Analysis of Ambient Conditions and Simulation of 

Hydrodynamics and Water-Quality Characteristics in 

Beaver Lake, Arkansas, 2001 through 2003

Prepared in cooperation with the

U.S. Army Corps of Engineers, the

Beaver Water District, and the

Arkansas Department of Environmental Quality

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2006-5003
.

Front cover: Photograph of Beaver Lake by Chuck Haralson, Arkansas Department of Parks and Tourism.
Analysis of Ambient Conditions and 

Simulation of Hydrodynamics and WaterQuality Characteristics in Beaver Lake, 

Arkansas, 2001 through 2003

By Joel M. Galloway and W. Reed Green

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2006-5003

Prepared in cooperation with the

U.S. Army Corps of Engineers, the

Beaver Water District, and the

Arkansas Department of Environmental Quality
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2006

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

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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.

Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report.
Contents

 iii

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

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

Purpose and Scope ...................................................................................................................................................................... 2

Description of Study Area ........................................................................................................................................................... 2

Methods ..................................................................................................................................................................................................... 4

Streamflow ..................................................................................................................................................................................... 4

Water-Quality Sampling ............................................................................................................................................................... 4

Constituent Loads ......................................................................................................................................................................... 5

Data Analysis ................................................................................................................................................................................. 5

Ambient Conditions .................................................................................................................................................................................. 5

Hydrologic Conditions .................................................................................................................................................................. 6

Water-Quality Conditions............................................................................................................................................................. 7

Inflow Water Quality.......................................................................................................................................................... 7

Reservoir Water Quality.................................................................................................................................................. 10

Temperature .......................................................................................................................................................... 10

Nutrients ................................................................................................................................................................ 12

Organic Carbon..................................................................................................................................................... 16

Chlorophyll a and Phytoplankton ....................................................................................................................... 18

Water Clarity.......................................................................................................................................................... 20

Simulation of Hydrodynamics and Water Quality............................................................................................................................. 23

Model Implementation ............................................................................................................................................................... 23

Computational Grid.......................................................................................................................................................... 23

Boundary and Initial Conditions .................................................................................................................................... 23

Hydraulic and Thermal Boundary Conditions.................................................................................................. 23

Chemical Boundary Conditions.......................................................................................................................... 23

Initial Conditions ................................................................................................................................................... 25

Model Parameters........................................................................................................................................................... 25

Model Calibration and Testing .................................................................................................................................................. 29

Water Balance ................................................................................................................................................................. 29

Temperature...................................................................................................................................................................... 30

Water Quality.................................................................................................................................................................... 35

Dissolved Oxygen ................................................................................................................................................. 35

Nitrogen and Phosphorus ................................................................................................................................... 35

Algae....................................................................................................................................................................... 48

Sensitivity ..................................................................................................................................................................................... 51

Model Limitations........................................................................................................................................................................ 51

Summary .................................................................................................................................................................................................. 53

References .............................................................................................................................................................................................. 55
iv 

Figures

1. Map showing Beaver Lake study area, Arkansas, with locations of data-collection sites ............................................ 3

2. Graphs showing daily inflow and hourly outflow for Beaver Lake, Arkansas, January 2001 through December

2003.......................................................................................................................................................................................... 6

3. Graph showing daily reservoir water-surface elevation near Beaver Lake dam, January 2001 through

December 2003 ...................................................................................................................................................................... 6

4. Boxplots showing distribution of nutrients, dissolved organic-carbon, and suspended-sediment concentrations

for the White River near Fayetteville, Richland Creek at Goshen, and War Eagle Creek near Hindsville,

2001-2003 ................................................................................................................................................................................ 7

5. Graphs showing time series of nutrients, dissolved organic-carbon, and suspended-sediment concentrations for

the White River near Fayetteville, Richland Creek at Goshen, and War Eagle Creek near Hindsville,

2001-2003 ................................................................................................................................................................................ 8

6. Graphs showing annual nutrient and organic-carbon loads computed for the White River near Fayetteville,

Richland Creek at Goshen, and War Eagle Creek near Hindsville, 2001-2003 ............................................................ 9

7. Boxplot and graph showing distribution and time series of turbidity for the White River near Fayetteville,

Richland Creek at Goshen, and War Eagle Creek near Hindsville, 2001-2003 .......................................................... 10

8. Graphs showing distribution of temperature and dissolved-oxygen concentration at sites L2 and L5 in

Beaver Lake, 2001-2002...................................................................................................................................................... 11

9. Graphs showing distribution of temperature and dissolved-oxygen concentration in Beaver Lake on

February 6, 2002 and August 22, 2002 .............................................................................................................................. 11

10. Boxplots showing distribution of nitrogen concentrations for five sites in Beaver Lake, 2001-2003 .......................... 12

11. Graphs showing time series of nitrogen concentrations for five sites in Beaver Lake, 2001-2003.............................. 13

12. Boxplots showing distribution of phosphorus concentrations for five sites in Beaver Lake, 2001-2003 .................... 14

13. Graphs showing time series of phosphorus concentrations for five sites in Beaver Lake, 2001-2003 ....................... 15

14. Boxplots showing distribution of organic-carbon concentrations for five sites in Beaver Lake, 2001-2003 ............. 16

15. Graphs showing time series of organic-carbon concentrations for five sites in Beaver Lake, 2001-2003................. 17

16. Boxplot showing distribution of chlorophyll a concentrations for five sites in Beaver Lake, 2001-2003 .................... 18

17. Graph showing time series of chlorophyll a concentrations for five sites in Beaver Lake, 2001-2003 ....................... 18

18. Graph showing distribution of phytoplankton and time series of chlorophyll a concentrations for five sites in

Beaver Lake, 2001-2002...................................................................................................................................................... 19

19. Boxplot showing distribution of Secchi depth for five sites in Beaver Lake, 2001-2003................................................ 20

20. Graph showing time series of Secchi depth for five sites in Beaver Lake, 2001-2003 ................................................... 21

21. Boxplot showing distribution of turbidity for five sites in Beaver Lake, 2001-2003......................................................... 22

22. Graph showing time series of turbidity for five sites in Beaver Lake, 2001-2003 ............................................................ 22

23. Plot showing side view, top view, and face view from the dam of the computational grid of Beaver Lake used in

the CE-QUAL-W2 model ..................................................................................................................................................... 24

24-30. Graphs showing:

24. Simulated and measured water-surface elevations near Beaver Lake dam, April 2001 to April 2003 ................. 29

25. Selected simulated and measured water-temperature profiles for Beaver Lake at Highway 412 bridge near

Sonora, Arkansas, April 2001 to April 2003‘ .................................................................................................................... 30

26. Selected simulated and measured water-temperature profiles for Beaver Lake near Lowell, Arkansas,

April 2001 to April 2003 ....................................................................................................................................................... 31

27. Selected simulated and measured water-temperature profiles for Beaver Lake at Highway 12 bridge

near Rogers, Arkansas, April 2001 to April 2003 ............................................................................................................ 32

28. Selected simulated and measured water-temperature profiles for Beaver Lake near Eureka Springs,

Arkansas, April 2001 to April 2003 ................................................................................................................................... 33

29. Selected simulated and measured dissolved-oxygen concentration profiles for Beaver Lake at Highway 412

bridge near Sonora, Arkansas, April 2001 to April 2003 ............................................................................................... 36

30. Selected simulated and measured dissolved-oxygen concentration profiles for Beaver Lake near

Lowell, Arkansas, April 2001 to April 2003....................................................................................................................... 37

31. Selected simulated and measured dissolved-oxygen concentration profiles for Beaver Lake at Highway

12 bridge near Rogers, Arkansas, April 2001 to April 2003........................................................................................... 38
v

32. Selected simulated and measured dissolved-oxygen concentration profiles for Beaver Lake near

Eureka Springs, Arkansas, April 2001 to April 2003........................................................................................................39

33. Simulated and measured ammonia concentrations for Beaver Lake, Arkansas, April 2001 to April 2003 ...........40

34. Simulated and measured nitrite plus nitrate concentrations for Beaver Lake, Arkansas, April 2001 to

April 2003...............................................................................................................................................................................41

35. Simulated and measured total nitrogen concentrations for Beaver Lake, Arkansas, April 2001 to

April 2003...............................................................................................................................................................................42

36. Simulated and measured orthophosphorus concentrations for Beaver Lake, Arkansas, April 2001 to

April 2003...............................................................................................................................................................................46

37. Simulated and measured total phosphorus concentrations for Beaver Lake, Arkansas, April 2001 to

April 2003...............................................................................................................................................................................47

38. Simulated and measured chlorophyll a concentrations for Beaver Lake, Arkansas, April 2001 to

April 2003...............................................................................................................................................................................49

39. Simulated phytoplankton distribution for Beaver Lake, Arkansas, April 2001 to April 2003....................................50

Tables

1. Water-quality and streamflow sites for Beaver Lake, Arkansas..........................................................................................4

2. Parameters and values used for the Beaver Lake model, April 2001 to April 2003 .........................................................25

3. Comparative statistics of simulated and measured temperature and dissolved-oxygen concentration

for Beaver Lake, April 2001 to April 2003 ................................................................................................................................34

4. Comparative statistics of simulated and measured nutrient concentrations for Beaver Lake, April 2001 to

April 2003......................................................................................................................................................................................43

5. Comparative statistics of simulated and measured chlorophyll a concentrations for Beaver Lake, April 2001

to April 2003 .................................................................................................................................................................................48

6. Results of sensitivity analysis for the Beaver Lake model, April 2001 to April 2003, showing the mean difference

of all computed values at five sites in Beaver Lake compared to calibrated values......................................................52
vi 

Conversion Factors, Vertical Datum, Abbreviations, and Acronyms

Multiply By To obtain

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

square meter (m2) 0.0002471 acre

square kilometer (km2) 247.1 acre

square meter (m2) 10.76 square foot (ft2)

square kilometer (km2) 0.3861 square mile (mi2)

liter (L) 0.2642 gallon (gal)

cubic meter (m3) 264.2 gallon (gal)

cubic centimeter (cm3) 0.06102 cubic inch (in3)

liter (L) 61.02 cubic inch (in3)

cubic meter (m3) 35.31 cubic foot (ft3)

cubic meter per second (m3/s) 70.07 acre-foot per day (acre-ft/d)

cubic meter per second (m3/s) 35.31 cubic foot per second (ft3/s)

cubic meter per day (m3/d) 35.31 cubic foot per day (ft3/d)

cubic meter per second (m3/s) 22.83 million gallons per day (Mgal/d)

kilogram per day (kg/d) 2.205 pound per day (lb/d)

kilogram per year (kg/yr) 2.205 pound per year (lb/yr)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 x °C) + 32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F-32)/1.8

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)

Abbreviations and acronyms used in this report:

mg/L, milligrams per liter

μg/L, micrograms per liter

USACE, U.S. Army Corps of Engineers

USGS, U.S. Geological Survey

AMLE, adjusted maximum likelihood estimator

LAD, least absolute deviation

LOWESS, locally weighted smooth line

NTU, nephelometric turbidity unit

AME, absolute mean error

RMSE, root mean square error
Analysis of Ambient Conditions and Simulation of 

Hydrodynamics and Water-Quality Characteristics in Beaver 

Lake, Arkansas, 2001 through 2003

By Joel M. Galloway and W. Reed Green

Abstract

Beaver Lake is a large, deep-storage reservoir located in 

the upper White River Basin in northwestern Arkansas. The 

purpose of this report is to describe the ambient hydrologic and 

water-quality conditions in Beaver Lake and its inflows and 

describe a two-dimensional model developed to simulate the 

hydrodynamics and water quality of Beaver Lake from 2001 

through 2003. 

Water-quality samples were collected at the three main 

inflows to Beaver Lake; the White River near Fayetteville, 

Richland Creek at Goshen, and War Eagle Creek near Hindsville. Nutrient concentrations varied among the tributaries 

because of land use and contributions of nutrients from point 

sources. The median concentrations of total ammonia plus 

organic nitrogen were greater for the White River than Richland 

and War Eagle Creeks. The greatest concentrations of nitrite 

plus nitrate and total nitrogen, however, were observed at War 

Eagle Creek. Phosphorus concentrations were relatively low, 

with orthophosphorus and dissolved phosphorus concentrations 

mostly below the laboratory reporting limit at the three sites. 

War Eagle Creek had significantly greater median orthophosphorus and total phosphorus concentrations than the White 

River and Richland Creek. Dissolved organic-carbon concentrations were significantly greater at the White River than at 

War Eagle and Richland Creeks. The White River also had significantly greater turbidity than War Eagle Creek and Richland 

Creek. 

The temperature distribution in Beaver Lake exhibits the 

typical seasonal cycle of lakes and reservoirs located within 

similar latitudes. Beaver Lake is a monomictic system, in which 

thermal stratification occurs annually during the summer and 

fall and complete mixing occurs in the winter. Isothermal conditions exist throughout the winter and early spring. 

Nitrogen concentrations varied temporally, longitudinally, 

and vertically in Beaver Lake for 2001 through 2003. Nitrite 

plus nitrate concentrations generally decreased from the 

upstream portion of Beaver Lake to the downstream portion and 

generally were greater in the hypolimnion. Total ammonia plus 

organic nitrogen concentrations also decreased from the 

upstream end of Beaver Lake to the downstream end and were 

substantially greater in the hypolimnion of Beaver Lake. Phosphorus concentrations mostly were near or below laboratory 

detection limits in the epilimnion and metalimnion in Beaver 

Lake and were substantially greater in the hypolimnion in the 

upstream and middle parts of the reservoir. Measured total and 

dissolved organic carbon in Beaver Lake was relatively uniform 

spatially, longitudinally, and vertically in the reservoir from 

January 2001 through December 2003. Chlorophyll a concentrations measured at sites in the upstream portion of the lake 

were significantly greater than at the other sites in the downstream portion of Beaver Lake. 

During the study period, water clarity in Beaver Lake was 

significantly greater at the downstream end of the reservoir than 

at the upstream end. The greatest Secchi depths at the downstream end of the reservoir generally were observed in 2001 

compared to 2002 and 2003, but did not have a seasonal pattern 

as observed at sites in the middle and upstream portion of the 

reservoir. Similar to Secchi depth results, turbidity results indicated greater water clarity in the downstream portion of Beaver 

Lake compared to the upstream portion. Turbidity also was 

greater in the hypolimnion than in the epilimnion in the reservoir during the stratification season. 

A two-dimensional, laterally averaged, hydrodynamic, 

and water-quality model using CE-QUAL-W2 Version 3.1 was 

developed for Beaver Lake and calibrated based on vertical profiles of temperature and dissolved oxygen, and water-quality 

constituent concentrations collected at various depths at four 

sites in the reservoir from April 2001 to April 2003. Simulated 

temperatures and dissolved-oxygen concentrations compared 

reasonably well with measured temperatures and dissolvedoxygen concentrations and differences varied spatially in Beaver Lake for April 2001 to April 2003. The greatest differences 

between measured and simulated temperature data occurred in 

the upstream portion of the reservoir, which is the most 

dynamic part of the reservoir. In general, the differences 

between measured and simulated temperature were the least in 

2001 at the two upstream sites and in 2002 at the two downstream sites, and greatest in 2003 for all four sites. Similar to 

temperature, differences between simulated and measured values of dissolved-oxygen concentrations were greater in the 

upstream portion of the reservoir compared to differences in the 

downstream portion. At the upstream portion of the reservoir, 

the greatest differences between simulated and measured dissolved oxygen generally occurred in 2002 and the least differences occurred in 2003. Simulated ammonia and total nitrogen 
2 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

concentrations in Beaver Lake compared relatively well with 

the measured concentrations and simulated nitrite plus nitrate 

concentrations generally were less then the measured concentrations. Simulated values for orthophosphorus were comparable to measured concentrations and simulated total phosphorus 

concentrations generally were greater than the measured concentrations in Beaver Lake. Simulated chlorophyll a values 

were comparable to measured chlorophyll a values both spatially and temporally in Beaver Lake. 

Introduction

Beaver Lake is a large, deep-storage reservoir located in 

the upper White River Basin in northwestern Arkansas. The reservoir was completed in 1963 for the purposes of flood control, 

hydroelectric power, and water supply. In addition, the reservoir is used for fish and wildlife habitat, recreation, and waste 

assimilation. 

Beaver Lake is affected by both point and nonpoint 

sources of contamination. The city of Fayetteville discharges 

about one-half of its sewage effluent into the White River 

immediately upstream from the backwater of the reservoir. The 

city of West Fork discharges its sewage effluent into the West 

Fork of the White River and the city of Huntsville discharges its 

effluent into a tributary of War Eagle Creek. Nutrients, sediment, pathogenic bacteria, and other constituents can enter Beaver Lake through its tributaries and around its shoreline. 

The water quality of Beaver Lake recently has become a 

focus of environmental concern because of the rapid population 

growth in northwestern Arkansas and because of agricultural 

activities in the basin. The greatest increase in population in the 

State of Arkansas from 1990 to 2000 occurred in Benton 

County (57 percent), Washington County (39 percent), and Carroll County (39 percent) (Arkansas Institute for Economic 

Advancement, 2004). The principal agricultural activity in the 

area is poultry production. As a result of the potential effects 

from population growth and activities in the watershed, there is 

concern about the current and future water-quality in Beaver 

Lake. Information is needed to assess current conditions and 

future reservoir water quality so water-resource managers can 

better manage the hydrologic system. From 2001 through 2003, 

a study was conducted by the U.S. Geological Survey (USGS) 

in cooperation with the U.S. Army Corps of Engineers 

(USACE), Beaver Water District, and the Arkansas Department 

of Environmental Quality (ADEQ) to assess the ambient water 

quality in Beaver Lake and its inflows and to develop a model 

that simulated current water-quality conditions. 

