U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2020–5016

Prepared in cooperation with the Lower Elkhorn Natural Resources District

Trends in Streamflow and Precipitation for Selected Sites in 

the Elkhorn River Basin and in Streamflow in the Salt Creek 

and Platte River Basins, Nebraska, 1961–2011
Cover. Photograph showing North Fork Elkhorn River near Pierce, Nebraska, downstream from the 

U.S. Geological Survey streamgage (station 06799100), taken November 4, 2014, by Brian Imig, 

U.S. Geological Survey. Stage 2.79 feet, discharge 64.7 cubic feet per second.
Trends in Streamflow and Precipitation for 

Selected Sites in the Elkhorn River Basin 

and in Streamflow in the Salt Creek and 

Platte River Basins, Nebraska, 1961–2011

By Benjamin J. Dietsch and Kellan R. Strauch

Prepared in cooperation with the Lower Elkhorn Natural Resources District

Scientific Investigations Report 2020–5016

U.S. Department of the Interior

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

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2020

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as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Dietsch, B.J., and Strauch, K.R., 2020, Trends in streamflow and precipitation for selected sites in the Elkhorn River 

Basin and in streamflow in the Salt Creek and Platte River Basins, Nebraska, 1961–2011: U.S. Geological Survey 

Scientific Investigations Report 2020–5016, 20 p., https://doi.org/10.3133/sir20205016.

ISSN 2328-0328 (online)
Contents

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

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

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

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

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

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

Streamflow Trends ................................................................................................................................4

Precipitation Trends .............................................................................................................................5

Residual Streamflow Trends ......................................................................................................5

Streamflow Trend Results ............................................................................................................................5

Synthesis of Trends in Streamflow ....................................................................................................9

Precipitation Trends ....................................................................................................................................14

Residual Streamflow Trends .............................................................................................................15

Summary........................................................................................................................................................18

References Cited..........................................................................................................................................19

Figures

1. Map showing the study area, U.S. Geological Survey and Nebraska 

Department of Natural Resources streamgages, and National Oceanic and 

Atmospheric Administration's precipitation stations used in this study in the 

Elkhorn River, Salt Creek, and Platte River Basins, Nebraska ..............................................3

2. Plots showing annual mean streamflow for selected streamgages in the 

Elkhorn River Basin, 1961–2011 ..................................................................................................8

3. Plots showing annual mean streamflow for selected U.S. Geological Survey 

streamgages in the Platte River and Salt Creek Basins, 1961–2011 ....................................9

4. Graphs showing annual water year precipitation composited for the areas 

upstream from four streamgages, 1961–2011 ........................................................................14

5. Plots showing annual-composited precipitation upstream from the streamgage 

and annual mean streamflow for four streamgages, 1961–2011 ........................................16

6. Plots showing June monthly composited precipitation upgradient of the 

streamgage and mean June streamflow for four streamgages, 1961–2011 .....................17

Tables

1. National Oceanic and Atmospheric Administration precipitation stations in or 

near the Elkhorn River Basin and selected streamgages in the Elkhorn River, 

Salt Creek, and Platte River Basins, Nebraska ........................................................................6

2. Percentage of Elkhorn River streamgage subbasins associated with each 

precipitation station .....................................................................................................................7

3. Trends in selected streamflow characteristics for study sites in the Elkhorn 

River, Salt Creek, and Platte River Basins, Nebraska, 1961–2011 ......................................10
iv

4. Comparison of streamflow trends for the complete period of record with trends 

for 1961–2011 at selected sites in the Elkhorn River, Salt Creek, and Platte River 

Basins, Nebraska ........................................................................................................................11

5. Effect of beginning year on trends in streamflow at selected sites in the Elkhorn 

River, Salt Creek, and Platte River Basins, Nebraska ...........................................................12

6. Monthly and annual trends in precipitation composited for the areas upstream 

from selected streamgages in the Elkhorn River Basin, Nebraska, 1961–2011 ...............15

7. Monthly and annual trends in precipitation-adjusted streamflow residuals for 

selected streamgages in the Elkhorn River Basin, Nebraska, 1961–2011 .........................18

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2)

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Datum

A water year begins October 1 of the previous calendar year and ends September 30 of the year 

of interest. Thus, the water year ending September 30, 2011, is called the “2011 water year.”

A climatic year begins April 1 and ends March 31 of the following year. A climatic year is 

designated by the calendar year during which most of the 12 months occur.

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

Abbreviations

LENRD Lower Elkhorn Natural Resources District

p-value probability value

R 

2 coefficient of determination

USGS U.S. Geological Survey
Trends in Streamflow and Precipitation for Selected Sites 

in the Elkhorn River Basin and in Streamflow in the Salt 

Creek and Platte River Basins, Nebraska, 1961–2011

By Benjamin J. Dietsch and Kellan R. Strauch

Abstract

To better understand the streamflow trends at the 

streamgages in the Elkhorn River Basin in Nebraska, the 

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

Lower Elkhorn Natural Resources District further investigated 

streamflow trends at the eight streamgages on the Elkhorn 

River, Salt Creek, and the Lower Platte River that indicated 

a positive trend in streamflow characteristics and analyzed precipitation trends in the four basins upstream from the Elkhorn 

River Basin streamgages. An analysis of four streamgages in 

the Elkhorn River Basin, one streamgage in Salt Creek Basin, 

and three streamgages in the Lower Platte River Basin that had 

previously indicated trends in selected annual mean streamflow, annual low flows, fall low flows, and growing season 

monthly mean streamflows metrics were analyzed for the 

period from 1961 to 2011. A streamgage in the Upper Elkhorn 

River Basin (Elkhorn River at Neligh, Nebraska [USGS station 06798500; maintained by USGS from water years 1930 

to 1993, maintained by Nebraska Department of Natural 

Resources from water years 1994 to 2019]) had significant 

positive trends in annual mean streamflow and insignificant trends for other streamflow metrics whereas the lower 

three sites (Logan Creek near Uehling, Nebr. [USGS station 06799500]; Maple Creek at Nickerson, Nebr. [USGS station 06800000]; and Elkhorn River at Waterloo, Nebr. [USGS 

station 06800500]) had significant positive trends for annual 

mean streamflow, for all durations of the annual low-flow 

periods (1-day, 2-day, 3-day, 7-day, 14-day, 30-day, 60-day, 

90-day, and 183-day periods), for all durations of the low-flow 

periods in October–November (1-day, 2-day, 3-day, 7-day, 

14-day, 30-day, and 60-day periods), and for monthly mean 

streamflow for July, August, and September. Upstream from 

the confluence of the Elkhorn River and the Platte River, the 

Platte River at North Bend, Nebr. (USGS station 06796000), 

streamgage indicated insignificant trends for most streamflow 

metrics. A streamgage in the Salt Creek Basin (Salt Creek at 

Greenwood, Nebr. [USGS station 06803555]) also indicated 

positive trends in some low-flows metrics. Streamflow at the 

Platte River at Louisville, Nebr. (USGS station 06805500), 

streamgage, downstream from the Salt Creek and Elkhorn 

River inflows, indicated significant positive trends in most 

annual and all October–November low flows and August mean 

streamflow but insignificant trends in annual mean streamflow 

and June, July, and September monthly mean streamflows. 

Streamflow records for the Platte River near Duncan, Nebr. 

(USGS station 06774000), streamgage only indicated a significant trend in the August mean streamflow; no other metrics 

had significant trends at the streamgage.

The trend analyses are sensitive to the period that is analyzed for trends. Sites with the most significant trends for lowflow metrics for the period 1961–2011 have fewer significant 

trends for low-flow metrics for the period after 1980–2011.

The results indicate that positive trends in low flows at 

the Salt Creek and Elkhorn River streamgages may be contributing to positive trends in low flows for the Platte River at 

Louisville, Nebr., streamgage. Likewise, streamflow in the Salt 

Creek and Elkhorn River Basins may be contributing to the 

positive trend in August mean streamflow for the Platte River 

at Louisville, Nebr., streamgage, three lower Elkhorn River 

streamgages, and the Salt Creek streamgage.

