U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2010–5163

Prepared in cooperation with the Metropolitan Council

Low-Flow Characteristics of the Mississippi River 

Upstream from the Twin Cities Metropolitan Area, 

Minnesota, 1932–2007

Low-Flow Characteristics of the 

Mississippi River Upstream from the 

Twin Cities Metropolitan Area, 

Minnesota, 1932–2007

By Erich Kessler and David L. Lorenz

Prepared in cooperation with the Metropolitan Council

Scientific Investigations Report 2010–5163

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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Suggested citation:

Kessler, Erich, and Lorenz, D.L., 2010, Low-flow characteristics of the Mississippi River upstream from the Twin Cities 

Metropolitan Area, Minnesota, 1932–2007: U.S. Geological Survey Scientific Investigations Report 2010–5163, 14 p.
iii

Contents

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

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

Methods...........................................................................................................................................................2

Superposition of Flows.........................................................................................................................2

Relations Among the Timing of Low Flows and Reservoir Elevations .........................................4

Measurements for Water-Surface Profile of the Mississippi River.............................................5

Low-Flow Characteristics of the Mississippi River..................................................................................5

Flow-Duration Statistics ......................................................................................................................5

Synthetic Superposed Flow Statistics ..............................................................................................5

Relations Among the Timing of Low-Flows and Reservoir Elevations.........................................6

Water-Surface Profile of the Mississippi River......................................................................................10

Implications of the Low-Flow Characteristics of the Mississippi River .............................................10

Summary........................................................................................................................................................13

References Cited..........................................................................................................................................13

Figures

1. Map showing location of study area and streamflow-gaging stations...............................3

2–4. Graphs showing:

2. Example of superposed hydrographs for the Mississippi River near 

Anoka (station 05288500) for 1976 and 2003 ....................................................................4

3. Recession index values and regression line for the Mississippi 

River near Anoka, 1932–2007 .............................................................................................7

4. Probability plot showing the synthetic superposed flows less 

than 700 cubic feet per second for the Mississippi River near Anoka.......................7

5. Map showing location of the low-flow water-surface profile 

measurements with selected landmarks along the Mississippi River ..............................11

6. Graph showing longitudinal profile of water-surface elevations along 

the Mississippi River with selected landmarks, October 8–9, 2008 , 

when flow ranged from 3,600 to 4,800 cubic feet per second 

(Mississippi River near Anoka, station 05288500) .................................................................12

Tables

1. Selected flow-duration statistics for Mississippi River near Anoka 

and four upstream streamflow-gaging stations for 1932–2007.............................................6

2. Number of occurrences of low flows (less than the 10th percentile) 

in the upper basin streams during low flows in the Mississippi River 

near Anoka by year for 1932–2007 .............................................................................................8

3. Number of occurrences of low flows (less than the 10th percentile) 

in the upper basin streams during low flows in the Mississippi River 

near Anoka by month for 1932–2007..........................................................................................9
iv

4. Number of occurrences of low-stage elevations for upper basin 

reservoirs during low flows in the Mississippi River near Anoka by 

year for 1960–2007 ........................................................................................................................9

5. Number of occurrences of low-stage elevations for upper basin 

reservoirs during low flows in the Mississippi River near Anoka by 

month for June–August 1960–2007..........................................................................................10

Conversion Factors and Datums

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

Flow rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Elevation, as used in this report, refers to distance above the vertical datum.
Low-Flow Characteristics of the Mississippi River 

Upstream from the Twin Cities Metropolitan Area, 

Minnesota, 1932–2007

By Erich Kessler and David L. Lorenz

Abstract

The U.S. Geological Survey, in cooperation with the 

Metropolitan Council, conducted a study to characterize 

regional low flows during 1932–2007 in the Mississippi River 

upstream from the Twin Cities metropolitan area in Minnesota 

and to describe the low-flow profile of the Mississippi River 

between the confluence of the Crow River and St. Anthony 

Falls. Probabilities of extremely low flow were estimated 

for the streamflow-gaging station (Mississippi River near 

Anoka) and the coincidence of low-flow periods, defined as 

the extended periods (at least 7 days) when all the daily flows 

were less than the 10th percentile of daily mean flows for the 

entire period of record, at four selected streamflow-gaging stations located upstream. The likelihood of extremely low flows 

was estimated by a superposition method for the Mississippi 

River near Anoka that created 5,776 synthetic hydrographs 

resulting in a minimum synthetic low flow of 398 cubic feet 

per second at a probability of occurrence of 0.0002 per year. 

Low-flow conditions at the Mississippi River near Anoka were 

associated with low-flow conditions at two or fewer of four 

upstream streamflow-gaging stations 42 percent of the time, 

indicating that sufficient water is available within the basin for 

many low flows and the occurrence of extremely low-flows is 

small. However, summer low-flow conditions at the Mississippi River near Anoka were almost always associated with 

low-stage elevations in three or more of the six upper basin 

reservoirs. A low-flow profile of the Mississippi River between 

the confluence of the Crow River and St. Anthony Falls was 

completed using a real-time kinematic global positioning 

system, and the water-surface profile was mapped during 

October 8–9, 2008, and annotated with local landmarks. This 

was done so that water-use planners could relate free-board 

elevations of selected water utility structures to the lowest 

flow conditions during 2008. 

