HomeMy WebLinkAboutSOLAR VILLAGE MAPLE - PDP - 23-07 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTNOTEPreliminary Drainage & Erosion Control Study
B E Y O N D E N G I N E E R I N G Solar Village
VII. References
1. City of Fort Collins Stormwater Utility Storm Drainage Design Criteria and
Construction Standards, City of Fort Collins, Colorado, May, 1984.
2. Soil Survey of Larimer County Area, Colorado United States Department of
Agriculture, Soil Conservation Service, in cooperation with the Colorado Agricultural
Experiment Station and Forest Service, 1975.
3. Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District,
Wright Water Engineers, Inc., Denver, Colorado, June 2001.
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NOLTEPreliminary Drainage & Erosion Control Study
BE YON D E N G IN E E R ING Solar Village
VI. Erosion and Sediment Control
A. Erosion and Sediment Control Measures
The following temporary Best Management Practices (BMP's) will be installed
and maintained to control on -site erosion and prevent sediment from traveling off -
site during construction:
• Silt Fence — a woven synthetic fabric that filters runoff. The silt fence is a
temporary barrier that is placed at the base of a disturbed area.
• Straw Wattles — wattles act as a sediment filter. They are a temporary BMP
and require proper installation and maintenance to ensure their performance.
B. Construction Materials & Equipment
The contractor shall store all construction materials and equipment and shall
provide maintenance and fueling of equipment in confined areas on -site from
which runoff will be contained and filtered.
C. Maintenance
The temporary BMP's will be inspected by the contractor at a minimum of once
every two weeks and after each significant storm event.
The property owner will be responsible for routine and non -routine maintenance
of the temporary sediment basin. Routine maintenance includes:
• Lawn mowing -maintain height of grass depending on aesthetic requirements
• Debris and litter removal -remove debris and litter to minimize outlet
clogging and improve aesthetics as necessary
• Inspection of the facility -inspect the facility annually to ensure that it
functions as initially intended
Non -routine maintenance includes:
• Erosion and sediment control -repair and re -vegetate eroded areas in the
basin and channels as necessary
• Structural -repair structural damage to the existing inlets as necessary
• Nuisance control -address odor, insects, and overgrowth issues associated
with stagnant or standing water in the bottom zone as necessary.
• Sediment Removal -remove accumulated sediment from the bottom of the
pond.
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BEYOND ENG INEERING
Preliminary Drainage & Erosion Control Study
Solar Village
B. Specific Details
The runoff generated by the site will be conveyed via overland flow and in the
gutters, concrete pans, and sidewalk chases to the detention pond.and streets.
The detention pond volume was based on the estimated 7281 square feet (0.17
acres) of additional impervious area based on the assumptions above. Basin A
which consists of the majority of the site, will be detained. The release rate of 0.77
cfs was calculated by subtracting the 100-year flows from Basins B, C, and D
(3.51 cfs at tc = 5minutes) which are not detained from the calculated existing
100-year runoff for Basin E (4.28 cfs at tc =19 minutes) so the total did not
exceed that of existing conditions. .
The total required 100-year detention volume is 553 cubic feet (0.01 acre-feet).
The 100-year water surface elevation is 4987.05 feet. The 100-year water surface
depth at the outlet is 0.75 feet. The outlet for the detention pond (and the
emergency spillway) will be via a concrete channel underneath the sidewalk grate
that discharges to the alley and will be designed as part of the Final Drainage
Study.
As part of the Final Drainage Study, the use of porous paving may be further
investigated which would result in a decreased difference between the existing
and proposed impervious areas. This would likely result in a decreased required
detention pond volume and increased water quality.
V. Conclusions
A. Compliance with Standards
Storm drainage calculations followed the guidelines provided by the City of Fort
Collins Storm Drainage Design Criteria.
B. Drainage Concept
The drainage system has been designed to convey the runoff to the designated
design points and the detention pond in an effective manner as safe as possible.
C. Water Quality
A water quality pond is not being proposed for the fully -developed conditions
based on the small required detention pond. However, water quality will be .
partially provided by the landscaped swale in the detention pond.
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IV. Drainage Facility Design
A. General Concept
Solar Village
This site proposes to increase the impervious area by over 5000 square feet.
Therefore, detention will be provided for the 5000+ square feet of increased
imperviousness. According to conversations with City personnel, the increase in
impervious area for the Old Town Drainage Basin is based on paved and building
areas only. However this site has a lot of existing hard packed gravel and semi -
paved surfaces (from old concrete cylinders) that has some impervious value.
