Explanation base modified by Denver Water Board, 1998 From U. S. Geological Survey Digital Line Graphs, 100,000, 1981-1983 Roads and cities from Colorado Department of Transportation, 50,000, 1998



Download 69.27 Kb.
Date conversion14.05.2016
Size69.27 Kb.
U.S. Geological Survey streamflow site

and name


Precipitation site and name

Fountain Creek watershed boundary



EXPLANATION

Base modified by Denver Water Board, 1998

From U.S. Geological Survey Digital Line Graphs, 100,000, 1981-1983

Roads and cities from Colorado Department of Transportation, 50,000, 1998.

Albers Equal-Area projection

Standard parallels 37¡30' N and 40¡30' N

Central meridian 105¡30' W

PUEBLO COUNTY

EL PASO COUNTY

TELLER COUNTY

PUEBLO

Fountain Creek

Arkansas River

Colorado Springs

Fountain

Pueblo


Nevada

Street


Security

Pinon


Pueblo

Fort Carson

Military Reservation

SPRINGS

COLORADO

SPRINGS

Fountain Creek

Pikes Peak

Ruxton


Park

Near Colorado Springs



MANITOU

Pikeview


Monument Creek

MONUMENT

WOODLAND

PARK

Cottonwood Creek



PALMER LAKE

105¡ 104¡30'

38¡

52'


30"

38¡


30'

COLORADO


Pueblo

Grand Junction

Colorado Springs

Denver


STUDY AREA

0 5 10 15 MILES

0 5 10 15 KILOMETERS

Introduction

The Fountain Creek watershed drains about 930 square

miles of parts of Teller, El Paso, and Pueblo Counties in

southeastern Colorado (fig. 1). Land use within the watershed

includes forests, urban areas, military reservations,

agriculture, and rangeland. Forested lands are located

predominantly in the northwestern mountainous part of the

watershed. The major urban center in the watershed is the

Colorado Springs metropolitan area that includes Colorado

Springs and several smaller communities in El Paso County.

Since 1977, population in El Paso County has increased by

about 75 percent. As population increased, the amount of

impervious area increased. Research has shown that as

impervious area increases, infiltration decreases, runoff

increases, and a quicker hydrologic response in the receiving

streams occurs, which enhances streambank erosion

(Goudie, 1986; Douglas, 1983; Dunne and Leopold, 1978).

Agriculture and rangeland are located predominantly south

of Colorado Springs. Agriculture is common along the alluvial

valley from Fountain to Pueblo and relies heavily on

water diverted from Fountain Creek. A large expanse of

rangeland is included within the boundaries of the military

reservation at Fort Carson.

Concerns by landowners, farmers, resource managers,

and municipal, county, and local agencies that (1) flooding

and associated streambank erosion may be worsening over

time, and (2) increases in precipitation, especially during

the 1990Õs, may be exacerbating the problem, resulted in a

study to determine whether precipitation and streamflow in

the Fountain Creek watershed has changed over time. The

study was done by the U.S. Geological Survey (USGS),

in cooperation with the Turkey Creek Soil Conservation

District, El Paso County Soil Conservation District, Central

Colorado Soil Conservation District, and Pueblo County.

Stogner (2000) indicated that no significant trends were

detected in precipitation or streamflow prior to 1977. Therefore,

this Fact Sheet summarizes trends in precipitation and

streamflow from 1977 through 1999. Readers interested in a

detailed discussion of trends in precipitation and streamflow

for the Fountain Creek watershed from 1939 through 1999

are referred to Stogner (2000).

USGS Fact Sheet 136Ð00

October 2000 U.S. Department of the Interior

U.S. Geological Survey



Trends in Precipitation and Streamflow in the Fountain Creek

Watershed, Southeastern Colorado, 1977Ð99

ÑRobert W. Stogner, Sr.

Prepared in cooperation with the Turkey Creek Soil Conservation District, El Paso County Soil Conservation District, Central Colorado Soil

Conservation District, and Pueblo County

Figure 1. Location of Fountain Creek watershed, precipitation

and streamflow sites.



Table 1. Description of streamflow statistics used to

evaluate trends in streamflow



Streamflow statistic and description

Annual peak streamflow is the single highest instantaneous

recorded streamflow for the water year1.

100 percentile (Q100) streamflow is the highest daily mean2

streamflow for the water year.

90th percentile (Q90) streamflow indicates 90 percent of the

annual daily mean streamflows are below this streamflow

or 10 percent are above it.

70th percentile (Q70) streamflow indicates 70 percent of the

annual daily mean streamflows are below this streamflow

or 30 percent are above it.

30th percentile (Q30) streamflow indicates 30 percent of the

annual daily mean streamflows are below this streamflow

or 70 percent are above it.

10th percentile (Q10) streamflow indicates 10 percent of the

annual daily mean streamflows are below this streamflow

or 90 percent are above it.

Annual minimum streamflow (Q0) equals the lowest daily

mean streamflow for the water year.

