The City will examine the long-term results of
each of these four monitoring elements to determine whether the new
storm water ordinance is protecting the river as new development
occurs. The project will use an “upstream/downstream” approach to
determine if storm water management practices in the Sterling Ponds
subdivision protect downstream river conditions. We will also take a
focused look at the performance of the 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 new development will be undetectable or greatly reduced.
River Falls Precipitation:
Due to the major
influence of precipitation on river flow, temperature, and water
quality, an analysis of seasonal precipitation is conducted as a part of
this project. During the April-September 2006 monitoring period, hourly
precipitation was measured in 0.01-inch increments with an electronic
tipping-bucket rain gauge. The rain gauge, provided by the Wisconsin
Department of Natural Resources (WDNR), is located in the Sterling Ponds
subdivision at the northwest corner of the City of River Falls. This
location places the rain gauge in very close proximity to all six North
Kinnickinnic River monitoring stations. A weather station at Rocky
Branch Elementary School, on the south side of River Falls, serves as an
alternate source of daily rainfall data. This station is part of an
extensive network of local weather stations supported by KSTP-TV in
Minneapolis, MN, via the Automated Weather Source. The Rocky Branch
Weather Station also serves as a source of daily mean, minimum, and
maximum air temperatures. In addition, daily precipitation data are
available from the United States Geological Survey (USGS) Kinnickinnic
River monitoring station at County Highway F, near Kinnickinnic State
Park, approximately five miles west of River Falls.
A total of 17.16 inches
of precipitation was recorded in River Falls during the April-September
2006 period, 3.5 inches less than the normal total of 20.67 inches for
the April-September time period. Rain fell on 61 days, or 33% of the
April-September 2006 period. In comparison, a near-normal total of
19.82 inches of precipitation was recorded in River Falls during the
April-September 2004 monitoring period, and an above-normal total of
36.45 inches was measured during the April-September 2005 period.
“Normal” monthly and seasonal rainfall amounts are based upon
measurements made by the National Weather Service at the Twin Cites
International Airport during the “climate normal period” of 1971-2000.
Daily rainfall amounts
during the April-September 2006 period are presented in
Figure 1.
Monthly rainfall amounts during the April-September 2006 period, with a
comparison to normal monthly rainfall amounts, are presented in
Figure
2. Except for April and August, all months during the April-September
2006 period were drier than normal, with monthly rainfall deficits
ranging from 0.4 inch to 3.6 inches. The greatest rainfall deficits
occurred in June and July, with the lowest monthly rainfall amount (0.73
inch) recorded in June. August was the wettest month (6.68 inches),
exceeding the normal monthly rainfall amount by 2.6 inches.
Besides being drier than
normal, the April-September 2006 monitoring period was warmer than
normal. The mean air temperature in River Falls during the
April-September 2006 period was 64.8º Fahrenheit (F), 1.6º F higher than
the normal mean of 63.2º F for the April-September period, as measured
at the Twin Cities International Airport. Monthly mean air temperatures
during the April-September 2006 period, with a comparison to normal
monthly mean temperatures during the “climate normal period” of
1971-2000, are presented in
Figure 3. With the exception of September,
all months during the April-September 2006 monitoring period were warmer
than normal. The month of April was nearly 7º F warmer than normal,
while the month of July was 4º F warmer than normal. The month of
September was 3º F colder than normal.
The distribution of
River Falls daily rainfall amounts during the April-September 2006
period is presented in
Figure 4. Although the 2006 monitoring season
was drier than normal, it was characterized by numerous (51) days with
rainfall amounts of 0.50 inch or less. On 43 (70%) of the 61 days with
measurable precipitation, rainfall amounts were 0.25 inch or less.
These 43 days contributed only 17% of the total April-September 2006
precipitation. The majority of these 43 days occurred in the cooler
months of April, May, June, and September (Figure 5). On 8 (13%) of the
61 days with measurable precipitation, rainfall amounts ranged from
0.26-0.50 inch. These 8 days contributed an additional 17% of the total
April-September 2006 precipitation. Six of these 8 days occurred in
April, May, and September (Figure 5), the coolest months. On 4 (7%) of
the 61 days with measurable precipitation, rainfall amounts ranged from
0.51-0.75 inch. These 4 days contributed 15% of the total
April-September 2006 precipitation, with the majority of these 4 days
occurring in July, August, and September (Figure 5). Only one (2%) of
the 61 days with measurable precipitation had a rainfall amount in the
0.76-1.00 inch range (Figure 5), contributing 6% of the total
April-September 2006 precipitation. On 5 (8%) of the 61 days with
measurable precipitation, rainfall amounts exceeded 1.00 inch. These 5
days with the largest rainfall events contributed 45% of the total
April-September 2006 precipitation. Rainfall amounts in excess of 1
inch occurred on April 2, July 24, and August 1, 2, and 24 (Figures
1
and 5). On 2 of the 5 days, rainfall amounts ranged from 1.01-1.25
inches. On 3 of the 5 days, rainfall amounts exceeded 1.50 inches.
Four of the 5 largest rainfall events occurred in July and August, and
were produced by convective thunderstorm activity during a warmer than
normal summer.
To achieve the
requirements of the City’s storm water ordinance, developers must
provide on-site infiltration of post-development storm water runoff from
24-hour rainfall events of 1.5 inches or less. Of the 61 days with
measurable precipitation during the April-September 2006 period, 58 days
(95%) had rainfall amounts less than 1.5 inches in 24 hours (a
midnight-to-midnight total). Based on that data, only rainfall amounts
on July 24 (1.80 inches), August 2 (2.26 inches), and August 24 (1.63
inches) exceeded this criterion. Even so, some infiltration would have
occurred under the requirements of the storm water ordinance, thereby
accounting for infiltration of approximately 93% (15.97 inches) of the
total rainfall (17.16 inches) that occurred during the April-September
2006 period. Figure 6 depicts the annual effectiveness of the River
Falls Storm Water Ordinance for infiltrating storm water runoff
generated by rainfall during the April-September period. This figure
was prepared for illustrative purposes only, and was created with the
assumption that the entire 1.5-inch event is infiltrated. This scenario
essentially assumes zero pre-development runoff, which may not
necessarily be the case.