The calibrated Beaver Lake model can be used in the 

future for the evaluation of different nutrient and sediment loading scenarios and conservative tracer simulations. Results of the 

nutrient and sediment loading scenarios for Beaver Lake can be 

used to assist the ADEQ in the development of water-quality 

criteria for its designated uses. Historically, Arkansas’ waterquality standards for lakes have been adapted from the surfacewater quality standards for streams. The standards, criteria, and 

assessment methodology for streams may not be well adapted 

to assess lake water quality where only a few data points exist. 

Another application of the model is the use of conservative 

tracer simulations to evaluate the time of travel of a conservative constituent from different locations on Beaver Lake to the 

four public water-supply intakes for response to possible spills 

that may occur on the reservoir.

Purpose and Scope

The purpose of this report is to describe the ambient hydrologic and water-quality conditions in Beaver Lake and its 

inflows and to describe a two-dimensional model developed to 

simulate the hydrodynamics and water quality of Beaver Lake 

from 2001 through 2003. Hydrologic and water-quality data are 

summarized for the period of January 2001 through December 

2003 for streamflow, reservoir water-surface elevation, outflow, and selected water-quality characteristics including temperature, dissolved-oxygen concentrations, nutrient concentrations, organic-carbon concentrations, and chlorophyll a

concentrations. Estimated loads of nutrients and organic carbon 

for the three main inflows to Beaver Lake are presented.

Hydrodynamics and water-quality characteristics in Beaver Lake were simulated using the USACE CE-QUAL-W2 

Version 3.1 model. The laterally averaged, two-dimensional 

model was calibrated by using data collected from April 2001 

to April 2003. The model was used to simulate the ambient conditions in Beaver Lake from April 2001 to April 2003. 

Description of Study Area

Beaver Lake was impounded in 1963 on the White River, 

northeast of the city of Fayetteville, Arkansas, and in 1968 the 

reservoir reached conservation capacity (Haggard and Green, 

2002). The conservation capacity of the reservoir is the storage 

capacity used for hydroelectric power, water supply, fish and 

wildlife, recreation, and water quality (U.S. Corps of Engineers, 

1997). The main inflows into Beaver Lake are the White River, 

Richland Creek, and War Eagle Creek (fig. 1). Several smaller 

tributaries also flow into the reservoir. The basin has a drainage 

area of 3,087 km2 at the Beaver Lake dam. Beaver Lake contains 2,040 million m3 of water at the top of the current conservation pool (341.4 m above NGVD of 1929) and the surface 

area is 114 km2 (Haggard and Green, 2002). The length of the 

reservoir is 80 km from the White River at the Highway 45 

Bridge to the Beaver Lake dam. The depth of the reservoir at the 

dam at conservation pool elevation is 60 m, and the average 

depth through the reservoir is 18 m (Haggard and Green, 2002).

Beaver Lake has three distinct zones with unique and 

dynamic physical, chemical, and biological characteristics that 

are typical for large reservoirs; a riverine, transitional, and a 

lacustrine zone (Wetzel, 2001). The riverine zone is relatively 

narrow, the water is well-mixed, and velocities are high enough 

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 Introduction 3

Figure 1. Beaver Lake study area, Arkansas, with locations of data-collection sites.
4 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

matter) through advective transport. High particulate turbidity 

reduces light penetration and limits algal production in this zone 

(Wetzel, 2001). Decomposition of organic matter usually is 

high, which consumes a substantial amount of dissolved oxygen 

in the water column. In the transitional zone, water velocities 

decrease as energy is dispersed over a larger area. A large portion of the suspended load settles out of the water column, 

enhancing the depth of light penetration, which increases the 

rates of photosynthetic productivity of algae in this zone. 

Anoxic conditions in the hypolimnion in the transitional zone 

usually occur early in the stratification season of the reservoir 

from sediment and biochemical demand from deposited material. The lacustrine zone (or lake-like zone) is characterized by 

having distinct stratification with small nutrient concentrations 

resulting in reduced algal production. Sedimentation of organic 

matter and decomposition in the lacustrine zone is less than in 

the riverine and transition zones, generally resulting in lower 

concentrations of nutrients and higher dissolved oxygen in the 

hypolimnion. The extent of the three zones can be spatially and 

temporally dynamic with changing inflow and outflow conditions in the reservoir.

Methods

This section describes the methods of data collection and 

analysis used to describe the ambient conditions in Beaver 

Lake, Arkansas. Streamflow and water-quality data were collected at four tributaries to Beaver Lake from January 2001 

through December 2003. Annual constituent loads were estimated from streamflow and water-quality data at three of the 

tributary sites for the period. Water-quality data also were collected at five sites in Beaver Lake for the same period. 

Streamflow

Stream stage was measured continuously at the White 

River near Fayetteville (site S1), Richland Creek at Goshen (site 

S2), War Eagle Creek near Hindsville (site S3), and Prairie 

Creek northeast of Rogers (site S4) (fig. 1 and table 1). Stage 

and instantaneous discharge were measured to compute the 

continuous streamflow from stage-discharge rating curves 

using methods described in Rantz and others (1982). Outflow 

data from Beaver Lake were produced by the USACE using 

stage-discharge relations and hourly power generation records 

for the period of January 2001 through December 2003 (John 

Kielczewski, U.S. Army Corps of Engineers, written commun., 

2003).

Water-Quality Sampling

Water-quality samples were collected from April 2001 

through December 2003 at five fixed sites established along the 

downstream gradient of Beaver Lake. Sample sites in the lake 

were located along the original stream channel, the deepest 

location within the lake cross section. Samples were collected 

on the White River near Goshen (site L1), at Highway 412 

Bridge near Sonora (site L2), near Lowell (site L3), at Highway 

Table 1. Water-quality and streamflow sites for Beaver Lake, Arkansas.

[Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD83)]

Site

identification

number

(figure 1) Station number Station name Station type Latitude Longitude 

S1 07048600 White River near Fayetteville Streamflow, water quality 36°04’23” 94°04’52”

S2 07048800 Richland Creek at Goshen Streamflow, water quality 36°06’15” 94°00’28”

S3 07049000 War Eagle Creek near Hindsville Streamflow, water quality 36°12’00” 93°51’18”

S4 07049563 Prairie Creek northeast of Rogers Streamflow 36°20’25” 95°05’51”

L1 07048700 White River near Goshen Water quality 36°06’21” 94°00’41”

L2 07048910 Beaver Lake at Highway 412 Bridge near Sonora Water quality 36°10’00” 94°00’26”

L3 07049200 Beaver Lake near Lowell Water quality 36°15’33” 94°04’08”

L4 07049500 Beaver Lake at Highway 12 Bridge near Rogers Water quality 36°19’56” 94°01’08”

L5 07049690 Beaver Lake near Eureka Springs Water quality 36°25’15” 93°50’50”
Ambient Conditions 5

12 Bridge near Rogers (site L4), and near Eureka Springs (site 

L5) (fig. 1 and table 1). Samples were collected using a peristaltic pump and hose to collect samples at 2 m below the water surface once a month when isothermal and well-mixed conditions 

were present. During thermal stratification, samples were collected twice a month at 2 m below the water surface to represent 

the epilimnion (near surface), at variable depths in the metalimnion depending on the depth of the thermocline (middle depth), 

and at 2 m above the reservoir bottom to represent the hypolimnion (near bottom). Water-quality samples were analyzed for 

concentrations of nutrients (dissolved nitrite plus nitrate, total 

ammonia plus organic nitrogen, dissolved orthophosphorus, 

dissolved phosphorus, total phosphorus), total and dissolved 

organic carbon, iron, manganese, and turbidity. Samples collected in the epilimnion also were analyzed for chlorophyll a

and phytoplankton composition. All sample analyses were conducted at USGS laboratories following USGS procedures (Fishman, 1993). Field measurements (water temperature, dissolvedoxygen concentration, pH, and specific conductance) also were 

measured at various depths at the time of sample collection. 

When thermal stratification was present, field measurements 

were made at depth intervals where the change in water temperature was approximately 1 °C or at 0.3-m intervals, whichever 

was greater. Secchi depth also was measured at each site as an 

indicator of water clarity. 

Water-quality samples also were collected from three 

fixed inflow sites including the White River near Fayetteville 

(site S1), Richland Creek at Goshen (site S2), and War Eagle 

Creek near Hindsville (site S3), from April 2001 through 

December 2003 (fig. 1 and table 1). Water-quality samples were 

collected following equal-width increment methods using 

depth-integrated samplers and processed using protocols 

described in Wilde and Radke (1998), Wilde and others (1998a, 

1998b, 1998c, 1999a, and 1999b), and Meyers and Wilde 

(1999). Samples were analyzed for nutrients, dissolved organic 

carbon, turbidity, suspended sediment, and fecal indicator bacteria (fecal coliform and fecal streptococci). Field measurements, including water temperature, dissolved-oxygen concentration, pH, and specific conductance, also were collected with 

each sample. Water-quality samples were collected monthly 

and during selected surface-runoff events.

Constituent Loads

Nutrient and organic carbon loads were estimated for three 

main inflows to Beaver Lake; the White River near Fayetteville 

(site S1), Richland Creek at Goshen (site S2), and War Eagle 

Creek near Hindsville (site S3) (fig. 1). Constituent load (L) is 

a function of the volumetric rate of water passing a point in the 

stream (Q) and the constituent concentration within the water 

(C). Regression methods used to estimate constituent loads use 

the natural logarithm (ln) transformed relation between Q and C

to estimate daily C (or L) of the constituent. The regression 

method can account for non-normal data distributions, seasonal 

and long-term cycles, censored data, biases associated with 

using logarithmic transformations, and serial correlations of the 

residuals (Cohn, 1995). The regression method uses discrete 

water-quality samples often collected over several years and a 

daily streamflow hydrograph. Seasonality and time were not 

included in the regression analysis described in this report 

because the period of data collection was too short (3 years) to 

describe or identify seasonal or temporal trends in the data for 

the regression model. Therefore, only the relations between natural logarithmic-transformed L and Q were used:

ln( ) L = βo + β1 ln( ) Q (1)

Transforming the results of the model from logarithmic 

space to real space was accomplished using two methods; an 

adjusted maximum likelihood estimator (AMLE) and a least 

absolute deviation (LAD) (Cohn and others, 1992). The AMLE 

method was used if the constituent had censored values and the 

LAD method was used to transform the results if no censored 

values were included in the data or if outliers in the residuals 

were present. The S-LOADEST computer program (Runkel 

and others, 2004) was used to estimate daily loads for calendar 

years 2001 through 2003.

Data Analysis

The resulting streamflow and water-quality data (inflow 

and lake samples) were analyzed or summarized using several 

statistical and graphical techniques. Boxplots and time-series 

plots were used to compare concentrations of selected waterquality constituents between sites for data collected from April 

2001 through December 2003. Concentrations reported as less 

than a laboratory reporting limit were converted to one-half the 

reporting limit for preparation of boxplots, calculation of total 

nitrogen concentrations (the sum of nitrite plus nitrate and 

ammonia plus organic nitrogen), and statistical analyses. The 

Wilcoxon rank sum test (Helsel and Hirsch, 1992) was used to 

test for differences in selected water-quality constituents 

between sites. The Wilcoxon rank sum test is a nonparametric 

test that determines the probability (p) that the mean of a dataset 

is similar to the mean of another dataset. A locally weighted 

smooth (LOWESS) line was included in some of the scatter 

plots of constituent concentrations with time. The LOWESS 

line is a locally weighted polynomial regression, where at each 

point along the line, a low-degree polynomial is fit to a subset 

of the data. The polynomial is fit using weighted least squares, 

giving more weight to points near the point whose response is 

being estimated and less weight to points further away.

Ambient Conditions

This section describes the ambient hydrologic and waterquality conditions for Beaver Lake from January 2001 through 

December 2003. Streamflow in the three major tributaries, outflow at Beaver Lake dam, and water-surface elevation for Bea-
6 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

ver Lake are described for the period. In addition, water-quality 

conditions for the three major tributaries and for five sites on 

Beaver Lake are described for January 2001 through December 

2003.

Hydrologic Conditions

Streamflow varied substantially during the period of January 2001 through December 2003 for the three major tributaries 

that provide inflow to Beaver Lake (fig. 2). The White River is

Figure 2. Daily inflow and hourly outflow for Beaver Lake, Arkansas,

January 2001 through December 2003.

the main inflow into Beaver Lake and approximately 34 percent 

of the drainage area at Beaver Lake dam is above the gaging station near Fayetteville (site S1; fig. 1). The daily mean streamflow for the White River ranged from 0.05 to 792 m3

/s for the 

period of January 2001 through December 2003. The streamflow was greatest in calendar year 2002 with an annual mean of 

16.1 m3

/s and 2003 had the least streamflow with an annual 

mean of 10.3 m3

/s. The mean daily streamflow for the period 

was 13.6 m3

/s, which was less than the mean daily streamflow 

for the period of record (1963-1994, 1998-2003; 15.7 m3/s) 

(Brossett and others, 2005). The drainage area of Richland 

Creek at the gaging station at Goshen (site S2; fig. 1) comprises 

12 percent of the drainage area at Beaver Lake dam. The daily 

mean streamflow for Richland Creek ranged from 0.012 to 225 

m3

/s for the period of January 2001 through December 2003, 

with a mean daily streamflow of 3.47 m3

/s for the period. Similar to the White River, the annual mean streamflow was greatest in 2002 (4.73 m3

/s) and least in 2003 (2.49 m3/s). War Eagle 

Creek at the gaging station near Hindsville (site S3; fig. 1) has 

a drainage area that comprises 22 percent of the drainage area at 

Beaver Lake dam. The daily mean streamflow for War Eagle 

Creek ranged from 0.26 to 479 m3/s for the period of January 

2001 through December 2003, with a mean daily streamflow of 

7.30 m3

/s for the period. All three tributaries had the greatest 

streamflow in March 2001 and from January 2002 to May of 

2002 (fig. 2). The least streamflow occurred from September 

through December during all 3 years (2001 through 2003).

The outflow from Beaver Lake also varied substantially 

for the period of January 2001 through December 2003 (fig. 2). 

Outflow discharge at Beaver Dam ranged from 1.76 m3

/s to 828 

m3

/s with a mean outflow discharge of 29.3 m3/s for the period. 

Four public water-supply withdrawals also are located on Beaver Lake. Total annual mean withdrawal from all four public 

water supplies was approximately 2.41 m3/s for the period (Terrance W. Holland, U.S. Geological Survey, oral commun., 

2004).

The pool elevation (water-surface elevation) for Beaver 

Lake varied according to changes in the inflow and outflow for 

the reservoir (fig. 3). The pool elevation remained below the top

DATE

1/1/01 7/1/01 1/1/02 7/1/02 1/1/03 7/1/03 1/1/04

WATER-SURFACE ELEVATION, IN

METERS ABOVE NGVD OF 1929

338

339

340

341

342

343

344

345

TOP ELEVATION OF

CONSERVATION POOL

Figure 3. Daily reservoir water-surface elevation near Beaver Lake dam, 

January 2001 through December 2003.
Ambient Conditions 7

of conservation pool (341.4 m above NGVD of 1929) for most 

of 2001 and reached a minimum elevation of 338.7 m above 

NGVD of 1929 on November 15, 2003. The pool elevation rose 

above the top of the conservation pool into the flood pool in 

February 2002 and reached a maximum elevation of 344.5 m 

above NGVD of 1929 on April 9, 2002.

Water-Quality Conditions

Inflow Water Quality

Water-quality samples were collected at the three main 

inflows to Beaver Lake; the White River near Fayetteville (site 

S1), Richland Creek at Goshen (site S2), and War Eagle Creek 

near Hindsville (site S3) (fig. 1). The inflows were sampled for 

nutrients, dissolved organic carbon, turbidity, and suspended 

sediment. Annual loads were estimated for nutrients and 

organic carbon using the constituent concentrations and daily 

streamflow at each station. 

Nutrient concentrations varied among the tributaries 

because of differences in land use and contributions of nutrients 

from point sources. The White River had significantly (p-value 

<0.05) greater concentrations of total ammonia plus organic 

nitrogen among the three tributaries (figs. 4 and 5), probably 

because of a wastewater discharge upstream from the site on the 

West Fork of the White River. The median concentration of 

total ammonia plus organic nitrogen for the White River was 

0.30 mg/L as nitrogen, Richland Creek had a median concentration of 0.20 mg/L as nitrogen, and War Eagle Creek had a 

median concentration of 0.10 mg/L as nitrogen. The White 

River (site S1) and Richland Creek (site S2) had median nitrite 

plus nitrate concentrations of 0.36 and 0.85 mg/L as nitrogen, 

respectively, and median concentrations of total nitrogen of 

0.74 and 1.1 mg/L as nitrogen, respectively. The greatest concentrations of nitrite plus nitrate and total nitrogen, however, 

were observed at War Eagle Creek (site S3). The median concentrations of nitrite plus nitrate and total nitrogen for War 

Eagle Creek were 1.2 and 1.4 mg/L as nitrogen, respectively. 

