HomeMy WebLinkAboutDrainage Reports - 06/25/2014Prepared for:
Steve Allen
Local Geico Office
115 E. Harmony Rd, Suite 110
Fort Collins CO 80525
Prepared by:
{ NORTHERN
ENGINEERING
200 South College Avenue, Suite 100
Fart Collins, Colorado 80524
Phone: 970.221.4158 Fax: 970.221.4159
w .northemengineedng.corn
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' NorthernEngineering.cohn // 970.221.4150
Project Number: 959-001
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NORTHERN
ENGINEERING
ADDRESS: PHONE:970221.4158
200 S. College Ave. Suite 10 WEBSI��
rthernengineering com
Fort Collins, CO80524 FAk970.221.4159
June 9, 2014
City of Fort Collins
' Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
' RE: Final Drainage and Erosion Control Report for
Geico Office Building
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report for
' your review. This report accompanies the 10.16.12 Basic Development Review submittal for the
proposed Geico Office Building. Comments from the Basic Development Review Letter dated May
13 , 2013 have been addressed. Written responses thereto can be found in the comprehensive
' response to comments letter on file with Current Planning.
This report has been prepared in accordance to Fort Collins Stormwater Criteria Manual (FCSCM),
' and serves to document the stormwater impacts associated with the proposed Engines Geico Office
Building project. We understand that review by the City is to assure general compliance with
standardized criteria contained in the FCSCM.
If you should have any questions as you review this report, please feel free to contact us.
Sincerely,
NORTHERN ENGINEERING SERVICES, INC.
Bud Curtiss, PE VC�Snowdon
' Principle Project Engineer
F
NORTHERN
ENGINEERING
TABLE OF CONTENTS
'
I.
GENERAL LOCATION AND DESCRIPTION................................................................... 1
A.
Location..:....................................................................................................................................1
'
B.
C.
Description of Property................................................................................................................2
Floodplain........................................................................................................................:...........3
'
II.
A.
DRAINAGE BASINS AND SUB-BASINS.......................................................................4
Major Basin Description...............................................................................................................4
B.
Sub -Basin Description..................................................................................................................4
'
III.
DRAINAGE DESIGN CRITERIA...................................................................................4
A.
Regulations..................................................................................................................................4
B.
Four Step Process........................................................................................................................5
C.
Development Criteria Reference and Constraints.........................................................................6
'
D.
E.
Hydrological Criteria....................................................................................................................6
Hydraulic Criteria.........................................................................................................................6
F.
G.
Floodplain Regulations Compliance..............................................................................................7
Modifications of Criteria..............................................................................................................7
'
IV.
A.
DRAINAGE FACILITY DESIGN....................................................................................
General Concept..........................................................................................................................7
7
B.
Specific Details.............................................................................................................................8
'
V.
CONCLUSIONS................................................................:.......................................9
A.
Compliance with Standards..........................................................................................................9
'
B. Drainage Concept........................................................................................................................9
References.......................................................................................................................
10
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APPENDICES:
APPENDIX
A — Hydrologic Computations
APPENDIX B — Hydraulic Computations
'
B.1 — Storm Sewers
B.2 — Inlets
B.3 — Detention Facilities
' APPENDIX C — Water Quality Design Computations
APPENDIX D — Erosion Control Report
IPreliminary Drainage Report
W I NORTHERN
ENGINEERING
LIST OF TABLES AND FIGURES:
Figure 1 — Aerial Photograph................................................................................................ 2
Figure 2— Proposed Site Plan................................................................................................3
Figure 3 — Existing Floodplains........................
.........
.:................
...........
............
................... 3
Figure 4 — Harmony Road Drainage Area................................................................................ 4
MAP POCKET:
C400 - Drainage Exhibit
Preliminary Drainage Report
.V NORTHERN
ENGINEERING
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
Geico Office Bui
2. The Geico Office Building site is located in the southwest quarter of Section 31,
Township 7 North, Range 68 West of the 6' Principal Meridian, City of Fort Collins,
County of Larimer, State of Colorado.