Kinnickinnic River Flow:
The flow of the
Kinnickinnic River is a reflection of strong ground water (spring)
contributions, as well as precipitation-induced storm water runoff from
predominantly agricultural and urban land uses throughout the 165-square
mile Kinnickinnic River Watershed. The United States Geological Survey
(USGS) operates a Kinnickinnic River monitoring station (number
05342000) at County Highway F, near Kinnickinnic State Park,
approximately five miles west of River Falls. The station measures
river stage (water height) and flow at 15-minute intervals, and
precipitation in 0.01-inch increments. Because accurate monitoring of
river stage and flow entails a significant investment in equipment and
labor, no continuous measurement of river flow is currently being
conducted within the North Kinnickinnic River Monitoring Project Area.
For this reason, the Kinnickinnic River flow information provided by the
USGS monitoring station is particularly valuable, as it clearly
documents when runoff events are occurring and storm water impacts may
be apparent. The City of River Falls, Kinnickinnic River Land Trust,
and Trout Unlimited provide annual cost-share funding for this USGS
monitoring station.
The daily mean (average)
flow of the Kinnickinnic River at County Highway F during the
April-September 2006 period is presented in
Figure 7. Due to a brief
equipment malfunction, the daily mean flow is not available for
September 7. Daily rainfall, as measured in River Falls at Sterling
Ponds, is also presented in
Figure 7.
The precipitation
pattern during the April-September 2006 period helps explain the changes
in the Kinnickinnic River hydrograph, due to runoff events in the
watershed. High river flows of 673 cubic feet per second (cfs) on March
30, 323 cfs on April 3, and 312 cfs on April 7 occurred as a result of
spring snowmelt and rain in late March, in combination with 1.11-inch
and 0.60-inch rainfall events on April 2 and 6, respectively. Numerous
small rain events (less than 0.50 inch) in April, May, June, and
September had little influence on the Kinnickinnic River hydrograph.
During the July-August
period, rainfall amounts in excess of 1 inch generally had the greatest
influence on the Kinnickinnic River hydrograph. A large rainfall event
on July 24 (1.80 inches) resulted in only a moderate increase in the
Kinnickinnic River hydrograph, with a peak daily mean flow of 117 cfs.
This moderate runoff event, in spite of heavy rainfall, can be
attributed to very dry antecedent conditions in June and July, and full
canopy closure in the agricultural and forested areas of the watershed.
Large, back-to-back rainfall events on August 1 (1.04 inches) and August
2 (2.26 inches) produced a significant increase in the Kinnickinnic
River hydrograph, with a peak daily mean flow of 232 cfs. Similarly,
large, back-to-back rainfall events on August 23 (0.71 inch) and August
24 (1.63 inches) also produced a significant increase in the
Kinnickinnic River hydrograph, with a peak daily mean flow of 342 cfs.
The Kinnickinnic River
hydrograph suggests that five significant runoff events occurred during
the April-September 2006 period. Two of these five significant runoff
events occurred in April (1-5 and 6-9), due to early spring rains on
April 2 and April 6. With cool air and water temperatures in early
April, thermal impacts of storm water runoff are generally not a
concern, but water quality impacts can be problematic, due to frozen
soils and a lack of vegetative cover in the watershed. Three of the
five significant runoff events occurred in July and August, during the
warmest time of the year (Figure 3), when thermal impacts of storm water
runoff can be a considerable concern. On July 24, one of the heaviest
rainfalls of the year (1.80 inches) resulted in a 3-day runoff event
(July 24-26), with a peak daily mean flow of 117 cfs. On August 1 and
2, back-to-back rainfall events totaling 3.30 inches resulted in a 5-day
runoff event (August 1-5), with a peak daily mean flow of 232 cfs. On
August 23 and 24, back-to-back rainfall events totaling 2.34 inches
resulted in a 6-day runoff event (August 23-28), with a peak daily mean
flow of 342 cfs. These three runoff events in July and August should be
the focus for evaluating possible storm water impacts in the North
Kinnickinnic River Monitoring Project Area in 2006, and are further
analyzed in this report. See Appendix A for reasons why smaller
rainfall and runoff events were not analyzed in 2006.
During dry periods
between runoff events, the Kinnickinnic River maintained a base flow
condition of approximately 85-95 cfs at County Highway F.
Temperature Monitoring:
In 2006, temperature
monitoring was conducted at five of the six City of River Falls
monitoring stations (Sites 1-6, except Site 2) in the North Kinnickinnic
River Monitoring Project Area. To evaluate the thermal performance of
the storm water management practices at Site 5, temperature monitoring
was conducted at three locations: the wet detention pond (Site 5P), the
wet detention pond outlet to the infiltration basin (Site 5IB), and the
wet detention pond outfall to Sumner Creek (Site 5MHW).
The local Kiap-TU-Wish
Chapter of Trout Unlimited (TU) also conducted temperature monitoring at
one Kinnickinnic River station (Site 1A) within the project area,
between Sites 1 and 2. The TU monitoring station is located along
Quarry Road on the northeast edge of River Falls, just east of the WI
Highway 35 bypass, and just upstream of the Sumner Creek confluence.
The TU station has been in service during all summer periods
(May-September) since 1992. In 2005, as an additional contribution to
the North Kinni Project, TU established a temperature monitoring station
in Sumner Creek (Site 4A), approximately 100 feet upstream of the creek
confluence with the Kinnickinnic River. This station was in service
during the summer periods (May-September) of 2005 and 2006. The thermal
impacts of Sumner Creek on the Kinnickinnic River, including any storm
water contributions from Sterling Ponds, can be evaluated at this
location.
Onset Computer
Corporation’s® HOBO Water Temp Pro Loggers are used to
measure water temperature at all City of River Falls monitoring stations
(Sites 1-6). A Ryan Instruments® RTM 2000 Temperature Logger
is used to measure water temperature at the TU monitoring station at
Quarry Road (Site 1A). Onset Computer Corporation’s® Optic
StowAway Templogger is used at the TU monitoring station in Sumner Creek
(Site 4A). All Onset and Ryan temperature loggers are programmed to
record temperatures at 10-minute intervals. Date and time stamps and
the 10-minute temperature data are electronically recorded by each
logger; and all recorded information is downloaded as necessary. The
brief 10-minute time interval was selected so that any rapid temperature
increases associated with warm storm water runoff could be documented.
With the exception of Site 2, Site 5MHW, and Site 6, all temperature
loggers were deployed throughout the May-September (summer) period.