War Eagle Creek has the greatest percentage of agricultural 

land use in the basin (36 percent) compared to the White River 

near Fayetteville drainage (23 percent) and Richland Creek 

drainage (34 percent) (U.S. Geological Survey, 2002), which 

may explain the greater nitrogen concentrations. Phosphorus 

concentrations were relatively low, with orthophosphorus and 

dissolved phosphorus concentrations mostly below the laboratory reporting limits (0.01 mg/L for orthophosphorus and 0.02 

mg/L for dissolved phosphorus) at the three sites. War Eagle 

Creek had significantly greater median orthophosphorus, dissolved phosphorus, and total phosphorus concentrations (0.03, 

0.03, and 0.04 mg/L as phosphorus, respectively) than the 

White River (0.01, 0.02, and 0.03 mg/L as phosphorus, respectively) and Richland Creek (0.01, 0.02, and 0.02 mg/L as phosphorus, respectively) (fig. 4).

TOTAL AMMONIA PLUS ORGANIC NITROGEN

AS NITROGEN

0.0

0.4

0.8

1.2

1.6

2.0

ORTHOPHOSPHORUS AS PHOSPHORUS

SITE

SITE S1 SITE S2 SITE S3

0.00

0.05

0.10

0.15

0.20

0.25

TOTAL NITROGEN AS NITROGEN

0.0

0.5

1.0

1.5

2.0

2.5

3.0

NITRITE PLUS NITRATE AS NITROGEN

CONCENTRATION, IN MILLIGRAMS PER LITER

0.0

0.5

1.0

1.5

2.0

2.5 TOTAL PHOSPHORUS AS PHOSPHORUS

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

DISSOLVED ORGANIC CARBON AS CARBON

CONCENTRATION, IN MILLIGRAMS PER LITER

0

2

4

6

8

SUSPENDED SEDIMENT

SITE

SITE S1 SITE S2 SITE S3

1

10

100

1000

10000

DISSOLVED PHOSPHORUS AS PHOSPHORUS

0.00

0.04

0.08

0.12

0.16

0.20

EXPLANATION

90th percentile

75th percentile

50th percentile

25th percentile

10th percentile

c Distributions associated

with the same letter

are not significantly

(p<0.05) different

Outlier

a b b

a

b

c

a b

c

a

b

c

a a b

a

b

c

a

b

b

a

b b

,

,

Figure 4. Distribution of nutrients, dissolved organic carbon, and suspended-sediment concentrations for the White River near Fayetteville (site S1), 

Richland Creek at Goshen (site S2), and War Eagle Creek near Hindsville (site S3), 2001-2003.
WAR EAGLE CREEK NEAR HINDSVILLE

DATE

1/1/01 7/1/01 1/1/02 7/1/02 1/1/03 7/1/03 1/1/04

0

2

4

6

8

RICHLAND CREEK AT GOSHEN

0

2

4

6

8

WHITE RIVER NEAR FAYETTEVILLE

DISSOLVED ORGANIC-CARBON CONCENTRATION,

IN MILLIGRAMS PER LITER AS CARBON 0

2

4

6

8

WHITE RIVER NEAR FAYETTEVILLE

NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER AS NITROGEN 0.0

0.5

1.0

1.5

2.0

2.5

RICHLAND CREEK AT GOSHEN

0.0

0.5

1.0

1.5

2.0

2.5

WAR EAGLE CREEK NEAR HINDSVILLE

DATE

1/1/01 7/1/01 1/1/02 7/1/02 1/1/03 7/1/03 1/1/04

0.0

0.5

1.0

1.5

2.0

2.5

TOTAL AMMONIA PLUS ORGANIC NITROGEN

NITRITE PLUS NITRATE

LOCALLY WEIGHTED SMOOTH LINE

OF TOTAL AMMONIA PLUS ORGANIC NITROGEN

LOCALLY WEIGHTED SMOOTH LINE

OF NITRITE PLUS NITRATE

CONCENTRATION BELOW LABORATORY

REPORTING LIMIT

EXPLANATION

WHITE RIVER NEAR FAYETTEVILLE

PHOSPHORUS CONCENTRATION, IN

MILLIGRAMS PER LITER AS PHOSPHORUS

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

WAR EAGLE CREEK NEAR HINDSVILLE

DATE

1/1/01 7/1/01 1/1/02 7/1/02 1/1/03 7/1/03 1/1/04

0.00

0.05

0.10

0.15

0.20

0.25

TOTAL PHOSPHORUS CONCENTRATION

BELOW LABORATORY REPORTING LIMIT

EXPLANATION

RICHLAND CREEK AT GOSHEN

0.00

0.02

0.04

0.06

0.08

0.10

WAR EAGLE CREEK NEAR HINDSVILLE

DATE

1/1/01 7/1/01 1/1/02 7/1/02 1/1/03 7/1/03 1/1/04

0

20

40

60

80

100

120

RICHLAND CREEK AT GOSHEN

0

20

40

60

80

100

120

WHITE RIVER NEAR FAYETTEVILLE

SUSPENDED-SEDIMENT CONCENTRATION, IN MILLIGRAMS PER LITER

0

200

400

600

800

1000

EXPLANATION

ORTHOPHOSPHORUS

TOTAL PHOSPHORUS

LOCALLY WEIGHTED SMOOTH LINE

OF ORTHOPHOSPHORUS

LOCALLY WEIGHTED SMOOTH LINE

OF TOTAL PHOSPHORUS

ORTHOPHOSPHORUS

CONCENTRATION

BELOW LABORATORY

REPORTING LIMIT

LOCALLY WEIGHTED SMOOTH LINE

MEASURED CONCENTRATION

,

8 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

Figure 5. Time series of nutrients, dissolved organic-carbon, and suspended-sediment concentrations for the White River near Fayetteville (site S1), 

Richland Creek at Goshen (site S2), and War Eagle Creek near Hindsville (site S3), 2001-2003.
Ambient Conditions 9

Dissolved organic-carbon concentrations were significantly greater for the White River than for War Eagle and Richland Creeks (figs. 4 and 5). The median dissolved organic-carbon concentration for the White River was 2.5 mg/L as carbon, 

which was approximately 1.5 percent greater than the median 

concentrations at War Eagle and Richland Creeks (1.7 mg/L as 

carbon).

Suspended-sediment concentrations also were significantly greater for the White River compared to War Eagle 

Creek and Richland Creek (figs. 4 and 5). The White River had 

suspended-sediment concentrations ranging from 2 to 950 mg/

L and a median concentration of 29 mg/L. War Eagle Creek had 

concentrations ranging from less than 1 to 95 mg/L with a 

median concentration of 25 mg/L. Richland Creek had a median 

concentration of 20 mg/L with concentrations ranging from 1 to 

102 mg/L.

Estimated annual nutrient and organic-carbon loads generally were greater for the White River than for Richland and War 

Eagle Creeks in 2001 through 2003 (fig. 6). Greater loads would 

be expected for the White River because of the greater volume 

of streamflow that occurs at the site. The greatest annual loads 

occurred in 2002 for all three tributaries and the least occurred 

in 2003 (fig. 6). Annual total ammonia plus organic nitrogen 

loads for the White River ranged from 220,000 to 401,000

kg/yr as nitrogen. Nitrite plus nitrate loads ranged from 182,000 

to 333,000 kg/yr as nitrogen. Richland Creek had substantially 

less total ammonia plus organic nitrogen loads and similar 

nitrite plus nitrate loads compared to the loads estimated for the 

White River. Total ammonia plus organic nitrogen loads for 

Richland Creek ranged from 28,000 to 54,400 kg/yr as nitrogen 

and nitrite plus nitrate loads ranged from 166,000 to 484,000 

kg/yr as nitrogen. Total ammonia plus organic nitrogen loads 

for War Eagle Creek ranged from 46,600 to 114,000 kg/yr as 

nitrogen and nitrite plus nitrate loads ranged from 171,000 to 

419,000 kg/yr as nitrogen. Total phosphorus loads for the White 

River (32,700 to 68,600 kg/yr as phosphorus) were approximately nine times greater than the loads for Richland Creek 

(3,560 to 7,640 kg/yr as phosphorus) and approximately three 

to four times greater than the loads for War Eagle Creek (8,580 

to 24,000 kg/yr as phosphorus). Similarly, dissolved organiccarbon loads for the White River (901,000 to 1,610,000 kg/yr as 

carbon) were approximately five to six times greater than the 

loads for Richland Creek (160,000 to 323,000 kg/yr as carbon) 

and approximately two to three times greater than the loads for 

War Eagle Creek (270,000 to 676,000 kg/yr as carbon).

TOTAL AMMONIA PLUS ORGANIC NITROGEN

AS NITROGEN

2001 2002 2003

LOAD, IN KILOGRAMS PER YEAR

0

100000

200000

300000

400000

500000

600000

WHITE RIVER NEAR FAYETTEVILLE (SITE S1)

RICHLAND CREEK AT GOSHEN (SITE S2)

WAR EAGLE CREEK NEAR HINDSVILLE (SITE S3)

TOTAL NITROGEN AS NITROGEN

YEAR

2001 2002 2003

0

200000

400000

600000

800000

1000000

ORTHOPHOSPHORUS AS PHOSPHORUS

2001 2002 2003

0

2000

4000

6000

8000

10000

12000

14000

16000

NITRITE PLUS NITRATE AS NITROGEN

2001 2002 2003

0

100000

200000

300000

400000

500000

600000

TOTAL PHOSPHORUS AS PHOSPHORUS

2001 2002 2003

LOAD, IN KILOGRAMS PER YEAR

0

20000

40000

60000

80000

100000

DISSOLVED ORGANIC CARBON AS CARBON

2001 2002 2003

0

400000

800000

1200000

1600000

2000000

EXPLANATION

TOTAL ORGANIC CARBON AS CARBON

YEAR

2001 2002 2003

0

200000

400000

600000

800000

1000000

,

,

,

,

,

,

,

,

,

,

,

,

, ,

,

,

,

,

,

,

,

,

,

,

,

, ,

, ,

, ,

,

,

,

,

,

,

,

,

,

,

,

,

,

,

Figure 6. Annual nutrient and organic-carbon loads computed for the White River near Fayetteville, Richland Creek at Goshen, and War Eagle Creek 

near Hindsville, 2001-2003.
10 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

Turbidity measured at the White River was significantly 

greater than Richland and War Eagle Creeks from 2001 through 

2003 (fig. 7). Turbidity is an expression of the optical properties

Figure 7. Distribution and time series of turbidity for the White River near 

Fayetteville (site S1), Richland Creek at Goshen (site S2), and War Eagle 

Creek near Hindsville (site S3), 2001-2003.

of a sample that causes light rays to be scattered and absorbed 

rather than transmitted in straight lines through the sample 

(Gray and Glysson, 2003). Turbidity of water is caused by the 

presence of suspended and dissolved matter such as clay, silt, 

small organic matter, plankton, other microscopic organisms, 

and organic acids. The median turbidity for the White River was 

8.6 nephlometric turbidity units (NTUs), and the median turbidities for Richland Creek and War Eagle Creek were 3.8 and 

3.4 NTUs, respectively. The greatest values of turbidity generally occurred from October 2001 through April 2002 at all three 

sites (fig. 7). This period of time also had a substantial number 

of high-flow events resulting in increased runoff of organic and 

inorganic material into the streams, which would increase the 

turbidity. The suspended-sediment concentrations followed a 

similar pattern with significantly greater median concentrations 

occurring at the White River (29 mg/L) compared to War Eagle 

Creek (25 mg/L) and Richland Creek (20 mg/L) (fig. 4), and 

generally greater concentrations occurring from October 2001 

through April 2002.

Reservoir Water Quality

Temperature

The temperature distribution in Beaver Lake exhibits the 

typical seasonal cycle of lakes and reservoirs located within 

similar latitudes (Wetzel, 2001) (figs. 8 and 9). Beaver Lake is 

a monomictic system, in which thermal stratification occurs 

annually during the summer (June through August) and fall 

(September through November) and complete mixing occurs in 

the winter (December through February). Isothermal conditions 

exist throughout the winter and early spring (March through 

May). Thermal stratification begins in Beaver Lake during May 

and June and generally becomes established by July (figs. 8 and 

9). Thermal stratification is fully developed by late summer. 

Stratification occurs as the layer of water near the surface heats 

up during the spring, more rapidly than the heat is distributed 

throughout the water column, causing temperature or density 

gradients to develop. The warmer, less dense water remains 

near the surface and the cooler, more dense water remains near 

the bottom. As a result of the density gradients, thermal resistance to mixing becomes established, physically isolating the 

epilimnion or mixing layer from the hypolimnion. 

The distribution of dissolved oxygen in Beaver Lake is 

affected by several factors including thermodynamics in the 

hypolimnion, algal photosynthesis and respiration, ammonia 

nitrification, decomposition of organic matter in the sediments 

and water column, and exchange with the atmosphere (Cole and 

Hannan, 1990). The solubility of oxygen increases with colder 

water, while warmer water holds less amounts of dissolved oxygen. Algal photosynthesis produces dissolved oxygen, while 

respiration consumes dissolved oxygen. Ammonia nitrification 

also can consume oxygen in the water column as ammonia 

(NH3) is converted to nitrate (NO3). The decomposition of dead 

algae as well as other organic matter in lake sediments can consume a substantial amount of oxygen in the overlying hypolimnion (Sullivan and Rounds, 2005). Exchange of the water in the 

epilimnion with the atmosphere can add oxygen to the water 

column through reaeration. Because the hypolimnion in Beaver 

Lake is isolated from the surface during periods of thermal stratification, reaeration from atmospheric exchange is eliminated 

and very little, if any, oxygen input from algal photosynthesis 

occurs below the thermocline (figs. 8 and 9). Dissolved-oxygen 
15

10

5

0

60

40

20

0

4

6

8

10

12

14

16

18

20

22

24

26

28

30

TEMPERATURE,

IN DEGREES

CELSIUS

DEPTH, IN METERS DEPTH, IN METERS

DATE

EXPLANATION

DATA POINT

LINE OF EQUAL

DISSOLVEDOXYGEN

CONCENTRATION,

IN MILLIGRAMS

PER LITER - Interval

2 milligrams per liter

4/19/01 7/28/01 11/5/01 2/13/02 5/24/02 9/1/02 12/10/02 3/20/02 6/28/02

4/19/01 7/28/01 11/5/01 2/13/02 5/24/02 9/1/02 12/10/02 3/20/02 6/28/02

SITE L2

SITE L5

32

 Ambient Conditions 11

Figure 8. Distribution of temperature and dissolved-oxygen concentration at sites L2 and L5 in Beaver Lake, 2001-2002.

50

40

30

20

10

0

AUGUST 22, 2002

HIGHWAY 45

BRIDGE AT

GOSHEN

BEAVER DAM

FEBRUARY 6, 2002

50

40

30

20

10

0

DEPTH, IN METERS DEPTH, IN METERS

HIGHWAY 45

BRIDGE AT

GOSHEN

BEAVER DAM

6

8

1 0

1 2

1 4

1 6

1 8

2 0

2 2

2 4

2 6

2 8

3 0

4

6

8

TEMPERATURE,

IN DEGREES

CELSIUS

EXPLANATION

TEMPERATURE,

IN DEGREES

CELSIUS

DATA POINT

LINE OF EQUAL

DISSOLVEDOXYGEN

CONCENTRATION,

IN MILLIGRAMS

PER LITER - Interval

2 milligrams per liter

L1 L2 L3 L4 L5

L1 L2 L3 L4 L5 3 2

10

Figure 9. Distribution of temperature and dissolved-oxygen concentration in Beaver Lake on February 6, 2002 and August 22, 2002.
12 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

concentrations during the winter remain fairly uniform and near 

saturation levels because of complete water column mixing and 

isothermal conditions. As stratification becomes established, 

dissolved-oxygen concentrations in the hypolimnion decrease 

because of sediment and biochemical demand, and by summer, 

conditions in the hypolimnion are nearly anoxic (devoid of oxygen) (figs. 8 and 9). 

Nutrients 

Nitrogen concentrations varied temporally, longitudinally, 

and vertically in Beaver Lake for 2001 through 2003. Nitrite 

(NO2) plus nitrate (NO3) concentrations generally decreased 

from the upstream portion of Beaver Lake (site L1) to the downstream portion (site L5) and generally were greater in the 

hypolimnion (fig. 10). The median epilimnetic concentration of 

nitrite plus nitrate ranged from 0.15 mg/L as nitrogen at site L5 

to 0.71 mg/L as nitrogen at site L1 and the median hypolimnetic 

concentration ranged from 0.36 mg/L as nitrogen at site L5 to 

0.69 mg/L as nitrogen at site L4. Nitrite plus nitrate concentrations were greatest when the reservoir was isothermal and well 

oxygenated in the winter and spring probably because of the 

conversion of ammonia (NH3) to nitrate (nitritification) (Wetzel, 2001) (fig. 11). Higher inflows also occur in the winter and 

spring (fig. 2) and may have caused higher nitrite plus nitrate 

concentrations. In this report, “ammonia” is used to refer to both 

NH4

+ (ammonium) and NH3. Concentrations were least in the 

summer and fall during stratification probably because of 

greater algal uptake in the epilimnion and the reduction of 

nitrate production in the anoxic hypolimnion because oxygen 

was not present to support nitrification. 

