 Storm
Water Management and the Kinni
by
Jeremy Cook
The city of River Falls is a growing community in west-central
Wisconsin. According
to 2000 Census information, the current population of River Falls
is estimated to be 11,762.
This is 1,952 more people than the last census in 1990, and
corresponds to a 10.86% change in population [Naylor].
The rapid growth rate of this municipality can be attributed
to its close proximity to the Twin Cities of Minnesota.
River Falls, along with neighboring communities on the Minnesota-Wisconsin
border, is rapidly becoming a suburb of St. Paul and Minneapolis.
One of the problems with this unchecked growth, and perhaps
the most startling, is that River Falls lies on the heart of one
the state’s greatest water resources and best trout fisheries; the
Kinnickinnic River.
The Kinnickinnic is an outstanding midwestern trout stream.
With populations of 1500 to 7500 trout per mile above the
city of River Falls and 1500 to 4000 trout per mile below the city,
the river retains healthy populations of reproducing brown trout
[Johnson 1]. This population,
however, is being threatened by the recent outburst of growth and
development in the city of River Falls and the surrounding region.
The clearing of trees and shrubs to make way for impervious
surfaces like parking lots and the roofs on houses can have a significant
effect on a watershed in the form of stormwater runoff.
The impacts of stormwater runoff include: thermal pollution,
the increased transportation of sediment and pollutants, and increased
stream flow, both volume and velocity [Wilding 1].
Therefore increased urbanization raises the valid concern
that the effect of stormwater runoff from the city of River Falls
is a potentially destructive influence on the Kinnickinnic watershed.
The
concern about development having negative impacts on local trout
streams is not unfounded.
The Twin Cities area once boasted numerous trout streams,
most of which have now been totally lost or degraded beyond reclamation.
To prevent the loss of another beautiful midwestern trout stream
to the hands of development, a temperature-monitoring project was
undertaken by the Kiap-TU-Wish Chapter of Trout Unlimited in 1992.
In coordination with the monitoring effort a water resource
consultant, Short Elliot Hendrickson, was hired in 1992 to conduct
storm event-based composite sampling [Johnson 1].
The goal of these efforts was to document the effect that
stormwater runoff had on the temperature and composition of the
stream.
The
temperature monitoring stations to be utilized in the study were
placed at four locations on the Kinnickinnic River.
The first was placed in the river upstream from the city
on Quarry Road, where the stream would be unaffected by stormwater
runoff. This would
serve as a control, from which the effect of stormwater could be
observed and measured. The
second was placed in the river near Cedar Street in a commercial
and residential area directly downstream from four of the city’s
stormwater discharges. A
third monitoring station was positioned further downstream in Upper
Glen Park, below two city impoundments, which also have thermal
impacts on the stream. The
final station was placed in Lower Glen Park at the lower city limits.
In conjunction with the four temperature monitors in the
stream, an additional station was used to measure actual stormwater
temperatures within storm sewers [Johnson 3].
The
temperature monitors were Ryan TempMentor data logging thermometers.
They were set to record temperatures on ten-minute intervals.
The stations were housed in in-ground shelters that locked
to provide security. Data
was retrievable using a laptop PC and was collected after each 44-day
deployment interval [Johnson 3].
The
storm event-based sampling of stormwater quality was conducted to
determine the chemical composition of the runoff and the rate and
depth of runoff flow. An
American Sigma 800 SL portable sampler was used to measure both
these characteristics from three different locations, representing
the three types of urban runoff:
residential, commercial, and industrial. There were three storm events monitored in the residential
and commercial sectors, and one in the industrial sector. For each of these events separate samples were collected, with
numerous samplings at the beginning of each event to better determine
the characteristics of the “first flush” of runoff. Samples were then analyzed and compared to EPA National Urban
Runoff Program results [Johnson 4].
By
the time it was undertaken in 1992, studies similar to the Kinnickinnic
temperature-monitoring project had already been conducted by organizations
around the nation. One
such study was conducted by the Maryland Department of the Environment
on several coldwater eastern streams in the late 1980’s through
the early 1990’s. The
purpose of this study, as in the Kinnickinnic project, was to determine
the exact relationship between development and urban stream quality.
The results confirmed that this relationship was not a beneficial
one to the stream.
The
conclusion of the Maryland study was that the single greatest influence
on the temperature of an urban stream is the combination of imperviousness
with local weather conditions [Galli x].
The correlation between imperviousness and stream temperature
was found to be so strong that the researches were able to fit a
linear model to the data.
The linear relationship was found to be an increase of 0.14
°
F in stream temperature for every increase of 1 % imperviousness
[Galli xi]. Although
an increase in 0.14 °
F may not itself be altogether devastating to aquatic life, the
Maryland researchers also found that as the percentage of impervious
surfaces due to development in a watershed increases so does its
susceptibility to inputs of stormwater runoff [Galli xi].
Jointly, a temperature increase due to increased imperviousness
in a watershed accompanied by stormwater induced temperature spikes,
could potentially have a significant impact on stream temperature.
The
Maryland researchers also found other adverse effects of development.
They determined that the loss of the riparian vegetation
that serves as stream’s canopy and insulator could cause increases
in temperature between 11- 20 °
F in the summertime [Galli xi].
The scientists also observed that a stream’s natural tendency
to increase in temperature in a downstream direction was magnified
by factors like loss of groundwater input and removal of vegetation
[Galli xi].
The
implications of these findings are significant in a coldwater stream.
The finding of the study was that combined, all the impacts
of development, could raise the average temperature of a small headwater
stream by 4 to 15 °
F [Galli xvi]. The
biological consequences of these findings are numerous.
One
such consequence of can be seen in the effect of increased stream
temperature on trout. Trout,
as a species, require a specific stream temperature range to survive.
The Brown Trout, the species prevalent in the Kinnickinnic,
is regarded as the most temperature tolerant as it can withstand
temperatures of up to 77 °F.
Temperatures of 70-77°
F, however, are considered very stressful for a trout [Galli 139].
While
trout may be able to survive certain fluctuations in temperature,
the food they rely on, mainly aquatic insects, may not.
In the Maryland study it was determined that many coldwater
insect species would be eliminated or reduced by the thermal enrichment
of a stream. Important
species to the trout, such as stoneflies, mayflies, and caddisflies,
would be severely impacted or stressed by stream temperature fluctuations
[Galli xvii]. Thus stream temperature fluctuations have not only the potential
to stress the trout directly, but indirectly through their food
source as well.
The
close relationship between development and quality of an urban watershed
determined by the Maryland experiment can be seen directly in the
results of the Kinnickinnic project as well.
The stream temperatures recorded in the Trout Unlimited project
and their implications are consistent with the impacts cataloged
by the Maryland researchers.
The
results of the monitoring were clear and as expected.
The station on Quarry Road recorded stream temperatures that
were very much dependent upon ambient air temperatures.
The groundwater discharge and canopy cover of the stream,
however, counteracts extremes in diurnal variation of temperature.
The Quarry Road location is less developed with a lower percentage
of impervious surfaces and thus groundwater discharge and canopy
cover have not yet been degraded.
The monitoring station in this location also reported few
impacts of precipitation [Johnson 6].
On
the other hand the Cedar Street location was directly affected by
precipitation because of its proximity to the stormwater discharges
draining the impervious surfaces of the city.
The diurnal variations in temperature recorded at this station
resembled closely those of Quarry Road, but the impacts of storm-events
were markedly different. At the Cedar Street location storm-events were almost always
marked by a runoff-induced temperature spike.
This spike varied depending on the amount and temperature
of the runoff, with the greatest spikes accompanying storm events
of greatest volume and temperature.
On July 25, 1993, a typical storm-event spike was observed.
Beginning at 2:20 with the initial discharge of runoff the
stream temperature at Cedar Street climbed ten degrees F in just
twenty minutes. The
ten-degree spike was the result of the first flush of runoff, which
had gained heat as it rushed over the warm impervious surfaces of
the city. The
progression of the event resulted in a return to baseline temperatures
in approximately three hours time.
The Quarry Road station recorded no temperature spike during
this storm event [Johnson 6].
The
same storm-event above produced a temperature spike of five degrees
at the Lower Glen Park station, despite its distance of approximately
a mile from the nearest stormwater discharge.
Average baseline temperatures for the stream at this station
were recorded to be 3-6 °
F higher than the two upstream stations [Johnson 6].
The
station used to monitor actual stormwater temperature in a storm
sewer recorded precipitation-events on ten days in June of 1992. On these days, where the precipitation ranged from .01 to 2.05
inches, the runoff temperatures ranged from 60 to 83 degrees F.
In these events the maximum temperatures were recorded almost
directly after the event began, coinciding with the “first flush”
of runoff seen in the July 25 storm event at Cedar Street.
The most likely causes for variation in stormwater temperature
are the temperatures and area of the impervious surfaces drained,
ambient air temperatures, and the rate of flow and volume of the
runoff [Johnson 7].
Results
from the stormwater quality monitoring conducted by Short Elliot
Hendrickson from June-August in 1992 confirmed the impacts of development
and stormwater on the Kinnickinnic watershed.
With median concentrations of suspended solids, total Kjedahl
nitrogen, and total phosphorus, averaging higher than National Urban
Runoff Program median concentrations, the stormwater runoff from
the city of River Falls was polluting the stream chemically as well
as physically [Johnson 8].
The
results of the monitoring project suggest numerous ramifications
of development for the Kinnickinnic watershed.
The drastic temperature spikes recorded during rain events
suggest that the percentage of impervious surfaces in the watershed
has already begun to affect the stream. The higher baseline temperatures of the stream at the Lower
Glen Park station compared to those at the Quarry Road and Cedar
Street imply impacts of urbanization as well.
This increase in average stream temperature can be attributed
to several factors. First,
there are two city impoundments between Cedar Street and Lower Glen
Park. Impoundments
are known to increase stream temperature in a downstream direction
[Johnson 6]. The loss of groundwater input and riparian vegetation, as experienced
in the Maryland project, may also contribute to this increase.
The Lower Glen Park station also recorded temperature spikes
during storm events despite the significant distance to the nearest
stormwater discharge. Coupled
with the already increased average stream temperature, the lower
section of the Kinnickinnic is potentially at great risk.
The
implications of these findings for aquatic life, specifically trout
and the insects they eat, in the Kinnickinnic watershed are similar
to those discussed in the Maryland study.
As stream temperatures increase beyond the preferred range
for trout, the stress on the fish will increase accordingly.
Temperature spikes upwards of ten degrees, like those witnessed
in a typical storm event at the Cedar Street monitoring station,
coupled with increased average baseline temperatures could easily
push stream temperatures towards the upper lethal limit of 77°
F for trout. These
temperature spikes could also have detrimental effects on resident
insect populations as well.
Temperature fluctuations in the Kinnickinnic’s temperature
could potentially reduce or eliminate certain temperature sensitive
insect species such as the stoneflies, caddisflies, and mayflies
[Galli xvii]. Given
that these insects are a main staple of a trout’s diet, their elimination
would mean severe consequences for the trout of the Kinnickinnic.
The result of these effects could ultimately mean reduction
or even destruction of the Kinnickinnic’s trout population.
Given the results of the Kiap-TU-Wish Chapter of Trout Unlimited’s
stormwater monitoring project, a water resource consultant, Short
Elliot Hendrickson, was selected to develop a management plan in
conjunction with Kiap-TU-Wish, the city of River Falls, local townships,
the Wisconsin Department of Natural Resources, the Kinnickinnic
River Land Trust, and the University of Wisconsin-River Falls.
The Kinnickinnic River Water Management Plan was completed
in 1994 at an estimated cost of $115,000.
The purpose of this plan is to regulate development along
the Kinnickinnic River watershed in order to limit the implications
of development on the river [Johnson 9].
One
of the main guidelines presented in the plan is to limit percent
imperviousness within the city to 10-12 % and thereby curb the effects
of stormwater runoff and promote groundwater recharge.
Other important features include the design of best management
practices (BMP’s) to counteract thermal and sedimentation impacts
of stormwater and the adoption and implementation of local ordinances
that relate to the management of water [Johnson Table 6.].
In
1995, the Kinnickinnic was also designated as a state priority watershed.
Inclusion in the Wisconsin Department of Natural Resources
priority watershed plan will provide the Kinnickinnic River Water
Management Plan with funds over a ten year period to establish and
implement nonpoint source BMP’s as determined by the management
plan [Johnson 9].
The
Kiap-TU-Wish’s stormwater monitoring project has been a great success.
Designed to assess the impacts of urban stormwater runoff
on the Kinnickinnic River, the project’s stream temperature monitoring
and stormwater quality assessment resulted in a clear picture of
these consequences. Temperature
spikes during storm events and median concentrations of suspend
solids above those recommended by the NURP suggested that the urban
development had already begun to affect the watershed.
Although the River’s trout populations were strong, the potential
existed for the degradation of stream quality with severe implications
for aquatic life.
Once
the extent of the impacts of development on the Kinnickinnic watershed
was known, steps could be taken to ensure protection of the River
and its trout. Through
the WDNR priority watershed program and the Kinnickinnic River Water
Management Plan, the growth of River Falls and development of the
land in the River’s watershed will be monitored and controlled.
The end result should be the preservation of water quality
and aquatic life in the Kinnickinnic River.
Thanks to the efforts of the Kiap-TU-Wish Chapter of Trout
Unlimited and their commitment to conservation, the Kinnickinnic
watershed may not fall victim to urbanization like so many of its
neighboring counterparts.
Its currently healthy population of brown trout should sustain
itself and the Kinnickinnic will retain its reputation as a first-rate
trout stream. As long as guidelines for development are considered and water
quality is protected, the pristine waters of the Kinnickinnic River
will be available for all to enjoy.
Bibliography
Galli,
John. 1990. “Thermal
Impacts Associated with Urbanization and Storm Water
Best Management Practices”- Final Report.
Johnson,
Kent. “Urban Stormwater
Impacts On A Coldwater Resource.”
Kiap-TU-Wish
Chapter, Trout Unlimited, Hudson-River Falls, WI.
Naylor,
Bob. “Demographics.”
http://www.state.wi.us
Wilding,
Duane A; Clarke, Raymond P. Ballantine.
“Stormwater Management:
Shifting
the Present Paradigm.” Public Works v.130 no. 8, July
1999, p. 54-56.
|
