

sediment and nutrients in surface water of the Yakima 

River Basin, and (2) trends in concentrations of these 

constituents. The report also discusses some of the 

factors that have caused changes in concentrations and 

loads. Data collected by the USGS as part of the cycle 

II study were obtained from a basinwide sampling of 

surface-water sites and wastewater discharges in 

August 1999, and from weekly and monthly sampling 

of three surface-water sites from May 1999 through 

January 2000. Additional data collected January 2001 

through August 2002 at the Yakima River at Kiona 

were used to help assess the results of estimating loads 

with regression models. Nutrient and sediment data 

dating from 1973 through 2001 and collected at 

different time intervals within that period by the USGS, 

Bureau of Reclamation (BOR), Washington State 

Department of Ecology (Ecology), and RozaSunnyside Board of Joint Control (RSBOJC) were used 

to assess trends in concentrations.

Availability of Data Used in This Report

U.S. Geological Survey data used in this report 

can be obtained from the Yakima River Basin NAWQA 

Web site at the URL <http://oregon.usgs.gov/yakima>.

Acknowledgments

We gratefully acknowledge the individuals and 

agencies who provided support and assistance to this 

project. Chris Coffin and Ryan Anderson, Washington 

State Department of Ecology, provided technical 

advice and assistance in the field during sample 

collection. Moses Squeochs and James Thomas, 

Yakama Indian Nation, worked with the Yakama Indian 

Nation Council to grant us access to sampling sites and 

accompanied us during site visits. William Rice, who 

was with the Roza-Sunnyside Board of Joint Control at 

the time of this study, helped with selection of 

sampling sites, installed water-quality monitors, gaged 

streams, collected samples, and made turbidity 

measurements. Steve Fanciullo, Bureau of 

Reclamation, allowed us access to their stream gages 

and provided streamflow data and advice on the mass 

balance of water discharges needed for computing 

constituent loads. Robert Stevens, soil scientist with 

Washington State University, provided helpful advice 

on sampling design and provided land-use maps of the 

Granger Basin. Scott Manley, Director of Benton 

Conservation District, provided water-quality data for 

Spring and Snipes Creeks. Assistance during sample 

collection was provided by Jennifer Key, student at 

Central Washington University; Paivikki "Vickie" Pihl, 

student at Tampere University of Technology, Finland; 

and Brent Morace, USGS volunteer. Wastewater 

treatment-plant operators in Cle Elum, Ellensburg, 

Selah, Yakima, Sunnyside, and Prosser collected 

effluent samples during the basinwide sampling.

We would like to thank Ecology, the BOR, and 

the RSBOJC for providing water-quality data for the 

analysis of trends. David Hallock, Ecology, provided 

historical data not available online for the Yakima 

River at Kiona. William Rice, formerly with the 

RSBOJC, provided statistical summaries of qualitycontrol data in addition to the raw data. William 

Stroud, BOR, provided the quality-assurance plan for 

the collection and analysis of water-quality samples.

 We gratefully acknowledge the individuals who 

provided information and data about the use of 

agricultural best management practices in the Yakima 

River Basin. Those individuals and agencies are cited 

throughout the report.

Finally, we would like to thank Joe Joy and Steve 

Butkus, Ecology, and Onni Perala, Roza Irrigation 

District, for their help and comments on technical 

aspects of data analysis and report content.
Description of Basin 5

DESCRIPTION OF BASIN

The Yakima River flows 214.5 mi (miles) from 

the outlet of Keechelus Lake in the central Washington 

Cascade Range to the Columbia River, draining an area 

of 6,155 mi2 (square miles) (fig. 1). The altitude of the 

Basin ranges from 8,184 ft (feet) above sea level in the 

Cascade Range to about 340 ft at the Columbia River. 

The Basin contains a variety of landforms, including 

the glaciated peaks and deep valleys of the Cascade 

Range, broad river valleys, and the lowlands of the 

Columbia Plateau. Mean annual precipitation ranges 

from 140 in. (inches) in the Cascade Range to less than 

10 in. near the mouth of the Basin.

Because the lower valleys are arid during 

summer, most agricultural land in the Basin is irrigated. 

Reservoirs in the upper Yakima and Naches River 

Basins (fig. 1) are used to augment flows for irrigation 

and instream uses. Reservoir releases provide most of 

the water used for irrigation during the July-October 

period, when natural streamflows are lowest and 

irrigation demand is highest. About 450,000 acres of 

cropland in the Yakima River Basin are irrigated, and 

annual surface-water diversions from the Yakima River 

system for irrigation are equivalent to about 60 percent 

of the mean annual streamflow leaving the Basin. 

During the summer months, the quality of agricultural 

return flows affects the quality of water in the Yakima 

River downstream from the city of Yakima because 

return flows contribute as much as 80 to 90 percent of 

the streamflow (Rinella and others, 1999). Agricultural 

return flows enter the Yakima River through 

agricultural drains and wasteways and through the 

lower reaches of some streams (fig. 2).

The chemical quality of the agricultural return 

flows is influenced by the amount of streamflow in the 

Yakima River during irrigation season, which is 

determined to a large extent by the amount of water 

released from headwater reservoirs. In years when the 

water supply is plentiful, more water is available for 

irrigation, and water in agricultural drains and the 

lower reaches of some streams contains a higher 

percentage of canal water (Onni Perala, Roza Irrigation 

District, written commun., July 2002). The canal water 

tends to dilute dissolved constituents, like nitrate, in 

drain water, thereby reducing their concentrations.

The Yakima River integrates a variety of hydrologic landscapes including 

forested head waters, deeply incised basalt canyons in the mid valley, and 

rich sedimentary and loess deposits in the lower valley.
6 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

KITTITAS

COUNTY

YAKIMA

COUNTY

YAKIMA

COUNTY

BENTON

COUNTY

KLICKITAT

COUNTY

Canal

Roza

Sunnyside Canal

Main Canal Extension

Kennewi ck

Main Ca n al

Marion Drain

North

Branch

Canal

Kittitas Main Canal

Bumping

Lake N Fk

S Fk

S Fk N Fk

S Fk

N Fk

N Fk

Cle Elum River

Swauk Creek

Caribou Cr

Coleman Cr

Naneum

Cr

Cooke Cr

Crow Creek

Bumping River

American River

Rattlesnake Cr

Little Rattlesnake Cr

Nile Creek

Manastash

Badger Cree k

Squaw Cr

Ahtanum Creek

Oak Creek

Tieton River

Wide Hollow Cr

Wenas Creek

Selah Creek

North For k

Dry Creek

Simco e Creek

Agency Creek

Creek

Toppenish

Corral Cr

Spring Cr

Logy Creek

Satus

Creek

Mule Dry

Creek

Cle

Elum

Lake

Rimrock

Lake

Kachess Lake

Keechelus Lake

Lake

Wallula

Priest

Rapids

Lake

Teanaway River Reecer Cr

Wilson Creek

Park Cr

Taneum Creek

Umtanum Creek

Little Naches River

Cr

Cowiche Cree k

Cowiche Creek

River

Naches

Snipes Cr

Sulphur Cr Wasteway

CherryCr

RIVE

Y

R

AKIMA

COLUMBIA RIVER

RIVER

YAKIMA

RIVER

YAKIMA

Cle Elum

Parker

Wapato

Ellensburg

Umtanum

Ahtanum

Thrall

Toppenish

Moxee City Union

Gap

Yakima

Selah

Naches

Sunnyside Richland

Kiona

Kennewick Prosser

Grandview

Mabton

Satus

Zillah

Granger

Roza

Easton

Teanaway

Tieton Rimrock

Snoqualmie

Pass

Van Epps

Pass

Esmeralda

Peaks

KITTITAS

VALLEY

M A N A S T A S H

KACHESS RIDGE

RIDGE

UNION GAP

CLEMAN

MOUNTAIN

TEANAWAY

NORTH RIDGE

U M T A N U M

R I D G E

Deception Pass

YAKIMA

 VALLEY

AHTANUM RIDGE

COWICHE MTN

AMERICAN RIDGE

CLE ELUM RIDGE

RIDGE

TOPPENISH RIDGE

R A T T L E S N A K E H I L L S

Y A K I M A R I D G E

H O R S E

H E A V E N H I L L S

C

A

S

C

A

D E R

A

N

G

E

W E N A T C H E E

M O U N T A I N S

Gilbert

Peak

121 ̊00'

47 ̊00'

47 ̊30'

46 ̊00'

120 ̊00'

121 ̊30' 120 ̊30'

119 ̊30'

46 ̊30'

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

WASHINGTON

Study

area

12

97

82

90

240

241

22

24

410

14

90

90

97

97

97

97

410 12

12

12

82

82

24

82

22

240

Figure 1. The Yakima River Basin, Washington.
Description of Basin 7

Land Use and Water Quality

Land use and land cover in the Yakima River 

Basin grade from the forested headwaters in the upper 

basin to agriculture and rangeland in the lower basin 

(fig. 3). In a summary of the pilot study, Morace and 

others (1999) described how the quality of surface 

water in the Yakima River Basin varied with the 

gradation in land use. The pilot study divided the 

Yakima River into three reaches based on changes in 

water quality as influenced by differences in geology 

and land use. The study determined that the quality of 

water in the upper reach, which extends from the foot 

of Keechelus Dam at river mile (RM) 214.5 to just 

upstream of Umtanum (RM 140.5) was better than the 

quality of water in both the middle (RM 140.5 to RM 

107.2) and lower (RM 107.2 to the mouth) reaches.

The pilot study concluded that erosion of soil 

from agricultural lands during irrigation season, which 

extends from mid-March until mid-October, was the 

major source of suspended sediment and turbidity in 

surface water of the Yakima River Basin. Although 

most suspended sediment is transported to the Yakima 

River during irrigation season, much of it is deposited 

on the riverbed and not transported downstream until it 

is resuspended during winter storms and spring 

snowmelt. Concentrations of suspended sediment were 

highest in agricultural drains during irrigation season, 

but were highest in the Yakima River during snowmelt 

in April and May (Morace and others, 1999). During 

irrigation season, the highest rates of sediment 

transport to drains generally were associated with the 

growing of hops. Soil erosion from apple and pear 

orchards had been reduced through the use of sprinkler 

irrigation and grass cover.

200 180 160 140 120 100 80 60 40 20

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

STREAMFLOW, IN CUBIC FEET PER SECOND

Computed Flow

Unmeasured Gain or Loss

Measured Flow

Yakima

Grandview

Kiona

Wilson Creek

Roza Canal

Roza Return

Wapato Canal

Naches River

Sunnyside Canal

Granger Drain

Satus Creek

Sulphur Creek Wasteway

Chandler Canal

Chandler Return

Cle Elum

RIVER MILE ABOVE MOUTH

Figure 2. Streamflow in the Yakima River during irrigation, August 2-6, 1999.
8 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Figure 3. Land use and land cover in the Yakima River Basin, Washington, 1999.

Yakima Canyon Creeks akima Canyon Creeks

Kittitas ittitas

Naches

Ahtanum-Wide Hollow Ahtanum-Wide Hollow

Toppenish oppenish

Satus

Moxee

Buena-Zillah uena-Zillah

Granger Sulphur

Downstream ownstream

Umtanum

Kittitas ittitas

EXPLANATION

Water, wetlands, perennial ice

and snow

Residential, commercial, industrial

Forest: evergreen, deciduous

Agriculture: row crops, orchards,

pasture, hay, small grains

Shrubland: evergreen, deciduous

Grasslands: herbaceous, urban

Bare ground, transitional, other

White lines - basin boundaries

Basin name

121°00'

47°00'

47°30'

46°00'

120°00'

121°30' 120°30'

119°30'

46°30'

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

LAND USE AND LAND COVER
Description of Basin 9

Because soil erosion also transports nutrients and 

pesticides along with sediment to surface water, 

limiting erosion is an important aspect of improving 

surface-water quality. For example, because of 

significant correlations between turbidity and 

concentrations of total suspended solids and total DDT 

in the Yakima River, the Washington State Department 

of Ecology established target levels for turbidity as a 

way to reduce concentrations of total suspended solids 

and total DDT in the Yakima River (Joy and Patterson, 

1997). The target turbidity levels were established to 

reduce concentrations of total DDT below 1 nanogram 

per liter (0.001 microgram per liter), which is the 

chronic toxicity criterion for the protection of aquatic 

life (State of Washington, 1997).

The pilot study concluded that cropland, dairies, 

feedlots, and wastewater treatment plants were 

important sources of nutrients in the Yakima River. 

Although nutrient loads discharged to the Yakima 

River from some wastewater treatment plants equaled 

those in some of the agricultural drains and wasteways, 

the drains and wasteways were considered the major 

source of nitrogen and phosphorus in the middle and 

lower reaches of the Yakima River (Pogue and others, 

1999).

Because drains and wasteways are a major 

source of nitrogen and phosphorus in the middle and 

lower reaches of the Yakima River, the effects of 

increased use of nitrogen and phosphorus fertilizers on 

agricultural land in the Basin is of interest. Rinella and 

others (1992) reported that concentrations of nitrate in 

the Yakima River at Kiona (near the terminus of the 

Basin) almost doubled from 1965 to 1985 in response 

to a two-fold increase in the use of nitrogen fertilizers 

during the same period. In contrast, concentrations of 

total phosphorus in the Yakima River at Kiona 

decreased over the same period, even though the use of 

phosphorus fertilizers also increased by about a factor 

of two. This difference serves to illustrate the complex 

relation between land-use practices and the transport of 

nutrients to surface water. 

Use of Agricultural Best Management Practices

Best management practices (BMPs) are defined 

as techniques and measures that prevent or reduce 

water pollution from nonpoint sources by using the 

most effective and practicable means of achieving 

water-quality goals. In the Yakima River Basin, 

agricultural BMPs focus primarily on farming 

techniques that reduce the transport of sediment, 

nutrients, and pesticides from cropland to surface 

water, and their use is encouraged as a way to reduce 

the environmental effects of agriculture on surfacewater quality and to help meet the goals recommended 

for total maximum daily loads of suspended sediment 

and DDT (Joy and Patterson, 1997). BMPs are 

implemented by a landowner, often in conjunction with 

the local conservation agency or irrigation district, and 

most of the BMPs in the Yakima River Basin entail 

changes in the way irrigation water is applied. As an 

example, rill irrigation is discouraged in favor of lesserosive methods, such as sprinkler and drip irrigation. 

Other types of BMPs include diversion of irrigation 

runoff to ponds and wetlands where sediments settle 

out before the runoff is released to drains, and the 

addition of polyacrylamide (PAM) to irrigation water 

to increase the cohesiveness of soil particles, making 

the soil less subject to erosion. “Best Management 

Practices to reduce or control runoff can range from 

sophisticated drip-irrigation systems, sprinkler 

systems, and constructed wetlands to simpler practices 

such as gated pipe, PAM, and small sediment detention 

ponds. Some of these BMPs are partially funded 

through government cost-share and loan programs 

while others are paid for entirely by the landowner” 

(Marie Zuroske, South Yakima Conservation District, 

written commun., February 2003.)
10 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Farmers have voluntarily constructed small ponds at low points in their 

fields in an attempt to remove sediment from runoff.

Farmers and ranchers in the Yakima River Basin 

have been encouraged to apply to local, State, and 

Federal agencies for grants and low-interest loans to 

help implement BMPs. For example, the 

Environmental Quality Incentives Program (EQIP) is a 

Federally funded cost-share program offered by the 

Farm Service Agency and the Natural Resources 

Conservation Service for farmers and ranchers in 

environmentally sensitive areas (U.S. Department of 

Agriculture, 1997). Created by Congress in 1996, EQIP 

provides technical, financial, and educational 

assistance. The Kittitas County, North Yakima, South 

Yakima, and Benton Conservation Districts (fig. 4) 

have prioritized areas for implementing BMPs. 

Prioritization has allowed conservation districts to 

optimally direct funds where needed and, together with 

EQIP funding, has resulted in grants of more than 4 

million dollars since 1997. The effects of these funds 

on application of new irrigation methods alone covered 

more than 11,000 acres, or nearly 4 percent of the total 

agricultural acreage in the Basin.

The implementation of EQIP-sponsored BMPs 

varies throughout the Yakima River Basin (fig. 5). In 

1996, Yakima Basin farmers competed for EQIP costshare funds under a single Geographic Priority Area. 

Farms using furrow irrigation were identified as the 

dominant resource issue and received a higher priority 

for BMP conversions. Farmers in the lower Basin 

generally had higher cash-value crops and 

consequently were able to finance larger proportions of 

their EQIP cost share. The North Yakima and South 

Yakima Conservation Districts are located in the lower 

Basin, and through the EQIP program they assisted 

farmers by paying an average of 23 percent of the BMP 

cost (Alan Fulk, Natural Resource Conservation 

Service, oral commun., January 2002). Farms in the 

upper Basin would have required approximately 55 

percent of the BMP cost to make the conversion 

economically feasible (Anna Lael, Kittitas County 

Conservation District, oral commun., April 2002). As a 

result, BMPs were underway in the lower Basin earlier 

than in the upper Basin. In 1997, the Kittitas 

Conservation District formed a single Geographic 

Priority Area for upper Basin farmers, and EQIPsponsored BMPs were initiated in 1998.

Because detailed records of EQIP-sponsored 

BMPs are maintained for administering loan funds, 

EQIP-program data can serve as an indicator of BMP 

activity in subbasins of the Yakima River Basin. The 

data are only an indicator, because some BMPs, like 

the addition of PAM to irrigation water and the 

construction of sediment basins at the downslope end 

of fields, are financed entirely by farmers and ranchers 

and are not included in the EQIP records. In this report, 

the chronology of the implementation of BMPs in the 

Yakima River Basin (table 1) is compared in a 

qualitative way with data showing trends, or the lack of 

trends, in concentrations of suspended solids and 

nutrients. More specific information about BMP 

activity within subbasins is presented in the section 

"Trends in Concentrations."

Drip irrigation system with buried line.
Description of Basin 11

Table 1. Chronology of implementation of best management practices sponsored by the Environmental 

Quality Incentives Program in the Yakima River Basin, Washington, 1996–2001—Continued

Year

BMP usage, in acres BMP usage, percentage of total cropland

Yearly Cumulative Yearly Cumulative

Wilson Creek above Cherry Creek at Thrall (201)

1996 – – – –

1997 – – – –

1998 191 191 0.9 0.9

1999 134 325 .6 1.5

2000 288 613 1.3 2.8

2001 – – – –

Cherry Creek at Thrall (202)

1996 – – – –

1997 – – – –

1998 337 337 0.9 0.9

1999 1,398 1,735 3.8 4.7

2000 395 2,130 1.1 5.8

2001 130 2,260 .4 6.2

Moxee Drain at Birchfield Road near Union Gap (69)

11996 1,148 1,148 6.2 6.2

1997 590 1,738 3.2 9.4

1998 344 2,082 1.9 11.3

1999 297 2,379 1.6 12.9

2000 527 2,906 2.9 15.8

2001 370 3,276 2.0 17.8

Granger Drain at Granger (67)

1996 532 532 2.4 2.4

1997 328 860 1.4 3.8

1998 189 1,049 .8 4.6

1999 105 1,154 .5 5.1

2000 397 1,551 1.8 6.9

2001 1,753 3,304 7.7 14.6

Marion Drain at Indian Church Road at Granger (210)

1996 121 121 0.2 0.2

1997 627 748 1.2 1.4

1998 267 1,015 .5 1.9

1999 243 1,258 .5 2.4

2000 180 1,438 .4 2.8

2001 1,051 2,489 2.1 4.9

Table 1. Chronology of implementation of best management practices sponsored by the Environmental 

Quality Incentives Program in the Yakima River Basin, Washington, 1996–2001

[Subbasin: Number following name of subbasin corresponds to map identification No. in table 2 and figure 6. 

BMP, best management practice. –, no data available]
12 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Toppenish Creek at Indian Church Road near Granger (211)

1996 121 121 0.1 0.1

1997 1,080 1,201 1.1 1.2

1998 373 1,574 .4 1.5

1999 746 2,320 .7 2.2

2000 574 2,894 .6 2.8

2001 1,223 4,117 1.2 4.0

Sulphur Creek Wasteway near Sunnyside (215)

1996 138 138 0.4 0.4

1997 634 772 1.7 2.1

1998 813 1,585 2.2 4.3

1999 579 2,164 1.5 5.8

2000 517 2,681 1.4 7.2

2001 1,449 4,130 3.9 11.1

1Includes acreage from 1995.

Table 1. Chronology of implementation of best management practices sponsored by the Environmental 

Quality Incentives Program in the Yakima River Basin, Washington, 1996–2001—Continued

Year

BMP usage, in acres BMP usage, percentage of total cropland

Yearly Cumulative Yearly Cumulative
Description of Basin 13

Ellensburg

Yakima River

North Yakima 

Conservation District

Cle Elum

South Yakima 

Conservation District

Kittitas County 

Conservation District

Benton

Conservation District

Sunnyside

Granger

Prosser

Benton City Richland

Mabton

Yakima

Grandview

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Union Gap

EXPLANATION

BASIN BOUNDARY

CONSERVATION DISTRICT BOUNDARY

Figure 4. Conservation districts in the Yakima River Basin, Washington.
14 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Figure 5. Status of agricultural best management practices sponsored by the Environmental Quality Incentives Program in subbasins of the 

Yakima River Basin through 2000.

218

217

215

67

102

215

211

209

69

121

205

66

202

201

214

206

MAP IDENTIFICATION NO. AND SAMPLING SITE NAME—

Map identification Nos. identify basins that correspond to

sampling sites listed below and in table 2

66 Umtanum Creek near mouth at Umtanum

67 Granger Drain at Granger

69 Moxee Drain at Birchfield Rd near Union Gap

102 South Drain near Satus

121 Ahtanum Creek at Union Gap

201 Wilson Creek above Cherry Creek at Thrall

202 Cherry Creek at Thrall

205 Naches River near North Yakima

206 Wide Hollow Creek near mouth at Union Gap

208 East Toppenish Drain at Wilson Road near Toppenish

209 Sub 35 Drain at Parton Road near Granger

210 Marion Drain at Indian Church Road at Granger

211 Toppenish Creek at Indian Church Road near Granger

214 Satus Creek at gage at Satus

215 Sulphur Creek Wasteway near Sunnyside

217 Spring Creek at Hess Road near Prosser

218 Snipes Creek below Chandler Canal near Prosser

BEST MANAGEMENT PRACTICE (BMP)

ACTIVITY THROUGH 2000*

Less than 5 percent conversion

5 percent to 10 percent conversion

More than 10 percent conversion

All reported BMP activity after 2000

No BMP activity reported

No BMP data available

*Percentage of total agricultural land converted to

BMP through 2000

218

217

215

67

102

210

211

209

69

121

205

66

202

201

214

206

208

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS
Methods 15

METHODS

Surface-water sites and selected wastewater 

treatment-plant (WWTP) discharges throughout the 

Yakima River Basin were sampled for suspended 

sediment and nutrients on August 2-6, 1999, during dry 

weather at the peak of the irrigation season (fig. 6,

table 2). Sampling of the Yakima River extended from 

Cle Elum (RM 182.5) to Kiona (RM 29.9). Other 

sampled surface-water sites and WWTP discharges 

were located along the reach of the Yakima River 

extending from RM 179.6 near Cle Elum to Spring and 

Snipes Creeks at RM 41.8 (fig. 6), but not all of them 

discharge directly to the Yakima River. Some discharge 

to tributaries of the Yakima River.

To the extent possible, basinwide sampling was 

timed according to the velocity of water as it moved 

downstream in the Yakima River. This is sometimes 

referred to as Lagrangian sampling, which can be 

visualized as sampling a distinct unit or "parcel" of 

water as it moves downstream. The advantage of this 

design is that it is possible to account for additions and 

losses of water, suspended sediment, nutrients, or any 

constituent, as the unit moves downstream. Some sites 

were sampled more than once during the basinwide 

sampling (table 2) to assess daily variations in 

concentrations and to bracket targeted sampling times 

if they were at night.

In addition to the basinwide sampling, the 

Yakima River at Kiona, Moxee Drain, and Granger 

Drain were sampled at fixed intervals (monthly or more 

frequently) from May 1999 through January 2000 to 

assess changes in concentrations of suspended 

sediment and nutrients over a longer period (fig. 6, 

table 2). Data from these samples also were used to 

estimate loads of sediment and nutrients transported 

during the sampling period. Additional data collected 

January 2001 through August 2002 at the Yakima River 

at Kiona, which are not included with the sample 

counts in table 2, were used to help evaluate the results 

of the regression models used to estimate loads.

This section presents an overview of standard 

USGS and NAWQA procedures governing sample 

collection, handling, and analysis in the field and 

laboratory. Procedures used by the BOR, Ecology, and 

RSBOJC to collect, process, and analyze samples are 

not presented here, but are discussed or referenced in 

Appendix A (at back of report). This section also 

includes information about quality assurance, methods 

used to estimate loads and test for trends, and sources 

of ancillary data. Additional information can be found 

in the publications cited in this section, some of which 

can be accessed on-line at the URLs 

<http://water.usgs.gov/>, 

<http://nwql.usgs.gov/Public/pubs-public.html>, and 

<http://nwql.usgs.gov/Public/nwql_memo.html>.