Introduction

Water-supply availability and planning are growing 

issues for the Twin Cities metropolitan area (TCMA) and other 

upstream municipalities on the Mississippi River in Minnesota. Currently (2009) about two-thirds of public supply water 

in the TCMA is obtained from groundwater, and about onethird is obtained from surface water (Metropolitan Council, 

2007). Most TCMA suburbs obtain water from increasingly 

stressed (Metropolitan Council, 2007) groundwater sources, 

whereas the more densely populated cities of Minneapolis, St. 

Paul, and St. Cloud (located upstream from the TCMA) obtain 

all or most of their water from the Mississippi River. The Metropolitan Council is investigating the option of using surfacewater sources and in particular, the Mississippi River, to help 

provide future demand for water in the TCMA. It is uncertain 

how much more water could be withdrawn from the river 

during low-flow conditions and maintain a minimum threshold of sustained flow necessary for existing water withdrawal 

infrastructure and other uses including downstream navigation channels, sustainable habitat for fisheries and wildlife, 

recreation, and point source inflow dilution. Mississippi River 

water levels are maintained in the Minneapolis and St. Paul 

area through a complicated array of upstream reservoir water 

releases, downstream locks and dams, and natural flow in tributaries to the Mississippi River. Understanding current wateruse needs and water management/release practices on the 

Mississippi River and its tributaries during drought conditions 

are keys to understanding water availability in the TCMA. 

The U.S. Geological Survey, in cooperation with the Metropolitan Council, conducted a study to characterize regional 

low flows from 1932 through 2007 in the Mississippi River 

Basin upstream from the TCMA in Minnesota, and to describe 

the water-surface profile of the Mississippi River between the 

confluence of the Crow River and St. Anthony Falls. Regional 
2 Low-Flow Characteristics of the Mississippi River Upstream from the Twin Cities Metropolitan Area, Minnesota

low-flow characterization and the water-surface profile can be 

used to plan for future demands of water supply. 

This report documents the methodology and results of 

the regional low-flow characteristics and river surveying. 

To characterize regional low flow in the Mississippi River 

Basin upstream from the TCMA, probabilities of extreme low 

flow were estimated for the streamflow-gaging station on the 

Mississippi River near Anoka (station 05288500; fig. 1) and 

the coincidence of low flows at selected streamflow-gaging 

stations located upstream within the basin. The selected 

upstream streamflow-gaging stations (fig. 1) are the Mississippi River at Grand Rapids (station 05211000), Crow Wing 

River at Nimrod (station 05244000), Crow River at Rockford 

(station 05280000), and Rum River near St. Francis (station 

05286000); hereinafter collectively referred to as the “upper 

basin streams.” These streams were selected because they 

comprise the largest drainage areas of upstream subbasins, 

and provide the long-term historical data that are needed for 

this analysis. A water-surface profile of the Mississippi River 

was obtained between the confluence of the Crow River and 

St. Anthony Falls, where future water-supply infrastructure 

most likely would be located (fig. 1). 

Methods

To characterize historical regional low flow and severity 

of regional drought conditions, daily-flow duration statistics 

were computed for selected streams using U.S. Geological 

Survey streamflow-gaging stations from 1932, which was the 

earliest year that all selected streamflow-gaging stations had 

flow records, to 2007 (U.S. Geological Survey, 2008). The 

Mississippi River near Anoka, located near the outlet of the 

study area, was selected as the base reference streamflowgaging station to which other stations are correlated. The 

flow in the Mississippi River near Anoka can fluctuate greatly 

diurnally and from day to day because of regulation by the 

Coon Rapids Dam and other upstream dams (fig. 1) generally 

associated with hydroelectric operations. These fluctuations 

in flow are not representative of the natural flow conditions. 

To better represent the natural flow conditions, a 7-day running mean using a quadratic smoothing operator (Wood and 

Hockens, 1970) was calculated for the daily flow values for 

all streamflow-gaging stations. The resulting 7-day running 

means were used in all of the analyses of daily-flow duration 

statistics within the study area. 

Superposition of Flows

To assess the probability of extremely low flows of 

the Mississippi River near Anoka, the hydrographs of all 

observed summer to fall flows during the 76 years of the 

period of record (1932–2007) were superposed on each of the 

76 observed spring peak flows to create a large set of synthetic 

hydrographs. From this dataset of 5,776 years of synthetic 

hydrographs, 76 years of summer-fall hydrographs superposed 

on 76 snowmelt peaks, the statistics of the range of minimum 

synthetic flows were computed. 

The superposition is a permutation type analysis based on 

the laws of conditional probability analysis (Ott and Longnecker, 2001, chapter 4) that synthesizes potential summer-fall 

hydrographs by superposing observed summer-fall hydrographs on all observed spring snowmelt peak flows. The concept of superposed flows for the study area is shown in figure 

2. The actual hydrograph for calendar year 2003 and the actual 

hydrograph for calendar year 1976 are used as an example 

that produced one of the 5,776 synthetic hydrographs for 

the study. The synthetic summer-fall hydrograph for 1976 is 

superposed on 2003 assuming the climatic conditions of 1976 

had occurred after the snowmelt peak flow of 2003. The arrow 

shows the superposition of the 1976 spring snowmelt peak 

flow that occurred in April to the spring peak flow of 2003 

that occurred in March; in this case, the 1976 spring snowmelt 

peak flow was superposed downward and backward in time 

(earlier) to match with the 2003 spring snowmelt peak flow. 

Similarly, the superposition translated the 433 cubic feet per 

second (ft3/s) flow increase during late May 1976 backward 

about 1 week in the synthetic flow hydrograph (fig. 2, inset). 

