Prepared in cooperation with the

LITTLE ROCK MUNICIPAL WATER WORKS

ANALYSIS OF AMBIENT CONDITIONS AND 

SIMULATION OF HYDRODYNAMICS, 

CONSTITUENT TRANSPORT, AND WATER-QUALITY 

CHARACTERISTICS IN LAKE MAUMELLE, 

ARKANSAS, 1991-92

Water-Resources Investigations Report 01-4045

U.S. Department of the Interior

U.S. Geological Survey
ANALYSIS OF AMBIENT CONDITIONS AND 

SIMULATION OF HYDRODYNAMICS, 

CONSTITUENT TRANSPORT, AND WATER-QUALITY 

CHARACTERISTICS IN LAKE MAUMELLE, 

ARKANSAS, 1991-92

By W. Reed Green

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 01-4045

Prepared in cooperation with the

LITTLE ROCK MUNICIPAL WATER WORKS

Little Rock, Arkansas

2001
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

For additional information Copies of this report can be

write to: purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey, WRD Branch of Information Services

401 Hardin Road Box 25286

Little Rock, Arkansas 72211 Denver Federal Center

Denver, Colorado 80225
Contents III

CONTENTS

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

Introduction .........................................................................................................................................................................1

Purpose and Scope.....................................................................................................................................................3

Description of Study Area .........................................................................................................................................3

Previous Studies ........................................................................................................................................................4

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

Methods of Data Collection.................................................................................................................................................5

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

Hydrologic Conditions ..............................................................................................................................................5

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

Temperature.....................................................................................................................................................7

Dissolved Oxygen..........................................................................................................................................10

Nitrogen.........................................................................................................................................................10

Phosphorus.....................................................................................................................................................10

Chlorophyll a.................................................................................................................................................15

Loads of Sediment and Nutrients in the Maumelle River .......................................................................................15

Simulation of Hydrodynamics, Constituent Transport, and Water Quality ......................................................................15

Model Implementation ............................................................................................................................................18

Computational Grid .......................................................................................................................................18

Boundary and Initial Conditions....................................................................................................................20

Hydraulic Boundary Conditions.......................................................................................................... 20

Chemical Boundary Conditions...........................................................................................................21

Initial Conditions .................................................................................................................................21

Model Parameters..........................................................................................................................................21

Other Model Options.....................................................................................................................................24

Model Calibration and Testing ................................................................................................................................24

Hydrodynamics..............................................................................................................................................24

Water Chemistry............................................................................................................................................32

Dissolved Oxygen................................................................................................................................ 32

Phosphorus, Ammonia, and Algae ...................................................................................................... 41

Sensitivity Analysis ....................................................................................................................................... 41

Model Applications .................................................................................................................................................52

Simulation of Conservative Material Transport ............................................................................................52

Simulation of Nursery Pond Release.............................................................................................................54

Simulation of Nutrient Enrichment ...............................................................................................................55

Summary............................................................................................................................................................................59

References..........................................................................................................................................................................60
IV Contents

ILLUSTRATIONS

Figure 1. Map showing Lake Maumelle Basin................................................................................................................ 2

2. Map showing Lake Maumelle and the nursery pond on Twin Creek .............................................................. 4

 3-12. Graphs showing:

3. Daily precipitation at Little Rock Adams Field between October 1, 1990 and August 31, 1998.................... 6

4. Daily discharge at Maumelle River gaging station .......................................................................................... 6

5. Annual hydraulic residence time for Lake Maumelle based on outflow and water-supply withdrawal.......... 7

6. Water temperature in Lake Maumelle for selected days during the study ....................................................... 8

7. Dissolved oxygen concentrations in Lake Maumelle for selected days during the study................................ 9

8. Concentrations of nitrite plus nitrate (A), ammonia, and total ammonia plus organic nitrogen (B) 

 at Maumelle River streamflow gaging site, water year 1991 through 1998 .........................................11

9. Concentrations of nitrite plus nitrate, ammonia, and total ammonia plus organic nitrogen at the three 

reservoir sites, water year 1991 through 1998 ..................................................................................... 13

10. Concentrations of total phosphorus and dissolved orthophosphorus at Maumelle River streamflow

gaging site, water year 1991 through 1998 .......................................................................................... 14

11. Concentrations of total phosphorus and dissolved orthophosphorus at three reservoir sites, water 

year 1991 through 1998........................................................................................................................ 14

12. Concentrations of chlorophyll a at reservoir sites, 1991 through 1998 ......................................................... 16

13. Diagram showing plan view of (A) cross section (B) and downstream view (C) of model grid ........................ 18

14-36. Graphs showing:

14. Surface area and volume curves for Lake Maumelle from pre-impoundment engineering data and

model grid ............................................................................................................................................ 19

15. Measured and simulated water-surface elevation at Lake Maumelle spillway, February 6 through

December 31, 1991 .............................................................................................................................. 25

16. Measured and simulated water-surface elevation at Lake Maumelle spillway, January 1 through

December 31, 1992 .............................................................................................................................. 26

17. Measured and simulated near-surface and near-bottom water temperatures for February 8 through

December 31, 1991, at Lake Maumelle sites 3, 8, and 10 ................................................................... 27

18. Measured and simulated vertical profiles of water temperature at Lake Maumelle sites 3, 5, 8, 9, and 10,

February 8 through November 6, 1991 ................................................................................................ 28

19. Relation of difference between measured and simulated water temperatures at Lake Maumelle for 

all sites to measured water temperature, date, and depth below water surface, February 8

through November 6, 1991................................................................................................................... 31

20. Measured and simulated vertical profiles of water temperature at Lake Maumelle sites 3, 5, 8, 9, 

and 10, February 6 through October 20, 1992 ..................................................................................... 33

21. Relation of difference between measured and simulated water temperatures at Lake Maumelle

for all sites to measured water temperature, date, and depth below water surface, February 8

through October 20, 1992..................................................................................................................... 36

22. Measured and simulated dissolved oxygen concentrations, February through December 1991, at

Lake Maumelle sites 3, 8, and 10......................................................................................................... 37

23. Measured and simulated vertical profiles of dissolved oxygen concentrations at Lake Maumelle

sites 3, 5, 8, 9 and 10, February 8 through November 6, 1991 ............................................................ 38

24. Relation of difference between measured and simulated dissolved oxygen concentrations at 

Lake Maumelle for all sites to measured dissolved oxygen concentration, date, and depth

below water surface, February 8 through November 6, 1991.............................................................. 42

25. Measured and simulated vertical profiles of dissolved oxygen concentrations at Lake Maumelle

sites 3, 5, 8, 9, and 10, February 6 through October 20, 1992 ............................................................. 43

26. Relation of difference between measured and simulated dissolved oxygen concentrations at 

Lake Maumelle for all sites to measured dissolved oxygen concentrations, date, and

depth below water surface, February 6 through October 20, 1992 ...................................................... 46

27. Measured and simulated phosphorus concentrations at Lake Maumelle sites 3, 8, and 10,

February through December 1991........................................................................................................ 47
Contents V

28. Measured and simulated ammonia concentrations at Lake Maumelle sites 3, 8 and 10,

February through December 1991........................................................................................................ 48

29. Measured and simulated algal biomass at Lake Maumelle sites 3, 8 and 10, February

through December 1991 ....................................................................................................................... 49

30. Vertical temperature distributions at site 10 on August 27, 1991, showing calibrated model profiles and

profiles as a result of differing wind sheltering, bottom heat exchange, and light extinction

coefficients ........................................................................................................................................... 50

31. Vertical dissolved oxygen distributions at site 10 on April 22 and August 27, 1991, showing

calibrated model profiles and profiles as a result of differing sediment oxygen demand and

wind-sheltering coefficients ................................................................................................................. 51

32. Daily discharges into Lake Maumelle from April 20 through May 10, 1991, showing location on the

hydrograph where spill was simulated ................................................................................................. 52

33. Simulated concentrations of a conservative material introduced at the upstream boundary at 

6:00 a.m. on April 26, 1991 ................................................................................................................. 53

34. Discharge from the nursery pond into Lake Maumelle.................................................................................. 54

35. Simulated temperatures in the receiving embayment of the nursery pond release ........................................ 55

36. Distance and depth plots of simulated tracer concentrations in the receiving embayment after

release of the nursery pond................................................................................................................... 56

37. Distance and depth plots of simulated conservative tracer released from the nursery pond

into Lake Maumelle ............................................................................................................................. 57

38. Time series of algal biomass resulting from various nutrient enrichment scenarios at segment 10,

layer 4, at the downstream end of Lake Maumelle .............................................................................. 58

TABLES

Table 1. Statistical summary of selected water-quality parameters at Lake Maumelle sites 3, 8, and 10,

water years 1991 through 1998 ................................................................................................................ 12

2. Annual sediment and nutrient loads and yields at the Maumelle River streamflow gaging site.................... 17

3. Hydraulic and thermal parameters specified as Lake Maumelle model input ............................................... 20

4. Rate coefficients used in water-chemistry simulations and specified as model input.................................... 22
VI Contents

Sea level: In this report “sea level” refers to the National Geodetic Vertical Datum of 

1929—a geodetic datum derived from a general adjustment of the first-order level nets of 

the United States and Canada, formerly called Sea Level Datum of 1929.

Water year: October 1 through September 30.

CONVERSION FACTORS AND VERTICAL DATUM

Multiply By To obtain

centimeter (cm) 0.3937 inch

meter (m) 3.281 foot

kilometer (km) 0.6214 mile (mi)

hectare (ha) 2.471 acre

square meter (m2) 10.76 square foot

square kilometer (km2) 0.3861 square mile

cubic meter (m3) 35.31 cubic foot

gram (g) 0.03527 ounce

kilogram (k) 2.205 pound

degree Celsius (°C) 1.8 x °C + 32 degree Fahrenheit
Abstract 1

Analysis of Ambient Conditions and Simulation of 

Hydrodynamics, Constituent Transport, and WaterQuality Characteristics in Lake Maumelle, Arkansas, 

1991-92

by W. Reed Green

ABSTRACT

Lake Maumelle is the major drinking-water 

source for the Little Rock metropolitan area in central 

Arkansas. Urban and agricultural development has 

increased in the Lake Maumelle Basin and information 

is needed related to constituent transport and waterquality response to changes in constituent loading or 

hydrologic regime. This report characterizes ambient 

conditions in Lake Maumelle and its major tributary, 

Maumelle River; describes the calibration and verification of a numerical model of hydrodynamics and water 

quality; and provides several simulations that describe 

constituent transport and water quality response to 

changes in constituent loading and hydrologic regime. 

Ambient hydrologic and water-quality conditions demonstrate the relatively undisturbed nature of 

Lake Maumelle and the Maumelle River. Nitrogen and 

phosphorus concentrations were low, one to two orders 

of magnitude lower than estimates of national background nutrient concentrations. Phosphorus and chlorophyll a concentrations in Lake Maumelle 

demonstrate its oligotrophic/mesotrophic condition. 

However, concentrations of chlorophyll a appeared to 

increase since 1990 within the upper and middle 

reaches of the reservoir.

A two-dimensional, laterally averaged hydrodynamic and water-quality model developed and calibrated for Lake Maumelle simulates water level, 

currents, heat transport and temperature distribution, 

conservative material transport, and the transport and 

transformation of 11 chemical constituents. Simulations included the movement and dispersion of spills or 

releases in the reservoir during stratified and unstratified conditions, release of the fish nursery pond off the 

southern shore of Lake Maumelle, and algal responses 

to changes in external loading. 

The model was calibrated using 1991 data and 

verified using 1992 data. Simulated temperature and 

dissolved oxygen concentrations related well when 

compared to measured values. Simulated nutrient and 

algal biomass also related reasonably well when compared to measured values. A simulated spill of conservative material at the upper end of Lake Maumelle 

during a major storm event took less than 102 hours to 

disperse the entire length of the reservoir. Simulation of 

a nursery pond release into a tributary to Lake 

Maumelle demonstrated how the released water 

plunges within the receiving embayment and enters the 

main stem of the reservoir at mid depths. Simulations 

of algal response to increases of nitrogen and phosphorus loads demonstrate the phosphorus limiting condition in Lake Maumelle.

Results from this study will provide waterresource management with information to better understand how changes in hydrology and water quality in 

the basin affects water quality in the reservoir. With this 

information, managers will be able to more effectively 

manage their drinking-water source supply.

INTRODUCTION

Lake Maumelle (fig. 1) was constructed in 1956 

for drinking-water supply for the Little Rock, Arkansas, metropolitan area. In addition to water supply, 

Lake Maumelle is used for recreation and provides 

habitat for fish and wildlife. Concerns about the sustainability of the quality of the drinking-water source 

have grown as urban and agricultural (grass farming, 

silviculture, cattle grazing) development have 

increased in the Lake Maumelle Basin during the past 

20 years.
2 Analysis of Ambient Conditions and Simulation of Hydrodynamics, Constituent Transport, and Water-Quality Characteristics

in Lake Maumelle, Arkansas, 1991-92

Figure 1. Lake Maumelle Basin.

Lake

Maumelle

Arkansas

River

Maumelle

River 10

10

9

324

113

300

9

10

92 52’30” o

92 45’ o

92 37’30” o

92 30’ o

34 52’30” o

34 55’ o

34 50’ o

WilliamsJunction

PULASKI CO

OCYRREP

OC ENI LAS

Little Rock

ARKANSAS

0 1 2 3 MILES0 1 2 3 KILOMETERS

EXPLANATIONSTREAMFLOW GAGING STATIONDRAINAGE AREA BOUNDARY OF LAKE MAUMELLE

Spillway
Introduction 3

Information regarding circulation and constituent transport in Lake Maumelle is lacking. This information is needed to more effectively manage the 

reservoir and its watershed and to predict water-quality 

responses to changes in constituent loading or hydrologic regime. Such changes may result from increased 

agricultural activity and urban expansion within the 

watershed. Runoff volume and loads of nonpointsource nutrients, pesticides, and other contaminants 

could change in response to conversion of forested 

areas to pasture, conversion of grass farms to pasture, 

and the associated increase in cattle, and conversion of 

non-urban areas to urban areas.