Sample Collection, Field Procedures, and Sample 

Preparation

The use of standard USGS sampling equipment, 

cleaning of equipment in preparation for the field, and 

the collection, processing, and handling of water 

samples generally followed the protocols and 

guidelines described in Ward and Harr (1990), Shelton 

(1994), and the National Field Manual for the 

Collection of Water-Quality Data (U.S. Geological 

Survey, 1997-99). Samples representative of the flow in 

the stream cross section were obtained by collecting 

depth-integrated subsamples at equally spaced verticals 

across the stream using either the US DH-81 or US D77TM sampler as described by Edwards and Glysson 

(1988) and Shelton (1994). Both samplers hold 3-liter 

Teflon sample bottles, and all parts of the sampler 

coming into contact with sample water were 

constructed of Teflon. Samples of the effluent from 

wastewater treatment plants were collected directly 

into 3-liter Teflon bottles. All equipment used to collect 

and process samples was cleaned with a 0.2-percent 

non-phosphate detergent, rinsed with deionized water, 

and then rinsed with native water prior to collection 

and processing.
16 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

97

97

97

97

97

12

12 12

12

82

82

82

90

90

90

14

240

241

22

24

24

410

410

240

KITTITAS

COUNTY

YAKIMA

COUNTY

YAKIMA

COUNTY

BENTON

COUNTY

KLICKITAT

COUNTY

Cle

Elum

Lake

Bumping

Lake

Rimrock

Lake

Kachess Lake

Keechelus Lake

Lake

Wallula

Priest

Rapids

Lake

Cle Elum River Teanaway River Reecer Creek

Wilson Creek

Caribou Creek

Coleman

Park Creek

Creek

Cooke Creek

Taneum Creek

Kittitas Main Canal

Umtanum Creek

Crow Creek

Bumping River

American River

Rattlesnake Creek

Little Rattlesnake Cr

Nile Creek

Little Naches River

Cr

Cowiche Creek

River

Naches

Canal

Roza

Sunnyside Canal

Manastash

Badger Creek

Squaw Creek

Ahtanum Creek

Oak Creek

Tieton River

Wide Hollow Creek

Wenas Creek

Selah Creek

Naches River

North Fork

Dry Creek

Simcoe Creek

Main Canal Extension

Agency Creek

Creek

Toppenish

Corral Cr

RIVER

Kennewi ck

Main Can al

Snipes Creek

Spring Cr

Marion Drain

Logy

Creek

Sulphur Creek Wasteway

Satus

Creek

Mule Dry Creek

Cherry Creek

COLUMBIA RIVER

YAKIMA

Deception Pass

CLEMAN

MOUNTAIN

YAKIMA

VALLEY

Gilbert

Peak

Yakima Valley

AHTANUM RIDGE

AMERICAN RIDGE

CLE ELUM RIDGE

TEANAWAY

RIDGE

NORTH RIDGE

TOPPENISH RIDGE

R A T T L E S N A K E H I L L S

Y A K I M A R I D G E

U M T A N U M

R I D G E

H O R S E

H E A V E N H I L L S

C

A

S

C

A

D E R

A

N

G

E

W E N A T C H E E

M O U N T A I N S

66

69

74 102

121

200

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

227

67

Cle Elum

Ellensburg

Umtanum

Thrall

Toppenish

Moxee City

Union

Gap

Yakima

Selah Naches Priest

Rapids

Sunnyside

Granger

Zillah

Richland

Kiona

Kennewick

Prosser

Grandview

Mabton

Satus

EXPLANATION

SAMPLING SITE AND MAP

IDENTIFICATION NO.—See

table 2

121°00'

47°00'

47°30'

46°00'

120°00'

121°30' 120°30'

119°30'

46°30'

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Figure 6. Location of surface-water sites and wastewater treatment plants sampled for suspended sediments and nutrients in the Yakima River 

Basin, Washington, 1999–2000.
Methods 17

Table 2. Surface-water sites and wastewater treatment plants sampled for suspended sediment and nutrients in the Yakima River Basin, Washington, 

1999–2000

[River mile sampled on Yakima River or where tributary or wastewater treatment plant (WWTP) discharges to Yakima River. Abbreviations: USGS, U.S. 

Geological Survey; RM, river mile; –, not applicable]

Map 

identification 

No.

(see fig. 6)

USGS site 

identification 

No.

Sampling site

River mile sampled Number of samples 

collected

On 

Yakima 

River

On 

tributary

During 

basinwide 

sampling 

August 1999

At fixed 

sites, May 

1999 through 

January 2000 

200 12479500 Yakima River at Cle Elum 182.5 – 1 –

227 471121120543400 Cle Elum WWTP 179.6 – 1 –

226 465748120325200 Ellensburg WWTP 151.6 – 1 –

201 12484100 Wilson Creek above Cherry Creek at Thrall 147 1.1 1 –

202 12484480 Cherry Creek at Thrall1 147 .1 1 –

203 12484500 Yakima River at Umtanum 140.4 – 1 –

66 12484550 Umtanum Creek near mouth at Umtanum 139.8 .1 1 –

225 463856120313000 Selah WWTP 117 – 1 –

204 12496510 Pacific Power and Light Company Wasteway2 116.3 .1 1 –

205 12499000 Naches River near North Yakima 116.3 .1 1 –

224 463447120275200 Yakima WWTP 111 – 1 –

206 12500445 Wide Hollow Creek near mouth at Union Gap 107.4 .8 1 –

69 12500420 Moxee Drain at Birchfield Road near Union Gap 107.3 1.4 2 25

207 12500450 Yakima River above Ahtanum Creek at Union Gap 107.3 – 1 –

121 12502500 Ahtanum Creek at Union Gap 106.9 .8 1 –

223 462357120153200 Zillah WWTP 89.5 – 1 –

208 12505350 East Toppenish Drain at Wilson Road near Toppenish 86 1.3 1 –

209 12505410 Sub 35 Drain at Parton Road near Granger 83.2 1.7 1 –

222 462013120113700 Granger WWTP 82.8 – 1 –

67 12505450 Granger Drain at Granger 82.8 .8 2 24

210 12505510 Marion Drain at Indian Church Road at Granger 82.6 1.4 1 –

211 12507508 Toppenish Creek at Indian Church Road near Granger 80.4 2.4 1 –

212 12507585 Yakima River at RM 72 above Satus Creek near 

Sunnyside

72 – 1 –

213 12507595 Satus Creek above Shinando Creek near Toppenish 69.6 41.3 1 –

74 12508500 Satus Creek below Dry Creek near Toppenish 69.6 15 1 –

214 12508620 Satus Creek at gage at Satus 69.6 2.7 1 –

102 12508630 South Drain near Satus 69.3 1.8 2 –

221 461850120005800 Sunnyside WWTP3 61 – 1 –

215 12508850 Sulphur Creek Wasteway near Sunnyside 61 .8 2 –

216 12509050 Yakima River at Euclid Bridge at RM 55 near 

Grandview

55 – 1 –

220 461246119454700 Prosser WWTP 47 – 1 –

217 461404119410400 Spring Creek at Hess Road near Prosser 41.8 .4 1 –

218 461414119404200 Snipes Creek below Chandler Canal near Prosser 41.8 .4 1 –

219 12510500 Yakima River at Kiona 29.9 – 3 16

1Cherry Creek discharges to Wilson Creek at RM 1.1.

2Pacific Power and Light Wasteway discharges to the Naches River at RM 9.7. 3Sunnyside WWTP discharges to Drainage Improvement District drain number 3, which discharges to Sulphur Creek.
18 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Because more than 3 liters of water was needed 

for all types of analyses performed, several Teflon 

sample bottles were filled at each site. Water from all of 

the sample bottles was composited and split into 

aliquots for the various laboratory procedures using a 

Teflon cone splitter, as described by Shelton (1994). 

Sample water to be analyzed for determining 

concentrations of suspended sediment was collected 

from the cone splitter in glass bottles, which were 

shipped to the USGS Cascades Volcano Observatory 

Sediment Laboratory in Vancouver, Wash. Sample 

water to be analyzed for determining concentrations of 

nutrients was collected from the cone splitter in 

polypropylene receiving bottles. Sub-samples needed 

for determining concentrations of nutrients using 

unfiltered sample water were obtained by pouring 

water in one or more of the receiving bottles back 

through the cone and capturing the required sample 

volume. Sub-samples for determining concentrations 

of nutrients using filtered sample water (formerly 

referred to as a dissolved concentration) were obtained 

by filtering sample water through a polypropyleneencapsulated filter with a 0.45-micrometer pore size. 

The unfiltered nutrient samples were preserved with 

sulfuric acid and shipped, along with the filtered 

nutrient samples, on ice to the USGS National Water 

Quality Laboratory (NWQL) in Lakewood, Colo.

Field Measurements

Water temperature, specific conductance, pH, 

and concentrations of dissolved oxygen (DO), 

alkalinity, and bicarbonate were measured in the field 

using procedures described in the National Field 

Manual for the Collection of Water-Quality Data (U.S. 

Geological Survey, 1997-99). Water temperature and 

the concentration of dissolved oxygen were measured 

instream using an electronic thermistor and a DO 

meter. Specific conductance and pH were measured 

using unfiltered sample water taken from the cone 

splitter. Alkalinity, bicarbonate, and carbonate 

concentrations were determined by titrating filtered 

sample water with sulfuric acid using a digital titrator.

Laboratory Procedures

Suspended-sediment samples were analyzed 

using the filtration method (Guy, 1969) at the USGS 

Cascades Volcano Observatory Sediment Laboratory in 

Vancouver, Wash. Turbidity was measured using the 

nephelometric method (American Public Health 

Association and others, 1998) in field laboratories 

operated by RSBOJC in Sunnyside, Wash., and by the 

USGS in Pasco, Wash. Nutrient samples were analyzed 

using colorimetric methods (table 3) at the NWQL. 

Because concentrations of nitrite in surface water 

usually were very low or below laboratory reporting 

levels (see table A1), nitrite was not a significant 

fraction of the concentration of nitrite-plus-nitrate. 

Therefore, "nitrite-plus-nitrate" is often shortened to 

"nitrate" in this report.

Quality Assurance

In order to interpret water-quality data properly, 

information is needed to estimate bias and variability 

that result from sample collection, processing, and 

analysis. Data used for this purpose include field 

blanks to measure bias from contamination, replicate 

samples to measure variability, and blank water spiked 

in the laboratory to measure bias from recovery of 

analytes. Quality-control charts and reports published 

by the USGS Branch of Quality Systems (see 

Appendix A) also were used to assess bias and 

variability. For more about the collection of qualitycontrol samples, see Shelton (1994). 
Methods 19

Data collected by the RSBOJC, the BOR, and 

Ecology were used in this report to assess trends. 

Quality-control data provided by the RSBOJC are 

included in Appendix A. References and links to 

quality-control data and quality-assurance plans for the 

BOR and Ecology also are listed in Appendix A.

An evaluation of quality-control data (see 

Appendix A) indicates that bias and variability 

resulting from sample collection, processing, and 

analysis usually were much smaller than differences in 

concentration upon which conclusions about spatial 

and temporal changes in water quality were based. 

Although numerical information about the quality of 

data from the BOR and Ecology are not presented in 

Appendix A, both agencies were contacted to confirm 

that sampling and analytical methods had not changed 

over the period that trend analyses were performed.

Methods Used to Compute Concentrations and 

Estimate Loads

Concentrations of all nutrient compounds were 

determined by laboratory analysis except for total 

nitrogen, which was computed as the sum of 

concentrations of filtered nitrite-plus-nitrate and 

unfiltered ammonia-plus-organic nitrogen. Low 

concentrations are sometimes estimated or censored 

(reported as less than the laboratory reporting level). 

Estimated values were used for computing 

concentrations of total nitrogen, but censored values 

were not and thus were treated as a zero value.

Substitutions were made for missing laboratory 

data for two samples. In one, the concentration of 

ammonia-plus-organic nitrogen in a filtered sample 

was substituted for the concentration in an unfiltered 

sample. In the other, the concentration of phosphorus in 

a filtered sample was substituted for the concentration 

in an unfiltered sample.

Concentrations of suspended sediment and total 

nitrogen and phosphorus in samples collected during 

basinwide sampling in August 1999 were compared 

with a similar set of data collected in July 1988. For 

sites sampled more than once (tables 9 and 13 in 

Morace and others, 1999; table 2 in this report), mean 

concentrations were used. Instantaneous loads of total 

nitrogen and phosphorus in 1999 also were compared 

with those in 1988. They were computed as the product 

of a single or mean concentration and an instantaneous 

or daily mean water discharge.

Table 3. Laboratory methods used to determine concentrations of nutrient compounds in samples collected by the U.S. Geological Survey in the Yakima 

River Basin, Washington, 1999–2000

Analyte Analytical method

Laboratory 

reporting level 

(milligrams per 

liter)

Reference

Nitrogen, ammonia Colorimetric, salicylate-hypochlorite 0.041 Fishman, 1993

Nitrogen, ammonia-plus-organic filtered Colorimetric, Kjeldahl digestion .10 Patton and Truitt, 2000

Nitrogen, ammonia-plus-organic unfiltered Colorimetric, Kjeldahl digestion .10 Patton and Truitt, 2000

Nitrogen, nitrite Colorimetric, diazotization .008 Fishman, 1993

Nitrogen, nitrite-plus-nitrate Colorimetric, cadmium reduction .047 Fishman, 1993

Phosphorus, filtered Colorimetric, Kjeldahl digestion .004 Patton and Truitt, 1992

Phosphorus, unfiltered Colorimetric, Kjeldahl digestion .004 Patton and Truitt, 1992

Orthophosphate, filtered Colorimetric, phosphomolybdate .018 Fishman, 1993
20 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Suspended-sediment and nutrient loads were 

estimated by the rating-curve method (Cohn and 

others, 1989; Crawford, 1991), which uses 

instantaneous sample concentrations and daily or unit 

streamflow data. The Loadest2 computer program was 

used to compute rating-curve estimates of annual, 

seasonal, and daily constituent loads. Rating-curve 

parameters are computed by the maximum-likelihood 

estimation (MLE) method (Dempster and others, 1977; 

Wolynetz, 1979) or the linear attribution estimation 

(LAE) method (Chatterjee and McLeish, 1986); either 

method can accommodate concentration data reported 

with multiple detection limits. The MLE method 

assumes that the rating-curve errors (regressionequation residuals) are normally distributed, whereas 

the LAE method does not (Charles Crawford, USGS, 

written commun., 1999). Output from Loadest2 

includes statistics using the Turnbull-Weiss likelihood 

ratio normality test (Turnbull and Weiss, 1978) to help 

evaluate the validity of the normality assumption. The 

program allows the user to define the period of interest 

by not restricting the load estimate to calendar or water 

year, and the user can specify a rating-curve equation 

or allow the program to choose the regression equation 

that best describes the data using Aikaike's information 

criterion (Charles Crawford, USGS, written commun., 

1999).

For estimating uncertainty in the average loads 

obtained by the MLE method, the program uses the 

method described by Likes (1980), which provides a 

minimum-variance unbiased estimate of the variance of 

a sum of lognormal variables, and Gilroy and others 

(1990), which calculates the exact variance of average 

constituent loads obtained by the rating-curve method 

when the rating-curve parameters and residual-error 

variance are known with certainty. For estimating 

uncertainty with the LAE method, the program uses the 

jackknife method (Efron, 1982), which is a robust 

method for examining sampling properties of a statistic 

with no requirement for distributional assumptions 

(Crawford, 1996). These methods and descriptions are 

detailed in Crawford (1996).

If there is no strong evidence of non-normality in 

the distribution of the residuals or the MLE and LAE 

methods result in similar estimates, then the results 

from the MLE method are typically selected for final 

load calculations (Charles Crawford, USGS, written 

commun., 1999). For these reasons, the MLE results 

were used for final load estimates of all constituents at 

Moxee Drain, Granger Drain, and Yakima River. The 

estimated average loads, standard deviations of the 

average loads, comparisons between measured and 

predicted loads, and the regression equations used to 

calculate suspended sediment and nutrient loads are in 

Appendix B, tables B1, B2, and B3 (at back of report).

Data sets used to calibrate the Loadest2 

regression equations (see Appendix B) consisted of 

suspended-sediment and nutrient data collected by 

USGS during calendar years 1999–2000 and daily 

streamflow values for water years 1999–2000. For 

Moxee Drain, daily streamflows were available only 

from January 1999 to early June 2000. Annual and 

seasonal load estimates were reported for the period 

1999–2000, water years 1999 and 2000, and calendar 

year 1999; loads for Moxee Drain were reported only 

for calendar year 1999. Seasonal loads for Granger 

Drain and Yakima River were calculated for the nonirrigation season using the period October 20 through 

March 20 and the irrigation season from the period 

March 21 through October 19. For Moxee Drain, 

seasonal loads for calendar year 1999 were calculated 

for the non-irrigation season using the periods January 

1 to March 20, 1999, plus October 20, 1999 through 

December 31, 1999, and the irrigation season from the 

period March 21 through October 19, 1999.

Methods Used to Test for Trends

Data collected by the BOR, the RSBOJC, and 

Ecology at seven sites corresponding to, or near, those 

sampled by the USGS were used to assess trends in 

concentrations. The seasonal Kendall test (Crawford 

and others, 1983) was used to analyze for trends in 
Methods 21

concentration data provided by the BOR and Ecology 

for water years 1991–2000. Because data collected by 

the RSBOJC covered a shorter period (1997–2001), 

time-series graphs of concentrations were inspected to 

detect potential trends, but no statistical tests were 

performed using their data. To eliminate a potential 

source of error, data sets used to test for trends in 

concentrations represented one agency and one 

laboratory. Sample collection and analytical methods 

were verified as consistent over the period that trend 

data were collected. When more than one agency 

collected samples at the same location, the data were 

analyzed separately.

The seasonal Kendall test is a nonparametric test 

that compares the relative ranks of the data rather than 

the actual concentration values. Because monthly data 

were available, the seasons were defined to be the 12 

months; therefore, only January data were compared 

with January data and so forth for the rest of the 

months. If more than one sample was collected during 

a month, the mean concentration was used determine 

the rank. All possible pairs of monthly data are 

compared in the test. If a value later in time is higher, 

then a plus is recorded; if a value later in time is lower, 

then a minus is recorded. If the values are the same, 

they are assigned an equal rank and neither a plus or 

minus is recorded. If an upward trend is present, there 

will be many more pluses than minuses. If no trend is 

present, then the numbers of pluses and minus are 

about equal. Because the seasonal Kendall test uses 

ranks instead of concentration values, it easily handles 

censored (less-than) values (Crawford and others, 

1983), but none of the data used to test for trends was 

censored.

Using flow-adjusted concentrations to test for 

trends is recommended if there is an indication that 

streamflow has a considerable influence on 

concentrations (Helsel and Hirsch, 1992). Streamflow 

is often a major source of variability in concentrations, 

and removing that variability can make it easier to 

detect a trend. Even though scatter plots indicated that 

the influence of streamflow on constituent 

concentrations varied by site and by constituent (the 

scatter plots are presented in section "Trends in 

Concentrations"), all trend tests were performed using 

both flow-adjusted concentrations and unadjusted 

concentrations.

The process of computing flow-adjusted 

concentrations involves modeling the effect of 

streamflow on concentration using regression or some 

other curve-fitting technique. For this study, the locally 

weighted scatter plot smoothing (LOWESS) technique 

(Cleveland, 1979) was used to fit a curve (the middle 

smooth line) to a scatter plot of concentrations and 

corresponding stream discharges. Flow-adjusted 

concentrations were computed by subtracting 

concentrations defined by the middle smooth line from 

corresponding measured concentrations, and then 

adding the results (the residuals) to the mean of the 

measured concentrations. In effect, this is the same as 

performing the trend tests on the residuals. Adding the 

residuals to the mean concentration was done so that 

trend slopes could be expressed in concentration units.

Scatter plots of the residuals versus 

corresponding values on the middle smooth line were 

used to check the fit of the LOWESS curve to the data. 

This was done by visual inspection to determine if the 

residuals trended upward or downward with 

concentration or if the scale of the residuals increased 

or decreased with concentration. If the residuals 

showed a trend or appeared to be scale dependent, the 

value of the smoothness factor, which was set to 0.5 

initially, was changed and the fit with the LOWESS 

curve was checked. The smoothness factor alters the 

number of data points included in each iteration of the 

regressions used to obtain the LOWESS curve (Helsel 

and Hirsch, 1992).
22 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

A trend was considered to be statistically 

significant if the p-value from the seasonal Kendall test 

was less than or equal to 0.10; however, the p-values 

are listed in this report so that it is possible for the 

reader to assign a different level of significance. 

Because no more than 10 years of data were used for 

trend testing, the p-values were not adjusted for serial 

correlation (Hirsch and Slack, 1984); however, keeping 

the number of seasons relatively small, such as the 

selection of 12 seasons, helps to reduce problems 

resulting from serial correlation (Crawford and others, 

1983).

Sources of Streamflow and Precipitation Data

Daily streamflow data were available from 

gaging stations at the three sites sampled at fixed 

intervals. The streamflow gaging station on the Yakima 

River at Kiona (station 12510500) is operated by the 

USGS. Data for Moxee Drain at Birchfield Road near 

Union Gap (station 12500420) were collected in 

cooperation with the North Yakima Conservation 

District and the BOR. Discharge records for the station 

on Granger Drain at Granger (station 12505450) were 

provided by the Sunnyside Valley Irrigation District 

and reviewed by the USGS.

Daily precipitation data from National Weather 

Service data-collection sites were obtained from 

monthly publications of climatological data by the 

National Oceanic and Atmospheric Administration 

(NOAA) National Climatic Data Center (National 

Oceanic and Atmospheric Administration, 1999 and 

2000). For Yakima River at Kiona, the weather site at 

Richland was the primary source of precipitation data 

and data from weather sites at Prosser or Smyrna were 

used for estimating brief periods of missing data at the 

Richland site. For Granger Drain, the weather site at 

Sunnyside was the primary source of precipitation data, 

and data from Wapato and Yakima Airport were 

substituted for missing data at the Sunnyside site. For 

Moxee Drain, the weather site at Moxee City was the 

primary source of data and precipitation data from 

Yakima Airport were used for estimating missing data 

at Moxee City.

Water leaking from the Roza Canal is captured and returned by an 

electrical pump.
Concentrations and Loads 23

CONCENTRATIONS AND LOADS

Because streamflow in agricultural drains in the 

Yakima River Basin is controlled mostly by the 

irrigation cycle, base flows are in winter and high flows 

are in spring and summer. As illustrated by data from 

Moxee and Granger Drains, variations in 

concentrations of nutrients and suspended sediment are 

linked to the irrigation cycle and resulting changes in 

streamflow (figs. 7A and 7B). Concentrations of nitrate 

and total nitrogen in both drains increase as streamflow 

decreases in late October and early November at the 

end of the irrigation season. After the irrigation season, 

water is not diverted from the Yakima River, and the 

drains carry no canal water, which dilutes nitrate 

discharged to them from the shallow ground-water 

system. Most of the total nitrogen in these drains is in 

the form of dissolved nitrate. Variations in streamflow 

and concentrations of nitrate and total nitrogen in 

Moxee and Granger Drains are typical of those in 

drains and wasteways in other irrigated parts of the 

Central Columbia Plateau (Williamson and others, 

1998).

There also was an inverse relation between 

streamflow and concentrations of nitrate and total 

nitrogen in the Yakima River at Kiona (fig. 7C). 

Because of diversions, flow regulation in the 

headwaters, and dry summers, the Yakima River at 

Kiona differs hydrologically from Moxee and Granger 

Drains, with a low-flow period during late summer 

instead of during winter and streamflows that generally 

vary more in magnitude during the remainder of the 

year. Nitrate and total nitrogen in the Yakima River are 

diluted by increased streamflow from storm runoff and 

snowmelt (Pogue and others, 1999).

Concentrations of suspended sediment in Moxee 

and Granger Drains were highest during the irrigation 

season because runoff of applied irrigation water 

transports soil from fields to the drains. Rainfall runoff 

also can transport sediment to drains, but there was no 

evidence of a large rain event in the streamflow record 

for November 1999 through January 2000 and 

concentrations of suspended sediment were relatively 

low during that period (figs. 7A and 7B). The highest 

concentration of suspended sediment in the Yakima 

River at Kiona was during high flow in June 1999 

(fig. 7C). High flows resulting from snowmelt in the 

spring and early summer scour sediment deposited in 

the river during the previous irrigation season 

(Bramblett and Fuhrer, 1999).

Because of the association between phosphorus 

and suspended sediment (Litke, 1999), concentrations 

of total phosphorus often increased when 

concentrations of suspended sediment increased 

(fig. 7). For example, the highest concentration of total 

phosphorus in the Yakima River at Kiona coincided 

with the highest concentration of suspended sediment 

(fig. 7C), and most of the phosphorus in that sample 

was in the form of sediment-sorbed phosphorus.

At lower flows when concentrations of 

suspended sediment generally were lower, 

concentrations of total phosphorus were also lower and 

dissolved orthophosphate made up a larger fraction of 

the total phosphorus (fig. 7). In Moxee Drain, however, 

concentrations of total phosphorus and dissolved 

orthophosphate increased after the irrigation season 

(fig. 7A), possibly because the drain receives effluent 

from the Moxee City wastewater treatment plant. After 

the irrigation season, there is less streamflow in the 

drain to dilute the orthophosphate.