Total ammonia plus organic nitrogen concentrations also 

decreased from the upstream end of Beaver Lake to the downstream end and were substantially greater in the hypolimnion of 

Beaver Lake (fig. 10). The median epilimnetic concentration of 

total ammonia plus organic nitrogen ranged from 0.15 mg/L as 

nitrogen at site L5 to 0.40 mg/L as nitrogen at site L1 and the 

median hypolimnetic concentration ranged from 0.10 mg/L as 

nitrogen at site L5 to 0.70 mg/L as nitrogen at site L2. Concentrations were greater in the hypolimnion probably because during stratification, when the hypolimnion becomes anoxic, 

ammonia can accumulate because oxygen is not present to support nitrification (fig. 11). Ammonia also can be released from 

organic matter in the sediments under anoxic conditions. When 

NITRITE PLUS NITRATE

SITE L1 SITE L2 SITE L3 SITE L4 SITE L5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

E M H E M H

E M H

E M

H

TOTAL AMMONIA PLUS ORGANIC NITROGEN

SITE L1 SITE L2 SITE L3 SITE L4 SITE L5

CONCENTRATION, IN MILLIGRAMS PER LITER AS NITROGEN

0.0

0.5

1.0

1.5

2.0

2.5

E M

H

E

M

H

E M

H

E M H

TOTAL NITROGEN

SITE L1 SITE L2 SITE L3 SITE L4 SITE L5

0

1

2

3

4

E M

H

E M H

E M H

E M

H

EXPLANATION

E

M

H

SAMPLES COLLECTED FROM EPILIMNION

SAMPLES COLLECTED FROM METALIMNION

SAMPLES COLLECTED FROM HYPOLIMNION

10th percentile

25th percentile

50th percentile

75th percentile

90th percentile

E

E

E

UPSTREAM DOWNSTREAM

Figure 10. Distribution of nitrogen concentrations for five sites in Beaver Lake, 2001-2003.
Ambient Conditions 13

the reservoir turns over in early winter and is oxygenated 

throughout the reservoir, the ammonia is mixed into the entire 

volume of the reservoir and production is diminished. Total 

nitrogen concentrations followed similar patterns as the nitrite 

plus nitrate and total ammonia plus organic carbon with greater 

concentrations at the upstream sites compared to the downstream sites and with the greatest concentrations in the hypolimnion.

Phosphorus concentrations mostly were near or below laboratory detection limits in the epilimnion and metalimnion in 

Beaver Lake and were substantially greater in the hypolimnion 

in the upstream and middle portions of the reservoir (fig. 12). 

Sources of phosphorus other than inputs from tributaries 

include algal respiration, decay of organic matter (dissolved, 

suspended, and sedimentary), and anaerobic release from the 

lake sediments. Sinks of phosphorus include algal uptake and 

settling of particles containing or adsorbing phosphorus. High 

concentrations of phosphorus in the hypolimnion of Beaver 

Lake occur during stratification in the summer and fall at the 

upstream (riverine zone) and middle portions (transitional zone) 

of the reservoir where anoxic conditions occur and most of the 

particles and suspended material from the inflows are deposited 

(fig. 13). The anoxic conditions in the hypolimnion allow for 

the release of phosphorus from the deposited sediments and 

decaying organic matter. Phosphorus that is adsorbed or coprecipitated to iron oxide solids in oxygenated conditions also can 

be released from sediments under anoxic conditions when the 

iron oxide solids can dissolve. Most of the phosphorus is consumed by algal uptake in the epilimnion and metalimnion 

through the transitional zone of the reservoir leaving low concentrations in the downstream portion (lacustrine zone) of the 

reservoir (figs. 12 and 13).

Figure 11. Time series of nitrogen concentrations for five sites in Beaver Lake, 2001-2003.
ORTHOPHOSPHORUS

SITE L1 SITE L2 SITE L3 SITE L4 SITE L5

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

E

M

H

E M

H

E M

H

E M H

DISSOLVED PHOSPHORUS

SITE L1 SITE L2 SITE L3 SITE L4 SITE L5

CONCENTRATION, IN MILLIGRAMS PER LITER AS PHOSPHORUS

0.00

0.05

0.10

0.15

0.20

E M

H

E M

H

E M H E M H

TOTAL PHOSPHORUS

SITE L1 SITE L2 SITE L3 SITE L4 SITE L5

0.00

0.05

0.10

0.15

0.20

E M

H

E

M

H

E

M

H

E M H

EXPLANATION

E

M

H

SAMPLES COLLECTED FROM EPILIMNION

SAMPLES COLLECTED FROM METALIMNION

SAMPLES COLLECTED FROM HYPOLIMNION

10th percentile

25th percentile

50th percentile

75th percentile

90th percentile

E

E

E

UPSTREAM DOWNSTREAM

14 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

Figure 12. Distribution of phosphorus concentrations for five sites in Beaver Lake, 2001-2003.
Figure 13. Time series of phosphorus concentrations for five sites in Beaver Lake, 2001-2003.
16 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

Organic Carbon

Measured dissolved and total organic carbon in Beaver 

Lake was relatively uniform spatially, longitudinally, and vertically in the reservoir from January 2001 through December 

2003. The main source of dissolved organic carbon is from the 

inflows and surface runoff into Beaver Lake, which is noticeable by the fluctuations in concentration at the most upstream 

lake sampling site (L1) (figs. 14 and 15). Another smaller 

source of organic carbon is from photosynthesis in algae. The 

median dissolved organic-carbon concentrations ranged from 

2.4 (site L4) to 2.9 mg/L as carbon (site L1) in the epilimnion 

and from 2.1 (site L5) to 3.2 mg/L as carbon (site L2) in the 

hypolimnion. The median total organic-carbon concentration in 

Beaver Lake ranged from 2.4 (site L4) to 2.9 mg/L as carbon 

(sites L1 and L2) in the epilimnion and from 2.2 (site L5) to 3.2 

mg/L as carbon (site L3) in the hypolimnion. 

DISSOLVED ORGANIC CARBON

SITE L1 SITE L2 SITE L3 SITE L4 SITE L5

0

1

2

3

4

5

6

E

M

H

E

M H

E M

H E

M

H

TOTAL ORGANIC CARBON

SITE

SITE L1 SITE L2 SITE L3 SITE L4 SITE L5

CONCENTRATION, IN MILLIGRAMS PER LITER AS CARBON

0

1

2

3

4

5

6

E

M

H E

M

H

E

M

H E

M

H

E

E

EXPLANATION

E

M

H

SAMPLES COLLECTED FROM EPILIMNION

SAMPLES COLLECTED FROM METALIMNION

SAMPLES COLLECTED FROM HYPOLIMNION

10th percentile

25th percentile

50th percentile

75th percentile

90th percentile

UPSTREAM DOWNSTREAM

Figure 14. Distribution of organic-carbon concentrations for five sites in Beaver Lake, 2001-2003.
 Ambient Conditions 17

Figure 15. Time series of organic-carbon concentrations for five sites on Beaver Lake, 2001-2003.
18 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

Chlorophyll a and Phytoplankton

Chlorophyll a concentrations varied spatially and temporally in Beaver Lake. Chlorophyll a is a photosynthetic pigment 

found in algae and other green plants. The concentration of chlorophyll a, from samples collected in open water, commonly is 

used as a measure of the density of the algal (phytoplankton) 

population of a lake (Ruttner, 1963). Chlorophyll a concentrations measured at sites L1 and L2 were significantly greater than 

at the other sites on Beaver Lake with median concentrations of 

7.2 micrograms per liter (μg/L) and 12.5 μg/L, respectively (fig. 

16). Sites L3, L4, and L5 had median concentrations

SITE L1 SITE L2 SITE L3 SITE L4 SITE L5

CHLOROPHYLL a CONCENTRATION,

IN MICROGRAMS PER LITER

0

5

10

15

20

25

30

EXPLANATION

10th percentile

25th percentile

50th percentile

75th percentile

90th percentile

a

a

b

b

c

Distributions associated

with the same letter are

not significantly(p<0.05)

different

UPSTREAM DOWNSTREAM

a

Figure 16. Distribution of chlorophyll a concentrations for five sites in 

Beaver Lake, 2001-2003.

of 5.5, 3.4, and 1.8 μg/L, respectively. The increased depth of 

light penetration as suspended particles settle out of the water 

column in the transition zone (near site L2), and the availability 

of nutrients from the three main inflows probably allow for 

greater phytoplankton productivity in the upstream end and 

transitional zone of the reservoir. As nutrients are assimilated 

through the transitional zone, phytoplankton populations become more limited by nutrients in the downstream portion of 

Beaver Lake. Chlorophyll a concentrations were greater in the 

months of July through October probably because phytoplankton productivity generally is greater in the warmer months (fig. 

17).

SITE L2

1/1/01 7/1/01 1/1/02 7/1/02 1/1/03 7/1/03 1/1/04

0

5

10

15

20

25

30

35

SITE L3

1/1/01 7/1/01 1/1/02 7/1/02 1/1/03 7/1/03 1/1/04

0

5

10

15

20

SITE L4

1/1/01 7/1/01 1/1/02 7/1/02 1/1/03 7/1/03 1/1/04

CHLOROPHYLL a CONCENTRATION, IN MICROGRAMS PER LITER

0

5

10

15

20

SITE L5

DATE

1/1/01 7/1/01 1/1/02 7/1/02 1/1/03 7/1/03 1/1/04

0

5

10

15

20

SAMPLE CONCENTRATION

LOCALLY WEIGHTED

SMOOTH LINE (LOWESS)

CONCENTRATIONS LESS THAN

LABORATORY REPORTING LIMIT

SITE L1

1/1/01 7/1/01 1/1/02 7/1/02 1/1/03 7/1/03 1/1/04

0

5

10

15

20

25

30

35

EXPLANATION

Figure 17. Time series of chlorophyll a concentrations for five sites in 

Beaver Lake, 2001-2003.
Ambient Conditions 19

Phytoplankton populations are highly dynamic in lakes and 

reservoirs and are controlled by the availability of light and 

nutrients, and the effects of temperature and zooplankton grazing (Wetzel, 2001). Different populations of phytoplankton 

grow depending on the tolerance of each species to these factors. 

Blue-green algae, diatoms, flagellates, and green algae generally 

are the most common phytoplankton taxa in Beaver Lake. 

Phytoplankton population dynamics varied over time 

among the five reservoir sites (fig. 18). Blue-green algae tended 

to be more abundant at the upstream sites, while diatoms tended 

to be more abundant at the downstream sites. The exception 

would be the abundance of flagellates at site L1 and L2 during 

2002. Inflows at these upstream sites (L1 and L2) were greater 

in 2002, compared to 2001 with more frequent high-flow events 

(fig. 2) possibly shifting the phytoplankton population from 

blue-green algae to flagellates. Green algae were present at all 

sites, but did not dominate the assemblage with the exception of 

a couple of instances during the late summer in 2002 at sites L3 

and L5. Chlorophyll a concentrations followed similar patterns 

as total phytoplankton cell numbers (concentrations), with the 

greatest concentrations at the upstream sites and decreasing concentrations downstream. At each site, chlorophyll a concentrations were greatest during the summer and early fall when water 

temperature was highest; concentrations were least during the 

winter and early spring when the water temperature was lowest.

a

a

Figure 18. Distribution of phytoplankton and time series of chlorophyll a concentrations for five sites in Beaver Lake, 2001-2002.
20 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

Water Clarity

During the study period, water clarity in Beaver Lake was 

significantly greater at the downstream end of the reservoir (site 

L5) than at the upstream end (site L1) (fig. 19). The median Secchi depth ranged from 0.6 m at site L1 to 5.4 m at site L5 from 

2001 through 2003. The lower values for Secchi depth, and, 

therefore, less water clarity, in the upstream portion of the reservoir is probably because of the input of organic and inorganic 

particulates from the main inflows. As water velocities decrease 

through the transitional zone, the particulates settle out of the 

water column and increase the water clarity in the downstream 

portion of the reservoir. 

Secchi depth was more variable during the study period at 

the downstream sites (L3 through L5) compared to the upstream 

sites (L1 and L2) (fig. 20). At sites L3 and L4, greater Secchi 

depth values (greater water clarity) were observed from June 

through September in 2001 and 2002. The greatest values for 

Secchi depth at site L5 generally were observed in 2001 compared to 2002 and 2003, but did not have a seasonal pattern 

observed at sites L3 and L4.

Similar to Secchi depth results, turbidity results indicated 

greater water clarity in the downstream portion of Beaver Lake 

compared to the upstream portion (figs. 21 and 22). Turbidity 

also was greater in the hypolimnion than in the epilimnion in the 

reservoir during the stratification season. The median turbidity 

measured in the epilimnion ranged from 0.5 (site L5) to 8.3 

NTUs (site L1). The median turbidity measured in the hypolimnion ranged from 1 (site L5) to 20 NTUs (site L2). The 

hypolimnetic turbidity was 5 times greater than the epilimnetic 

turbidity at sites L2 and L4 and nearly 10 times greater than the 

epilimnetic turbidity at site L3.

SITE L1 SITE L2 SITE L3 SITE L4 SITE L5

SECCHI DEPTH, IN METERS

0

2

4

6

8

10

a

b

c

d

e

EXPLANATION

10th percentile

25th percentile

50th percentile

75th percentile

90th percentile

UPSTREAM DOWNSTREAM

a Distributions associated

with the same letter are

not significantly(p<0.05)

different

Figure 19. Distribution of Secchi depth for five sites in Beaver Lake, 2001-2003.
SITE L2

1/1/01 7/1/01 1/1/02 7/1/02 1/1/03 7/1/03 1/1/04

SECCHI DEPTH,

IN METERS

0

2

4

6

8

10

SITE L1

1/1/01 7/1/01 1/1/02 7/1/02 1/1/03 7/1/03 1/1/04

SECCHI DEPTH,

IN METERS

0

2

4

6

8

10

SITE L3

1/1/01 7/1/01 1/1/02 7/1/02 1/1/03 7/1/03 1/1/04

SECCHI DEPTH,

IN METERS

0

2

4

6

8

10

SITE L4

1/1/01 7/1/01 1/1/02 7/1/02 1/1/03 7/1/03 1/1/04

SECCHI DEPTH,

IN METERS

0

2

4

6

8

10

SITE L5

DATE

1/1/01 7/1/01 1/1/02 7/1/02 1/1/03 7/1/03 1/1/04

SECCHI DEPTH,

IN METERS

0

2

4

6

8

10

SECCHI DEPTH

MEASUREMENT

LOCALLY WEIGHTED SMOOTH

LINE (LOWESS)

EXPLANATION

 Ambient Conditions 21

Figure 20. Time series of Secchi depth for five sites in Beaver Lake, 2001-2003.
SITE L1 SITE L2 SITE L3 SITE L4 SITE L5

TURBIDITY, IN NEPHELOMETRIC TURBIDITY UNITS

0

10

20

30

40

50

60

70

80

E

M

H

E

M

H

E M

H

E M

H

EXPLANATION

E

M

H

SAMPLES COLLECTED

FROM EPILIMNION

SAMPLES COLLECTED

FROM METALIMNION

SAMPLES COLLECTED

FROM HYPOLIMNION

10th percentile

25th percentile

50th percentile

75th percentile

90th percentile

E

UPSTREAM DOWNSTREAM

22 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

Figure 21. Distribution of turbidity for five sites in Beaver Lake, 2001-2003.

Figure 22. Time series of turbidity for five sites in Beaver Lake, 2001-2003.
Simulation of Hydrodynamics and Water Quality 23

Simulation of Hydrodynamics and Water 

Quality

A two-dimensional, laterally averaged, hydrodynamic and 

water-quality model using CE-QUAL-W2 Version 3.1 (Cole 

and Wells, 2003) was developed for Beaver Lake and calibrated 

based on vertical profiles of temperature and dissolved oxygen, 

and water-quality constituent concentrations collected at various depths at four sites in the reservoir from April 2001 to April 

2003. The Beaver Lake CE-QUAL-W2 model simulates watersurface elevation and vertical and longitudinal gradients in 

water-quality constituents. The model includes routines for 18 

state variables in addition to temperature, including any number 

of inorganic suspended solids groups, phytoplankton groups, 

nitrogen and phosphorus species, dissolved and particulate 

organic matter, total inorganic carbon, dissolved oxygen, and 

organic sediments. Additionally, over 60 derived variables can 

be computed from the state variables (Cole and Wells, 2003). 

Model Implementation

Implementation of the CE-QUAL-W2 model for Beaver 

Lake included development of the computational grid, specification of boundary and initial conditions, and preliminary selection of model parameter values. Model development and associated assumptions in the selection of boundary and initial 

conditions are described, and model parameters are listed in this 

section.

Computational Grid

The computational grid is the geometric scheme that 

numerically represents the space and volume of the reservoir. 

The model extends 80 km from the upstream boundary (White 

River at the Highway 45 bridge) to the Beaver Lake dam (figs. 

1 and 23). The grid originally was developed by Haggard and 

Green (2002) to simulate the hydrodynamics and distribution of 

temperature and dissolved oxygen in Beaver Lake for calendar 

years 1994 and 1995. Thirty-five computational segments exist 

along the mainstem of the White River in Beaver Lake and 12 

computational segments are in War Eagle Creek. In addition, 

four other downstream branches are modeled with three computational segments each. Volumes of the smaller embayments 

not included in the computational grid were added to associated 

mainstem segments so that reservoir volume was preserved. 

Each segment was divided vertically into 1-m layers. Two tributaries also were included in the model at the most upstream 

segment. Tributaries allow for the application of boundary conditions to the grid without affecting the geometry. One tributary 

was used to simulate the input from the Fayetteville wastewater-treatment plant discharge at the upstream segment and 

another to simulate the inflow from Richland Creek. A third 

tributary was used to simulate the inflow from Prairie Creek 

(fig. 1).