During 1991, a study was undertaken to characterize ambient conditions and hydrodynamics in Lake 

Maumelle by calibrating a model and using it to simulate the effects of changes in external loads to the reservoir. This study was part of a larger study conducted 

by the U.S. Geological Survey (USGS) in cooperation 

with Little Rock Municipal Water Works (LRMWW) 

to monitor water levels, streamflow, and water quality 

in the drinking-water-supply reservoir, Lake 

Maumelle. 

Purpose and Scope

Purposes of this report were to (1) describe ambient hydrologic and water-quality conditions in Lake 

Maumelle and its major tributary, the Maumelle River; 

(2) describe calibration and verification of a model 

developed by the U.S. Army Corps of Engineers (CEQUAL-W2) to simulate ambient water-quality conditions and hydrodynamics in Lake Maumelle; and (3) 

describe several model simulations of movement and 

dispersion of spills or releases in the reservoir during 

thermally stratified and unstratified conditions, of an 

adjacent fish nursery pond release, and the response of 

water quality (nutrient, algal, and dissolved-oxygen 

concentrations) to possible changes in external loads. 

This report describes ambient conditions and presents 

the results of model calibration, verification, and simulations.

Hydrologic and water-quality data are summarized for the period October 1990 through September 

1998 for precipitation, streamflow, and selected waterquality characteristics including temperature, dissolved 

oxygen (DO), nitrogen and phosphorus species, and 

chlorophyll a. Estimated loads of nitrogen and phosphorus to Lake Maumelle from the Maumelle River are 

presented.

Hydraulic circulation and water-quality characteristics in Lake Maumelle were simulated by using the 

U.S. Army Corps of Engineers CE-QUAL-W2 model. 

This laterally averaged, two-dimensional model was 

calibrated by using data collected from January 

through December 1991 and verified using data collected from January through December 1992. The calibrated model was used to simulate the effects of 

nutrient loads from the Maumelle River and the nursery 

pond release on reservoir water quality. 

Description of Study Area

Lake Maumelle is a surface-water-supply reservoir completed in 1956 on the Maumelle River, west of 

the city of Little Rock (fig. 1). The Maumelle River 

Basin has a drainage area of 355 km2 at the Lake 

Maumelle dam, and is part of the Arkansas River 

Basin. The average annual precipitation within the 

Maumelle River Basin is about 137 cm (Freiwald, 

1984). Lake Maumelle contains 2.70 x 108

 m3 of water 

at spillway elevation (88.39 m above sea level) and has 

2.31 x 108 m3 of usable water. The surface area of Lake 

Maumelle at spillway elevation is 36 km2. The maximum length of the reservoir is 19.3 km, with a maximum depth of 13.7 m, and an average depth of 7.5 m 

(Green, 1993). 

The general land use classification for the 

Maumelle basin is “forest and woodland grazed” (U.S. 

Geological Survey, 1970, p. 159). The upper one-third 

of the watershed primarily is forest land owned and 

managed by the Ouachita National Forest. The forest 

land is classified by the U.S. Forest Service, U.S. 

Department of Agriculture (USDA) as moderate to low 

productive land with a full range of site conditions that 

have been determined to be suitable for timber production ( U.S. Department of Agriculture, 1989). The general soil type, defined by the USDA soil surveys of 

Pulaski and Perry Counties (Haley and others, 1975; 

Townsend and Williams, 1982), is Carnasaw-Pirum 

Clebit: well drained gently sloping to very steep, deep, 

moderately deep, and shallow, loamy, gravelly and 

stony soils; on uplands. The remainder of the watershed primarily is forest with some agriculture existing 

in the lowland area of the Maumelle River above the 

lake. Turf (sod) farming is the most common agricultural practice in the flood plain of the basin.

Adjacent to the reservoir is a fish nursery pond 

formed by a dam on Twin Creek, a small lateral tributary entering Lake Maumelle on the southern shore 
4 Analysis of Ambient Conditions and Simulation of Hydrodynamics, Constituent Transport, and Water-Quality Characteristics 

in Lake Maumelle, Arkansas, 1991-92

(fig. 2). At its spillway elevation (108.2 m above sea 

level), the nursery pond contains about 1.38 × 106 m3 

of water, about 0.5 percent of the volume of Lake 

Maumelle, and covers about 0.28 km2

. The drainage 

area of the nursery pond is about 5.1 km2, about 1.4 

percent of the area of the Lake Maumelle Basin. The 

maximum depth of the nursery pond is about the same 

as Lake Maumelle (13.7 m) and the average depth is 

about 5.0 m.

Previous Studies

USGS and LRMWW have collected reservoir 

elevation, streamflow, and water-quality data for the 

Maumelle River and Lake Maumelle since 1989 as part 

of an ongoing monitoring program. Data are stored in 

the USGS National Water Information System database and published annually (Moore and others, 1990; 

Porter and others, 1991; Morris and others, 1992; Porter and others, 1993; Westerfield and others, 1994; 

Evans and others, 1995; Porter and others, 1996; 1997; 

1998; 1999; 2000). Hydrologic data collected in Lake 

Maumelle from May 1989 through October 1992 

(Green and Louthian, 1993) were used to assess water 

quality (Green, 1993). Green (1993) concluded that the 

water quality of the Maumelle River and Lake 

Maumelle when compared to other streams and reservoirs in the region is more pristine (oligotrophic). From 

these comparisons, it can be considered that the water 

quality of the Maumelle Basin represents relatively 

undisturbed water-quality conditions within the region. 

The trophic condition of Lake Maumelle can be considered oligo-mesotrophic (Green, 1993) based on nutrient concentrations, chlorophyll a, and secchi disk 

transparency. If nutrient inputs are maintained at 1993 

levels, the water quality of Lake Maumelle should 

remain relatively stable. However, increases in nutrient 

loads may alter trophic conditions from oligomesotrophic to more eutrophic.

Nursery pond releases into Lake Maumelle are a 

major water-quality issue. A report assessing the 

impact of nursery pond releases into the lake determined that the water-quality impact of the nursery pond 

release was variable and appeared to be related to the 

volume of the nursery pond at the time of release and 

the amount of fertilizer applied to the nursery pond earlier in the year (Green, 1998). Much of the material 

released from the nursery pond originated in the cooler, 

anoxic, hypolimnetic water of the pond. Because the 

initial water released from the nursery pond was cooler 

(and denser) than the receiving surface water, it 

plunged into the hypolimnion of Lake Maumelle.

Figure 2. Lake Maumelle and the nursery pond on Twin Creek.

92 37' 30" o

34 52' 30"

o

92 30' o

Base from U.S. Geological Survey Digital Line Graphs

Universal Transverse Mercator

1:100,000 scale

Shaded relief from U.S. Geological Survey Digital Elevation Models

Universal Transverse Mercator

1:24,000 scale

Hwy. 10

3

5

8

9

10

Nursery 

Pond

Twin Creek

34 55'

o

Explanation

WATER-QUALITY SAMPLING

SITE AND IDENTIFICATION 

NUMBER

3

Dam

Spillway

0

0 1KILOMETER

1 MILE
Methods of Data Collection 5

Acknowledgments

Tom Cole of the U.S. Army Corps of Engineers 

provided valuable guidance on the CE-QUAL-W2 

model. Jerad Bales of the USGS provided valuable 

model calibration and report preparation support. 

METHODS OF DATA COLLECTION

Continuous 1-hour interval reservoir elevation 

and 15-minute interval streamflow gaging sites were 

installed on Lake Maumelle and the Maumelle River in 

August 1989. The drainage basin above the discharge 

site (fig. 1) on the Maumelle River accounts for about 

34 percent of the Lake Maumelle drainage. The rating 

curve established for the Maumelle River was based on 

instantaneous discharge measurements following 

methods described by Rantz and others (1982) and continues to be updated. The reservoir-elevation site measures water-surface elevation at the spillway and 

accounts for reservoir volume based on established elevation-volume curves provided by LRMWW. A theoretical rating curve for discharge flowing over the 

spillway was established and verified with periodic discharge measurements immediately downstream.

Fixed water-quality sampling sites were established at the streamflow-gaging site (fig. 1) and along 

the downstream gradient within the reservoir (fig. 2). 

Sample sites in the reservoir were located along the 

original stream channel, the deepest location within the 

reservoir cross section. Samples were collected in Lake 

Maumelle at sites 3, 8, and 10 from 1991 through 1998 

using a 1-m by 5-cm bailer to collect depth-integrated 

composite samples representing the entire water column when isothermal conditions were present. During 

thermal stratification, depth-integrated samples were 

collected representing the epilimnion (surface) and 

hypolimnion (bottom). Samples were collected 

monthly during the winter and twice monthly during 

the summer during 1991 through 1992. Field parameters (water temperature, DO concentration, pH, and 

specific conductance) were measured at various depths 

within the water column at sites 3, 5, 8, 9, and 10 during 

1991 through 1992 and 3, 8, and 10 the rest of the 

period. When thermal stratification was present, measurements were taken at depth intervals where the 

change in temperature was 1 °C or at 0.3-m intervals, 

whichever was greater. Water-quality samples were 

analyzed for nutrients (dissolved orthophosphorus, 

total phosphorus, total ammonia plus organic nitrogen, 

dissolved ammonia, and dissolved nitrite plus nitrate 

nitrogen), total and dissolved organic carbon, and chlorophyll a. All sample analyses were conducted at 

USGS laboratories following USGS methods.

Water-quality samples were collected at the 

Maumelle River gaging site following equal width 

increment methods using depth-integrated samplers 

described by Wilde and others (1999). Field parameters 

(water temperature, DO concentration, pH, and specific conductance) were measured using a multiparameter-metering unit. Water-quality samples were 

collected from October 1990 through September 1998 

using depth-integrated techniques covering various 

depth ranges.

AMBIENT CONDITIONS

Hydrologic and water-quality conditions for the 

period 1990 through 1998 describe the nature of Lake 

Maumelle and its major tributary, the Maumelle River. 

In its present condition, Lake Maumelle appears to 

have little stress from anthropogenic sources. However, changes in land use and urban migration into the 

basin can be expected to affect the water quality of this 

drinking-water source. 

Hydrologic Conditions

Over the period October 1990 through August 

1998, precipitation at Little Rock Adams Field 

(National Oceanographic Atmospheric Administration 

(NOAA) station 13963) (fig. 3) averaged 121.8 cm/yr. 

Little Rock Adams Field is located about 26 km southeast of Lake Maumelle dam. Streamflow at the 

Maumelle River gaging station from January 1991 

through December 1998 (fig. 4) averaged 1.74 m3/sec. 

Hydraulic residence time based on reservoir volume, 

discharge over the spillway, and water-supply withdrawal, varied during the period water year 1990 

through 1997 (fig. 5). The mean annual residence time 

during this period was 1.51 years. The average spillway 

outflow was 4.82 m3

/s and the average withdrawal rate 

was 1.56 m3/s.
6 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92 1/1/90 

1/1/91 1/1/92 1/1/93 1/1/94 1/1/95 1/1/96 1/1/97 1/1/98 1/1/99 

DAILY PRECIPITATION, IN CENTIMETERS

0

2

4

6

8

10

12

Figure 3. Daily precipitation at Little Rock Adams Field between October 1, 1990 and August 31, 1998. 1/1/90 1/1/91 1/1/92 1/1/93 1/1/94 1/1/95 1/1/96 1/1/97 1/1/98 1/1/99 DISCHARGE, IN CUBIC METERS PER SECOND

0

20

40

60

80

Figure 4. Daily discharge at Maumelle River gaging station.
Ambient Conditions 7

WATER YEAR

1990 1991 1992 1993 1994 1995 1996 1997

HYDRAULIC RESIDENCE TIME,

IN YEARS

0

1

2

3

4

Figure 5. Annual hydraulic residence time for Lake Maumelle based on outflow and water-supply withdrawal.

Water-Quality Conditions

In order to develop a model that simulates hydrodynamics, constituent transport, and water-quality 

characteristics, ambient conditions need to be defined 

and understood. Water-quality conditions most important in this study include temperature, DO, nitrogen 

phosphorus, and chlorophyll a. Water temperature and 

DO concentration were measured at five sites and 

nitrogen, phosphorus, and chlorophyll a at three sites 

in Lake Maumelle (fig. 2) and at the Maumelle River 

streamflow gaging site (fig. 1). Temperature and DO 

data collected during 1991 and 1992 from the five reservoir sites are presented graphically as depth-distance 

diagrams (figs. 6 and 7). Each diagram shows conditions for one date and represents a longitudinal cross 

section of the reservoir along the thalweg from the 

upper end of the reservoir to the dam. Lines of equal 

temperature or concentration delineate regions with 

similar values. Results for eight selected sampling 

dates over the 2-year period illustrate seasonal patterns 

in temperature and DO. 

Temperature

Temperature varied annually, seasonally, and 

spatially in Lake Maumelle (fig. 6). Water temperature 

was generally cooler in 1992 than at similar dates in 

1991, with the exception of February. In early February 

1991, temperature varied somewhat between the surface and bottom. However, in early February 1992, 

temperature of the entire water body was within 1.0 °C 

of 8.0 °C. Thermal stratification was well established in 

June 1991 with temperatures ranging from 18.5 °C near 

the bottom to nearly 30.0 °C at the surface. In June 

1992, the temperature ranged from about 17.0 °C near 

the bottom to 22.0 °C at the surface. By the end of 

August 1991, temperature ranged from about 19.0 °C 

near the bottom to almost 29.0 °C near the surface. By 

the end of August 1992, temperature ranged from 19.5 

°C near the bottom to almost 28.0 °C near the surface. 
8 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

Figure 6. Water temperature in Lake Maumelle for selected days during the study.

14

12

10

8

6

4

2

0

0 2 4 6 8 10 12 14 16

June 5, 1991

14

12

10

8

6

4

2

0

0 2 4 6 8 10 12 14 16

August 27, 1991

14

12

10

8

6

4

2

0

0 2 4 6 8 10 12 14 16

October 3, 1991

14

12

10

8

6

4

2

0

0 2 4 6 8 10 12 14 16

August 31, 1992

14

12

10

8

6

4

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0

0 2 4 6 8 10 12 14 16

June 1, 1992

14

12

10

8

6

4

2

0

0 2 4 6 8 10 12 14 16

October 21, 1992

DEPTH, IN METERS

DOWNSTREAM DISTANCE, IN KILOMETERS

14

12

10

8

6

4

2

0

0 2 4 6 8 10 12 14 16

February 6, 1991

14

12

10

8

6

4

2

0

0 2 4 6 8 10 12 14 16

February 5, 1992

 EXPLANATION

 Measurement location

 7.5 Line of equal water temperature, in degrees Celsius
Ambient Conditions 9

Figure 7. Dissolved oxygen concentrations in Lake Maumelle for selected days during the study.