Rill irrigation can mobilize sediment to adjacent water ways.
24 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations CONCENTRATION, IN MILLIGRAMS PER LITER STREAMFLOW, IN CUBIC FEET PER SECOND CONCENTRATION, IN MILLIGRAMS PER LITER

NITROGEN

PHOSPHORUS

Suspended sediment

Total phosphorus

Orthophosphate phosphorus

Precipitation

EXPLANATION

Total nitrogen

Streamflow

Nitrite-plusnitrate nitrogen

PRECIPITATION, IN INCHES PRECIPITATION, IN INCHES

0.8

0.2

0.4

0.6

0

0.8

0.2

0.4

0.6

0

100

40

7

0

2

4

6

100

20

40

60

80

0.4

0

0.1

0.2

0.3

0

20

60

80

0

CONCENTRATION, IN MILLIGRAMS PER LITER

SUSPENDED

SEDIMENT

PRECIPITATION, IN INCHES

0

0.8

0.2

0.4

0.6

250 100

0

50

100

150

200

0

20

40

60

80

JFMAMJ J A S O ND J

1998 1999 2000

A. Moxee Drain at Birchfield Road near Union Gap

Figure 7. Daily streamflow and concentrations of suspended sediment, total and nitrite-plus-nitrate nitrogen, total 

phosphorus and orthophosphate (as P) in samples collected from selected surface-water sites in the Yakima River Basin, 

Washington, May 1999-January 2000. 
Concentrations and Loads 25

CONCENTRATION, IN MILLIGRAMS PER LITER CONCENTRATION, IN MILLIGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

CONCENTRATION, IN MILLIGRAMS PER LITER

Suspended sediment

Total phosphorus

Orthophosphate phosphorus

Precipitation

EXPLANATION

Total nitrogen

Streamflow

Nitrite-plusnitrate nitrogen

PRECIPITATION, IN INCHES PRECIPITATION, IN INCHES PRECIPITATION, IN INCHES

0

0.8

0.2

0.4

0.6

0.8

0

0.2

0.4

0.6

0.8

0

0.2

0.4

0.6

JFMAMJ J A S O ND J

1998 1999 2000

0

800

200

400

600

100

20

40

60

80

0

0.2

0.4

0.6

0.8

1.0

20

100

40

60

80

1.2

7

0

2

4

6

100

20

40

60

80

NITROGEN

PHOSPHORUS

SUSPENDED

SEDIMENT

B. Granger Drain at Granger

Figure 7.—Continued.
26 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations CONCENTRATION, IN MILLIGRAMS PER LITER STREAMFLOW, IN CUBIC FEET PER SECOND CONCENTRATION, IN MILLIGRAMS PER LITER CONCENTRATION, IN MILLIGRAMS PER LITER

Suspended sediment

Total phosphorus

Orthophosphate phosphorus

Precipitation

EXPLANATION

Total nitrogen

Streamflow

Nitrite-plusnitrate nitrogen

NITROGEN

PHOSPHORUS

SUSPENDED

SEDIMENT

PRECIPITATION, IN INCHES PRECIPITATION, IN INCHES PRECIPITATION, IN INCHES

0.5

0.2

0.3

0.4

0

0.5

0.1

0.2

0.3

0.4

0

0.5

0.1

0.2

0.3

0.4

0

0.1

0

250

50

100

150

200

0

15,000

5,000

10,000

0 0

15,000

5,000

10,000

0

1

0

15,000

5,000

10,000

JFMAMJ J A S O ND J

1998 1999 2000

0.3

2

0.1

0.2

C. Yakima River at Kiona

Figure 7.—Continued.
Concentrations and Loads 27

Results of Basinwide Sampling, August 1999 and 

July 1988

Data collected during basinwide sampling on 

August 2-6, 1999, when streamflow in the Yakima 

River was relatively steady, were used to develop 

profiles of concentrations and instantaneous loads of 

suspended sediment and nutrients in surface water. 

Streamflow in the Yakima River during 1999 was 

above average. The annual mean streamflow in the 

Yakima River at Kiona during the 1999 water year was 

4,374 ft3/s (cubic feet per second), compared with the 

mean annual flow of 3,569 ft3/s for water years 1934-

99 (Zembrzuski and others, 2001). Except for some 

differences in constituents analyzed for and sites 

sampled, sampling in August 1999 was a repeat of 

basinwide sampling conducted by the USGS on July 

26-29, 1988, when streamflow in the Yakima River was 

much less than average. The annual mean streamflow 

in the Yakima River at Kiona during the 1988 water 

year was only 1,905 ft3/s (Miles and others, 1989).

Relatively pristine water is captured in the upper basin to meet demands 

during peak irrigation. 

Morace and others (1999) observed that during 

July and August, concentrations of suspended sediment 

and nutrients in the Yakima River increase as the 

relatively pristine water from the forested headwaters 

flows into the areas of agricultural and urban land use 

(fig. 3) where streams, agricultural drains, and 

wastewater treatment plants discharge suspended 

sediment and nutrients to the river. When streamflow in 

the Yakima River is relatively steady and there is little 

or no scour of streambed sediment, concentrations of 

nutrients and suspended sediment in the river should be 

governed to some degree by the proportion of water 

from the forested headwaters that mixes with water 

discharged to the river from streams, drains, and 

wastewater treatment plants. When there is more flow 

from forested headwaters, concentrations of 

constituents discharged to the river should be lower 

because of dilution. A comparison of constituent 

concentrations in the Yakima River in August 1999 

with concentrations in July 1988 provides a test of this 

hypothesis.

For the most part, the data from August 1999 and 

July 1988 are consistent with the predictions of a 

simple dilution model. Except for concentrations of 

suspended sediment in the Yakima River at RM 72 and 

concentrations of total nitrogen in the Yakima River 

above Ahtanum Creek at Union Gap (RM 107.3) and 

Kiona (RM 29.9), concentrations of suspended 

sediment and total nitrogen and phosphorus in the 

middle and lower reaches of the Yakima River (RM 

140.5 to the mouth) were lower in August 1999 than in 

July 1988 (table 4, fig. 8). Although the data are 

consistent with predictions of a simple dilution model, 

a more detailed analysis is needed to examine how 

dilution affects constituent concentrations in the 

Yakima River because the amount of flow and the 

quality of water in agricultural drains discharging to the 

river are affected by the availability of irrigation water. 

Compared with 1999, irrigation water was in short 

supply in 1988.
28 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Table 4. Comparison of concentrations of suspended sediment, total nitrogen, and total phosphorus in surface water of the Yakima River Basin, 

Washington, during basinwide sampling, July 26–29, 1988, and August 2–6, 1999—Continued

USGS site 

identification 

No.

Sampling site 

(map identification No. 

in fig. 6)

Date sampled and

relative percentage 

of difference (RPD)

Concentration, 

in milligrams per liter

Suspended 

sediment

Total 

nitrogen

Total 

phosphorus

12479500 Yakima River at Cle Elum (200) July 26, 19881 5 0.16 0.01

August 2, 1999 3 .16 .01

RPD -50 0 0

471121120543400 Cle Elum WWTP (227) July 25, 1988 – 5.7 2.3

August 2, 1999 46 4.6 3.8

RPD nc -21 49

465748120325200 Ellensburg WWTP (226) July 26, 1988 – 2.2 1.2

August 2, 1999 4 4.3 1.2

RPD nc 65 0

12484100 Wilson Creek above Cherry Creek at Thrall (201) July 26, 1988 10 1.1 .16

August 2, 1999 16 .97 .12

RPD 46 -13 -29

12484480 Cherry Creek at Thrall (202) July 26, 1988 82 3.8 .25

August 2, 1999 38 .65 .25

RPD -73 -142 0

12484500 Yakima River at Umtanum (203) July 27, 19882 20 .15 .04

August 2, 1999 10 .41 .04

RPD -67 93 0

12484550 Umtanum Creek near mouth at Umtanum (66) September 18, 1990 – .20 .08

August 2, 1999 3 .18 .11

RPD nc -11 32

463856120313000 Selah WWTP (225) July 26, 1988 – 12 6.3

August 3, 1999 6 9.5 5.4

RPD nc -23 -15

12499000 Naches River near North Yakima (205) July 16, 1988 3 .16 .02

August 3, 1999 9 .05 .02

RPD 100 -105 0

463447120275200 Yakima WWTP (224) July 26, 1988 – 12 3.7

August 3, 1999 5 8.1 1.7

RPD nc -39 -74

12500445 Wide Hollow Creek near mouth at Union Gap (206) July 27-28, 19882 8 1.4 .14

August 3, 1999 6 2.1 .11

RPD -29 40 -24

Table 4. Comparison of concentrations of suspended sediment, total nitrogen, and total phosphorus in surface water of the Yakima River Basin, 

Washington, during basinwide sampling, July 26–29, 1988, and August 2–6, 1999

[Date sampled: 1988 and 1999 samples were collected at the same site unless otherwise indicated. Some samples were collected outside the July 26–29, 1988 

period. Relative percentage of difference (RPD) = (1999 value – 1988 value) × 100/(0.5 × (1999 value + 1988 value)). Abbreviations: USGS, U.S. Geological 

Survey; WWTP, wastewater treatment plant; RM, river mile; nc, not computed; –, no sample]
Concentrations and Loads 29

12500430 Moxee Drain at Thorp Road July 26-29, 19883 530 1.8 0.32

12500420 Moxee Drain at Birchfield Road near Union Gap (69) August 3, 19992 170 1.5 .31

RPD -107 -18 -3.2

12500450 Yakima River above Ahtanum Creek at Union Gap (207) July 27, 1988 22 0.16 .09

August 3, 1999 13 .25 .05

RPD -51 44 -57

12502500 Ahtanum Creek at Union Gap (121) July 26, 1988 3 .87 .13

August 3, 1999 8 .47 .13

RPD -91 -60 0

462357120153200 Zillah WWTP (223) July 27, 1988 – 8.0 9.7

August 3, 1999 5 21 5.0

RPD nc 90 -64

12505350 East Toppenish Drain at Wilson Road near Toppenish (208) July 27, 1988 20 4.5 .31

August 3, 1999 39 3.2 .19

RPD 64 -34 -48

12505410 Sub 35 Drain at Parton Road near Granger (209) July 27, 1988 7.0 2.4 .09

August 3, 1999 170 2.5 .17

RPD 184 4.1 62

12505460 Granger Drain at mouth July 28, 19882 430 3.4 .52

12505450 Granger Drain at Granger (67) August 3-4, 19992 310 3.1 .45

RPD -32 -9.2 -14

462013120113700 Granger WWTP (222) July 27, 1988 – 4.0 3.7

August 4, 1999 4 22 1.2

RPD nc 138 -102

12505510 Marion Drain at Indian Church Road at Granger (210) July 28, 19882 7 2.8 .11

August 4, 1999 17 2.7 .12

RPD 83 -3.6 8.7

12507508 Toppenish Creek at Indian Church Road near Granger 

(211)

July 28, 1988 13 2.9 .11

August 4, 1999 19 2.5 .13

RPD 38 -15 17

12507585 Yakima River at RM 72 above Satus Creek near Sunnyside 

(212)

July 28, 1988 21 1.5 .10

August 4, 1999 22 1.0 .06

RPD 4.6 -40 -50

Table 4. Comparison of concentrations of suspended sediment, total nitrogen, and total phosphorus in surface water of the Yakima River Basin, 

Washington, during basinwide sampling, July 26–29, 1988, and August 2–6, 1999—Continued

USGS site 

identification 

No.

Sampling site 

(map identification No. 

in fig. 6)

Date sampled and

relative percentage 

of difference (RPD)

Concentration, 

in milligrams per liter

Suspended 

sediment

Total 

nitrogen

Total 

phosphorus
30 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

12508620 Satus Creek at gage at Satus (214) July 29, 1988 21 2.6 .13

August 4, 1999 54 1.9 .17

RPD 88 -31 27

12508630 South Drain near Satus4 (102) August 16, 1986 140 3.7 0.13

August 4-5, 19992 36 2.6 .22

RPD -118 -35 51

12508850 Sulphur Creek Wasteway near Sunnyside (215) July 28, 19882 99 3.8 .27

August 4-5, 19992 91 2.6 .24

RPD -8.4 -38 -12

12509050 Yakima River at Euclid Bridge at RM 55 near Grandview 

(216)

July 28, 19882 26 1.9 .14

August 5, 1999 19 1.4 .10

RPD -31 -30 -33

461246119454700 Prosser WWTP (220) July 29, 1988 – 4.1 17

August 5, 1999 6 1.5 2.7

RPD nc -93 -145

12509710 Spring Creek at mouth July 29, 19882 140 1.2 .14

461404119410400 Spring Creek at Hess Road near Prosser (217) August 5, 1999 53 0.84 .12

RPD -90 -35 -15

12509829 Snipes Creek at mouth July 29, 1988 53 .38 .09

461414119404200 Snipes Creek below Chandler Canal near Prosser (218) August 5, 1999 15 .83 .07

RPD -112 74 -25

12510500 Yakima River at Kiona (219) July 29, 1988 22 1.5 .14

August 5-6, 19995 20 1.5 .13

RPD -9.5 0 -7.4

Median of the 

absolute value of 

RPD

66 35 24

1Total nitrogen and phosphorus concentrations in a sample collected July 12, 1988. 2Two samples collected. Concentrations are mean values.

3Four samples collected. Concentrations are mean values. 4Concentration of suspended sediment in a sample collected June 27, 1989. 5Three samples collected. Concentrations are mean values.

Table 4. Comparison of concentrations of suspended sediment, total nitrogen, and total phosphorus in surface water of the Yakima River Basin, 

Washington, during basinwide sampling, July 26–29, 1988, and August 2–6, 1999—Continued

USGS site 

identification 

No.

Sampling site 

(map identification No. 

in fig. 6)

Date sampled and

relative percentage 

of difference (RPD)

Concentration, 

in milligrams per liter

Suspended 

sediment

Total 

nitrogen

Total 

phosphorus
Concentrations and Loads 31

0 50 100 150 200 550

530

Cle Elum WWTP

Ellensburg WWTP

Cherry Creek at Thrall

Yakima River at Umtanum

Yakima River at Cle Elum

Untanum Creek near mouth

Selah WWTP

Naches River near North Yakima

Yakima WWTP

Wide Hollow Creek near mouth

Moxee Drain at Birchfield Road

Yakima River above Ahtanum Creek

Anthanum Creek at Union Gap

Zillah WWTP

East Toppenish Drain at Wilson Road

Sub 35 Drain at Parton Road

Granger Drain at Granger

Granger WWTP

Marion Drain at Indian Church Road

Toppenish Creek at Indian Church Road

Yakima River at RM 72

Satus Creek at Satus

Sulphur Creek Wasteway

Yakima River at Euclid Bridge

Prosser WWTP

Spring Creek at Hess Road

Snipes Creek below Chandler Canal

Yakima River at Kiona

South Drain near Satus

SUSPENDED-SEDIMENT CONCENTRATION, IN MILLIGRAMS PER LITER

Wilson Creek above Cherry Creek at Thrall

SAMPLING SITE

310

430

July 26-29, 1988

August 2-6, 1999

NS No sample

NS

NS

NS

NS

NS

NS

NS

NS

A. Suspended sediment

DATE SAMPLED

ABBREVIATIONS

WWTP, wastewater treatment plant

RM, river mile

Figure 8. Concentrations of suspended sediment, total nitrogen, and total phosphorus in the main stem Yakima River, selected major tributaries, and 

discharges from wastewater treatment plants, Yakima River Basin, Washington, July 26-29, 1988, and August 2-6, 1999.

In plentiful water-supply years, some irrigation water is spilled directly 

into agricultural drains.

Morace and others (1999) used mass-balance 

analyses to study the dynamics of suspended-sediment 

and nutrient transport in the Yakima River in July 1988. 

For selected reaches of the river, loads of suspended 

sediment and nutrients were computed at the 

downstream end of a reach by subtracting loads leaving 

the reach through diversions from loads entering the 

upstream end of the reach plus loads discharged to the 

reach from drains, streams, and wastewater treatment 

plants. Computed loads were compared with loads 

measured at the downstream ends of reaches to 

determine how well the mass-balance computations 

accounted for gains and losses. If a measured load was 

greater than a computed load, the analysis suggested 

the presence of unmeasured contributions. If a 

measured load was less than a computed load, the
32 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Cle Elum WWTP

Ellensburg WWTP

Cherry Creek at Thrall

Yakima River at Umtanum

Yakima River at Cle Elum

Untanum Creek near mouth

Selah WWTP

Naches River near North Yakima

Yakima WWTP

Wide Hollow Creek near mouth

Moxee Drain at Birchfield Road

Yakima River above Ahtanum Creek

Anthanum Creek at Union Gap

Zillah WWTP

East Toppenish Drain at Wilson Road

Sub 35 Drain at Parton Road

Granger Drain at Granger

Granger WWTP

Marion Drain at Indian Church Road

Toppenish Creek at Indian Church Road

Yakima River at RM 72

Satus Creek at Satus

Sulphur Creek Wasteway

Yakima River at Euclid Bridge

Prosser WWTP

Spring Creek at Hess Road

Snipes Creek below Chandler Canal

Yakima River at Kiona

South Drain near Satus

Wilson Creek above Cherry Creek at Thrall

SAMPLING SITE

01 23 10

TOTAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

12

12

21

22

4 5 6 7 8 9 25

July 26-29, 1988

August 2-6, 1999

NS No sample

DATE SAMPLED

ABBREVIATIONS

WWTP, wastewater treatment plant

RM, river mile

B. Total nitrogen

Figure 8.—Continued.

analysis suggested unmeasured losses. Other factors, 

including temporal variability (non-steady state 

conditions), measurement errors, settling or scouring of 

sediment and associated nutrients, and uptake and(or) 

degradation of nutrients, also could account for 

differences.

A comparison of the results of mass-balance 

analyses performed using the August 1999 nutrient 

data with the results of the analyses performed by 

Pogue and others (1999) using the July 1988 nutrient 

data indicates that nitrogen and phosphorus loads 

discharged to the river were diluted more in August 

1999 than in July 1988 (table 5 and table C1, 

Appendix C, at back of report). In August 1999, for 

example, streamflow in the reach of the Yakima River 

extending from river mile 103.7 to river mile 72 

exceeded streamflow in July 1988 by a factor of almost 

2.5, but loads of total nitrogen and phosphorus 

discharged to this reach from streams, drains, and 

wastewater treatment plants were only 1.2 and 1.1 

times larger (table 5). The higher ratio of streamflow to 

loads of nitrogen and phosphorus discharged to this 

reach of the river in August 1999 resulted in lower 

concentrations.

Overall, the mass-balance analyses indicate that 

more of the flow in the reach of the Yakima River 

extending from river mile 103.7 to river mile 55 was 

derived from tributary discharges in July 1988 than in 

August 1999 (table 5). This, coupled with the fact that 

average concentrations of total nitrogen and 

phosphorus in the tributaries were higher than 

concentrations in the Yakima River (tables 5 and C1), 

means that in July 1988, more of the nitrogen and 

phosphorus in this reach of the Yakima River was 

derived from tributary discharges.
Concentrations and Loads 33

Cle Elum WWTP

Ellensburg WWTP

Cherry Creek at Thrall

Yakima River at Umtanum

Yakima River at Cle Elum

Untanum Creek near mouth

Selah WWTP

Naches River near North Yakima

Yakima WWTP

Wide Hallow Creek near mouth

Moxee Drain at Birchfield Road

Yakima River above Ahtanum Creek

Anthanum Creek at Union Gap

Zillah WWTP

East Toppenish Drain at Wilson Road

Sub 35 Drain at Parton Road

Granger Drain at Granger

Granger WWTP

Marion Drain at Indian Church Road

Toppenish Creek at Indian Church Road

Yakima River at RM 72

Satus Creek at Satus

Sulphur Creek Wasteway

Yakima River at Euclid Bridge

Prosser WWTP

Spring Creek at Hess Road

Snipes Creek below Chandler Canal

Yakima River at Kiona

South Drain near Satus

Wilson Creek above Cherry Creek at Thrall

SAMPLING SITE

0 1 2 18

TOTAL PHOSPHORUS CONCENTRATION, IN MILLIGRAMS PER LITER

3.8

6.3

5.4

3.7

9.7

5.0

3.7

17

2.7

2.3

C. Total phosphorus

July 26-29, 1988

August 2-6, 1999

NS No sample

DATE SAMPLED

ABBREVIATIONS

WWTP, wastewater treatment plant

RM, river mile

Figure 8.—Continued.

The fact that average concentrations of total 

nitrogen in tributaries discharging to the Yakima River 

were lower in August 1999 than in 1988 (table 5) 

indicates that there is increased dilution of nitrogen in 

drain water during years when the water supply is 

relatively good. In years when the water supply is 

plentiful, there is more water available for irrigation, 

and water in agricultural drains contains a higher 

percentage of canal water. Because irrigation water is 

diverted from the Yakima and Naches Rivers, the 

concentration of total nitrogen in canal water is 

relatively low compared with concentrations in ground 

water and excess irrigation water collected at the 

downslope ends of fields. The reason that there was 

little or no difference between average concentrations 

of total phosphorus in the tributaries in July 1988 and 

August 1999 (table 5) is that concentrations of 

phosphorus in ground water in irrigated areas are much 

lower than concentrations of nitrate (Williamson and 

others, 1998), and nitrate makes up much of the total 

nitrogen in the drain water (figs. 7A and 7B).

Concentrations of phosphorus are of interest 

because phosphorus is often the nutrient that limits 

undesirable plant growth in streams (Wetzel, 1983). 

Even with more dilution, concentrations of total 

phosphorus in all but one sample (at RM 72) collected 

from the middle and lower reaches of the river in 

August 1999 were greater than 0.1 mg/L, which is the 

recommended maximum concentration for limiting 

undesirable plant growth in streams (U.S. 

Environmental Protection Agency, 1986). Revised 

nutrient criteria are being developed on a regional basis 

(U.S. Environmental Protection Agency, 1998), but 

they are not yet available for the Yakima River Basin, 

and it is not known how the criterion for phosphorus 

might change.
34 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

In July 1988, concentrations of total phosphorus 

in all samples collected from the reach of the Yakima 

River from RM 72 to Kiona at RM 29.9 were greater 

than or equal to 0.1 mg/L (fig. 8C). Pogue and others 

(1999) reported that although conditions conducive to 

accelerated plant growth existed in this reach of the 

river, measurements of phytoplankton density and 

biovolume made in 1992 did not indicate 

eutrophication of the water column. They postulated 

that stream turbidity may inhibit phytoplankton 

growth, and that if turbidity were to decrease 

significantly, increased sunlight penetration would 

promote accelerated plant growth. Sampling to 

determine phytoplankton density and biovolume was 

not repeated in 1999.

Loads During 1999–2000 Water Years and 

Comparisons With Historical Load Estimates

Loads of suspended sediment, total nitrogen, and 

total phosphorus in Granger Drain, Moxee Drain, and 

Yakima River at Kiona were estimated for water years 

1999 and 2000 and for the irrigation and non-irrigation 

seasons during those years. Over the 2 years, Granger 

Drain transported an average of 42,000 lb/d (pounds 

per day) of suspended sediment, 860 lb/d of total 

nitrogen, and 78 lb/d of total phosphorus (table 6).

Nuisance algal growth in a Yakima River Basin agricultural drain.

Table 5. Results of mass-balance computations comparing streamflow and loads of total nitrogen and phosphorus in the reach of the Yakima River 

extending from river mile 103.7 to river mile 55, Yakima River Basin, Washington

[Tributaries include streams, agricultural drains, and wastewater treatment plants. Details of mass-balance computations appear in table C1. Streamflow, 

Concentration, Load: Measured at downstream end of reach; data for 1988 are from Pogue and others (1999). Fraction of flow and load: From tributaries 

discharging to the reach. Abbreviations: ft3/s, cubic feet per second; mg/L; milligrams per liter; lb/d, pounds per day; RM, river mile] 

Reach of 

Yakima River Year

Measured Inflow to reach

(ft3/s) Fraction 

of flow 

(percent)

Loading to reach

(lb/d) Fraction 

of load 

(percent)

Average 

concentration in 

tributary 

inflows

(mg/L)

Streamflow

(ft3

/s)

Concentration

(mg/L)

Load

(lb/d) River Tributaries

Unmeasured 

River Tributaries

Unmeasured

Total nitrogen

RM 103.7 –72 1988 513 1.5 4,100 163 235 115 45.7 440 4,000 -339 97.5 3.16

1999 1,270 1.03 7,060 725 337 209 26.5 993 4,770 1,290 67.6 2.63

RM 72 – 55 1988 972 1.9 10,000 513 403 56 41.5 4,100 6,960 -1,060 69.6 3.20

1999 2,050 1.41 15,600 1,270 421 359 20.5 7,060 5,340 3,200 34.2 2.35

Total phosphorus

RM 103.7 – 72 1988 513 0.10 280 163 235 115 45.7 44 335 -99 120 0.26

1999 1,270 .06 440 725 337 209 26.5 199 370 -131 84.3 .20

RM 72 –55 1988 972 .14 680 513 403 56 41.5 280 432 -32 63.5 .20

1999 2,050 .10 1,150 1,270 421 359 20.5 439 454 258 39.5 .20
Concentrations and Loads 35

Loads transported in the Yakima River at Kiona 

averaged 850,000 lb/d (about 430 tons per day) of 

suspended sediment, 20,000 lb/d of total nitrogen, and 

2,800 lb/d of total phosphorus. Generally, loads 

transported in Granger Drain and in the Yakima River 

at Kiona during water year 1999 were greater than 

those during 2000. In 1999, Granger Drain transported 

to the Yakima River a total of 13,000 tons of suspended 

sediment and 19 tons of total phosphorus, and in water 

year 2000 transported 3,000 tons of suspended 

sediment and 9.6 tons of total phosphorus. Total 

nitrogen loads, however, were 160 tons during both 

years. With daily streamflows averaging about 40 ft3/s 

each year, the higher loads of suspended sediment and 

total phosphorus corresponded to concentrations of 

suspended sediment and total phosphorus that were, on 

average, at least two times greater in 1999 than in 2000.

During water year 1999, the Yakima River at 

Kiona transported 200,000 tons of suspended sediment, 

3,800 tons of total nitrogen, and 570 tons of total 

phosphorus. In 2000, the river transported 110,000 tons 

of suspended sediment, 3,600 tons of total nitrogen, 

and 450 tons of total phosphorus. Loads in the Yakima 

River for all constituents in 1999 ranged from 4 to 45 

percent higher than in 2000 (table 6) and corresponded 

to streamflows that were about 14 percent higher in 

1999.

