HomeMy WebLinkAboutMemo - Mail Packet - 10/08/2024 - Memorandum from Diana Schmidt re: 2024 Summer Water Quality Update – Upper Cache la Poudre WatershedUtilities
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700 Wood Street
PO Box 580, Fort Collins, CO 80522
970-221-6700
utilities@fcgov.com
CC: Jill Oropeza, Senior Director of Water Planning and Sciences, Utilities
Leslie Hill, Director of Water Quality Services Division, Utilities
Richard Thorp, Watershed Program Manager, Utilities
Water Commission
MEMORANDUM
Date: September 30th, 2024
To: Mayor Arndt and City Councilmembers
Through: Kelly DiMartino, City Manager
Tyler Marr, Deputy City Manager
Nicole Poncelet-Johnson, One Water Director
From: Diana Schmidt, Specialist, Sciences
Subject: 2024 Summer Water Quality Update – Upper Cache la Poudre Watershed
BOTTOM LINE
The Upper Cache la Poudre (CLP) Watershed Collaborative Water Quality Monitoring Program
is a partnership between the cities of Fort Collins, Greeley and Thornton, Northern Water
Conservancy District and Soldier Canyon Water Treatment Authority. The goal of this
monitoring program is to assist participants with meeting current and future drinking water
treatment goals by reporting current water quality conditions and trends within the Upper CLP
Watershed. The attached water quality update provides a summary of precipitation and drought,
streamflow, and water quality conditions observed in the Upper CLP watershed during summer
2024.
BACKGROUND
Seasonal updates are published annually during spring, summer, and fall each year. These
updates are meant to inform program partners, their customers and other community
stakeholders about the current condition of our source watershed and the quality of the raw
drinking water supply. In-depth water quality trend reporting is accomplished through annual
and five-year technical reports. Water quality reports and seasonal updates are publicly
available on the Fort Collins Utilities’ website, https://www.fcgov.com/utilities/what-we-
do/water/water-quality/source-water-monitoring/upper-poudre-quality-monitoring.
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SPRING 2024 WATER QUALITY UPDATE HIGHLIGHTS
The 2024 summer update summarizes Poudre Watershed conditions during peak snowmelt
runoff and the receding streamflow that follows through the summer monsoon season. The
Upper CLP Watershed experienced drought conditions during the summer season, including
slightly below average precipitation and above average air temperatures. Additionally,
streamflow was below average, and the duration of snowmelt runoff was shorter in 2024. While
measurements of average water temperature, pH, conductivity, and turbidity at several sites
were somewhat elevated, they still were within expected ranges. These elevated values can
likely be attributed to persistent post-fire effects from the Cameron Peak Wildfire that continue to
influence Poudre River water quality during the monsoon season. However, water quality
conditions are generally trending toward recovery following the fire.
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Upper Cache la Poudre Watershed Collaborative Monitoring Program
SUMMER 2024 WATER QUALITY UPDATE
Source Water Monitoring
The Upper Cache la Poudre (CLP) Watershed Collaborative Water Quality Monitoring Program
is a partnership between the cities of Fort Collins, Greeley, and Thornton, Soldier Canyon Water
Treatment Authority, and Northern Water Conservancy District. The goal of the program is to help
these water providers meet present and future drinking water treatment goals.
Water quality monitoring of the CLP River drinking water supply is conducted from April through
November using sites strategically located throughout the watershed. Water quality data provide
valuable information about the health of our source watershed and quality of our raw water supply.
Water quality begins to stabilize following spring snowmelt runoff and routine monitoring is
reduced to monthly sampling. Routine water quality monitoring results are reported for six key
monitoring sites located throughout the CLP watershed. Monitoring sites capture water quality
conditions above and below major tributaries and near water supply intake structures (Figure
1). Current water quality conditions are compared to baseline water quality conditions over the
period of 2008 to 2012. Additionally, two water quality meters installed at Manners Bridge and
Indian Meadows on the Mainstem CLP capture and report real-time water quality changes to water
treatment staff.