To correctly represent the superposition of flows, the 

relation between flow and recession rate must be known. For 

example, if the expected daily decrease in flow is 1 percent 

at 5,000 ft3/s and 2 percent at 50,000 ft3/s, then the synthetic 

decrease in daily flow values must be corrected when the 

flow at 50,000 ft3/s is superposed to 5,000 ft3/s to prevent the 

synthetic decrease from being unreasonably large. The recession rate generally is expressed as the index value in days per 

common log cycle rather than percent per day.

Rutledge (1998) described a computer program to estimate the rates of flow recessions. That program was modified to run in S-PLUS® (TIBCO Software, Inc., 2008). The 

program generates recession index values for all log-linear 

recessions longer than a specified duration. The specified duration used for this analysis was at least 10 days. For the Mississippi River near Anoka, 227 recessions were used to compute 
Figure 1. Location of study area and streamflow-gaging stations.

97° 96° 95° 94° 93° 92° 91° 90° 89°

49°

46°

45°

44°

48°

47°

)

)

)

) )

)

#

#

0 25 50 100 MILES

0 25 50 75 100 KILOMETERS

75 Base data from Minnesota Department of Natural Resources, 1:100,000 Hydrography and 1:24,000 Counties

North American Datum of 1983 (NAD 83)

Universal Transverse Mercator projection

Zones 14 and 15

EXPLANATION

Study area boundary

Streamflow-gaging station

 and number

Dam Red

Red Lake

Kettle

Sauk R

Thief River

Ottertail

Big Fork R

S F Crow

River

Cloquet

Pine

Zumbro R

Rapid River

Buffalo

Cottonwood

Root

River

Minnesota

Chippewa

Clearwater

Cannon R

North Fork 

Crow

Mustinka R

Sand Hill

Snake R

Crow Wing R

Rock

River

Cedar

Rum

River

River

River

River

River

Mississippi

Mississippi

Two River

St. Louis

Des Moines

Tamarac River

Roseau

Red Eye R

Le Sueur R

Blue Earth R

Little Fork

Vermilion R

Lac qui Parle

Nemadji R

Watonwan

Prairie R

Long

River

River

River

River

River

River

River

River

River

de terre

Pomme

River

River

River

River

River

River

River

eht f o North

River

River

River

Lake

Winnibigoshish

Lake

Pokegama

Gull

Lake

Leech

Lake

Coon Rapids

Twin Cities Metropolitan Area,

Includes Minneapolis, St. Paul,

Anoka, and St. Anthony Falls

Pine River

Reservoir

Big Sandy

Lake

05211000

05244000

05286000

05280000 05288500 #

St. Croix 

River 

Wild

Rice

River

Redwood

Methods 3
Figure 2. Example of superposed hydrographs for the Mississippi River near Anoka (station 05288500) for 1976 and 

2003.

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

0

5,000

10,000

15,000

20,000

25,000

30,000

Flow 1976

Flow 2003

Synthetic flow

D (ft3/s) NOCES REP TEEF CI BUC IN, WOLF M

AERTS

0

 (ft3/s) DNOCES REP TEEF IC BUC IN, WOLF MAERTS

Apr. May June

1,000

2,000

3,000

4,000

433 ft /s increase 3

433 ft /s increase 3

5,000

Synthetic flow

Translation of the 

spring peak from 

1976 to 2003

INSET

4 Low-Flow Characteristics of the Mississippi River Upstream from the Twin Cities Metropolitan Area, Minnesota

a master recession curve, which described the general recession rate for differing flow conditions and seasons. A linear 

regression analysis (Helsel and Hirsch, 2002) of the recession 

index values with flow and seasonal terms indicated that only 

season was a significant explanatory variable—the recession 

rate does not vary significantly by flow based on a 5-percent 

significance level. 

The 76 years of flow record for the Mississippi River 

near Anoka were used to produce 5,776 years of synthetic 

hydrographs. The lowest synthetic superposed flow was determined from these data, along with a probability of occurrence. 

Probability occurrences for all flows less than 700 ft3/s also 

were computed and plotted. For example, a 1 percent probability means that there is a 1 in 100 chance of occurrence in 

a given year. The analysis of the likelihood of extremely low 

flows provides an estimate of the likelihood of observing an 

extremely low flow in the future based on observed events in 

the past 76 years. The effects of any change in flow characteristics because of climate change are not accounted for in this 

analysis.

Relations Among the Timing of Low Flows and 

Reservoir Elevations

Reservoir elevation data were analyzed to assess the 

capacity to maintain flow in the Mississippi River by relating recent (since about 1960) reservoir capacity to low-flow 

conditions in the Mississippi River near Anoka. The year 1960 

was chosen based on a review of reservoir levels indicating a 

change in reservoir management that has been consistent since 

then. In addition, daily elevation (stage) duration statistics 

were computed for the six headwaters reservoirs gaged by the 

U.S. Army Corps of Engineers (Gull Lake Reservoir, Leech 

Lake Dam and Reservoir, Pine River Dam and Reservoir, Lake 

Pokegama Dam and Reservoir, Big Sandy Lake and Reservoir, 

Lake Winnibigoshish Dam and Reservoir). The U.S. Army 

Corps of Engineers previously has studied reservoir releases in 

relation to travel times (U.S. Army Corps of Engineers, 2009). 