Table 6. Suspended-sediment and nutrient loads transported during water years 1999–2000 in Granger Drain and Yakima River at Kiona, Yakima River 

Basin, Washington

[Total nitrogen is based on the sum of total ammonia-plus-organic and nitrite-plus-nitrate nitrogen concentrations. Average Loads: Loads during irrigation 

season are averages for March 21–October 19, and during the non-irrigation season for October 20–March 20]

Sampling site

Annual total loads, in tons Average loads, in pounds per day

1999

water year

2000

water year

1999–2000

water years Irrigation season Non-irrigation season

Suspended sediment

Granger Drain 13,000 3,000 42,000 58,000 21,000

Yakima River at Kiona 200,000 110,000 850,000 1,130,000 468,000

Total nitrogen

Granger Drain 160 160 860 910 790

Yakima River at Kiona 3,800 3,600 20,000 20,000 21,000

Ammonia-plus-organic nitrogen

Granger Drain 30 21 140 190 75

Yakima River at Kiona 1,100 990 5,800 6,000 5,600

Nitrite-plus-nitrate nitrogen

Granger Drain 120 130 690 690 680

Yakima River at Kiona 2,700 2,600 14,000 13,000 16,000

Total phosphorus

Granger Drain 19 9.6 78 110 37

Yakima River at Kiona 570 450 2,800 2,900 2,600

Orthophosphate phosphorus

Granger Drain 4.3 4.4 24 33 11

Yakima River at Kiona 200 190 1,100 1,000 1,100
36 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Rinella and others (1992) determined that loads 

of suspended sediment and nutrients transported by the 

Yakima River were related to hydrologic events and 

annual mean streamflow. They showed that annual 

loads of suspended sediment, total nitrogen, and total 

phosphorus in the Yakima River at Kiona increased 

progressively as a function of annual mean streamflow 

for water years 1977 (low-flow year), 1980 (medianflow year), and 1974 (high-flow year). Loads of 

suspended sediment and nutrients in the Yakima River 

at Kiona were computed by Morace and others (1999) 

for water years 1988 and 1989, but they did not 

compare them with other years.

Loads of suspended sediment and nutrients in the 

Yakima River at Kiona were estimated for water years 

1999 and 2000 (table 6) using data collected from May 

1999 through January 2000 to calibrate the regression 

models. When the loads for water years 1999 and 2000 

are overlain on graphs showing the relation between 

average daily loads and annual mean streamflow 

during previous years (fig. 9), loads of suspended 

sediment, ammonia-plus-organic nitrogen, and total 

nitrogen in 1999 and 2000 (circles on fig. 9) are lower 

than those in other water years with similar annual 

mean streamflow. Because the data used to calibrate 

the regression models affect model results (see 

discussion in section "Effects of Calibration Period on 

Load Computation" and in Appendix B), loads for 

water years 1999 and 2000 also were estimated using 

calibration data from two other periods—May 1999 

through January 2000 plus part of water year 2001, and 

water years 1974–2001— to compare with the initial 

results. For most constituents, the difference between 

loads in water years 1999 and 2000 and loads in other 

water years with similar streamflow decreased when 

the models were calibrated using all available data 

from water years 1974 through 2001 (fig. 9).

The effect of calibration data on the load 

estimates introduced some uncertainty as to whether 

the loads of suspended sediment, ammonia-plusorganic nitrogen, and total nitrogen in water years 1999 

and 2000 are low compared to those in previous years 

with similar streamflows. From an analysis of the 

effects of calibration data on model results 

(Appendix B), it was determined that loads computed 

using calibration data collected from May 1999 

through January 2000 provided the best estimate of 

loads in the Yakima River at Kiona for water years 

1999 and 2000. Therefore, it seems reasonable to 

conclude that loads of the three constituents in water 

years 1999 and 2000 were indeed low when compared 

with corresponding loads in other water years with 

similar streamflow.

Because daily streamflow data for Moxee Drain 

were not available for all of water years 1999 and 2000, 

calendar year 1999 was the only annual period 

common to all three sites. Rinella and others (1992) 

stressed the importance of comparing loads among 

sites during the same water year or at least during 

periods with similar flow conditions, therefore 

suspended-sediment and nutrient loads for the three 

fixed sites were estimated for calendar year 1999 so 

that loads could be compared. In calendar year 1999, 

Moxee Drain transported an average of 28,000 lb/d of 

suspended sediment, 380 lb/d of total nitrogen, and 46 

lb/d of total phosphorus to the Yakima River (table 7). 

These loads were about half the average loads 

transported by Granger Drain during the same period. 

Average streamflows were similar for the two streams 

(40 ft3/s at Granger Drain and 35 ft3/s at Moxee Drain), 

therefore the difference in loads was due to differences 

in concentrations. Constituent concentrations in Moxee 

Drain ranged from about 40 to 60 percent less than 

concentrations in Granger Drain.

Except for nitrate, more nutrients and suspended 

sediment were transported in Moxee and Granger 

Drains during irrigation season than during the nonirrigation season (tables 6 and 7). There is more flow in 

the drains during irrigation season, and concentrations 

of suspended sediment and some nutrients are higher 

during irrigation season (figs. 7A and 7B). Loads of 

suspended sediment and total phosphorus in Moxee 

and Granger Drains were nearly four times higher 

during irrigation season; however, loads of nitrate were 

about the same in both seasons. There is little 

difference in nitrate loads between seasons because 

much of the nitrate enters the drains from subsurface 

field drains and in discharges from the shallow groundwater system. Higher concentrations of nitrate in the 

drains during non-irrigation season illustrate the 

influence of ground-water discharges on nitrate 

concentrations (figs. 7A and 7B). 
Concentrations and Loads 37

Figure 9. Average daily loads of suspended sediment and nutrients in the Yakima River at Kiona for selected water years from 1974–2001, 

Yakima River Basin, Washington. 

Loads for water years 1974, 1977, and 1980 were estimated by Rinella and others (1992). Loads for water years 1988 and 1989 were estimated by 

Morace and others (1999).

1,000 7,000 2,000 4,000 6,000

0

20,000

5,000

10,000

15,000

1,000 7,000 2,000 4,000 6,000 6,000

20,000

8,000

10,000

12,000

14,000

16,000

18,000

1,000 7,000 2,000 4,000 6,000

0

3,500

1,000

2,000

3,000

1,000 7,000 2,000 4,000 6,000 10,000

35,000

15,000

20,000

25,000

30,000

6,000

0

2,000

4,000

2,000

500

1,000

1,500

1,000 7,000 2,000 4,000 6,000 1,000 7,000 2,000 4,000 6,000

SUSPENDED SEDIMENT LOAD, IN TONS PER DAY

TOTAL NITROGEN LOAD, IN POUNDS PER DAY

AMMONIA-PLUS-ORGANIC NITROGEN LOAD,

NITRITE-PLUS-NITRATE NITROGEN LOAD,

TOTAL PHOSPHORUS LOAD, IN POUNDS PER DAY

ORTHOPHOSPHATE LOAD, IN POUNDS

PER DAY, AS P

ANNUAL MEAN STREAMFLOW, IN CUBIC FEET PER SECOND ANNUAL MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

IN POUNDS PER DAY, AS N

IN POUNDS PER DAY, AS N

EXPLANATION

Loads for water years 1974-1994; models

calibrated with data from 1974-2001

Loads for water years

1974, 1977, 1980, 1988-89

Loads for water years 1999-2000; models calibrated with data from 1999-2000 plus 2001

Loads for water years 1999-2000; models calibrated with data from 1974-2001

Loads for water years 1999-2000; models calibrated with data from May 1999-January 2000
38 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Loads of nutrients in the Yakima River at Kiona 

were similar during irrigation and non-irrigation 

season, generally differing by less than 20 percent 

(tables 6 and 7). This is because average streamflows 

and concentrations of nutrients were similar between 

the two seasons. Average streamflow during the 

irrigation season was within about 6 percent of the 

average streamflow during the non-irrigation season 

and average nutrient concentrations differed by less 

than 13 percent. The suspended-sediment load during 

irrigation season was about 60 percent larger than the 

load transported during the non-irrigation season. 

Large fractions of the total annual loads in the Yakima 

River were transported during the first half of the 

Table 7. Annual and seasonal average suspended-sediment and nutrient loads transported during calendar year 1999 in Moxee Drain, Granger Drain, 

and Yakima River at Kiona, Yakima River Basin, Washington

[Total nitrogen is based on the sum of total ammonia-plus-organic and nitrite-plus-nitrate nitrogen concentrations. Average loads: Loads during irrigation 

season are averages for March 21 – October 19; Loads during non-irrigation season are averages from January 1, 1999–March 20, 1999, plus October 20, 

1999–December 31, 1999. Abbreviations: ft3/s, cubic feet per second; mg/L, milligrams per liter]

Sampling site

Annual 

streamflow

(ft3/s)

Average 

concentration 

(mg/L)

Average loads, in pounds per day

Annual Irrigation season Non-irrigation 

season

Suspended sediment

Moxee Drain 35.4 116 28,000 46,000 1,200

Granger Drain 39.9 269 60,000 86,000 23,000

Yakima River at Kiona 4,820 41 1,240,000 1,630,000 690,000

Total nitrogen

Moxee Drain 35.4 2.1 380 430 290

Granger Drain 39.9 3.37 860 910 790

Yakima River at Kiona 4,820 1.11 22,000 21,000 23,000

Ammonia-plus-organic nitrogen

Moxee Drain 35.4 0.51 100 150 28

Granger Drain 39.9 0.78 160 220 75

Yakima River at Kiona 4,820 0.3 6,700 6,800 6,600

Nitrite-plus-nitrate nitrogen

Moxee Drain 35.4 1.59 280 310 260

Granger Drain 39.9 2.59 670 660 680

Yakima River at Kiona 4,820 0.81 15,000 14,000 17,000

Total phosphorus

Moxee Drain 35.4 0.24 46 67 18

Granger Drain 39.9 .47 96 140 37

Yakima River at Kiona 4,820 .12 3,500 3,600 3,400

Orthophosphate phosphorus

Moxee Drain 35.4 0.1 17 22 11

Granger Drain 39.9 .12 24 33 11

Yakima River at Kiona 4,820 .06 1,200 1,100 1,200
Concentrations and Loads 39

irrigation season. For example, 38 percent or more of 

the annual loads of suspended sediment, total nitrogen, 

ammonia-plus-organic nitrogen, total phosphorus, and 

orthophosphate were transported in the spring, from 

March through June (table 8).

In Moxee Drain, monthly loads of suspended 

sediment, ammonia-plus-organic nitrogen, and total 

phosphorus were highest from April through July 

(fig. 10A), and in Granger Drain, from May through 

August (fig. 10B). In the Yakima River at Kiona, 

transport of suspended sediment, total nitrogen, 

organic-plus-ammonia nitrogen, and total phosphorus 

peaked during January, May, June, and December 1999 

and in April 2000 (fig. 10C), coinciding with high 

streamflows at these times. Large loads of phosphorus 

and ammonia-plus-organic nitrogen at Kiona in the 

winter and spring of water years 1988 and 1989 also 

generally coincided with high streamflows generated 

by storm events and spring snowmelt (Pogue and 

others, 1999). The increase of suspended-sediment and 

nutrient concentrations because of re-suspension of 

sediments contributes to the large loads during high 

streamflows (Morace and others, 1999). 

Water from a series of detention ponds is discharged to Sunnyside Canal 

for reuse; prior to 1998, this water would have flowed untreated to Granger 

Drain.

Effect of Calibration Period on Load Computations

As noted by Rinella and others (1992), the 

accuracy of the load models and the estimated loads 

depends on collecting representative samples over the 

range of hydrologic conditions that control constituent 

transport. In practice, this is rarely achieved, so the 

actual errors associated with the load computations are 

undefined and the results depend on how well the 

calibration data represent the range of hydrologic 

conditions.

Table 8. Spring (March through June) suspended-sediment and nutrient loads and their fraction of the annual loads transported in the Yakima River at 

Kiona, Yakima River Basin, Washington

[Total nitrogen is based on the sum of unfiltered organic-plus-ammonia and filtered nitrite-plus-nitrate nitrogen concentrations]

Constituent

1999 water year 2000 water year

March–June load, 

in tons

March–June load, 

percentage of annual 

total

March–June load, 

in tons

March–June load, 

percentage of annual 

total

Suspended sediment 150,000 73 64,000 59

Total nitrogen 1,500 40 1,400 38

Ammonia-plus-organic nitrogen 540 48 380 38

Nitrite-plus-nitrate nitrogen 880 33 810 31

Total phosphorus 320 57 180 41

Orthophosphate phosphorus 85 42 74 39
40 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Rinella and others (1992) illustrated this effect 

by comparing loads of suspended sediment and 

nutrients for water years 1974, 1977, and 1980 that 

were estimated using load models calibrated with 

streamflow and concentration data from two different 

periods: (1) water years 1970-85, and (2) the specified 

water year (1974, 1977, or 1980) and 3 months prior to 

and following the specified water year. Relative percent 

differences in loads for a given water year that were 

computed using models calibrated with data from the 

two different periods ranged from 0.0 to 92.8 percent; 

the mean and median relative percent differences were 

22.4 and 18.5 percent, respectively.

The dependency of the model results on the 

calibration data is an important factor in assessing the 

validity of the observed departure of 1999–2000 wateryear loads of suspended sediment, ammonia-plusorganic nitrogen, and total nitrogen from the historical 

relation between streamflow and loads in the Yakima 

River at Kiona (fig. 9). To help assess the variation in 

loads calculated for the 1999–2000 water years that is 

caused by selection of calibration data, average daily 

loads of suspended sediment and nutrients in the 

Yakima River at Kiona were estimated using load 

models calibrated with streamflow and concentration 

data from three different periods: May 1999–January 

2000; May 1999–January 2000 plus January 2001–

September 2001; and October 1974–September 2001 

(table 9). Consistent with the findings of Rinella and 

others (1992), the calibration period did affect model 

results, so models calibrated with data for the period 

May 1999–January 2000 were selected to represent 

loads of suspended sediment and nutrients in the 

Yakima River at Kiona during water years 1999–2000. 

The selection of this calibration period was based on 

several criteria (discussed in Appendix B), including 

minimizing the differences between measured and 

predicted loads and between measured concentrations 

and concentrations predicted by the regression models.

Table 9. Estimates of average daily loads of suspended sediment and nutrients in the Yakima River at Kiona, computed using streamflow and 

concentration data from three different periods to calibrate the load models, Yakima River Basin, Washington, water years 1999–2000

[Bold values indicate loads used for data interpretation in this report. Abbreviations: ft3/s, cubic feet per second]

Water 

years

Annual 

mean 

discharge 

(ft3/s)

Suspended sediment, 

tons per day

Total nitrogen, 

pounds per day

Ammonia-plus-organic 

nitrogen as N,

pounds per day

Calibration period

May 1999–

Jan. 2000

May 1999–

Jan 2000

plus

Jan. 2001–

Sept. 2001

Oct. 1974 -

Sept. 2001

May 1999–

Jan. 2000

May 1999–

Jan 2000

plus

Jan. 2001–

Sept. 2001

Oct. 1974 -

Sept. 2001

May 1999–

Jan. 2000

May 1999–

Jan 2000

plus

Jan. 2001–

Sept. 2001

Oct. 1974 -

Sept. 2001

1999–2000 4,070 426 463 613 20,419 21,039 23,179 5,808 5,433 7,637

Water 

years

Annual 

mean 

discharge 

(ft3

/s)

Nitrite-plus-nitrate as N, 

pounds per day

Total phosphorus, 

pounds per day

Orthophosphate as P, 

pounds per day

Calibration period

May 1999–

Jan. 2000

May 1999–

Jan 2000

plus

Jan. 2001–

Sept. 2001

Oct. 1974 -

Sept. 2001

May 1999–

Jan. 2000

May 1999–

Jan 2000

plus

Jan. 2001–

Sept. 2001

Oct. 1974 -

Sept. 2001

May 1999–

Jan. 2000

May 1999–

Jan 2000

plus

Jan. 2001–

Sept. 2001

Oct. 1974 -

Sept. 2001

1999–2000 4,070 14,398 14,446 16,263 2,785 2,808 2,556 1,065 1,097 1,131
Concentrations and Loads 41

Suspended sediment

Total nitrogen

Nitrite-plus-nitrate

nitrogen

Ammonia-plus-organic

nitrogen

Total phosphorus

Orthophosphate

phosphorus

Streamflow

EXPLANATION

0

2,500,000

500,000

1,000,000

1,500,000

2,000,000

0

100

20

40

60

80

0

3,000

1,000

2,000

0

100

20

40

60

80

0

20,000

5,000

10,000

15,000

0

100

20

40

60

80

SUSPENDED SEDIMENT, IN POUNDS NITROGEN, IN POUNDS

STREAMFLOW, IN CUBIC FEET PER SECOND

PHOSPHORUS, IN POUNDS

O ND JFMAM J JA SO ND J FMAM J JA S

1998 1999 2000

STREAMFLOW, IN CUBIC FEET PER SECOND STREAMFLOW, IN CUBIC FEET PER SECOND

A. Moxee Drain at Birchfield Road at Union Gap

Figure 10. Monthly total suspended-sediment and nutrient loads, and daily streamflows in selected surface-water sites, Yakima 

River Basin, Washington.

(Shaded areas bracket the irrigation season.)
42 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Suspended sediment

Total nitrogen

Nitrite-plus-nitrate

nitrogen

Ammonia-plus-organic

nitrogen

Total phosphorus

Orthophosphate

phosphorus

Streamflow

EXPLANATION

6,000,000

0

2,000,000

4,000,000

40,000

0

10,000

20,000

30,000

8,000

100

0

20

40

60

80

100

0

20

40

60

80

0

2,000

4,000

6,000

100

0

20

40

60

80

O

O ND JFMAM J JA SO ND J FMAM J JA S

O ND JFMAM J JA SO ND J FMAM J JA S

ND JFMAM J JA SO ND J FMAM J JA S

1998 1999 2000

SUSPENDED SEDIMENT, IN POUNDS

STREAMFLOW, IN CUBIC FEET PER SECOND

1998 1999 2000

NITROGEN, IN POUNDS

STREAMFLOW, IN CUBIC FEET PER SECOND

1998 1999 2000

PHOSPHORUS, IN POUNDS

STREAMFLOW, IN CUBIC FEET PER SECOND

B. Granger Drain at Granger

Figure 10.—Continued.
Concentrations and Loads 43

Suspended sediment

Total nitrogen

Nitrite-plus-nitrate

nitrogen

Ammonia-plus-organic

nitrogen

Total phosphorus

Orthophosphate

phosphorus

Streamflow

EXPLANATION

0

100,000

60,000

40,000

20,000

80,000

13,000

2,000

4,000

6,000

8,000

10,000

12,000

0

1,000,000

200,000

400,000

600,000

800,000

0

13,000

2,000

4,000

6,000

8,000

10,000

12,000

0

300,000

100,000

200,000

0

13,000

2,000

4,000

6,000

8,000

10,000

12,000

0

O

O ND JFMAM J JA SO ND J FMAM J JA S

O ND JFMAM J JA SO ND J FMAM J JA S

ND JFMAM J JA SO ND J FMAM J JA S

1998 1999 2000

SUSPENDED SEDIMENT, IN TONS

STREAMFLOW, IN CUBIC FEET PER SECOND

1998 1999 2000

NITROGEN, IN POUNDS

STREAMFLOW, IN CUBIC FEET PER SECOND

1998 1999 2000

PHOSPHORUS, IN POUNDS

STREAMFLOW, IN CUBIC FEET PER SECOND

C. Yakima River at Kiona

Figure 10.—Continued.
44 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

TRENDS IN CONCENTRATIONS

Trends in turbidity and concentrations of 

suspended solids, total nitrogen, nitrate, and total 

phosphorus were assessed using data collected by the 

BOR, RSBOJC, and Ecology at nine sites 

corresponding to, or near, those sampled by the USGS 

(table 10). The seasonal Kendall test (Crawford and 

others, 1983) was used analyze for trends in 

concentration data provided by the BOR and Ecology 

for water years 1991–2000. Trends in streamflow 

measured at the time of sample collection also were 

determined. Because data collected by the RSBOJC 

covered a shorter period (1997–2001), time-series 

graphs of concentrations were inspected to detect 

potential trends, but no statistical tests were performed 

using their data.

Table 10. Proximity of surface-water sites sampled during 1999–2000 by the U.S. Geological Survey to sites sampled by the Bureau of Reclamation, RozaSunnyside Board of Joint Control, and Washington State Department of Ecology in the Yakima River Basin, Washington

[Degrees, minutes, seconds: Rounded to whole seconds. River mile: Approximate for trend-assessment sites that do not correspond to USGS sites. 

Abbreviations: USGS, U.S. Geological Survey; BOR, Bureau of Reclamation; RSBOJC, Roza-Sunnyside Board of Joint Control; Ecology, Washington State 

Department of Ecology]

USGS sampling site 1999–2000 Site assessed for trends

Site name and 

USGS identification No.

(map identification No. 

in fig. 6)

Latitude Longitude

River 

mile

Site name and

identification No.

Latitude Longitude

River 

mile Agency (degrees, minutes, 

seconds)

(degrees, minutes, 

seconds)

Wilson Creek above Cherry 

Creek at Thrall 

12484100 (201)

46 55 35 120 30 01 1.1 Wilson Creek at Thrall Road

YAV146

46 55 36 120 30 02 1.1 BOR

Cherry Creek at Thrall 

12484480 (202)

46 55 34 120 29 51 0.1 Cherry Creek SE 1/4, Section 

29, R.17N., T.19E.

46 56 15 120 29 00 1.4 BOR

YAV022

Wide Hollow Creek near 

mouth at Union Gap 

12500445 (206)

46 32 35 120 28 27 0.8 Wide Hollow Creek at West 

Washington Avenue 

YAV107

46 34 16 120 31 56 4 BOR

Moxee Drain at Birchfield 

Road near Union Gap 

12500420 (69)

46 32 46 120 26 13 1.4 Moxee Drain at Birchfield 

Road 

YAV104

46 32 47 120 26 14 1.4 BOR

Granger Drain at Granger 

12505450 (67)

46 20 37 120 11 09 0.8 Granger Drain at Highway 

223 above Granger

YAV137

46 20 36 120 11 03 0.8 BOR, 

RSBOJC

Sulphur Creek Wasteway near 

Sunnyside 

12508850 (215)

46 15 03 120 01 07 0.8 Sulfur Creek Wasteway

none

46 15 03 120 01 07 0.8 RSBOJC

Spring Creek at Hess Road 

near Prosser 

461404119410400 (217)

46 14 04 119 41 04 0.4 Spring Creek

none

46 14 04 119 41 04 0.4 RSBOJC

Snipes Creek below Chandler 

Canal near Prosser 

461414119404200 (218)

46 14 15 119 40 42 0.4 Snipes Creek at Old Inland 

Empire Road1

YAV139

46 14 03 119 41 02 0.7 BOR, 

RSBOJC

Yakima River at Kiona 

12510500 (219)

29.9 Yakima River at Kiona

37A090

46 15 13 119 28 37 29.9 Ecology

1Location sampled by BOR. RSBOJC and USGS sampled below Chandler Canal.
Trends in Concentrations 45

Trend statistics were computed using both 

unadjusted (unmodified) concentration data and flowadjusted concentration data (see section "Methods" for 

an explanation of the procedure used to compute flowadjusted concentrations). In this report, inferences 

about trends in concentrations usually are based on 

statistics obtained using flow-adjusted concentration 

data, unless streamflow data were not available to 

compute flow-adjusted concentrations. Trend statistics 

computed using both unadjusted and flow-adjusted 

concentrations are reported because they facilitate 

interpretation of the results. For example, if statistics 

indicate significant increases in streamflow and 

unadjusted concentrations of a constituent but no 

significant change in flow-adjusted concentrations, 

then the increase in unadjusted concentrations is not 

independent of streamflow. If the indicated increase in 

streamflow represented an actual trend, then it would 

be correct to conclude that constituent concentrations 

were increasing over time along with streamflow, but 

not independent of streamflow. If the indicated increase 

in streamflow did not represent an actual trend, but was 

simply an artifact of the sample collection schedule, 

then it would be incorrect to conclude that constituent 

concentrations were increasing over time.

 The summary of trend statistics for 1991–2000 

indicates that some of the factors affecting constituent 

transport to surface water may be common to multiple 

subbasins (table 11). For example, concentrations of 

nitrate and total nitrogen increased in five of six 

streams and drains while concentrations of suspended 

solids and total phosphorus either did not change or 

decreased. This difference is consistent with no change, 

or a decrease, in amounts of suspended solids and 

phosphorus transported to surface water in runoff and 

an increase in the amount of nitrate transported to 

surface water from ground-water discharges and 

subsurface drains, as discussed in previous sections of 

the report. 

Some agreement was found between trend 

statistics for the 1991–2000 data and graphical analysis 

of data collected 1997–2001 by the RSBOJC (as shown 

in subsequent figures), in that the RSBOJC data show a 

decrease in turbidity and concentrations of suspended 

solids and total phosphorus in some drains and streams 

receiving agricultural return flows. The RSBOJC data 

also suggest that in some instances concentrations of 

nitrate in streams and drains have leveled off or may be 

decreasing. Trends in streamflow, turbidity, and 

concentrations of nutrients and suspended solids at 

individual sampling sites are discussed in more detail 

in this section.

Differences between statistics for turbidity, 

which either did not change or increased, and statistics 

for concentrations of suspended solids, which either 

did not change or decreased (table 11), were somewhat 

unexpected because previous work showed that they 

are highly correlated in the Yakima River Basin (Joy 

and Patterson, 1997). However, significant trends in 

concentrations of these constituents were small, as 

indicated by the magnitude of their trend slopes 

(table 11), and the relation between turbidity and 

concentrations of suspended solids is affected by 

changes in the ratio of suspended mineral particles to 

fine particulate organic matter (Packman and others, 

2000). An increase in low-mass fine particulate organic 

matter can increase turbidity without having much 

effect on the concentration of suspended solids.