Precipitation was also examined as a primary cause for 

streamflow trends in the Elkhorn River Basin. For the four 

streamgages in the Elkhorn River Basin, relations between 

precipitation and streamflow were examined on an annual and 

monthly basis using linear regression. In general, the goodness of fit for the linear relations was poor with coefficient 

of determination values of less than or equal to 0.10 for four 

of the eight relations. Only one significant increase in annual 

precipitation upstream from the four streamgages and the 

frequent detection of significant increases in streamflow after 

removing the effect of precipitation indicate that other factors 

besides precipitation may have played a role in the significant 

positive trends in low-flow periods in the lower Elkhorn River 

and its tributaries.

Introduction

The sustainability of water resources in the Elkhorn 

River Basin is a critical issue for Nebraska (fig. 1). 

Understanding streamflow trends is important in determining 
2 Streamflow and Precipitation for the Elkhorn River Basin and Streamflow in the Salt Creek and Platte River Basins, Nebr.

the sustainable use of surface water and groundwater in the 

Elkhorn River Basin. Nebraska State Statute, section 46–713 

of the Ground Water Management and Protection Act 

(https://nebraskalegislature.gov/laws/ statutes.php?statute= 46- 

713), requires the Nebraska Department of Natural Resources 

to annually evaluate the expected long-term availability of 

hydrologically connected water supplies. This annual evaluation is required for every river basin, subbasin, or reach that 

has not previously been determined to be fully or overappropriated; at the present time (2020), an annual evaluation 

is required for the Elkhorn River Basin. As such, the Lower 

Elkhorn Natural Resources District (LENRD) is collecting 

data and developing water-management strategies to assist 

with water-resources planning. Specifically, the LENRD 

is concerned with the effect of groundwater withdrawal on 

the availability of surface water and the long-term effects of 

groundwater withdrawal on groundwater and surface-water 

resources.

Previously, the LENRD, the Upper Elkhorn Natural 

Resources District, and the U.S. Geological Survey (USGS) 

cooperatively studied trends in streamflow characteristics 

of streamgages in the Elkhorn River, Salt Creek, and Lower 

Platte River Basins to provide information for developing 

water-resources management and planning strategies (Dietsch 

and others, 2009). The study examined the contributions of 

streamflow from major tributaries (Elkhorn River and Salt 

Creek) to the Lower Platte River. The results of the study 

indicated positive (upward) temporal trends in streamflow for 

the period of record at eight streamgages. The trend analysis 

for the study was completed on the period of record at each 

streamgage; therefore, the period of analysis was not consistent from one streamgage to another. In addition, precipitation,

often the primary driver of streamflow, was not analyzed for 

trends as part of Dietsch and others (2009). Trends in precipitation that exist over the same period as trends in streamflow might indicate that streamflow trends are the result of 

changes in precipitation. To better understand the trends at 

the streamgages, in this present study, the USGS in cooperation with the LENRD further investigated streamflow trends 

at the eight streamgages on the Elkhorn River, Salt Creek, 

and the Lower Platte River Basins that indicated a positive 

trend in streamflow characteristics and analyzed precipitation in the four basins upstream from the Elkhorn River Basin 

streamgages.

Purpose and Scope

The purpose of this report is to present the trends in 

20 selected streamflow metrics (annual mean streamflow, 

annual low flows, fall low flows, and growing season monthly

mean streamflows) for four streamgages in the Elkhorn River 

Basin, one streamgage in the Salt Creek Basin, and three 

streamgages in the Platte River Basin for a common period 

(from 1961 to 2011). This report also describes the detection 

of streamflow trends on subsets of the period of record. In 

addition, the results of tests for trends in precipitation and for 

precipitation-adjusted streamflow in the basins are presented.

Study Area Description

The study area includes streamgages on the Elkhorn 

River (Elkhorn River at Neligh, Nebr. [USGS station 06798500; maintained by USGS from water years 1930 

to 1993, maintained by Nebraska Department of Natural 

Resources from water years 1994 to 2019]; Logan Creek 

near Uehling, Nebr. [USGS station 06799500]; Maple Creek 

near Nickerson, Nebr., [USGS station 06800000]; and 

Elkhorn River at Waterloo, Nebr. [USGS station 06800500]), 

Salt Creek (Salt Creek at Greenwood, Nebr. [USGS station 06803555]), and the Lower Platte River (Platte River 

near Duncan, Nebr. [USGS station 06774000]; Platte River 

at North Bend, Nebr. [USGS station 06796000]; and Platte 

River at Louisville, Nebr. [USGS station 06805500]; fig. 1). 

The confluences of the Elkhorn River and Salt Creek with 

the Platte River are within a reach of the Platte River that is 

important to instream flow rights (Nebraska Department of 

Natural Resources, 2013) and municipal water supplies (Steele 

and Verstraeten, 1999).

The Elkhorn River Basin is in northeastern Nebraska 

(fig. 1), within two distinct landforms—the migrating sand 

dunes to the west and the windblown loess deposits to the 

east (Bentall and others, 1971), and has a drainage area of 

5,870 square miles (mi2) at the USGS streamgage Elkhorn 

River at Waterloo, Nebr. The Elkhorn River flows eastsoutheast through the Sand Hills in north-central Nebraska and 

the glacial till of northeastern Nebraska and joins the Platte 

River about 20 miles (mi) downstream from Fremont, Nebr. 

(Bentall and others, 1971). The topography is characteristic 

of many basins in Nebraska, with a moderately flat surface 

near the stream transitioning to rolling hills and dunes or loess 

deposits at the basin margins. The Elkhorn River streamflow is 

fairly uniform throughout the year with base flow provided by 

groundwater; however, the possibility for large precipitation 

events in the spring, coupled with winter thaw and snowmelt runoff, can produce large rises in stream stage and large 

increases in streamflow. Logan Creek, a principal tributary 

of the Elkhorn River that drains much of the glaciated area 

of northeastern Nebraska, enters the Elkhorn River north of 

Fremont, Nebr. (fig. 1). The flow regimes of the eastern and 

western parts of the Elkhorn River Basin contrast because of 

the differences in the sediment composition and the positive (increasing) gradient of precipitation from west to east 

(Bentall and others, 1971). Streamflows in the Sand Hills or 

western part of the Elkhorn River Basin, which is characterized by extremely permeable sediments, are derived primarily 

from groundwater as base flow. In contrast, streamflows in 

the eastern part of the Elkhorn River Basin, where loesscapped glacial deposits generally are less permeable, are more 
Study Area Description 3

X

X

X

X

X

X

X

X

X

X X

X

X

X

X

X

X

X

X

#

#

#

#

#

#

#

# !

!

!

!

!

Duncan

Ainsworth

Norfolk

Fremont

Ashland

North 

Bend

Platte River Basin

Elkhorn River Basin

−99° −98° −97° −96°

43°

42°

41°

0 200 400 800 MILES

0 200 400 600

600

800 KILOMETERS

SOUTH DAKOTA

NEBRASKA

IOWA

Base modified from U.S. Geological Survey and U.S. Department of Agriculture digital data, various scales, various dates

Universal Transverse Mercator projection, Zone 14 N.

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

Fremont

Columbus 3 NE

Burwell

O Neill

Ewing

Neligh

Elgin

Oakdale

Creighton

Bloomfield Newcastle

Wayne

Emerson

Walthill

Tekamah

West Point

Wakefield

06803555

06774000

06798500

06805500

06800500

06796000

06800000

06799500

South Fork Elkhorn River

North Fork Big Nemaha River

Little Nemaha River

Platte River

Loup River

Clearwater Creek

Logan Creek

Wahoo Creek

Little Blue River

Maple Creek

Elkhorn River

UnionCr eek

West Fork Big Blue River

Little Blue River

Holt Cr eek

Niobrara River

Missouri River

Missouri River

Willow Creek

Middle Loup River

South Loup River

North Loup River

North Fork Elkhorn River

EXPLANATION

Sand Hills—Adapted from U.S. Soil Conservation

Service, 1970, 1:2,000,000

Glaciated till—Conservation and Survey Division, 

University of Nebraska–Lincoln, 2019

Basin boundary

Streamgage and station number

X Precipitation station and name Fremont

# 06774000

Surficial geology

SD 

WY

MN

IA

MO

NE

KS CO

Study area

Figure 1. Study area, U.S. Geological Survey and Nebraska Department of Natural Resources streamgages, and National Oceanic 

and Atmospheric Administration's precipitation stations used in this study in the Elkhorn River, Salt Creek, and Platte River Basins, 

Nebraska.
4 Streamflow and Precipitation for the Elkhorn River Basin and Streamflow in the Salt Creek and Platte River Basins, Nebr.

variable and responsive to precipitation events. Surface-water 

use in the Elkhorn River Basin includes irrigation, livestock, 

and recreational supplies. Extensive straightening on the 

Elkhorn River and some of its tributaries, including Logan 

Creek and Maple Creek, from the 1910s through the 1960s 

contributed to streambed adjustments of as much as 10 feet 

(ft) of degradation in some parts of the basin (Rus and others, 2003).