The Summer 2024 Water Quality Update provides a seasonal summary of watershed conditions
in the Upper CLP watershed by highlighting weather, drought, streamflow, and water quality
conditions over the summer season (June – August).
Figure 1 – Upper Cache la Poudre
Collaborative Monitoring Program
water quality sampling sites and real-
time water quality instrument locations.
JWC - Joe Wright Creek above the
confluence with the Poudre River
PJW - Poudre River above the
confluence with Joe Wright Creek
PBR - Poudre River below Rustic
PSF - Poudre River below the
confluence with the Little South Fork
PNF - Poudre River above the
confluence with the North Fork at the
City of Fort Collins’ Intake
PBD - Poudre River below the
confluence with the North Fork at the
Bellvue Diversion
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Temperature
Air temperature measured at the Joe Wright Snowpack Telemetry (SNOTEL) station over the 2024 summer season was 1.7°F warmer than
the long-term average and ranked as the 11th hottest summer on record (out of 34 years). The monthly mean air temperature was well
above average in June and August, but slightly below average in July. The months of June and August both ranked as the ninth hottest on
record, while July ranked as the 10th coolest (Table 1).
Temperature
2024
(ºF)
Average
(ºF)
Departure
(ºF)2024 Rank
June 50.6 47.1 +3.5 9th (H)
July 51.9 52.5 -0.6 10th (C)
August 52.7 50.5 +2.2 9th (H)
Summer 51.7 50.0 +1.7 11th (H)
Precipitation
Precipitation measured at the Joe Wright SNOTEL over the 2024 summer season was slightly below average and ranked as the 20th driest
summer on record (out of 45 years). Precipitation was well below average in June and July and above average in August (Table 2). The
month of August ranked as the 8th wettest on record. Drought conditions persisted across the Upper CLP watershed and, despite the wetter
conditions in August, extended into the headwaters in the late summer (Figure 2).
Total Precipitation
2024
(inches)
Average
(inches)
% of
Average 2024 Rank
June 1.3 2.2 58%14th (D)
July 1.5 2.1 70%12th (D)
August 3.5 2.2 157%8th (W)
Summer 6.3 6.6 96%20th (D)
Table 1 – Monthly mean air temperatures
measured at the Joe Wright SNOTEL over
the summer months of 2024 compared to
the long-term average (1991 – 2020)
Note: H = hottest and C = coldest
Table 2 – Monthly accumulated precipitation totals
measured at the Joe Wright SNOTEL over the
2024 summer season compared to the long-term
average (1991 – 2020).
Note: W = wettest and D = driest
Figure 2 – Drought conditions for the state of Colorado as monitored by the United States Drought Monitor on June 4, 2024 (left) and August 27,
2024 (right). (Map source: https://droughtmonitor.unl.edu/)
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Streamflow Conditions
Streamflow at the Cache la Poudre River near the Canyon Mouth (CLAFTCCO) stream gage measured 123,627 acre-feet of water over the
summer season, which was 73% of the long-term average (calculated over the 1881 – 2023 measurement period). Peak streamflow was
observed on June 9th and measured 2,190 cubic feet per second – 110% of average. The timing of the 2024 peak occurred two days earlier
than the long-term average. However, the duration of snowmelt runoff was notably shorter in 2024. Following peak streamflow, flows
dropped quickly compared to the long-term average. Baseflow (low flow) conditions were observed earlier in the summer season than
normal. The total amount of water was much lower than average in all summer months (Figure 3).
Figure 3 –
Streamflow
conditions on the
Poudre River over
the 2024 summer
season (left) and
monthly total
water volume
measured over the
summer season
(right).
Water Quality Indicators
The Upper CLP Collaborative Water Quality Monitoring Program uses several key water quality indicators, including pH, conductivity,
temperature, and turbidity, which act as surrogates for other parameters. (Table 3). These indicators provide a snapshot of water quality
conditions and are useful for identifying trends or changes in water quality. Significant changes in these water quality indicators may
provide an early warning of potential water pollution.