Boundary and Initial Conditions

Hydraulic and Thermal Boundary Conditions

Daily reservoir inflows used in the model were obtained 

from streamflow-gaging station data on the three main inflows 

(White River, Richland Creek, and War Eagle Creek) and were 

estimated for the three smaller branches. The mean daily 

streamflow recorded for War Eagle Creek (site S3) was used to 

estimate the streamflow for the other three other branches based 

on their respective drainage areas. Streamflow gaging station 

data were used to simulate inflow from the Prairie Creek tributary from April 2001 to October 2001. Because the gaging station was discontinued, streamflow was estimated from October 

2001 to April 2003.

The downstream boundary for the Beaver Lake model 

consists of the outflow from Beaver Lake dam. Hourly outflow 

data was produced by the USACE using stage-discharge relations and hourly power generation records for the period of 

April 2001 to April 2003 (John Kielczewski, U.S. Army Corps 

of Engineers, written commun., 2003). The release structure 

(penstock) was simulated as a point release, and the middle of 

the structure was at an elevation of 302.2 m above NGVD of 

1929, model layer 45 (fig. 23).

Other hydraulic boundary conditions included water withdrawal by four public water-supply districts (Beaver Water District, Carroll-Boone County Water District, Madison County 

Water District, and Benton-Washington County Water District). Withdrawal rates for each water-supply district were variable by month and based on reported 2001 through 2003 

monthly intakes (Terrance W. Holland, U.S. Geological Survey, written commun., 2004).

Hydraulic boundary conditions at the water surface 

included evaporation, wind stress, and surface heat exchange. 

Meteorological data required for these computations were measured at the Northwest Arkansas Regional Airport (fig. 1) 

(National Climatic Data Center, Asheville, North Carolina, 

written commun., 2004) and generally were recorded at hourly 

intervals. 

Hourly inflow water temperatures were estimated from the 

meteorological data and from periodic measurements at the 

three main inflow sites (White River, Richland Creek, and War 

Eagle Creek). Water temperatures for the smaller tributaries 

were estimated only from the meteorological data. 

Chemical Boundary Conditions

Daily nutrient and dissolved organic-carbon concentrations were derived from daily loads calculated from sample 

concentrations and streamflow measured at sites S1, S2, and S3. 

Daily loads (kg/d) were divided by the daily mean streamflow 

(m3/s) and multiplied by a conversion factor for a daily mean 

concentration (mg/L) for each of the main inflow sites. Daily 

streamflow is used to calculate daily concentrations from daily 

loads because it probably more accurately reflects the variation 

in constituent concentrations compared to using discrete concentrations as input, where the model linearly interpolates daily 

concentrations between sample collection dates. Daily
        

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7UHDWPHQW

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3UDLULH

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24 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

Figure 23. Side view (A), top view (B), and face view from the dam (C) of the computational grid of Beaver Lake used in the CE-QUAL-W2 model.
Simulation of Hydrodynamics and Water Quality 25

concentration data for the Fayetteville wastewater treatment 

plant discharge were obtained from daily outflow sample data 

(Paul R. Noland, city of Fayetteville Wastewater-Treatment 

Plant, written commun., 2003). 

Hourly inflow dissolved-oxygen concentrations were estimated from measured data and from the meteorological data. 

Estimated values were computed as 80 percent dissolved-oxygen saturation from the temperature and barometric pressure 

when measured values for dissolved-oxygen concentration 

were missing. Daily dissolved-oxygen concentrations for the 

smaller tributaries were estimated only from the meteorological 

data.

Initial Conditions

Initial water-surface elevation, water temperature, and 

constituent concentrations for each model segment are required 

at the start of a model simulation. Initial water-surface elevations were set to the measured value on April 1, 2001. Beaver 

Lake was assumed to be in isothermal conditions throughout the 

entire reservoir and equal to 6 °C. Initial constituent concentrations also were assumed to be uniform, and concentrations measured at the five sampling sites on March 30, 2001, were used 

as the initial values.

Model Parameters

Parameters are used to describe the physical and chemical 

processes that are not explicitly modeled and to provide the 

chemical kinetic rate information. Many parameters cannot be 

measured directly and often are adjusted during the model calibration process until simulated values agree with measured 

observations. Most of the hydrodynamic and thermal processes 

are modeled in CE-QUAL-W2, which results in very few 

adjustable hydraulic and thermal parameters. There are many 

chemical and biological rate coefficients required for the application of CE-QUAL-W2, which are all temporally constant 

(table 2). Many of the coefficients were based on suggested values given as default values for CE-QUAL-W2 and others were 

based on other model applications (Haggard and Green, 2002; 

Galloway and Green, 2002 and 2003; Green and others, 2003; 

Bales and others, 2001; Sullivan and Rounds, 2005).

Table 2. Parameters and values used for the Beaver Lake model, April 2001 to April 2003.

Parameter Value

Hydraulic and thermal input parameters

Coefficient of bottom heat exchange, watts/square meter/ second 7×10-7

Sediment temperature, degrees Celsius 16

Wind-sheltering coefficient, dimensionless 0.70

Horizontal eddy viscosity, square meters /second 1

Horizontal eddy diffusivity, square meters/second 1

Rate coefficients for water-chemistry and biological simulations

Light extinction coefficient for pure water, 1/meter 0.4

Light extinction coefficient for organic solids, 1/meter 0.01

Light extinction coefficient for inorganic solids, 1/meter 0.01

Light extinction coefficient because of algae (blue-green), 1/meter 0.1

Light extinction coefficient because of algae (diatoms), 1/meter 0.1

Light extinction coefficient because of algae (flagellates), 1/meter 0.1

Light extinction coefficient because of algae (green), 1/meter 0.1

Fraction of incident solar radiation absorbed at 

water surface, dimensionless 

0.32

Suspended solids settling rate, meters/day 2

Algal growth rate (blue-green), 1/day 2

Algal growth rate (diatoms), 1/day 2

Algal growth rate (flagellates), 1/day 2

Algal growth rate (green), 1/day 2
26 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

Algal mortality rate (blue-green), 1/day 0.08

Algal mortality rate (diatoms), 1/day 0.08

Algal mortality rate (flagellates), 1/day 0.08

Algal mortality rate (green), 1/day 0.08

Algal excretion rate (blue-green), 1/day 0.04

Algal excretion rate (diatoms), 1/day 0.04

Algal excretion rate (flagellates), 1/day 0.04

Algal excretion rate (green), 1/day 0.04

Algal dark respiration rate (blue-green), 1/day 0.04

Algal dark respiration rate (diatoms), 1/day 0.04

Algal dark respiration rate (flagellates), 1/day 0.04

Algal dark respiration rate (green), 1/day 0.04

Algal settling rate (blue-green), meters/day 0.08

Algal settling rate (diatoms), meters/day 0.08

Algal settling rate (flagellates), meters/day 0.08

Algal settling rate (green), meters/day 0.08

Saturation light intensity (blue-green), watts/square meter 75

Saturation light intensity (diatoms), watts/square meter 75

Saturation light intensity (flagellates), watts/square meter 75

Saturation light intensity (green), watts/square meter 75

Fraction of algal biomass lost by mortality to particulate 

organic matter (blue-green), dimensionless

0.8

Fraction of algal biomass lost by mortality to particulate 

organic matter (diatoms), dimensionless

0.8

Fraction of algal biomass lost by mortality to particulate

organic matter (flagellates), dimensionless

0.8

Fraction of algal biomass lost by mortality to particulate 

organic matter (green), dimensionless

0.8

Lower temperature for algal growth (blue-green), degrees Celsius 15

Lower temperature for algal growth (diatoms), degrees Celsius 10

Lower temperature for algal growth (flagellates), degrees Celsius 10

Lower temperature for algal growth (green algae), degrees Celsius 10

Fraction of algal growth at lower temperature (blue-green),

dimensionless

0.1

Fraction of algal growth at lower temperature (diatoms), 

dimensionless

0.2

Fraction of algal growth at lower temperature (flagellates),

dimensionless

0.1

Fraction of algal growth at lower temperature (green), 

dimensionless

0.1

Table 2. Parameters and values used for the Beaver Lake model, April 2001 to April 2003.—Continued

Parameter Value
 Simulation of Hydrodynamics and Water Quality 27

Lower temperature for maximum algal growth (blue-green), degrees Celsius 20

Lower temperature for maximum algal growth (diatoms), 

degrees Celsius 

15

Lower temperature for maximum algal growth flagellates), 

degrees Celsius 

15

Lower temperature for maximum algal growth (green), degrees Celsius 20

Fraction of maximum algal growth at lower temperature (blue-green), dimensionless 0.99

Fraction of maximum algal growth at lower temperature (diatoms)

dimensionless

0.99

Fraction of maximum algal growth at lower temperature

(flagellates), dimensionless

0.99

Fraction of maximum algal growth at lower temperature (green),

dimensionless

0.99

Upper temperature for algal growth (blue-green), degrees Celsius 35

Upper temperature for algal growth (diatoms), degrees Celsius 20

Upper temperature for algal growth (flagellates), degrees Celsius 25

Upper temperature for algal growth (green), degrees Celsius 30

Fraction of algal growth at upper temperature (blue-green), 

dimensionless

0.99

Fraction of algal growth at upper temperature (diatoms), 

dimensionless

0.99

Fraction of algal growth at upper temperature (flagellates),

dimensionless

0.99

Fraction of algal growth at upper temperature (green), 

dimensionless

0.99

Upper temperature for maximum algal growth (blue-green), degrees Celsius 40

Upper temperature for maximum algal growth (diatoms), degrees Celsius 35

Upper temperature for maximum algal growth (flagellates), degrees Celsius 35

Upper temperature for maximum algal growth (green), degrees Celsius 35

Fraction of maximum algal growth at upper temperature (blue-green), dimensionless 0.1

Fraction of maximum algal growth at upper temperature (diatoms), dimensionless 0.1

Fraction of maximum algal growth at upper temperature (flagellates), dimensionless 0.1

Fraction of maximum algal growth at upper temperature (green), dimensionless 0.1

Algal half-saturation constant for phosphorus (blue-green), grams/cubic meter 0.003

Algal half-saturation constant for phosphorus (diatoms), grams/cubic meter 0.003

Algal half-saturation constant for phosphorus (flagellates), grams/cubic meter 0.003

Algal half-saturation constant for phosphorus (greens), grams/cubic meter 0.003

Algal half-saturation constant for nitrogen (blue-green), grams/cubic meter 0.014

Algal half-saturation constant for nitrogen (diatoms), grams/cubic meter 0.014

Algal half-saturation constant for nitrogen (flagellates), grams/cubic meter 0.014

Table 2. Parameters and values used for the Beaver Lake model, April 2001 to April 2003.—Continued

Parameter Value
28 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

Algal half-saturation constant for nitrogen (greens), grams/cubic meter 0.014

Algal half-saturation constant for silica (blue-green), grams/cubic meter 0

Algal half-saturation constant for silica (diatoms), grams/cubic meter 0

Algal half-saturation constant for silica (flagellates), grams/cubic meter 0

Algal half-saturation constant for silica (greens), grams/cubic meter 0

Chlorophyll-algae ratio, dimensionless 0.4

Labile dissolved organic matter decay rate, 1/day 0.1

Refractory dissolved organic matter decay rate, 1/day 0.015

Labile to refractory dissolved organic matter decay rate, 1/day 0.01

Labile particulate organic matter decay rate, 1/day 0.1

Refractory particulate organic matter decay rate, 1/day 0.01

Labile to refractory particulate organic matter decay rate, 1/day 0.001

Particular organic matter settling rate, meters/day 0.1

Lower temperature for organic matter decay, degrees Celsius 5

Upper temperature for organic matter decay, degrees Celsius 30

Fraction of organic matter decay at lower temperature, dimensionless 0.1

Fraction of organic matter decay at upper temperature, dimensionless 0.99

Sediment decay rate, 1/day 0.1

Zero-order sediment oxygen demand, grams/square meter/day 1

Fraction of sediment oxygen demand, dimensionless 1.4

5-day biological oxygen demand decay rate, 1/day 0.25

Biological oxygen demand temperature rate coefficient, dimensionless 1.0147

Ratio of 5-day biological oxygen demand to ultimate biological oxygen demand, dimensionless 1.85

Release rate of phosphorus from bottom sediment, fraction of sediment oxygen demand 0.001

Phosphorus partitioning coefficient, dimensionless 0

Release rate of ammonia from bottom sediment, fraction of sediment oxygen demand 0.2

Ammonia decay rate, 1/day 0.12

Lower temperature for ammonia decay, degrees Celsius 5

Fraction of nitrification at lower temperature, dimensionless 0.1

Upper temperature for ammonia decay, degrees Celsius 20

Fraction of maximum nitrification at lower temperature, dimensionless 0.99

 Nitrate decay rate, 1/day 0.03

Lower temperature for nitrate decay, degrees Celsius 5

Fraction of denitrification at lower temperature, dimensionless 0.1

Upper temperature for nitrate decay, degrees Celsius 20

Fraction of maximum denitrification at lower temperature, dimensionless 0.99

Iron release from bottom sediment, fraction of sediment oxygen demand 0.5

Table 2. Parameters and values used for the Beaver Lake model, April 2001 to April 2003.—Continued

Parameter Value
Simulation of Hydrodynamics and Water Quality 29

Iron settling velocity, meters/day 2

Oxygen stoichiometric equivalent for ammonia decay, dimensionless 4.57

Oxygen stoichiometric equivalent for organic matter decay, dimensionless 1.4

Oxygen stoichiometric equivalent for algal dark respiration (blue-green), dimensionless 1.8

Oxygen stoichiometric equivalent for algal dark respiration (diatoms), dimensionless 1.8

Oxygen stoichiometric equivalent for algal dark respiration (flagellates), dimensionless 1.8

Oxygen stoichiometric equivalent for algal dark respiration (greens), dimensionless 1.8

Oxygen stoichiometric equivalent for algal growth (blue-green), dimensionless 1.1

Oxygen stoichiometric equivalent for algal growth (diatoms), dimensionless 1.1

Oxygen stoichiometric equivalent for algal growth (flagellates), dimensionless 1.1

Oxygen stoichiometric equivalent for algal growth (green), dimensionless 1.1

Table 2. Parameters and values used for the Beaver Lake model, April 2001 to April 2003.—Continued

Parameter Value

Model Calibration and Testing

Successful model application requires model calibration 

that includes comparing simulated results with measured reservoir conditions. The Beaver Lake model calibration was completed by adjusting parameters for the 2-year period from April 

2001 to April 2003. Calibration was achieved generally by first 

calibrating the water balance and thermodynamics, then calibrating the water-quality conditions (dissolved oxygen, nutrients, and algae).

Two statistics were used to compare simulated and measured water-surface elevation, water temperature, dissolvedoxygen, and nutrient concentrations. The absolute mean error 

(AME) indicates the average difference between simulated and 

measured values and is computed by equation 2.

AME Σ simulated value - measured value

number of observations = -------------------------------------------------------------------------------------- (2)

An AME of 0.5 °C means that the average difference between 

simulated temperatures and measured temperature is 0.5 °C.

The root mean square error (RMSE) indicates the spread of 

how far simulated values deviate from the measured values and 

is computed by equation 3:

RMSE Σ( ) simulated value - measured value

number of observations ----------------------------------------------------------------------------------------2

= (3)

An RMSE of 0.5 °C means that the simulated temperatures are 

within 0.5 °C of the measured temperatures about 67 percent of 

the time.

Water Balance

Simulated water-surface elevations in Beaver Lake were 

adjusted to the measured water surface for the model period of 

April 2001 to April 2003 (fig. 24). The water-surface elevations 

were corrected to the measured values by adjusting the unmeasured inflow into the lake that was distributed to all the segments within a branch. Inflow was added or subtracted so that 

the simulated water-surface elevation reflected the measured 

water-surface elevation, therefore, accounting for unmeasured 

inflow and ground-water interaction in Beaver Lake. By correcting the distributed inflow, the temperature and water quality 

could be calibrated without the uncertainty incurred with having differences between simulated and measured water-surface 

elevations.

DATE

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

WATER-SURFACE ELEVATION, IN

METERS ABOVE NGVD OF 1929

338

339

340

341

342

343

344

345

MEASURED ELEVATION

SIMULATED ELEVATION

TOP ELEVATION OF

CONSERVATION POOL

Figure 24. Simulated and measured water-surface elevations near Beaver Lake dam, April 2001 to April 2003.
30 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

Temperature

Simulated water temperatures in Beaver Lake were compared to 144 depth profiles of temperature measured at four 

sites on Beaver Lake (fig. 1). Temperatures were adjusted to the 

measured values for the model period of April 2001 to April 

2003.

Simulated temperatures compared reasonably well with 

measured temperatures and differences varied spatially in Beaver Lake for April 2001 to April 2003. Differences in temperature between simulated and measured values decreased from 

site L2 to site L5. The AME ranged from 0.8 °C at site L5 to 3.1 

°C at L2 and the RMSE ranged from 0.9 °C at site L5 to 3.2 °C 

at site L2 from April 2001 to April 2003 (figs. 25-28; table 3). 

The greatest differences between measured and simulated data 

occurred in the upstream portion of the reservoir, which is the 

most dynamic part of the reservoir. The upstream portion of the 

reservoir is the shallowest section of Beaver Lake and has more 

riverine characteristics than the deep lacustrine-type characteristics of the downstream portion of the reservoir. The upstream 

portion also receives most of the inflow to the reservoir, which 

creates more dynamic conditions. The greatest differences 

between simulated and measured temperatures generally 

occurred in simulating the location of the thermocline (figs. 25-

28).