14

12

10

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6

4

2

0

0 2 4 6 8 10 12 14 16

February 6, 1991

14

12

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0

0 2 4 6 8 10 12 14 16

June 5, 1991

14

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0

0 2 4 6 8 10 12 14 16

August 27, 1991

14

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0

0 2 4 6 8 10 12 14 16

October 3, 1991

14

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2

0

0 2 4 6 8 10 12 14 16

June 1, 1992

14

12

10

8

6

4

2

0

0 2 4 6 8 10 12 14 16

August 31, 1992

14

12

10

8

6

4

2

0

0 2 4 6 8 10 12 14 16

October 21, 1992

14

12

10

8

6

4

2

0

0 2 4 6 8 10 12 14 16

February 5, 1992

DEPTH, IN METERS

DOWNSTREAM DISTANCE, IN KILOMETERS

 EXPLANATION

 Measurement location

 7.5 Line of equal DO concentration, in degrees Celsius
10 Analysis of Ambient Conditions and Simulation of Hydrodynamics, Constituent Transport, and Water-Quality Characteristics 

in Lake Maumelle, Arkansas, 1991-92

Breakdown of the thermocline had occurred by early 

October 1991. Temperature ranged from 19.0 °C near 

the bottom to 23.5 °C near the surface. Likewise, in 

1992, the thermocline had disintegrated by late October.

Dissolved Oxygen

DO concentrations in Lake Maumelle are 

strongly related to vertical temperature distributions. In 

general, DO in Lake Maumelle remains near saturation 

and well mixed in the water column from late October 

through mid-April. By early June 1991 and 1992, DO 

concentrations approached zero (0.7 and 0.6 mg/L, 

respectively) near the bottom and were less than 2.0 

mg/L within much of the hypolimnion (fig. 7). Anoxic 

conditions (DO <2.0 mg/L) remained in the hypolimnion during both years until turnover and by late October, DO concentrations were more uniformly 

distributed throughout the water column. 

Nitrogen

Nitrogen (N) and phosphorus (P) are primary 

nutrients that usually regulate algal productivity in 

lakes and reservoirs (Wetzel, 1983). Three nitrogen 

species—dissolved nitrite plus nitrate (NO2+NO3), 

dissolved ammonia (NH4), and total ammonia plus 

organic nitrogen— were measured during this study. 

At the Maumelle River streamflow-gaging site, 

NO2+NO3 and NH4 were present at similar concentrations (fig. 8). Concentrations of NO2+NO3 ranged from 

less than 0.002 to 0.203 mg/L as N with a median value 

of 0.0135 mg/L as N. Concentrations of NH4 ranged 

from less than 0.002 to 0.087 mg/L as N with a median 

value of 0.011 mg/L as N. Concentrations of total 

ammonia plus organic nitrogen ranged from less than 

0.20 to 0.90 mg/L as N with a median value of less than 

0.2 mg/L as N. 

Concentrations of nitrite plus nitrate varied little 

between reservoir sites and depth (table 1, fig. 9). 

Nitrite plus nitrate nitrogen concentrations ranged from 

less than 0.002 to 0.075 mg/L as N, considering all 

samples at all sites with the exception of one sample 

collected in the bottom water at site 10 (0.25 mg/L as 

N). No site-to-site or surface (top) and bottom sample 

groups were statistically different (p < 0.05) based on 

the Kruskal-Wallis one-way analysis of variance on 

ranks (Helsel and Hirsch, 1992). Ammonia concentrations in surface samples varied somewhat among reservoir sites and depth (fig. 9). Concentrations ranged 

from less than 0.002 to 0.170 mg/L as N. Concentrations in surface water did not differ among sites. 

Ammonia concentrations in bottom water at site 8 were 

statistically different (p < 0.05) than surface water at all 

sites and bottom water at site 3. Median concentrations 

in bottom water at sites 8 and 10 were greater than 

twice the median concentrations in surface water as a 

result of sediment release during stratified anoxic periods. Total ammonia plus organic nitrogen concentrations varied little between sites and depth (fig. 9). 

Concentrations ranged from less than 0.2 to 0.7 mg/L 

as N. More than one-half of all concentrations were less 

than 0.2 mg/L.

Considering estimates of national background 

nutrient concentrations (U.S. Geological Survey, 

1999), nitrogen concentrations in Lake Maumelle were 

considerably lower relative to undeveloped areas 

across the Nation minimally affected by agriculture, 

urbanization, and associated land uses. Nitrite plus 

nitrate concentrations in Lake Maumelle were one to 

two orders of magnitude lower than estimates of 

national background concentrations (0.6 mg/L as N). 

Likewise, ammonia concentrations were one to two 

orders of magnitude lower than estimates of national 

background concentrations (0.1 mg/L as N). Total 

nitrogen (sum of nitrite, nitrate, ammonia, and organic 

nitrogen) concentrations in Lake Maumelle were at 

least an order of magnitude lower than estimates of 

national background concentrations (1.0 mg/L as N). 

Phosphorus

At the Maumelle River streamflow-gaging site, 

total phosphorus and dissolved orthophosphorus concentrations were low and varied little through time (fig. 

10). Concentrations of total phosphorus ranged from 

less than 0.001 to 0.100 mg/L with a median value of 

0.011 mg/L. Concentrations of dissolved orthophosphorus ranged from less than 0.001 to 0.060 mg/L with 

a median of 0.001 mg/L.

Concentrations of total phosphorus varied 

between sites and with depth (table 1, fig. 11). Total 

phosphorus concentrations ranged from 0.001 to 0.035 

mg/L in both surface and bottom samples at all sites. 

The median concentration at site 10 near the surface 

was 0.011 mg/L and was lower than both surface and 

bottom water at site 3, and bottom water at sites 8 and 

10. Dissolved orthophosphorus concentrations did not 

vary much between sites and depth (fig. 11). More than 

one-half of all dissolved orthophosphorus concentrations were less than 0.001 mg/L. 
Ambient Conditions 11

0.00

0.05

0.10

0.15

0.20

0.25

NO2+NO3

NO2+NO3 LESS THAN OR EQUAL

 TO INDICATED VALUE

WATER YEAR

1991 1992 1993 1994 1995 1996 1997 1998

CONCENTRATION, IN MILLIGRAMS PER LITER AS NITROGEN

0.0

0.5

1.0

1.5

2.0

NH4

NH4 LESS THAN OR EQUAL TO

 INDICATED VALUE

TOTAL NH4+ORGANIC NITROGEN

TOTAL NH4+ORGANIC NITROGEN

 LESS THAN OR EQUAL TO

 INDICATED VALUE

B.

A.

Figure 8. Concentrations of nitrite plus nitrate (A), ammonia, and total ammonia plus organic nitrogen (B) at Maumelle River 

streamflow gaging site, water year 1991 through 1998.
12 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

Table 1. Statistical summary of selected water-quality parameters at Lake Maumelle sites 3, 8, and 10, water years 1991 

through 1998

[m, meter; mg/L, milligrams per liter; μg/L, microgram per liter; <, less than; --, no data]

Site 3, surface Site 3, bottom

Constituent of property Minimum Median Maximum Minimum Median Maximum

Secchi disk transparency (meters) 0.20 1.40 3.70 -- -- --

Nitrogen, nitrite plus nitrate dissolved (mg/L as N) <0.002 0.005 0.058 <0.002 0.006 0.039

Nitrogen, ammonia dissolved (mg/L as N) <0.002 0.008 0.071 <0.002 0.010 0.049

Nitrogen, ammonia plus organic total (mg/L as N) <0.2 <0.2 0.7 <0.2 <0.2 0.5

Phosphorus, total (mg/L as P) 0.004 0.011 0.030 0.001 0.014 0.035

Phosphorus, orthophosphate dissolved (mg/L as P) <0.001 <0.001 0.010 <0.001 <0.001 0.010

Carbon, total organic (mg/L) 1.1 3.7 7.2 1.1 3.7 7.2

Carbon, dissolved (mg/L) 1.5 3.0 6.7 1.5 3.0 6.7

Chlorophyll a (μg/L) 0.4 2.4 7.0 -- -- --

Site 8, surface Site 8, bottom

Constituent of property Minimum Median Maximum Minimum Median Maximum

Secchi disk transparency (meters) 1.20 1.40 3.70 -- -- --

Nitrogen, nitrite plus nitrate dissolved (mg/L as N) <0.002 0.008 0.053 <0.002 0.010 0.075

Nitrogen, ammonia dissolved (mg/L as N) <0.002 0.009 0.058 <0.002 0.025 0.170

Nitrogen, ammonia plus organic total (mg/L as N) <0.2 <0.2 0.5 <0.2 <0.2 0.7

Phosphorus, total (mg/L as P) 0.005 0.010 0.020 0.005 0.013 0.029

Phosphorus, orthophosphate dissolved (mg/L as P) <0.001 <0.001 0.010 <0.001 <0.001 0.010

Carbon, total organic (mg/L) 2.2 3.3 6.7 2.1 3.3 6.9

Carbon, dissolved (mg/L) 2.0 3.0 6.2 2.0 3.1 6.3

Chlorophyll a (μg/L) 0.6 2.3 6.9 -- -- --

Site 10, surface Site 10, bottom

Constituent of property Minimum Median Maximum Minimum Median Maximum

Secchi disk transparency (meters) 1.50 2.35 4.60 -- -- --

Nitrogen, nitrite plus nitrate dissolved (mg/L as N) <0.002 0.005 0.062 <0.002 0.008 0.25

Nitrogen, ammonia dissolved (mg/L as N) <0.002 0.008 0.065 <0.002 0.019 0.17

Nitrogen, ammonia plus organic total (mg/L as N) <0.2 <0.2 0.32 <0.2 <0.2 0.5

Phosphorus, total (mg/L as P) 0.003 0.009 0.020 0.005 0.011 0.033

Phosphorus, orthophosphate dissolved (mg/L as P) <0.001 <0.001 0.005 <0.001 <0.001 0.023

Carbon, total organic (mg/L) 1.7 3.4 6.6 1.7 3.4 7.5

Carbon, dissolved (mg/L) 1.7 3.0 6.5 1.7 2.9 7.3

Chlorophyll a (μg/L) 0.5 1.6 7.0 -- -- --
Ambient Conditions 13

Figure 9. Concentrations of nitrite plus nitrate, ammonia, and total ammonia plus organic nitrogen at the three reservoir sites, 

water year 1991 through 1998 (3, site number; S, surface samples; B, bottom samples).

AMMONIA NITROGEN

3-S 3-B 8-S 8-B 10-S 10-B

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

NITRITE PLUS NITRATE NITROGEN

CONCENTRATION, IN MILLIGRAMS 

3-S 3-B 8-S 8-B 10-S 10-B

PER LITER AS NITROGEN

0.00

0.05

0.10

0.15

0.20

0.25

0.30

TOTAL AMMONIA PLUS ORGANIC NITROGEN

CONCENTRATION, IN MILLIGRAMS 

3-S 3-B 8-S 8-B 10-S 10-B

PER LITER AS NITROGEN

0.0

0.2

0.4

0.6

0.8

 36 34 35 35 33 37 36 34 36 35 37 37

 36 33 34 36 36 37 EXPLANATION

50th PERCENTILE

75th PERCENTILE

25th PERCENTILE

90th PERCENTILE

10th PERCENTILE

DATA OUTSIDE 10th - 90th PERCENTILES

36 NUMBER OF SAMPLES
14 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

Figure 10. Concentrations of total phosphorus and dissolved orthophosphorus at Maumelle River streamflow gaging site, 

water year 1991 through 1998.

Figure 11. Concentrations of total phosphorus and dissolved orthophosphorus at three reservoir sites, water year 1991 

through 1998 (3, site number; S, surface samples; B, bottom samples).

WATER YEAR

1991 1992 1993 1994 1995 1996 1997 1998

CONCENTRATION, IN MILLIGRAMS 

PER LITER AS PHOSPHORUS

0.00

0.02

0.04

0.06

0.08

0.10

0.12

TOTAL PHOSPHORUS

DISSOLVED ORTHOPHOSPHORUS

DISSOLVED ORTHOPHOSPHORUS 

LESS THAN INDICATED VALUE

DISSOLVED ORTHOPHOSPHORUS

CONCENTRATION, IN MILLIGRAMS 

3-S 3-B 8-S 8-B 10-S 10-B

PER LITER AS PHOSPHORUS

0.000

0.005

0.010

0.015

0.020

0.025

TOTAL PHOSPHORUS

3-S 3-B 8-S 8-B 10-S 10-B

CONCENTRATION,

IN MILLIGRAMS PER LITER

0.00

0.01

0.02

0.03

0.04 35 34 34 35 36 37 36 34 35 36 37 37

EXPLANATION

50th PERCENTILE

75th PERCENTILE

25th PERCENTILE

90th PERCENTILE

10th PERCENTILE

DATA OUTSIDE 10th - 90th PERCENTILES

36 NUMBER OF SAMPLES
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 15

Considering estimates of national background 

nutrient concentrations (U.S. Geological Survey, 

1999), total phosphorus concentrations were considerably lower relative to undeveloped areas across the 

Nation minimally affected by agriculture, urbanization, 

and associated land uses. Total phosphorus concentrations in Lake Maumelle were one to two orders of magnitude lower than estimates of national background 

concentrations (0.1 mg/L). 

Chlorophyll a

Concentrations of chlorophyll a varied little 

among reservoir sites. Concentrations ranged from 0.4 

to 7.0 μg/L. The median concentrations at sites 3, 8, 

and 10 were 2.4, 2.3, and 1.6 μg/L, respectively. Concentrations of chlorophyll a at each site were not statistically different from one another. However, 

concentrations tended to increase over time at sites 3 

and 8 (fig. 12). Positive trends in chlorophyll a concentrations were identified using Kendall's rank correlation coefficient (tau) (Helsel and Hirsch, 1992) at site 3 

(tau = 0.218, p = 0.044) and site 8 (tau = 0.271, p = 

0.015). No trend was identified for chlorophyll a concentrations at site 10 (tau = 0.143, p = 0.199). 