3. The project site is located just northwest of the intersection of Harmony Road and
Timberline Road.
4. Currently the existing lot does not have any stormwater or water quality facilities. All
runoff from the site is routed via overland and discharged directly into the Dixon
Canyon Lateral. Harmony Road is slightly elevated to the project site creating a ridge
line running east and west along the right-of-way line. There are currently two drive
cuts into Harmony Road. The west drive cut is slightly graded back to Harmony, but
flows within the gutter above 0.7 feet will overtop the sidewalk and be routed through
the site and into Dixon Canyon Lateral. The east drive cut is graded back towards the
site and any drainage within the northern section of Harmony is currently routed
through the site and into Dixon Canyon Lateral. The overall site grades from the
south to the north.
5. The project is currently border to the south by Harmony Road, west by a commercial
building, north by Dixon Canyon Lateral and east by Timberline Road.
Preliminary Drainage Report
NORTHERN
ENGINEERING
B. Description of Property
Geico Office Buildi
1. The Geico Office Building property is approximately 0.55 net acres.
Figure 1 — Aerial Photograph
2. The Geico Office Building project consists of two properties, 2024 & 2016 East
Harmony Road. The 2024 East Harmony Road or western property consisted of two
building used for commercial use. A single drive access point exists from East
Harmony Road. The areas in front of the two buildings consist of gravel parking area
and the remaining property consists of over grown weeds. Stormwater is routed
though the site from south to north via overland flow and is discharged directly into
Dixon Canyon Lateral. Earlier this year, the existing buildings were deconstructed
because of the "Dangerous Building Issue" policy through the City. The 2016 East
Harmony Road or eastern property currently consists of a commercial office building
with associated outbuildings. There is an existing drive access point from East
Harmony Road. The area to the west of the building consists of a paved parking area
with associated landscaped areas. Stormwater is routed though the site from south to
north via overland flow and is discharged directly into Dixon Canyon Lateral.
3. According to the United States Department of Agriculture (USDA) Natural Resources
Conservation Service (NRCS) Soil Survey, 74 percent of the site consists of Nunn clay,
which falls into Hydrologic Soil Groups B, while the remaining site consists of Fort
Collins loam, which falls into Hydrologic Soil Groups B. More site -specific exploration
found primarily sandy lean clays with a groundwater encountered 15 to 17 feet below
existing site grades. See the Geotechnical Engineering Report by EEC (EEC Project
No. 1132073) for additional information.
4. The proposed development will include the deconstruction of the existing commercial
building on the western property and the existing paved parking area. The proposed
site will a new commercial building located to the east of the project along Timberline
road. It will include two drive access points from Harmony and an associated parking
lot. The majority of the parking lot will be paved with permeable pavers and will act
as the projects water quality and detention facility.
Preliminary Drainage Report
2
NORTHERN
ENGINEERING
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SITE PLAN - 2024 East Harmony Road
Figure 2— Proposed Site Plan
5. The project is bordered to the north by Dixon Canyon Lateral Irrigation Ditch. There is
an existing private irrigation system associated with the existing property to the west.
No other irrigation facilities are known at this time.
6. The project site is within the Harmony Corridor District (H-C) Zoning District. The
proposed project is not requesting a change in the land use.
C. Floodplain
1. The subject property is not located in a FEMA or City regulatory floodplain.
2. The FEMA Panel 08069C1000F has not been printed for this location. It is noted
that the vertical datum utilized for site survey work is the City of Fort Collins
Benchmark #1-96 (Elevation = 4941.81, Fort Collins NVGD 29 — Unadjusted)
, • Existing City Floodpldn Nap
_ ❑ 41�
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Figure 3 — Existing Floodplains
Preliminary Drainage Report 3
NORTHERN
' ENGINEERING
Geic
' II. DRAINAGE BASINS AND SUB -BASINS
' A. Major Basin Description
1. The Geico Office Building project is located within the Fox Meadows Basin, which is
located between East Horsetooth Road and East Harmony Road from north to south
' and approximately South Lemay Avenue and Fossil Creek Reservoir Inlet Ditch from
west to east.