Relations between reservoir elevation data and Mississippi 

River flow were assumed to represent a consistent operating 
Low-Flow Characteristics of the Mississippi River 5

strategy during that period. No attempt was made to separately 

account for losses because of evapotranspiration. 

A statistical comparison between flow of the Mississippi 

River near Anoka and elevations of the upper basin reservoirs 

also was made. Low flows for the Mississippi River near 

Anoka and elevations from the six upstream reservoirs were 

tabulated to determine how often and how many reservoirs 

were below the lower summer operating-limit elevation (U.S. 

Army Corps of Engineers, 2009). 

To understand the patterns of low flows in the Mississippi River Basin upstream from Anoka, the co-occurrence 

of low flows near Anoka and low flows in the upper basin 

streams were tabulated. The low-flow periods were defined as 

the extended periods (at least 7 days) when all the daily flows 

were less than the 10th percentile of daily mean flows for the 

entire period of record. Low-flow periods that were separated 

by fewer than 10 days were combined into a single period. A 

percentile is a value on a scale of 100 that indicates the percent 

of a distribution that is equal to or below it. For example, 

streamflow at the 10th percentile is equal to or greater than 10 

percent of streamflow recorded during all years that measurements have been made. 

Measurements for Water-Surface Profile of the 

Mississippi River

The longitudinal profile of water-surface elevations along 

the Mississippi River between the confluence with the Crow 

River and St. Anthony Falls was surveyed during October of 

2008 by using a real-time kinematic global positioning system 

(RTK-GPS) with a nominal vertical accuracy of 0.03 feet (ft) 

(Trimble, 2009). The water-surface profile data were collected 

on October 8–9, 2008, when flow rates ranged from 3,600 to 

4,800 ft3/s, as recorded by the streamflow-gaging station Mississippi River near Anoka. The following projection parameters were used for this study: Universal Transverse Mercator 

(UTM) North Zone 15, North American Datum of 1983 (NAD 

83), and Geoid g2003u03. These parameters were used based 

on the location of the survey and the time the survey was 

conducted. Water-surface elevations at many points along 

both sides of the river were collected to define the profile. 

The interval spacing used was a balance between maximizing 

the profile information of the river reach, while minimizing 

the likelihood that diurnal flow fluctuations and associated 

changes in river stage would adversely affect data collection 

efforts. The points were selected upstream and downstream 

from rapids and at reasonably spaced intervals (roughly 500 ft) 

through runs. In pools upstream from the dams at Coon Rapids 

and St. Anthony Falls, fewer elevation points were collected. 

RTK-GPS points were analyzed for accuracy by comparing 

them with base points located in the surrounding area. A few 

of the points were rated as poor because accuracy of 0.03 ft 

could not be verified because the unit could not adequate radio 

link to the base station. This did not have a negative effect 

on the profile data because the points were located within the 

Coon Rapids Dam pool, in which the slope is considered to be 

linear from the start of the pool to the Coon Rapids Dam. The 

elevation points of the Mississippi River were plotted relative to distance from the confluence with the Crow River and 

resulted in a longitudinal profile of the Mississippi River. 

River profile data are useful for understanding the watersurface elevation in response to flow in the river. With additional cross-section information that is beyond the scope of 

this study, the data can be used for calibrating a water-surface 

profile model to estimate elevations at lower flow values.

Low-Flow Characteristics of the 

Mississippi River

Low-flow characteristics and statistics are presented in 

this section for the Mississippi River near Anoka, upper basin 

streams, and the six headwater reservoirs. Statistics are based 

on 5,776 years of synthetic flow record. The occurrences of 

low-flow periods between reservoirs and flow in the Mississippi River near Anoka were tabulated. 

Flow-Duration Statistics

Selected flow-duration statistics for the Mississippi River 

near Anoka and the four upstream streamflow-gaging stations, 

based on daily-mean flow from 1932–2007, are presented in 

table 1. The minimum flow for the Mississippi River at Grand 

Rapids (station 05211000) was 0 ft3/s on October 2, 1948. This 

is likely the result of flow regulation by the Pokegama Dam 

(at Lake Pokegama) because the average flow for the previous 

5 days was 542 ft3/s. A visual inspection of the flow record 

for the Mississippi River at Grand Rapids and elevations at 

Pokegama Lake indicates a change in regulation at the dams 

beginning in about 1960, which resulted in a much reduced 

daily fluctuation in flow.

Synthetic Superposed Flow Statistics

A linear regression analysis of recession index values 

with flow and seasonal terms indicated that only the seasonal 

terms were significant and flow was not significant at the 

5-percent significance level. The following regression equation was determined for the log-transformed recession index:

log (K) = 4.171−0.0993 sin (2πDectime)+0.2630 cos (2πDectime) (1)

where 

K is the recession index value, 

Dectime is the decimal part of the year, 

log is the natural logarithm, and 

sin and cos are the sine and cosine functions. 
Table 1. Selected flow-duration statistics for Mississippi River near Anoka and four upstream streamflow-gaging 

stations for 1932–2007.

Station (number)

Daily mean streamflow, in cubic feet per second

based on data from 1932 to 2007

Minimum 5th percentile 10th percentile 

Mississippi River at Grand Rapids (05211000) 10 199 287

Crow Wing River at Nimrod (05244000) 80.0 188 231

Crow River at Rockford (05280000) 3.80 28.0 40.0

Rum River near St. Francis (05286000) 30.0 100 123

Mississippi River near Anoka (05288500) 602 1,610 2,240

1

Result of regulation, the minimum streamflow since 1960 was 83 cubic feet per second.