These loggers malfunctioned this year. The thermal impacts of storm
water runoff are most likely to occur during this summer period, when
air temperatures are highest. The summer 2006 deployment periods (and
locations) for the temperature loggers at the ten monitoring stations
were as follows:
Site: Deployment Period:
Location:
Site 1: May 1-September 30, 2006 Kinnickinnic
River
Site 1A: May 1-September 30, 2006 Kinnickinnic
River
Site 2: No Deployment
Kinnickinnic River
Site 3: May 1-September 30, 2006 Kinnickinnic
River
Site 4: May 1-September 30, 2006 Sumner
Creek: Wet Pool in Culvert
Site 4A: May 1-September 30, 2006 Sumner Creek:
Mouth
Site 5P: May 1-September 30, 2006 Sterling
Ponds: Wet Pond
Site 5IB: May 1-September 30, 2006 Sterling
Ponds: Infiltration Basin
Site 5MHW: May 1-July 25, 2006 Sterling
Ponds: Wet Pond Outlet
Site 6: May 1-July 25, 2006 Sumner
Creek: Dry Box Culvert
Due to instrumentation
problems, the temperature logger at Site 2 was not deployed during the
summer of 2006, and the loggers at Site 5MHW and Site 6 were only
deployed through July 25. In conversations with Onset, this model of
the logger is prone to such errors; therefore the City is looking into
upgrading to the newest model of the Hobo Water Temp Pro to reduce the
risk of future complications and gaps in data.
Kinnickinnic River
Temperature Monitoring Results:
The May-September
(summer) 2006 temperature monitoring data obtained for the Kinnickinnic
River at Sites 1, 1A, and 3 are presented as thermographs in Figures
8,
9 and
10, respectively. Of immediate note in these thermographs is the
strong diurnal (daily) temperature pattern in the river. Although cold
groundwater continually feeds the river via springs along the entire riverway, the temperature of the Kinnickinnic River is greatly
influenced by ambient air temperature. During the daylight hours, the
river gradually warms and generally reaches a daily maximum temperature
in the late afternoon or early evening (4:30-6:30 PM). At night, the
river gradually cools and typically reaches a daily minimum temperature
just after sunrise (7:30-9:30 AM). These diurnal temperature
fluctuations in the river are natural, and the river’s residents,
including macroinvertebrates and trout, have become accustomed to a
constantly but slowly changing temperature regime.
Also of note in the 2006
Kinnickinnic River thermographs are the relatively frequent changes in
the daily minimum and maximum river temperatures and daily temperature
ranges that are influenced by local weather patterns (cold fronts and
warm fronts) and seasonal climate changes. During the summer 2006
period, for example, the monthly mean river temperature in the North
Kinnickinnic River Project Area (Sites 1, 1A, and 3) was coolest in May
(12.7 degrees Celsius (°C)) and warmest in July (17.1° C).
At Sites 1, 1A, and 3,
river temperatures averaged 14.6° C and ranged from 5.9-23.1° C over the
course of the summer. Monthly and summer mean temperatures at each of
these three monitoring sites are presented in
Figure 11. These monthly
and summer mean temperatures were nearly identical at Sites 1 and 1A,
but slightly cooler at Site 3, especially during the July-September
period.
For the second
consecutive year, slightly higher-than-normal river temperatures
probably prevailed in the North Kinnickinnic River Project Area during
the summer of 2006, since the 2006 summer average air temperature of
19.4º C (67.0º F) was slightly higher than the normal summer average air
temperature of 19.2° C (66.5° F). A comparison of 2004-2006 summer
average air temperatures and river temperatures (at Sites 1, 1A, and 2)
can be found in the North Kinnickinnic River Monitoring Project
Indicators.
The most direct way to
determine if any thermal impacts occurred in the Kinnickinnic River as a
result of the Sterling Ponds subdivision is to compare the temperature
monitoring data at Site 1, located immediately downstream from Sumner
Creek, to the temperature monitoring data at Sites 1A and 2, located
immediately upstream from Sumner Creek. These two upstream sites serve
as control or reference sites, which are not impacted by Sterling Ponds
storm water discharges. The 2006 temperature data were compared at
Sites 1 and 1A, as no data were obtained at Site 2.
A comparison of all
upstream summer temperature data at Site 1A to all downstream summer
temperature data at Site 1 is presented in
Figure 12. This comparison
indicates that summer temperatures were nearly identical at these two
locations. The temperature similarity at Sites 1 and 1A is even more
evident in the monthly thermographs for May, June, July, August, and
September 2006 (Figures 13-17, respectively). Figures 12-17 indicate
that daily maximum and minimum temperatures tended to be slightly higher
at Site 1A, due to less canopy cover and shading at this location.
Figure 11 shows that the monthly and summer mean temperatures at Sites 1
and 1A were also nearly identical. The following should be noted
concerning aquatic life in the Kinnickinnic River:
-
Approximately 81% of all temperatures recorded at Sites 1 and 1A
during the May-September 2006 period were less than or equal to (≤)
17° C, which is considered to be the top of the optimum temperature
range for a healthy coldwater macroinvertebrate community (Galli,
1990). A temperature of 17° C is considered to be the physiological
optimum for brown trout survival (Armour, 1994).
-
Approximately 95% of all temperatures recorded at Sites 1 and 1A
during the May-September 2006 period were ≤ 19° C, which is considered
to be the top of the optimum temperature range for brown trout growth
(Armour, 1994).
-
Approximately 98% of all temperatures recorded at Sites 1 and 1A
during the May-September 2006 period were ≤ 20° C, which is considered
to be the top of the optimum temperature range for brown trout
survival (Armour, 1994). River temperatures exceeding 20º C were only
recorded on two dates in late May and eight dates in mid-to-late July,
when air temperatures ranged from 32-37º C (90-99° F).
During three significant rainfall and runoff events in July and August
2006, thermographs at Sites 1 and 1A can be compared to determine if
rapid temperature increases (thermal spikes), which are characteristic
of warm storm water discharges, were apparent at Site 1. In spite of a
major rainfall event on July 24 (1.80 inches), no thermal spike was
evident at Site 1 in July (Figure 15). A closer examination of the
thermographs for Sites 1 and 1A during the 1.80-inch rainfall event on
July 24 (Figure 18) indicates that no thermal spike occurred at Site 1,
downstream from Sumner Creek and the Sterling Ponds subdivision. During
the same rain event, however, the thermograph for the Trout Unlimited
temperature monitoring site at Division Street (Figure 18) shows three
very prominent thermal spikes, due to the thermal impacts of direct
storm water discharges from the downtown area of River Falls.