1A water year extends from October 1 through September 30

of the following year and is identified by the year in which it ends.

2Daily mean streamflow is the average of all instantaneous

streamflow recordings made each day.

How were Changes or Trends in Precipitation and

Streamflow Determined?

Trends in precipitation and streamflow were determined

by compiling precipitation data at four sites and stream-

flow data at six sites from 1977 through 1999 (fig. 1).

Statistical trend tests were done on daily, seasonal,

and annual precipitation data for each site to determine

whether precipitation had changed since 1977. To determine

whether streamflow had changed since 1977, statistical

trend tests were done on several high (annual peak,

Q100, Q90, Q70) and low (Q30, Q10, Q0) streamflow statistics

computed for each site (table 1). The statistical trend

test used was the Kendall test, which provides a probability

of precipitation or streamflow to increase or decrease

over time. The trend was defined as highly significant if

the probability that a trend existed was 99 percent or

greater, significant if the probability was between 95

and 99 percent, and moderately significant if the probability

was between 90 and 95 percent. No trend was indicated

when the probability was less than 90 percent. The

Kendall test also provides an estimate of the average

annual rate of change.

To determine whether streamflow changed within

certain reaches of the watershed, differences in the daily

mean streamflow between the upstream and downstream

sites within a stream reach were computed. The differences

then were divided by the intervening drainage area,

resulting in streamflow data normalized to drainage area,

and trends were evaluated on the normalized data.



Precipitation

Precipitation is highly variable throughout the watershed;

annual precipitation ranges from about 30 inches at

the summit of Pikes Peak, an elevation of 14,110 feet, to

about 12 inches at Pueblo, an elevation of 4,640 feet.

Depending on location, from 40 to 60 percent of the

daily precipitation that occurs is less than or equal to

0.1 inch, and from about 70 to 80 percent of daily precipitation

that occurs is less than or equal to 0.25 inch. Daily

precipitation of greater than 0.25 inch occurs most frequently

from July through September. Many of the precipitation

events that occur during this period are associated

with thunder storms that generally are strong, localized

storms that occur during the late afternoon and early

evening. These localized storms frequently result in large

variations in annual precipitation over short distances.



Trends in Precipitation

During 1977 through 1999, annual precipitation

generally was above average, and increasing trends

were detected at the Ruxton Park and Pueblo sites.

No trends were detected in precipitation at the Colorado

Springs and Fountain sites. Additionally, seasonal trend

analysis indicated moderately significant increases in

spring (AprilÐJune) precipitation at the Ruxton Park and

Pueblo precipitation sites. This analyses indicates that the

increasing trends detected in annual precipitation at these

sites were likely the result of trends in spring precipitation

and were not associated with changes in precipitation that

occurred during the summer season or throughout the

entire year.



Streamflow

Streamflow in the Fountain Creek watershed varies

seasonally and has three distinct flow regimes: base flow,

snowmelt, and summer flow. The base-flow period begins

in late September or early October and extends until the

following April. During the base-flow period, streamflow

is fairly uniform. Depending on temperature and winter

snowfall amounts, the snowmelt period begins about

mid-April and extends until about mid-June. Early in

detected for the reach from Pinon to Pueblo. In the



reach from Nevada Street to Security (fig. 1),

the average annual per-square-mile increase in

streamflow for the Q70 and Q90 statistics was

about five times greater than the other reaches

that had increasing trends. Additionally, the

reach from Nevada Street to Security showed

the greatest annual change in total streamflow

during high flows (fig. 2). This indicates that,

on average, the intervening drainage area for

the reach between Nevada Street and Security

contributed more total flow and more flow per

square mile than any of the other drainage

areas studied. This trend probably is attributable to

changes in land use from rangeland to urban that occurred

in the intervening drainage area over the past 23 years,

which altered the hydrologic response and increased storm

runoff.

The larger frequencies and high significance level of



trends detected in the 70th percentile streamflow statistic

may indicate that changes in land use within the watershed

have increased the rate and magnitude of runoff for more

moderate rainfall events that occur more frequently in the

watershed than extreme rainfall events that affect the

instantaneous peak and annual maximum daily mean

streamflows.

the snowmelt period, streamflow increases substantially

from base-flow conditions. Streamflow decreases fairly

quickly after peaking in early to mid-May. The summer

flow period follows the snowmelt period and generally

begins about mid-June and extends through September,

sometimes into October. Streamflow during the summer

period is highly variable. Changes in streamflow during

the summer are primarily affected by afternoon and

evening thunderstorms.



Trends in High Streamflow

A significant increasing trend in annual peak

streamflow at the Pikeview site was detected for the

post mid-1970Õs. No trends were detected in annual

peak streamflow at the other five sites during this period.