6 Low-Flow Characteristics of the Mississippi River Upstream from the Twin Cities Metropolitan Area, Minnesota

The residual standard error of the linear regression was 

0.3185, the r-squared value (coefficient of determination) was 

0.1493, and the attained p-value was less than 0.0001. The 

coefficients for the sine and cosine functions indicate a minimum recession index value of about 49 days per log cycle. 

This corresponds to a recession rate with the greatest slope of 

about 4.6 percent per day, which occurs in early June (fig. 3). 

A more typical recession index value of 60 days per log cycle, 

which occurs in late March and late August, corresponds to a 

recession rate of about 3.8 percent per day.

Calendar year data from 1932 to 2007 were used in the 

permutation analysis of synthetic hydrographs. The 76 years 

of record produced 5,776 years of synthetic hydrographs: 

76 years of summer-fall hydrographs superposed on 76 snowmelt peaks. A correlation analysis (Helsel and Hirsch, 2002) 

between snowmelt peak flows and range of summer-fall flows 

was performed to determine whether or not permutations 

were reasonable. The correlation analysis indicated that there 

was not a strong relation between snowmelt peak flows and 

summer-fall flows, therefore no permutations were removed 

from the analysis. Because the recession rate does not vary 

as a function of flow rate and the shift in seasonal timing is 

small, no adjustments were made to the recession rate of the 

superposed flows. Flow rises that occurred in the actual record 

were transferred linearly into the superposed record to account 

for the actual increase in water in the system. For example, the 

433 ft3/s increase in measured flow during May 26–31, 1976 

(fig. 2, inset) is maintained by the 433 ft3/s increase in flow in 

the synthetic flow.

The probability distribution of synthetic superposed flows 

less than 700 ft3/s are shown in figure 4. Based on synthetic 

superposed hydrograph results, the lowest flow generated was 

398 ft3/s. This corresponds to a probability of 0.0002 (0.02 

percent) per year (fig. 4). The greatest risk for such an event is 

in the late spring to early summer after a dry winter. The probability that the flow in the Mississippi River near Anoka will 

be less than 660 ft3/s in any 1 year is 1 percent and the probability that the flow will be less than 510 ft3

/s is 0.1 percent. 

Relations Among the Timing of Low-Flows and 

Reservoir Elevations

Low flows (less than the 10th percentile) in the Mississippi River near Anoka were compared with low flows in the 

four upper basin streams, and with stage elevations from the 

six upstream reservoirs. Four tables were compiled summarizing the occurrences, defined by separate rises in flow, by year 

and by month. The number of occurrences of low flow in the 

upper basin streams during years when low flows occurred in 

the Mississippi River near Anoka is shown in table 2. These 

same occurrences are shown by month in table 3. Low-flow 

conditions in the Mississippi River near Anoka were associated with low-flow conditions at two or fewer of the four 

upper basin streams 42 percent of the time, indicating that for 

many low-flow scenarios sufficient water is available in the 

basin and that the occurrence of extremely low flows in the 

Mississippi River near Anoka is small.

Stage elevations of reservoirs were examined to determine how often they were below the summer lower operating 

levels for 1960–2007. The correlation between the number of 

occurrences of low-stage elevations in the upper basin reservoirs during years when low flows occurred in the Mississippi 

River near Anoka is shown in table 4. These same occurrences 

are shown by month, with the months spanning from June 

through August, in table 5. Fall through spring stage elevations 

were not used because of regulatory effects. 

Drought severity can be determined from the tables 

by the number of occurrences of low flow or stage from the 

basins or reservoirs, respectively, and the Mississippi River 

near Anoka. For example, all four upper basins had six occurrences of low flow in 1934, whereas the Mississippi River 

near Anoka had 12 occurrences of low flow in that same 

year; in 2003, only the Mississippi River near Anoka had an 

occurrence of low flow. Thus, 1934 had more severe regional 

drought than 2003, when the flow in the tributaries was greater 

than the 10th percentile but the flow in the Mississippi River 

near Anoka was low. 
Figure 4. Probability plot showing the synthetic superposed flows less than 700 cubic feet 

per second for the Mississippi River near Anoka.

Figure 3. Recession index values and regression line for the Mississippi River near Anoka, 1932–2007.

20

30

40

50

60

70

80

100

200

RECESSION INDEX RATE, IN DAYS PER LOG CYCLE

Mar. Apr. May June July Aug. Sept. Oct.

0.01 0.02 0.05 0.10 0.20 0.50 1.00 2.00

PROBABILITY OF OCCURRENCE, IN PERCENT PER YEAR

350

400

450

500

550

600

650

700

MINIMUM SUMMER STREAMFLOW, IN CUBIC FEET PER SECOND

Low-Flow Characteristics of the Mississippi River 7
Table 2. Number of occurrences of low flows (less than the 10th percentile) in the upper basin streams during 

low flows in the Mississippi River near Anoka by year for 1932–2007.