6/1/01

0 5 10 15 20 25 30

7/24/01

0 5 10 15 20 25 30

9/18/01

0 5 10 15 20 25 30

11/8/01

0 5 10 15 20 25 30

4/19/01

0 5 10 15 20 25 30

DEPTH, IN METERS

14

12

10

8

6

4

2

0

10/30/01

0 5 10 15 20 25 30

12/12/01

0 5 10 15 20 25 30

2/5/02

0 5 10 15 20 25 30

DEPTH, IN METERS

14

12

10

8

6

4

2

0

8/22/02

0 5 10 15 20 25 30

11/14/02

0 5 10 15 20 25 30

12/10/02

0 5 10 15 20 25 30

6/19/02

0 5 10 15 20 25 30

10/30/02

0 5 10 15 20 25 30

1/7/03

0 5 10 15 20 25 30

DEPTH, IN METERS

14

12

10

8

6

4

2

0

2/10/03

TEMPERATURE, IN DEGREES CELSIUS

0 5 10 15 20 25 30

3/12/03

0 5 10 15 20 25 30

4/16/02

0 5 10 15 20 25 30

EXPLANATION

MEASURED

SIMULATED

Figure 25. Selected simulated and measured water-temperature profiles for Beaver Lake at Highway 412 bridge near Sonora, Arkansas (site L2),

April 2001 to April 2003.
6/1/01

0 5 10 15 20 25 30

7/24/01

0 5 10 15 20 25 30

11/7/01

0 5 10 15 20 25 30

4/19/01

0 5 10 15 20 25 30

DEPTH, IN METERS

25

20

15

10

5

0

10/30/01

0 5 10 15 20 25 30

12/11/01

0 5 10 15 20 25 30

9/20/01

0 5 10 15 20 25 30

10/30/02

0 5 10 15 20 25 30

11/14/02

0 5 10 15 20 25 30

12/11/02

0 5 10 15 20 25 30

1/8/03

0 5 10 15 20 25 30

DEPTH, IN METERS

25

20

15

10

5

0

2/11/03

0 5 10 15 20 25 30

3/12/03

TEMPERATURE, IN DEGREES CELSIUS

0 5 10 15 20 25 30

2/5/02

0 5 10 15 20 25 30

DEPTH, IN METERS

25

20

15

10

5

0

4/17/02

0 5 10 15 20 25 30

8/21/02

0 5 10 15 20 25 30

6/19/02

0 5 10 15 20 25 30

EXPLANATION

MEASURED

SIMULATED

 Simulation of Hydrodynamics and Water Quality 31

Figure 26. Selected simulated and measured water-temperature profiles for Beaver Lake near Lowell, Arkansas (site L3), April 2001 to April 2003.
5/31/01

0 5 10 15 20 25 30

7/25/01

0 5 10 15 20 25 30

9/19/01

0 5 10 15 20 25 30

11/27/01

0 5 10 15 20 25 30

4/18/01

0 5 10 15 20 25 30

DEPTH, IN METERS

30

20

10

0

10/31/01

0 5 10 15 20 25 30

EXPLANATION

MEASURED

SIMULATED

12/12/01

0 5 10 15 20 25 30

2/5/02

0 5 10 15 20 25 30

DEPTH, IN METERS

30

20

10

0

4/17/02

0 5 10 15 20 25 30

8/21/02

0 5 10 15 20 25 30

11/14/02

0 5 10 15 20 25 30

12/10/02

0 5 10 15 20 25 30

6/18/02

0 5 10 15 20 25 30

10/29/02

0 5 10 15 20 25 30

1/6/03

0 5 10 15 20 25 30

DEPTH, IN METERS

30

20

10

0

2/11/03

TEMPERATURE,IN DEGREES CELSIUS

0 5 10 15 20 25 30

3/11/03

0 5 10 15 20 25 30

32 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

Figure 27. Selected simulated and measured water-temperature profiles for Beaver Lake at Highway 12 bridge near Rogers, Arkansas (site L4),

April 2001 to April 2003.
5/31/01

0 5 10 15 20 25 30

03/27/01

0 5 10 15 20 25 30

DEPTH, IN METERS

60

50

40

30

20

10

0

7/25/01

0 5 10 15 20 25 30

DEPTH, IN METERS

9/11/01

0 5 10 15 20 25 30

11/27/01

0 5 10 15 20 25 30

10/31/01

0 5 10 15 20 25 30

12/17/01

0 5 10 15 20 25 30

2/4/02

0 5 10 15 20 25 30 60

50

40

30

20

10

0

6/18/02

0 5 10 15 20 25 30

4/17/02

0 5 10 15 20 25 30

8/15/02

0 5 10 15 20 25 30

10/24/02

0 5 10 15 20 25 30

11/13/02

0 5 10 15 20 25 30

12/19/02

0 5 10 15 20 25 30

1/7/03

0 5 10 15 20 25 30

DEPTH, IN METERS

60

50

40

30

20

10

0

2/11/03

0 5 10 15 20 25 30

3/11/03

0 5 10 15 20 25 30

3/18/03

TEMPERATURE,IN DEGREES CELSIUS

0 5 10 15 20 25 30

MEASURED

SIMULATED

EXPLANATION

 Simulation of Hydrodynamics and Water Quality 33

Figure 28. Selected simulated and measured water-temperature profiles for Beaver Lake near Eureka Springs, Arkansas (site L5), April 2001 to April 

2003.
Table 3. Comparative statistics of simulated and measured temperature and dissolved-oxygen concentration for Beaver Lake, April 2001 to April 2003.

[Difference is simulated minus measured]

L2 2001 153 4.7 -3.9 1.0 1.0 1.4 1.8

2002 161 4.5 -2.1 1.6 1.6 1.7 2.0

2003 28 4.3 2.4 3.0 3.1 3.1 3.2

All 342 4.7 -3.9 1.4 1.4 1.7 2.0

L3 2001 296 5.2 -3.5 0.5 0.5 0.9 1.2

2002 302 4.1 -4.0 0.8 0.7 1.3 1.6

2003 48 3.4 1.1 2.1 2.1 2.1 2.2

All 646 5.2 -4.0 0.7 0.7 1.2 1.5

L4 2001 334 4.2 -3.8 0.1 0.0 1.0 1.3

2002 289 2.4 -2.7 0.7 0.6 0.9 1.1

2003 57 2.3 0.5 1.5 1.4 1.4 1.5

All 680 4.2 -3.8 0.4 0.4 1.0 1.2

L5 2001 628 6.2 -5.9 0.2 0.1 0.9 1.2

2002 576 2.1 -2.4 0.8 0.5 0.8 0.9

2003 103 1.5 -0.9 1.0 0.9 0.9 1.0

All 1,307 6.2 -5.9 0.5 0.4 0.8 1.0

 Dissolved-oxygen concentration, in milligrams per liter 

L2 2001 153 3.4 -6.8 -1.8 -1.7 2.0 2.6

2002 161 3.9 -8.5 -1.1 -1.2 2.1 2.8

2003 28 1.6 -1.4 0.7 0.4 0.8 0.9

All 342 3.9 -8.5 -1.2 -1.3 2.0 2.6

L3 2001 296 3.2 -8.7 -2.1 -1.6 1.9 2.4

2002 302 1.5 -9.1 -1.9 -1.9 2.0 2.7

2003 48 -0.3 -2.2 -1.5 -1.3 1.3 1.3

All 646 3.2 -9.1 -1.8 -1.7 1.9 2.5

L4 2001 334 6.0 -8.8 -0.6 -1.1 1.5 2.2

2002 289 5.3 -8.0 -1.3 -1.3 1.5 1.9

2003 57 0.5 -1.2 -0.3 -0.3 0.5 0.6

All 680 6.0 -8.8 -0.8 -1.1 1.4 2.0

L5 2001 628 10.3 -6.2 -0.3 0.3 1.7 2.4

2002 576 6.3 -5.9 -1.1 -0.7 1.5 1.9

2003 103 4.8 -2.4 -1.2 -0.8 1.2 1.5

All 1,307 10.3 -6.2 -0.8 -0.3 1.6 2.1

34 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

Statistic

Site

identification

number 

(figure 1) Year

Number of 

compared data

points

Maximum

difference

Minimum

difference

Median

difference

Mean

difference

Absolute

mean

error

Root mean

square error

Temperature, in degrees Celsius 
Simulation of Hydrodynamics and Water Quality 35

Differences between simulated and measured temperatures also varied temporally in Beaver Lake for April 2001 to 

April 2003. In general, the AME and RMSE were the least in 

2001 at the two upstream sites (L2 and L3) and in 2002 at the 

two downstream sites (L4 and L5) and greatest in 2003 for all 

four sites (table 3). At site L5, near the dam (fig. 1), the AMEs 

for 2001 (April through December) and 2003 (January through 

March) were both 0.9 °C and RMSEs were 1.2 °C for 2001 and 

1.0 °C for 2003. The AME for 2002 was 0.8 °C and RMSE was 

0.9 °C. In comparison, at site L2, in the upstream portion of the 

reservoir (fig. 1), the AME ranged from 1.4 °C in 2001 to 3.1 

°C in 2003 and the RMSE ranged from 1.8 °C in 2001 to 3.2 °C 

in 2003. Variations in the spatial differences between simulated 

and measured temperature generally were because of the wide 

variation of hydrologic conditions that occurred during the simulation. 

Water Quality

Simulated data were compared to measured depth profile 

data (144 depth profiles) for dissolved-oxygen concentration at 

four sites in Beaver Lake. Simulated nutrient data were compared to samples collected in the epilimnion, metalimnion, and 

hypolimnion. 

Dissolved Oxygen

In general, simulated dissolved-oxygen concentrations 

were spatially similar to measured values in Beaver Lake from 

April 2001 to April 2003 (figs. 29-32). Similar to temperature, 

differences between simulated and measured values of dissolved-oxygen concentrations were greater in the upstream portion of the reservoir compared to differences in the downstream 

portion. The AME for the entire simulated period for site L2 

was 2.0 mg/L and the RMSE was 2.6 mg/L (table 3). The AME 

and RMSE for site L4 was 1.4 mg/L and 2.0 mg/L, respectively. 

Again, greater differences between simulated and measured 

values in the upstream portion of the reservoir compared to the 

downstream portion may be because of the more dynamic, riverine-type conditions in the upstream portion. The model generally overestimated the dissolved-oxygen concentration with 

the median difference (measured minus simulated) between 

simulated and measured values ranging from -2.1 mg/L (site L3 

in 2001) to 0.7 mg/L (site L2 in 2003) (table 3).

Simulated dissolved-oxygen concentrations also compared well to measured values temporally in Beaver Lake. At 

the upstream portion of the reservoir at sites L2 and L3, the 

greatest differences between simulated and measured dissolved 

oxygen generally occurred in 2002 and the least differences 

occurred in 2003 (table 3). At sites L4 and L5 the greatest differences occurred in 2001 and the least differences occurred in 

2003. A possible explanation for the greater differences in 2002 

at the upstream portion of the reservoir may be that during that 

time there was an increase in the number of high flow events 

from the tributaries, which may have changed the dynamics of 

dissolved oxygen because of loading and distribution of nutrients and organic matter, which was not simulated as well as in 

2001 and 2003.

Nitrogen and Phosphorus

Simulated ammonia and total nitrogen concentrations in 

Beaver Lake compared relatively well with the measured concentrations, and simulated nitrite plus nitrate concentrations 

generally were less then the measured concentrations (figs. 33-

35). The greatest differences between simulated and measured 

nitrogen concentrations generally occurred in the upstream portion of the reservoir and generally were greatest in the hypolimnion. The AME for ammonia ranged from 0.03 (site L5) to 0.14 

mg/L (site L3) and the RMSE ranged from 0.05 to 0.27 mg/L 

for all of the compared data at each site (table 4). The measured 

concentrations of ammonia were greater in samples collected in 

the hypolimnion and similarly, the differences in simulated and 

measured concentrations also were greater in the hypolimnion 

(fig. 33). Simulated nitrite plus nitrate had AMEs ranging from 

0.19 to 0.37 mg/L and RMSEs ranging from 0.26 to 0.52 mg/L 

when compared to all of the measured data at each site. The 

AME for total nitrogen ranged from 0.21 (site L5) to 0.45

mg/L (site L2) and the RMSE ranged from 0.29 to 0.57 mg/L 

for all of the compared data at each site. Similar to ammonia 

concentrations, measured nitrite plus nitrate and total nitrogen 

concentrations were greater in the hypolimnion, and likewise, 

the differences between simulated and measured concentrations 

also were greater (figs. 34 and 35). Because the simulated total 

nitrogen was comparable to the measured data and the nitrite 

plus nitrate was less, the model may be simulating greater concentrations of nitrogen in the form of organic nitrogen, instead 

of in the form of nitrite plus nitrate as is shown in the measured 

data. However, the temporal changes in the concentrations of 

nitrogen in the reservoir in the Beaver Lake model were adequately simulated (figs. 33-35). 
6/1/01

0 5 10 15 20

7/24/01

0 5 10 15 20

9/18/01

0 5 10 15 20

11/8/01

0 5 10 15 20

4/19/01

0 5 10 15 20

DEPTH, IN METERS

141210

86420

10/30/01

0 5 10 15 20

12/12/01

0 5 10 15 2

2/5/02

0 5 10 15 20

DEPTH, IN METERS

141210

86420

4/16/02

0 5 10 15 20

8/22/02

0 5 10 15 20

11/14/02

0 5 10 15 20

12/10/02

0 5 10 15 2

6/19/02

0 5 10 15 20

10/30/02

0 5 10 15 20

1/7/03

0 5 10 15 20

DEPTH, IN METERS

141210

86420

2/10/03

DISSOLVED-OXYGEN CONCENTRATION, IN MILLIGRAMS PER LITER

0 5 10 15 20

3/12/03

0 5 10 15 20

EXPLANATION

MEASURED

SIMULATED

Figure 29. Selected simulated and measured dissolved-oxygen concentration profiles for Beaver Lake at Highway 412 bridge near Sonora, Arkansas (site L2), April 2
6/1/01

0 5 10 15 20

7/24/01

0 5 10 15 20

9/20/01

0 5 10 15 20

11/7/01

0 5 10 15 20

4/19/01

0 5 10 15 20

DEPTH, IN METERS

25201510

50

10/30/01

0 5 10 15 20

12/11/01

0 5 10 15 20

2/5/02

0 5 10 15 20

DEPTH, IN METERS

25201510

50

4/17/02

0 5 10 15 20

8/21/02

0 5 10 15 20

10/30/02

0 5 10 15 20

6/19/02

0 5 10 15 20

11/14/02

0 5 10 15 20

12/11/02

0 5 10 15 20

1/8/03

0 5 10 15 20

DEPTH, IN METERS

25201510

50

2/11/03

0 5 10 15 20

3/12/03

DISSOLVED-OXYGEN CONCENTRATION, IN MILLIGRAMS PER LITER

0 5 10 15 20

EXPLANATION

MEASURED

SIMULATED

Figure 30. Selected simulated and measured dissolved-oxygen concentration profiles for Beaver Lake near Lowell, Arkansas (site L3), April 2001 to April 2003.
5/31/01

0 5 10 15 20

7/25/01

0 5 10 15 20

9/19/01

0 5 10 15 20

11/27/01

0 5 10 15 20

4/18/01

0 5 10 15 20

DEPTH, IN METERS

302010

0

10/31/01

0 5 10 15 20

EXPLANATION

MEASURED

SIMULATED

12/12/01

0 5 10 15 2

2/5/02

0 5 10 15 20

DEPTH, IN METERS

302010

0

4/17/02

0 5 10 15 20

8/21/02

0 5 10 15 20

11/14/02

0 5 10 15 20

12/10/02

0 5 10 15 2

6/18/02

0 5 10 15 20

10/29/02

0 5 10 15 20

1/6/03

0 5 10 15 20

DEPTH, IN METERS

302010

0

2/11/03

DISSOLVED-OXYGEN CONCENTRATION, IN MILLIGRAMS PER LITER

0 5 10 15 20

3/11/03

0 5 10 15 20

Figure 31. Selected simulated and measured dissolved-oxygen concentration profiles for Beaver Lake at Highway 12 bridge near Rogers, Arkansas (site L4), April 200
5/31/01

0 5 10 15 20

3/27/01

0 5 10 15 20

DEPTH, IN METERS

605040302010

0

7/25/01

0 5 10 15 20

9/11/01

0 5 10 15 20

11/27/01

0 5 10 15 20

10/31/01

0 5 10 15 20

12/17/01

0 5 10 15 20

2/4/02

0 5 10 15 20

DEPTH, IN METERS

605040302010

0

6/18/02

0 5 10 15 20

4/17/02

0 5 10 15 20

8/15/02

0 5 10 15 20

10/24/02

0 5 10 15 20

11/13/02

0 5 10 15 20

12/19/02

0 5 10 15 20

1/7/03

0 5 10 15 20

DEPTH, IN METERS

605040302010

0

2/11/03

0 5 10 15 20

3/11/03

0 5 10 15 20

3/18/03

DISSOLVED-OXYGEN CONCENTRATION, IN MILLIGRAMS PER LITER

0 5 10 15 20

MEASUREDSIMULATED

EXPLANATION

Figure 32. Selected simulated and measured dissolved-oxygen concentration profiles for Beaver Lake near Eureka Springs, Arkansas (site L5), April 2001 to April 200
SITE L2

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.00.10.20.30.4

SITE L3

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

AMMONIA CONCENTRATION, IN MILLIGRAMS PER LITER AS NITROGEN 0.0 0.1 0.2 0.3 0.4 SITE L4 4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03 0.0 0.1 0.2 0.3 0.4 SITE L5