Evaluation of long-term streamflow data at Pueblo

(1941Ð65, 1971Ð99) indicates instantaneous streamflows

of 10,000 cubic feet per second or greater occurred more

frequently during the 1990Õs than any decade since the

1940Õs. Annual peak streamflows during 1994Ð97 and

1999 ranked in the top 27 percent of all time recorded

annual peak streamflows. However, although large stream-

flow events occurred more frequently during the 1990Õs

than during previous decades since the 1940Õs, the magnitudes

of streamflows that occurred during the 1990Õs were

not atypical of historical peaks.

Examination of streamflow data and historical accounts

of the period indicates that the four largest streamflow

events at Pueblo occurred during the spring snowmelt

period, mid-April to mid-June. Each of these events were

caused by several inches of rainfall that fell during intense

storms over large areas of the Fountain Creek watershed.

In some areas, rainfall amounts that occurred during these

intense storms exceeded the average annual rainfall in the

Colorado Springs area. Also significant is that the most

recent event, the flood of April 30, 1999, was estimated to

be about a 15-year flood for the Pueblo site (Stogner,

2000). A 15-year flood is a streamflow with a probability

of recurring once every 15 years.

Since 1977, highly to moderately significant increasing

trends in at least one high-streamflow statistic were

detected at all sites; most sites had increasing trends in all

three daily mean high-streamflow statistics (Q70, Q90, and

Q100). Analysis of changes in streamflow for five stream

reaches also indicated that significant increasing trends in

the 70th percentile (Q70) streamflow statistic occurred in

four reaches: Pikeview to Nevada Street, Near Colorado

Springs to Nevada Street, Nevada Street to Security, and

Security to Pinon. No trends in high streamflow were

1977 2000 1980 1990

0

100


20

40

60



80

DIFFERENCE BETWEEN 70TH PERCENTILE OF DAILY MEAN STREAMFLOW

BETWEEN UPSTREAM AND DOWNSTREAM SITES, IN CUBIC FEET PER SECOND

70th Percentile

Security to Pinon

Nevada Street to Security

Pikeview to Nevada Street

Near Colorado Springs to Nevada Street



Figure 2. Trend of change in the 70th percentile of daily mean

streamflow for selected stream reaches, 1977Ð99.



Printed on recycled paper

Trends in Low Streamflow

Analysis of low streamflow statistics generally indicates

that low streamflows have significantly increased throughout

most of the watershed, particularly since the early

1980Õs. In addition, the average annual rate of increase

in the low streamflow statistics have tended to be largest at

the sites downstream from Nevada Street. Downstream

from Nevada Street, effluent from the Colorado Springs

Waste-Water Treatment Plant (WWTP) and several

other WWTPÕs discharge to Fountain Creek. Analysis of

changes in streamflow for five stream reaches indicated that

significant increasing trends in the 30th percentile (Q30)

streamflow statistic occurred in four reaches: Pikeview

to Nevada Street, Near Colorado Springs to Nevada

Street, Nevada Street to Security, and Security to Pinon.

The average annual increase in streamflow for

the low streamflow statistics (Q0, Q10, Q30)

generally was from 5 to 10 times greater in the

reach from Nevada Street to Security than the

other reaches that had increasing trends. Additionally,

the reach between Nevada Street and

Security generally showed the greatest annual

change in total streamflow during low flows

(fig. 3). The large annual increases in the low streamflows

in the reach between Nevada Street and Security have

resulted from increased waste-water treatment-plant discharge

associated with population growth, importation of

transbasin water, and management of the Fountain Creek

transbasin return-flow exchange decree, which allows

Colorado Springs to exchange return flows from transbasin

imports to other locations in the Arkansas River basin.



Cited References

Douglas, Ian, 1983, The urban environment: Baltimore, Edward

Arnold Publishers Ltd., 229 p.

Dunne, Thomas, and Leopold, L.B., 1978, Water in environmental

planning: New York,W.H. Freeman and Company, 818 p.

Goudie, Andrew, 1986, The human impact on the natural environment:

Cambridge, Mass., The MIT Press, 338 p.

Stogner, R.W., Sr., 2000, Trends in precipitation and streamflow

and changes in stream morphology in the Fountain Creek

Watershed, 1939Ð99: U.S. Geological Survey Water-

Resources Investigations 00Ð4130, 49 p.

For more information,

please contact:

Patrick Edelmann

U.S. Geological Survey

201 W. 8th Street

Pueblo, CO 81003

(719) 544Ð7155, ext. 106

1975 2000 1980 1990

WATER YEAR

-60


80

-40


-20

0

20



40

60

DIFFERENCE BETWEEN 30TH PERCENTILE OF DAILY MEAN STREAMFLOW



BETWEEN UPSTREAM AND DOWNSTREAM SITES, IN CUBIC FEET PER SECOND

30th Percentile

Near Colorado Springs to Nevada Street

Pikeview to Nevada Street

Security to Pinon

Nevada Street to Security



Figure 3. Trend of change in the 30th percentile of daily mean

streamflow for selected stream reaches, 1977Ð99.


The database is protected by copyright ©essaydocs.org 2016
send message

    Main page