Yeara

Number of upper basin streamsb that had low flow when low flow occurred near Anokac

0d 1 2 3 4

1932 0 4 2 1 3

1933 0 3 1 1 5

1934 0 0 2 4 6

1935 0 0 1 6 2

1936 0 0 0 5 5

1937 0 0 0 6 2

1938 0 1 2 1 0

1939 0 1 2 1 1

1940 0 0 0 4 3

1941 0 0 1 0 0

1949 0 0 0 1 0

1950 0 1 0 0 0

1955 1 0 0 0 0

1958 0 1 0 2 0

1959 1 0 0 3 1

1960 1 0 1 2 0

1961 0 1 5 1 2

1962 0 1 0 3 0

1963 0 0 1 0 0

1964 0 0 1 0 0

1967 0 1 1 0 0

1968 0 0 2 1 0

1969 1 0 0 0 0

1970 0 3 0 0 0

1976 0 0 1 0 5

1977 0 0 0 1 3

1980 0 1 1 0 0

1981 0 0 0 2 0

1988 0 0 3 2 0

1989 0 0 2 0 0

1990 1 0 1 0 0

2003 1 0 0 0 0

2004 0 1 2 0 0

2006 0 2 2 0 0

a

Only years for which flow of the Mississippi River near Anoka (station 05288500) was less than the 10th percentile are included.

b

Upper basin streams are the Mississippi River at Grand Rapids (station 05211000), Crow Wing River at Nimrod (station 05244000), 

Crow River at Rockford (station 05280000), and Rum River near St. Francis (station 05286000).

c

Mississippi River near Anoka (station 05288500).

d

Values indicate number of occurrences of low flow near Anoka by year (less than 10th percentile of flow for at least 7 days).

8 Low-Flow Characteristics of the Mississippi River Upstream from the Twin Cities Metropolitan Area, Minnesota
Table 3. Number of occurrences of low flows (less than the 10th percentile) in the upper basin streams during 

low flows in the Mississippi River near Anoka by month for 1932–2007.

Month

Number of upper basin streamsa that had low flow when low flow occurred near Anokab

0c 1 2 3 4

January 0 3 3 8 2

February 0 2 4 5 3

March 0 2 3 7 1

April 0 0 0 1 0

May 0 0 0 1 0

June 0 0 3 2 1

July 0 1 2 4 5

August 0 2 5 5 8

September 1 1 4 3 6

October 1 1 1 2 6

November 2 4 2 4 4

December 2 5 7 5 2

Total 6 21 34 47 38

a

Upper basin streams are the Mississippi River at Grand Rapids (station 05211000), Crow Wing River at Nimrod (station 05244000), 

Crow River at Rockford (station 05280000), and Rum River near St. Francis (station 05286000).

b

Mississippi River near Anoka (station 05288500). 

c

Values indicate number of occurrences of low flow near Anoka during the month (less than 10th percentile of flow for at least 

7 days).

Table 4. Number of occurrences of low-stage elevations for upper basin reservoirs during low flows in the 

Mississippi River near Anoka by year for 1960–2007.

Year

Number of upper basin reservoirsa that were lowb when low flow occurred near Anokac

2 3 4 5 6

1960 0 2 0 0 0

1961 0 0 2 1 0

1964 0 1 0 0 0

1970 0 0 0 1 0

1976 0 0 1 1 0

1977 0 1 0 0 0

1980 0 1 0 0 0

1988 1 0 0 0 2

1989 0 0 0 1 0

2004 0 1 0 0 0

2006 0 0 1 1 0

2007 0 0 1 0 1

a

The upper basin reservoirs are Gull Lake Reservoir, Leech Lake Dam and Reservoir, Pine River Dam and Reservoir, Lake Pokegama Dam and Reservoir, Big Sandy Lake and Reservoir, Lake Winnibigoshish Dam and Reservoir. 

b

Low is defined as the stage elevation below the summer threshold from U.S. Army Corps of Engineers stage volume graphs available at http://www.mvp-wc.usace.army.mil/.

c

Mississippi River near Anoka (station 05288500).

Low-Flow Characteristics of the Mississippi River 9
Table 5. Number of occurrences of low-stage elevations for upper basin reservoirs during low flows in the 

Mississippi River near Anoka by month for June–August 1960–2007.

Month

Number of upper basin reservoirsa that were lowb when low flow occurred near Anokac

2 3 4 5 6

June 1 0 1 0 0

July 0 1 4 0 1

August 0 5 0 5 2

Total 1 6 5 5 3

a

The upper basin reservoirs are Gull Lake Reservoir, Leech Lake Dam and Reservoir, Pine River Dam and Reservoir, Lake 

Pokegama Dam and Reservoir, Big Sandy Lake and Reservoir, Lake Winnibigoshish Dam and Reservoir. 

b

Low is defined as the stage elevation below the summer threshold from U.S. Army Corps of Engineers stage volume graphs 

available at http://www.mvp-wc.usace.army.mil/.

c

Mississippi River near Anoka (station 05288500).

10 Low-Flow Characteristics of the Mississippi River Upstream from the Twin Cities Metropolitan Area, Minnesota

The analysis of the upper basin streams indicates that 

they can be used as an indicator to whether or not the drought 

severity is regional or local. If all the upper basin streams 

have an occurrence of low flow and the Mississippi River 

near Anoka has an occurrence, the drought could be considered severe, with minimal rain in the basin for a long period. 

However, if the basin streams have no occurrence of low flow 

and the Mississippi River near Anoka does, the drought period 

would be less severe because rain events were occurring 

within the upper basins, but the events were not large enough 

to bring the Mississippi River near Anoka out of a low-flow 

condition.

Summer low-flow conditions at the Mississippi River 

near Anoka almost always were associated with low-stage 

elevations in 3 or more of the 6 upper basin reservoirs. Thus, 

flows through the reservoir are being maintained but little 

water is being held in reserve to sustain flow anywhere in the 

Mississippi River main stem.