Therefore, it was assumed that the increase in imperviousness was the difference
.between the proposed pavement, building, and 40% of gravel areas and the
existing pavement, building, and 40% gravel areas (i.e., gravel was assumed to be
40% impervious per Urban Drainage).
The time of concentration for all proposed basins was assumed to be the 5 minute
minimum. Because the time of concentration for the existing conditions is very
difficult to calculate due to the lack of positive drainage for the existing site and
the various design points, an overall time of concentration that was fairly
conservative (high) was estimated and used for the existing conditions. The area,
time of concentration, and runoff of each proposed sub -basin as well as referenced
tables, charts, and formulas are summarized in the Appendix.
The project site was divided into several different developed sub -basins. For
detention requirement purposes, because this site in concerned with the increase in
impervious area due to development and for simplicity of defining basin
boundaries, the total area for all the sub -basins within the site is slightly greater
than the area defined by the property boundaries. The basins, which typically
consist of rooftop, pavement, and landscaping are described below:
• Basin A consists of the majority of the site and drains to the central courtyard
that acts as a detention pond for Basin A.
• Basin B consists of area draining to Meldrum Street where runoff continues
northerly to Cherry Street
• Basin C consists of area draining to Maple Street where it continues easterly.
Basin C has been separated into Sub -basins C1 and C2 to differentiate the
flow that is tributary to the alley.
• Basin D consists of runoff to the alley that is directed northerly in the alley to
Cherry Street.
• Basin P (not shown) is the total of A, B, C, and D basins for the proposed
conditions.
• Basin E (not shown) is the total of A, B, C, and D basins for the existing
conditions.
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BEYOND E NGIN EERING Solar Village
• This small site may use the Modified FAA Procedure to determine detention
pond volume.
• Because this site is a redevelopment, additional pond volume for water quality
may not be required provided a valid variance request is accepted.
C. Hydrological Criteria
In accordance with the Fort Collins policy, a minor and major storm for the Fort
Collins area is identified as the 2-year and 100-year storms, respectively. A major
storm for the Fort Collins area has a recurrence interval of 100 years and a total
rainfall depth of 3.67 inches for a 2-hour design storm, with a peak intensity of
9.95 in/hr. ,
These storms have been used as a basis for planning and system design. The peak
flow rates for design points have been calculated based on the rational method as
described in the Storm Drainage Design Criteria with storm duration set equal to
the time of concentration for each sub -basin.
D. Hydraulic Criteria
The developed site will convey runoff to the detention pond and adjacent streets in
a safe and effective manner via overland flow, curb and gutter, concrete pans, and
streets.
Detention Pond
The runoff produced by the interior site sub -basin will be conveyed to the
proposed detention pond within the courtyard. The pond was sized utilizing
the Rational Formula -Based Modified FAA Procedure for the difference in
proposed versus existing impervious area only. The release rate will be based
on the difference between the estimated proposed and existing runoff.
Swales
There are no proposed swales within the site other than the one located in the
detention pond.
Storm Sewer
There is no proposed storm sewer.
E. Variance Request
This report acts as a variance request to not require additional water quality other
than the vegetated swale within the detention pond. The proposed detention pond
is less than 1-foot deep which would make an extended detention pond not
feasible.
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BEYOND ENGINEERING
Preliminary Drainage & Erosion Control Study
Solar Village
18, 1996 which shows the site in Zone X (areas outside of the 500-year
floodplain).
The Old Town Drainage Basin is located in north -central Fort Collins. The basin
has a drainage area of approximately 2,120 acres, including approximately 400
acres of the Colorado State University campus. The entire basin is urbanized, with
some development dating back to the late 1800s. Generally, the basin drains from
west to east. The Old Town Basin receives some runoff water from the Canal
Importation Basin directly west of Old Town. Most of the water from Old Town
drains to the Poudre River, just to the east.
The BFE information shown on the Drainage Plans was estimated based on
information provided by the City of Fort Collins.
B. Sub -Basin Description
The site will ultimately consist of ground covered by pavement, rooftop, and
landscape. The majority of the onsite runoff will be conveyed to the interior
courtyard where it will be detained as described further below. The perimeter
areas of the site will be conveyed westerly, southerly, and easterly towards the
streets/alley, with a very small amount of landscaped runoff conveyed northerly.
It is assumed that other than the floodplain information provided by the City and
mentioned above, there is very little offsite runoff entering the site.
Drainage Design Criteria
A. Regulations
The design criteria for this study are directly from the City of Fort Collins
Stormwater Utility Storm Drainage Design. Criteria and Construction Standards
Manual and the Urban Storm Drainage Criteria Manuals Volumes 2, and 3
(referred to herein as USDCM).