Another factor complicating the comparison 

between statistics for turbidity and suspended solids is 

the use of the analytical method that reports suspendedsediment concentrations as concentrations of total 

suspended solids (TSS). All suspended-sediment 

(solids) data used for trend analyses in this report were 

produced using the TSS analytical method, rather than 

the traditional suspended-sediment concentration 

(SSC) analysis method used to determine 

concentrations of suspended sediment in samples 

collected by the USGS. An evaluation of data collected 

and analyzed by the USGS and others has shown that 

the variation in TSS analytical results is considerably 

larger than that for SSC analytical results (Glysson and 

Gray, 2002). A TSS analysis generally entails 

withdrawal of an aliquot of the original sample for 

subsequent analysis, whereas the SCC analysis uses the 

entire sample for analysis. The withdrawal step, usually 

done by pipette or pouring, is an additional source of 

variation in the TSS analysis.
46 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Table 11. Trend statistics for streamflow, turbidity, and concentrations of suspended solids, total nitrogen, nitrite-plus-nitrate nitrogen, and total 

phosphorus for data collected during the 1991–2000 water years at surface-water sites in the Yakima River Basin, Washington

[Seasonal Kendall tests were performed using 12 seasons, and trends are considered significant if p-values are less than or equal to 0.1. All data were provided 

by Bureau of Reclamation except those for the Yakima River at Kiona, which were provided by Washington State Department of Ecology. Stream discharge:

Discharge at the time of sample collection. Turbidity FTU, formazin turbidity unit; nephelometric turbidity units (NTU) for Yakima River at Kiona. 

Abbreviations: unadj, unadjusted concentration data tested for trends; adj, flow-adjusted concentrations tested for trends. ft3/s, cubic feet per second; mg/L, 

milligrams per liter; nt, no trend; <, less than; SE, southeast; N, north; E, east; –, unable to compute because streamflow was not determined]

Site name

and trend

(map identification No. 

in fig. 6)

Stream 

discharge 

(ft3/s)

Turbidity

FTU

Suspended solids 

(mg/L)

Total nitrogen 

(mg/L)

Nitrate as N 

(mg/L)

Total phosphorus 

(mg/L)

unadj adj unadj adj unadj adj unadj adj unadj adj

Wilson Creek above Cherry Creek at Thrall (201)

Trend up nt nt down down up up up up down down

p-value 0.01 0.87 0.66 0.03 0.01 0.01 0.03 0.01 <0.01 0.03 0.08

Slope, in units per year 5.0 <.01 -.02 -.75 -.81 .020 .022 .017 .021 -.002 -.003

Cherry Creek at SE 1/4, Section 29, T. 17N, R. 19E

Trend up up nt nt down up up nt up nt nt

p-value 0.01 <0.01 0.11 0.95 0.06 0.05 <0.01 0.87 0.01 0.73 0.71

Slope, in units per year 7.0 .33 .23 <.01 -1.1 .033 .047 <.001 .022 <-.001 -.001

Wide Hollow Creek at West Washington Avenue

Trend no data up – nt – up – up – nt –

p-value – <0.01 – 0.89 – <0.01 – <0.01 – 0.67 –

Slope, in units per year – .17 – <.01 – .065 – .050 – <-.001 –

Moxee Drain at Birchfield Road near Union Gap (69)

Trend nt nt nt down down up up up up down down

p-value 0.40 0.16 0.11 <0.01 0.02 0.04 0.07 <0.01 0.01 <0.01 <0.01

Slope, in units per year -.17 -.14 -.42 -1.9 -3.3 .050 .058 .048 .038 -.010 -.009

Granger Drain at Highway 223

Trend down nt nt down nt up up up up down nt

p-value 0.10 0.39 0.73 0.01 0.27 <0.01 0.07 <0.01 <0.01 <0.01 0.12

Slope, in units per year -.80 -.29 .22 -6.9 -3.1 .11 .084 .16 .13 -.029 -.016

Snipes Creek at Old Inland Empire Road

Trend nt up up nt nt nt nt nt nt nt nt

p-value .56 <.01 .01 .24 .91 .19 .27 .82 .86 .73 .86

Slope, in units per year .67 .20 .22 .25 <.01 .020 .035 <.001 .004 <.001 <.001

Yakima River at Kiona1 (219)

Trend up up up up nt down nt nt up up up

p-value <0.01 <0.01 <0.01 0.04 0.26 0.10 0.16 0.82 0.01 0.06 0.01

Slope, in units per year 142 .65 .42 .90 .35 -.034 -.013 -.004 .27 .0032 .0035

1Total nitrogen samples collected 1994–2000 water years at Yakima River at Kiona.
Trends in Concentrations 47

Wilson Creek

An upward trend in streamflow (table 11, 

fig. 11), coupled with downward trends in 

corresponding concentrations of suspended solids and 

total phosphorus (table 11, fig. 12), suggest some 

reduction in the transport of sediment to Wilson Creek. 

In contrast, concentrations of both total nitrogen and 

nitrate have increased slowly at a similar rate 

(table 11), which is an indication that the increase in 

concentrations of total nitrogen is caused by an 

increase in concentrations of nitrate. 

Nitrate concentrations in Wilson Creek, which 

were usually 1 mg/L or less, are low compared with 

other streams and drains sampled during this study. For 

example, concentrations of nitrate in nearby Cherry 

Creek ranged between 0.5 and 3.0 mg/L (see fig. 13). 

Low concentrations of nitrate in Wilson Creek 

probably can be attributed to several factors (Anna 

Lael, Kittitas County Conservation District, oral 

commun., October 2002). Only about 19 percent of the 

land in the Wilson Creek Basin is used for agricultural 

purposes, compared with about 27 percent in the 

Cherry Creek Basin. Also, the agricultural land in the 

Cherry Creek Basin is more extensively developed, 

with deeply incised drains and ditches that discharge 

shallow ground water to the creek.

In 2000, EQIP-sponsored BMPs were used on 

only 2.8 percent of the cropland in the Wilson Creek 

Basin (table 1). However, if the trend statistics showing 

a decrease in concentrations of suspended solids and 

total phosphorus are an indication of less erosion and 

transport of sediment to Wilson Creek, the 

improvement may be the result of the widespread use 

of polyacrylamide (PAM) on cropland in the Basin 

(Anna Lael, Kittitas County Conservation District, oral 

commun., April, 2002). Data on the use of PAM are not 

included in table 1.

1990

0

800

100

200

300

400

500

600

700

STREAMFLOW, IN CUBIC FEET PER SECOND

300

0

50

100

150

200

250

SUSPENDED SOLIDS, IN

MILLIGRAMS PER LITER

4

0

1

2

3

NITRATE PLUS NITRITE, IN

MILLIGRAMS PER LITER AS N

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

CALENDAR YEAR

0 800 100 200 300 400 500 600 700

STREAMFLOW, IN CUBIC FEET PER SECOND

Figure 11. Temporal variations in streamflow and variations in concentrations of suspended solids and nitrate with streamflow in Wilson Creek above 

Cherry Creek at Thrall, Yakima River Basin, Washington, 1991–2000 water years. 

(Data provided by the Bureau of Reclamation.)
48 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

0

100

20

40

60

80

TURBIDITY, IN FORMAZIN UNITS

6

0

1

2

3

4

5

TOTAL NITROGEN, IN MILLIGRAMS PER LITER

1990

0

1. 0

0. 2

0. 4

0. 6

0. 8

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

0

300

50

100

150

200

250

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0

6

1

2

3

4

5

NITRITE PLUS NITRATE,

IN MILLIGRAMS PER LITER AS N

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

CALENDAR YEAR

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

CALENDAR YEAR

Figure 12. Temporal variations in turbidity and concentrations of suspended solids, total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in 

Wilson Creek above Cherry Creek at Thrall, Yakima River Basin, Washington, 1991–2000 water years. 

(Data provided by the Bureau of Reclamation.)
Trends in Concentrations 49

Cherry Creek

Small, but significant, increases in streamflow 

and concentrations of total nitrogen in Cherry Creek 

from 1991 to 2000 (table 11) appear to be part of 

upward trends starting in 1995 (figs. 13 and 14). A 

significant increase in flow-adjusted concentrations of 

total nitrogen suggests that the increase in 

concentrations is independent of the increase in 

streamflow. The increase in concentrations of total 

nitrogen at a rate of 0.047 mg/L per year is probably 

caused, in part, by an upward trend in concentrations of 

nitrate, which increased at a rate of 0.022 mg/L per 

year (table 11).

The trend statistics computed using flowadjusted concentrations indicate a significant decrease 

in concentrations of suspended solids in Cherry Creek 

but no change in concentrations of total phosphorus 

(table 11). It is not known if the decrease in 

concentrations of suspended solids in Cherry Creek is 

related to the application of BMPs. By the end of 2000, 

EQIP-sponsored BMPs were applied to 5.8 percent of 

cropland in the Cherry Creek Basin (table 1). 

Conversion of rill-irrigation of timothy hay and alfalfa 

to sprinkler and gated-pipe irrigation methods 

represents most of the 5.8 percent. Also, like Wilson 

Creek, the Cherry Creek Basin is in the Kittitas 

Conservation District, where there has been 

widespread use of PAM on cropland (Anna Lael, 

Kittitas County Conservation District, oral commun., 

April, 2002).

2,000

250

500

750

1,000

1,250

1,500

1,750

STREAMFLOW, IN CUBIC FEET PER SECOND

1990 2001 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

0 1,000 0 100 200 300 400 500 600 700 800 900

STREAMFLOW, IN CUBIC FEET PER SECOND

NITRATE PLUS NITRITE, IN

MILLIGRAMS PER LITER AS N

0

200

50

100

150

SUSPENDED SOLIDS, INMILLIGRAMS PER LITER

Not shown: (streamflow 1,600;

suspended solids 1,390)

Not shown: (streamflow 1,600,

nitrite+nitrate 0.7)

0

0

3

1

2

Figure 13. Temporal variations in streamflow and variations in concentrations of suspended solids and nitrite-plus-nitrate nitrogen with streamflow in 

Cherry Creek at Southeast 1/4, Section 29, Township 17N, Range 19E, Yakima River Basin, Washington, 1991–2000 water years.

(Data provided by Bureau of Reclamation.)
50 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

0

100

20

40

60

80

TURBIDITY, IN FORMAZIN UNITS

0

300

50

100

150

200

250

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0

6

1

2

3

4

5

TOTAL NITROGEN, IN MILLIGRAMS PER LITER

0

6

1

2

3

4

5

NITRITE PLUS NITRATE,

IN MILLIGRAMS PER LITER AS N

1990 2001 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

1990 2001 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

0. 2

0. 4

0. 6

0. 8

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

Not shown: Turbidity = 370

January 31, 1995 Not shown: Suspended solids = 1,390

January 31, 1995

0

1. 0

Not shown: Total phosphorus = 2.2

January 31, 1995

Figure 14. Temporal variations in turbidity and concentrations of suspended solids, total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in 

Cherry Creek Southeast 1/4, Section 29, Township 17N, Range 19E, Yakima River Basin, Washington, 1991–2000 water years. 

(Data provided by Bureau of Reclamation.)

Wide Hollow Creek

No streamflow data were available for Wide 

Hollow Creek, so trend statistics were based on tests 

using unadjusted concentration data. Results indicate 

that concentrations of nitrate and total nitrogen 

increased at similar rates (table 11), and concentrations 

of both constituents form two distinct trend lines 

(fig. 15), with lower concentrations occurring during 

the irrigation season when canal water in the creek 

dilutes nitrate discharged to Wide Hollow Creek.
Trends in Concentrations 51

0

50

10

20

30

40

TURBIDITY, IN FORMAZIN UNITS

0

100

20

40

60

80

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0

8

1

2

3

4

5

6

7

TOTAL NITROGEN, IN MILLIGRAMS PER LITER

0

8

1

2

3

4

5

6

7

NITRITE PLUS NITRATE,

IN MILLIGRAMS PER LITER AS N

1990

0

1. 0

0. 2

0. 4

0. 6

0. 8

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

CALENDAR YEAR

1990 2001 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

Not shown: Total phosphorus = 1.7

January 31, 1995

Figure 15. Temporal variations in turbidity and concentrations of suspended solids, total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in 

Wide Hollow Creek at West Washington Avenue, Yakima River Basin, Washington, 1991–2000 water years.

(Data provided by the Bureau of Reclamation.)

Higher concentrations of nitrate in Wide Hollow Creek 

during the non-irrigation season are indicative of a 

ground-water source, and the trend showing increasing 

concentrations in the creek means that the 

concentration of nitrate in ground water discharging to 

the creek is increasing.

Like nitrate, concentrations of total phosphorus 

in Wide Hollow Creek also are lower during the 

irrigation season, indicating dilution of phosphorus by 

canal water. It is not known if the source of phosphorus 

is from ground water or some other source, but there 

was no overall trend in concentrations (table 11).
52 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

No BMP data were available for the Wide 

Hollow Creek Basin, but the North Yakima 

Conservation District has reported the use of PAM on 

cropland in the Basin (Mike Tobin, North Yakima 

Conservation District, oral commun., April 2002).

Moxee Drain

Significant downward trends in concentrations of 

suspended solids and total phosphorus (table 11) are 

probably indicative of the widespread use of BMPs in 

the Moxee subbasin (table 1). The dominant EQIPsponsored BMP in Moxee subbasin is the conversion of 

rill irrigation of hops to drip irrigation. By the end of 

1999, this practice accounted for more than 90 percent 

of EQIP-sponsored BMPs in the Basin, and by the end 

of 2001, the percentage of drip-irrigated hops had 

increased from less than 1 to 63 percent. These BMPs, 

coupled with the earlier adoption of sprinkler 

technology in orchards and the use of PAM on rillirrigated hops, have markedly lowered sediment 

deliveries to Moxee Drain (Mike Tobin, North Yakima 

Conservation District, oral commun., April, 2002).

Like many of the agricultural drains sampled 

during this study, the inverse relation between 

streamflow and concentrations of nitrate in Moxee 

Drain (fig. 16) indicates that nitrate, derived from 

ground-water discharges, is diluted during the 

irrigation season by canal water in the drain. This 

results in a seasonal pattern with higher concentrations 

of nitrate and total nitrogen in Moxee Drain during the 

non-irrigation season, reflected by the upper row of 

data points in figure 17. Trend statistics (table 11) 

indicate that concentrations of nitrate and total nitrogen 

in Moxee Drain are increasing, and inspection of the 

trend plots shown in figure 17 indicate that the 

increasing trends are a result of the increase in 

concentrations of nitrate during the non-irrigation 

season.

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

CALENDAR YEAR

0

100

20

40

60

80

STREAMFLOW, IN CUBIC FEET PER SECOND

0

800

100

200

300

400

500

600

700

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0 100 20 40 60 80

STREAMFLOW, IN CUBIC FEET PER SECOND

0

10

2

4

6

8

NITRATE PLUS NITRITE, IN M

ILLIGRAMS PER LITER AS N

1990

Figure 16. Temporal variations in streamflow and variations in concentrations of suspended solids and nitrite-plus-nitrate nitrogen with streamflow in 

Moxee Drain at Birchfield Road near Union Gap, Yakima River Basin, Washington, 1991–2000 water years. 

(Data provided by the Bureau of Reclamation.)
Trends in Concentrations 53

0

100

20

40

60

80

TURBIDITY, IN FORMAZIN UNITS

0

800

100

200

300

400

500

600

700

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0

10

1

2

3

4

5

6

7

8

9

TOTAL NITROGEN, IN MILLIGRAMS PER LITER

0

10

1

2

3

4

5

6

7

8

9

NITRITE PLUS NITRATE,

IN MILLIGRAMS PER LITER AS N

1990 2001 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

1990 2001 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

0

2. 0

0. 5

1. 0

1. 5

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

Figure 17. Temporal variations in turbidity and concentrations of suspended solids, total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in 

Moxee Drain at Birchfield Road near Union Gap, Yakima River Basin, Washington, 1991–2000 water years.

(Data provided by the Bureau of Reclamation.)
54 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Granger Drain

Trend statistics for 1991–2000 indicate a 

decrease in streamflow, an increase in concentrations 

of total nitrogen and nitrate, and no trend in flowadjusted concentrations of suspended solids and total 

phosphorus (table 11, figs. 18 and 19).

Trend statistics for 1991–2000 may not be 

indicative of recent improvements in the quality of 

water in Granger Drain because the implementation of 

BMPs in the Basin has been recent. After a slow 

increase during the years 1996-99, the acres under new 

BMPs nearly tripled to 14.6 percent by the end of 2001 

(table 1). The positive effects of the BMPs may be 

indicated by RSBOJC data showing no change in 

streamflow but a consistent decrease in concentrations 

of suspended solids and total phosphorus in 1997-99, 

followed by a large decrease in 2000-01 (figs. 20

and 21). Also, the RSBOJC data suggest that 

concentrations of nitrate and total nitrogen, which 

increased over the period 1991–2000, have leveled off 

and may be decreasing.

According to William Rice (Roza-Sunnyside 

Joint Board of Control, oral commun., March 2002), 

the BMP data in table 1 do not include many of the 

management practices that are in place in the Basin. 

BMPs applied but not reflected in table 1 include some 

changes in the way irrigation water is applied, 

diversion of irrigation runoff to ponds and wetlands 

where sediments settle out before the runoff is released 

to drains, and the addition of polyacrylamide (PAM) to 

irrigation water to increase the cohesiveness of soil 

particles, making the soil less subject to erosion.

Another project designed to improve the quality 

of water in Granger Drain was the construction of a 

12.5-acre wetland by RSBOJC (see photo). The 

wetland, which can capture up to 2 ft3/s of incoming 

flow, diverts the water through stands of plants 

including cattail and bulrush, which reduce sediment 

load by lowering flow velocities and promote uptake of 

nutrients. Currently, 0.6 ft3/s of agricultural runoff is 

being diverted to the wetland and retained for 9 to 10 

days. Preliminary data show reductions in turbidity and 

concentrations of fecal coliform, total phosphorus, and 

nitrite-plus-nitrate (Mark Barnett, Roza Irrigation 

District, written commun., November 2001).

The Roza-Sunnyside Board of Joint Control routes agricultural-return 

flow into two separate networks of inter-connected ponds (constructed 

wetland) to reduce sediment and nutrients in Yakima River.
Trends in Concentrations 55

1990 2001 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

0

200

50

100

150

STREAMFLOW, IN CUBIC FEET PER SECOND

0

1,000

100

200

300

400

500

600

700

800

900

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0 100 20 40 60 80

STREAMFLOW, IN CUBIC FEET PER SECOND

0

8

2

4

6

NITRATE PLUS NITRITE, IN

MILLIGRAMS PER LITER AS N

Figure 18. Temporal variations in streamflow and variations in concentrations of suspended solids and nitrite-plus-nitrate nitrogen with streamflow in 

Granger Drain at Highway 223 near Granger, Yakima River Basin, Washington, 1991–2000 water years. 

(Data provided by the Bureau of Reclamation.)
56 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

0

250

50

100

150

200

TURBIDITY, IN FORMAZIN UNITS

0

1,200

100

200

300

400

500

600

700

800

900

1,000

1,100

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0

20

2

4

6

8

10

12

14

16

18

TOTAL NITROGEN, IN MILLIGRAMS PER LITER

0

20

2

4

6

8

10

12

14

16

18

NITRITE PLUS NITRATE,

IN MILLIGRAMS PER LITER AS N

1990 2001 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

1990 2001 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

0

4.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

Not shown: Total nitrogen = 26

January 31, 1995

Figure 19. Temporal variations in turbidity and concentrations of suspended solids, total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in 

Granger Drain at Highway 223 near Granger, Yakima River Basin, Washington, 1991–2000 water years.

(Data provided by the Bureau of Reclamation.)
Trends in Concentrations 57

STREAMFLOW, IN CUBIC FEET PER SECOND

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

1997 2002 1998 1999 2000 2001

CALENDAR YEAR

0

200

50

100

150

0

1,000

100

200

300

400

500

600

700

800

900

0 100 20 40 60 80

10

0

2

4

6

8

NITRATE PLUS NITRITE, IN

MILLIGRAMS PER LITER AS N

Figure 20. Temporal variations in streamflow and variations in concentrations of suspended solids and nitrite-plus-nitrate nitrogen with streamflow in 

Granger Drain at Granger, Yakima River Basin, Washington, 1997–2001.

(Data provided by Roza-Sunnyside Board of Joint Control.)
58 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

0

250

50

100

150

200

TURBIDITY, IN NEPHELOMETRIC UNITS

0

1,200

100

200

300

400

500

600

700

800

900

1,000

1,100

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0

10

2

4

6

8

TOTAL NITROGEN, IN MILLIGRAMS PER LITER

0

10

2

4

6

8

NITRITE PLUS NITRATE,

IN MILLIGRAMS PER LITER AS N

1997 2002 1997 1998 1999 2000 2001

CALENDAR YEAR

1997 2002 1998 1999 2000 2001

CALENDAR YEAR

0

2.0

0.5

1.0

1.5

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

Figure 21. Temporal variations in turbidity and concentrations of suspended solids, total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in 

Granger Drain at Granger, Yakima River Basin, Washington, 1997–2001.

(Data provided by Roza-Sunnyside Board of Joint Control.)
Trends in Concentrations 59

Sulphur Creek Wasteway

Data collected over a 10-year period were not 

available to compute trend statistics for Sulphur Creek 

Wasteway, but an inspection of graphs showing 

temporal variations in streamflow (fig. 22) and 

concentration data (fig. 23) suggests that even though 

streamflow measured during irrigation season (the 

higher flows shown on figure 22) appears to be 

increasing, concentrations of suspended solids are 

decreasing. Concentrations of total nitrogen, nitrate, 

and total phosphorus also appear to be decreasing. 

Similar to some of the other streams, concentrations of 

nitrate and total nitrogen form two distinct trend lines, 

with lower concentrations occurring during the 

irrigation season when canal water in the wasteway 

dilutes nitrate discharged to Sulphur Creek Wasteway 

from field drains and ground water. From 1996 through 

2000, there has been a consistent increase in the use of 

BMPs in the Sulphur Creek Basin (table 1).

A small tributary to Sulphur Creek Wasteway receives runoff from rillirrigated corn.

1997 2002 1997 1998 1999 2000 2001

CALENDAR YEAR

0

800

100

200

300

400

500

600

700

STREAMFLOW, IN CUBIC FEET PER SECOND

0

400

100

200

300

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0 800 100 200 300 400 500 600 700

STREAMFLOW, IN CUBIC FEET PER SECOND

0

10

2

4

6

8

NITRATE PLUS NITRITE, IN

MILLIGRAMS PER LITER AS N

Figure 22. Temporal variations in streamflow and variations in concentrations of suspended solids and nitrite-plus-nitrate nitrogen with streamflow in 

Sulphur Creek Wasteway near Sunnyside, Yakima River Basin, Washington, 1997–2001. 

(Data provided by Roza-Sunnyside Board of Joint Control.)
60 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

250

0

50

100

150

200

TURBIDITY, IN NEPHELOMETRIC UNITS

0

400

100

200

300

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0

10

2

4

6

8

TOTAL NITROGEN, IN MILLIGRAMS PER LITER

0

10

2

4

6

8

NITRITE PLUS NITRATE,

IN MILLIGRAMS PER LITER AS N

1997 2002 1997 1998 1999 2000 2001

CALENDAR YEAR

1997 2002 1997 1998 1999 2000 2001

CALENDAR YEAR

0

1.0

0.2

0.4

0.6

0.8

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

Figure 23. Temporal variations in turbidity and concentrations of suspended solids, total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in 

Sulphur Creek Wasteway near Sunnyside, Yakima River Basin, Washington, 1997–2001. 

(Data provided by Roza-Sunnyside Board of Joint Control.)
Trends in Concentrations 61

Spring and Snipes Creeks

Data collected over a 10-year period were not 

available to compute trend statistics for Spring Creek, 

and no BMP data were available for the drainage basin. 

Graphs showing temporal variations in streamflow 

(fig. 24A), turbidity (fig. 25A), and concentrations of 

suspended solids and nutrients (fig. 25A) suggest that 

there might be a slight decrease in turbidity and 

concentrations of suspended solids. No change is 

evident in concentrations of nitrate, total nitrogen, and 

total phosphorus.

Ten-year trend statistics for Snipes Creek 

indicate an upward trend in turbidity and no trend in 

concentrations of suspended solids and nutrients 

(table 11). Ten-year records for Snipes Creek (figs. 24B

and 25B) are complemented by data collected 1997–

2001 by the RSBOJC (figs. 24C and 25C). The 

RSBOJC data indicate that concentrations of nitrate 

and total nitrogen may be decreasing during the nonirrigation season when concentrations are higher. No 

BMP data were available for the Snipes Creek 

subbasin. Turbidity and concentrations of suspended 

solids and total phosphorus also appear to be 

decreasing. 

1997 2002 1997 1998 1999 2000 2001

CALENDAR YEAR

0

100

20

40

60

80

STREAMFLOW, IN CUBIC FEET PER SECOND

400

0

100

200

300

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0 100 20 40 60 80

STREAMFLOW, IN CUBIC FEET PER SECOND

0

10

2

4

6

8

NITRATE PLUS NITRITE, INMILLIGRAMS PER LITER AS N

A. Spring Creek at mouth at Whitstran

Figure 24. Temporal variations in streamflow and variations in concentrations of suspended solids and nitrite-plus-nitrate nitrogen with streamflow in 

selected surface-water sites in Yakima River Basin, Washington, 1997–2001. 