Water-Surface Profile of the 

Mississippi River

Water-use planners want to relate free-board elevations 

of selected water utility structures to low-flow conditions. To 

do this, RTK-GPS was used to collect water-surface elevation data during October 8–9, 2008, along the Mississippi 

River from immediately downstream from the confluence of 

the Crow River to the upstream end of the pool created by 

St. Anthony Falls (fig. 5). The nominal vertical accuracy was 

0.03 ft, confirmed by five observations at benchmarks. The 

actual vertical accuracy was affected by fluctuations in flow 

and wind effects, which may have resulted in small increases 

in elevation in subsequent downstream observations. The 

longitudinal profile of water-surface elevations collected along 

the banks of the Mississippi River and the selected landmarks 

is shown in figure 6. A large drop in elevation of the water-surface profile occurs at the Coon Rapids Dam. The total elevation drop from the Crow River to the upstream end of the pool 

created by St. Anthony Falls was 42 ft. The slope of the profile 

was steeper below the Coon Rapids Dam than above the dam. 

Implications of the Low-Flow 

Characteristics of the Mississippi 

River

In contrast to historical record, which determined that 

the lowest daily flows occurred in late summer, the analysis 

of the synthetic hydrographs indicates that the greatest risk 

for extremely low flows in the Mississippi River near Anoka 

would occur in the late spring to early summer after a dry 

winter. This is likely because historical record has never 

experienced a dry late spring and early summer following a 

dry winter. Of the lowest 1 percent of the synthetic flows (58, 

corresponding to a flow of less than 660 ft3/s), 44 occurred 

before the end of June. All 44 had snowmelt peak flows of less 

than 11,300 ft3/s. There also is a risk for low flows anytime 

during the summer. Most of the lowest 3 percent of the synthetic flows, corresponding to a flow less than 779 ft3

/s, occur 

after the end of June. Even though low snowmelt peak flows 

contribute to the likelihood of low seasonal flows, at least one 

synthetic seasonal low flow of less than 1,000 ft3/s occurred 

after a snowmelt peak flow of 74,200 ft3/s.

The analysis of the relation between low flows in the 

Mississippi River near Anoka and upper basin streams 
Figure 5. Location of the low-flow water-surface profile measurements with selected landmarks along the 

Mississippi River.

I#

I#

I#

#I

#I

#I

#I

#I

#I

#I

#I

#I#I

I-94

I-494

US Hwy 169

US Hwy 10

Un vi ersity

Central

State Hwy 55

Main

State Hwy 100

State Hwy 65

State Hwy 610

US Hwy 12

State Hwy 47

US Hwy 10

I-94

I-394

US Hwy 10

I-494

Main

Central

State Hwy 101

I 694

Hwy 169

42nd Ave 

North Bridge

Broadway

Ave Bridge

Lowry Ave 

North Bridge

HENNEPIN

ANOKA

WRIGHT

Base data from Minnesota Department of Natural Resources, 1:100,000 Hydrography 

 and 1:24,000 Counties 

North American Datum of 1983 (NAD 83)

Universal Transverse Mercator projection

Zone 15

93°30' 93°22'30" 93°15'

45°15'

45°7'30”

45°

Elm Creek

Mississippi

Mississippi

Mississippi

River

River

River

Coon Creek

Shingle Creek

0 1 2 3 4 MILES 

0 1 2 3 4 KILOMETERS

I-694

Durnam Island

Banfill Island

Coon Rapids Dam

Hwy 610

Hwy 169

Cloquet Island

Crow River

St. Anthony Falls

Nicollet Island

EXPLANATION

#I Location shown in figure 6

Profile measurement

Area shown 

on map

Index map

Implications of the Low-Flow Characteristics of the Mississippi River 11
Figure 6. Longitudinal profile of water-surface elevations along the Mississippi River with selected landmarks, October 8–9, 

2008, when flow ranged from 3,600 to 4,800 cubic feet per second (Mississippi River near Anoka, station 05288500).

Crow River

Cloquet Island

Hwy 169

Coon Rapids

Dam 

Hwy 610

Banfill Island

Durnam Island

I–694

42nd Ave Bridge

Lowry Ave Bridge 

Broadway Ave 

Bridge 

Nicollet Island 

St. Anthony 

Falls 

0 4 8 12

DISTANCE, IN MILES

790

800

810

820

830

840

ELEVATION, IN FEET ABOVE NORTH AMERICAN VERTICAL DATUM OF 1988 (NAVD 88)

2 6 10 14

850

Coon Rapids Dam 

12 Low-Flow Characteristics of the Mississippi River Upstream from the Twin Cities Metropolitan Area, Minnesota
References Cited 13

indicates that many times when the flow near Anoka is less 

than the 10th percentile, at least one upper basin stream has 

flow greater than the 10th percentile. This indicates that the 

risk for continued low flow in the Mississippi River near 

Anoka is lower when this occurs and that the flow in the upper 

basin streams needs to be monitored to assess the risk for 

continued low flow near Anoka.

The analysis of the relation between low flows in the 

Mississippi River near Anoka and the upper basin reservoirs 

indicates that many times when the flow near Anoka is less 

than the 10th percentile, most reservoir levels are below the 

summer operating limit elevation. This indicates that the flow 

through the reservoir is being maintained and that minimal 

water is held in reserve to sustain flow anywhere in the Mississippi River main stem. 