Salt Creek, whose confluence with the Platte River is 

about 7 mi downstream from the confluence of the Elkhorn 

and Platte Rivers (fig. 1), flows north to northeast through 

southeastern Nebraska. The 1,650-mi2 Salt Creek Basin generally slopes from southwest to northeast. Wahoo Creek, a principal tributary of Salt Creek, enters Salt Creek near Ashland, 

or upstream from the confluence with the Platte River. The 

Platte River is a braided stream that begins at the confluence of the North Platte and South Platte Rivers near North 

Platte, Nebr. (not shown), and has a drainage area of about 

71,000 mi2 at the Platte River at Louisville, Nebr., streamgage 

(fig. 1).

Previous Studies

Several investigations of annual mean streamflow trends 

have been completed on nationwide and regional scales (Lins 

and Slack, 1999; McCabe and Wolock, 2002). Results of 

these studies indicated positive (upward) trends in median 

and low flows in the upper Midwest, including the Elkhorn 

River Basin.

Dietsch and others (2009) detected increases in annual 

mean streamflow, monthly streamflows, and low flows by 

applying the Kendall’s tau nonparametric test at selected sites 

within the Elkhorn River Basin. The increases in annual mean 

streamflow conflicted with similar studies to detect trends at 

streamgages in Nebraska (Wen and Chen, 2006). However, 

different periods were used for the Wen and Chen (2006)

analysis, and the probability values for three streamgages in 

the Elkhorn River Basin (Logan Creek near Uehling, Nebr.; 

Maple Creek near Nickerson, Nebr.; and Elkhorn River at 

Waterloo, Nebr.) were characterized as having insignificant 

trends because each of the three streamgages had probability 

(p) values within 0.024 of the significance level (0.05). Wen 

and Chen (2006) also investigated trends in annual mean 

streamflows by adjusting for annual precipitation; however, 

analysis was limited to the Republican River (not shown).

More recent research (Norton and others, 2014) indicated 

that sites in the western and southern parts of the Missouri 

River Basin (not shown) had downward trends in annual mean 

streamflow, whereas the eastern part of the Missouri River 

Basin, including the Elkhorn River Basin, had positive trends 

in streamflow. Trends in precipitation and the possible effects 

on streamflow trends have not been investigated in detail for 

the Elkhorn River Basin.

Methods

Trends in long-term streamflow at the eight sites were 

assessed using Kendall’s tau test, a nonparametric method 

to detect trends in time-series data (Helsel and Hirsch, 

1992). The four streamgages in the Elkhorn River Basin 

were selected because the previous studies (see “Previous 

Studies” section of this report) indicated trends in at least one 

streamflow metric, and because each streamgage represents 

a major subbasin (with the exception of Elkhorn River at 

Waterloo, Nebr., which integrates flows from the basin). The 

streamgages on the Platte River and Salt Creek that are near 

the Elkhorn River’s confluence with the Platte River were 

included to expand on the analysis done in previous studies 

and to determine if significant trends in the Lower Platte River 

were concurrent with trends in the major Lower Platte River 

tributaries. A total of 20 streamflow metrics were tested in this 

study: annual mean streamflow, 1-day low flow, 2-day low 

flow, 3-day low flow, 7-day low flow, 14-day low flow, 30-day 

low flow, 60-day low flow, 90-day low flow, 183-day low 

flow, 1-day low flow (October–November), 3-day low flow 

(October–November), 7-day low flow (October–November), 

14-day low flow (October–November), 30-day low flow 

(October–November), 60-day low flow (October–November), 

June mean flow, July mean flow, August mean flow, and 

September mean flow.

National Oceanic and Atmospheric Administration’s 

meteorological data for U.S. Climate Reference Network precipitation stations (Diamond and others, 2013) were compiled 

for 18 long-term precipitation stations in the study area that 

were in or near the Elkhorn River Basin (fig. 1; table 1). Daily 

precipitation data for 1961–2011 from the precipitation stations were obtained from the U.S. Climate Reference Network 

(Diamond and others, 2013). The Kendall’s tau test was used 

to detect temporal trends in the time-series data representing 

precipitation in the area above each streamgage. The Kendall’s 

tau test was completed on annual and monthly mean precipitation data.

Streamflow Trends

Daily streamflow records were used to compute streamflow characteristics for eight long-term streamgages in the 

Elkhorn River Basin and adjacent basins. All eight of the 

streamgages (table 1) were established by the USGS before 

October 1, 1960, and were operated as continuous recording streamgages through 2011 or longer. Since 1994, the 

streamgage on the Elkhorn River at Neligh, Nebr., has been 

operated by the Nebraska Department of Natural Resources. 

Streamflow records are available through the USGS National 

Water Information System database (U.S. Geological 

Survey, 2017) and from the Nebraska Department of Natural 

Resources (Nebraska Department of Natural Resources, 

2017). Periods of streamgage operation ranged from 1896 to 

present (2020) in the Platte River and Elkhorn River Basins 
Streamflow Trend Results 5

and from the 1950s to present in the Salt Creek Basin. Periods 

of daily streamflow records at these sites ranged from 1928 

to 2013. The time frame used for trend analysis was limited 

to 1961–2011, which provided a common period of analysis 

across the streamgages. Daily streamflows were aggregated 

to monthly mean streamflows and annual mean streamflows. 

Additionally, low-flow characteristics were computed as the 

lowest mean streamflow over a specified number of consecutive days in a given period (n-day). Annual low-flow 

indices were computed for 1-, 2-, 3-, 7-, 14-, 30-, 60-, 90-, 

and 183-day intervals. Because low flows are common during the fall season, an additional set of low-flow indices was 

computed specifically for the bimonthly period of October–

November for 1-, 2-, 3-, 7-, 14-, 30-, and 60-day intervals.

The annual mean streamflows were computed using the 

water year. A water year begins October 1 of the previous calendar year and ends September 30 of the year of interest. The 

annual low flows (n-day) were computed using the climatic 

year, which begins April 1 and ends March 31. Climatic years 

typically are used in low-flow analyses because low flows in 

much of the United States are common in late summer and 

early fall, and the designation of the flow period by water year 

may separate one low-flow period into 2 water years.

Trends in long-term streamflow at the eight streamgages 

were assessed using Kendall’s tau test, a nonparametric 

method to detect trends in time-series data (Helsel and Hirsch, 

1992). The tau statistic is a measure of the level of monotonic positive (upward) or negative (downward) change in a 

dataset over time; a tau value of +1 indicates each element in 

the series is greater than the previous element in the series, 

and −1 indicates each element in the series is less than the 

previous element in the series. The probability that the tau 

test identifies a trend when none actually exists is represented by the p-value. For this study, a significance level of 

0.95 (p-value less than or equal to 0.05) was used to declare 

a trend. At each site, Kendall’s tau tests were completed for 

annual mean streamflows; monthly mean streamflows for 

June, July, August, and September; annual low flows (n-day); 

and bimonthly (October–November) low flows (n-day) for the 

period of 1961–2011.

Linear-regression analyses (using ordinary least-squares 

techniques) were used to estimate the trend slope in timeseries data for sites with significant temporal trends. This slope 

represents the median magnitude of the annual increase or 

decrease in the respective streamflow statistic over the period 

analyzed.