The increasing trend in chlorophyll a concentration at sites 3 and 8 (the more upstream sites) suggests 

that eutrophication may be increasing within the reservoir, although no trends were identified for nutrient 

concentrations. However, changes in residence time 

(fig. 5) and/or air temperature also could influence 

changes in concentration. Chlorophyll a concentrations 

of 2 μg/L or less indicate oligotrophic conditions (Carlson, 1977; Olem and Flock, 1990). Concentrations 

between 2 and 10 μg/L indicate mesotrophic conditions. Likewise, total phosphorus concentrations less 

than 0.010 mg/L indicate oligotrophic conditions and 

between 0.010 and 0.030 mg/L indicate mesotrophic 

conditions. Both chlorophyll a and total phosphorus 

concentrations in Lake Maumelle generally occur 

within the range of oligotrophic to mesotrophic conditions. The positive trends in chlorophyll a concentrations at site 3 and 8 might suggest that the system is 

progressing from a more oligotrophic condition to a 

more mesotrophic condition. The lack of trend in chlorophyll a concentration at site 10 might suggest a lag in 

trophic response within the farthest downstream water 

in the reservoir. 

Loads of Sediment and Nutrients in the 

Maumelle River

Loads of suspended sediment and nutrients were 

estimated for the Maumelle River streamflow-gaging 

site. Loads were estimated for water years 1990 

through 1997.

Simultaneous measurements of streamflow and 

constituent concentrations collected by USGS were 

used to develop regression relations (Cohn and others, 

1989) for the Maumelle River site. Continuous records 

of streamflow were used to compute monthly and 

annual loads. Annual loads were divided by drainage 

area to provide annual yield. Annual loads and yields 

are summarized in table 2.

Constituent loads and yields were consistently 

lower in 1996 than other years (table 2). Precipitation 

(fig. 3) and streamflow (fig. 4) were considerably lower 

during 1996 than other years, accounting for the lower 

loads and yields. Loads and yield during years other 

than 1996 (1990 - 1995, 1997) were consistently low, 

representative of relatively undeveloped areas, minimally affected by agriculture, urbanization, and associated land uses (U.S. Geological Survey, 1999). 

Background concentrations and yields in undeveloped 

areas are controlled primarily by naturally occurring 

minerals and biological activity in soil and streambed 

sediment. Chemical properties of the atmosphere and 

rainwater, which can reflect human-related fuel combustion and other activities both within and external to 

the Maumelle River watershed, could lead to an 

increase in concentrations and yields.

SIMULATION OF HYDRODYNAMICS, 

CONSTITUENT TRANSPORT, AND 

WATER QUALITY

A two-dimensional, laterally averaged, hydrodynamic and water-quality model (CE-QUAL-W2) was 

constructed for Lake Maumelle, calibrated using data 

collected during January 1991 through December 

1991, and verified using data collected during January 

1992 through December 1992. The model simulates 

water level, currents, heat transport and temperature 

distribution, conservative material transport, and the 

transport and transformation of 11 chemical constituents. Complete details of model theory and structure, 

and extensive bibliography for theoretical development 

and application, are given by Cole and Buchak (1995). 
16 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

Figure 12. Concentrations of chlorophyll a at reservoir sites, 1991 through 1998. LOWESS is locally weighted scatter plot 

smooth line (Helsel and Hirsch, 1992).

SITE 3

1991 1992 1993 1994 1995 1996 1997 1998

CONCENTRATION, IN

MICROGRAMS PER LITER

0

1

2

3

4

5

6

7

8

SITE 8

1991 1992 1993 1994 1995 1996 1997 1998

0

1

2

3

4

5

6

7

8

MEASURED CONCENTRATION

LOWESS FITTED LINE

SITE 10

1991 1992 1993 1994 1995 1996 1997 1998

CONCENTRATION, IN

MICROGRAMS PER LITER

0

1

2

3

4

5

6

7

8

EXPLANATION
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 17

Table 2. A	
	
	the 	

		[kg, kilogram; yr, year; ha, hectare]

Constituent Water year

1990 1991 1992 1993 1994 1995 

Sediment load (kg/yr) 2.08×106 2.11×106 1.66×106 1.53×106 1.99×106 1.49×106 

Sediment yield (kg/ha/yr) 175 177 139 128 167 125 Nitrite plus nitrate nitrogen load (kg/yr) 2,030 1,860 1,370 1,090 1,340 928 Nitrite plus nitrate nitrogen yield (kg/ha/yr) 0.170 0.156 0.115 0.092 0.112 0.078 Ammonia nitrogen load (kg/yr) 2,760 2,310 1,450 992 986 586 Ammonia nitrogen yield (kg/ha/yr) 0.231 0.194 0.122 0.083 0.083 0.049 Total ammonia plus organic nitrogen load 

(kg/yr)

24,300 23,600 17,900 15,300 18,700 13,500 4

Total ammonia plus organic nitrogen yield 

(kg/ha/yr)

2.04 1.97 1.50 1.28 1.57 1.13 

Total phosphorus load (kg/yr) 1,340 1,470 1,290 1,110 1,600 1,210 Total phosphorus yield (kg/ha/yr) 0.113 0.123 0.108 0.093 0.134 0.101 Dissolved orthophosphorus load (kg/yr) 561 488 332 243 262 164 Dissolved orthophosphorus yield (kg/ha/yr) 0.047 0.041 0.028 0.020 0.022 0.014 
18 Analysis of Ambient Conditions and Simulation of Hydrodynamics, Constituent Transport, and Water-Quality Characteristics 

in Lake Maumelle, Arkansas, 1991-92

Model Implementation

Implementation of the CE-QUAL-W2 model for 

Lake Maumelle included (1) development of the computational grid, (2) specification of boundary and initial 

conditions, and (3) preliminary selection of model 

parameter values. 

Computational Grid

The model domain extends from west of the 

Highway 10 bridge to the Lake Maumelle dam and 

spillway, a distance of 17.4 km along the longitudinal 

axis of the reservoir. There are 11 computational segments along the mainstem of the reservoir (fig. 13). 

Segments 1 and 11 are inactive boundary segments. 

Segments 2 and 10 are the farthest upstream and downstream active segments. The mathematical formulation 

of the model suggests that segment lengths generally 

should exceed the maximum reservoir width in that 

segment. Segments ranged in length from 294 to 3,667 

m. Each segment was divided vertically into 1-m layers. Depth from the elevation of the spillway crest to 

the bottom of the reservoir ranged from about 5 m at the 

upstream end to 14 m at the dam. The orientation of the 

longitudinal axis of each segment relative to north was 

determined for each segment. This information is used 

in the computation of surface wind stress in each segment.

Original grid geometry was developed using preimpoundment elevation contours of the reservoir bottom. In April 1999, reservoir bathymetry was determined from surveys made by the USGS using a 

recording fathometer and global positioning system. 

The bathymetry data were used to revise the computational grid. Reservoir surface area and volume of the 

pre-impoundment engineering data compared to that of 

the final model grid were similar (fig. 14). The estimated full-pool volume in the model is about 276 million m3

, which is a little greater than the original 

engineering design volume of 270 million m3

.

Figure 13. Plan view of (A) cross section (B) and downstream view (C) of model grid. Segments 1 and 12 are inactive 

boundary cells.

2

3 4 5

6 7 8

9

10

11

A.

B.

C.

1

UPSTREAM 12

BOUNDARY

DOWNSTREAM

BOUNDARY

1 234 5 6 7 8 9 10 11 12
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 19

Figure 14. Surface area and volume curves for Lake Maumelle from pre-impoundment engineering data and model grid.

74 76 78 80 82 84 86 88 90 92

AREA, IN MILLION SQUARE METERS

0

10

20

30

40

50

ELEVATION, IN METERS ABOVE SEA LEVEL

74 76 78 80 82 84 86 88 90 92

VOLUME, IN MILLION CUBIC METERS

0

50

100

150

200

250

300

350

PRE-IMPOUNDMENT ENGINEERING DATA

MODEL GRID DATA

EXPLANATION
20 Analysis of Ambient Conditions and Simulation of Hydrodynamics, Constituent Transport, and Water-Quality Characteristics 

in Lake Maumelle, Arkansas, 1991-92

Boundary and Initial Conditions

Boundaries of the Lake Maumelle model include 

the reservoir bottom, the shoreline, the upstream 

boundary, the downstream boundary, and the water 

surface. Both hydraulic (which includes temperature) 

and chemical boundary conditions are required.

Hydraulic Boundary Conditions

The reservoir bottom is assumed to be an impermeable boundary with no discharge of ground water to 

the reservoir within the model domain or loss of water 

from the reservoir to the ground-water system. The 

magnitude of ground-water recharge or discharge from 

Lake Maumelle is unknown and not considered in the 

model. The reservoir bottom also is assumed to be 

immobile; that is, sediments are not resuspended by 

flow. The reservoir bottom causes resistance to the 

flow and thereby extracts energy from mean flow. The 

Chezy formulation is used in CE-QUAL-W2 to 

describe this phenomenon and varies with the magnitude of the flow. A single resistance coefficient, which 

is an empirical value and cannot be measured directly, 

is applied to all of the bottom computational gridcells 

(table 3).

Heat exchange between the reservoir bottom and 

overlying water is computed from (1) the reservoir bottom temperature, (2) the simulated water temperature, 

and (3) a coefficient of bottom heat exchange (table 3). 

The reservoir bottom temperature and coefficient of 

heat exchange are assumed to be constant in space and 

time. Heat exchange at the reservoir bottom is typically 

quite small (about two orders of magnitude less than 

surface heat exchange). 

The reservoir shoreline is defined as a boundary 

across which there is no flow. The exact position of the 

shoreline changes during a model simulation because 

of changing water level. 

The drainage area of the Maumelle River Basin 

almost doubles between the Maumelle River streamflow-gaging site and the upstream end of the reservoir 

(119.4 km2

 to 231.5 km2). The drainage area increases 

by 38 percent between the point where the Maumelle 

River enters the reservoir and the dam (231.5 km2

 to 

318.8 km2) not counting the reservoir pool area. 

For the purposes of this model, daily streamflow 

measured at the Maumelle River gaging site was multiplied by a drainage-area ratio of 1.94 to account for all 

flow entering the reservoir from the Maumelle River. 

Drainage entering the reservoir from around the perimeter, between the upper end and the dam, was considered to be distributed equally among segments. To 

account for flow entering the reservoir from around the 

perimeter of the reservoir, daily streamflow measured 

at the Maumelle River gaging site was multiplied by a 

drainage-area ratio of 1.5. This flow was accounted for 

in the model as distributed tributary inflow.

Table 3. Hydraulic and thermal parameters specified as Lake Maumelle model input

[m0.5/s, meter to the one-half power per second; (watts/m2)/°C, watts per square meter per degree Celsius; m2/s, square meter per second]

Parameter Purpose

Value in

Lake Maumelle

model

Constant or

temporally

 variable

Chezy resistance coefficient Represents turbulent exchange

of energy at reservoir bottom

70 m0.5/s Constant

Coefficient of sediment-water heat exchange Computes heat exchange

between reservoir bottom

and overlying water

2.0×10-7

(watts/m2)/°C

Constant

Wind-sheltering coefficient Reduces measured wind speed

to effective wind speed at water

surface

1.0 (dimensionless) Temporally

 variable

Longitudinal eddy viscosity Represents laterally averaged

longitudinal turbulent transport

of momentum

1 m2/s Constant

Longitudinal eddy diffusivity Represents laterally averaged

longitudinal turbulent transport

of mass and heat

1 m2/s Constant
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 21

Discharge over the spillway (88.39 m above sea 

level) was monitored by a stage recorder. Outflow over 

the spillway was positioned in the farthest downstream 

active segment. Daily drinking-water-supply withdrawal was monitored by LRMWW. The withdrawal 

structure was positioned at an elevation of 87 m, in the 

farthest downstream active segment.

Hydraulic boundary conditions at the water surface included (1) precipitation, (2) evaporation, (3) 

wind stress, and (4) surface heat exchange. All meteorological data, with the exception of precipitation, 

required for these computations were measured at Little Rock (Adams Field) airport, about 29 km southeast 

of the Lake Maumelle dam, and generally were 

recorded at hourly intervals.

Precipitation on the reservoir pool was based on 

data collected near the Lake Maumelle dam. Evaporation was computed from a time series of water surface 

temperature, dewpoint temperature, wind speed, width 

of the surface layer, and length of the segment. Wind 

stress was computed from a time series of wind speed 

and direction, the orientation of the computational segment, and a wind-sheltering coefficient (table 3). The 

temporally variable wind-sheltering coefficient 

reduces the effects of wind on the reservoir because of 

topographic sheltering of the water surface. 

Surface heat exchanges were computed from reservoir latitude and longitude, and from a time series of 

measured air temperature, dewpoint temperature, cloud 

cover, and wind speed and direction. Simulated surface-water temperature also is required for the computation of surface heat exchange. Surface heat exchange 

can be computed from the heat exchange equation as 

the sum of seven separate terms, or by using a more 

simple linearization of the heat exchange equation and 

an estimated equilibrium temperature (the temperature 

at which incoming radiation heat rates are balanced by 

outgoing water-surface temperature-dependent processes). The estimation of equilibrium temperature was 

the method used in this application. The loss of heat 

from the reservoir resulting from evaporation was 

included in the heat budget.

Chemical Boundary Conditions

In addition to temperature, concentrations of the 

following constituents were simulated for Lake 

Maumelle: labile dissolved organic matter, refractory 

dissolved organic matter, algae, particulate organic 

matter, nitrite plus nitrate nitrogen, ammonia nitrogen, 

phosphate, and dissolved oxygen. A time series of 

concentrations of selected constituents at all inflow 

boundaries is required for model operation. However, 

boundary conditions need not be supplied for all constituents that are included in model simulations.

Inflow chemical boundary conditions for the 

Maumelle River at the upstream end of the reservoir 

and distributed tributary inflow were based on monthly 

or semimonthly measurements at the Maumelle River 

streamflow gaging site (Green and Louthian, 1993). 