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.00.10.20.30.4

SITE L2

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.00.20.40.60.8

SITE L3

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.00.20.40.60.8

SITE L4

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.00.20.40.60.8

SITE L5

DATE

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.00.20.40.60.8

SITE L2

4/1/01 8/1/01 12/1/01 4/1/02 8/1/0

0.00.51.01.52.02.53.0

SITE L3

4/1/01 8/1/01 12/1/01 4/1/02 8/1/0

0.00.51.01.52.02.53.0

SITE L4

4/1/01 8/1/01 12/1/01 4/1/02 8/1/0

0.00.51.01.52.02.53.0

SITE L5

4/1/01 8/1/01 12/1/01 4/1/02 8/1/0

0.00.51.01.52.02.53.0

EPILIMNION METALIMNION HYPOLIMNION

EXPLANATION

MEASURED CONCENTRATION

SIMULATED CONCENTRATION

CONCENTRATION LESS THANTHE LABORATORY REPORTING LIMIT

Figure 33. Simulated and measured ammonia concentrations for Beaver Lake, Arkansas, April 2001 to April 2003.
SITE L2

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.00.51.01.52.0

SITE L3

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

NITRATE PLUS NITRITE CONCENTRATION, IN MILLIGRAMS PER LITER AS NITROGEN 0.0 0.5 1.0 1.5 2.0 SITE L4 4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03 0.0 0.5 1.0 1.5 2.0 SITE L5 4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03 0.0 0.5 1.0 1.5 2.0 SITE L2 4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03 0.0 0.5 1.0 1.5 2.0 SITE L3 4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03 0.0 0.5 1.0 1.5 2.0 SITE L5

DATE

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.00.51.01.52.0

SITE L2

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 

0.00.51.01.52.0

SITE L3

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 

0.00.51.01.52.0

SITE L4

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 

0.00.51.01.52.0

SITE L5

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 

0.00.51.01.52.0

EPILIMNION METALIMNION HYPOLIMNION

EXPLANATION

MEASURED CONCENTRATION

SIMULATED CONCENTRATION

SITE L4

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.00.51.01.52.0

CONCENTRATION LESS THANTHE LABORATORY REPORTING LIMIT

Figure 34. Simulated and measured nitrite plus nitrate concentrations for Beaver Lake, Arkansas, April 2001 to April 2003.
SITE L2

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.00.51.01.52.02.53.03.5

SITE L3

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

TOTAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER AS NITROGEN 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 SITE L4 4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 SITE L5

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.00.51.01.52.02.53.03.5

SITE L2

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.00.51.01.52.02.53.03.5

SITE L3

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.00.51.01.52.02.53.03.5

SITE L4

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.00.51.01.52.02.53.03.5

SITE L5

DATE

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.00.51.01.52.02.53.03.5

SITE L2

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 

0.00.51.01.52.02.53.03.5

SITE L3

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 

0.00.51.01.52.02.53.03.5

SITE L4

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 

0.00.51.01.52.02.53.03.5

SITE L5

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 

0.00.51.01.52.02.53.03.5

EPILIMNION METALIMNION HYPOLIMNION

EXPLANATION

MEASURED CONCENTRATION

SIMULATED CONCENTRATION

Figure 35. Simulated and measured total nitrogen concentrations for Beaver Lake, Arkansas, April 2001 to April 2003.
 Simulation of Hydrodynamics and Water Quality 43

Table 4. Comparative statistics of simulated and measured nutrient concentrations for Beaver Lake, April 2001 to April 2003.

[Difference is simulated minus measured]

Site

identification

number Year

Number of

compared data

Mean

difference

Maximum

difference

Minimum

difference

Absolute

mean

error

Root mean

square error

 Ammonia, in milligrams per liter as nitrogen

L2 2001 45 -0.09 0.22 -1.08 0.15 0.28

2002 47 0.07 1.31 -0.20 0.13 0.24

2003 3 0.04 0.09 -0.01 0.04 0.06

All 95 -0.01 1.31 -1.08 0.13 0.26

L3 2001 45 0.02 0.65 -0.55 0.12 0.20

2002 43 0.04 0.92 -1.35 0.17 0.33

2003 3 0.09 0.14 0.05 0.09 0.10

All 91 0.03 0.92 -1.35 0.14 0.27

L4 2001 45 -0.05 0.15 -0.67 0.07 0.15

2002 41 0.05 0.34 -0.10 0.05 0.09

2003 3 0.04 0.05 0.04 0.04 0.04

All 89 0.00 0.34 -0.67 0.06 0.12

L5 2001 53 0.01 0.14 -0.03 0.01 0.03

2002 49 0.03 0.26 -0.04 0.04 0.07

2003 4 0.04 0.04 0.03 0.04 0.04

All 106 0.02 0.26 -0.04 0.03 0.05

 Nitrite plus nitrate, in milligrams per liter as nitrogen

L2 2001 45 -0.35 0.60 -1.44 0.39 0.55

2002 47 -0.11 1.31 -0.99 0.32 0.46

2003 3 -0.74 -0.38 -1.26 0.74 0.83

All 95 -0.24 1.31 -1.44 0.37 0.52

L3 2001 45 -0.38 0.06 -1.28 0.38 0.54

2002 43 -0.30 0.09 -0.95 0.31 0.42

2003 3 -0.27 -0.11 -0.46 0.27 0.30

All 91 -0.34 0.09 -1.28 0.34 0.48

L4 2001 45 -0.45 0.00 -1.08 0.45 0.54

2002 41 -0.36 0.03 -0.93 0.36 0.49

2003 3 -0.07 -0.05 -0.09 0.07 0.08

All 89 -0.39 0.03 -1.08 0.40 0.51
44 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

L5 2001 53 -0.06 1.07 -0.40 0.17 0.25

2002 49 -0.20 0.15 -0.57 0.21 0.26

2003 4 -0.18 0.10 -0.28 0.23 0.24

All 106 -0.13 1.07 -0.57 0.19 0.26

 Total nitrogen, in milligrams per liter as nitrogen

L2 2001 45 -0.26 1.00 -1.43 0.44 0.57

2002 47 0.24 1.47 -1.14 0.46 0.57

2003 3 -0.31 -0.07 -0.45 0.31 0.36

All 95 -0.02 1.47 -1.43 0.45 0.57

L3 2001 45 -0.21 0.62 -1.29 0.33 0.48

2002 43 -0.04 1.01 -1.57 0.44 0.53

2003 3 -0.24 -0.12 -0.41 0.24 0.27

All 91 -0.13 1.01 -1.57 0.38 0.50

L4 2001 45 -0.38 0.16 -1.06 0.40 0.51

2002 41 -0.13 0.66 -1.10 0.45 0.51

2003 3 0.03 0.12 -0.10 0.10 0.10

All 89 -0.25 0.66 -1.10 0.41 0.50

L5 2001 53 0.02 1.22 -0.99 0.21 0.31

2002 49 -0.02 0.42 -0.47 0.21 0.26

2003 4 -0.03 0.35 -0.34 0.21 0.25

All 106 0.00 1.22 -0.99 0.21 0.29

Orthophosphorus, in milligrams per liter as phosphorus

L2 2001 45 0.01 0.03 -0.04 0.01 0.02

2002 47 0.01 0.05 -0.01 0.02 0.02

2003 3 0.02 0.03 0.00 0.02 0.02

All 95 0.01 0.05 -0.04 0.02 0.02

L3 2001 45 0.00 0.03 -0.09 0.01 0.02

2002 43 0.01 0.04 -0.07 0.02 0.02

2003 3 0.01 0.02 0.00 0.01 0.02

All 91 0.00 0.04 -0.09 0.02 0.02

Table 4. Comparative statistics of simulated and measured nutrient concentrations for Beaver Lake, April 2001 to April 2003.—Continued

[Difference is simulated minus measured]

Site

identification

number Year

Number of

compared data

Mean

difference

Maximum

difference

Minimum

difference

Absolute

mean

error

Root mean

square error
Simulation of Hydrodynamics and Water Quality 45

L4 2001 45 0.00 0.02 -0.01 0.01 0.01

2002 41 0.01 0.03 -0.02 0.01 0.01

2003 3 0.01 0.01 0.01 0.01 0.01

All 89 0.01 0.03 -0.02 0.01 0.01

L5 2001 53 0.00 0.01 -0.02 0.01 0.01

2002 49 0.01 0.02 -0.02 0.01 0.01

2003 4 0.02 0.02 0.01 0.02 0.02

All 106 0.00 0.02 -0.02 0.01 0.01

Total phosphorus, in milligrams per liter as phosphorus

L2 2001 45 0.02 0.07 -0.14 0.03 0.04

2002 47 0.03 0.08 -0.09 0.04 0.04

2003 3 0.03 0.06 0.01 0.03 0.04

All 95 0.03 0.08 -0.14 0.04 0.04

L3 2001 45 0.01 0.03 -0.22 0.03 0.04

2002 43 0.01 0.05 -0.10 0.03 0.03

2003 3 0.02 0.03 0.02 0.02 0.02

All 91 0.01 0.05 -0.22 0.03 0.04

L4 2001 45 0.01 0.03 0.00 0.01 0.01

2002 41 0.00 0.05 -0.95 0.04 0.15

2003 3 0.02 0.02 0.02 0.02 0.02

All 89 0.01 0.05 -0.95 0.03 0.10

L5 2001 53 0.00 0.03 -0.01 0.01 0.01

2002 49 0.02 0.04 0.00 0.02 0.02

2003 4 0.02 0.04 0.02 0.02 0.03

All 106 0.01 0.04 -0.01 0.01 0.02

Table 4. Comparative statistics of simulated and measured nutrient concentrations for Beaver Lake, April 2001 to April 2003.—Continued

[Difference is simulated minus measured]

Site

identification

number Year

Number of

compared data

Mean

difference

Maximum

difference

Minimum

difference

Absolute

mean

error

Root mean

square error

Simulated values for orthophosphorus were comparable to 

measured concentrations and simulated total phosphorus concentrations generally were greater than the measured concentrations in Beaver Lake for April 2001 to April 2003 (figs. 36-37). 

Measured orthophosphorus concentrations mostly were below 

laboratory reporting limits and simulated concentrations were 

very low, resulting in AMEs and RMSEs ranging from 0.01 to 

0.02 mg/L for all the compared data at each site (table 4). The 

AME for total phosphorus ranged from 0.01 to 0.04 mg/L and 

the RMSE ranged from 0.02 to 0.10 mg/L for all the compared 

data at each site. Because simulated total phosphorus was 

greater than the measured total phosphorus although the simulated orthophosphorus was consistent with the measured data 

suggested that the model simulated more organic phosphorus 

(stored in the algal biomass) than evident from the measured 

data. 
SITE L2

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.000.050.100.150.20

SITE L3

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

ORTHOPHOSPHORUS CONCENTRATION, IN MILLIGRAMS PER LITER AS PHOSPHORUS 0.00 0.05 0.10 0.15 0.20 SITE L4 4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03 0.00 0.05 0.10 0.15 0.20 SITE L5 4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03 0.00 0.05 0.10 0.15 0.20 SITE L2 4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03 0.00 0.05 0.10 0.15 0.20 SITE L3 4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03 0.00 0.05 0.10 0.15 0.20 SITE L5

DATE

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.000.050.100.150.20

SITE L2

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 

0.000.050.100.150.20

SITE L3

4/1/01 8/1/01 12/1/01 4/1/02 8/1/0

0.000.050.100.150.20

SITE L4

4/1/01 8/1/01 12/1/01 4/1/02 8/1/0

0.000.050.100.150.20

SITE L5

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 

0.000.050.100.150.20

EPILIMNION METALIMNION HYPOLIMNION

MEASURED CONCENTRATION

SIMULATED CONCENTRATION

EXPLANATION

SITE L4

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.000.050.100.150.20

CONCENTRATION LESS THANTHE LABORATORY REPORTING LIMIT

Figure 36. Simulated and measured orthophosphorus concentrations for Beaver Lake, Arkansas, April 2001 to April 2003.
SITE L2

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.000.050.100.150.20

SITE L3

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

TOTAL PHOSPHORUS CONCENTRATION, IN MILLIGRAMS PER LITER AS PHOSPHORUS 0.00 0.05 0.10 0.15 0.20 SITE L4 4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03 0.00 0.05 0.10 0.15 0.20 SITE L5 4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03 0.00 0.05 0.10 0.15 0.20 SITE L2 4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03 0.00 0.05 0.10 0.15 0.20 SITE L3 4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03 0.00 0.05 0.10 0.15 0.20 SITE L5

DATE

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.000.050.100.150.20

SITE L2

4/1/01 8/1/01 12/1/01 4/1/02 8/1/0

0.000.050.100.150.20

SITE L3

4/1/01 8/1/01 12/1/01 4/1/02 8/1/0

0.000.050.100.150.20

SITE L4

4/1/01 8/1/01 12/1/01 4/1/02 8/1/0

0.000.050.100.150.20

SITE L5

4/1/01 8/1/01 12/1/01 4/1/02 8/1/0

0.000.050.100.150.20

EPILIMNION METALIMNION HYPOLIMNION

MEASURED CONCENTRATION

SIMULATED CONCENTRATION

EXPLANATION

SITE L4

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0.000.050.100.150.20

CONCENTRATION LESS THANTHE LABORATORY REPORTING LIMIT

Figure 37. Simulated and measured total phosphorus concentrations for Beaver Lake, Arkansas, April 2001 to April 2003.
48 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

Algae

Simulated algal biomass was compared to measured chlorophyll a at the four sites in Beaver Lake from April 2001 to 

April 2003. The concentration of chlorophyll a commonly is 

used as a measure of the density of the algal population of a 

lake. Algal biomass in the CEQUAL-W2 model is converted to 

chlorophyll a using a ratio (table 2) for comparison with measured data. Limited phytoplankton data were used to adjust the 

distribution of the four phytoplankton groups in the model 

(green, blue-green, diatoms, and flagellates) to reflect the ambient conditions in Beaver Lake.

Simulated chlorophyll a values were comparable to measured chlorophyll a values in Beaver Lake (fig. 38). The greatest differences between simulated and measured chlorophyll a

occurred at site L2 with an AME of 5.6 μg/L and an RMSE of 

7.3 μg/L (table 5). The AME and RMSE for simulated chlorophyll a concentrations at site L5 were 1.8 and 2.3 μg/L, respectively. Some of the differences between simulated and measured data can be explained by the variability in the measured 

concentrations because of the uneven vertical distribution of 

phytoplankton in the water column. However the simulated 

chlorophyll a followed the measured pattern of occurrence in 

the measured data with greater concentrations in May through 

November and lower concentrations in December through April 

(fig. 38). 

The composition and dynamics of the algal community in 

a reservoir can be complex. Modeling of the algal dynamics and 

composition is a large simplification of what actually occurs in 

a reservoir. In Beaver Lake, at least 114 different species have 

been identified from samples collected from 2001 through 2003 

(Russell Rhodes, Missouri State University, written commun., 

2003). To reduce the complexity and uncertainty in the Beaver 

Lake model because of limited information, the diverse species 

composition was generalized into four main groups; blue-green 

algae, green algae, diatoms, and flagellates.

The occurrence and distribution of the four simulated phytoplankton groups generally reflected the measured distribution 

in Beaver Lake (fig. 39). Blue-green and green algae tended to 

be more abundant at the upstream sites, while diatoms and 

flagellates tended to be more abundant at the downstream sites 

as was reflected in the measured data (fig. 18). The Beaver Lake 

model simulated the occurrence and distribution better at the 

downstream sites (L3, L4, and L5) than at the upstream sites 

(L1 and L2). The model generally simulated higher concentrations of blue-green and green algae in the upstream sites than 

were observed in the measured data (fig. 18). Diatoms and 

flagellates also were more abundant when water temperatures 

were lower and blue-green and green algae were more abundant 

when water temperatures were higher.

Table 5. Comparative statistics of simulated and measured chlorophyll a concentrations for Beaver Lake, April 2001 to April 2003.