Precipitation Trends

NWS precipitation data were compiled for 18 long-term 

precipitation stations in the study area that were in or near 

the Elkhorn River Basin (fig. 1; table 1). Daily precipitation 

data for 1961–2011 from the stations were obtained from the 

U.S. Climate Reference Network (Diamond and others, 2013).

Using the data from the NWS precipitation stations, composite precipitation time series were created for the basins of 

the four streamgages in the Elkhorn River Basin. The Thiessen 

method (Linsley and others, 1982) was used to delineate the 

representative areas associated with each of the 18 NWS precipitation stations. The fractions of the Thiessen areas overlapping the drainage area of the four streamgages were used to 

compute areal weighting factors (table 2). The NWS precipitation data were then multiplied by those factors and summed to 

derive a composite rainfall time series for each streamgage.

The Kendall’s tau test was used to detect temporal trends 

in the composite time-series data representing precipitation 

in the drainage area upstream from each streamgage. The 

Kendall’s tau test was completed on annual and monthly mean 

precipitation data.

Residual Streamflow Trends

Linear-regression models were constructed to relate precipitation to streamflow. The annual or monthly precipitation 

value was fit to the log-transformed streamflow for the corresponding year using linear regression in the R statistical software (Venables and others, 2017). The residual annual mean 

streamflow was then computed by applying each precipitation 

time series (annual and monthly) as an input to the linear 

models to calculate a predicted streamflow; then, the predicted 

streamflow was subtracted from the observed streamflow to 

compute residual streamflow. The Kendall’s tau test was then 

applied to the resulting times series of residual values.

Streamflow Trend Results

Streamflow trends for a variety of flow periods at the 

eight streamgages for the 1961–2011 period are listed in 

tables 3, 4, and 5. Although five of the eight streamgages 

did not indicate significant trends in water year annual mean 

streamflow (figs. 2 and 3), significant trends in streamflow 

during low-flow periods or months during the growing season 

were detected at seven of the eight streamgages (table 3). All 

the significant trends in streamflow metrics were positive, 

indicating increases in streamflow over time.

All four streamgages in the Elkhorn River Basin had 

previously indicated positive trends in streamflows when computed for their periods of record (Dietsch and others, 2009). 

With a few exceptions, those trends were maintained when 

the analyses were constrained to the 1961–2011 period for 

this study (table 3). Annual mean streamflows at the Elkhorn 

River at Neligh, Nebr., streamgage indicated a significant 

positive trend, but trends during low-flow periods or in growing season monthly mean streamflow were not significant. 

This finding is in contrast to similar analyses done for the 

1931–2003 period that identified positive trends in several 

low-flow characteristics at this site (Dietsch and others, 2009). 

This finding is also in contrast to the fall low-flow trends and 
6 Streamflow and Precipitation for the Elkhorn River Basin and Streamflow in the Salt Creek and Platte River Basins, Nebr.

growing season monthly mean streamflow trends detected for 

the other three streamgages in the Elkhorn River Basin for 

this study. Trends in annual mean streamflows were detected 

for the Logan Creek near Uehling, Nebr., and Elkhorn River 

at Waterloo, Nebr., streamgages but not for the Maple Creek 

near Nickerson, Nebr., streamgage. Trend analyses indicated 

significant positive trends at the Logan Creek near Uehling, 

Nebr.; Maple Creek near Nickerson, Nebr.; and Elkhorn River 

at Waterloo, Nebr., streamgages for all the annual low-flow 

indices, all the fall low-flow indices, and the monthly mean 

streamflow for July, August, and September (table 3).

Streamflow records for the Platte River near Duncan, 

Nebr., and the Platte River at North Bend, Nebr., streamgages 

did not indicate significant trends in annual mean streamflow (table 3). Both streamgages incorporate the hydrologic 

responses of the Platte River upstream from the Elkhorn 

River confluence, but the Platte River at North Bend, Nebr., 

streamgage also includes responses of the Loup River, a major 

tributary to the Platte River. The Platte River near Duncan, 

Nebr., and the Platte River at North Bend, Nebr., streamgages 

indicated no significant trends in most of the annual lowflow characteristics; however, a significant positive trend 

Table 1. National Oceanic and Atmospheric Administration precipitation stations in or near the Elkhorn River Basin and selected 

streamgages in the Elkhorn River, Salt Creek, and Platte River Basins, Nebraska.

[Nebr., Nebraska; --, no data]

Shortened name or station number (fig. 1) Name Basin

U.S. Climate Reference Network precipitation stations1

Columbus 3 NE COLUMBUS 3 NE US --

Tekamah TEKAMAH NE US --

Ainsworth AINSWORTH NE US --

Fremont FREMONT NE US --

Oakdale OAKDALE NE US --

Elgin ELGIN NE US --

Wakefield WAKEFIELD NE US --

Burwell BURWELL NE US --

Walthill WALTHILL NE US --

Emerson EMERSON NE US --

Ewing EWING NE US --

O Neill O NEILL NE US --

West Point WEST POINT NE US --

Wayne WAYNE NE US --

Neligh NELIGH NE US --

Creighton CREIGHTON NE US --

Newcastle NEWCASTLE NE US --

Bloomfield BLOOMFIELD NE US --

U.S. Geological Survey and Nebraska Department of Natural Resources streamgages

06774000 Platte River near Duncan, Nebr.2 Platte

06796000 Platte River at North Bend, Nebr.2 Platte

06798500 Elkhorn River at Neligh, Nebr.3 Elkhorn

06799500 Logan Creek near Uehling, Nebr.2 Elkhorn

06800000 Maple Creek near Nickerson, Nebr.2 Elkhorn

06800500 Elkhorn River at Waterloo, Nebr.2 Elkhorn

06803555 Salt Creek at Greenwood, Nebr.2 Salt

06805500 Platte River at Louisville, Nebr.2 Platte

1Precipitation station data from U.S. Climate Reference Network (Diamond and others, 2013).

2Streamgage data from the U.S. Geological Survey.

3Streamgage operated by U.S. Geological Survey from water years 1930 to 1993, maintained by Nebraska Department of Natural Resources from water years 

1994 to 2019.
Streamflow Trend Results 7

was detected for August mean streamflows. No trends were 

detected in the fall low-flow statistics at either streamgage. 

August mean streamflows at both sites indicated a significant 

positive trend. Monthly mean streamflows in June, July, and 

September were insignificant for the Platte River near Duncan, 

Nebr., and the Platte River at North Bend, Nebr., streamgages.

Annual mean streamflow at the Salt Creek at Greenwood, 

Nebr., streamgage, which is on a tributary of the Platte River 

that enters downstream from the Elkhorn River and contributes to streamflows at the Platte River at Louisville, Nebr., 

streamgage, did not have a significant trend for the period 

(table 3). However, significant positive trends were indicated 

for all the low-flow periods. Of the monthly mean streamflows 

during the growing season, only August had a significant positive trend for the Salt Creek at Greenwood, Nebr., streamgage.

The Platte River at Louisville, Nebr., streamgage, which 

is downstream from all major tributaries, including the 

Elkhorn River and Salt Creek, integrates the streamflow trends 

from all the upstream sites. Annual mean streamflow at the 

Platte River at Louisville, Nebr., streamgage did not have a 

significant trend for the period (table 3); however, significant 

positive trends are indicated for most annual and all October–

November low-flow periods. Monthly mean streamflows 

during the growing season in August had a significant positive trend, whereas streamflows for June, July, and September 

were not significant at the Platte River at Louisville, Nebr., 

streamgage.

Significant trends over a full period of record for a 

streamgage were compared to the 1961–2011 period (table 4). 

For the 20 streamflow metrics tested in this study, most trends 

that were significant for the full period of record were also 

significant for the 1961–2011 period. Of the trends that were 

different, depending on the analysis period, all but one trend 

was significant for the full period and insignificant for the 

1961–2011 period. The remaining trend indicated insignificant 

trends for the full period of record but significant trends for 

1961–2011. A description of the changes in significance status 

follows. For three streamgages (Maple Creek near Nickerson, 

Nebr.; Salt Creek at Greenwood, Nebr.; and Platte River at 

Louisville, Nebr.), a positive significant trend in annual mean 

streamflows was indicated for the full period of record; however, when the period of analysis was limited to 1961–2011, 

Table 2. Percentage of Elkhorn River streamgage subbasins associated with each precipitation station.