'
B. Sub -Basin Description
1. The subject property historically drains away from the existing buildings. Stormwater
is routed through the site via overland flow and discharges directly into the Dixon
'
Canyon Lateral (0.7 cfs for the 2-year storm and 3.2 cfs for the 100-year event —
onsite only). A more detailed description of the projects proposed drainage patterns
follows in Section IV.A.4., below.
'
2. No drainage is routed onto the property from the east, west or north. Due to an
existing drive access cut from Harmony Road, all of the drainage conveyed through
the northern curb and gutter is discharged directly onto the property. Through the
'
widening design done by the City of Fort Collins, this existing drive cut is located at
the high point within the curb and gutter and the amount of runoff that is conveyed to
the existing drive cut is minimal. This stormwater is routed through the site and
'
discharged directly into the Dixon Canyon Lateral with an overall 100-year release
rate of 3.23 cfs. See the figure below illustrating this area.
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W
HARMONY ROAD
Figure 4 — Harmony Road Drainage Area
DRAINAGE DESIGN CRITERIA
A. Regulations
There are no optional provisions outside of the FCSCM proposed with the Geico Office
Building project.
Preliminary Drainage Report
4
■� I NORTHERN
ENGINEERING
B. Four Step Process
The overall stormwater management strategy employed with the Geico Office Building
project utilizes the "Four Step Process" to minimize adverse impacts of urbanization on
receiving waters. The following is a description of how the proposed development has
incorporated each step.
Step 1— Employ Runoff Reduction Practices
'
Several techniques have been utilized with the proposed development to facilitate the
reduction of runoff peaks, volumes, and pollutant loads as the site is developed from the
current use by implementing multiple Low Impact Development (LID) strategies including:
'
Conserving existing amenities in the site including the existing vegetated along the
Dixon Canyon Lateral.
Providing large vegetated open areas throughout the site to reduce the overall
impervious area and to minimize directly connected impervious areas (MDCIA).
Routing flows, to the extent feasible, through vegetated swales and grass buffers to
increase time of concentration, promote infiltration and provide initial water quality.
'
Providing permeable paver areas with underground detention area to increase time of
concentration promote infiltration and provide water quality.
Step 2 — Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with
'
Slow Release
The efforts taken in Step 1 will facilitate the reduction of runoff; however, this
development will still generate stormwater runoff that will require additional BMPs and
'
water quality. Stormwater generated from the proposed building will be routed through
landscaped swales and into a proposed storm collection system. This storm collection
system is proposed to discharge directly into the permeable paver area and routed through
'
this section to achieve water quality. The stormwater generated from the proposed
parking area will be routed via overland flow to the permeable paver area.
Step 3 — Stabilize Drainageways
'
The project site currently discharges to the Dixon Canyon Lateral. While these drainage
patterns are being maintained with the proposed grading, measures have been proposed to
decrease the amount of run-off discharging into Dixon Canyon Lateral as well as the
'
quality of the storm water being released. The existing onsite area is releasing 0.7 cfs for
the 2-year event and 3.2 cfs for the 100-year event undetained and untreated. Currently
'
the existing drive cut is located within a high point of Harmony Road and a minimal
amount of runoff generated from Harmony Road and routed through the site. Within the
proposed design, the runoff from Harmony Road is being rerouted to remain within the
street section. The western half of the drive access will drain to the west and the eastern
'
half of the drive access will drain east. The additional runoff that will be generated from
closing the drive access is negligible. Water quality will be provided through a permeable
paver section and will treat all runoff generated by onsite site improvements. Furthermore,
'
this project will pay onetime stormwater development fees, as well as ongoing monthly
stormwater utility fees, both of which help achieve City-wide drainageway stability.
' Preliminary Drainage Report 5
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.V I NORTHERN
ENGINEERING
Geico Office B
Step 4 — Implement Site Specific and Other Source Control BMPs.