B. Development Criteria Reference and Constraints
There are no known drainage studies for this site other than the Old Town Master
Drainage Plan. The following are requirements for this site.
• Any structure in the 100-year floodplain must have the lowest floor and all
HVAC and mechanical elevated or flood -proofed 18" above the flood
elevation.
• A floodplain use permit will be required for any structure built in the
floodplain.
• Detention is required if the increase in imperviousness is greater than 5000 SF
W but only for the 5000 SF+ of new impervious area.
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NOTEPreliminary Drainage & Erosion Control Study
BE YON D E N G IN E E R ING Solar Village
I. General Location and Description
A. Location
The Solar Village site is located in Section 11, Township 7 North, Range 69 West
of the 6`h Principal Meridian to the City of Fort Collins, Larimer County,
Colorado.
The site is located in the northeast corner of the intersection of North Meldrum
Street and Maple Street in Lots 14, 15, and 16 of Block 43, Fort Collins.
B. Description of Property
The Solar Village site (referred herein as "the site" or "this site") is approximately
0.65 acres in size. The site currently contains three existing single -story
commercial buildings and one single -story residential house plus various storage
sheds, sidewalks, paved and gravel parking, and some landscaping. The existing
commercial buildings are located along the Maple Street Frontage, south of the
single family residence which fronts North Meldrum Street.
This project includes the removal of all existing structures and the construction of
mixed -use buildings along Maple Street, North Meldrum Street, Lot 14's northern
property boundary, and the alley along the eastern property boundary.
Historically, this site is very flat and flows are split around the existing buildings
but the overall site runoff tends to want to flow northeasterly towards the Poudre
River via mostly Maple Street. According to the Old Town Master Drainage Plan
and conversations with City personnel, the floodplain boundary is mapped for
flows at or exceeding 200 cfs (typical Old Town street capacities), which in the
vicinity of the site is in Maple Street. There is some flow that splits and continues
northerly via Meldrum Street (approximately 39 cfs) and there is an undetermined
amount of flow that splits at the alley (although it can be assumed negligible).
There are no known existing major open channels, drainage facilities, or irrigation
ditches within the site. There are existing inlets at both western corners of
Meldrum and Maple Streets.
II. Drainage Basins and Sub -Basins
A. Major Basin Description
Portions of the site lie within the 100-year floodplain of the City of Fort Old Town
Basin. The current Flood Insurance Rate Map (FIRM) published by the Federal
Emergency Management Agency (FEMA) is number 0801020004C, dated March
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Preliminary Drainage & Erosion Control Study
Solar Village
BEYOND
ENGINEERING
TABLE OF CONTENTS
PAGE
I.
GENERAL PROJECT LOCATION AND DESCRIPTION ...........................................
1
A. Location................................................................................................................I
B. Description of Property ........................................................................................
I
H.
DRAINAGE BASINS AND SUB-BASINS....................................................................
1
A. Major Basin Description......................................................................................
1
B. Sub -Basin Description.........................................................................................
2
III.
DRAINAGE DESIGN CRITERIA..................................................................................
2
A. Regulations...........................................................................................................2
B. Development Criteria Reference and Constraints ................................................
2
C. Hydrological Criteria............................................................................................
3
D. Hydraulic Criteria.................................................................................................
3
D. Variance Request.................................................................................................
3
IV.
DRAINAGE FACILITY DESIGN..................................................................................
4
A. General Concept...................................................................................................
4
B. Specific Details....................................................................................................
5
V.
CONCLUSIONS..............................................................................................................5
A. Compliance with Standards.................................................................................
5
B. Drainage Concept.................................................................................................
5
C. Water Quality .......................................................................................................
5
VI.
EROSION AND SEDIMENT CONTROL......................................................................
6
A. Erosion and Sediment Control Measures............................................................. 6
B. Construction Materials And Equipment.............................................................. 6
C. Maintenance.........................................................................................................6
VII. REFERENCES.................................................................................................................7
APPENDIX A - Calculations & References
MAP POCKET — Preliminary Drainage and Erosion Control Plan
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SOLAR VILLAGE
PRELIMINARY DRAINAGE &
EROSION CONTROL STUDY
for
Solar Village LLC
2795 Pearl Street, #200
Boulder, CO 80302
by
Nolte Associates, Inc.
1901 Sharp Point Drive, Suite A
Fort Collins, Colorado 80525
(970) 221-2400
July 25, 2007