Thermographs for Sites 1, 1A, and Division Street can be similarly
compared during the two large back-to-back rainfall events on August 1-2
(Figure 19) and August 23-24 (Figure 20). During the August 1-2 and
August 23-24 rainfall events, no thermal spikes were evident at Site 1,
while prominent thermal spikes were evident at Division Street. During
the July and August rainfall events, the thermal spikes at Division
Street ranged in magnitude from 0.4-3.6 degrees Celsius. While the
presence of thermal spikes at Division Street is attributed to the
thermal impacts of untreated storm water discharges to the Kinnickinnic
River, the lack of thermal spikes at Site 1 could be attributed to
several factors, including effective storm water management at the
Sterling Ponds subdivision, or simply a lack of Sterling Ponds storm
water discharges and/or storm water conveyance down Sumner Creek, even
during the largest runoff events.
Sumner Creek and Sterling Ponds Temperature Monitoring Results:
Sumner Creek
Sumner Creek is a low-gradient tributary of the Kinnickinnic River that
exhibits only intermittent flow for the majority of its length.
Permanent flow begins in the vicinity of the WI Highway 35 bypass, near
the creek confluence with the Kinnickinnic River (Site 4A). From this
location, the creek drainage way extends upstream to Radio Road on the
far northwest corner of River Falls. This upper portion of the Sumner
Creek drainage way, including Sites 4 and 6, conveys no flow for the
majority of the year. The headwaters area near Site 6 is a dry run;
however, rather extensive wetland areas are apparent in the Sumner Creek
drainage way through the Sterling Ponds subdivision, and for an
appreciable distance downstream of Site 4. Anecdotal evidence suggests
that flow may occur during the spring snowmelt period and perhaps during
large summer rain events. During large summer rain events, however, the
wetland areas and dry portions of the Sumner Creek channel likely
provide considerable water storage, making it very difficult to
determine if and when any upstream flow is conveyed all the way
downstream to the Kinnickinnic River.
The
May-September (summer) 2006 temperature monitoring data obtained for
Sumner Creek at Site 4A are presented as a thermograph in
Figure 21.
Site 4A near the creek mouth was the only Sumner Creek monitoring
location with permanent flow throughout the summer. At Site 4A, Sumner
Creek temperatures averaged 12.4° C and ranged from 7.6-22.0° C during
the May-September 2006 period. The summer mean temperature of Sumner
Creek (12.4º C) was notably colder than the summer mean temperature of
the Kinnickinnic River (14.6º C) at Sites 1, 1A, and 3, reflecting
strong spring activity. Approximately 99% of all temperatures recorded
at Site 4A during the May-September 2006 period were ≤ 17° C, and
approximately 99.5% of all temperatures were ≤ 20° C. Temperatures
exceeding 20º C were only recorded during the large back-to-back
rainfall events on August 1-2.
Based
upon the 2005 and 2006 temperature data, lower Sumner Creek may have
potential as a brook trout stream, and is regardless an important
contributor of cold water to the Kinnickinnic River. Of significant
concern, however, are several prominent thermal spikes that occurred at
Site 4A after the large rain events in July and August (Figure 21). The
thermal spikes in lower Sumner Creek ranged from 4.1-7.1 degrees
Celsius, and were of even greater magnitude than those observed at the
Division Street monitoring site. In spite of their magnitude, none of
these thermal spikes had a discernible impact on Kinnickinnic River
temperatures at Site 1, downstream from Sumner Creek. However, thermal
spikes of this magnitude and frequency may have detrimental impacts on
aquatic life in lower Sumner Creek, especially macroinvertebrates.
Numerous thermal spikes were also apparent in lower Sumner Creek (Site
4A) during the summer of 2005. Possible sources contributing to thermal
spikes in Sumner Creek may include: storm water runoff from WI Highway
35, located immediately upstream from Site 4A; warm water from natural
wetland areas in the upper Sumner Creek drainage way; and storm water
discharges from the Sterling Ponds subdivision.
Sterling Ponds
The
May-September (summer) 2006 temperature monitoring data obtained for the
Sterling Ponds wet detention pond at Site 5P are presented as a
thermograph in Figure 22. At Site 5P, wet detention pond temperatures
averaged 21.4° C and ranged from 10.4-30.4° C during the summer period.
Approximately 68% of all summer temperatures exceeded 20° C. With the
exception of a short time period from June 10-13, wet pond temperatures
remained above 20° C from May 24 until September 8. Substantial warming
of small, shallow ponds such as this can be expected, especially with no
shading or canopy cover. The summer mean temperature of the Sterling
Ponds wet detention pond (21.4° C) was substantially higher than
the summer mean temperature of Sumner Creek at Site 4A (12.4º C),
clearly demonstrating the potential for thermal impact when the pond
discharges to the creek, and emphasizing the importance of the River
Falls Storm Water Management Ordinance, which requires storm water
infiltration.
Assessment of
Sterling Ponds Storm Water Infiltration and Discharge to Sumner Creek
Temperature data from
the three Sterling Ponds monitoring stations (Sites 5P, 5IB, and Site
MHW) and the two downstream Sumner Creek monitoring stations (Sites 4
and 4A) can be used to evaluate the effectiveness of the Sterling Ponds
storm water management practices for infiltrating storm water and
minimizing warm storm water discharges to Sumner Creek. Given the warm
and relatively stable thermal regime (Figure 22) in the Sterling Ponds
wet detention pond (measured at Site 5P), pond discharges to the
infiltration basin can be readily identified when the temperature at
Site 5IB closely matches that at Site 5P. Similarly, pond discharges to
Sumner Creek can be readily identified when the temperature at Site 5MHW
closely matches that at Site 5P. Warm storm water discharges to Sumner
Creek may be detectable as thermal spikes at Sites 4 and 4A.
During the summer of
2006, the thermal performance of Sterling Ponds stormwater management
practices can be evaluated monthly by comparing the Sterling Ponds and
Sumner Creek thermographs. Performance of these stormwater management
practices during the three significant rainfall and runoff events in
July and August is of particular interest, and may help explain the
possible causes of the thermal impacts observed in lower Sumner Creek
(Site 4A). These July and August events were characterized by rainfall
amounts in excess of 1.5 inches, beyond the infiltration requirement of
the River Falls Storm Water Management Ordinance.
May
The comparative Sterling
Ponds and Sumner Creek thermographs for May 2006 are presented in
Figure
23. As indicated by the nearly identical temperatures at Sites 5P and
5IB, the Sterling Ponds wet detention pond was already discharging to
the infiltration basin on May 1, due to rainfall events on April 29
(0.46 inch) and April 30 (0.25 inch). With numerous smaller rainfall
events during the May 1-19 period, the wet pond continued discharging to
the infiltration basin until May 21. No further discharges to the
infiltration basin occurred through the end of May, in spite of two
small rainfall events on May 25 (0.08 inch) and May 29 (0.03 inch). No
wet pond discharges to Sumner Creek occurred in May, and no thermal
spikes were apparent in Sumner Creek (Sites 4 and 4A), downstream from
Sterling Ponds. The entire May rainfall amount of 2.10 inches (11 small
events ranging from 0.01-0.39 inch and 1 moderate event of 0.97 inch)
(Figure 5) was infiltrated.