The Geico Office Building project includes a new building with an associated drive and
parking area, all of which will require the need for site specific source controls including:
IKa A localized trash enclosure at the rear of the building for the disposal of office waste.
C. Development Criteria Reference and Constraints
1. There are no known drainage studies for the existing properties.
2. There are no known drainage studies for any adjacent properties that will have any
effect on the Geico Office Building project.
3. The subject property is essentially an "in -fill" development project as the property is
surrounded by currently developed properties. As such, several constraints have been
identified during the course of this analysis that will impact the proposed drainage
system including:
n� Existing elevations along the south and east property lines adjacent to Harmony
Road and Timberline Road will be maintained. Existing elevations along the west
property lines will be maintained.
N� Existing elevations and vegetation on the north side of the subject property will be
preserved.
N� As previously mentioned, overall drainage patterns of the existing site will be
maintained.
D. Hydrological Criteria
1. The City of Fort Collins Rainfall Intensity -Duration -Frequency Curves, as depicted in
Figure RA-16 of the FCSCM, sere as the source for all hydrologic computations
associated with the Regency Lakeview development. Tabulated data contained in
Table RA-7 has been utilized for Rational Method runoff calculations.
2. The Rational Method has been employed to compute stormwater runoff utilizing
coefficients contained in Tables RO-11 and RO-12 of the FCSCM.
3. The Rational Formula -based Modified Federal Aviation Administration (FAA)
procedure has been utilized for detention storage calculations.
4. Three separate design storms have been utilized to address distinct drainage
scenarios. A fourth design storm has also been computed for comparison purposes.
The first design storm considered is the 801 percentile rain event, which has been
employed to design the project's water quality features. The second event analyzed is
the "Minor," or "Initial" Storm, which has a 2-year recurrence interval. The third
event considered is the "Major Storm," which has a 100-year recurrence interval.
The fourth storm computed, for comparison purposes only, is the 10-year event.
5. No other assumptions or calculation methods have been used with this development
that are not referenced by current City of Fort Collins criteria.
E. Hydraulic Criteria
' 1. As previously noted, the subject property historically drains directly to the Dixon
Canyon Lateral, The majority of the site drains stormwater via overland and swale
flow.
' 2. All drainage facilities proposed with the Geico Office Building project are designed in
accordance with criteria outlined in the FCSCM and/or the Urban Drainage and Flood
Control District's (UDFCD) Urban Storm Drainage Criteria Manual.
' Preliminary Drainage Report 6
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.� I NORTHERN
ENGINEERING
3. As stated in Section I.C.1, above, the subject property is not located within a FEMA
regulatory floodplain.
4. The Geico Office Building project does not propose to modify any natural
drainageways.
F. F000dplain Regulations Compliance
' 1. As previously mentioned, all structures are located outside of any FEMA 100-year
floodplain, and thus are not subject to any floodplain regulations.
G. Modifications of Criteria
1. The proposed Engines and Energy Conversion Lab development is not requesting any
modifications to criteria at this time.
' IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objectives of the Geico Office Building drainage design are to maintain
' existing drainage patterns and ensure no adverse impacts to any adjacent properties,
and to maintain the detention concepts as outlined within the "Fox Meadows Master
Drainage Plan Update," by Icon Engineering, August 1999.
2. The existing site does have off -site from Harmony Road. The existing runoff will be
'
rerouted to remain within the existing Harmony Road street section.
3. A list of tables and figures used within this report can be found in the Table of
Contents at the front of the document. The tables and figures are located within the
'
sections to which the content best applies.
4. The Geico Office Building project divided the site into four (4) major drainage basins,
'
designated as Basins A, OS, OE and ON. The project further subdivided Basin A in to
four (4) sub -basins, designated as Basins Al, A2, A3, and A4. The drainage patterns
anticipated for each basin and sub -basin are further described below.