(Data provided by Roza-Sunnyside Board of Joint Control.)
62 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

1990 2001 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

0

200

50

100

150

STREAMFLOW, IN CUBIC FEET PER SECOND

500

0

50

100

150

200

250

300

350

400

450

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0 200 20 40 60 80 100 120 140 160 180

STREAMFLOW, IN CUBIC FEET PER SECOND

0

6

1

2

3

4

5

Not shown: streamflow 38

suspended solids 1,120

NITRATE PLUS NITRITE, IN

MILLIGRAMS PER LITER AS N

B. Snipes Creek at Old Inland Empire Road

(Data provided by the Bureau of Reclamation)

C. Snipes Creek at mouth at Whitstran

(Data provided by Roza-Sunnyside Board of Joint Control)

1997 2002 1997 1998 1999 2000 2001

0

200

50

100

150

STREAMFLOW, IN

CUBIC FEET PER SECOND

0 0

200

50

100

150

SUSPENDED SOLIDS, IN

MILLIGRAMS PER LITER

0 200 50 100 150

STREAMFLOW, IN CUBIC FEET PER SECOND

0

8

2

4

6

NITRATE PLUS NITRITE, IN

MILLIGRAMS PER LITER AS N

Not shown: discharge 19.3

suspended solids 540

CALENDAR YEAR

Figure 24.—Continued.
Trends in Concentrations 63

0

100

20

40

60

80

TURBIDITY, IN NEPHELOMETRIC UNITS

0

400

100

200

300

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

10

0

2

4

6

8

TOTAL NITROGEN, IN MILLIGRAMS PER LITER

10

0

2

4

6

8

NITRITE PLUS NITRATE,

IN MILLIGRAMS PER LITER AS N

1997 2002 1997 1998 1999 2000 2001

CALENDAR YEAR

1997 2002 1997 1998 1999 2000 2001

CALENDAR YEAR

0

1.0

0.2

0.4

0.6

0.8

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

A. Spring Creek at mouth at Whitstran

Figure 25. Temporal variations in turbidity and concentrations of suspended solids, total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus, in 

Spring Creek at mouth at Whitstran, Yakima River Basin, Washington 1997–2001. 

(Data provided by Roza-Sunnyside Board of Joint Control.)
64 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

100

0

20

40

60

80

TURBIDITY, IN FORMAZIN UNITS

500

0

50

100

150

200

250

300

350

400

450

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0

8

1

2

3

4

5

6

7

TOTAL NITROGEN, IN MILLIGRAMS PER LITER

8

0

1

2

3

4

5

6

7

NITRITE PLUS NITRATE,

IN MILLIGRAMS PER LITER AS N

1990 2001 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

1990 2001 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

1.0

0

0.2

0.4

0.6

0.8

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

Not shown: suspended solids 1,120

January 31, 1995

Not shown: Total phosphorus 1.

January 31, 1995

8

B. Snipes Creek at Old Inland Empire Road

(Data provided by the Bureau of Reclamation)

Figure 25.—Continued.
Trends in Concentrations 65

0

100

20

40

60

80

TURBIDITY, IN NEPHELOMETRIC UNITS

200

0

50

100

150

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0

8

2

4

6

TOTAL NITROGEN, IN MILLIGRAMS PER LITER

0

8

2

4

6

NITRITE PLUS NITRATE,

IN MILLIGRAMS PER LITER AS N

1997 2002 1997 1998 1999 2000 2001

CALENDAR YEAR

0

0. 5

0. 1

0. 2

0. 3

0. 4

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

Not shown: suspended solids=540

June 13, 1997

1997 2002 1997 1998 1999 2000 2001

CALENDAR YEAR

C. Snipes Creek at mouth at Whitstran

(Data provided by the Roza-Sunnyside Board of Joint Control)

Figure 25.—Continued.
66 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Yakima River at Kiona

Trend statistics computed using both unadjusted 

and flow-adjusted data indicate small, but significant, 

increases in turbidity and concentrations of total 

phosphorus in the Yakima River at Kiona from 1991 to 

2000 (table 11). The rates of increase in flow-adjusted 

values of turbidity and flow-adjusted concentrations of 

total phosphorus were similar to those reported by 

Butkus and others (2001) (table 12). However, they did 

not consider the increase in concentrations of total 

phosphorus significant because their test for 

significance was based on a p-value of 0.05 or less, 

rather than 0.10 as used in this study. Both studies used 

the same data to test for trends, but Butkus and others 

(2001) used a different regression model to obtain 

flow-adjusted concentrations.

Butkus and others (2001) also tested flowadjusted concentrations of total nitrogen for trends and 

found none, which agrees with the results of the trend 

test performed in this study (table 12). This study found 

a significant increase in flow-adjusted concentrations 

of nitrate in the Yakima River at Kiona, a result that is 

consistent with increasing concentrations of nitrate in 

some streams and drains flowing to the Yakima River 

(table 11). Even though nitrogen discharged from the 

streams and drains makes up a significant fraction of 

the nitrogen load in the Yakima River (see table 5), a 

relation between increasing concentrations of nitrate in 

streams and drains and increasing concentrations in the 

Yakima River at Kiona was not established by this 

study.

Based on the trend test performed using flowadjusted concentrations, there was no trend in the 

concentration of suspended solids over the 1991–2000 

water years (table 11). This result seems reasonable 

because concentrations of suspended solids correlated 

with streamflow (fig. 26), and higher values of both 

were observed after 1995 (figs. 26 and 27).

Table 12. Comparison of trend statistics for turbidity and concentrations of total nitrogen and total phosphorus in samples collected from the Yakima River 

at Kiona, Yakima River Basin, Washington

[Ecology, trend statistics computed by the Washington State Department of Ecology from samples collected monthly October 1990–September 2000 (Butkus 

and others, 2001). Total nitrogen samples were collected during 1994–2000 water years only. USGS, U.S. Geological Survey statistics computed for this report 

(see table 11) using the same data but different methods to compute flow-adjusted concentrations. NTU, nephelometric turbidity unit; <, less than]

Turbidity

(NTU)

Total nitrogen

(milligrams per liter)

Total phosphorus

(milligrams per liter)

p-value Slope units 

per year p-value Slope units per year p-value Slope units per year

Ecology (flow-adjusted concentrations) 0.002 0.509 0.957 0.0008 0.063 0.0035

USGS (flow-adjusted concentrations) <.01 .42 .16 -.013 .01 .0035

USGS (unadjusted concentrations) <.01 .65 .10 -.034 .06 .0032
Trends in Concentrations 67

1990 2001 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

0

25,000

5,000

10,000

15,000

20,000

STREAMFLOW, IN CUBIC FEET PER SECOND

300

0

50

100

150

200

250

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0 25,000 0 5,000 10,000 15,000 20,000

STREAMFLOW IN CUBIC FEET PER SECOND

0

2.0

0.5

1.0

1.5

NITRATE PLUS NITRITE, IN

MILLIGRAMS PER LITER AS N

1990 2001 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

0

25,000

5,000

10,000

15,000

20,000

STREAMFLOW, IN CUBIC FEET PER SECOND

300

0

50

100

150

200

250

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0 25,000 0 5,000 10,000 15,000 20,000

STREAMFLOW, IN CUBIC FEET PER SECOND

0

2.0

0.5

1.0

1.5

NITRATE PLUS NITRITE, IN

MILLIGRAMS PER LITER AS N

Figure 26. Temporal variations in streamflow and variations in concentrations of suspended solids and nitrite-plus-nitrate nitrogen with streamflow in Yakima 

River at Kiona, Yakima River Basin, Washington, 1991–2000 water years. 

(Concentration data provided by the Washington State Department of Ecology.)
68 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

100

0

20

40

60

80

TURBIDITY, IN NEPHELOMETRIC UNITS

0

300

50

100

150

200

250

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0

6

1

2

3

4

5

TOTAL NITROGEN, IN MILLIGRAMS PER LITER

6

0

1

2

3

4

5

NITRITE PLUS NITRATE,

IN MILLIGRAMS PER LITER AS N

1990 2001 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

0

1. 0

0. 2

0. 4

0. 6

0. 8

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

1990 2001 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

100

0

20

40

60

80

TURBIDITY, IN NEPHELOMETRIC UNITS

0

300

50

100

150

200

250

SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0

6

1

2

3

4

5

TOTAL NITROGEN, IN MILLIGRAMS PER LITER

6

0

1

2

3

4

5

NITRITE PLUS NITRATE,

IN MILLIGRAMS PER LITER AS N

1990 2001 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

0

1. 0

0. 2

0. 4

0. 6

0. 8

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

1990 2001 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

CALENDAR YEAR

Figure 27. Temporal variations in turbidity and concentrations of suspended solids, total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus in 

Yakima River at Kiona, Yakima River Basin, Washington, 1991–2000 water years. 

(Data provided by the Washington State Department of Ecology.)
Summary and Conclusions 69

SUMMARY AND CONCLUSIONS

Spatial and temporal variations in concentrations 

and loads of suspended sediment and nutrients in 

surface water of the Yakima River Basin were assessed 

using data collected during 1999–2000 as part of the 

U.S. Geological Survey (USGS) National WaterQuality Assessment (NAWQA) Program. Samples 

were collected at 34 sites located throughout the Basin 

in August 1999 using a Lagrangian sampling design, 

and were collected weekly and monthly from May 

1999 through January 2000 at three of the sites 

(Granger Drain, Moxee Drain, and Yakima River at 

Kiona). Additional data collected by the USGS January 

2001 through August 2002 at the Yakima River at 

Kiona were used to help assess the results of estimating 

suspended-sediment and nutrient loads for water years 

1999–2000 using regression equations. Nutrient and 

sediment data collected at various time intervals from 

1973 through 2001 by the USGS, Bureau of 

Reclamation (BOR), Washington State Department of 

Ecology (Ecology), and Roza-Sunnyside Board of 

Joint Control (RSBOJC) were used to assess trends in 

concentrations.

 During irrigation season (mid-March to midOctober) concentrations of suspended sediment and 

nutrients in the Yakima River increase as relatively 

pristine water from the forested headwaters moves 

downstream and mixes with discharges from streams, 

agricultural drains, and wastewater treatment plants. 

Concentrations of nutrients in the Yakima River depend 

partly on the proportions of mixing between river water 

and discharges, and in years when ample water is 

stored in headwater reservoirs, more water is released 

during irrigation season, and nutrients discharged to the 

river downstream are more diluted. In August 1999, 

streamflow in the reach of the Yakima River extending 

from river mile (RM) 103.7 to RM 72 exceeded 

streamflow in July 1988 by a factor of almost 2.5, but 

loads of total nitrogen and phosphorus discharged to 

the reach from streams, drains, and wastewater 

treatment plants were only 1.2 and 1.1 times larger. In 

August 1999 concentrations of total nitrogen and total 

phosphorus at RM 72 were 1.0 mg/L (milligrams per 

liter) and 0.06 mg/L, compared with 1.5 mg/L and 0.10 

mg/L in July 1988.

The water supply also affects concentrations of 

nutrients, especially nitrate, in drains and streams 

carrying agricultural return flows. Canal water, which 

is diverted from either the Yakima or Naches River, 

makes up more of the flow in drains and streams in 

years with an ample water supply. The canal water 

dilutes nutrients transported to the drains and streams 

in runoff from fields and in discharges from subsurface 

field drains and the shallow ground-water system. In 

August 1999, the average concentrations of total 

nitrogen and total phosphorus in drains and streams 

discharging to the reach of the Yakima River from RM 

103.7 to RM 72 were 2.63 mg/L and 0.20 mg/L, 

compared with 3.16 mg/L and 0.26 mg/L in July 1988.

Streamflow in agricultural drains decreases after 

irrigation season because irrigation water is no longer 

diverted from the Yakima and Naches Rivers. As a 

result, concentrations of total nitrogen in drains 

increase because nitrate, which makes up much of the 

total nitrogen, continues to enter the drains from 

subsurface drains and shallow ground water. In 

contrast, concentrations of total phosphorus and 

suspended sediment often decrease after irrigation 

season because they are transported to the drains in 

runoff of irrigation water from fields. Also, at the lower 

flows during the post-irrigation season, dissolved 

orthophosphate typically makes up a larger fraction of 

the total phosphorus concentration. In Moxee Drain, 

concentrations of total nitrogen ranged from about 1.5-

2 mg/L during irrigation season and increased to about 

6 mg/L after irrigation season. Concentrations of total 

phosphorus ranged from about 0.2-0.4 mg/L during 

May-July of the irrigation season, then decreased to 

about 0.2 mg/L during August-October of the irrigation 

season. After the irrigation season, total phosphorus 

concentrations increased to about 0.3 mg/L from 

November 1999-January 2000 in response to increased 

concentrations of dissolved orthophosphate. Dissolved 

orthophosphate concentrations increased because 

sources of the nutrient (possibly the effluent from the 

Moxee City wastewater treatment plant) continued to 

discharge to Moxee Drain during the post-irrigation 

season when less streamflow is available to dilute the 

orthophosphate. Concentrations of suspended sediment 

ranged from about 50-250 mg/L during irrigation 

season and dropped to less than 50 mg/L after 

irrigation season. In Granger Drain, concentrations of 

total nitrogen ranged between 2 and 4 mg/L during 

irrigation season and increased to about 6 mg/L after 

irrigation season, and concentrations of total 

phosphorus decreased to about 0.2 mg/L after being as 

high as 1 mg/L during irrigation season.
70 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

There also was an inverse relation between 

streamflow and concentrations of nitrate and total 

nitrogen in the Yakima River at Kiona. Because of 

diversions, flow regulation in the headwaters, and dry 

summers, the Yakima River at Kiona differs 

hydrologically from Moxee and Granger Drains, 

having a low-flow period during late summer instead of 

winter and streamflows that generally vary more in 

magnitude during the remainder of the year. The 

highest concentrations of suspended sediment and total 

phosphorus in the Yakima River at Kiona were 

observed during high flow in June 1999.

Not all crops respond ideally to fertilization with manure; more than 18,000 

tons of commercial-nitrogen fertilizer was applied in Yakima County in 

1998.

Perhaps because of dilution, concentrations of 

total phosphorus in the Yakima River from RM 72 to 

Kiona at RM 29.9 were somewhat lower in August 

1999 than in July 1988, when there was less 

streamflow in this reach of the river. Even with more 

dilution in August 1999, concentrations of total 

phosphorus in all but one sample were greater than 0.1 

mg/L, the recommended concentration for limiting 

accelerated plant growth in streams. In July 1988, 

concentrations of total phosphorus in all samples 

collected from this reach were greater than or equal to 

0.1 mg/L.

A regression model was used to estimate loads in 

Granger Drain and Yakima River at Kiona for the 

period October 1, 1998–September 30, 2000. Granger 

Drain transported an average of 42,000 lb/d (pounds 

per day) of suspended sediment, 860 lb/d of total 

nitrogen, and 78 lb/d of total phosphorus. Loads 

transported in the Yakima River at Kiona averaged 

850,000 lb/d (about 430 tons per day) of suspended 

sediment, 20,000 lb/d of total nitrogen, and 2,800 lb/d 

of total phosphorus. Lack of streamflow data made it 

necessary to estimate loads in Moxee Drain for only the 

1999 calendar year: it discharged an average of 28,000 

lb/d of suspended sediment, 380 lb/d of total nitrogen, 

and 46 lb/d of total phosphorus to the Yakima River. 

These loads were about half the average loads 

transported by Granger Drain during the same period. 

Average streamflows were similar for the two streams 

(40 ft3/s, cubic feet per second, at Granger Drain and 

35 ft3/s at Moxee Drain), therefore the difference in 

loads was due to differences in concentrations. 

Constituent concentrations in Moxee Drain ranged 

from about 40 to 60 percent less than concentrations in 

Granger Drain.

Departure from relations between average daily 

loads plotted as a function of annual mean streamflow 

suggests some reduction in loads of suspended 

sediment, ammonia-plus-organic nitrogen, and total 

nitrogen in the Yakima River at Kiona in water years 

1999 and 2000. A relation between loads and 

streamflow was established using loads previously 

estimated for water years 1974, 1977, 1980, 1988 and 

1989 and loads estimated for this study for other water 

years from 1974 through 1994. 

Loads of suspended sediment and total 

phosphorus in Moxee and Granger Drains were nearly 

4 times higher during the irrigation season than during 

the non-irrigation season. There is more flow in the 

drains during irrigation season and concentrations of 

suspended sediment and total phosphorus usually are 

higher. Loads of nitrate in the drains were about the 

same in both seasons because nitrate concentrations are 

higher during the non-irrigation season. Loads of 

nutrients in the Yakima River at Kiona were similar 

during irrigation and non-irrigation season, generally 

differing by less than 20 percent. The suspendedsediment load during irrigation season was about 60 

percent larger than during the non-irrigation season. 

Large fractions of the total annual loads in the Yakima 

River were transported during the first half of the 

irrigation season. For example, 38 percent or more of 

the annual loads of suspended sediment, total nitrogen, 

ammonia-plus-organic nitrogen, total phosphorus, and 

orthophosphate were transported from March through 

June.
Summary and Conclusions 71

The summary of trend statistics for concentration 

data collected 1991–2000 by the BOR and Ecology 

indicates that some of the factors affecting constituent 

transport to surface water may be common to many of 

the agricultural subbasins. For example, concentrations 

of nitrate and total nitrogen increased in five of six 

streams and drains while concentrations of suspended 

solids and total phosphorus either did not change or 

decreased. This difference is consistent with no change, 

or a decrease, in amounts of suspended solids and 

phosphorus transported to surface water in runoff and 

an increase in the amount of nitrate transported to 

streams and drains from ground-water discharges and 

subsurface drains. Decreased transport of sediment and 

associated phosphorus to streams and drains is likely 

due to the increased use of agricultural best 

management practices that reduce runoff from 

cropland. Because much of the nitrate in drains enters 

from subsurface drains and shallow ground water, 

management practices designed to reduce runoff from 

cropland have less effect. Increasing concentrations of 

nitrate in some drains over the period 1991–2000 

suggest that concentrations of nitrate in ground water 

are increasing.

Data collected 1997–2001 by the RSBOJC also 

indicate a decrease in concentrations in suspended 

solids total phosphorus in some drains and streams 

receiving agricultural return flows, as well as a 

decrease in turbidity. These data indicate that 

concentrations of nitrate in some of the streams and 

drains have leveled off and may be decreasing. This 

observation is not in conflict with the trend statistics for 

1991–2000, but suggests that a slow increase over a 

decade may be leveling off.

Trend statistics computed using both unadjusted 

and flow-adjusted data indicate small, but significant, 

increases in turbidity and concentrations of total 

phosphorus in the Yakima River at Kiona from 1991 

through 2000. This study also found a significant 

increase in flow-adjusted concentrations of nitrate in 

the Yakima River at Kiona, a result consistent with 

increasing concentrations of nitrate in some streams 

and drains flowing to the Yakima River. Even though 

nitrogen discharged from the streams and drains makes 

up a significant fraction of the nitrogen load in the 

Yakima River, a relation between increasing 

concentrations of nitrate in streams and drains and 

increasing concentrations in the Yakima River at Kiona 

was not established.

The trend test using flow-adjusted concentrations 

showed no trend in the concentration of suspended 

solids in the Yakima River at Kiona from 1991 through 

2000. This result seems reasonable because 

concentrations of suspended solids correlated with 

streamflow, and higher values of both were observed 

after 1995.

The lower basin is host to a variety of agricultural practices, crop types, 

and irrigation methods.
72 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

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W.T., Fuhrer, G.J., and Morace, J.L., 1999, Surfacewater-quality assessment of the Yakima River Basin, 

Washington: Distribution of pesticides and other 

organic compounds in water, sediment, and aquatic 

biota, 1987-91, U.S. Geological Survey Water-Supply 

Paper 2354-B, 180 p.

Shelton, L. R., 1994, Field guide for collecting and 

processing stream-water samples for the National 

Water-Quality Assessment Program: U.S. Geological 

Survey Open-File Report 94-455, 42 p.

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furrow irrigation, an erosion control breakthrough: 

Proceedings of the First European Conference and 

Trade Exposition on Erosion Control May 29-31, 1996, 

v. 1, p. 183-189.

State of Washington, 1997, Water quality standards for 

surface waters of the State of Washington: Olympia, 

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18 p.

Turnbull, B.W., and Weiss, L., 1978, A likelihood ratio 

statistic for testing goodness of fit with randomly 

censored data: Biometrics, v. 34, p. 367-375.

U.S. Department of Agriculture, 1997, Environmental 

Quality Incentives Program: USDA Natural Resources 

Conservation Service: at URL 

http://www.nrcs.usda.gov/programs/adopt, accessed 

April 2002.

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collection of water-quality data: U.S. Geological 

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book 9, chaps. A1-A9, 2 v., variously paged. [Chapters 

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ongoing and can be viewed at URL 

http://water.usgs.gov/owq/FieldManual

———2001 National Water-Quality Assessment Program: 

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accessed October 2001.

Ward, J.R. and Harr, C.A., 1990, Methods for collection and 

processing of surface-water and bed-material samples 

for physical and chemical analyses: U.S. Geological 

Survey Open-File Report 90-140, 71 p.

Wetzel, R.G., 1983, Limnology: Philadelphia, Saunders 

College Publishing, 767 p.

Williamson, A.K., Munn, M.D., Ryker, S.J., Wagner, R.J., 

Ebbert, J.C., and Vanderpool, A.M., 1998, Water 

quality in the Central Columbia Plateau, Washington 

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1144, 35 p.

Wolynetz, M.S., 1979, Algorithm 139—Maximum 

likelihood estimation in a linear model with confined 

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Woodworth, M.T., and Conner, B.T., 2002, Results of the 

U.S. Geological Survey's analytical evaluation program 

for standard reference samples distributed in March 

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Geological Survey Water-Data Report WA-99-1, 508 p.
74 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

APPENDIX A.—EVALUATION OF QUALITYCONTROL DATA

U.S. Geological Survey Data

Data quality was evaluated using (1) replicate 

and blank samples (tables A1 and A2) that were 

prepared in the field and sent to the laboratory for 

analysis; (2) data provided by the USGS National 

Water-Quality Laboratory on the recovery of analytes 

in spiked inorganic blank water (table A3); (3) qualitycontrol charts and reports published by the USGS 

Branch of Quality Systems Inorganic Blind Sample 

Project, available online at URL 

<http://bqs.usgs.gov/bsp/mainpage.html>; and (4) 

quality-control charts and reports published by the 

USGS Branch of Quality Systems Quality Assurance 

Program for Sediment Analysis, available online at 

URL <http://sedserv.cr.usgs.gov/>.

Because they are available online, the qualitycontrol charts and reports used to help assess data 

quality are not reproduced in this report. Qualitycontrol charts are graphical displays of the analytical 

deviation from the most probable concentration of a 

standard reference sample over time. These samples, 

which are usually a mixture of natural water collected 

from different sources, are disguised as environmental 

samples before they are sent to the laboratory. The 

most probable concentration is determined by repeated 

analysis of the sample. The charts show if analytical 

results are within expected control limits and can 

illustrate a systematic or sudden shift in bias or 

variability. The Inorganic Blind Sample Project sets 

control limits at ± 2 standard deviations of the most 

probable value. The Quality Assurance Program for 

Sediment Analysis sets control limits at ±3 

F-pseudosigma of the most probable value. For a 

definition of F-pseudosigma, see table A3.

Median relative percent differences in 

concentrations of nutrients in replicate surface-water 

samples ranged from 0.0 to 20.2 percent and were less 

than 5 percent, except for ammonia and unfiltered and 

filtered ammonia-plus-organic nitrogen (table A1). The 

median relative percent difference in concentrations of 

suspended sediment in replicate samples was 4.6 

percent (table A1).

Small concentrations of ammonia and both 

unfiltered and filtered ammonia-plus-organic nitrogen 

were reported in some blank samples (table A2), but 

these very low concentrations are not indicative of a 

significant bias or contamination problem. Of possible 

concern are the relatively high concentrations of 

orthophosphate in two of four blank samples as 

compared with the laboratory reporting level of 0.01 

mg/L (table A2). Recoveries of orthophosphate in 

spiked laboratory-reagent (blank) water do indicate a 

positive bias (table A3); however, these samples are 

spiked to very low concentrations for the determination 

of laboratory reporting levels. Control charts for 

orthophosphate indicate a positive bias with higher 

than expected variability for the period February 

through June 1999. Beginning in mid-July, the 

variability for this determination improved and the 

positive bias was corrected. Overall, however, 

variability in the determination of orthophosphate was 

relatively large compared with other nutrients. Control 

charts for suspended sediment and all other nutrient 

determinations except nitrite, for which no chart was 

available, indicate that analytical results were within 

expected control limits.