Daily loads of constituents at the Maumelle River 

streamflow-gaging site were divided by daily discharge 

to estimate daily concentrations. Atmospheric inputs of 

nitrate and ammonia nitrogen were supplied from data 

obtained at the National Atmospheric Deposition Program site at Caddo Valley located about 90 km southwest of Lake Maumelle. No phosphorus deposition 

data were available. Constituent inputs from the reservoir bottom boundary generally were computed within 

the model and were based on the value of selected 

parameters (table 4) and the concentration of the constituent in the overlying waters.

Initial Conditions

Initial water level, velocity, temperature, and 

constituent concentrations for each computational cell 

are required prior to beginning a simulation. Initial 

water level was set to the measured value at the Lake 

Maumelle spillway for the day simulations were to 

begin. Velocities were assumed to be zero. Initial water 

temperature and constituent concentrations were 

defined at appropriate spatial locations based on measurements obtained at the various sites at the time simulations were to begin.

Model Parameters

Parameters are used to describe physical and 

chemical processes that are not explicitly modeled and 

provide chemical kinetic rate information. Many 

parameters cannot be measured directly and are often 

adjusted during the model calibration process until 

simulated values agree with measured observations. 

Most of the relevant hydrodynamic and thermal 

processes are simulated in CE-QUAL-W2, so that there 

are relatively few adjustable hydraulic and thermal 

parameters (table 3). The resistance, bottom heat 

exchange, and wind-sheltering coefficients were previously described. The longitudinal eddy viscosity and 

the eddy diffusivity describe horizontal turbulent mixing of mass and heat. Simulation results are relatively 
22 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

Table 4. Rate coefficients used in water-chemistry simulations and specified as model input

[m, meters; (m3/m)/g, cubic meter per meter per gram; *, dimensionless parameter; m/d, meters per day; d, day; watts/m2, watts per square meter;

°C, degrees Celsius; (g/m2

)/d, grams per square meter per day; BOD, biochemical oxygen demand; g/m, grams per meter; mg/L, milligrams per liter]

Parameter Computational purpose

Value in

 Lake Maumelle

 model

Light extinction coefficient for water Amount of solar radiation absorbed in the

surface layer

0.66/m

Light extinction coefficient for organic solids Amount of solar radiation absorbed in the surface layer0.10/m

Light extinction coefficient for inorganic solids Amount of solar radiation absorbed in the surface layer0.01/m

Fraction of incident solar radiation absorbed at water 

surface

Amount of solar radiation absorbed in the surface layer0.49*

Suspended solids settling rate Settling rates and sediment accumulation on 

reservoir bottom 2.0 m/d

Algal growth rate Maximum gross algal production rate, uncorrected for respiration, mortality, excretion or 

settling; temperature dependent

2.0/d

Algal mortality rate Maximum algal mortality rate; temperature 

dependent

0.08/d

Algal excretion rate Maximum algal photorespiration rate, which 

becomes labile dissolved organic matter

0.005/d

Algal dark respiration rate Maximum algal dark respiration rate 0.005/d

Algal settling rate Representative settling velocity for algal 

assemblages

0.1 m/d

Saturation light intensity Saturation light intensity at maximum algal 

photosynthesis rate 100 watts/m2

Fraction of algal biomass lost by mortality to detritus Detritus and dissolved organic matter concentrations; remaining biomass becomes labile 

dissolved organic matter

0.8*

Lower temperature for algal growth Algal growth rate as a function of water temperature5.0 °C

Fraction of algal growth at lower temperature Algal growth rate as a function of water temperature0.01*

Lower temperature for maximum algal growth Algal growth rate as a function of water temperature10.0 °C

Fraction of maximum growth at lower temperature Algal growth rate as a function of water temperature0.99*

Upper temperature for maximum algal growth Algal growth rate as a function of water temperature 35 °C

Fraction of maximum growth at upper temperature Algal growth rate as a function of water temperature0.99*

Upper temperature for algal growth Algal growth rate as a function of water temperature 40 °C

Fraction of algal growth at upper temperature Algal growth rate as a function of water temperature0.01*

Labile dissolved organic matter decay rate Dissolved oxygen loss and production of inorganic carbon, ammonia, and phosphate from 

algal decay; temperature dependent

0.01/d

Labile to refractory decay rate Transfer of labile to refractory dissolved 

organic matter

0.001/d

Maximum refractory dissolved organic matter decay 

rate

Dissolved oxygen loss and production of inorganic carbon, ammonia, and phosphate from 

decay of refractory dissolved organic matter; temperature dependent

0.001/d
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 23

Detritus decay rate Dissolved oxygen loss and production of inorganic carbon, ammonia, and phosphate from 

decay of particulate organic matter, temperature dependent

0.001/d

Detritus settling velocity Loss of particulate organic matter to bottom 

sediment

1.0 m/d

Lower temperature for organic matter decay Organic matter decay as a function of temperature5.0 °C

Fraction of organic matter decay at lower temperature Organic matter decay as a function of temperature0.10*

Lower temperature for maximum organic matter 

decay

Organic matter decay as a function of temperature30.0 °C

Fraction of maximum organic matter decay at lower 

temperature

Organic matter decay as a function of temperature0.99*

Sediment decay rate Decay rate of organic matter in bed sediments 0.1/d

Sediment oxygen demand Zero-order sediment oxygen demand for each 

computational segment 0.1-0.2 (g/m2

)/d

5-day BOD decay rate Effects of BOD loading on dissolved oxygen 0.15/d

BOD temperature rate coefficient Adjusts 5-day BOD decay rate at 20°C to 

ambient temperature

1.047*

Ratio of 5-day BOD to ultimate BOD Effects of BOD loading on dissolved oxygen 1.2*

Release rate of phosphorus from bottom sediments Phosphorus balance; computed as a fraction of 

sediment oxygen demand

0.001*

Phosphorus partitioning coefficient Describes sorption of phosphorus on suspended solids2.0*

Algal half-saturation constant for phosphorus The phosphorus concentration at which the 

uptake rate is one-half the maximum uptake 

rate; upper concentration at which algal 

growth is proportional to phosphorus concentration

0.005 mg/L

Release rate of ammonia from bottom sediments Nitrogen balance; computed as a fraction of the 

sediment oxygen demand 

0.001*

Ammonia decay rate Rate at which ammonia is oxidized to nitrate 0.1/d

Algal half-saturation constant for ammonia Nitrogen concentration at which the algal 

uptake rate is one-half the maximum uptake 

rate; upper concentration at which algal 

growth is proportional to ammonia concentration

0.1 mg/L

Lower temperature for ammonia decay Ammonia nitrification as a function of temperature5.0 °C

Fraction of nitrification at lower temperature Ammonia nitrification as a function of temperature0.1*

Lower temperature for maximum ammonia decay Ammonia nitrification as a function of temperature20.0 °C

Fraction of maximum nitrification at lower temperatureAmmonia nitrification as a function of temperature0.99*

Nitrate decay rate Rate at which nitrate is denitrified; temperature 

dependent

100.0/d

Lower temperature for nitrate decay Denitrification as a function of temperature 5.0 °C

Fraction of denitrification at lower temperature Denitrification as a function of temperature 0.1*

Lower temperature for maximum nitrate decay Denitrification as a function of temperature 20.0 °C

Fraction of maximum denitrification at lower temperatureDenitrification as a function of temperature 0.99*

Table 4. Rate coefficients used in water-chemistry simulations and specified as model input--Continued

[m, meters; (m3/m)/g, cubic meter per meter per gram; *, dimensionless parameter; m/d, meters per day; d, day; watts/m2, watts per square meter;

°C, degrees Celsius; (g/m2

)/d, grams per square meter per day; BOD, biochemical oxygen demand; g/m, grams per meter; mg/L, milligrams per liter]

Parameter Computational purpose

Value in

 Lake Maumelle

 model
24 Analysis of Ambient Conditions and Simulation of Hydrodynamics, Constituent Transport, and Water-Quality Characteristics 

in Lake Maumelle, Arkansas, 1991-92

Iron release from bottom sediments Iron balance; computed as a fraction of sediment oxygen demand0.5*

Iron settling velocity Particulate iron settling velocity under oxic 

conditions

2.0 m/d

Oxygen stoichiometric equivalent for ammonia 

decay

Relates oxygen consumption to ammonia 

decay

4.57*

Oxygen stoichiometric equivalent for organic matter 

decay

Relates oxygen consumption to decay of 

organic matter

1.4*

Oxygen stoichiometric equivalent for dark respiration Relates oxygen consumption to algal dark respiration0.005*

Oxygen stoichiometric equivalent for algal growth Relates oxygen production to algal growth 1.4*

Stoichiometric equivalent between organic matter 

and phosphorus

Relates phosphorus release to decay of organic 

matter

0.008*

Stoichiometric equivalent between organic matter 

and nitrogen

Relates nitrogen release to decay of organic 

matter 

0.10*

Dissolved oxygen limit Dissolved oxygen concentration below which 

anaerobic processes such as nitrification and 

sediment nutrient releases occur

0.1 mg/L

Table 4. Rate coefficients used in water-chemistry simulations and specified as model input--Continued

[m, meters; (m3/m)/g, cubic meter per meter per gram; *, dimensionless parameter; m/d, meters per day; d, day; watts/m2, watts per square meter;

°C, degrees Celsius; (g/m2

)/d, grams per square meter per day; BOD, biochemical oxygen demand; g/m, grams per meter; mg/L, milligrams per liter]

Parameter Computational purpose

Value in

 Lake Maumelle

 model

insensitive to changes in all five of these parameters, 

with the exception of the wind-sheltering coefficient.

There are 57 chemical kinetic rate coefficients 

required for application of CE-QUAL-W2 (table 4). 

The values specified for most of the coefficients were 

based on suggestions given by Cole and Buchak 

(1995), and all of the coefficients are temporally and 

spatially invariant.

Other Model Options

The maximum computational time step was limited to 1 hour, so that the computational time step 

would not exceed the interval at which boundary data 

were supplied to the model; the model-selected computational interval generally was about 5 minutes. The 

"QUICKEST" numerical scheme (Leonard, 1979) was 

used for solving the transport equations. A CrankNicholson scheme (Roache, 1982) was used to solve 

the vertical advection equation.

Model calculations occurred at time steps 

smaller than the time increments at which boundary 

data were provided. Boundary data can be assumed to 

vary linearly between measured values or remain constant between measured values. For this application, all 

boundary data were assumed to vary linearly between 

measured values.

Model Calibration and Testing

Model calibration was achieved by adjusting 

model parameters, within reasonable ranges, for the 

period February 7 through December 31, 1991. Verification of model parameters was achieved for the period 

January 21 through December 31, 1992. 

Hydrodynamics

There was good agreement between measured 

and simulated water levels at Lake Maumelle spillway 

(fig. 15) between February 6 and December 31, 1991. 

The root mean square difference between measured and 

simulated water levels was 0.17 m. The difference 

between measured and simulated water levels ranged 

from -0.57 to 0.11 m, and the mean difference was -0.06 

m. The total range in measured and modeled water level 

during the simulation period was 1.38 and 1.49 m, 

respectively. Measured water level was about 0.5 m 

higher than the model elevation during the NovemberDecember period after large rainfall events occurred. It 

is possible that a considerable amount of rainfall and 

runoff occurred downstream of the Maumelle River 

streamflow gage and was not accounted for in the 

model input data. The 0.5 m error represents about 10 

percent of reservoir volume at spillway elevation. 

Water-budget adjustments in the model could have 

been made to better represent measured elevations, but 

these adjustments would be specific for the period of 

error and could not be applied to other periods.
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 25

Figure 15. Measured and simulated water-surface elevation at Lake Maumelle spillway, February 6 through December 31, 

1991.

1991

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

WATER-SURFACE ELEVATION, 

IN METERS ABOVE SEA LEVEL

87.0

87.5

88.0

88.5

89.0

89.5

90.0

MEASURED ELEVATION

SIMULATED ELEVATION

Agreement between measured and simulated 

water levels at Lake Maumelle spillway during 1992 

(fig. 16), using the same distributed tributary correction 

factor as in 1991 (1.5 times discharge at the Maumelle 

River gaging station) was not as good as in 1991. The 

root mean square difference between measured and 

simulated water levels was 0.31 m. The difference 

between measured and simulated water levels ranged 

from -0.57 to 0.08 m, and the mean difference was -

0.25 m. The total range in measured and simulated 

water level during the 1992 simulation period was 1.09 

and 1.27 m, respectively. A divergence between measured and simulated water level occurred during March 

1992, and after about April, the two levels paralleled 

each other until mid December, at which time simulated levels approached measured levels again. Considering that all inflow data are estimated using gage data 

that represents only 42 percent of the basin, (not including the reservoir pool), these results are within reason. 

Precipitation events that occur downstream of the gage 

would not be included in the inflow data, resulting in 

error in the simulation.

Simulated water temperatures agreed well with 

seasonal variations in near-surface and near-bottom 

ambient water temperature measured in Lake 

Maumelle (fig. 17). Simulated near-surface and nearbottom water temperatures were generally within 

2 °C of the corresponding measured values. Differences between simulated and measured values ranged 

from -2.4 to 2.8 °C and the average difference was 0.3 

°C. 

The vertical distribution of water temperature 

affects vertical mixing of dissolved and suspended 

materials and can be used to define the general location 

of the epilimnion and hypolimnion of the reservoir. 

The epilimnion and hypolimnion are typically separated by a thermocline, in which there is a relatively 

large change in temperature over a small change in 

depth. A strong thermocline existed in Lake Maumelle 

during June through August 1991 (fig. 18). Simulated 

vertical distributions agreed quite closely with measured distributions, even for complex temperature profiles.
26 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

Figure 16. Measured and simulated water-surface elevation at Lake Maumelle spillway, January 1 through December 31, 

1992.

