HomeMy WebLinkAboutDrainage Reports - 06/19/2014City of Ft. Collins A�proved Plans
Approved By�-
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LAY of
Fort Collins
To:
From:
Date:
RE:
Streets Department
625 9'" Street
P.O. Box 580
Fort Collins, CO 80522.0580
970.221.6615
970.224-62'1
Icgov.comA
Memorandum
Rob Mosbey, City of Fort Collins Engineering
Clint Wood, EIT, and Tom Knostman, P.E.
Friday, June 13th, 2014
Irish Drive: Hydrology and Hydraulic evaluati
add sidewalk to east side of street from Vine ll..._ _.._.
Background
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The Engineering Department wishes to construct a new sidewalk along the east side of Irish
Drive from Vine Dr. to Cherry St. to improve pedestrian access to and from Irish Elementary
School and the residences along this busy street. The Streets Department has led the design effort
for this project, which needs to be completed ahead of a scheduled pavement upgrade in early
July.
Irish Drive was built in the late 1960s, with the majority of the houses on the east side of the
street being built within Larimer County in the early 1970s. Irish Elementary and the road itself
were annexed by the City of Fort Collins in 2000, with the adjacent properties to the east and
west being excluded from the annexation and remaining in the county.
Currently, there are concerns about storm water drainage along the east side of the street. Survey
information shows that many of the driveways and surrounding land drain toward the houses;
this is corroborated by site visits and photographs (see Figure 1 below). Hence, curb, gutter, and
sidewalk will need to be constructed in a manner improves drainage and protects homes from
flooding.
Figure 1. Examples of ponding and drainage issues on east side of street near 524 (L) and 600 (R) Irish Drive.
Page 1 of 4
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Fort Collins
Street, curb, gutter, and sidewalk section selection'
Because curb cuts would likely allow gutter flow to enter driveways, a continuous curb with roll-
over gutter, rather than vertical curb with drive cuts, was selected to intercept street runoff and
mitigate stormwater inundation of homes and garages.
To maintain or improve drainage patterns, the proposed sidewalk needs to slope toward the
gutter and be flush with, or below, existing grade at or near the right-of-way. To achieve a
flowline lower than existing grades, it was necessary to set the street cross slope to 4% or more
and push the crown of the street to the edge of the west parking lane (see page one of Appendix
B for sketch).
Hydrologic and Hydraulic Analysis
Current Drainage Pattern
Please refer to Appendix A for a project area map. The project is located in the West Vine
Stormwater Basin. The majority of the roadway currently drains southward. A small portion (100
feet or less) at the north end drains to the north into a ditch along the south side of W Vine Drive;
this section was not analyzed.
Sheet flow from Irish Drive is divided by the road crown into two flow paths. The west side is
confined to an existing concrete curb and gutter system for its entire length to Cherry Street to
the south. The east side is less defined, with flow generally following a shallow and ill-defined
roadside swale, interrupted by disconnected sections of curb and gutter.
At Cherry St, flow from the west gutter of Irish Drive enters a cross pan and joins the flow from
the east side of Irish. Both combined flows then travel east along Cherry St and ultimately empty
into a small wetland before entering the New Mercer Canal or, in times of higher flow, the
floodway draining to the east.
Many of the homes on the east side of Irish are at the same elevation as the street, with only a
small hump in the drive keeping drainage in the street. Even during times of moderate rainfall
(less than 1 inch per hour, as shown in the left photo in Figure 1), flow overtops these humps and
flows down driveways toward homes. This flow ultimately drains between the homes to Impala
Drive and then south to Cherry St where it discharges to the New Mercer Canal.
Proposed Drainage Pattern
The proposed improvements on the east side of Irish Drive will intercept stormwater flows and
confine them to a south -flowing gutter. For hydraulic analysis, a rainfall catchment was defined
by the following boundaries (please refer to PDF documents received from Mike Oberlander for
design documents and stationing):
• Street crown to the west
• A high point near the north end of Irish Drive at Station 12+05
• The proposed street gutter to the east, and
• A chosen point of interest to the south (described below)
Page 2 of 4
City of
Fort Collins
The point of interest is the flattest stretch of flowline (longitudinal slope of 0.45%) in the vicinity
of Station 4+50. According to the description provided above, this forms a catchment of
approximately 0.5 acres. All of this area is impervious surface.