[Nebr., Nebraska; GHCND, Global Historical Climatology Network Daily]

Precipitation station U.S. Geological Survey and Nebraska Department of Natural Resources streamgages 

and station numbers

Station number Short name

(fig. 1)

Elkhorn River at 

Neligh, Nebr., 

station 067985001

Logan Creek near 

Uehling, Nebr., 

station 067995002

Maple Creek near 

Nickerson, Nebr., 

station 068000002

Elkhorn River at 

Waterloo, Nebr., 

station 068005002

GHCND:USC00256135 Oakdale 0.1 11.1 0 0

GHCND:USC00259200 West Point 0 13.7 13 39.2

GHCND:USC00251990 Creighton 0 2.9 0 0

GHCND:USC00255830 Neligh 4.7 3.6 0 0

GHCND:USC00252595 Elgin 7.8 2.7 0 0

GHCND:USC00259045 Wayne 0 13.9 38.5 0

GHCND:USC00258935 Walthill 0 1.9 12.4 0

GHCND:USC00258915 Wakefield 0 2.7 16.5 0

GHCND:USC00253050 Fremont 0 5.2 0 12.6

GHCND:USC00258480 Tekamah 0 2.5 1.7 0

GHCND:USC00251825 Columbus 3 NE 0 6.7 0 48.2

GHCND:USC00250945 Bloomfield 0 3.2 3.2 0

GHCND:USC00251345 Burwell 5.8 1.8 0 0

GHCND:USC00255895 Newcastle 0 1 6.9 0

GHCND:USC00250050 Ainsworth 19.4 6.2 0 0

GHCND:USC00252805 Ewing 20.2 6.4 0 0

GHCND:USC00252715 Emerson 0 1.1 7.8 0

GHCND:USC00256290 O Neill 42 13.4 0 0

1Streamgage operated by the U.S. Geological Survey from water years 1930 to 1993, maintained by Nebraska Department of Natural Resources from water 

years 1994 to 2019.

2Streamgage data from the U.S. Geological Survey.
8 Streamflow and Precipitation for the Elkhorn River Basin and Streamflow in the Salt Creek and Platte River Basins, Nebr.

the trends were insignificant. For three streamgages (Elkhorn 

River at Neligh, Nebr.; Logan Creek near Uehling, Nebr.; and 

Elkhorn River at Waterloo, Nebr.), a positive significant trend 

in annual mean streamflows was indicated for the full period 

of record and the 1961–2011 period. For fall low-flow periods, 

trends that were significant for the full period of record were 

also significant for the 1961–2011 period with exceptions at 

three sites (Elkhorn River at Neligh, Nebr.; Platte River at 

North Bend, Nebr.; and Platte River near Duncan, Nebr.). At 

the Elkhorn River at Neligh, Nebr., streamgage, all fall lowflow metrics indicated significant trends for the full period of 

record but no significant trends for 1961–2011. At the Platte 

River at North Bend, Nebr., streamgage, October–November 

low-flow periods except the 1-day low flow indicated significant trends for the full period of record but no significant 

trends for 1961–2011. The streamflow record for the Platte 

River near Duncan, Nebr., streamgage indicated significant 

positive trends in all low flows and in all October–November 

low-flow durations over the full period of record but no significant trends for 1961–2011, with the exception of August 

monthly mean streamflow.

The starting year of the period for trend analysis was 

varied to further examine whether trends were evenly distributed over time or streamflows changed during more distinct 

periods. Kendall’s tau was calculated for streamflow characteristics on progressively shorter periods ending in 2011. 

A procedure was followed whereby the starting year of the 

period analyzed was advanced 1 year and Kendall’s tau was 

computed. This procedure was done such that Kendall’s tau 

was computed for the periods of 1961–2011, 1962–2011, 

100

1,000

10,000

 1960 1970 1980 1990 2000 2010 2020

10

100

1,000

 1960 1970 1980 1990 2000 2010 2020

1

10

100

1,000

 1960 1970 1980 1990 2000 2010 2020

Annual mean streamflow, in cubic feet per second

Water year

100

1,000

10,000

 1960 1970 1980 1990 2000 2010 2020

A. 06798500 B. 06799500

C. 06800000 D. 06800500

EXPLANATION

Observed, annual

Figure 2. Plots of annual mean streamflow for selected streamgages in the Elkhorn River Basin, 1961–2011. A, Nebraska 

Department of Natural Resources Elkhorn River at Neligh, Nebraska (station 06798500); B, U.S. Geological Survey Logan Creek 

near Uehling, Nebr. (station 06799500); C, U.S. Geological Survey Maple Creek near Nickerson, Nebr. (station 06800000); D, U.S. 

Geological Survey Elkhorn River at Waterloo, Nebr. (station 06800500).
Streamflow Trend Results 9

1963–2011, and so on until the period of 2001–11 was examined. Periods shorter than 2001–11 were considered to be too 

short for the Kendall’s tau analysis. The results of the progressive shortening of the period of analysis indicate that many of 

the stream characteristics with significant trends for the period 

of 1961–2011 become insignificant for the period from about 

1974 to 1977 through 2011 (table 5).

Synthesis of Trends in Streamflow

The annual mean streamflow trends for the eight sites 

in this study agree with the findings of McCabe and Wolock 

(2002) and Norton and others (2014), which were significant 

positive (upward) trends in annual, seasonal, and monthly 

streamflow. Wen and Chen (2006) determined no significant 

trends in the Elkhorn River Basin for the period of 1960 to 

2003 for annual mean streamflows; however they reported 

p-values close to significance for three of the streamgages in 

this study (Logan Creek near Uehling, Nebr.; Maple Creek 

near Nickerson, Nebr.; and Elkhorn River at Waterloo, Nebr.).

For most streamflow metrics at most sites in this study, 

significant trends do not become insignificant or negative 

(downward) if the period of record is contracted from the full 

period of record to 1961–2011(table 5). Annual and low-flow 

trends tend to become insignificant after about the mid-1970s 

for streamgages in the lower Elkhorn River Basin (table 5). 

This finding indicates that in the 20-year period before about 

1980, the streams in this study carried less streamflow during 

low-flow periods than in the 30 years after.

100

1,000

10,000

 1960 1970 1980 1990 2000 2010 2020

B. Observed (06796000)

1,000

10,000

100,000

 1960 1970 1980 1990 2000 2010 2020

100

1,000

10,000

 1960 1970 1980 1990 2000 2010 2020

A. Observed (06774000)

C. Observed (06803555) D. Observed (06805500)

Annual mean streamflow, in cubic feet per second

1,000

10,000

100,000

 1960 1970 1980 1990 2000 2010 2020

Water year

EXPLANATION

Observed, annual

Figure 3. Plots of annual mean streamflow for selected U.S. Geological Survey streamgages in the Platte River and Salt 

Creek Basins, 1961–2011. A, Platte River near Duncan, Nebraska (station 06774000); B, Platte River at North Bend, Nebr. (station 

06796000); C, Salt Creek at Greenwood Nebr. (station 06803555); D, Platte River at Louisville, Nebr. (station 06805500).
Table 3. Trends in selected streamflow characteristics for study sites in the Elkhorn River, Salt Creek, and Platte River Basins, Nebraska, 1961–2011. [Significant trends had probability values less than or equal to 0.05; Oct., October; Nov., November; Nebr., Nebraska; I, insignificant trend; P, significant trend] U.S. Geological Survey and Nebraska Department of Natural Resources streamgages Period analyzed

Water year annual mean streamflowClimatic year annual low flows Fall low flows 

1-day low flow

2-day low flow

3-day low flow

7-day low flow

14-day low flow

30-day low flow

60-day low flow

90-day low flow

183-day low flow

1-day low flow (Oct.–Nov.)

3-day low flow (Oct.–Nov.)

7-day low flow (Oct.–Nov).