'
Basin A
Basin A consists of the improvements within the project area. Basin Al encompasses
the most areas within Basin A. This basin includes all of the proposed parking area
'
and a portion of the proposed sidewalk. Runoff through this basin is routed through a
combination of overland and gutter. Runoff from this basin is primarily routed across
the proposed permeable pavers and underground detention. The portion of runoff that
'
is not intercepted by the permeable paver system will be intercepted by a proposed
curb inlet. An orifice plate is proposed within the curb inlet to restrict the released
flow from the underground and above ground detention. Basin A2 is composed of the
northwest quarter of the building and the building frontage. The stormwater is routed
via overland and swale flow. All runoff from this basin is intercepted by a stormwater
collection system that discharges directly into the permeable paver system discussed
'
above. Basin A3 is composed of the southwest quarter of the building and the
building frontage. The stormwater is routed via overland and swale flow. All runoff
from this basin is intercepted by a stormwater collection system that discharges
'
directly into the permeable paver system discussed above. Basin A4 is composed of
the eastern half of the building and the landscaped areas around the building. The
stormwater is routed via overland and swale flow. All runoff from this basin is
' Preliminary Drainage Report 7
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NORTHERN
' ENGINEERING
Geico Office Buildii
intercepted by a stormwater collection system that discharges directly into the
' permeable paver system discussed above.
Basin OS
' Basin OS consists of two sub -basins and is composed of primarily of the landscaping
south of the parking area. This area was redesigned with the closing of the two
existing drives and the proposed landscape design.
Basin ON
Basin ON1 consists of the northern property boundary. No improvements are
proposed in this area and historic drainage patterns will be maintained.
Basin OE
Basin OE1 consists of the eastern property boundary. No improvements are proposed
in this area and historic drainage patterns will be maintained.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of
this report.
B. Specific Details
1. The main drainage problem associated with this project site is the deficiency of water
quality present within the existing site and the amount of offsite runoff being conveyed
onto the property from Harmony Road. Currently the entire site drains overland and
discharges directly into the Dixon Canyon Lateral without water quality. The existing
two outbuildings also drain directly into Dixon Canyon Lateral without any water
quality. The proposed site will mitigate this issue by instituting the following water
quality devices:
N9 All of the runoff generated from the proposed building will be routed through a
landscape area.
NB All improvements generated from the site will be routed through a permeable
paver detention system.
2. A hybrid approach was utilized to compute the maximum allowable release rate
associated with the FAA detention sizing calculations. The 100-year peak runoff rate
was calculated for the pre -development impervious areas for the eastern lot. This
essentially "grandfathers" the existing impervious areas by allowing the respective
100-year peak discharge to be added to the maximum allowable release rate. The
release rate for the remaining undeveloped land (pre -development pervious areas and
the entire western lot) was established by calculating the prescribed 0.23 cfs per
acre. The total of these two discharges (i.e., 1.07 cfs and 0.13 cfs) establishes the
overall maximum allowable release rate, 1.20 cfs, from the project site. The
allowable release rate of 0.92 cfs utilized within the FAA procedure detention storage
computations (Refer to Appendix A for these calculations) and was established by
subtracting the undetained release of 0.28 cfs, from the overall maximum allowable
release rate. The overall existing runoff being routed through the site and discharged
directly into Dixon Lateral was 3.23 cfs for the 100-year event. The total runoff
leaving the proposed site through the use of detention is only 1.20 cfs for the 100-
year event.
Preliminary Drainage Report
8
NORTHERN
ENGINEERING Geico Office Building
3. The FAA method was used to size the on -site pond for quantity detention.
' Calculations for this area, based on the characteristics of basin A and adjusted release
rate, indicated a detention volume of 2917 cu. Ft. This includes the 384 cu.ft. of
Water Quality Capture Volume (WQCV). During the water quality events the water
' quality capture volume will release over 12-hours. This section is considered a no -
infiltration section because the in -situ soils in this area are USCS Nunn Clay Loam.
4. The storage volume available within the reservoir areas (i.e., No. 57 and No. 2 open -
graded aggregate) of the MBP section is ±2917 cu. ft. The MBP section is designed
with an increased No. 2, open -graded aggregate, material depth in order to provide
storage for storm events in excess of the water quality (80"' percentile) storm event.