Roza-Sunnyside Board of Joint Control Data

The Water-Quality Monitoring Program of 

RSBOJC used USGS techniques to collect and process 

samples (see "Methods" section) and measured 

turbidity and determined concentrations of suspended 

solids in samples in their laboratory. Samples were sent 

to the Bureau of Reclamation Laboratory in Boise, Ida., 

for the determination of nutrient concentrations. The 

summary of quality-control data (table A4) indicates 

that errors caused by bias, variability, and potential 

contamination of samples were small compared with 

concentrations of analytes in samples.
Appendix A.—Evaluation of quality-control data 75

Table A1. Concentration and precision data for nutrients and suspended sediment in replicate surface-water samples, Yakima River Basin, Washington, 

1999–2000—Continued

Sample date

Concentration 

and precision 

data

Nitrogen, 

ammonia

Nitrogen, 

ammonia 

+ organic 

filtered

Nitrogen, 

ammonia 

+ organic 

unfiltered

Nitrogen, 

nitrite

Nitrogen, 

nitrite + 

nitrate

Phosphorus, 

filtered

Phosphorus,

unfiltered

Orthophosphate

as P, 

filtered

Sediment, 

suspended

USGS site No. 12500420

Aug. 18, 1999 Concentration <0.020

–

0.22

–

0.26

–

<0.010

–

1.03

–

0.093

–

0.217

–

0.078

–

113

116

RPD nc nc nc nc nc nc nc nc 2.6

Sept. 29, 1999 Concentration <.020

<.020

<.020

.20

.20

.24

.22

–

.38

.010

<.010

<.010

1.76

1.78

1.78

.106

.106

.107

.178

–

.176

.090

.093

.091

50

–

–

RPD nc 18.2 53.3 nc 1.1 .94 1.1 3.3 nc

USGS site No. 12505420

Dec. 8, 1999 Concentration 0.021

.025

0.30

.29

0.40

.37

0.026

.026

5.91

5.87

0.247

.241

0.259

.263

0.236

.238

13

–

RPD 17.4 3.4 7.8 .0 .68 2.5 1.5 .84 nc

USGS site No. 12505450

June 3, 1999 Concentration 0.069

.065

0.31

.30

1.2

1.1

0.020

.020

2.19

2.17

0.160

.159

1.05

1.06

0.156

.150

645

690

RPD 6.0 3.3 8.7 .0 .92 .63 .95 3.9 6.7

Aug. 3, 1999 Concentration .096

.102

.92

.91

1.3

–

<.010

<.010

2.59

2.59

.154

.154

.443

–

.164

.185

253

–

RPD 6.1 1.1 nc nc .0 .0 nc 12.0 nc

Aug. 19, 1999 Concentration .024

.022

.026

.25

.21

.27

.66

.59

.89

.022

.022

.022

1.89

1.89

1.92

.152

.156

.155

.415

.388

.656

.139

.138

.135

199

–

–

RPD 16.7 25.0 40.5 .0 1.6 2.6 51.3 2.9 nc

Nov. 17, 1999 Concentration .037

–

.37

–

.52

–

.035

–

6.12

–

.109

–

.171

–

.088

–

47

44

RPD nc nc nc nc nc nc nc nc 6.6

Table A1. Concentration and precision data for nutrients and suspended sediment in replicate surface-water samples, Yakima River Basin,

Washington, 1999–2000

[Phosphorus, unfiltered: referred to as total phosphorus in this report; Concentrations are in milligrams per liter; Abbreviations: USGS, U.S. Geological 

Survey; +, plus; <, less than; –, no data; nc, not calculated; RPD, relative percentage of difference; relative percentage of difference = × 100, 

where R1 = maximum value and R2 = minimum value]

( ) R1 – R2

R1 + R2

2 --------------------    

-------------------------
76 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

USGS site No. 12510500

July 13, 1999 Concentration <0.02

–

0.16

–

0.28

–

<0.010

–

0.473

–

0.044

–

0.116

–

0.033

–

51

50

RPD nc nc nc nc nc nc nc nc 2.0

Aug. 5, 1999 Concentration <0.02

<.02

0.18

.15

0.49

.40

0.017

.017

1.03

1.03

0.083

.085

0.125

.123

0.072

.076

15

20

RPD nc 18.2 20.2 .0 .0 2.4 1.6 5.4 28.6

Aug. 31, 1999 Concentration 0.021

.027

0.13

.14

0.34

.34

.010

.010

1.19

1.19

.098

.096

0.129

.126

0.081

.077

20

–

RPD 25.0 7.4 .0 .0 .0 2.1 2.4 5.1 nc

USGS site No. 463447120275200

Aug. 3, 1999 Concentration 0.072

.078

0.91

.86

0.96

1.2

<0.010

<.010

7.12

7.05

1.90

1.92

1.68

2.12

1.80

1.78

5

5

RPD 8.0 5.6 22.2 nc .99 1.0 23.2 1.1 0.0

Summary

Minimum RPD 6.0 1.1 0.0 0.0 0.0 0.0 0.95 0.84 0.0

Maximum RPD 25.0 25.0 53.3 .0 1.6 2.6 51.3 12.0 28.6

Median RPD 12.3 6.5 20.2 .0 .80 1.6 1.6 3.6 4.6

Table A1. Concentration and precision data for nutrients and suspended sediment in replicate surface-water samples, Yakima River Basin, Washington, 

1999–2000—Continued

Sample date

Concentration 

and precision 

data

Nitrogen, 

ammonia

Nitrogen, 

ammonia 

+ organic 

filtered

Nitrogen, 

ammonia 

+ organic 

unfiltered

Nitrogen, 

nitrite

Nitrogen, 

nitrite + 

nitrate

Phosphorus, 

filtered

Phosphorus,

unfiltered

Orthophosphate

as P, 

filtered

Sediment, 

suspended

Table A2. Concentrations of nutrients and suspended sediment in field blank samples, Yakima River Basin, Washington, 1999–2000

[Phosphorus, unfiltered: referred to as total phosphorus in this report. Concentrations are in milligrams per liter. Abbreviations: <, less than; E, detections 

above or below the lowest calibration standard, or otherwise less reliable than average because of sample-specific or compound-specific considerations. –, no 

data]

USGS site 

identification No.

Sample date Nitrogen, 

ammonia

Nitrogen, 

ammonia 

+ organic 

filtered

Nitrogen, 

ammonia 

+ organic 

unfiltered

Nitrogen, 

nitrite

Nitrogen, 

nitrite + 

nitrate

Phosphorus, 

filtered

Phosphorus, 

unifltered

Orthophosphate

as P, 

filtered

Sediment, 

suspended

12505450 July 22, 1999 <0.020 <0.10 E0.07 <0.010 <0.05 <0.004 <0.004 <0.01 –

12508850 August 4, 1999 <.020 E.06 E.08 <.010 <.05 <.004 <.004 .036 2

12510500 May 19, 1999 .023 <.10 <.10 <.010 <.05 <.004 <.004 .011 1

12510500 November 18, 1999 <.020 <.10 <.10 <.010 <.05 <.006 <.008 <.01 –
Appendix A.—Evaluation of quality-control data 77

Bureau of Reclamation Data

 Bureau of Reclamation (BOR) data were used in 

this report to compute trend statistics for turbidity and 

concentrations of nutrients and suspended solids at 

selected surface-water sites. The quality of data 

produced by the BOR Laboratory in Boise, Ida., is 

maintained by adhering to procedures outlined in their 

quality-assurance plan (Bureau of Reclamation, 2000). 

Also, because this laboratory performed nutrient 

analyses for the Water-Quality Monitoring Program of 

RSBOJC, the quality-control data for nutrients 

presented in table A4 are indicative of the laboratory's 

performance. The BOR laboratory participates in the 

USGS standard reference sample program.

Washington State Department of Ecology Data

Data from samples collected by the Washington 

State Department of Ecology (Ecology) Environmental 

Assessment Program and analyzed in Ecology's 

Manchester Environmental Laboratory in Port Orchard, 

Wash., were used to compute trend statistics for 

turbidity and concentrations of nutrients and suspended 

solids at the Yakima River at Kiona. The quality of data 

published by the Environmental Assessment Program 

is maintained by adhering to published sampling 

protocols available online at URL 

<http://www.ecy.wa.gov/biblio/0103036.html>, and 

the performance of the Manchester Environmental 

Laboratory is documented online at URL 

<http://www.ecy.wa.gov/programs/eap/manchester/mel

qual.htm>.

Table A3. Summary of recoveries for laboratory-reagent-spike nutrient analyses for the period October 1999 through September 2000

[Blind samples were submitted by the U.S. Geological Survey (USGS) Branch of Quality Systems to the USGS National Water Quality Laboratory. 

F-pseudosigma, which is the interquartile range divided by 1.349, is a distribution-free measure of precision comparable to a standard deviation (Woodworth 

and Conner, 2002). Smaller values of F-pseudosigma indicate better precision. Abbreviations: mg/L milligrams per liter)

Analyte name Count

Spike 

concentration

(mg/L)

Mean 

analytical 

result

(mg/L)

Median 

analytical 

result

(mg/L)

Mean 

percent 

recovery

Standard 

deviation 

(mg/L)

F-pseudosigma

(mg/L)

Relative 

standard 

deviation 

(percent)

Nitrogen, nitrite 24 0.010 0.015 0.016 151 0.002 0.001 14.1

Orthophosphate as P, filtered 24 .038 .044 .044 115 .007 .009 14.8

Nitrogen, nitrite plus nitrate 24 .078 .088 .088 112 .011 .010 12.9

Nitrogen, ammonia 24 .091 .090 .086 98 .011 .007 11.9

Phosphorus, dissolved 21 .181 .181 .181 100 .012 .010 6.9

Phosphorus, unfiltered (total) 20 .181 .181 .182 100 .013 .016 7.3

Nitrogen, ammonia plus organic, filtered 21 .363 .368 .378 101 .037 .035 10.2

Nitrogen, ammonia plus organic, unfiltered 20 .363 .390 .382 107 .079 .021 20.3
78 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Table A4. Summary of quality-control data for samples collected by the Water-Quality Monitoring Program of the Roza-Sunnyside Board of Joint 

Control, Yakima River Basin, 1997–2000

[Data were provided by William Rice, Roza-Sunnyside Board of Joint Control, February 2002. Abbreviations: RPD, relative percentage of difference; mg/L, 

milligrams per liter; NTU, nephelometric turbidity unit; PR, percentage of recovery; <, less than]

Measured parameter Quality-control 

parameter

Qualitycontrol 

measure

Number Minimum Mean Median Maximum

Total suspended solids Field replicate (RPD) 206 0.0 3.1 2.2 26.7

Lab replicate (RPD) 277 .0 1.4 .9 20.3

Check standard 

(250 mg/L)

(RPD) 51 .3 1.0 .9 1.6

Field blank (mg/L) 79 -3.6 -.6 -.7 2.2

Turbidity Field replicate (RPD) 206 .0 1.8 1.2 20.7

Lab replicate (RPD) 260 .0 1.1 0.9 7.4

Check standard 

(200 NTU)

(RPD) 37 .5 2.6 3.0 4.4

Field blank (NTU) 78 .06 .09 .09 .20

Nitrite plus nitrate Field replicate (RPD) 208 .0 1.1 .7 12.2

Field split (RPD) 190 .0 1.0 .6 6.8

Field spike (PR) 66 55.5 97.0 97.2 115

Field blank (mg/L as N) 79 <.01 <.01 <.01 .01

Phosphorus, total Field replicate (RPD) 208 .0 3.7 3.2 20.4

Field split (RPD) 190 .0 3.8 3.5 16.7

Field blank (mg/L as P) 79 <.01 <.01 <.01 .02

Nitrogen, ammonia plus 

organic, unfiltered

Field replicate (RPD) 208 .0 6.3 4.7 32.5

Field split (RPD) 190 .0 6.1 4.7 26.9

Field blank (mg/L as N) 79 <.003 <.03 <.03 .06
Appendix B.—Regression Models Used to Estimate Loads 79

APPENDIX B.—REGRESSION MODELS 

USED TO ESTIMATE LOADS

The computer program Loadest2 was used to 

estimate loads of suspended sediment and nutrients 

transported in Moxee Drain, Granger Drain, and the 

Yakima River at Kiona. The regression models used in 

this study and the criteria used to select them are 

presented in this appendix.

For Moxee Drain, all estimates of suspended 

sediment and nutrient loads were based on Loadest2 

default regression models selected by Aikaike 

information criteria. The relative percent difference 

between the average of the measured load minus the 

model-predicted load on the days of sample collection 

from May 1999 through July 2000 (the calibration 

period) ranged from 0.3 percent for orthophosphate 

phosphorus to –13 percent for suspended sediment 

(table B1). The standard deviation expressed as a 

percentage of the predicted loads for calendar year 

1999 was less than 3.6 percent of the nitrite-plus-nitrate 

and total nitrogen loads, but was 25 percent of the 

average suspended-sediment load. Using the pattern of 

measured loads as a guide, the regression models 

predicted daily loads of orthophosphate, total nitrogen, 

and ammonia-plus-organic nitrogen that tended to 

underestimate a peak and overestimate a trough in the 

early part of the calibration period (fig. B1A); however, 

the average of the relative percentage of differences 

between the absolute values of measured and predicted 

daily loads was equal to or less than 18 percent. The 

pattern of daily loads for the remaining period, as well 

as the pattern for suspended sediment, total 

phosphorus, and nitrite-plus-nitrate nitrogen, tended to 

agree with measured loads.

For Granger Drain, all loads of suspended 

sediment and nutrients also were estimated by 

Loadest2 default regression models as selected by 

Aikaike information criteria. The relative percent 

difference between the average of the measured load 

minus the model-predicted load on the days of sample 

collection from May 1999 through July 2000 (the 

calibration period) ranged from –0.05 percent or less 

for total nitrogen, nitrite-plus-nitrate nitrogen, and 

orthophosphate phosphorus to 0.8 percent for total 

phosphorus (table B2). The standard deviations 

expressed as a percentage of the predicted loads for 

water years 1999-2000 ranged from 3 percent of the 

nitrite-plus-nitrate load to 9 percent of the ammoniaplus-organic nitrogen load. The pattern of predicted 

daily loads of suspended sediment, total phosphorus, 

orthophosphate phosphorus, and nitrite-plus-nitrate 

nitrogen agreed reasonably well with measured loads 

(fig. B1B). The average of the relative percent 

differences between the absolute values of measured 

and predicted daily loads was 16 percent for suspended 

sediment and 13 percent or less for the nutrients except 

ammonia-plus-organic nitrogen. The average of the 

relative percent differences between the absolute values 

of measured and predicted daily loads of ammoniaplus-organic nitrogen was fairly large (27 percent), 

which is also reflected in the scattering of the measured 

loads about the pattern of predicted daily loads in 

figure B1B.

At various times from 1974 through 2002 water 

years, the USGS has collected water samples for the 

analysis of suspended-sediment and nutrient 

concentrations from the Yakima River at Kiona. The 

resulting data set contains both historical and recent 

data with gaps of varying length. Data collected from 

May 1999 through January 2000 were used to estimate 

loads of suspended sediment and nutrients in the 

Yakima River at Kiona. However, additional data from 

January 2001– August 2002, available at the time of 

data analysis and report preparation, were used to help 

evaluate the results from the regression models.

Data sets used to calibrate the regression models 

generated by the Loadest2 computer program were 

selected to match the period for which loads were 

estimated. Thus, annual load estimates for water years 

1974-2001 were based on a large calibration data set 

consisting of historical concentration and streamflow 

data from October 1973 – September 1994 and from 

May 1999 – September 2001. For estimating annual 

loads for 1999 through 2000, Loadest2 was run 

twice—once calibrated with the May 1999 – January 

2000 data set and once calibrated with the May 1999 – 

January 2000 plus the January 2001 – September 2001 

data set. Estimates of suspended-sediment, total 

nitrogen, ammonia-plus-organic nitrogen, and nitriteplus-nitrate loads were sufficiently different to require 

a choice between loads based on the two calibration 

data sets for representing constituent transport in the 

Yakima River during 1999-2000.
80 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

0

100

20

40

60

80

AMJ JA SOND J

1999 2000

10

30

15

20

25

0

300

100

200

AMJ JA SOND J

1999 2000

200

500

300

400

0

200,000

50,000

100,000

150,000

200

600

300

400

500

A. Moxee Drain

EXPLANATION

Daily loads, predicted using

regression equations

Daily load, measured

SUSPENDED SEDIMENT

TOTAL PHOSPHORUS

ORTHOPHOSPHATE PHOSPHORUS

TOTAL NITROGEN

AMMONIA - PLUS - ORGANIC - NITROGEN

NITRiTE-PLUS-NITRATE NITROGEN

LOAD, IN POUNDS PER DAY

Figure B1. Predicted and measured daily loads of suspended sediment and nutrients for 1999-2000 water years at Moxee and Granger Drains, 

Yakima River Basin, Washington.
Appendix B.—Regression Models Used to Estimate Loads 81

0

400

100

200

300

AMJ JA SOND J

1999 2000

0

60

20

40

0

500

200

400

AMJ JA SOND J

1999 2000

400

1,000

600

800

0

200,000

50,000

100,000

150,000

600

1,200

800

1,000

EXPLANATION

Daily loads, predicted using

regression equations

Daily load, measured

B. Granger Drain

SUSPENDED SEDIMENT

TOTAL PHOSPHORUS

ORTHOPHOSPHATE PHOSPHORUS

AMMONIA - PLUS - ORGANIC NITROGEN

TOTAL NITROGEN

NITRITE-PLUS-NITRATE NITROGEN

LOAD, IN POUNDS PER DAY

Figure B1.—Continued.
82 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Table B1. Suspended-sediment and nutrient loads transported during calendar year 1999, standard deviations, differences between measured and 

predicted loads, regression equations for load estimates, and concentration summary statistics at Moxee Drain, Yakima River Basin, Washington

[Daily loads are in pounds; ln, natural logarithm; Q, streamflow in cubic feet per second; sin, sine; cos, cosine; dectime, time in fractional years; MLE, 

maximum likelihood estimate; dload, daily load. Total nitrogen is based on the sum of unfiltered ammonia-plus-organic and nitrite-plus-nitrate nitrogen 

concentrations in the calibration data set, which included data collected from May 1999 through January 2000, June 2000 and July 2000.]

Constituent

Daily load for 

calendar year 

1999 and

(standard 

deviation)

Number of 

samples 

(number 

censored)

Average of the relative 

percentage of differences 

between the absolute 

values of the measured and 

predicted daily loads for 

May 1999 through January 

2000

Relative percentage of 

difference between the 

average of the measured 

loads minus the average of 

the predicted loads for May 

1999 through January 2000

MLE regression equation

Suspended 

sediment

28,000 

(7,000)

27 (0) 43 –13 ln(dload) = 10.601 + 1.8958 ln(Q) 

+ 0.50252 sin(dectime)

– 0.38767 cos(dectime)

– 0.6893 (dectime)

Total nitrogen 380

(13)

27 (0) 7.2 –.9 ln(dload) = 6.0752 – 0.10122 ln(Q)

– 0.19119 ln(Q)2

Ammonia-plusorganic 

nitrogen

100

(11)

27 (0) 18 –4.9 ln(dload) = 4.8532 – 0.016179 ln(Q)

– 0.49134 ln(Q)2

+ 0.47316 sin(dectime)

– 0.25963 cos(dectime)

Nitrite-plusnitrate nitrogen280

(10)

27 (0) 5.8 .5 ln(dload) = 5.9108 + 0.041921 ln(Q)

– 0.19438 ln(Q)2

– 0.063975 sin(dectime) 

+ 0.37723 cos(dectime)

Total phosphorus 46

(3)

27 (0) 11 –1.1 ln(dload) = 4.2599 + 0.57632 ln(Q)

+ 0.05805 sin(dectime)

– 0.26075 cos(dectime)

– 0.47549 (dectime)

Orthophosphate 

phosphorus

17

(1)

27 (0) 10 .3 ln(dload) = 3.0026 + 0.31272 ln(Q)

– 0.1314 sin(dectime)

– 0.070569 cos(dectime)

Concentration summary statistics (milligrams per liter), calendar year 1999

Minimum 25th

percentile Median 75thpercentile

90th

percentile

95th

percentile Maximum

Suspended sediment

Predicted 10 26 73 170 220 250 350

Measured 2 65 113 165 184 193 237

Total nitrogen

Predicted .73 1.5 1.8 6.1 6.3 6.5 6.7

Measured 1.2 1.3 1.6 1.8 4.6 6.0 6.3

Ammonia-plus-organic nitrogen

Predicted .24 .40 .50 .70 .84 .89 1.2

Measured .22 .34 .47 .59 .66 .77 1.1

Nitrite-plus-nitrate nitrogen

Predicted .57 1.0 1.4 5.1 5.8 5.9 5.9

Measured .76 .94 1.0 1.3 4.2 5.5 5.9

Total phosphorus

Predicted .15 .23 .27 .29 .44 .49 .54

Measured .16 .20 .24 .28 .30 .32 .36

Orthophosphate phosphorus

Predicted .042 .075 .084 .23 .24 .25 .26

Measured .057 .071 .084 .096 .185 .244 .249
Appendix B.—Regression Models Used to Estimate Loads 83

Table B2. Suspended-sediment and nutrient loads transported during water years 1999–2000, standard deviations, differences between measured and 

predicted loads, regression equations for load estimates, and concentration summary statistics at Granger Drain, Yakima River Basin, Washington

[Daily loads are in pounds; ln, natural logarithm; Q, streamflow in cubic feet per second; sin, sine; cos, cosine; dectime, time in fractional years; MLE, 

maximum likelihood estimate; dload, daily load. Total nitrogen is based on the sum of unfiltered ammonia-plus-organic and nitrite-plus-nitrate nitrogen 

concentrations in the calibration data set, which included data collected from May 1999 through January 2000, June 2000 and July 2000]

Constituent

Daily load for 

water years

1999 –2000, and

(standard 

deviation)

Number of 

samples 

(number 

censored)

Average of the relative 

percent differences 

between the absolute 

values of the measured and 

predicted daily loads for 

1999 through 2000

Relative percentage of 

difference between the 

average of the measured 

loads minus the average of 

the predicted loads for

1999 through 2000

MLE regression equation

Suspended 

sediment

42,000

(3,000)

26 (0) 16 0.2 ln(dload) = 0.11813 + 2.2404 ln(Q)

+ 1.3185 ln(Q)2

+ 0.38515 sin(dectime)

– 0.60583 cos(dectime)

– 1.4561 (dectime)

Total nitrogen 860

(31)

27 (0) 11 –.05 ln(dload) = 6.8223 + 0.18547ln(Q)

Ammonia-plusorganic 

nitrogen

140

(13)

27 (0) 27 .2 ln(dload) = 5.1934 + 0.32399 ln(Q)

– 0.0014707 sin(dectime)

– 0.61991 cos(dectime)

– 0.37393 (dectime)

Nitrite-plusnitrate nitrogen690

(20)

27 (0) 6.9 –.04 ln(dload) = 6.4805 + 0.070781 ln(Q)

– 0.1004 sin(dectime)

+ 0.069966 cos(dectime)

+ 0.098542 (dectime)

Total phosphorus 78

(4)

27 (0) 13 .8 ln(dload) = 5.0541 + 0.91036 ln(Q)

+ 0.19505 sin(dectime)

– 0.52981 cos(dectime)

– 0.70337 (dectime)

Orthophosphate 

phosphorus

24

(1)

27 (0) 13 –.03 ln(dload) = 3.3643 + 0.94708 ln(Q)

– 0.17835 sin(dectime)

– 0.28399 cos(dectime)

Concentration summary statistics (milligrams per liter), water years 1999–2000

Minimum 25th

percentile Median 75thpercentile

90th

percentile

95th

percentile Maximum

Suspended sediment

Predicted 25 69 120 320 410 40 660

Measured 47 113 228 367 446 452 645

Total nitrogen

Predicted 2.0 3.0 4.0 6.0 7.0 7.0 7.0

Measured 2.3 2.75 3.0 3.65 4.78 6.3 6.6

Ammonia-plus-organic nitrogen

Predicted .31 .49 .61 .77 .95 1.0 1.1

Measured .30 .49 .70 1.02 1.26 1.33 1.4

Nitrite-plus-nitrate nitrogen

Predicted 2.0 2.0 3.0 5.0 6.0 6.0 6.0

Measured 1.9 2.1 2.2 2.6 4.2 5.8 6.1

Total phosphorus

Predicted .13 .22 .33 .45 .63 .67 .70

Measured .20 .28 .40 .61 .70 .75 1.1

Orthophosphate phosphorus

Predicted .072 .080 .099 .12 .13 .13 .14

Measured .074 .100 .125 .138 .148 .155 .164
84 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

The decision was made to use only regression 

models calibrated with the May 1999 – January 2000 

data set and was based in part on keeping the 

calibration period consistent among the constituents, 

particularly the nitrogen species. The main impetus, 

however, that determined the choice of using only the 

May 1999 – January 2000 data set was based on indepth examination of several factors.

The factors, alone and in combination, used to 

evaluate the Loadest2 results included (1) minimizing 

the relative percent difference between the average of 

the measured loads minus the average of the predicted 

loads for the May 1999 – January 2000 period; (2) 

optimizing for better agreement between the models' 

summary statistics of predicted concentrations and the 

summary statistics calculated for the measured 

concentration data; (3) optimizing for the lower 

standard deviation of the average daily load estimated 

for the calibration period; (4) minimizing the average 

of the relative percent differences between absolute 

values of the measured daily and predicted daily loads; 

and (5) using the general pattern of predicted daily 

loads graphed over time to assist in evaluating whether 

or not the models' extrapolations of loads for periods 

outside the calibration data set were reasonable. Some 

compromises and judgment were also used in choosing 

the calibration period and selected regression models. 

Load estimates for the nitrogen species are an example. 

Results of the Loadest2 default models (selected with 

Aikaike information criteria) for ammonia-plusorganic and nitrite-plus-nitrate nitrogen using the data 

set for May 1999 – January 2000 plus January 2001 –

September 2001 gave slightly smaller percent 

differences with measured loads and measured 

concentration summary statistics than the results with 

the data set for May 1999 – January 2000. However, 

the opposite was the case for loads of total nitrogen. 

The compromise was to use the May 1999 – January 

2000 data for all estimates of nitrogen loads, 

particularly because total nitrogen loads are based on 

total nitrogen concentrations, which are simply 

calculated sums from the two other species of nitrogen.

In the case of ammonia-plus-organic nitrogen 

and nitrite-plus-nitrate, warning messages generated by 

Loadest2 indicated that the models were 

overestimating maximum predicted concentrations 

compared with observed maximum concentrations. 

The program was calibrated again with the May 1999 – 

January 2000 concentration data, in combination with 

specific regression models, and the results were 

evaluated using the factors listed previously to select a 

particular model. When no single calibrationconcentration data set or specific model fit the data 

particularly well, some judgments and compromises 

were made, including using the default model based on 

the Aikaike information criteria.