14-day low flow (Oct.–Nov.)

30-day low flow (Oct.–Nov.)

60-day low flow (Oct.–Nov.)

06774000 Platte River near 

Duncan, Nebr1.

1961–2011 I I I I I I I I I I I I I I I I 

06796000 Platte River at North 

Bend, Nebr.1

1961–2011 I I I I I P P P I I I I I I I I 

06798500 Elkhorn River at 

Neligh, Nebr.2

1961–2011 P I I I I I I I I I I I I I I I 

06799500 Logan Creek near 

Uehling, Nebr.1

1961–2011 P P P P P P P P P P P P P P P P 

06800000 Maple Creek near 

Nickerson, Nebr.1

1961–2011 I P P P P P P P P P P P P P P P 

06800500 Elkhorn River at 

Waterloo, Nebr.1

1961–2011 P P P P P P P P P P P P P P P P 

06803555 Salt Creek at 

Greenwood, Nebr.1

1961–2011 I P P P P P P P P P P P P P P P 

06805500 Platte River at 

Louisville, Nebr.1

1961–2011 I P P P P I I P I P P P P P P P 

1Streamgage data from the U.S. Geological Survey.2Streamgage operated by the Nebraska Department of Natural Resources.
Table 4. Comparison of streamflow trends for the complete period of record with trends for 1961–2011 at selected sites in the Elkhorn River, Salt CreNebraska.[Significant trends had probability values less than or equal to 0.05; red shading indicates the period of record had a significant trend but 1961–2011 indicated an insignificant treperiod of record had an insignificant trend but 1961–2011 indicated a significant positive trend; Oct., October; Nov., November; Nebr., Nebraska; I, insignificant trend; P, signififor period of record analysis (X) and 1961–2011 analysis (Y)]

U.S. Geological Survey and 

Nebraska Department of Natural 

Resources streamgages

Period 

of record 

analyzed

Water year annual mean streamflowClimatic year annual low flows Fall low flows 

1-day low flow

2-day low flow

3-day low flow

7-day low flow

14-day low flow

30-day low flow

60-day low flow

90-day low flow

183-day low flow

1-day low flow (Oct.–Nov.)

3-day low flow (Oct.–Nov.)

7-day low flow (Oct.–Nov.)

14-day low flow (Oct.–Nov.)

30-day low flow (Oct.–Nov.)

60-day low flow (Oct.–Nov.)

06774000 Platte River near 

Duncan, Nebr.1

1929–2011 I–I P–I P–I P–I P–I P–I P–I P–I P–I P–I P–I P–I P–I P–I P–I P–I 

06796000 Platte River at North 

Bend, Nebr.1

1950–2011 I–I I–I I–I I–I I–I I–P P–P P–P I–I P–I I–I P–I P–I P–I P–I P–I 

06798500 Elkhorn River at 

Neligh, Nebr.2

1931–2011 P–P P–I P–I P–I P–I P–I P–I P–I P–I P–I P–I P–I P–I P–I P–I P–I 

06799500 Logan Creek near 

Uehling, Nebr.1

1942–2011 P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P 

06800000 Maple Creek near 

Nickerson, Nebr.1

1952–2011 P–I P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P 

06800500 Elkhorn River at 

Waterloo, Nebr.1

1929–2011 P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P 

06803555 Salt Creek at 

Greenwood, Nebr.1

1952–2011 P–I P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P P–P 

06805500 Platte River at 

Louisville, Nebr.1

1954–2011 P–I P–P P–P P–P P–P P–I P–I P–P P–I P–P P–P P–P P–P P–P P–P P–P 

1Streamgage data from the U.S. Geological Survey.2Streamgage operated by U.S. Geological Survey from water years 1930 to 1993, maintained by Nebraska Department of Natural Resources from water years 1994 to 2019.
Table 5. Effect of beginning year on trends in streamflow at selected sites in the Elkhorn River, Salt Creek, and Platte River Basins, Nebraska. [Period of analysis beginning in year indicated through 2011; low-flow periods use the climatic water year; annual mean flow periods are in water years; significant trends are shnificant trend with probability (p) value greater than 0.05; S, significant trend with p-value less than or equal to 0.05] Period Year

1961

1962

1963

1964

1965

1966

1967

1968

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

Platte River near Duncan, Nebr. (U.S. Geological Survey station 06774000)

1-day low flow I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 

7-day low flow I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 

30-day low flow I I I I I I I I I I I I I I I I I I I I I S S I I I I I I I I I I I 

Annual mean flow I I I I I I I I I I I I I I I I I I I I S S S I I I I I I I I I I I 

Platte River at North Bend, Nebr. (U.S. Geological Survey station 06796000)

1-day low flow I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 

7-day low flow I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 

30-day low flow S S S S S S S S S I I I I I I I I I I I I I I I I I I I I I I I I I 

Annual mean flow I I I I I I I I I I I I I I I I I I I I S S S I I I I I I I I I I I 

Elkhorn River at Neligh, Nebr. (Nebraska Department of Natural Resources streamgage; U.S. Geological Survey station 06798500)

1-day low flow S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S 

7-day low flow I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 

30-day low flow I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 

Annual mean flow I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 

Logan Creek near Uehling, Nebr. (U.S. Geological Survey station 06799500)

1-day low flow S S S S S S S S S S S S S S S S S S S S S S S S I I S S S I I I I I 

7-day low flow S S S S S S S S S S S S S S S S S S S S S S S I I I S S I I I I I I 

30-day low flow S S S S S S S S S S S S S S S S S S S S S I I I I I I I I I I I I I 

Annual mean flow S S S S S S S S S S S S S S S S I I I I I I I I I I I I I I I I I I 

Maple Creek near Nickerson, Nebr. (U.S. Geological Survey station 06800000)

1-day low flow S S S S S S S S S S S S S S S S S I I I I I I I I I I I I I I I I I 

7-day low flow S S S S S S S S S S S S S S S S S I I I I I I I I I I I I I I I I I 

30-day low flow S S S S S S S S S S S S S S S S I I I I I I I I I I I I I I I S S S 

Annual mean flow I S I I S S S S I I I I I I I I I I I I I I I I I I I I I I I S I I 
Table 5. Effect of beginning year on trends in streamflow at selected sites in the Elkhorn River, Salt Creek, and Platte River Basins, Nebraska.—Cont[Period of analysis beginning in year indicated through 2011; low-flow periods use the climatic water year; annual mean flow periods are in water years; significant trends are shnificant trend with probability (p) value greater than 0.05; S, significant trend with p-value less than or equal to 0.05]

Period

Year

1961

1962

1963

1964

1965

1966

1967

1968

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

Elkhorn River at Waterloo, Nebr. (U.S. Geological Survey station 06800500)

1-day low flow S S S S S S S S S S S S S S S S I I I I I I I I I I I I I I I I I I 

7-day low flow S S S S S S S S S S S S S S S S I I I I I I I I I I I I I I I I I I 

30-day low flow S S S S S S S S S S S S S S S S I I I I I I I I I I I I I I I I I I 

Annual mean flow I S I I S S S S I I I I I I I I I I I I I I I I I I I I I I I S I I 

Salt Creek at Greenwood, Nebr. (U.S. Geological Survey station 06803555)

1-day low flow S S S S S S S S I I I I I I I I I I I I I I I I I I I I I I I I I I 

7-day low flow S S S S S S S I I I I I I I I I I I I I I I I I I I I I I I I I I I 

30-day low flow S S S S S S S I I I I I I I I I I I I I I I I I I I I I I I I I I I 

Annual mean flow I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 

Platte River at Louisville, Nebr. (U.S. Geological Survey station 06805500)

1-day low flow S S S S S S S S S S S S S S I I I I I I I I I I I I I I I I I I I I 

7-day low flow S S S S S S S S S S S S S S I I I I I I I I I I I I I I I I I I I I 

30-day low flow I I S I I I S I I I I I I I I I I I I I I I I I I I I I I I I I I I 

Annual mean flow I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 

1Streamgage operated by U.S. Geological Survey from water years 1930 to 1993, maintained by Nebraska Department of Natural Resources from water years 1994 to 2019.
14 Streamflow and Precipitation for the Elkhorn River Basin and Streamflow in the Salt Creek and Platte River Basins, Nebr.