1992

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

WATER-SURFACE ELEVATION, 

IN METERS ABOVE SEA LEVEL

87.0

87.5

88.0

88.5

89.0

89.5

90.0

MEASURED ELEVATION

SIMULATED ELEVATION
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 27

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

5

10

15

20

25

30

35

WATER TEMPERATURE, IN DEGREES CELSIUS

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

5

10

15

20

25

30

35

SIMULATED SURFACE

SIMULATED BOTTOM

MEASURED SURFACE

MEASURED BOTTOM

1991

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

5

10

15

20

25

30

35

SITE 3

SITE 8

SITE 10

Figure 17. Measured and simulated near-surface and near-bottom water temperatures for February 8 through December 31, 

1991, at Lake Maumelle sites 3, 8, and 10.
28 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

Site 3

Site 5

DEPTH, IN METERS

TEMPERATURE, IN DEGREES CELSIUS

EXPLANATION

February 8, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

March 5, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

April 3, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

April 22, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 6, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 26, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

July 9, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

August 7, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

August 27, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

September 10, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

October 2, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

November 6, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

November 6, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

MEASURED

SIMULATED

February 8, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

March 5, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

April 3, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

April 22, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 6, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 26, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

July 9, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

August 7, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

August 27, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

September 10, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

October 2, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

Figure 18. Measured and simulated vertical profiles of water temperature at Lake Maumelle sites 3, 5, 8, 9, and 10, February 

8 through November 6, 1991 (page 1 of 3).
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 29

Site 8

Site 9

DEPTH, IN METERS

TEMPERATURE, IN DEGREES CELSIUS EXPLANATION

February 8, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

March 5, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

April 3, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

April 22, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 6, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 26, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

July 9, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

August 7, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

August 27, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

September 10, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

October 2, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

November 6, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

February 8, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

March 5, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

April 3, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

April 22, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 6, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 26, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

July 9, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

August 7, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

August 27, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

September 10, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

October 2, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

November 6, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

MEASURED

SIMULATED

Figure 18. Measured and simulated vertical profiles of water temperature at Lake Maumelle sites 3, 5, 8, 9, and 10, February 

8 through November 6, 1991 (page 2 of 3).
30 Analysis of Ambient Conditions and Simulation of Hydrodynamics, Constituent Transport, and Water-Quality Characteristics 

in Lake Maumelle, Arkansas, 1991-92

Figure 18. Measured and simulated vertical profiles of water temperature at Lake Maumelle sites 3, 5, 8, 9, and 10, February 

8 through November 6, 1991 (page 3 of 3).

Site 10

DEPTH, IN METERS

TEMPERATURE, IN DEGREES CELSIUS

EXPLANATION

February 8, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

March 5, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

April 3, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

April 22, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 6, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 26, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

July 9, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

August 7, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

August 27, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

September 10, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

October 2, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

November 6, 1991

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

MEASURED

SIMULATED

All measured water temperatures (611 observations) for February through November 1991 were compared with corresponding simulated values for all five 

sites (fig. 18). Measured water temperatures ranged 

from 6.5 to 31.4 °C. Differences between measured and 

simulated temperatures ranged from -3.6 to 4.3 °C with 

a root mean square difference of 1.11. The mean and 

median difference between measured and simulated 

water temperatures was 0.1 °C, indicating little bias 

toward overprediction or underprediction of temperatures during the calibration period. Sixty-five percent 

of the simulated temperatures were within 1 °C of the 

measured temperature.

Although the calibrated model generally provided an excellent simulation of water temperature in 

Lake Maumelle, the accuracy of simulated temperatures varied with temperature, season, and depth (fig. 

19). Simulated water temperatures during the 1991 calibration period were lower than measured temperatures 

more often when measured temperatures were greater 

than 25 °C. Error in simulated water temperatures 

tended to be greater during the stratification season and 

at depths near the surface through the thermocline. 

Results from the water temperature simulations 

provide information on physical characteristics and 

processes in the reservoir—information that might not 

be obtained from monthly or semimonthly measurements. For example, the measurements of water temperature indicate only that the reservoir became 

thermally mixed between early September and early 

October. The simulations, however, indicate that the 

reservoir was mixed in late September, a few days 

before the early October measurements (fig. 17). Had 

the October measurements occurred later in the month, 

the turnover date would have been more difficult to 

estimate without the simulation. 
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 31

TEMPERATURE, IN DEGREES CELSIUS

0 5 10 15 20 25 30 35

-4

-2

0

2

4

6

1991

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

MEASURED MINUS SIMULATED WATER TEMPERATURE, IN DEGREES CELSIUS -4

-2

0

2

4

6

DEPTH BELOW WATER SURFACE, IN METERS

0 2 4 6 8 10 12 14

-4

-2

0

2

4

6

TEMPERATURE

DATE

DEPTH

Figure 19. Relation of difference between measured and simulated water temperatures at Lake Maumelle for all sites to 

measured water temperature, date, and depth below water surface, February 8 through November 6, 1991.
32 Analysis of Ambient Conditions and Simulation of Hydrodynamics, Constituent Transport, and Water-Quality Characteristics 

in Lake Maumelle, Arkansas, 1991-92

Simulated water temperatures in 1992, using the 

same parameter values as in the 1991 calibration, were 

very similar to measured temperatures (fig. 20). All 

measured water temperatures (574 observations) for 

February through October 1992 were compared with 

corresponding simulated values for all five sites. Measured water temperatures in 1992 ranged from 7.4 to 

29.9 °C. Differences between measured and simulated 

temperatures ranged from -2.5 to 6.1 °C with a root 

mean square difference of 1.03. The mean and median 

difference between measured and simulated water temperature was 0.2 and 0.0 °C, respectively, indicating little bias toward overprediction or underprediction of 

temperatures during the verification period. Seventysix percent of the simulated temperatures were within 1 

°C of the measured temperature.

Simulated water temperatures during the 1992 

verification period, like the 1991 calibration period, 

were generally underpredicted more often when measured temperatures were greater than 25 °C (fig. 21). 

Error in simulated water temperatures tended to be 

greater during the stratification season and at depths 

near the surface through the thermocline (fig. 21). In 

general, the verification (1992) provided an excellent 

simulation of water temperature in Lake Maumelle, 

with most simulated values within plus or minus 1 °C 

of the actual value. 

Water Chemistry

Complex biochemical reactions affecting the 11 

simulated water-chemistry constituents in the Lake 

Maumelle model are expressed in part within the simulated dissolved oxygen results. Algal biomass (chlorophyll a) is used as an indicator of the trophic state of 

a reservoir and additional information on simulated 

algal biomass is presented. Algal growth in Lake 

Maumelle appears to be limited by orthophosphate 

concentrations and light availability. Nitrate and 

ammonia concentrations appear to have only a limited 

effect on DO and algal concentrations in Lake 

Maumelle. Oxygen is used during the decay of labile 

and refractory dissolved organic matter, BOD, organic 

sediments, and detritus. Decay processes consume DO 

and release phosphate and ammonia to the system. Particulate matter affects light penetration and heat distribution affecting algal growth and DO production. 

Results of DO simulations provide an indicator of how 

well other processes are simulated.

Dissolved Oxygen

Simulated DO concentrations for Lake 

Maumelle exhibited the same general patterns and 

magnitudes as measured values (fig. 22). The onset of 

low DO levels and the recovery to higher DO levels 

were well simulated throughout the reservoir. 

Near-bottom DO concentrations at site 3 were 

overpredicted by as much as 3.7 mg/L on August 8, 

1991, and throughout the stratification season. DO profiles were measured at site 3 above the thalweg, which 

was about 3 to 4 m deep and only about 6 to 8 m wide. 

Near-bottom measurements were collected within the 

thalweg. The resolution of the model grid at site 3, as 

well as throughout the reservoir, did not represent the 

spatial geometry of the thalweg and did not accurately 

simulate the DO dynamics occurring within. Farther 

downstream (sites 8 and 10, fig. 22), near-bottom dissolved oxygen concentrations were better simulated. 

All measured DO concentrations (611 observations) for February through November 1991 were compared with corresponding simulated concentrations for 

all five sites (fig. 23). Measured DO concentrations in 

Lake Maumelle ranged from 0.6 to 11.8 mg/L. Differences between simulated and measured concentrations 

ranged from -4.2 to 5.3 mg/L with a root mean square 

difference of 1.04. The mean and median differences 

were -0.3 and -0.1 mg/L, respectively. Seventy-four 

percent of the simulated concentrations were within 1.0 

mg/L of the measured concentration.

Simulated vertical profiles of DO concentrations 

generally agreed with measurements (fig. 23). Agreement was better at sites 5, 8, 9, and 10, than at site 3. 

Simulated values had the greatest departures from measured values within the thermocline during the stratification season. In many cases, measured DO changed 

from near saturation to anoxic conditions within a vertical distance of 1.0 m or less (for example, June 26, 

July 9, August 7, and August 27, 1991 at sites 8, 9, and 

10). Such abrupt changes in measured DO concentrations could not be simulated within 1-m-thick layers 

represented in the model grid. Generally, within 2 

meters below the measured oxycline, simulated concentrations again agreed with measured concentrations.
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 33

Site 3

Site 5

DEPTH, IN METERS

TEMPERATURE, IN DEGREES CELSIUS

EXPLANATION

February 6, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

March 24, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

April 28, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 2, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 17, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

July 9, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

July 29, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

August 13, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

September 2, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

September 26, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

October 20, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

February 6, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

March 24, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

April 28, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 2, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 17, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

July 9, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

July 29, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

August 13, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

September 2, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

September 26, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

October 20, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

MEASURED

SIMULATED

Figure 20. Measured and simulated vertical profiles of water temperature at Lake Maumelle sites 3, 5, 8, 9, and 10, 

February 6 through October 20, 1992 (page 1 of 3).
34 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

Site 8

Site 9

DEPTH, IN METERS

TEMPERATURE, IN DEGREES CELSIUS

EXPLANATION

February 6, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

March 28, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

April 28, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 2, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 17, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

July 9, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

July 29, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

August 13, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

September 2, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

September 26, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

October 26, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

MEASURED

SIMULATED

February 6, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

March 28, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

April 28, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 2, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 17, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

July 9, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

July 29, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

August 13, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

September 2, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

September 26, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

October 26, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

Figure 20. Measured and simulated vertical profiles of water temperature at Lake Maumelle sites 3, 5, 8, 9, and 10,

February 6 through October 20, 1992 (page 2 of 3).
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 35

Figure 20. Measured and simulated vertical profiles of water temperature at Lake Maumelle sites 3, 5, 8, 9, and 10,

February 6 through October 20, 1992 (page 3 of 3).

Site 10

DEPTH, IN METERS

TEMPERATURE, IN DEGREES CELSIUS

EXPLANATION

February 6, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

March 24, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

April 28, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 2, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

June 17, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

July 9, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

July 29, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

August 13, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

September 2, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

September 26, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

October 20, 1992

5 10 15 20 25 30 35

14

12

10

8

6

4

2

0

MEASURED

SIMULATED
36 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

Figure 21. Relation of difference between measured and simulated water temperatures at Lake Maumelle for all sites to 

measured water temperature, date, and depth below water surface, February 8 through October 20, 1992.

TEMPERATURE, IN DEGREES CELSIUS

0 5 10 15 20 25 30 35

-4

-2

0

2

4

6

8

1992

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

MEASURED MINUS SIMULATED WATER TEMPERATURE, IN DEGREES CELSIUS -4

-2

0

2

4

6

8

DEPTH BELOW WATER SURFACE, IN METERS

0 2 4 6 8 10 12 14

-4

-2

0

2

4

6

8

TEMPERATURE

DATE

DEPTH
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 37

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

0

2

4

6

8

10

12

14

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

0

2

4

6

8

10

12

14

SIMULATED SURFACE

SIMULATED BOTTOM

MEASURED SURFACE

MEASURED BOTTOM

1991

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

0

2

4

6

8

10

12

14

SITE 3

SITE 8

SITE 10

Figure 22. Measured and simulated dissolved oxygen concentrations, February through December 1991, at Lake Maumelle 

sites 3, 8, and 10.
38 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

Site 3

Site 5

DEPTH, IN METERS

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

EXPLANATION

February 8, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

March 5, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

April 3, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

April 22, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

June 6, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

June 26, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

July 9, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

August 7, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

August 27, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

September 10, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

October 2, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

November 6, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

February 8, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

March 5, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

April 3, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

April 22, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

June 6, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

June 26, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

July 9, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

August 7, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

August 27, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

September 10, 1991

0 4 8 12

14

12

10

8

6

4

2

0

October 2, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

November 6, 1991

0 5 10 15

14

12

10

8

6

4

2

0

MEASURED

SIMULATED

Figure 23. Measured and simulated vertical profiles of dissolved oxygen concentrations at Lake Maumelle sites 3, 5, 8, 9, and 

10, February 8 through November 6, 1991 (page 1 of 3).
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 39

Site 8

Site 9

DEPTH, IN METERS

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

EXPLANATION

February 8, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

March 5, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

April 3, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

April 22, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

June 6, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

June 26, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

July 9, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

August 7, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

August 27, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

September 10, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

October 2, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

November 6, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

February 8, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

March 5, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

April 3, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

April 22, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

June 6, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

June 26, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

July 9, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

August 7, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

August 27, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

September 10, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

October 2, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

November 6, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

MEASURED

SIMULATED

Figure 23. Measured and simulated vertical profiles of dissolved oxygen concentrations at Lake Maumelle sites 3, 5, 8, 9, and 

10, February 8 through November 6, 1991 (page 2 of 3).
40 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

Figure 23. Measured and simulated vertical profiles of dissolved oxygen concentrations at Lake Maumelle sites 3, 5, 8, 9, and 

10, February 8 through November 6, 1991 (page 3 of 3).

Site 10

DEPTH, IN METERS

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

EXPLANATION

February 8, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

March 5, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

April 3, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

April 22, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

June 6, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

June 26, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

July 9, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

August 7, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

August 27, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

September 10, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

October 2, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

November 6, 1991

0 4 8 12 16

14

12

10

8

6

4

2

0

MEASURED

SIMULATED
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 41

Differences between measured and simulated 

DO concentrations at all sites were compared to the 

corresponding measured DO concentrations, to the 

date, and to the depth below water surface (fig. 24). 

There appeared to be a greater tendency to overestimate DO concentrations, during periods of thermal 

stratification, and at depths within the thermocline than 

at other depths. At the upper depths within the epilimnion and lower depths within the hypolimnion and during periods of isothermal conditions, simulated DO 

concentrations generally were within plus or minus 1 

mg/L of measured values.

