The Thermal Impact of Untreated Storm Water:
The thermal impacts of
untreated storm water discharges to segments of the Kinnickinnic River
within the City of River Falls, especially in the downtown and Glen
Park areas, have been clearly documented by temperature monitoring
research conducted by the local Kiap-TU-Wish Chapter of Trout
Unlimited. These thermal impacts are also evident in the South
Fork of the Kinnickinnic River. For more information on the
impacts of storm water on the Kinnickinnic, the
local Trout Unilimted Chapter (Kiap-TU-Wish)
has some good papers available on their website:
Urban
Storm Water Impacts on a Cold Water Stream
by: Kent Johnson
Storm Water Management and the Kinni
by: Jeremy Cook
When summer rainfall
flows over warm impervious surfaces, it absorbs heat (thermal pollution)
that is discharged to the Kinnickinnic River through storm sewers,
causing a rapid and marked temperature increase at the beginning (first
flush) of a storm water runoff event. These rapid temperature increases
(thermal spikes) in the Kinnickinnic River may be particularly harmful
to macroinvertebrates (aquatic insects), which serve as a critical food
source for trout. Scientific research (Galli, 1990) shows that
macroinvertebrates have little ability to compensate for rapid
temperature changes. Hence temperature changes of 1-2 degrees
centigrade can reduce insect size and reproduction, while temperature
changes of 2-3 degrees centigrade could eliminate sensitive insect
species.
The Citys Storm Water
Ordinance targets new development, however, large quantities of runoff
come from the old parts of town also. Due to this, the City of River
Falls has been evaluating several storm water management options for 24
direct storm sewer discharges to the Kinnickinnic River between County
Road MM and Lake George. In June 2005, the city, with consulting
assistance from Bonestroo Rosene Anderlik and Associates, completed the
Lake George Area Stormwater Treatment Concept Plan, which presents
several alternatives for managing untreated stormwater from these 24
discharges.
Thermal Preferences of Brown Trout
for Survival and Growth
(Armour, 1994)
Physiological Optimum: 17.0 C (12.0 20.0 C)
Growth Optimum: 16.4 C (7.0 19.0 C)
Zero Net Gain Range: 19.5 21.2 C
(No Growth; Survival = Mortality)
Visible Thermal Stress: 19 30
C
Lower Value: Avoidance, restlessness, disturbing temperature
Upper Value: Maximum survival temperature for brief periods
Upper Ultimate Incipient Lethal Temperature: 25 30 C
Critical Thermal Maximum: 29.8
Summary: Brown trout will begin showing stress at 19 C (66F) and will
die above temperatures of 29 C (84F)
Thermal Preferences of Macroinvertebrates
(Galli, 1990)
Many aquatic insects (esp. mayflies) require a fluctuating diurnal
temperature regime
Temperatures > 17 C (63F) exceed the optimum for many stoneflies,
mayflies, and caddisflies
For more information about macroinvertebrates,
click here.