Water Quality Indicator Explanation
Temperature
Water temperature influences other water quality parameters and is a
major driver of biological activity and algal growth in rivers, including
certain phytoplankton species that produce the taste and odor
compounds, geosmin and 2-methlyisoborneol.
pH
pH is an important water quality parameter to monitor, because
it influences the solubility and biological availability of chemical
constituents, including nutrients and heavy metals. pH near 7 is
considered neutral, with more acidic conditions occurring below 7 and
more basic, or alkaline, conditions occurring above 7.
Specific Conductivity
Conductivity is an index of dissolved ionic solids in water. Conductivity
is used as a general measure of water quality. Significant increases in
conductivity can be used as an indicator of increased pollution.
Turbidity
Turbidity is monitored to track changes in water clarity. Clarity
is influenced by the presence of algae and/or suspended solids
introduced to surface waters through various land use activities,
including runoff and erosion, urban stormwater runoff and drainage
from agricultural lands. For water treatment, turbidity is an important
indicator of the amount of suspended material that is available
to harbor pollutants, such as heavy metals, bacteria, pathogens,
nutrients and organic matter.
Table 3 – Water
quality indicators
measured as part of
the Upper Cache la
Poudre Collaborative
Water Quality
Monitoring Program.
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Summer monitoring captures water quality conditions during the Poudre River’s highest flow levels (peak streamflow) and when flow levels
gradually decrease (the falling limb of the hydrograph) in the months following peak streamflow. Water quality conditions generally stabi-
lize during this time of year. Constituents that were once diluted by high streamflow begin to concentrate as streamflow recedes. In general,
water temperature and specific conductivity increase, while turbidity and pH levels decrease. The summer season also marks the beginning
of the summer monsoon, which can lead to increased frequency and intensity of rain events. An active monsoon season, in combination
with a post-fire landscape, can lead to flash flooding, debris flows, and severe impacts to water quality.
All water quality indicators at key sites along the CLP River were within the baseline range of values over the 2024 summer season (Figure
4). Water temperature was warmer than normal at all key monitoring sites – normal is defined as the median value over the baseline period
of record. pH levels were near normal at nearly all key monitoring sites. The exceptions were Joe Wright Creek (JWC), the Mainstem Poudre
River above Joe Wright Creek (PJW), and below the City of Greeley’s diversion (PBD) where the pH was elevated. Specific conductivity
values were higher than normal at all key sites. Turbidity was elevated in the Poudre below Rustic (PBR), below the South Fork (PSF), and
at the City of Fort Collins’ diversion (PNF).
The 2024 summer season experienced periods of extended dry, hot, and drought conditions in the Upper CLP watershed. The combination
of these stressors likely contributed to the rapid runoff rate, shorter runoff duration, and ultimately earlier return to low-flow conditions,
resulting in higher water temperatures across the watershed. Additionally, an emerging post-fire impact observed in the watershed is a de-
layed nutrient response in high mountain reservoirs in the Cameron Peak burn scar. Extended hot, dry conditions paired with high nutrient
concentrations in reservoirs can prompt an increase in algal activity, resulting in the observed increase in pH at sites downstream of these
reservoirs. High-intensity precipitation events driven by the summer monsoon continued to cause several post-fire erosion, sedimentation,
and flooding events on the Poudre River over the summer season (Figure 5). These events briefly impacted water quality, resulting in an
increase in turbidity, and required water treatment plants to shut down their raw water intakes on the Poudre River. Ongoing erosion and
sedimentation likely also contributed to increased pH and specific conductivity across the watershed.
City of Greeley Water
Quality Technician,
Lucas Lane,
collecting water
quality samples
from the Mainstem
Poudre River below
the City of Greeley’s
diversion (PBD).
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Joe Wright Creek Canyon Mouth
Figure 4–
Water quality indicator
data collected at key
monitoring sites over the
2024 summer monitoring
season (June, July, and
August) compared to
baseline (2008 - 2012)
summer water quality
conditions.
Spring 2024
Median
Maximum
Median
Minimum
Graphic Explanation
Baseline data
range based
on long-term
data record
2008-2012
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Figure 5 – Turbidity measured in the Poudre River at the Manners Bridge Water Quality Alert System over the summer season. The water intake
shutdown threshold is 100 NTU.
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