June
The comparative Sterling
Ponds and Sumner Creek thermographs for June 2006 are presented in
Figure 24. As indicated by the nearly identical temperatures at Sites
5P and 5IB, the Sterling Ponds wet detention pond discharged to the
infiltration basin during the June 6-8 period (Figure 25), due to small
rainfall events on June 5 (0.08 inch) and June 6 (0.25 inch). No wet
pond discharges to Sumner Creek occurred during the June 6-8 period, and
no thermal spikes were apparent in Sumner Creek (Sites 4 and 4A),
downstream from Sterling Ponds (Figure 25). The remainder of June was
very dry, and no further discharges to the infiltration basin occurred
through the end of the month (Figure 24). The entire June rainfall
amount of 0.73 inch (11 small events ranging from 0.01-0.25 inch)
(Figure 5) was infiltrated.
July
The comparative Sterling
Ponds and Sumner Creek thermographs for July 2006 are presented in
Figure 26. The July 1-23 period was hot and dry, with small rainfall
events recorded on only three dates. During this time period, no wet
pond discharges occurred to either the infiltration basin or Sumner
Creek, and no thermal spikes were apparent in Sumner Creek (Sites 4 and
4A), downstream from Sterling Ponds. The three small rain events,
totaling 0.77 inch, were likely stored in the wet pond and/or evaporated
from the pond, given the high ambient air and pond temperatures.
The comparative Sterling
Ponds and Sumner Creek thermographs for the large July 24 rain event
(1.80 inches) are presented in
Figure 27. As indicated by the nearly
identical temperatures at Sites 5P and 5IB, the Sterling Ponds wet
detention pond began discharging to the infiltration basin at 18:30 CDT
(6:30 PM) on July 24, shortly after the onset of heavy rainfall at 18:00
CDT (6:00 PM). Wet pond discharge to the infiltration basin, due to the
July 24 rainfall event, continued for four days, until 19:00 CDT (7:00
PM) on July 28. As indicated by the nearly identical temperatures at
Sites 5P and 5MHW, the Sterling Ponds wet detention pond began
discharging to the Sumner Creek drainage way at 18:40 CDT (6:40 PM) on
July 24 and continued discharging until 22:40 CDT (10:40 PM). During
this 4-hour period, the wet pond discharge temperature averaged 24.5º C
and ranged from 23.4-26.5º C. Some storage of this storm water
discharge likely occurred in the wetland that comprises the creek
drainage way upstream from Site 4. A marked temperature increase (2.3º
C) was apparent downstream at Site 4 in Sumner Creek by 23:30 CDT (11:30
PM) on July 24, and is likely due to the release of warm water
(including storm water) from the upstream wetland. The thermal spike
(5.3º C) evident near the mouth of Sumner Creek (Site 4A) at 19:50 CDT
(7:50 PM) on July 24 cannot be attributed to the Sterling Ponds storm
water discharge, since the spike at Site 4A, located 1.5 miles
downstream, occurred shortly after the storm water discharge, but well
before the thermal spike was evident at Site 4. It seems apparent that
the thermal spike at Site 4A had a more “local” cause, perhaps including
storm water runoff from WI Highway 35 and/or warm water flowing from
natural wetland or storage areas in the upstream Sumner Creek drainage
way.
During the July 24 rain
event, the wet pond began discharging to Sumner Creek shortly (10
minutes) after it began discharging to the infiltration basin. However,
the duration of discharge to Sumner Creek (4 hours) was relatively
short, compared to the duration of discharge to the infiltration basin
(96 hours). It seems likely that most of this rain event was
infiltrated, but a brief discharge of warm storm water occurred, with a
downstream impact in Sumner Creek at Site 4.
August
The comparative Sterling
Ponds and Sumner Creek thermographs for August 2006 are presented in
Figure 28. August was the wettest month of the summer 2006 monitoring
season, with 6.68 inches of rain. As indicated by the nearly identical
temperatures at Sites 5P and 5IB, the Sterling Ponds wet detention pond
discharged to the infiltration basin during the August 1-8, August
13-14, and August 23-31 periods, after large back-to-back rainfall
events on August 1-2 (1.04 and 2.26 inches), a smaller rainfall event on
August 13 (0.48 inch), and large back-to-back rainfall events on August
23-24 (0.71 and 1.63 inches). Unfortunately, the temperature logger at
Site 5MHW malfunctioned after July 26, making it impossible to directly
determine if the wet pond was discharging to Sumner Creek after rainfall
events in August and September. However, no thermal spikes were
apparent in Sumner Creek (Sites 4 and 4A), downstream from Sterling
Ponds, after the August 13 rain event (0.48 inch), suggesting that this
entire event was infiltrated. Similarly, smaller rainfall events on
August 6 (0.28 inch) and August 25 (0.11 inch) were likely infiltrated,
while the smaller event on August 17 (0.13 inch) was likely stored in
the wet detention pond.
The comparative Sterling
Ponds and Sumner Creek thermographs for the large back-to-back rainfall
events on August 1-2 (1.04 and 2.26 inches) are presented in
Figure 29.
As indicated by the nearly identical temperatures at Sites 5P and 5IB,
the Sterling Ponds wet detention pond began discharging to the
infiltration basin at 04:30 CDT (4:30 AM) on August 1, shortly after the
onset of rainfall at 03:00 CDT (3:00 AM). Wet pond discharge to the
infiltration basin, due to the August 1-2 rainfall events, continued for
nearly seven days, until 03:00 CDT (3:00 AM) on August 8. Since no
temperature data are available at Site 5MHW, it is not possible to
directly determine if the wet pond discharged to Sumner Creek. However,
after heavy rainfall commenced again at 23:00 CDT (11:00 PM) on August
1, a marked temperature increase (2.8º C) was apparent downstream at
Site 4 in Sumner Creek by 06:00 CDT (6:00 AM) on August 2, and is likely
due to the discharge of Sterling Ponds storm water and release of warm
water from the upstream wetland. At Site 4A near the mouth of Sumner
Creek, a series of three thermal spikes occurred on August 1 and 2. The
large (primary) thermal spike (5.3º C) at 22:30 CDT (10:30 PM) on August
1 and a smaller secondary spike (1.5º C) at 04:00 CDT (4:00 AM) on
August 2 cannot be attributed to a Sterling Ponds storm water discharge,
since both spikes occurred prior to the thermal spike at Site 4 upstream
(06:00 CDT). The first two thermal spikes had a more local cause (see
the discussion of the July 24 rain event, above). However, the “plug”
of warm water passing through Site 4 (at 06:00 CDT on August 2) may have
contributed to the third thermal spike (3.6º C) downstream at Site 4A
(at 15:30 CDT on August 2). The time-of-travel (9.5 hours) and speed of
travel (0.2 miles per hour) for water flowing between Sites 4 and 4A in
Sumner Creek seem plausible for this low-gradient stream with extensive
wetland areas. Furthermore, the peak temperature at Site 4 (24.0º C)
was sufficiently high enough to create the peak temperature at Site 4A
(22.0º C).