In addition to the volume within the MBP section, parking lot detention is designed to
account for an additional 203 cu. ft.
' 5. There is a Nyloplast Drain Basin located on the southern, eastern and a portion of the
western building boundary. These area inlets are designed to intercept local flows, as
well as the flow generated by the proposed buildings. These basins will convey runoff
through landscape areas before discharging into the drain system. The drain basin is
' connected directly to the MBP section; therefore, runoff conveyed through the drain
system will be treated.
'
6.
The emergency spillway will be located at the low point on the northern side of the
parking area. The spillway will utilize the low point within the curb with an elevation
1' lower than the lowest finish floor elevation. In the event that an emergency
overflow occurs, the drainage will flow to the north, into the existing irrigation lateral.
'
V. CONCLUSIONS
'
A. Compliance with Standards
1.
The drainage design proposed with the Geico Office Building project complies with the
'
City of Fort Collins' Stormwater Criteria Manual.
2.
The drainage design proposed with the Geico Office Building project complies with the
City of Fort Collins' Master Drainage Plan for the Fox Meadows.
'
3.
There are no regulatory floodplains associated with the Geico Office Building
development.
'
4.
The drainage plan and stormwater management measures proposed with the Geico
Office Building development are compliant with all applicable State and Federal
regulations governing stormwater discharge.
B. Drainage Concept
1. The drainage design proposed with this project will effectively limit any potential
' damage or erosion associated with its stormwater runoff. Geico Office Building will
detain for the pervious area converted to impervious areas to release at the historic
100-year release during the 100-year event.
2. The proposed Geico Office Building development will not have any impact on the
Master Drainage Plan recommendations for the Fox Meadows.
' Preliminary Drainage Report 9
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References
1. City of Fort Collins Landscape Design Guidelines for Stormwater and Detention Facilities,
November 5, 2009, BHA Design, Inc. with City of Fort Collins Utility Services.
2. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by Ordinance No.
174, 2011, and referenced in Section 26-500 (c) of the City of Fort Collins Municipal Code.
3. Subsurface Exploration Report, Geico Insurance Office Building 2024 East Harmony Road,
October 14, 2013, Earth Engineering Consultants, Inc.(EEC Project No. 1132073).
4. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and
Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007.
5. Soils Resource Report for Larimer County Area. Colorado, Natural Resources Conservation
Service, United States Department of Agriculture.
6. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control
District, Wright -McLaughlin Engineers, Denver, Colorado, Revised April 2008.
Preliminary Drainage Report
10
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' NorthernEngineering.com // 970.221.4158
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DESIGN PEAK FLOW FOR ONE-HALF OF STREET BY THE RATIONAL METHOD Woiksnael Protected
Project: Galan Office Building
Inlet ID: Design Point Al
I (Design Flow a Gutter Flow i Carty -over (Flow
I
10 i-LOVNp ` STREET I iOVFLpVNp y
—GUTTCR rLOV PLUS LORRY -AVER rLOW ♦�—Iiiiiiiiiiiiii ♦GUTTER FLOW Stow Details
INLET INLET
——1/eSTREET —
Design flow: ONLY a already defetminecT ugh inner atedtodi Minor Sbrm Me' r term
(local peak flow for 112 of street. pka flow Eypassing upstreem subratcarmanls): 'O = 0.5 2./ cfs I
it uahn d I: fah., Furs 'loci tt- mSt of in sheet and prutiesid IO sha¢t O-AaaW
eogra0 a Information: Later data In the blw ce nt %
I1{^�e�.,��.