Summary

Water-supply availability and planning are growing issues 

for the Twin Cities metropolitan area and other upstream 

municipalities on the Mississippi River in Minnesota. The 

U.S. Geological Survey, in cooperation with the Metropolitan 

Council, conducted a study to characterize regional low flows 

during 1932–2007 in the Mississippi River Basin upstream 

from the Twin Cities metropolitan area in Minnesota and to 

describe the low-flow profile of the Mississippi River between 

the confluence of the Crow River and St. Anthony Falls.

Probabilities of extreme low flow were estimated for 

the streamflow-gaging station on the Mississippi River near 

Anoka (station 05288500) and the coincidence of low-flows 

at four selected streamflow-gaging stations located upstream 

within the Mississippi River Basin. The likelihood of 

extremely low flows was estimated by a superposition method; 

5,776 synthetic hydrographs were computed resulting in a 

minimum synthetic low flow of 398 cubic feet per second at a 

probability of occurrence of 0.0002 per year. The greatest risk 

for such an event is in the late spring to early summer after a 

dry winter. The likelihood of a low flow of 660 cubic feet per 

second or less in any one year in the Mississippi River near 

Anoka is 0.01 (1 percent) annually. 

Low-flow conditions at the Mississippi River near 

Anoka, defined as the extended periods (at least 7 days) when 

all the daily flows were less than the 10th percentile of daily 

mean flows for the entire period of record, were associated 

with low-flow conditions at two or fewer of four upstream 

streamflow-gaging stations 42 percent of the time, indicating 

that sufficient water is available within the basin for many 

low-flow scenarios and the occurrence of extremely low flows 

is small. However, summer low-flow conditions at the Mississippi River near Anoka were almost always associated with 

low-stage elevations in three or more of the six upper basin 

reservoirs. 

The analysis of the upper basin streams indicates that 

they can be used as an indicator to whether or not the drought 

severity is regional or local. If all the upper basin streams 

have an occurrence of low flow and the Mississippi River near 

Anoka has an occurrence of low flow, the drought could be 

considered severe, with minimal rain in the basin for a long 

period of time. However, if the upper basin streams have no 

occurrence of low flow and the Mississippi River near Anoka 

does, the drought period would be less severe because rain 

events were occurring within the basins, but the events were 

not large enough to bring the Mississippi River near Anoka out 

of a low-flow condition. 

A water-surface profile of the Mississippi River between 

the confluence of the Crow River and St. Anthony Falls was 

completed using a real-time kinematic global positioning 

system. The water-surface profile was mapped and annotated 

with local landmarks. This was done so that water-use planners could relate free-board elevations of selected water utility 

structures to potential low-flow conditions. The data collected 

for the profile can be useful for low-flow water-surface profile 

models of the Mississippi River in that reach.

References Cited

Helsel, D.R., and Hirsch, R.M., 2002, Statistical methods in 

water resources: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 4, chap. A3, 522 p.

Metropolitan Council, 2007, Water supply planning in the 

Twin Cities metropolitan area—Report to the 2007 Minnesota State Legislature, accessed September 21, 2009, at 

http://www.metrocouncil.org/Environment/Watersupply/

documents/WaterSupplyReporttoLeg07_Final_web.pdf.

Ott, R.L., and Longnecker, M., 2001, An introduction to 

statistical methods and data analysis (5th ed.): Pacific 

Growth, Calif., Duxbury, 1,152 p.

Rutledge, A.T., 1998, Computer programs for describing the 

recession of ground-water discharge and estimating mean 

ground-water recharge and discharge from flow records—

Update: U.S. Geological Survey Water-Resources Investigations Report 98–4148, 43 p. (Also available at http://pubs.

usgs.gov/wri/wri984148/.)

TIBCO Software, Inc., 2008, TIBCO Spotfire S+ 8.1 for Windows: Palo Alto, Calif., TIBCO Software, Inc., 572 p.
14 Low-Flow Characteristics of the Mississippi River Upstream from the Twin Cities Metropolitan Area, Minnesota

Publishing support provided by:

Rolla and Denver Publishing Service Centers

For more information concerning this publication, contact:

Director, USGS Minnesota Water Science Center

2280 Woodale Drive

Mounds View, MN 55112

(763) 783-3100

Or visit the Minnesota Water Science Center Web site at:

http://mn.water.usgs.gov

Trimble, 2009, Trimble R4 GPS System Data Sheet, accessed 

August 16, 2010, at http://trl.trimble.com/docushare/

dsweb/Get/Document-468267/022543-490A_TrimbleR4_

DS_1109_LR.pdf.

U.S. Army Corps of Engineers, 2009, U.S. Army Corps of 

Engineers-St Paul District—Water Control Center, accessed 

May 13, 2009, at http://www.mvp-wc.usace.army.mil/.

U.S. Geological Survey, 2008, National Water Information System: U.S. Geological Survey Real-Time Data for 

USGS 05288500 Mississippi River near Anoka, Minnesota, 

accessed January 10, 2008, at http://waterdata.usgs.gov/mn/

nwis/uv/?site_no=05288500. 

Wood, L.C., and Hockens, S.N., 1970, Least squares smoothing operators: Geophysics, v. 35, no. 6, p. 1,005–1,019.

Kessler and Lorenz—Low-Flow Characteristics of the Mississippi River Upstream from the Twin Cities Metropolitan Area, Minnesota—SIR 2010–5163