The comparative Sterling
Ponds and Sumner Creek thermographs for the large back-to-back rainfall
events on August 23-24 (0.71 and 1.63 inches) are presented in
Figure
30. As indicated by the nearly identical temperatures at Sites 5P and
5IB, the Sterling Ponds wet detention pond began discharging to the
infiltration basin at 05:30 CDT (5:30 AM) on August 23, shortly after
the onset of rainfall at 05:00 CDT (5:00 AM). Wet pond discharge to the
infiltration basin, due to the August 23-24 rainfall events, continued
for eight and one-half days, until 17:30 CDT (5:30 PM) on August 31.
Since no temperature data are available at Site 5MHW, it is not possible
to directly determine if the wet pond discharged to Sumner Creek. After
the August 23 rainfall event (0.71 inch), no thermal spike was apparent
downstream at Site 4 in Sumner Creek, suggesting that no discharge of
Sterling Ponds storm water occurred. However, after heavy rainfall
commenced again at 17:00 CDT (5:00 PM) on August 24, a marked
temperature increase (2.1º C) was apparent downstream at Site 4 in
Sumner Creek by 22:40 CDT (10:40 PM), and is likely due to the discharge
of Sterling Ponds storm water and release of warm water from the
upstream wetland. At Site 4A near the mouth of Sumner Creek, no thermal
spike was apparent after the August 23 rain event, but two thermal
spikes occurred on August 24 and 25, after the August 24 rain event.
The large (primary) thermal spike (4.1º C) at 21:00 CDT (9:00 PM) on
August 24 cannot be attributed to a Sterling Ponds storm water
discharge, since the spike occurred prior to the thermal spike at Site 4
upstream (22:40 CDT). The first thermal spike had a more local cause
(see the discussion of the July 24 rain event, above). However, the
“plug” of warm water passing through Site 4 (at 22:40 CDT on August 24)
may have contributed to the smaller (secondary) thermal spike (1.8º C)
downstream at Site 4A (at 07:00 CDT on August 25). The time-of-travel
(8.5 hours) and speed of travel (0.2 miles per hour) for water flowing
between Sites 4 and 4A in Sumner Creek seem plausible for this
low-gradient stream with extensive wetland areas. Furthermore, the peak
temperature at Site 4 (19.8º C) was sufficiently high enough to create
the peak temperature at Site 4A (17.8º C).
September
The comparative Sterling
Ponds and Sumner Creek thermographs for September 2006 are presented in
Figure 31. Like May and June, September was characterized by numerous
smaller rainfall events (14 events less than 0.50 inch) and a moderate
event (0.66 inch) on September 3 (Figure 5), resulting in below-normal
precipitation for the month. As indicated by the nearly identical
temperatures at Sites 5P and 5IB, the Sterling Ponds wet detention pond
discharged to the infiltration basin during the September 3-9, September
16-18, and September 22-30 periods.
During the moderate
rainfall event (0.66 inch) on September 3, the Sterling Ponds wet
detention pond began discharging to the infiltration basin at 16:40 CDT
(4:40 PM) on September 3, shortly after the onset of rainfall at 16:00
CDT (4:00 PM) (Figure 32). Wet pond discharge to the infiltration basin
continued for six days, until 16:30 CDT (4:30 PM) on September 9. Since
no temperature data are available at Site 5MHW, it is not possible to
directly determine if the wet pond discharged to Sumner Creek. However,
after the September 3 rainfall event, no thermal spike was apparent
downstream at Site 4 in Sumner Creek, suggesting that no discharge of
Sterling Ponds storm water occurred. In addition, no thermal spike was
evident at Site 4A, near the mouth of Sumner Creek.
Small, back-to-back
rainfall events occurred on September 16 (0.28 inch) and September 17
(0.10 inch). After the September 16 event, the Sterling Ponds wet
detention pond began discharging to the infiltration basin at 20:30 CDT
(8:30 PM) on September 16 and continued discharging until 10:40 CDT
(10:40 AM) on September 18 (Figure 33). During this time period, no
thermal spikes were apparent downstream at Site 4 in Sumner Creek,
suggesting that no discharges of Sterling Ponds storm water occurred.
In addition, no thermal spikes were evident at Site 4A, near the mouth
of Sumner Creek.
Three consecutive days
of rainfall occurred on September 21 (0.38 inch), September 22 (0.24
inch), and September 23 (0.37 inch). During the September 21 event, the
Sterling Ponds wet detention pond began discharging to the infiltration
basin at 21:50 CDT (9:50 PM) on September 21 and continued discharging
through the end of September (Figure 34). During the September 21-30
period, no thermal spikes were apparent downstream at Site 4 in Sumner
Creek, suggesting that no discharges of Sterling Ponds storm water
occurred. In addition, no thermal spikes were evident at Site 4A, near
the mouth of Sumner Creek.
Based upon the Sterling
Ponds and Sumner Creek temperature data, it appears that the entire
September rainfall amount of 2.30 inches (15 small-to-moderate events
ranging from 0.01-0.66 inch) (Figure 5) was infiltrated.
Effectiveness of Sterling Ponds Storm Water
Management Practices:
During the May-September
(summer) 2006 period, the extent of storm water discharge to the
Sterling Ponds infiltration basin could be readily determined, as
temperature monitoring of the basin (Site 5IB) was conducted throughout
the summer. The extent of storm water discharge to Sumner Creek could
be directly determined via temperature monitoring at the wet pond outlet
(Site 5MHW) and/or indirectly determined by the presence of thermal
spikes in Sumner Creek (Sites 4 and 4A). Due to equipment malfunction
at Site 5MHW, discharges to Sumner Creek could not be directly
determined after July 26.