Precipitation Trends

Precipitation was examined as a primary cause for 

streamflow trends for the period 1961–2011. Composite 

precipitation data series upstream from each of the four 

streamgages in the Elkhorn River Basin (Elkhorn River at 

Neligh, Nebr.; Logan Creek near Uehling, Nebr.; Maple Creek 

near Nickerson, Nebr.; and Elkhorn River at Waterloo, Nebr.) 

were synthesized by computing an area-weighted mean of 

volumes reported from precipitation stations in and around 

the study area and were summarized for each month or year 

(fig. 4). Of the four sites, only the Elkhorn River at Neligh, 

Nebr., streamgage indicated a significant increase in annual 

precipitation (table 6). When the data were separated into 

monthly precipitation, few trends were indicated; only 4 of 

the 48 site-month combinations indicated significant trends 

(table 6).

For the four streamgages in the Elkhorn River Basin, 

relations between precipitation and streamflow were examined on an annual and monthly basis using linear regression. 

Linear models were developed in the R statistical software 

(Venables and others, 2017) between the annual-composited 

precipitation and a logarithmic transformation of annual 

mean streamflow (fig. 5). Similarly, linear models compared 

the monthly composited precipitation time series against the 

logarithmically transformed streamflow for the same month 

over the 1961–2011 period (fig. 6). In general, the goodnessof-fit values for the linear relations were poor and coefficient 

0

5

10

15

20

25

30

35

40

45

50

A. 06798500 B. 06799500

C. 06800000 D. 06800500

0

5

10

15

20

25

30

35

40

45

50

 1961 1971 1981 1991 2001 2011

Annual precipitation, in inches

Year

 1961 1971 1981 1991 2001 2011

EXPLANATION

Observed, annual

 1961 1971 1981 1991 2001 2011 1961 1971 1981 1991 2001 2011

Figure 4. Annual water year precipitation composited for the areas upstream from four streamgages, 1961–2011. 

A, Nebraska Department of Natural Resources Elkhorn River at Neligh, Nebraska (station 06798500); B, U.S. Geological 

Survey Logan Creek near Uehling, Nebr. (station 06799500); C, U.S. Geological Survey Maple Creek near Nickerson, Nebr. 

(station 06800000); D, U.S. Geological Survey Elkhorn River at Waterloo, Nebr. (station 06800500).
Precipitation Trends 15

of determination (R2) values were 0.10 or less in 50 percent 

of the relations. The relation with the overall highest R2 value 

was for July precipitation and streamflow at the Maple Creek 

near Nickerson, Nebr., streamgage with an R2 value of 0.58. 

For each of the remaining three streamgages (Logan Creek 

near Uehling, Nebr.; Elkhorn River at Neligh, Nebr.; and 

Elkhorn River at Waterloo, Nebr.), the highest goodness-of-fit 

values were for the June precipitation-streamflow relations (R2

values of 0.50, 0.20, and 0.42, respectively).

Residual Streamflow Trends

Though the relation of streamflow to precipitation is not 

well constrained, it is still desirable to remove the effect of 

precipitation on streamflow to identify the streamflow trends 

resulting from other factors. The linear models were used 

to remove the effect of precipitation from the flow data. For 

each precipitation time series (annual and for each calendar 

month), the precipitation was used as an input to the linear 

models to calculate a predicted streamflow; then, the predicted 

streamflow was subtracted from the observed streamflow to 

compute the residual streamflow. The Kendall’s tau test was 

then applied to the resulting times series of residual values. If 

the trend in the residual streamflow is significant and positive, it implies that something other than precipitation is 

causing that increase. Significant increases were detected for 

the annual mean streamflow residuals for the Logan Creek 

near Uehling, Nebr.; Maple Creek near Nickerson, Nebr.; and 

Elkhorn River at Waterloo, Nebr., streamgages. In general, 

monthly streamflow residuals indicated positive trends, 

with a greater frequency of those trends at the Logan Creek 

near Uehling, Nebr.; Maple Creek near Nickerson, Nebr.; 

and Elkhorn River at Waterloo, Nebr., streamgages than the 

Elkhorn River at Neligh, Nebr., streamgage (table 7). Only 

one significant increase in annual precipitation above the 

streamgages and the frequent detection of significant increases 

in streamflow after removing the effect of precipitation indicate that other factors besides precipitation may have played 

a role in the positive trends in low-flow periods in the lower 

Elkhorn River and its tributaries.

Table 6. Monthly and annual trends in precipitation composited for the areas upstream from selected streamgages in the Elkhorn 

River Basin, Nebraska, 1961–2011.

[The probability (p) value is shown in parentheses; P, significant positive (upward) trend with a p-value less than or equal to 0.05; I, insignificant trend with a 

p-value greater than 0.05]

Period

U.S. Geological Survey streamgages and station numbers

Elkhorn River at Waterloo, 

Nebr., station 06798500

Logan Creek near Uehling, 

Nebr., station 06799500

Maple Creek near Nickerson, 

Nebr., station 06800000

Elkhorn River at Waterloo, 

Nebr., station 06800500

Annual1 P (0.04) I (0.09) I (0.22) I (0.08)

January I (0.26) P (0.04) I (0.05) I (0.17)

February I (0.24) I (0.40) I (0.54) I (0.31)

March I (0.50) I (0.88) I (0.90) I (0.77)

April I (0.07) P (0.02) I (0.07) P (0.03)

May I (0.10) I (0.64) I (0.54) I (0.40)

June I (0.58) I (0.69) I (0.59) I (1.00)

July I (0.44) I (0.84) I (0.94) I (0.57)

August I (0.15) I (0.70) I (0.81) I (0.24)

September I (0.85) I (0.88) I (0.57) I (0.95)

October P (0.04) I (0.13) I (0.37) I (0.13)

November I (0.42) I (0.14) I (0.14) I (0.22)

December I (0.23) I (0.31) I (0.79) I (0.65)

1Computation based on water year. A water year begins October 1 of the previous calendar year and ends September 30 of the year of interest. Thus, the water 

year ending September 30, 2011, is called the “2011 water year.”
16 Streamflow and Precipitation for the Elkhorn River Basin and Streamflow in the Salt Creek and Platte River Basins, Nebr.

100

1,000

10,000

 14 16 18 20 22 24 26 28 30 32 34

10

100

1,000

 15 20 25 30 35 40 45

1

10

100

1,000

 15 20 25 30 35 40 45

Annual mean streamflow, in cubic feet per second

EXPLANATION

Observed, annual

Linear fit using a logarithmic 

transformation of streamflow

100

1,000

10,000

 16 18 20 22 24 26 28 30 32 34 36 38

A. 06798500 B. 06799500

C. 06800000 D. 06800500

Precipitation, in inches

R 2=0.44

R 2=0.37 R 2=0.16

R 2=0.37

[R 2

, coefficient of determination]

Figure 5. Plots of annual-composited precipitation upstream from the streamgage and annual mean streamflow for four streamgages, 

1961–2011. A, Nebraska Department of Natural Resources Elkhorn River at Neligh, Nebraska (station 06798500); B, U.S. Geological 

Survey Logan Creek near Uehling, Nebr. (station 06799500); C, U.S. Geological Survey Maple Creek near Nickerson, Nebr. (station 

06800000); D, U.S. Geological Survey Elkhorn River at Waterloo, Nebr. (station 06800500).
Precipitation Trends 17

R 2=0.20 R 2=0.50

R 2 R =0.42 2

=0.58

EXPLANATION

Observed, June

Linear fit using a logarithmic 

transformation of streamflow

[R 2, coefficient of determination]

100

1,000

10,000

 1 2 3 4 5 6 7 8 9

10

100

1,000

10,000

 0 2 4 6 8 10 12

1

10

100

1,000

10,000

 0 2 4 6 8 10 12 14

Monthly streamflow, in cubic feet per second

100

1,000

10,000

100,000

 1 2 3 4 5 6 7 8 9 10 11

A. 06798500 B. 06799500

C. 06800000 D. 06800500

Precipitation, in inches

Figure 6. Plots of June monthly composited precipitation upgradient of the streamgage and mean June streamflow for four 

streamgages, 1961–2011. A, Nebraska Department of Natural Resources Elkhorn River at Neligh, Nebraska (station 06798500); 

B, U.S. Geological Survey Logan Creek near Uehling, Nebr. (station 06799500); C, U.S. Geological Survey Maple Creek near Nickerson, 

Nebr. (station 06800000); D, U.S. Geological Survey Elkhorn River at Waterloo, Nebr. (station 06800500).
18 Streamflow and Precipitation for the Elkhorn River Basin and Streamflow in the Salt Creek and Platte River Basins, Nebr.