The new curb, gutter, and sidewalk will not significantly increase impervious area because the
existing pavement on the east side of Irish Drive extends to the limits of the proposed back of
walk for most of the project's length. The current basin area for the road and sidewalk portion of
Irish Drive tributary to Cherry is 61,325 square feet, of which 58,700 sq. ft. is asphalt or concrete
(100% impervious) and the remaining area is gravel shoulder along the east side of Irish Drive.
The proposed 1080 feet of new rollover curb and 5-foot sidewalk work creates 7,560 sq. ft. of
impervious concrete, but much of this is removing and replacing existing asphalt or existing
concrete gutter and walk from Cherry north through 616 Irish Drive. The east edge of the road
north of 616 Irish for approximately 375 feet will replace existing gravel shoulder with concrete
gutter and walk (7-foot wide). This creates a new impervious increase of 2,625 sq. ft., which will
change from 50% impervious (gravel) to 100% impervious (concrete).
It is unclear that this is truly an increase in impervious area from the historic situation.
Conversations with long standing residents determined that a waterline project in 1985 removed
a portion of the east edge of asphalt to place/repair a waterline. With that project, the asphalt
was replaced with gravel instead of asphalt.
The overall effects of the proposed gutter are to prevent street runoff from inundating homes and
to slightly increase the amount of flow entering the wetland and thence the New Mercer Canal or
adjacent floodway. This increase is negligible because the catchment area is small and
channelization is only slightly increased. Finally, the new curb and gutter system is expected to
reduce sediment runoff because fine soils and silts will not be eroding from the road's edge (see
Figure 2 below for illustration of current erosion).
Figure 2. Erosion along east side of street
near 505 Irish Drive.
Page 3of4
Fort Collins
City of Fort Collins Stormwater Criteria
The street encroachment standards for local streets in Fort Collins are as follows:
• Major (100 yr) storm:
o The depth of water at street crown may not exceed 6 inches
o Depth of water over the gutter flow line may not exceed twelve inches
o Flow must be contained within the right-of-way
• Minor (2 yr) storm
o No curb topping
o Flow may spread to crown of street
Hydrologic and Hydraulic Results
Key hydrologic and hydraulic results for Station 4+50 are presented here. Please refer to
Appendix B for sketches and calculations.
Criteria
Catchment area:
Channel (gutter) flow distance:
Overland flow time:
Time of concentration:
Rainfall intensity
Flow, major (100 yr) storm:
Flow, minor (2 yr) storm:
Spread into street for major storm:
Spread into street for minor storm:
Flow depth for major storm:
Flow depth for minor storm:
Model Results
0.5 acre
800 ft
0.97 min
7.64 min
9.0 in/hr
4.63 cfs
1.34 cfs
6.6 ft
Ok by inspection
Ok by inspection (calculated depth for vertical curb
section is 3.6", which is less than drive over curb
height)
Ok by inspection
Areas downstream of Station 4+50, while having slightly greater flow, will have lower cross -
sectional flow area because longitudinal slopes are significantly greater.
Appendix A: Project area map
Refer to attached map.
Appendix B: Storm water calculations for Irish Drive
Refer to attached sheets numbered 1-10. Please note:
• There are several intermediate sheets, comprising a total of 13 sheets of calculations.
• Many of the calculations on pages 3 through 7 were intermediate or unused steps that
were a product of becoming familiar with the drainage manuals and formulae. Please
contact Clint Wood at 970416-2173 or cwood@fcgov.com if you have questions.
Page 4 of 4
Fort Collins
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Appendix A: Irish Drive Project Area
P iSH
ELEMENTARY
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STREET MAINTENANCE PROGRAM (SMP)
Revised May s 2014
Legend
City Floodway Schools
rle City High Risk Floodplains _�_�City Limits
City Moderate Risk Floodplain Parcels
Drainage analysis area
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Glen Schlueter
From:
Jon Haukaas
Sent:
Thursday, June 19, 2014 8:51 AM
To:
Glen Schlueter
Cc:
Wes Lamarque
clltile�+-
RE: Irish Drive design memo
Fort Collins
Let it go.
Jon Haukaas, P.E.