Simulated dissolved oxygen concentrations during the 1992 verification period provided results similar to the 1991 calibration period (fig. 25). Measured 

dissolved oxygen concentrations (574 observations) 

for February through October 1992 ranged from 0.1 to 

11.6 mg/L. Simulated dissolved oxygen concentrations 

ranged from 0.0 to 11.8 mg/L. Differences between 

simulated and measured concentrations ranged from -

4.2 to 5.6 mg/L with a root mean square difference of 

1.06 mg/L. The mean and median differences were -0.2 

mg/L. Seventy-nine percent of the simulated concentrations were within 1.0 mg/L of the measured concentration. 

The 1992 verification period provided an excellent simulation of dissolved oxygen concentrations in 

Lake Maumelle, with most simulated values within 1 

mg/L of the actual value. Simulated dissolved oxygen 

concentrations during the 1992 verification period, like 

the 1991 calibration period, tended to overpredict DO 

concentrations during periods of thermal stratification 

at depths within the thermocline (fig. 26). Error in simulated DO concentrations tended to be greater during 

the stratification season and at depths near the surface 

through the thermocline (fig. 26). 

Phosphorus, Ammonia, and Algae

Considering the oligo-mesotrophic condition of 

Lake Maumelle, simulated algae, phosphorus, and 

ammonia concentrations compared well with measured 

values. As discussed earlier, phosphorus and ammonia 

concentrations in Lake Maumelle were low— one to 

two orders of magnitude lower than estimates of 

national background concentrations. Chlorophyll a 

concentrations in Lake Maumelle reflect the nutrient 

stressed condition. The CE-QUAL-W2 model uses 

algal biomass (mg/L) as carbon as the algal response 

variable. To convert chlorophyll a into algal biomass, 

measured chlorophyll a concentrations (μg/L) were 

multiplied by a factor of 0.067 (Cole and Buchak, 

1995) to provide an estimate of algal biomass (mg/L). 

Simulated phosphorus concentrations in the 

near-surface water (top three meters) in segments 3, 8, 

and 10 tracked measured concentrations rather well 

(fig. 27). Simulated concentrations at segment 3, the 

upper end of the reservoir, were more variable because 

of variable inflow concentrations. This variability was 

reduced farther downstream in the reservoir (segments 

8 and 10). Phosphorus concentrations tended to be lowest at the downstream sites during the summer stratification period and increased slightly following 

turnover, during the winter nonstratification period.

Simulated ammonia concentrations in the nearsurface water (top three meters) at segments 3, 8, and 

10 also tracked measured concentrations rather well 

(fig. 28). As with phosphorus concentrations, simulated ammonia concentrations were slightly more variable at segment 3 than farther downstream. Ammonia 

concentrations, like phosphorus, tended to be lowest 

during the summer stratification period and increased 

following turnover, during the winter nonstratification 

period.

Simulated algal biomass concentrations in the 

near-surface water (top three meters) at segments 3, 8, 

and 10 did not relate as well to chlorophyll a converted 

biomass concentrations (fig. 29), as did simulated to 

measured phosphorus and ammonia concentrations. 

Many factors are involved in the production of algae. 

However, it appears that if a multiplication factor other 

than 0.067 was used to convert chlorophyll a to algal 

biomass, differences between simulated and measured 

concentrations could be less. A different multiplication 

factor might require changes in algal growth parameters that also may affect nutrient dynamics. Again, concentrations at the upper end of the reservoir, at segment 

3, were more variable than farther downstream. Algal 

biomass also was lower during the summer stratification period when nutrient concentrations were lowest. 

Algal biomass peaked following turnover when nutrient concentrations were greatest.

Sensitivity Analysis

Sensitivity analysis is the determination of the 

effects of small changes in calibrated model parameters 

on model results. A complete sensitivity analysis for all 

model parameters in the Lake Maumelle model was not 

conducted. The Lake Maumelle model includes more 

than 50 parameters (tables 3 and 4), and a complete 

sensitivity analysis would be a very lengthy process. 
42 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

MEASURED DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

0 2 4 6 8 10 12 14

-6

-4

-2

0

2

4

6

1991

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

MEASURED MINUS SIMULATED DISSOLVED OXYGEN CONCENTRATION, IN MILLIGRAMS PER LITER -6

-4

-2

0

2

4

6

DEPTH BELOW WATER SURFACE, IN METERS

0 2 4 6 8 10 12 14

-6

-4

-2

0

2

4

6

DISSOLVED OXYGEN

DATE

DEPTH

Figure 24. Relation of difference between measured and simulated dissolved oxygen concentrations at Lake Maumelle for all 

sites to measured dissolved oxygen concentration, date, and depth below water surface, February 8 through November 6, 

1991.
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 43

Site 3

Site 5

DEPTH, IN METERS

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

EXPLANATION

February 6, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

March 24, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

April 28, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

June 2, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

June 17, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

July 9, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

July 29, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

August 13, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

September 2, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

September 26, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

October 20, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

February 6, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

March 24, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

April 28, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

June 2, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

June 17, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

July 9, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

July 29, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

August 13, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

September 2, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

September 26, 1992

0 4 8 12

14

12

10

8

6

4

2

0

October 20, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

MEASURED

SIMULATED

Figure 25. Measured and simulated vertical profiles of dissolved oxygen concentrations at Lake Maumelle sites 3, 5, 8, 9, and 

10, February 6 through October 20, 1992 (page 1 of 3).
44 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

Site 8

Site 9

DEPTH, IN METERS

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

EXPLANATION

February 6, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

March 28, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

April 28, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

June 2, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

June 17, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

July 9, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

July 29, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

August 13, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

September 2, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

September 26, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

October 26, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

February 6, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

March 24, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

April 28, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

June 2, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

June 17, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

July 9, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

July 29, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

August 13, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

September 2, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

September 26, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

October 20, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

MEASURED

SIMULATED

Figure 25. Measured and simulated vertical profiles of dissolved oxygen concentrations at Lake Maumelle sites 3, 5, 8, 9, and 

10, February 6 through October 20, 1992 (page 2 of 3).
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 45

Figure 25. Measured and simulated vertical profiles of dissolved oxygen concentrations at Lake Maumelle sites 3, 5, 8, 9, and 

10, February 6 through October 20, 1992 (page 3 of 3).

Site 10

DEPTH, IN METERS

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

EXPLANATION

February 6, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

March 24, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

April 28, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

June 2, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

June 17, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

July 9, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

July 29, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

August 13, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

September 2, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

September 26, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

October 20, 1992

0 4 8 12 16

14

12

10

8

6

4

2

0

MEASURED

SIMULATED
46 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

MEASURED DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

0 2 4 6 8 10 12 14

-6

-4

-2

0

2

4

6

8

1992

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

MEASURED MINUS SIMULATED DISSOLVED OXYGEN CONCENTRATION, IN MILLIGRAMS PER LITER -6

-4

-2

0

2

4

6

8

DEPTH BELOW WATER SURFACE, IN METERS

0 2 4 6 8 10 12 14

-6

-4

-2

0

2

4

6

8

DISSOLVED OXYGEN

DATE

DEPTH

Figure 26. Relation of difference between measured and simulated dissolved oxygen concentrations at Lake 

Maumelle for all sites to measured dissolved oxygen concentrations, date, and depth below water surface, 

February 6 through October 20, 1992.
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 47

SITE 3

0.000

0.002

0.004

0.006

0.008

0.010

SITE 8

DISSOLVED ORTHOPHOSPHORUS, 

IN MILLIGRAMS PER LITER AS PHOSPHORUS 0.000

0.002

0.004

0.006

0.008

0.010

SITE 10

1/1/91 5/1/91 9/1/91 1/1/92 

0.000

0.002

0.004

0.006

0.008

0.010

SIMULATED CONCENTRATION

MEASURED CONCENTRATION

EXPLANATION

Figure 27. Measured and simulated phosphorus concentrations (PO4 as P) at Lake Maumelle sites 3, 8, and 10, February 

through December 1991. Simulated values are the mean of top 3 meters in the model grid.
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 48

SITE 3

0.00

0.02

0.04

0.06

0.08

0.10

SITE 8

DISSOLVED AMMONIA, IN MILLIGRAMS PER LITER AS NITROGEN 0.00

0.02

0.04

0.06

0.08

0.10

SIMULATED CONCENTRATION

MEASURED CONCENTRATION

SITE 10

1/1/91 5/1/91 9/1/91 1/1/92 

0.00

0.02

0.04

0.06

0.08

0.10

EXPLANATION

Figure 28. Measured and simulated ammonia concentrations (NH4 as N) at Lake Maumelle sites 3, 8, and 10, February 

through December 1991. Simulated values are the mean of top 3 meters in the model grid.
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 49

SITE 3

0.0

0.5

1.0

1.5

2.0

SIMULATED CONCENTRATION

MEASURED CHLOROPHYLL a CONCENTRATION x 0.067

SITE 8

ALGAL BIOMASS, IN MILLIGRAMS PER LITER 0.0

0.5

1.0

1.5

2.0

SITE 10

1/1/91 5/1/91 9/1/91 1/1/92 

0.0

0.5

1.0

1.5

2.0

EXPLANATION

Figure 29. Measured and simulated algal biomass at Lake Maumelle sites 3, 8, and 10, February through December 1991. 

Simulated values are the mean of top 3 meters in the model grid.
50 Analysis of Ambient Conditions and Simulation of Hydrodynamics, Constituent Transport, and Water-Quality Characteristics 

in Lake Maumelle, Arkansas, 1991-92

However, many hydrodynamic and water-quality simulations were conducted as a component of model calibration. Results from these simulations form the basis 

for the sensitivity analysis.

Of the hydraulic parameters (table 3), simulated 

temperatures were most sensitive to changes in the 

wind-sheltering coefficient (WSC), and the coefficient 

of bottom heat exchange (CBHE) (fig. 30). Wind speed 

was not adjusted (WSC = 1.0) in the calibrated Lake 

Maumelle model. Vertical mixing was overpredicted 

when WSC was increased (>1.0) and underpredicted 

when WSC was decreased (<1.0). Wind speed appears 

to be a major factor affecting the development, duration, and vertical location of the thermocline in Lake 

Maumelle. The CBHE was the primary determinant of 

thermal condition in the lower depths of the reservoir 

(fig. 30). Water in lower depths did not heat as rapidly, 

from winter to summer, in model simulations when 

CBHE values were less than the calibrated value 

(2.0×10-7 watts/m2

/°C). In addition, temperatures in 

lower depths did not reach measured temperatures 

when CBHE values were lower than the calibrated values. When CBHE values were greater than the calibrated value, temperatures in lower depths tended to 

mimic measured values, but temperatures through and 

above the thermocline were reduced. 

Wind-Sheltering

Coefficient (WSC)

15 20 25 30

DEPTH, IN METERS 

BELOW WATER SURFACE

14

12

10

8

6

4

2

0

WSC = 1.0 

 (calibrated model)

WSC = 0.8

WSC = 1.2

Coefficient of Bottom

Heat Exchange (CBHE)

WATER TEMPERATURE, IN DEGREES CELSIUS

15 20 25 30

14

12

10

8

6

4

2

0

CBHE = 2.0x10-7

 (watts/m2/

o

C)

 (calibrated model)

CBHE = 2.0x10-8

CBHE = 2.0x10-6

Light Extinction

Coefficient (α)

15 20 25 30

14

12

10

8

6

4

2

0

α = 0.66 

 (calibrated model)

α = 0.33

α = 0.99

EXPLANATION

igure 30. Vertical temperature distributions at site 10 on August 27, 1991, showing calibrated model profiles and profiles

s a result of differing wind sheltering, bottom heat exchange, and light extinction coefficients.
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 51

The light extinction coefficient (α) also affected 

position of the thermocline and temperatures above and 

below the thermocline (fig. 30). When α was less than 

the calibrated value (α = 0.66), the thermocline was 

lowered, extending the depth of the epilimnion. When 

α was greater than the calibrated value, temperatures in 

the epilimnion were reduced, reducing the depth of the 

epilimnion. 

Simulated DO appeared to be most sensitive to 

changes in sediment oxygen demand and thermal patterns (fig. 31). Sediment oxygen demand (SOD) in the 

Lake Maumelle model was set at 0.7 g/m2

/d for all segments. SOD above 0.7 g/m2

/d tended to underpredict 

DO concentrations in the lower depths during early 

stages of stratification. SOD lower than 0.7 g/m2

/d 

overpredicted DO concentrations in the hypolimnion 

during the peak of the stratification season. Changes in 

the wind-sheltering coefficient, which affected thermal 

patterns, also affected DO concentration. Lower and 

higher WSC values than the 1.0 calibration value 

tended to affect DO concentrations in the thermocline 

and immediately above and below the thermocline. DO 

concentrations were underpredicted when WSC values 

were reduced (increased wind sheltering) in the thermocline. DO concentrations were overpredicted in the 

thermocline and upper levels of the hypolimnion when 

WSC values were increased.

Sediment Oxygen

Demand (SOD),

April 22, 1991

0 2 4 6 8 10

DEPTH, IN METERS 

BELOW WATER SURFACE

14

12

10

8

6

4

2

0

SOD = 0.7 g/m2/d

 (calibrated model)

SOD = 0.1 g/m2/d

SOD = 1.4 g/m2/d

Sediment Oxygen

Demand (SOD),

August 27, 1991

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

0 2 4 6 8 10

14

12

10

8

6

4

2

0

SOD = 0.7 g/m2/d

 (calibrated model)

SOD = 0.1 g/m2/d

SOD = 1.4 g/m2/d

Wind-Sheltering

Coefficient (WSC)

August 27, 1991

0 2 4 6 8 10

14

12

10

8

6

4

2

0

WSC = 1.0 

 (calibrated model)

WSC = 0.8

WSC = 1.2

EXPLANATION

Figure 31. Vertical dissolved oxygen distributions at site 10 on April 22 and August 27, 1991, showing calibrated model 

profiles and profiles as a result of differing sediment oxygen demand and wind-sheltering coefficients.
52 Analysis of Ambient Conditions and Simulation of Hydrodynamics, Constituent Transport, and Water-Quality Characteristics 

in Lake Maumelle, Arkansas, 1991-92

Model parameters affecting chemical and algal 

kinetics are summarized in table 4. Cole and Buchak 

(1995) suggested reasonable values, and in some cases 

a range of values, for each parameter. Initial Lake 

Maumelle model simulations were made using the values suggested by Cole and Buchak (1995). 

