HomeMy WebLinkAboutMemo - Mail Packet - 6/26/2018 - Memorandum From Matt Fater And Theresa Connor Re: May 22, 2018 Storm AssessmentUtilities
700 Wood St.
PO Box 580
Fort Collins, CO 80522
970.221-6700
970.221-6619 - fax
fcgov.com
MEMORANDUM
DATE: June 18, 2018
TO: Mayor Troxell and Councilmembers
THROUGH: Darin Atteberry, City Manager
Jeff Mihelich, Deputy City Manager
Kevin Gertig, Utilities Executive Director
FROM: Matt Fater, Special Projects Manager
Theresa Connor, Water Engineering and Field Operations Manager
RE: May 22, 2018 Storm Assessment
Bottom Line
The City experienced a severe rain and hail storm the evening of May 22, 2018. Urban flooding
occurred in the northwest portion of the City including numerous intersections and major
drainageways. While the storm confirmed known flood risks, the storm also highlighted the
benefit of prior investments into the stormwater infrastructure. Several areas of downtown and
the western side of the City did not experience damage due to capital improvements that have
been made in the stormwater system.
Background
The storm began around 6:00 pm MST with pea sized hail followed by intense rain. Several of
the City’s flood warning rainfall gages reported alarms for rainfall intensity. Rain gages in
northwest Fort Collins received the highest rainfall with storm totals of close to 2-inches for a 30
– 40-minute duration. For reference, the 100-year design storm is 3.67” for a 2-hour duration.
Figure 1 shows the location of the City’s rain gages as well as recorded totals for the storm.
Of the City’s 12 major stormwater basins, the Old Town basin, the Canal Importation basin and
portions of the Spring Creek basin received the highest intensity rainfall. There were numerous
reports of flooded intersections in known problem areas where the stormwater system is not
sufficient. There were also reports of first floor and basement flooding in these areas. Staff is
conducting a survey to understand the extent of the structure flooding. City crews responded to
many of these areas to clean storm drain inlets overwhelmed by debris and hail.
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Figure 1 – May 22, 2018 rainfall totals (inches) from 6:00 pm to 8:00 pm, City of Fort Collins Rain Gages
Old Town Basin
The Old Town basin has some of the most vulnerable areas to flooding in the City especially for
short duration high intensity storms such as the storm of May 22
nd
. The rain gage at the City
Park Golf Course measured 2.17 inches in 2 hours which is directly to the west and at the
upstream portion of the basin. Much of the basin was developed prior to stormwater design
standards so there’s a lack of infrastructure to handle such rain events.
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Figure 2 – Old Town Basin
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The Old Town Master Drainage Plan was adopted by the City in 2003. The master plan
identified the 100-year floodplain as shown in Figure 2. Many of the problem areas for the May
22
nd
storm were identified as known flooding areas within the 100-year floodplain. Had the
storm continued, the extent of the flooding could have been much worse as indicated on the
floodplain map. The master plan also identified a system of improvements to address the
flooding. The City is currently in the feasibility and alternative analysis phase of the largest of
those projects, the Magnolia St. Outfall. The photo documentation below shows the flooding
and high-water marks due to the May 22
nd
storm.
Photo 1 – College Ave and Mulberry St. Intersection looking south. Photo by Linsey Chalfant.
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Photo 2 – Mulberry St. and Mason St. Intersection looking southeast. Reports from the Fort Collins Coloradoan stated the vehicle in the photo
was abandon after a woman and her two kids were rescued from the vehicle after their car stalled due to the high water. Photo by Matt Fater.
Photo 3 – Howes St. looking north from Mulberry St. The building on the right side of the photo, 420 Howes St., reported water inside the
garden level offices. Photo by Linsey Chalfant.
High-Water Mark
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Photo 4 – Mulberry St. looking east from Howes St. Mulberry St. closed due to stalled vehicles. Photo by Matt Fater.
Photo 5 – Magnolia St. and Meldrum St. Intersection looking southeast. Photo by Linsey Chalfant.