The default model 1 for total nitrogen resulted in 

a relative percent difference between the average of the 

measured and the average of predicted loads for 1999-

2000 of 0.59, which was third highest among the 

different models (table B3). However, model 1 had one 

of the lowest standard deviations (4.6 percent) for the 

average daily load and one of the lowest average 

percent difference between measured and predicted 

concentration percentiles. The similarity in results 

among the different models and the pattern of daily 

loads over time (fig. B2A) did not warrant selecting a 

particular model over the Loadest2 default selection.

Regression model estimates of average 

ammonia-plus-organic nitrogen loads were highly 

variable, ranging from 5,500 to 6,200 lb/d (pounds per 

day) for 1999-2000, from 5,900 to 9,500 lb/d for water 

year 1999, and from 2,900 to 5,600 lb/d for water year 

2000. For the purposes of this report, model 2 was 

selected over the default model (model 3) because of 

the low relative percent difference between the average 

of the measured and the average of predicted loads (4.7 

percent), a low standard deviation of the average daily 

load (9.7 percent), and a lower percent difference 

between measured and predicted concentration 

percentiles than the default model (table B3). 

Figure B2B shows the daily loads over time for three of 

the different regression models and different calibration 

periods, which included the results of the model 

calibrated with the data set for May 1999 – January 

2000 plus January 2001 – September 2001 and the 

results from a trial model calibrated with all data 

available from 1999 to 2002. The selection of model 2 

was also due partly to the similarity with the 1999-

2002 test model in the peaks and troughs of predicted 

daily loads and the match to the measured loads 

(fig. B2B).
Appendix B.—Regression Models Used to Estimate Loads 85

Table B3. Factors used to assist in selecting calibration periods and regression models for loads of total 

nitrogen, ammonia-plus-organic nitrogen, nitrite-plus-nitrate nitrogen, and suspended sediment in the Yakima 

River at Kiona, Yakima River Basin, Washington

[Calibration data set: *, model selected by Aikaike information criteria of Loadest2. Bold indicates selected 

model for this report RPD, relative percentage of difference]

Calibration data set

RPD between 

average of 

measured and 

average of 

predicted loads, 

1999–2000

Average of RPD between absolute 

values of measured and predicted Standard 

deviation of 

average daily load 

Daily loads (percent)

Concenration 

percentiles

Total Nitrogen

1999–2000, model 1* 0.59 14 8.7 4.6

1999–2000, model 2 .64 14 14 4.6

1999–2000, model 3 .56 13 13 5.7

1999–2000, model 4 .50 13 6.7 7.5

1999–2001, model 2 -.63 17 13 4.8

Ammonia-plus-Organic Nitrogen

1999–2000, model 1 5.8 28 23 10

1999–2000, model 2 4.7 25 19 9.7

1999–2000, model 3* 5.4 20 43 14

1999–2000, model 4 5.5 20 11 14

1999–2001, model 4 6.0 24 16 11

Nitrite-plus-Nitrate Nitrogen

1999–2000, model 1 0.20 15 13 4.8

1999–2000, model 2 .03 14 9.4 5.0

1999–2000, model 3* -.19 11 49 7.5

1999–2000, model 4 -.29 11 11 6.1

1999–2001, model 2 .59 17 23 8.6

Suspended Sediment

1999–2000, model 1 16 46 20 18

1999–2000, model 2 -5.2 31 35 20

1999–2000, model 3 3.8 30 54 20

1999–2000, model 4 5.9 22 20 12

1999–2000, model 5* -1.0 22 50 14

1999–2001, model 4 7.3 26 31 11
86 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

1999-2000 calibration period,

model 1, default

1999-2000, model 4

1999-2000, model 3

1999-2000, model 2

1999-2001 calibration period, model 2 default

Measured

O ND JFMAM J J A S O ND J FMAM J J A S

1998 1999 2000

5,000

45,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

TOTAL NITROGEN LOAD, IN POUNDS

A. Total Nitrogen

Figure B2. Predicted and measured daily loads of total nitrogen, ammonia-plus-organic nitrogen, and nitrite-plus-nitrate nitrogen, and 

suspended sediment with different regression models and calibration periods for the Yakima River at Kiona, Yakima River Basin, 

Washington.
Appendix B.—Regression Models Used to Estimate Loads 87

AMMONIA-PLUS-ORGANIC NITROGEN LOAD, IN POUNDS

O ND JFMAM J J A S O ND J FMAM J J A S

1998 1999 2000

0

40,000

5,000

10,000

15,000

20,000

25,000

30,000

35,000 1999-2000, model 4

1999-2000, model 3, default

1999-2000, model 1

1999-2001 calibration period,

model 4, default

1999-2002 calibration period

model 2, default

Measured

1999-2000 calibration period,

model 2

B. Ammonia-plus-Organic Nitrogen

Figure B2.—Continued. 
88 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

1999-2000 calibration period, model 4

1999-2000, model 3, default

1999-2000, model 2

1999-2000, model 1

1999-2001 calibration period, model 2, default

Measured

O ND JFMAM J J A S O ND J FMAM J J A S

1998 1999 2000

5,000

30,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

22,000

24,000

26,000

28,000

NITRITE-PLUS-NITRATE NITROGEN LOAD, IN POUNDS

C. Nitrite-plus-Nitrate Nitrogen

Figure B2.—Continued. 
Appendix B.—Regression Models Used to Estimate Loads 89

1999-2000 calibration period,

model 4

1999-2000, model 5, default

1999-2000, model 3

1999-2000, model 2

1999-2001 calibration period, model 4, default

1999-2000, model 1

Measured

O ND JFMAM J J A S O ND J FMAM J J A S

1998 1999 2000

10,000

50,000,000

20,000

30,000

40,000

50,000

70,000

100,000

200,000

300,000

400,000

500,000

700,000

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

7,000,000

10,000,000

20,000,000

30,000,000

40,000,000

SUSPENDED-SEDIMENT LOAD, IN POUNDS

D. Suspended Sediment

Figure B2.—Continued. 
90 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Model 4 was selected for nitrite-plus-nitrate load 

estimates largely because the average of the percent 

differences between measured and predicted 

concentration percentiles and the standard deviation of 

the average daily load were less than those for the 

default model (model 3) (table B3). The default model 

was rejected because its pattern of continuously 

increasing daily loads from the beginning of the 1999-

2000 period, culminating in high estimates after 

February 2000, differed greatly from the patterns of 

three other regression models (fig. B2C). Also, model 4 

was selected over models 1 and 2 because of lower 

percent differences in the concentration percentiles, or 

lower average difference between measured and 

predicted daily loads, or both, and because the pattern 

of peaks and troughs in the daily loads matched the 

peaks and troughs of the measured loads a little better 

than models 1 and 2. It was noted above for nitriteplus-nitrate nitrogen that the May 1999 – January 2000 

plus January 2001 – September 2001 calibration data 

set appeared to give better load estimates than the May 

1999 – January 2000 calibration data set. Model 4, 

calibrated with the May 1999 – January 2000 data, 

resulted in an average daily load that was similar to the 

result from the default model (model 2) calibrated with 

the longer period in the data set (table B3).

As was the case for the nitrogen species, 

Loadest2 also generated a warning message for 

suspended sediment indicating the model was 

overestimating maximum concentrations compared 

with observed maximum concentrations. The program 

was calibrated again with May 1999 – January 2000 

concentration data and with specific regression models 

to improve the model's relation to measured 

concentrations while providing reasonable estimates of 

loads for the 1999-2000 period. The average loads 

predicted by the different models varied greatly, 

ranging from 426 to 662 tons per day for the 1999-

2000 period, from 557 to 1,173 tons per day for water 

1999, and from 153 to 477 tons per day for water year 

2000 (table B4). The decision was to use the results 

from model 4 because its average of the relative percent 

differences between the absolute values of measured 

and predicted daily loads, the standard deviation of the 

daily loads, and the average of relative percent 

differences between measured and predicted 

concentrations were among the lowest of the model 

results (table B3). Although model 1 or 2 might have 

been selected on the basis of some of the values in 

table B3, the graph of predicted daily loads over time 

(fig. B2D) showed that model 4 predictions fit the 

measured loads fairly well, thus the results of model 4 

were selected over those of the default and other 

models.

For total phosphorus and orthophosphate 

phosphorus loads in the Yakima River at Kiona, the 

results of the default regression models selected by 

Aikaike information criteria in Loadest2 were used for 

this report. Figure B3 show the relation between 

predicted loads and measured loads for total 

phosphorus and orthophosphate phosphorus, 

respectively. The average loads, standard deviations, 

percentiles of measured and predicted concentrations, 

and relative percent differences between measured and 

predicted loads are presented in table B5.
Appendix B.—Regression Models Used to Estimate Loads 91

Figure B3. Predicted and measured daily loads of phosphorus for 1999-2000 water years, Yakima River at Kiona, Yakima River Basin, 

Washington.

Daily loads, predicted using

regression equations

Daily load, measured

AM J J A SO ND JFM

1999 2000

700

25,000

1,000

2,000

3,000

4,000

5,000

7,000

10,000

20,000

AM J J A SO ND JFM

1999 2000

400

3,000

500

600

700

800

900

1,000

1,500

2,000

2,500

TOTAL PHOSPHORUS LOAD, IN POUNDS ORTHOPHOSPHATE LOAD, IN POUNDS
92 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Table B4. Estimates of average daily loads of suspended sediment and nutrients in the Yakima River at Kiona, Yakima River Basin, Washington for the 

period 1999–2000, water year 1999, and water year 2000 computed using discharge and concentration data from different calibration periods and different 

regression equations

[Bold indicates loads used for data interpretation in this report. Default models are the Loadest2 computer program selections using Aikaike information 

criteria. Abbreviations: ft3/s, cubic feet per second; WY, water year]

Year

Annual 

mean 

discharge 

(ft3/s)

Suspended sediment, tons per day

Calibration period

May 1999–January 2000

May 1999–

Jan. 2000

plus

Jan. 2001–

Sept. 2001

Oct. 1974–

Sept. 2001

May 1999–

Jan. 2000 

plus

Jan. 2001–

Aug. 2002

Model 5 

(default) Model 1 Model 2 Model 3 Model 4 Model 4 (default) Model 2 Model 8 Model 7

1999–2000 4,070 635 551 648 662 426 463 597 613 465

WY 1999 4,374 1,072 642 819 1,173 557 592 721 773 568

WY 2000 3,766 200 461 477 153 295 335 473 452 361

Year

Annual 

mean 

discharge 

(ft3/s)

Total nitrogen, pounds per day

Calibration period

May 1999–January 2000

May 1999–

Jan. 2000

plus

Jan. 2001–

Sept. 2001

Oct. 1974–

Sept. 2001

May 1999–

Jan. 2000 

plus

Jan. 2001–

Aug. 2002

Model 1 

(default) Model 2 Model 3 Model 4 Model 2 (default) Model 8 Model 8 Model 7

1999–2000 4,070 20,419 20,261 20,522 19,964 21,039 21,573 23,179 23,008

WY 1999 4,374 21,069 20,903 19,954 20,647 21,783 23,412 24,263 24,711

WY 2000 3,766 19,770 19,621 21,088 19,283 20,296 19,740 22,097 21,310

Year

Annual 

mean 

discharge 

(ft3/s)

Unfiltered ammonia-plus-organic nitrogen, pounds per day

Calibration period

May 1999–January 2000

May 1999–

Jan. 2000

plus

Jan. 2001–

Sept. 2001

Oct. 1974–

Sept. 2001

May 1999–

Jan. 2000 

plus

Jan. 2001–

Aug. 2002

Model 3 

(default) Model 1 Model 2 Model 4 Model 4 (default) Model 8 Model 6 Model 2

1999–2000 4,070 6,194 5,957 5,808 5,492 5,433 5,510 7,637 6,637

WY 1999 4,374 9,486 6,296 6,192 5,894 5,928 6,310 8,271 7,331

WY 2000 3,766 2,911 5,619 5,425 5,091 4,940 4,711 7,004 5,946
Appendix B.—Regression Models Used to Estimate Loads 93

Table B4. Estimates of average daily loads of suspended sediment and nutrients in the Yakima River at Kiona, Yakima River Basin, Washington for the 

period 1999–2000, water year 1999, and water year 2000 computed using discharge and concentration data from different calibration periods and different 

regression equations—Continued

Year

Annual 

mean 

discharge 

(ft3/s)

Nitrite-plus-nitrate nitrogen, pounds per day

Calibration period

May 1999–January 2000

May 1999–

Jan. 2000

plus

Jan. 2001–

Sept. 2001

Oct. 1974–

Sept. 2001

May 1999–

Jan. 2000 

plus

Jan. 2001–

Aug. 2002

Model 4 Model 1 Model 2 Model 3 

(default)

Model 2 

(default) Model 8 Model 6 Model 7

1999–2000 4,070 14,398 14,182 14,310 15,864 14,446 15,082 16,263 21,074

WY 1999 4,374 14,654 14,419 14,578 11,356 14,825 15,753 16,749 24,047

WY 2000 3,766 14,143 13,946 14,044 20,361 14,068 14,413 15,779 18,110

Year

Annual 

mean 

discharge 

(ft3/s)

Total phosphorus, pounds per day Orthophosphate, pounds per day

Calibration period

May 1999– 

Jan. 2000

May 1999– 

Jan. 2000 

plus

Jan. 2001–

Sept. 2001

Oct. 1974–

Sept. 2001

May 1999–

Jan. 2000 

plus

Jan. 2001–

Aug. 2002

May 1999– 

Jan. 2000

May 1999– 

Jan. 2000 

plus

Jan. 2001–

Sept. 2001

Oct. 1974–

Sept. 2001

May 1999–

Jan. 2000 

plus

Jan. 2001–

Aug. 2002

Model 2 

(default)

Model 2 

(default) Model 5 Model 2 Model 1 (default)

Model 1 

(default) Model 8 Model 1

1999–2000 4,070 2,785 2,808 2,556 3,075 1,065 1,097 1,131 1,223

WY 1999 4,374 3,121 3,100 2,802 3,444 1,109 1,150 1,189 1,275

WY 2000 3,766 2,450 2,520 2,311 2,707 1,021 1,050 1,073 1,171
94 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Table B5. Suspended-sediment and nutrient loads transported during water years 1999–2000, standard deviations, differences between measured 

and predicted loads, regression equations, and concentration summary statistics for load estimates at Yakima River at Kiona, Washington

[Daily loads are in pounds; ln, natural logarithm; Q, streamflow in cubic feet per second; sin, sine; cos, cosine; dectime, time in fractional years; MLE, 

maximum likelihood estimate; dload, daily load in pounds. Total nitrogen is based on the sum of unfiltered ammonia-plus-organic and nitrite-plus-nitrate 

nitrogen concentrations in the calibration data set, which included data collected from May 1999 through January 2000.]

Constituent

Daily load for 

water years

1999 –2000, and

(standard 

deviation)

Number of 

samples 

(number 

censored)

Average of the relative 

percent differences 

between the absolute 

values of the measured and 

predicted daily loads for 

the period 1999–2000

Relative percent difference 

between the average of the 

measured loads minus the 

average of the predicted 

loads for the period

1999–2000

MLE regression equation

Suspended 

sediment

850,000

(104,000)

16 (0) 22 5.9 ln(dload) = 4.8794 + 2.3744 ln(Q)

-0.26501 sin(dectime)

- 0.56849 cos(dectime)

Total nitrogen 20,000

(920)

16 (0) 14 0.6 ln(dload) = 9.821 + 0.42383 ln(Q)

Ammonia-plusorganic 

nitrogen

5,800

(560)

16 (0) 25 4.7 ln(dload) =8.2734 + 0.42454 ln(Q)

+ 0.63416 ln(Q)2

Nitrite-plusnitrate nitrogen14,000

(860)

16 (0) 11 -.3 ln(dload) = 9.5066 + 0.30862 ln(Q)

- 0.12726 sin(dectime)

+ 0.14316 cos(dectime)

Total phosphorus 2,800

(140)

16 (0) 12 1.1 ln(dload) = 7.3134 + 0.76782 ln(Q)

+ 0.81213 ln(Q)2

Orthophosphate 

phosphorus

1,100

(68)

16 (0) 19 -1.1 ln(dload) = 6.8201 + 0.54726 ln(Q)

Concentration summary statistics (milligrams per liter), water years 1999–2000

Minimum 25th

percentile Median 75thpercentile

90th 

ercentile

95th

percentile Maximum

Suspended sediment

Predicted 7 12 16 31 57 79 180

Measured 9 15 20 40 72 110 204

Total nitrogen

Predicted 0.5 0.83 1.0 1.4 1.6 1.7 1.9

Measured .50 .77 1.12 1.48 1.52 1.54 1.57

Ammonia-plus-organic nitrogen

Predicted .22 .23 .24 .34 .42 .48 .61

Measured .12 .25 .28 .34 .42 .48 .49

Nitrite-plus-nitrate nitrogen

Predicted .26 .54 .73 1.1 1.3 1.3 1.5

Measured .30 .49 .88 1.1 1.21 1.23 1.23

Total phosphorus

Predicted .091 .094 .11 .13 .16 .18 .33

Measured .079 .099 .12 .13 .13 .17 .27

Orthophosphate phosphorus

Predicted .03 .045 .053 .067 .074 .077 .084

Measured .028 .046 .074 .081 .088 .093 .127
Appendix C.—Mass-Balance Computations 95

APPENDIX C.—MASS-BALANCE COMPUTATIONS

Table C1. Mass-balance analyses for instantaneous streamflows and loads of total nitrogen and phosphorus in the reach of the Yakima River extending 

from river mile 103.7 to river mile 55, Yakima River Basin, Washington, August 1999 and July 1988—Continued

Site name River mile

Measured 

streamflow

(ft3/s)

Cumulative 

flows

(ft3/s)

Measured 

concentration 

(mg/L)

Measured 

load 

(lb/d)

Cumulative 

loading to 

reach

(lb/d)

Computed 

concentration 

(mg/L)

Total nitrogen (1999)

Yakima River near Parker1,2 103.7 685 685 0.25 939 939

Return from Sunnyside fish bypass2 103.6 40 725 .25 55 993

Zillah WWTP 89.5 .3 725 20.8 34 1,027

East Toppenish Drain 86.0 27.5 753 3.22 478 1,505

Sub-Drain 35 83.2 62.5 815 2.53 853 2,358

Granger Drain 82.8 62 877 2.35 786 3,144

Granger WWTP 82.8 .4 878 22.2 48 3,192

Marion Drain 82.6 66.8 945 2.72 980 4,172

Toppenish Creek 80.4 117 1,062 2.52 1,591 5,763

Yakima River at River Mile 72 72.0 1,270 – 1.03 7,057 – 0.84

Yakima River at River Mile 72 72.0 1,270 1,270 1.03 7,057 7,057

Satus Creek at Satus 69.6 128 1,398 1.86 1,284 8,342

South Drain near Satus 69.3 33.1 1,431 2.73 488 8,829

Sulphur Creek Wasteway 61.0 260 1,691 2.54 3,563 12,392

Yakima River at River Mile 55 55.0 2,050 – 1.41 15,594 – 1.12

Other statistics for river mile 103.7 to river mile 72

Unmeasured flow (ft3/s) 209

Unmeasured load (lb/d) 1,294

Unmeasured concentration (mg/L) 1.15

Total flow from tributaries (ft3/s) 337

Flow from tributaries as a percentage of total 26.5

Total load from tributaries (lb/d) 4,769

Load from tributaries as a percentage of total 67.6

Mean concentration in tributaries (mg/L) 2.63

Other statistics for river mile 72 to river mile 55

Unmeasured flow (ft3/s) 359

Unmeasured load (lb/d) 3,202

Unmeasured concentration (mg/L) 1.65

Total flow from tributaries (ft3/s) 421

Flow from tributaries as a percentage of total 20.5

Total load from tributaries (lb/d) 5,335

Load from tributaries as a percentage of total 34.2

Mean concentration in tributaries (mg/L) 2.35

Table C1. Mass-balance analyses for instantaneous streamflows and loads of total nitrogen and phosphorus in the reach of the Yakima River

extending from river mile 103.7 to river mile 55, Yakima River Basin, Washington, August 1999 and July 1988

[Cumulative and unmeasured flows and loads in bold computed by Pogue and others (1999) do not always agree with computed values in this table because 

more mainstem sites were sampled in July 1988 than in August 1999, and residuals in the mass-balance computations were set to zero at each mainstem site 

sampled; Abbreviations: ft3/s, cubic feet per second; lb/d, pounds per day; mg/L, milligrams per liter; nc, not computed because concentration would be a 

negative number; –, Except for data from Pogue and others (1999), no value is listed because cumulative flows and loading apply to inflows upstream from the 

downstream end of the reach on the Yakima River]
96 Suspended Sediment and Nutrients in Surface Water of the Yakima River Basin, Washington, 1999–2000—With an Analysis of Trends in Concentrations

Total nitrogen (1988) (data from Pogue and others, 1999)

Yakima River near Parker1,2 103.7 163 163 0.16 440 440

Zillah WWTP 89.5 0.3 163 8.0 12 452

East Toppenish Drain 86.0 30 193 4.5 730 1,182

Sub-Drain 35 83.2 34 227 2.4 480 1,662

Granger Drain 82.8 49 276 3.4 1,000 2,662

Granger WWTP 82.8 .3 277 4.0 7 2,669

Marion Drain 82.6 39 316 2.8 610 3,279

Toppenish Creek 80.4 54 370 2.9 840 4,119

Coulee Drain 77.0 28 398 2.1 320 4,439

Yakima River at River Mile 72 72.0 513 456 1.5 4,100 4,520 1.60

Yakima River at River Mile 72 72.0 513 513 1.5 4,100 4,100

Satus Creek at Satus 69.6 84 597 2.6 1,200 5,300

South Drain near Satus 69.3 82 679 3.7 1,600 6,900

DID No. 7 65.1 25 704 3.7 500 7,400

Sulphur Creek Wasteway 61.0 151 855 3.8 2,900 10,300

Mabton sewage plant 60.5 .9 856 3.1 15 10,315

Satus Drain 303 60.2 60 916 2.3 740 11,055

Yakima River at River Mile 55 55.0 972 916 1.9 10,000 11,055 2.11

Other statistics for river mile 103.7 to river mile 72

Unmeasured flow (ft3/s) 115 57

Unmeasured load (lb/d) -339 -420

Unmeasured concentration (mg/L) nc

Total flow from tributaries (ft3/s) 235

Flow from tributaries as a percentage of total 45.7

Total load from tributaries (lb/d) 3,999

Load from tributaries as a percentage of total 97.5

Mean concentration in tributaries (mg/L) 3.16

Other statistics for river mile 72 to river mile 55

Unmeasured flow (ft3/s) 56 56

Unmeasured load (lb/d) -1,055 -1,055

Unmeasured concentration (mg/L) nc

Total flow from tributaries (ft3/s) 403

Flow from tributaries as a percentage of total 41.5

Total load from tributaries (lb/d) 6,955

Load from tributaries as a percentage of total 69.6 

Mean concentration in tributaries (mg/L) 3.20

Table C1. Mass-balance analyses for instantaneous streamflows and loads of total nitrogen and phosphorus in the reach of the Yakima River extending 

from river mile 103.7 to river mile 55, Yakima River Basin, Washington, August 1999 and July 1988—Continued

Site name River mile

Measured 

streamflow

(ft3/s)

Cumulative 

flows

(ft3/s)

Measured 

concentration 

(mg/L)

Measured 

load 

(lb/d)

Cumulative 

loading to 

reach

(lb/d)

Computed 

concentration 

(mg/L)
Appendix C.—Mass-Balance Computations 97

Total phosphorus (1999)

Yakima River near Parker1,2 103.7 685 685 0.05 188 188

Return from Sunnyside fish bypass2 103.6 40 725 .05 11 199

Zillah WWTP 89.5 0.3 725 5.03 8 208

East Toppenish Drain 86.0 27.5 753 .19 27 235

Sub-Drain 35 83.2 62.5 815 .17 56 291

Granger Drain 82.8 62 877 .46 155 446

Granger WWTP 82.8 .4 878 1.18 3 449

Marion Drain 82.6 66.8 945 .12 41 490

Toppenish Creek 80.4 117 1,062 .13 79 569

Yakima River at River Mile 72 72.0 1,270 – .06 439 – 0.08

Yakima River at River Mile 72 72.0 1,270 1,270 .06 439 439

Satus Creek at Satus 69.6 128 1,398 .17 120 559

South Drain near Satus 69.3 33.1 1,431 .22 39 598

Sulphur Creek Wasteway 61.0 260 1,691 .21 295 893

Yakima River at River Mile 55 55.0 2,050 – .10 1,150 – 0.08

Other statistics for river mile 103.7 to river mile 72

Unmeasured flow (ft3/s) 209

Unmeasured load (lb/d) -131

Unmeasured concentration (mg/L) nc

Total flow from tributaries (ft3/s) 337

Flow from tributaries as a percentage of total 26.5

Total load from tributaries (lb/d) 370

Load from tributaries as a percentage of total 84.3

Mean concentration in tributaries (mg/L) 0.20

Other statistics for river mile 72 to river mile 55

Unmeasured flow (ft3/s) 359

Unmeasured load (lb/d) 258

Unmeasured concentration (mg/L) .13

Total flow from tributaries (ft3/s) 421

Flow from tributaries as a percentage of total 20.5

Total load from tributaries (lb/d) 454

Load from tributaries as a percentage of total 39.5

Mean concentration in tributaries (mg/L) .20

Table C1. Mass-balance analyses for instantaneous streamflows and loads of total nitrogen and phosphorus in the reach of the Yakima River extending 

from river mile 103.7 to river mile 55, Yakima River Basin, Washington, August 1999 and July 1988—Continued

Site name River mile

Measured 

streamflow

(ft3/s)

Cumulative 

flows

(ft3/s)

Measured 

concentration 

(mg/L)

Measured 

load 

(lb/d)

Cumulative 

loading to 

reach

(lb/d)

Computed 

concentration 

(mg/L)