Algal concentrations were most sensitive to the 

algal growth rate and were sensitive to mortality and 

settling rates. Algal growth during the cooler seasons 

also was sensitive to light saturation, light intensity, 

and algal temperature-rate multipliers. Algal growth 

also was affected by algal half saturation constants for 

phosphorus and ammonia. The algal half saturation 

constants affected nutrient uptake, and therefore, nutrient concentrations. Also, phosphorus and nitrogen concentrations were sensitive to release rates from bottom 

sediments. According to model simulations, algal 

growth in Lake Maumelle was limited by phosphorus 

concentrations and light at lower depths. 

Model Applications

The calibrated Lake Maumelle model was used 

to run various water-resource management scenarios. 

Simulations were developed to evaluate the movement 

of water, conservative material (a hypothetical spill), 

nitrogen, and phosphorus; algal response from a nursery pond release on a lateral tributary of Lake 

Maumelle; and simulations also were developed to 

assess the effects of increasing nitrogen and phosphorus load on algal production in Lake Maumelle.

Simulation of Conservative Material 

Transport

To assess material transport from a hypothetical 

spill at the western end of Lake Maumelle, where Highway 10 crosses the reservoir, the following simulation 

was applied. Initial concentration of conservative 

material (no decay or production) in the reservoir was 

set at 0.1 mg/L. On April 26, 1991, a major storm event 

occurred (fig. 32). At 6:30 a.m. on this day, 19 m3 of 

liquid (equivalent to a 5,000-gallon tanker truck) containing 1,000 kg of conservative material was introduced into the upper boundary of the reservoir model 

over a 14.4-minute (0.01 day) period. Figure 33 shows 

the simulated transport of this material in terms of 

Figure 32. Daily discharges into Lake Maumelle from April 20 through May 10, 1991, showing location on the hydrograph 

where spill was simulated.

1991

MAY 20 MAY 25 MAY 30 APRIL 5 APRIL 10

DAILY DISCHARGE, 

IN CUBIC METERS PER SECOND

0

20

40

60

80

100

120

POINT OF 

SIMULATED SPILL
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 53

Figure 33. Simulated concentrations of a conservative material introduced at the upstream boundary at 6:00 a.m. on 

April 26, 1991.

0 5,000 10,000 15,000

DOWNSTREAM DISTANCE, IN METERS

15

10

5

0

DEPTH BELOW SURFACE, IN METERS

0.5 mg/L

1.5 mg/L

1.0 mg/L

LAKE BOTTOM

DAM

6 HOURS

0 5,000 10,000 15,000

DOWNSTREAM DIS TANCE, IN METERS

15

10

5

0

DEPTH BELOW SURFACE, IN METERS

30 HOURS

0 5,000 10,000 15,000

DOWNSTREAM DISTANCE, IN METERS

15

10

5

0

DEPTH BELOW SURFACE, IN METERS

54 HOURS

0 5,000 10,000 15,000

DOWNSTREAM DIS TANCE, IN METERS

15

10

5

0

DEPTH BELOW SURFACE, IN METERS

78 HOURS

0 5,000 10,000 15,000

DOWNSTREAM DISTANCE, IN METERS

15

10

5

0

DEPTH BELOW SURFACE, IN METERS

102 HOURS

EXPLANATION

0.15 LINES OF EQUAL TRACER CONCENTRATION

-- Interval, in milligrams per liter, is variable
54 Analysis of Ambient Conditions and Simulation of Hydrodynamics, Constituent Transport, and Water-Quality Characteristics 

in Lake Maumelle, Arkansas, 1991-92

downstream distance and depth through time. Six hours 

after the simulated spill, a small plume of concentrated 

material had been displaced downstream from the 

upstream boundary. By noon on April 27 (30 hours), 

the front of conservative material had reached 5,000 to 

6,000 m downstream. There was very little variability 

in concentration with depth at this time but some difference in concentration with distance was indicated. By 

noon on April 28 (54 hours), the front of conservative 

material had reached 8,000 m downstream. Concentrations varied with depth below about 7 m; concentrations were higher in water less than 7 m deep. By noon 

on April 29 (78 hours), the front of conservative material had reached about 10,000 m at the surface. Downstream movement of material appeared to be limited to 

water less than 7 m deep. By noon on April 30, (102 

hours after loading), conservative material at concentrations above pre-spill concentrations (0.10 mg/L) had 

reached the downstream boundary. 

Simulation of Nursery Pond Release

 The Arkansas Game and Fish Commission manages a fish nursery pond on a lateral tributary that 

enters Lake Maumelle (fig. 2). The entire contents of 

this pond are discharged into Lake Maumelle every 

summer or fall. Nursery pond releases were not simulated in the calibration of the Lake Maumelle model. 

Green (1998) assessed the water-quality impacts of the 

nursery pond release from 1991 through 1996. A modeling application was prepared to simulate a typical 

nursery pond release to further assess impacts in Lake 

Maumelle.

The nursery pond, in general, took about 3 days 

to drain its entire contents into Lake Maumelle (Green, 

1998) depending on volume (stage) of the pond at the 

time of release and size of the gate opening (fig. 34). 

The location of the release structure in the pond was at 

the bottom, about 14 meters below the normal surface 

elevation. The cold, anoxic, bottom water is the first to 

be released from the nursery pond. This cold water 

enters the receiving embayment and plunges under the 

less dense embayment water (fig. 35). After the cold 

water is removed from the pond, warmer water is 

released and mixes with the embayment water before 

entering the main part of Lake Maumelle. 

Figure 34. Discharge from the nursery pond into Lake Maumelle.

SIMULATION DAY

July 14 July 15 July 16 July 17

DISCHARGE, IN CUBIC 

METERS PER SECOND

0

2

4

6

8

10
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 55

Figure 35. Simulated temperatures in the receiving embayment of the nursery pond release.

0 200 400 600

DISTANCE, IN METERS

8

6

4

2

0

DEPTH BELOW SURFACE, IN METERS

5 HOURS

0 200 400 600

DISTANCE, IN METERS

8

6

4

2

0

DEPTH BELOW SURFACE, IN METERS

29 HOURS

0 200 400 600

DISTANCE, IN METERS

8

6

4

2

0

DEPTH BELOW S URFACE, IN METERS

53 HOURS

25.0

EXPLANATION

LINE OF EQUAL TEMPERATURE

--Interval, in degrees Celsius, is variable

To understand transport of the release water 

from the nursery pond, a simulation was developed by 

adding a branch to the calibrated model to represent the 

receiving embayment. A conservative tracer (100 mg/

L) was added to the nursery pond water and released 

into the receiving embayment branch. This tracer material was tracked through the embayment and into the 

main part of Lake Maumelle (fig. 36). The tracer 

entered the main part of Lake Maumelle at the level of 

the bottom of the embayment (7 m) (fig. 37). After the 

first day, the tracer plume in Lake Maumelle moved 

both upstream and downstream from the point of entry, 

but stayed in the middle depth layers. The tracer continued to dissipate and 2 weeks later concentrations of 

tracer were present in about one-half the water contained in Lake Maumelle. 

Simulated nutrient concentrations tended to 

mimic the tracer results, although nutrient persistence 

was reduced because of uptake and transformation. 

Algal growth did not appear to differ as a result of the 

simulated nursery pond release 2 weeks following the 

release. This is presumably because of the plunging of 

the initial plume that contained the greatest concentrations of nutrients. This nutrient load was not delivered 

into the upper layers of the lake where algal production 

is greatest. 

Simulation of Nutrient Enrichment

To obtain a general understanding of the relation 

between algal growth and nutrient enrichment, an 

application was developed wherein nitrogen as ammonia and phosphorus as phosphate loads in the main tributary were increased by a factor of 10, separately and 

together. Algal production was only sensitive to 

increases in phosphorus load (fig. 38). Increase in 

ammonia load did not increase algal production. 

Increasing both phosphorus and ammonia by a factor of 

10 provided almost the same algal response as 10 times 

phosphorus alone. Results indicate that increases in 

phosphorus load will allow increasing algal production.
56 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

Figure 36. Distance and depth plots of simulated tracer concentrations in the receiving embayment after release of the nursery 

pond.

0 200 400 600

DISTANCE, IN METERS

8

6

4

2

0

DEPTH BELOW SURFACE, IN METERS

5 HOURS

0 200 400 600

DISTANCE, IN METERS

8

6

4

2

0

DEPTH BELOW SURFACE, IN METERS

29 HOURS

0 200 400 600

DISTANCE, IN METERS

8

6

4

2

0

DEPTH BELOW SURFACE, IN METERS

53 HOURS

0 200 400 600

DISTANCE, IN METERS

8

6

4

2

0

DEPTH BELOW SURFACE, IN METERS

77 HOURS

0 200 400 600

DISTANCE, IN METERS

8

6

4

2

0

DEPTH BELOW S URFACE, IN METERS

9 DAYS

0 200 400 600

DISTANCE, IN METERS

8

6

4

2

0

DEPTH BELOW S URFACE, IN METERS

2 WEEKS

10.0

EXPLANATION

LINE OF EQUAL TRACER CONCENTRATION

-- Interval in milligrams per liter, is variable
Simulation of Hydrodynamics, Constituent Transport, and Water Quality 57

Figure 37. Distance and depth plots of simulated conservative tracer released from the nursery pond into Lake Maumelle.

15

10

5

0

DEPTH BELOW S URFACE, IN METERS

0 5,000 10,000 15,000

DOWNSTREAM DISTANCE, IN METERS

5 HOURS

RESERVOIR BOTTOM

0 5,000 10,000 15,000

DOWNSTREAM DISTANCE, IN METERS

15

10

5

0

DEPTH BELOW S URFACE, IN METERS

29 HOURS

0 5,000 10,000 15,000

DOWNSTREAM DISTANCE, IN METERS

15

10

5

0

DEPTH BELOW S URFACE, IN METERS

53 HOURS

0 5,000 10,000 15,000

DOWNSTREAM DISTANCE, IN METERS

15

10

5

0

DEPTH BELOW SURFACE, IN METERS

0 5,000 10,000 15,000

DOWNSTREAM DISTANCE, IN METERS

15

10

5

0

DEPTH BELOW SURFACE, IN METERS

77 HOURS

101 HOURS

0 5,000 10,000 15,000

DOWNSTREAM DISTANCE, IN METERS

15

10

5

0

DEPTH BELOW S URFACE, IN METERS

9 DAYS

10.0

EXPLANATION

 LINE OF EQUAL TRACER CONCENTRATION

-- Interval, in milligrams per liter, is variable
58 Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics in 

Lake Maumelle, Arkansas, 1991-92

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan

ALGAL BIOMASS, IN MILLIGRAMS PER LITER

0.0

0.2

0.4

0.6

0.8

1.0

Calibrated base condition

10 x phosphorus inflow load

10 x ammonia inflow load

1991

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan

0.0

0.2

0.4

0.6

0.8

1.0

Calibrated base condition

10 x phosphorus and ammonia inflow load

Figure 38. Time series of algal biomass resulting from various nutrient enrichment scenarios at segment 10, layer 4, at the 

downstream end of Lake Maumelle.
Summary 59

SUMMARY

Lake Maumelle is the major drinking-water 

source for the Little Rock metropolitan area in central 

Arkansas. Urban and agricultural development has 

increased in the Lake Maumelle Basin and so have concerns about the sustainability and quality of this 

resource. Information is needed concerning constituent 

transport and water-quality response to changes in constituent loading or hydrologic regime. The purpose of 

this report was to (1) characterize ambient conditions in 

Lake Maumelle and its major tributary, Maumelle 

River; (2) calibrate a numerical model of hydrodynamics and water quality; and (3) run several model simulations to describe constituent transport and waterquality response to changes in constituent loading and 

hydrologic regime. 

Ambient hydrologic and water-quality conditions demonstrate the relatively undisturbed nature of 

Lake Maumelle and the Maumelle River. Nitrogen and 

phosphorus concentrations are low, one to two orders 

of magnitude lower than estimates of national background nutrient concentrations. Phosphorus and chlorophyll a concentrations in Lake Maumelle 

demonstrate its oligotrophic/mesotrophic condition. 

However, concentrations of chlorophyll a appear to be 

increasing since 1990 within the upper and middle 

reaches of the reservoir. 

A two-dimensional, laterally averaged hydrodynamic and water-quality model (CE-QUAL-W2) was 

constructed, calibrated, and verified for Lake 

Maumelle. The model simulates water level, currents, 

heat transport and temperature distribution, conservative material transport, and the transport and transformation of 11 chemical constituents. Objectives were to 

develop the capability to simulate the movement and 

dispersion of spills or releases in the reservoir during 

stratified and unstratified conditions, simulate and 

track the release of the fish nursery pond off the southern shore of Lake Maumelle, and simulate water-quality response to possible changes in external loads. The 

model was calibrated using 1991 data and verified 

using 1992 data. Simulated temperature and DO concentrations related well when compared to measured 

values. Simulated nutrient and algal biomass also 

related reasonably well when compared to measured 

values. Although, it would be recommended that chlorophyll a to biomass ratios be determined in the modeled system to get a better calibration.

A simulated spill of conservative material at the 

upper end of Lake Maumelle during a major storm 

event took less than 102 hours (4.25 days) to disperse 

the entire length of the reservoir. Simulation of the 

nursery pond release demonstrated how the released 

water plunges within the receiving embayment and 

enters the mainstem of the reservoir at mid depths. 

Simulations of algal response to increases of nitrogen 

and phosphorus loads by a factor of 10, demonstrate the 

phosphorus limiting condition in Lake Maumelle. 

Increasing nitrogen load without increasing phosphorus resulted in no change in algal biomass from the calibrated or base condition. Increasing phosphorus load 

resulted in an increase in algal biomass. The algal biomass resulting from the increases in both phosphorus 

and nitrogen was very similar to the biomass resulting 

from an increase of phosphorus only.

Results from this study will aid in the protection 

and management of the Lake Maumelle drinking-water 

resource. Management can use the existing simulations 

and others to evaluate how changes in hydrology and 

water quality in the basin may affect water quality in 

the reservoir. With this information, water resources 

management can more effectively manage their source 

supply.
60 Analysis of Ambient Conditions and Simulation of Hydrodynamics, Constituent Transport, and Water-Quality Characteristics 

in Lake Maumelle, Arkansas, 1991-92

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