High-Water Mark
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Old Town Capital Improvement Projects
The City has made significant investments in stormwater infrastructure in portions of the Old
Town basin outside of the Mulberry/Magnolia corridor. The Howes St., Oak St., and Locust
St. Outfalls were constructed in the late 1990’s and early 2000’s to address flooding downtown
and surrounding neighborhoods. Figure 2 shows the location of these outfalls. If these outfalls
were not in place for the May 22
nd
storm there would have been more areas of flooding
including: Laporte St./ Mason St. Intersection, along Mountain Ave. from Mason to Riverside,
and along Locust St. from College Ave to Stover St. These projects effectively reduced the
flooding in these areas demonstrating the benefits of proactive flood mitigation.
Canal Importation Basin
The Canal Importation Basin also received intense hail and rainfall the evening of May 22
nd
.
The rain gages at Avery Park and the Ponds at Overland received 2.13 inches and 1.87 inches for
the 2-hour duration, respectively. The basin is defined by three west-east flow paths: Plum
Channel on the north end, the Clearview Channel in the middle and the Canal Importation
Channel on the south ends. The Canal Importation Channel flow path contains a higher degree
of stormwater infrastructure. Consequently, this area was not surveyed for post-storm
documentation. However, the Plum and Clearview Channel areas have known problem areas
that were surveyed for documentation. The two channels are historic flow paths that have been
encroached upon by development that occurred prior to stormwater design standards and
floodplain regulations.
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Figure 3 – Canal Importation Basin
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The Canal Importation Basin Master Drainage Plan was adopted by the City in 2003. The
master plan identified the 100-year floodplain as shown in Figure 3. Many of the problem areas
for the May 22
nd
storm were identified flooding areas within the 100-year floodplain. Had the
storm continued, the extent of the flooding could have been much worse as indicated on the
floodplain map. The master plan also identified a system of improvement to address the flooding
including extensive work for the Plum Channel and limited work on Clearview Channel. The
photo documentation below shows high water marks due to the May 22
nd
storm.
Photo 6 – Plum Channel between Gallup Rd. and Tyler St. looking east. Photo by Matt Fater, May 23, 2018.
High-Water Mark
Basement
Windo
w
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Photo 7 – Plum Channel at Tyler St. looking west. Photo by Matt Fater, May 23, 2018.
Photo 8 – Clearview Channel looking west to Ponderosa. Photo by Matt Fater, May 23, 2018.
High-Water Mark
High-Water Mark
Basement
Entranc
e
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Photo 9 – Springfield Court south of Clearview Channel looking north. Photo by Matt Fater, May 23, 2018.
Canal Importation Basin Capital Improvements
The City has made significant investments in stormwater infrastructure in portions of the Canal
Importation Basin downstream of the Plum Channel and Clearview Channel corridors. The
Canal Importation Ponds and Outfall (CIPO) project was constructed from 2008 to 2012. The
project consisted of the Castlerock Storm Sewer as well as five detention basins: including the
Glenmoor Detention Pond, the Avery Park Detention Pond, and the Red Fox Meadows Natural
Detention Pond. Figure 3 shows the location of these facilities. This project intercepted
stormwater during the May 22
nd
storm coming from the west from Plum and Clearview Channels
and safely conveyed it to Red Fox Meadows and downstream to Spring Creek. If the CIPO
project had not been in place, flooding in Campus West and the surrounding neighborhoods
would have been worse.
High-Water Mark
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Photo 10 – Red Fox Meadows Detention Pond looking south east. Functioned as designed. Photo by Chris Wolf.
Spring Creek Basin
The Spring Creek Basin received slightly less intense hail and rain the evening of May 22
nd
. The
rain gages in the western half of the basin received around 1.5 inches for the 2-hour duration.
The storm was not of sufficient duration or extent to generate significant flooding along the main
reach of Spring Creek. In addition, the City has proactively invested significantly in
improvements to Spring Creek to handle a storm such as this. However, intersection flooding on
the north end of the basin were reported due to inadequate storm drain capacity most notably
Prospect/College and Lake/Remington. These intersections are known problem areas for
flooding. The City has been evaluating options to address the issue with the Remington St.
Outfall Project. The first phase is a recommended project in the 2019/2020 Stormwater budget.
The flooding at Lake and Remington would be a future phase of the Remington St. Outfall
project. The photo documentation below shows high water marks for these intersections the day
after the May 22
nd
storm.
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Photo 11 – Prospect and College Intersection southeast corner looking north on College Ave.
Photo by Matt Fater, May 23, 2018.
Photo 12 – Lake and Remington Intersection southwest corner looking west. Photo by Matt Fater, May 23, 2018.
High-Water Mark
High-Water Mark
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