Summary

To better understand the streamflow trends at the 

streamgages on the Elkhorn River Basin, the U.S. Geological 

Survey (USGS), in cooperation with the Lower Elkhorn 

Natural Resources District, further investigated streamflow 

trends at the eight streamgages on the Elkhorn River, Salt 

Creek, and the Lower Platte River that indicated a positive 

trend in streamflow characteristics and analyzed precipitation 

trends in the four basins upstream from the Elkhorn River 

Basin streamgages. Trend analyses of four streamgages in 

the Elkhorn River Basin, one streamgage in the Salt Creek 

Basin, and three streamgages in the Platte River Basin that 

had previously indicated trends in various selected streamflow 

metrics (annual mean streamflow, annual low flows, fall low 

flows, and growing season monthly mean streamflows) were 

completed for the period from 1961 to 2011. One streamgage 

in the Elkhorn River Basin (Elkhorn River at Neligh, 

Nebraska [Nebraska Department of Natural Resources station 06798500]) had significant trends in annual mean streamflow but insignificant trends for other streamflow metrics, 

whereas the remaining three streamgage in the Elkhorn River 

Basin, all lower in the basin (Logan Creek near Uehling, Nebr. 

[USGS station 06799500]; Maple Creek at Nickerson, Nebr. 

[USGS station 06800000]; and Elkhorn River at Waterloo, 

Nebr. [USGS station 06800500]), had significant positive 

trends for annual mean streamflow, for all durations of the 

annual low-flow periods (1-day, 2-day, 3-day, 7-day, 14-day, 

30-day, 60-day, 90-day, and 183-day periods), for all durations 

of the low-flow periods in October–November (1-day, 2-day, 

3-day, 7-day, 14-day, 30-day, and 60-day periods), and for 

monthly mean streamflow for July, August, and September. 

Streamflow records for the Platte River near Duncan, Nebr. 

(USGS station 06774000), streamgage only indicated a significant trend in the August mean streamflow, no other metrics 

had significant trends at the streamgage.

Upstream from the confluence of the Elkhorn River and 

the Platte River, the Platte River at North Bend, Nebr. (USGS 

station 06796000), streamgage indicated insignificant trends 

for most streamflow metrics. Streamflows at the Salt Creek at 

Greenwood, Nebr. (USGS station 06803555), streamgage indicated positive trends in annual and October–November low 

flows and August mean streamflows but insignificant trends 

in annual mean streamflow and June, July, and September 

monthly mean streamflows. Streamflows at the Platte River 

at Louisville, Nebr. (USGS station 06805500), streamgage 

indicated significant positive trends in most annual and all 

October–November low flows and August mean streamflows 

but insignificant trends in annual mean streamflow and June, 

July, and September monthly mean streamflows.

The results indicate that positive trends in low flows in 

the Salt Creek and Elkhorn River streamgages may be contributing to positive trends in low flows for the Platte River at 

Louisville, Nebr., streamgage. Likewise, streamflow in the Salt 

Creek and Elkhorn River Basins may be contributing to the 

Table 7. Monthly and annual trends in precipitation-adjusted streamflow residuals for selected streamgages in the Elkhorn River 

Basin, Nebraska, 1961–2011.

[The probability (p) value is shown in parentheses; P, significant positive (upward) trend with a p-value less than or equal to 0.05; I, insignificant trend with a 

p-value greater than 0.05]

Period

U.S. Geological Survey streamgages and station numbers

Elkhorn River at Waterloo, 

Nebr., station 06798500

Logan Creek near Uehling, 

Nebr., station 06799500

Maple Creek near Nickerson, 

Nebr., station 06800000

Elkhorn River at Waterloo, 

Nebr., station 06800500

Annual1 P (0.01) P (0.00) P (0.02) P (0.00)

January P (0.01) P (0.00) P (0.01) P (0.00)

February I (0.09) P (0.01) I (0.26) I (0.07)

March I (0.36) I (0.13) I (0.56) I (0.50)

April I (0.20) P (0.00) P (0.01) P (0.02)

May P (0.05) P (0.00) P (0.01) P (0.00)

June P (0.03) P (0.00) I (0.12) P (0.00)

July P (0.00) P (0.00) P (0.00) P (0.00)

August I (0.13) P (0.00) P (0.00) P (0.01)

September I (0.10) P (0.00) P (0.00) P (0.01)

October I (0.15) P (0.00) P (0.04) P (0.01)

November P (0.05) P (0.00) P (0.00) P (0.00)

December P (0.01) P (0.00) P (0.00) P (0.00)

1Computation based on water year. A water year begins October 1 of the previous calendar year and ends September 30 of the year of interest. Thus, the water 

year ending September 30, 2011, is called the “2011 water year.”
References Cited 19

positive trend in August mean streamflow for the Platte River 

at Louisville, Nebr., streamgage, three lower Elkhorn River 

streamgages, and the Salt Creek streamgage.

The trend analyses are sensitive to the period that is analyzed for trends. Sites with the most significant trends for lowflow metrics for the period 1961–2011 have fewer significant 

trends for low-flow metrics for the period after 1980–2011. 

This result indicates that in the 20-year period before about 

1980, the streams in this study carried less streamflow during low-flow periods than in the 30 years after. Annual mean 

streamflow trends remain significant at the Logan Creek near 

Uehling, Nebr.; Maple Creek at Nickerson, Nebr.; and Elkhorn 

River at Waterloo, Nebr., streamgages when the record is 

shortened until about 1974–2011; thereafter, the annual 

mean streamflow generally becomes insignificant. Similarly, 

low-flow trends remain significant at the Logan Creek near 

Uehling, Nebr.; Maple Creek at Nickerson, Nebr.; and Elkhorn 

River at Waterloo, Nebr., streamgages when the record is 

shortened to about 1976–2011; thereafter, fewer trends are 

significant.

Precipitation was examined as a primary cause for 

streamflow trends. Composite precipitation data series 

upstream from each of the four streamgages in the Elkhorn 

Basin (Elkhorn River at Neligh, Nebr.; Logan Creek near 

Uehling, Nebr.; Maple Creek near Nickerson Nebr.; and 

Elkhorn River at Waterloo, Nebr.) were synthesized by 

computing an area-weighted mean of volumes reported from 

precipitation gages in and around the study area and were 

summarized for each month or year. Of the four sites, only 

Elkhorn River at Neligh, Nebr., indicated a significant increase 

in annual precipitation. In general, the goodness of fit for the 

linear relations was poor with coefficient of determination 

values of less than or equal to 0.10 for four of the eight relations. When separated into monthly precipitation, few trends 

were indicated, with only 4 of the 48 site-month combinations 

indicating significant trends. Only one significant increase in 

annual precipitation upstream from the streamgages and the 

frequent detection of significant increases in streamflow after 

removing the effect of precipitation indicate that other factors 

besides precipitation may have played a role in the positive 

trends in low-flow periods in the lower Elkhorn River and its 

tributaries.

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For more information about this publication, contact:

Director, USGS Nebraska Water Science Center 

5231 South 19th Street

Lincoln, NE 68512

402–328–4100

For additional information, visit: https://www.usgs.gov/centers/ne-water

Publishing support provided by the 

Rolla Publishing Service Center
Dietsch and Strauch—Streamflow and Precipitation for the Elkhorn River Basin and Streamflow in the Salt Creek and Platte River Basins, Nebr.—SIR 2020–5016

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20205016