The available
temperature data for Site 5P, Site 5IB, and Site 5MHW suggest that the
performance of the Sterling Ponds storm water management practices (wet
detention pond and infiltration basin) was excellent during 49 summer
rain events, ranging in magnitude from 0.01-1.04 inches, representing
8.72 inches of precipitation, or 60% of the total summer rainfall amount
(14.41 inches). All runoff from these events was infiltrated.
All 38 rainfall events in May, June, and September were infiltrated.
These events ranged from 0.01-0.97 inch in magnitude and represented
monthly totals of 2.10, 0.73, and 2.30 inches, respectively, or 36% of
the total summer rainfall amount. Four small-to-moderate rain
events in July, ranging from 0.03-0.52 inch and totaling 0.80 inch, were
either infiltrated or stored in the wet detention pond. Seven
small-to-moderate rain events in August, ranging from 0.11-1.04 inches
and totaling 2.79 inches, were largely infiltrated.
With the exception of
the three largest rain events in July and August (1.80 inches on July
24, 2.26 inches on August 2 and 1.63 inches on August 24), all summer
(May-September) rainfall events were fully infiltrated. The discharges to
Sumner Creek due to these three large events were directly measured at
Site 5MHW during the July event, and indirectly measured as thermal
spikes at Site 4 during the two August events. Although the magnitude
of all three events exceeded the River Falls Storm Water Management
Ordinance requirement (to infiltrate additional runoff of a 1.5-inch,
24-hour rainfall compared to pre-development conditions), it seems
likely that substantial infiltration of these events occurred. The
duration of the storm water discharges to Sumner Creek was relatively
short (4 hours), compared with lengthy discharges of storm water to the
infiltration basin (4-8.5 days), suggesting that the majority of storm
water from these three rain events was infiltrated rather than
discharged. Since the storm water volumes discharged to the
infiltration basin and Sumner Creek were not measured, it is not
possible to precisely determine the amount of water infiltrated.
Although the magnitude of these rain events clearly exceeded the
1.5-inch infiltration requirement of the storm water management
ordinance, the events nonetheless resulted in warm storm water
discharges that produced pronounced thermal spikes in Sumner Creek
(2.1-2.8 ºC at Site 4 and 3.6 ºC at Site 4A).
During the July 24 rain
event (1.80 inches), the wet pond began discharging to the Sumner Creek
drainage way shortly (10 minutes) after it began discharging to the
infiltration basin. Although the intensity of this rain event was high
(1.5 inches in two hours), it is desirable to infiltrate as much of the
first 1.5 inches of rainfall as possible, prior to discharging any
excess amount. At a minimum, it is especially desirable to capture the
“first-flush” component of storm water runoff, which generally conveys
the greatest thermal impact and highest concentrations of pollutants.
Very warm water (23.4-26.5º C) from the wet detention pond was almost
immediately conveyed to Sumner Creek during the July 24 event, in spite
of very dry antecedent conditions and potential storage capacity in the
wet detention pond. The two large rain events in August (2.26 and 1.63
inches) may also have caused early discharges of warm storm water to
Sumner Creek. Although temperature data at Site 5MHW are not available
for direct comparison of wet pond discharge time to the onset of
rainfall, thermal spikes were evident at Site 4 within five hours after
the onset of rainfall, suggesting a release of warm storm water at the
wet pond outlet. Compared to the early wet pond discharges to Sumner
Creek during the July and August rain events, wet pond discharges to the
infiltration basin occurred for extended periods, ranging from 4-8.5
days.
The pipe leading from
the wet pond to the infiltration pond is inverted to provide a skimming
device, so that oils and other debris floating in the wet pond are not
transferred to the infiltration basin. Due to the hydraulics of an
inverted pipe, water will continue to trickle into the infiltration
basin for an extended time period following a rain event. More rapid
delivery of storm water to the infiltration basin may be desirable.
During the summer of 2006, rather lengthy infiltration times (1.5-8.5
days) were evident for a variety of rainfall events (0.33-2.26 inches).
An extended infiltration time may be desirable when there is adequate
time between rain events, as it also maximizes total suspended solids
(TSS) and total phosphorus (TP) removal in the wet pond. However, it
certainly limits the available storage volume in the wet pond when the
next rain event occurs, possibly causing a premature discharge of storm
water to the creek drainage way. This is particularly true for larger,
back-to-back rainfall events, such as those that occurred on August 1-2
and August 23-24. During both of these back-to-back August events, wet
pond discharge to the infiltration basin was already underway due to the
first rain event, but was not yet complete when the second rain event
began. A moderate rain event on August 1 (1.04 inches) caused a
discharge to the infiltration basin at 04:30 CDT, but the large event on
August 2 (2.26 inches) began at 24:00 CDT (midnight) on August 1, with
infiltration of the first event not yet complete. Similarly, a moderate
rain event on August 23 (0.71 inch) caused a discharge to the
infiltration basin at 05:30 CDT, but the large event on August 24 (1.63
inches) began at 14:00 CDT, with infiltration of the first event not yet
complete. The August 1-2 events were only separated by a 13-hour
period, but the August 23-24 events were separated by a 31-hour period.
The current ordinance requires water to be infiltrated within 48 hours.
Therefore, these events did not violate the ordinance, but perhaps some
provisions should be made for back-to-back events.
The relatively small
diameter of the pipe (8 inches) leading to the infiltration basin may be
limiting the ability of the wet detention pond to deliver the
appropriate storm water volume to the infiltration basin before the pond
discharges to the creek. As stated above, the ordinance requires
infiltration within 48 hours; however the inverted pipe extends that
timeline greatly. Modeling of the Sterling Ponds storm water management
practices was conducted in 2006 to further investigate performance and
determine if any corrective action is necessary. The current pond
configurations were put into a HydroCAD model. The outlet structure of
the pond to Sumner Creek is controlled by a weir in the structure, which
allows storage of water to be diverted to the infiltration basin, but
anything above the weir discharges to the creek. By adjusting the
height of that weir we are able to hold back additional water for
infiltration and provide added storage to the basin. However rate
control requirements must still be complied with. It was determined
through modeling that the weir could be raised from 922.5 to 923.0 and
still meet rate control requirements. This adjustment will be made by
City maintenance staff prior to the deployment of the temperature
monitors in the spring of 2007. Results will be monitored and examined
with data gathered throughout the 2007 monitoring season.
While this project is
primarily focused on evaluating long-term trends, annual information is
important as well. The storm water management practices at Sterling
Ponds caused no major thermal impacts on the Kinnickinnic River during
the May-September (summer) 2006 period. The following should be noted:
·
The summer temperature regime in the Kinnickinnic River at
Sites 1A and 1 (above and below the Sumner Creek confluence) was
generally excellent for coldwater macroinvertebrate and brown trout
communities.