[Values in micrograms per liter. Difference is simulated minus measured]

L2 2001 15 -6.4 1.8 -17.3 6.7 8.3

2002 14 -1.2 15.1 -14.2 4.4 6.4

2003 3 -5.5 -3.5 -9.5 5.5 6.2

All 32 -4.0 15.1 -17.3 5.6 7.3

L3 2001 15 -0.9 3.4 -6.5 1.9 2.5

2002 15 1.9 7.0 -4.5 3.2 3.9

2003 3 -3.6 -1.9 -4.6 3.6 3.9

All 33 0.1 7.0 -6.5 2.6 3.3

L4 2001 15 0.2 4.5 -2.4 2.1 2.5

2002 14 0.5 4.7 -8.3 3.2 4.1

2003 3 -0.9 -0.2 -1.5 0.9 1.0

All 32 0.2 4.7 -8.3 2.5 3.2

L5 2001 15 1.5 7.0 -0.7 1.6 2.4

2002 14 1.5 5.0 -1.2 1.9 2.4

2003 4 1.5 2.6 0.8 1.5 1.7

All 32 1.5 7.0 -1.2 1.8 2.3

Site

identification

number

(figure 1) Year

Number of

compared

data

Mean

difference

Maximum

difference

Minimum

difference

Absolute

mean

error

Root mean

square error
SITE L2

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0

5

10

15

20

25

30

35

SITE L3

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0

2

4

6

8

10

12

14

16

18

SITE L4

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

CHLOROPHYLL

a CONCENTRATION, IN MICROGRAMS PER LITER

0

2

4

6

8

10

12

14

16

18

SITE L5

DATE

4/1/01 8/1/01 12/1/01 4/1/02 8/1/02 12/1/02 4/1/03

0

2

4

6

8

10

12

14

16

18

MEASURED CONCENTRATION

SIMULATED CONCENTRATION

MEASURED CONCENTRATION BELOW LABORATORY REPORTING LIMIT

EXPLANATION

 Simulation of Hydrodynamics and Water Quality 49

Figure 38. Simulated and measured chlorophyll a concentrations in the epilimnion for Beaver Lake, Arkansas, April 2001 to April 2003.
SITE L1

DATE

4/1/01 6/1/01 8/1/01 10/1/01 12/1/01 2/1/02 4/1/02 6/1/02 8/1/02 10/1/02 12/1/02 2/1/03 4/1/03

0

1

2

3

4

BLUE-GREEN

ALGAE

DIATOMS

FLAGELLATES

GREEN ALGAE

SITE L5

DATE

4/1/01 6/1/01 8/1/01 10/1/01 12/1/01 2/1/02 4/1/02 6/1/02 8/1/02 10/1/02 12/1/02 2/1/03 4/1/03

0

1

2

3

4

SITE L4

4/1/01 6/1/01 8/1/01 10/1/01 12/1/01 2/1/02 4/1/02 6/1/02 8/1/02 10/1/02 12/1/02 2/1/03 4/1/03

0

1

2

3

4

SITE L3

4/1/01 6/1/01 8/1/01 10/1/01 12/1/01 2/1/02 4/1/02 6/1/02 8/1/02 10/1/02 12/1/02 2/1/03 4/1/03

PHYTOPLANKTON CONCENTRATION, IN MILLIGRAMS PER LITER

0

1

2

3

4

SITE L2

4/1/01 6/1/01 8/1/01 10/1/01 12/1/01 2/1/02 4/1/02 6/1/02 8/1/02 10/1/02 12/1/02 2/1/03 4/1/03

0

1

2

3

4

EXPLANATION

50 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

Figure 39. Simulated phytoplankton distribution for Beaver Lake, Arkansas, April 2001 to April 2003.
Simulation of Hydrodynamics and Water Quality 51

Eddy coefficients are used to model turbulence in a reservoir in which vertical turbulence equations are written in the 

conservative form using the Boussinesq and hydrostatic 

approximations (Cole and Wells, 2003). Since vertical momentum is not included, the model may give inaccurate results 

where there is substantial vertical acceleration. 

Some other limitations of the water-quality interactions in 

the model are that zooplankton or macrophytes are not included 

and the model uses simplistic sediment-oxygen demand computations. The zooplankton and macrophyte communities not represented in the model may have an effect on how the phytoplankton community or recycling of nutrients are simulated. 

The model does not have a sediment compartment that models 

kinetics in the sediment and at the sediment-water interface. 

The simplistic sediment computation in the model places a limitation on long-term predictive capabilities of the water-quality 

portion of the model. 

Sensitivity

Sensitivity analysis is the determination of the effects of 

small changes in calibrated model parameters and input on 

model results. A complete sensitivity analysis for the Beaver 

Lake model was not conducted because the model includes a 

large number of parameters (table 2). However, testing of how 

changes in different parameters affect the hydrodynamics, temperature, and water quality was conducted as part of the model 

development and calibration. Results from these simulations 

and information from previous model studies (Haggard and 

Green, 2002; Galloway and Green, 2002; 2003; Green and others, 2003; Bales and others, 2001; Sullivan and Rounds, 2005) 

were used to identify several parameters for evaluation in the 

sensitivity analysis. The sensitivity of simulated water temperature and water quality were assessed with changes in the windsheltering coefficient, light extinction coefficient for pure 

water, fraction of sediment-oxygen demand, algal growth rate, 

algal half-saturation constant for phosphorus, algal half-saturation constant for nitrogen, saturation of light intensity, inflow 

phosphorus, inflow nitrogen, and inflow organic matter. Each 

selected parameter was increased and decreased by 40 percent 

with all other parameters held constant. Vertical profiles, at 1 m 

depth intervals, of water temperature and concentrations of dissolved oxygen, ammonia, nitrite plus nitrate, total nitrogen, 

orthophosphorus, total algae, and chlorophyll a between the 

calibrated model and the sensitivity test were compared at sites 

L2 through L5.

Water temperature in the Beaver Lake model was the most 

sensitive to wind speed (wind-sheltering coefficient) and light 

extinction in the water column (table 6). The wind speed, 

adjusted using the wind-sheltering coefficient, affects the 

amount of mixing in the reservoir, which can change the depth 

of the thermocline and increase or decrease the evaporative 

cooling. Higher wind speeds result in more mixing, thus a 

deeper thermocline and lower surface temperatures, while 

lower wind speeds result in a shallower thermocline and higher 

surface temperatures. The changes in the thermocline depth 

resulted in the greatest differences at the thermocline between 

the calibrated model and the sensitivity test because of the rapid 

change in water temperature with depth that occurs at the thermocline.

Dissolved-oxygen concentrations were most affected by 

changes in light extinction, wind speed, and sediment-oxygen 

demand (fraction of sediment oxygen demand) (table 6). Dissolved-oxygen dynamics are controlled mainly by changes in 

temperature, which were most sensitive to changes in wind 

speed and light extinction. Wind speed also can affect dissolved-oxygen dynamics by aeration in the epilimnion. Sediment-oxygen demand is a substantial sink for dissolved oxygen 

in the Beaver Lake model and had the greatest affect on the concentrations.

Nitrogen concentrations were affected by changes in several parameters in the Beaver Lake model (table 6). Ammonia 

was sensitive to changes in the sediment-oxygen demand and 

wind speed. Increases in sediment-oxygen demand decreases 

the amount of dissolved oxygen in the hypolimnion, and, therefore, limits the amount of nitrification (conversion of ammonia 

to nitrate) and increases the amount of release of ammonia from 

the sediments resulting in higher ammonia concentrations. 

Nitrite plus nitrate concentrations were sensitive to changes in 

the two sources of nitrate in the model, inflow nitrogen, and 

nitrification from ammonia as a result of changes in wind speed. 

Total nitrogen was most sensitive to sediment-oxygen demand, 

mainly because of changes in ammonia, and sensitive to parameters affecting algal concentrations such as algal growth rate, 

inflow nitrogen, inflow phosphorus, and inflow organic matter, 

which affected the organic nitrogen concentrations in the 

model.

Phosphorus was relatively insensitive to changes in the 

selected model parameters for the Beaver Lake model (table 6). 

Orthophosphorus concentrations were slightly decreased by a 

40 percent decrease in algal growth and slightly increased with 

a 40 percent increase in the inflow phosphorus concentrations. 

Total phosphorus was slightly increased by a 40 percent 

increase in inflow organic matter and phosphorus. 

Total algae and chlorophyll a in the Beaver Lake model 

were most sensitive to changes in the algal growth rate, light 

extinction, and inflow of phosphorus and organic matter (table 

6). Because Beaver Lake generally is phosphorus limited, 

changes in inflow phosphorus had the greatest effect on the 

chlorophyll a and algal concentrations in the reservoir, while 

changes in inflow nitrogen concentrations had little effect. 

Because algae are dependent on light in the water column for 

photosynthesis, changes in light penetration (light extinction) 

have a substantial effect on algal growth.

Model Limitations

An understanding of model limitations is essential for 

effective use of reservoir models. The accuracy of the Beaver 

Lake model is limited by the simplification of complexities of 
Table 6. Results of sensitivity analysis for the Beaver Lake model, April 2001 to April 2003, showing the mean difference of all computed values at five sites in Beav

values.

[°C, degrees Celsius; mg/L, milligrams per liter]; N, nitrogen; P, phosphorus; μg/L, micrograms per liter

Algal growth rate 0.01 0.09 0.00 -0.01 0.01 0.00 0.00 

0.01 -0.03 -0.01 0.01 -0.05 0.01 0.00 

Saturation of light intensity -0.01 -0.07 0.00 0.00 0.00 0.00 0.00 

-0.01 0.13 -0.01 0.00 0.00 0.00 0.00 

Algal half-saturation constant for nitrogen 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

-0.01 -0.07 0.00 0.00 0.00 0.00 0.00 

Algal half-saturation constant for phosphorus -0.01 0.01 0.00 0.00 0.00 0.00 0.00 

-0.01 0.00 0.00 0.00 0.00 0.00 0.00 

Light extinction coefficient for pure water -0.12 -0.17 0.00 0.00 -0.01 0.00 0.00 

0.19 0.36 -0.01 0.00 0.00 0.00 0.00 

Fraction of sediment oxygen demand 0.00 -0.52 0.06 0.01 0.08 0.00 0.00 

0.00 0.66 -0.05 0.00 -0.07 0.00 0.00 

Wind-sheltering coefficient 2.24 -0.19 0.04 -0.02 0.03 0.00 0.00 

-1.98 0.60 -0.02 0.06 0.04 0.00 0.00 

Inflow nitrogen -0.02 -0.16 0.01 0.05 0.10 0.00 0.00 

0.00 -0.11 0.00 -0.03 -0.02 0.00 0.00 

Inflow organic matter -0.03 -0.26 0.02 0.01 0.13 0.00 0.01 

0.00 -0.04 0.00 0.01 -0.03 0.00 0.00 

Inflow phosphorus -0.03 -0.19 0.01 0.01 0.07 0.01 0.01 

0.01 -0.09 0.00 0.01 0.01 0.00 0.00 

Mean differences (sensitivity test value minus calibrated valu

Constituent

 Input, in

percent

change from

calibrated

value 

 Temperature,

°C 

 Dissolved

oxygen,

mg/L 

 Ammonia, 

mg/L as N

 Nitrite

plus

nitrate, 

mg/L

as N

Total

nitrogen,

mg/L as 

N

 Orthophosphorus,

mg/L as P

Total

phosphor

mg/L as 

+40

-40

+40

-40

+40

-40

+40

-40

+40

-40

+40

-40

+40

-40

+40

-40

+40

-40

+40

-40
Summary 53

the water quality and hydrodynamics within the reservoir, by 

spatial and temporal discretization effects, and by assumptions 

made in the formulation of the governing equations. Model 

accuracy also is limited by segment size, boundary conditions, 

accuracy of calibration, and parameter sensitivity. Model accuracy also is limited by the availability of data and by the interpolations and extrapolations that are inherent in using data in a 

model. Although a model might be calibrated, calibration 

parameter values are not necessarily unique in yielding acceptable values for the selected water-quality constituents, algal biomass, and reservoir water-surface elevation. 

Another limitation of the Beaver Lake model is that it is a 

two dimensional representation of a three dimensional waterbody. The governing equations are laterally and vertically averaged within layers. Although the model may accurately represent vertical and longitudinal processes within the reservoir, 

processes that occur laterally, or from shoreline to shoreline 

perpendicular to the downstream axis, may not be properly represented. 

Summary

Beaver Lake is a large, deep-storage reservoir located in 

the upper White River Basin in northwestern Arkansas. The 

water quality of Beaver Lake recently has become a focus of 

environmental concern because of the rapid population growth 

in northwestern Arkansas and because of agricultural activities 

in the basin. The purpose of this report is to describe the ambient hydrologic and water-quality conditions in Beaver Lake and 

its inflows and describe a two-dimensional model developed to 

simulate the hydrodynamics and water quality of Beaver Lake 

from 2001 through 2003. 

Water-quality samples were collected at the three main 

inflows to Beaver Lake; the White River near Fayetteville, 

Richland Creek at Goshen, and War Eagle Creek near Hindsville. Nutrient concentrations varied among the tributaries 

because of land use and contributions of nutrients from point 

sources. The median concentration of total ammonia plus 

organic nitrogen for the White River was 0.30 mg/L as nitrogen, 

Richland Creek had a median concentration of 0.20 mg/L as 

nitrogen, and War Eagle Creek had a median concentration of 

0.10 mg/L as nitrogen. The greatest concentrations of nitrite 

plus nitrate and total nitrogen, however, were observed at War 

Eagle Creek. The median concentrations of nitrite plus nitrate 

and total nitrogen for War Eagle Creek were 1.2 and 1.4 mg/L 

as nitrogen, respectively. The White River and Richland Creek 

had median nitrite plus nitrate concentrations of 0.36 and 0.85 

mg/L as nitrogen, respectively, and median concentrations of 

total nitrogen of 0.74 and 1.1 mg/L as nitrogen, respectively. 

Phosphorus concentrations were relatively low, with orthophosphorus and dissolved phosphorus concentrations mostly below 

the laboratory reporting limit at the three sites. War Eagle Creek 

had significantly greater median orthophosphorus and total 

phosphorus concentrations (0.03 and 0.04 mg/L as phosphorus, 

respectively) than the White River (0.01 and 0.03 mg/L as phosphorus, respectively) and Richland Creek (0.01 and 0.02 mg/L 

as phosphorus, respectively). Dissolved organic-carbon concentrations were significantly greater at the White River than at 

War Eagle and Richland Creeks. Estimated annual nutrient and 

dissolved organic-carbon loads generally were greater for the 

White River than for Richland and War Eagle Creeks in 2001 

through 2003. Greater loads would be expected for the White 

River because of the greater volume of streamflow that occurs 

at the site. The greatest annual loads occurred in 2002 for all 

three tributaries and the least occurred in 2003. The White River 

had significantly greater turbidity than Richland Creek and War 

Eagle Creek. The median turbidity for the White River was 8.6 

NTUs, and the median turbidities for Richland Creek and War 

Eagle Creek were 3.8 and 3.4 NTUs, respectively. 

The temperature distribution in Beaver Lake exhibits the 

typical seasonal cycle of lakes and reservoirs located within 

similar latitudes. Beaver Lake is a monomictic system, in which 

thermal stratification occurs annually during the summer and 

fall and complete mixing occurs in the winter. Isothermal conditions exist throughout the winter and early spring. 

Nitrogen concentrations varied temporally, longitudinally, 

and vertically in Beaver Lake for 2001 through 2003. Nitrite 

plus nitrate concentrations generally decreased from the 

upstream portion of Beaver Lake to the downstream portion and 

generally were greater in the hypolimnion. Total ammonia plus 

organic nitrogen concentrations also decreased from the 

upstream end of Beaver Lake to the downstream end and were 

substantially greater in the hypolimnion of Beaver Lake. Phosphorus concentrations mostly were near or below laboratory 

detection limits in the epilimnion and metalimnion in Beaver 

Lake and were substantially greater in the hypolimnion in the 

upstream and middle parts of the reservoir. Measured total and 

dissolved-organic carbon in Beaver Lake was relatively uniform spatially, longitudinally, and vertically in the reservoir 

from January 2001 through December 2003. Chlorophyll a concentrations measured at sites L1 and L2 (upper lake) were significantly greater than at the other sites on Beaver Lake with 

median concentrations of 7.2 μg/L and 12.5 μg/L, respectively. 

Sites L3, L4, and L5 had median concentrations of 5.5, 3.4, and 

1.8 μg/L, respectively.

During the study period, water clarity in Beaver Lake was 

significantly greater at the downstream end of the reservoir than 

at the upstream end. The median Secchi depth ranged from 0.6 

m at site L1 to 5.4 m at site L5 from January 2001 through 

December 2003. The greatest values for Secchi depth at site L5 

generally were observed in 2001 compared to 2002 and 2003, 

but did not have a seasonal pattern observed at sites L3 and L4. 

Similar to Secchi depth results, turbidity results indicated 

greater water clarity in the downstream portion of Beaver Lake 

compared to the upstream portion. Turbidity was also greater in 

the hypolimnion than in the epilimnion in the reservoir during 

the stratification season.

A two-dimensional, laterally averaged, hydrodynamic, 

and water-quality model using CE-QUAL-W2 Version 3.1 was 

developed for Beaver Lake and calibrated based on vertical pro-
54 Analysis of Ambient Conditions and Simulation of Hydrodynamics and Water-Quality Characteristics in Beaver Lake,

Arkansas, 2001 through 2003

files of temperature and dissolved oxygen, and water-quality 

constituent concentrations collected at various depths at five 

sites in the reservoir from April 2001 to April 2003. Simulated 

temperatures compared reasonably well with measured temperatures and differences varied spatially in Beaver Lake for April 

2001 to April 2003. The greatest differences between measured 

and simulated data occurred in the upstream portion of the reservoir, which is the most dynamic part of the reservoir. In general, the AME and RMSE were the least in 2001 at the two 

upstream sites (L2 and L3) and in 2002 at the two downstream 

sites (L4 and L5) and greatest in 2003 for all four sites. In general, simulated dissolved-oxygen concentrations were spatially 

similar to measured values in Beaver Lake from April 2001 to 

April 2003. Similar to temperature, differences between simulated and measured values of dissolved-oxygen concentrations 

were greater in the upstream portion of the reservoir compared 

to differences in the downstream portion. At the upstream portion of the reservoir at sites L2 and L3, the greatest differences 

between simulated and measured dissolved oxygen generally 

occurred in 2002 and the least differences occurred in 2003. 

Simulated ammonia and total nitrogen concentrations in Beaver 

Lake compared relatively well with the measured concentrations and simulated nitrite plus nitrate concentrations generally 

were less than the measured concentrations. Simulated values 

for orthophosphorus were comparable to measured concentrations and simulated total phosphorus concentrations generally 

were greater than the measured concentrations in Beaver Lake. 

Simulated chlorophyll a values were comparable to measured 

chlorophyll a values both spatially and temporally in Beaver 

Lake. The greatest differences between simulated and measured 

chlorophyll a occurred at site L2.
Summary 55

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