Water Engineering and Field Services Manager
Fort Collins Utilities
970-221-6671
From: Glen Schlueter
Sent: Wednesday, June 18, 2014 1:45 PM
To: Jon Haukaas
Cc: Wes Lamarque
Subject: RE: Irish Drive design memo
Jon,
This is one of the items I wanted to discuss at the Water Utilities Engineering meeting yesterday. When I went over it
with you previously I got the impression that we should stick to our criteria and require detention and water quality
treatment since the sidewalk was adding impervious area. The Streets Dept. hasn't been able to confirm how much
asphalt had washed away from a 1985 waterline break so cannot determine how much new impervious area is being
added. They make a statement that "It is unclear that this is truly an increase in impervious area".
What they have shown is that with the curb and gutter the water will no longer be spread out between homes but
instead will stay in the street and continue south and then turn the corner onto Cherry. There are street capacity
calculations in the letter but I will need to check with Wes to see if he checked them. Just looking at them I wonder if
they did it correct.
Since there isn't really a choice for detention and WQtreatment I am leaning toward dropping this issue on Irish Dr. and
accepting the report as is without a formal variance.
Is that Okay with you?
Glen
6065
From: Robert Mosbey
Sent: Monday, June 16, 2014 3:10 PM
To: Glen Schlueter
Subject: RE: Irish Drive design memo
Between you and me ... I'm just as confused as well, that's what I was told on Friday. I don't understand why he doesn't
contact you directly, but oh well, I'll be the go through guy. Let me know if you need anything else from me.
Thanks,
Rob V. Mosbey
Chief Construction Inspector
rmosbeYPfcgov.com
(970)221-6659(ofrce)
(970) 213-8537 (cell)
From: Glen Schlueter
Sent: Monday, June 16, 2014 2:44 PM
To: Robert Mosbey
Cc: Wes Lamarque
Subject: RE: Irish Drive design memo
Rob,
Your email from Friday says you will be emailing over the information but now you tell me it is already in the report. I'm
confused but that isn't new. Us old guys get confused easily.
I'm not sure a variance is needed since it sounds like it may or may not be an increase in impervious area. We have a
Stormwater Engineering meeting tomorrow. I'll bring it up if the agenda allows it.
Glen
Wes, add this to the discussions tomorrow, thanks.
From: Robert Mosbey
Sent: Monday, June 16, 2014 2:21 PM
To: Glen Schlueter
Cc: Wes Lamarque
Subject: RE: Irish Drive design memo
Glen,
Based on the report information I just emailed you from Tom, what do you think I need to do for the variance since it's
unable to determine if there's actually an increase from the past work in the area?
Thanks,
Rob V. Mosbey
Chief Construction Inspector
rmosbev(a)fcaov.com
(970) 221-6659 (office)
(970) 213-8537 (cell)
From: Glen Schlueter
Sent: Monday, June 16, 2014 2:07 PM
To: Robert Mosbey; Wes Lamarque
Cc: Tom Knostman; Clint Wood
Subject: RE: Irish Drive design memo
Rob,
The increase in impervious area needs to be documented in the report since that determines the drainage design
requirements. If it is over 1000 sq.-ft. they may need a formal variance from the director of utilities or his designee
because I don't see how they can detain or treat the runoff.
Glen
From: Robert Mosbey
Sent: Friday, June 13, 2014 3:55 PM
To: Glen Schlueter; Wes Lamarque
Subject: FW: Irish Drive design memo
Glen and Wes,
Attached is the stamped design memo from the Street Department. I talked to Tom earlier today and he mentioned he
was working on getting the additional information regarding the 1,000SF imperious area. I suspect he'll be emailing that
over once the amount has been determined.
Let me know if there's anything I can do to help this project move forward.
Thanks,
04
Rob V. Mosbey
Chief Construction Inspector
rmosbev Mcaov.com
(970) 221-6659 (office)
(970) 213-8537 (cell)
From: Clint Wood
Sent: Friday, June 13, 2014 3:03 PM
To: Robert Mosbey
Cc: Tom Knostman; Darren Moritz
Subject: Irish Drive design memo
Rob,
I have attached the Irish Drive design memo, stamped by Tom. Please let me know if you have questions.
Thank you,
Clint
of
Cotfins
Clint Wood, M.S.
Engineering Technician
p. 970.416.2173 // m. 970.402.3077
e. cwood@fceov.com H W. fceov.com/streets
Physical Address: 625 Ninth Street
Mailing Address: PO Box 580, Fort Collins, CO 80522