·
The performance of the Sterling Ponds storm water
management practices (wet detention pond and infiltration basin) was
excellent during 49 summer rain events, ranging in magnitude from
0.01-1.04 inches and totaling 8.72 inches (60% of the total summer
precipitation). All storm water runoff from these events was
infiltrated, as required by the River Falls Storm Water Management
Ordinance.
·
During the three largest summer rain events (in excess of
1.5 inches), the Sterling Ponds wet detention pond discharged very warm
water (23.4-26.5º C) to the Sumner Creek drainage way, often for
extended periods (4 hours). These warm storm water discharges produced
pronounced thermal spikes (2.1-2.8 ºC) in Sumner Creek at Site 4.
After the largest rain event of the summer on August 2 (2.26 inches), a
“plug” of warm water (including Sterling Ponds storm water) moved
downstream from Site 4, also causing a thermal spike (3.6 ºC) at Site
4A, near the mouth of Sumner Creek. However, no thermal spike was
apparent downstream in the Kinnickinnic River, at Site 1. We will watch
for these thermal spikes in the years to come and monitor their
intensity and frequency.
·
The very prominent “first-flush” thermal spikes (4.1-7.1
°C) observed in lower Sumner Creek (Site 4A) during the three largest
summer rain events appear unrelated to the storm water discharges at
Sterling Ponds, and seem to have a more local cause.
Water Quality Monitoring:
No runoff event-based
water quality monitoring was conducted in 2006. With below-normal
precipitation during the April-September period (Figure 2), very few
significant runoff events occurred in the North Kinnickinnic River
Monitoring Project Area. Numerous small rain events (less than 0.50
inch) in April, May, June, and September had little influence on the
Kinnickinnic River hydrograph (Figure 7). A large rainfall event on
July 24 (1.80 inches) resulted in only a moderate increase in the
Kinnickinnic River hydrograph, due to very dry antecedent conditions.
Large back-to-back rainfall events on August 1-2 (3.30 inches) and
August 23-24 (2.34 inches) produced significant increases in the
Kinnickinnic River hydrograph, but no water quality samples were
obtained during these two events. Given more normal precipitation and
runoff conditions, the water quality monitoring component of the North
Kinnickinnic River Monitoring Project will be initiated in 2007.
Base Flow Surveys:
The USGS stream flow
gauge located at County Highway F, as described earlier in this report,
was used to determine when a base flow condition existed in the
Kinnickinnic River. 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 of approximately 85-95 cfs at County Highway F.
Real-time and recent (31-day) stage, flow, and precipitation data for
this monitoring station are web-accessible at:
http://waterdata.usgs.gov/wi/nwis/uv?dd_cd=02&format=gif&period=7&site_no=05342000
In the spring and autumn
of 2006, instantaneous measurements of base flow were obtained 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 2006
base flow surveys were conducted using a SonTek® FlowTracker
handheld acoustic doppler velocimeter (ADV).
The spring 2006 survey
was conducted on May 24 & 25. Kinnickinnic River base flows were lowest
at Site 3 (54 cfs) and nearly identical at Sites 1 (64 cfs) and 2 (65
cfs). Sumner Creek provided a small contribution (1 cfs) to the
Kinnickinnic River, just upstream of Site 1. An additional 52% increase
in Kinnickinnic River base flow occurred between Site 1 and County
Highway F (97 cfs), including contributions from the South Fork of the
Kinnickinnic River (unmeasured), Mann Valley Creek (unmeasured), and
Rocky Branch Creek (6 cfs).
The fall 2006 survey was
conducted on October 10. These autumn 2006 survey results are presented
in
Figure 35, with a comparison to the autumn 2005 survey results. In
autumn 2006, Kinnickinnic River base flows were nearly identical at
Sites 2 and 3 (52 cfs). The base flow at Site 1 (55 cfs) was only
slightly higher, with Sumner Creek providing a small contribution (1 cfs)
upstream of Site 1. An additional 84% increase in Kinnickinnic River
base flow occurred between Site 1 and County Highway F (101 cfs),
including contributions from the South Fork of the Kinnickinnic River
(unmeasured), Mann Valley Creek (unmeasured), and Rocky Branch Creek (6
cfs). The autumn 2006 Kinnickinnic River base flows in the project area
(Sites 1-3) were reduced, compared to autumn 2005, likely due to
below-normal precipitation during the summer of 2006. A reduction was
especially apparent at Site 1. The autumn 2005 and 2006 Sumner Creek
base flows were essentially identical. In autumn 2006, slight base flow
increases were apparent in Rocky Branch Creek, and in the Kinnickinnic
River at County Highway F.
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 surveys in 2005 and 2006 will
provide a baseline for determining if base flow conditions will be
sustained in the future as development progresses in the North
Kinnickinnic River Monitoring Project Area.
Macroinvertebrate Monitoring:
Biotic indicators such
as macroinvertebrates (aquatic insects) are often used to complement
physical and chemical measurements in stream monitoring programs.
Biological data add a significant dimension to monitoring procedures
because they provide an analysis that measures long-term phenomena.
Because many aquatic organisms live in the stream environment for a year
or more, they are excellent indicators of past as well as present water
quality conditions. Annual macroinvertebrate samples are collected at
Sites 1-3 within the North Kinnickinnic River Monitoring Project Area.
Organisms are identified and counted in the laboratory, and various
biological indices can then be calculated for each monitoring site. The
index values are indicative of water quality, depending upon the
pollution tolerances of the macroinvertebrates collected at the
monitoring sites.
The use of benthic
macroinvertebrates (bottom-dwelling aquatic insects and crustaceans) was
initiated in Wisconsin with the work of W. L. Hilsenhoff at the
University of Wisconsin-Madison, and has been modified and refined (Hilsenhoff
1982, 1987). The Hilsenhoff Biotic Index (HBI) is particularly useful
for determining the influence of organic pollution on macroinvertebrates.
The Wisconsin Department of Natural Resources has used this index for
many years in long-term stream monitoring efforts.
Macroinvertebrate HBI
determinations follow a sequence of field collection, laboratory
sorting, identification, and index calculation. Each macroinvertebrate
taxon has been assigned a specific tolerance value at the genus or
species level. These values range from 0 (extremely intolerant of
organic pollution) to 10 (extremely tolerant of organic pollution).
Because the HBI calculation is based on multiplying the count of a given
taxon (number of individuals in the sample) by its specific tolerance
value, the more intolerant taxa that are present, the lower the biotic
index, indicating better water quality, as follows:
