The City will examine the
long-term results of each of these four monitoring elements to determine
how new developments, specifically Sterling Ponds Subdivision, are or
are not affecting the river under the new storm water ordinance. The
project will use an “upstream/downstream” approach to see if the
development will make river conditions worse downstream. We will also
take a focused look at on-site storm water management practices that are
incorporated into new developments. Our hope is that due to the
ordinance requirements, the water quality and thermal impacts of
development will be undetectable or greatly reduced.
River
Falls Precipitation:
Due to the
influence of precipitation on river flow, temperature, and water
quality, an analysis of annual precipitation is conducted as a part of
this project. A total of 36.45 inches of precipitation was recorded in
River Falls during the April-September 2005 period, nearly twice the
normal total of 20.67 inches for this time period. Rain fell on 71
days, or 39% of the April-September 2005 period.
All months during the April-September
2005 period were wetter than normal, with monthly rainfall amounts
exceeding seven inches in June, July, and September. Rainfall amounts
in June and July were nearly twice the normal levels, while September
rainfall was almost three times the normal level. Nearly 65% of the
total April-September rainfall occurred during these three months. The
lowest monthly rainfall amount was recorded in April.
Besides being much wetter than normal,
the April-September 2005 monitoring period was warmer than normal. The
mean air temperature in River Falls during the April-September 2005
period was 64.6º Fahrenheit (F), nearly 1.5º F higher than the normal
mean of 63.2º F for this time period. “Summer” months that were warmer
than normal (June, July, and September) also had the highest rainfall
amounts (all in excess of seven inches). The warmer summer weather may
have generated more convective thunderstorm activity that produced
heavier rainfall.
The City of River Falls Storm Water
Management Ordinance would have provided infiltration of approximately
91% (33.01 inches) of the total rainfall (36.45 inches) that occurred
during the April-September 2005 period. This percentage was determined
using some conservative estimates further described in the technical
report.
Kinnickinnic River Flow:
The flow of the Kinnickinnic River is a
reflection of precipitation and storm water runoff from predominantly
agricultural and urban land uses throughout the 165-square mile
Kinnickinnic River Watershed. The daily mean (average) flow of the
Kinnickinnic River at County Highway F during the April-September 2005
period is presented in the figure below. Daily rainfall, as measured in
River Falls, is also presented in the figure below.
During the April-September 2005 period,
rainfall amounts in excess of 1 inch generally had the greatest
influence on the Kinnickinnic River hydrograph. Rainfall events on
April 16, June 8, June 11, and September 21 resulted in moderate
increases in the Kinnickinnic River hydrograph, with peak daily mean
flows ranging from 127-133 cfs. Rainfall events on July 8, July 23
and 25, and September 24-25 produced the three largest runoff events of
the year, with peak daily mean flows ranging from 212-265 cfs. During
dry periods between runoff events, the Kinnickinnic River maintained a
base flow condition of approximately 80-90 cfs at County Highway F.
Temperature Monitoring:
The thermal impacts of untreated storm
water can be found by clicking here.
The intent of the City of River Falls
Storm Water Management Ordinance is to prevent storm water impacts on
the Kinnickinnic River, including thermal pollution, in areas of the
city with new development, such as the Sterling Ponds Subdivision.
A direct storm sewer
discharge to the Kinnickinnic River at Division Street
Kinnickinnic River Temperature
Monitoring Results:
May-September 2005 (summer) temperature
monitoring data were obtained for the Kinnickinnic River at Sites 1, 1A,
2, and 3. River temperatures at these four monitoring sites averaged
14.4° C and ranged from 4.5-21.5° C over the course of the summer.
Slightly higher-than-normal river temperatures probably prevailed in the
North Kinnickinnic River Monitoring Project Area during the summer of
2005, since the 2005 summer average air temperature of 19.7º C (67.4º F)
was slightly higher than the normal summer average air temperature of
19.2° C (66.5° F).
Upstream summer temperatures at Sites 1A
and 2 were nearly identical to downstream summer temperatures at Site
1. A comparison of temperatures at Site 1A (upstream) and Site 1
(downstream) is shown below.
The monthly and summer average
temperatures at Sites 1, 1A, 2, and 3 were also nearly identical, as
shown below.
The summer 2005 temperature regime in
the Kinnickinnic River at Sites 1, 1A, and 2 was excellent for coldwater
macroinvertebrate and brown trout communities. Approximately 86% of all
temperatures recorded at Sites 1, 1A, and 2 during the May-September
2005 period were less than or equal to (≤) 17° C, which is the top of
the optimum temperature range for a healthy coldwater macroinvertebrate
community. A temperature of 17° C is also considered to be the optimum
for brown trout survival. Approximately 98% of all temperatures
recorded at Sites 1, 1A, and 2 during the May-September 2005 period were
≤ 19° C, which is the top of the optimum temperature range for brown
trout growth. Approximately 99.5% of all temperatures recorded at Sites
1, 1A, and 2 during the May-September 2005 period were ≤ 20° C, which is
the top of the optimum temperature range for brown trout survival.
River temperatures exceeding 20º C were only recorded on four dates in
late June and mid-July, when air temperatures exceeded 32º C (90º F).
No storm water-related thermal impacts
were apparent at Site 1 during five significant rainfall and runoff
events in June, July, and September 2005. However, the largest rainfall
event of the summer on July 8 (4.00 inches) produced two distinct
thermal spikes at Site 1, downstream from Sumner Creek and Sterling
Ponds, as indicated below. As expected, a prominent thermal spike of
4.0º C also occurred at Division Street (below). The Sumner Creek and
Sterling Ponds temperature monitoring results (below) help document the
effectiveness of the City of River Falls Storm Water Management
Ordinance in 2005, and also identify the cause of the thermal impact
observed at Site 1 during the July 8 storm.
Sumner Creek and Sterling Ponds
Temperature Monitoring Results:
May-September 2005 (summer) temperature
monitoring data were obtained for Sumner Creek at Site 6 (upstream from
Sterling Ponds) and at Sites 4 and 4A (downstream from Sterling Ponds).
Site 4A, near the mouth of Sumner Creek, was a new monitoring site in
2005. Temperature monitoring data for the Sterling Ponds storm water
management practices were obtained in the wet detention pond (Site 5P),
at the wet pond discharge to the infiltration basin (Site 5IB), and at
the wet pond discharge to Sumner Creek (Site 5MH).
Temperature monitoring data indicate
that the storm water management practices at Sterling Ponds caused no
major thermal impacts on Sumner Creek and the Kinnickinnic River during
the May-September 2005 period. The summer mean temperature of the
Sterling Ponds wet detention pond at Site 5P was 21.7º C, but much of
this warm storm water was effectively discharged to the adjacent
infiltration basin, as required by the River Falls Storm Water
Management Ordinance. However, during all major rain events (in excess
of one inch), warm storm water (17.9-27.2º C) from the wet detention
pond was also discharged to the wetland area within the Sumner Creek
drainage way. Due to water storage capacity in the wetland, these warm
storm water discharges generally caused no downstream thermal impacts.
However, after the largest rain event of the summer on July 8 (4.00
inches), a “plug” of warm water (including Sterling Ponds storm water)
moved downstream from the wetland area, causing minor thermal spikes at
Sites 4 and 4A in Sumner Creek and at Site 1 in the Kinnickinnic River.
Permanent flow occurred in lower Sumner
Creek at Site 4A throughout the summer. The summer mean temperature
(12.3º C) reflects strong spring flow, and the creek potentially
provides a good thermal environment for a brook trout fishery. However,
thermal spikes of significant magnitude (2.1-7.6º C) occurred at this
location after numerous summer rain events in excess of 0.50 inch (see
figure below). These spikes appear unrelated to the storm water
discharges at Sterling Ponds, and seem to have a more local cause that
needs further investigation.
With limited development in the Sterling
Ponds subdivision in 2005, with some Sterling Ponds storm water
management practices (erosion control measures, wet detention ponds, and
a storm water infiltration basin) in place, and with Sumner Creek
providing a lengthy buffer between the subdivision and the Kinnickinnic
River, any Sterling Ponds storm water impacts on the river were
projected to be minimal in 2005.
Base Flow Survey:
The USGS gauge located at County Highway
F, as described in the technical report, was used to determine when a
river base flow. When 3-4 days of “flat-line” flow was observed at this
station, the river was assumed to be at a base flow condition. During
dry periods between runoff events, the Kinnickinnic River maintained a
base flow condition of approximately 80-90 cfs at County Highway F.
In the autumn of 2005, base flow
measurements were obtained for the first time at Sites 1-3 in the
Kinnickinnic River and at the mouth of Sumner Creek (Site 4A) within the
North Kinnickinnic River Monitoring Project Area. The survey results
are presented below. Base flows were very similar at Sites 2 and 3, but
a 30% increase in base flow was evident at Site 1, with Sumner Creek
contributing only a small proportion of this increase.
One goal of the River Falls Storm Water
Management Ordinance is to maintain strong base flow conditions in the
Kinnickinnic River by requiring storm water management practices that
promote infiltration of rainfall, thereby maintaining shallow aquifer
levels, as well as the springs that provide cold water for the river.
The initial base flow survey in 2005 will provide a baseline for
determining if the present base flow condition will be sustained in the
future as development progresses in the North Kinnickinnic River
Monitoring Project Area.
Macroinvertebrate
Monitoring:
Aquatic macroinvertebrates are excellent
indicators of water quality, as they live in the stream environment for
extended periods (up to a year or more), thereby reflecting past as well
as present water quality conditions. In May 2005, macroinvertebrate
samples were obtained from the Kinnickinnic River at Sites 1, 2, and 3.
Organisms were identified and counted in the laboratory, and Hilsenhoff
Biotic Index (HBI) values were then calculated for each monitoring
site. The Hilsenhoff Biotic Index (HBI) is particularly useful for
determining the influence of organic pollution on macroinvertebrates.
This index has been used for many years by the Wisconsin Department of
Natural Resources in long-term stream monitoring efforts. Each HBI
organism has been assigned a specific tolerance value, ranging from 1
(extremely intolerant of organic pollution) to 10 (extremely tolerant of
organic pollution). The more intolerant macroinvertebrates that are
present at a monitoring site, the lower the HBI value, indicating better
water quality.
The 2005 Kinnickinnic River
macroinvertebrate HBI values at Sites 1, 2, and 3 are presented below.
HBI values at Sites 1 and 3 are indicative of excellent water quality,
while the HBI value at Site 2 is indicative of very good water quality.