SubmeM raltliArse {J
PerceInaervlousress =
NRCS Sall Type= B. C. or
Site Type. Slope (fHf[
• Slat S Utw� Ooenand Flow =
O 5e a Bon-lahan GMer Fbw=
am a n orma an: rel Y = tp1mc."PrTIM Minor mlatl Storat
Design Storm Reran Period. T,=m
1 lyears
Rohm Period One-Hour
Pbn Pt'1 liclws
UserAefined Stofm Runoff Coeffiders (leave INS Gamic to accept a calwleled value), C =
User -Defined Syr. Rutafl Coefficient (leave tie Mark to accept a ralcubted value), Cs =
Bypea (CWW4)ver) Flow from upstream Subcalckments, Oy' ant
Total Design Peak Flow, D al 0.6 1 1.5 de
.. IN THIS SECTION
IN THE
.TIONS BELOW
Inlet DP Al As, O-Peak 3/512014, 3:26 PM
INLET IN A SUMP OR SAG LOCATION
Project = Sunshine House - FC 139
Inlet 10 = Design Point A2
RGed, MWd
we
Lo IGI
ka an Infurmrtbn flnout)
'Yoe of Inlet
Inlet Type
arai Depression Additional a cor/mwus gueer Eepmsswn'a'fmm'Q-AlbW)
any
lumber of Unit Inlets (Grate or Gum Opening)
No
'bw, Depth outside of Local Depresson at Inlet
Flow Depth
:role Taft .rstlon
ergth of a Unit Grate
4 (G)
Volt, of a UM Gets
W.
area Opsmlg Ratio for a Grate (tyyical values 0.IM 90)
A.
Ibgging Factor for a Santis Grate (typical valor 0.50 - 0.10)
Ci (G)
Irate Web Coefficient (ypbel value 2,15 - 3,60)
C,. (GI
lane Danes Coefficient (typical value 0.60 - 0,80)
C, (G)
:urb Operi 1Morawboa
engtn of a Um Cum Openrg
L. (C)
lariat of Vemoal Cum Doering in hones
Hwe
(eight of Curb QMae Throat in Inches
H.
mile of Throat I. USDCM Figure ST-5)
Thais
'ae Width for Depression Pan (typically the gutter width of 2 feet)
We'
:bilging Factor for a Single Curb Operung (typical value 0.10)
Cf (C)
:urb Open t, Weir Cpsti RM.1 value 2.3.3.6)
G (C)'
:ua Opei4g Orifice Coefficient (rypI i value 0.60 -0.70)
Ce (C)'
-01al Inlet Interception Capacity (assumes clogged condition)
Q. e
rot Capaclty IS GOOD for Mn. ,.-. .or Storms (O PEAK)
0esvweeo.!
MINOR MAJOR
CDOTlDemrer 13 combination
2.W
1
6.0 120
3.00
1.73
0.43
0.50
0 50
3.30
0.60
3.D0
6.50
5.25
D.00
2.00
0.10
0.10
3.70
0.66
IILna,
ncrns
eel
eel
net
tones
ones
agrees
eel
Inlet OP At.As, Inlet In Sump 31512014, 3:26 PM
(sla) f4pedeo
' Project No. 959-001 Northern Engineering Services, Inc. Geico Office Building
Calculations By: CNS
1]
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins ID -
Project Number 959-001
Project Name Geico Office Building
Project Location Fort Collins, Colorado
Pond No Permeable Paver Detention
Input Variables Results
Design Point a1
Design Storm 100-yr
C = 0.82
Tc = 5.00 min
A = 0.56 acres
Max Release Rate = 0.92 cfs
Required Detention Volume
01117 ft3
0.07 ac-ft
Time (min)
Ft Collins
100-yr
Intensity
in/hr)
Inflow
Volume
a
(ft)
Outflow
Adjustment
Factor
0;,,,
(cfs)
Outflow Volume
3
(ft)
Storage
Volume
W)
5
9.950
1364
1.00
0.92
276
1088
10
7.720
2117
0.75
0.69
414
1703
15
6.520
2682
0.67
0.61
552
2130
20
5.600
3072
0.63
0.58
690
2382
25
4.980
3415
0.60
0.55
828
2587
30
4.520
3719
0.58
0.54
966
2753
35
4.080
3917
0.57
0.53
1104
2813
40
3.740
4103
0.56
0.52
1242
2861
45
3.460
4270
0.56
0.51
1380
2890
50
3.230
4429
0.55
0.51
1518
2911
55
3.030
4571
0.55
0.50
1656
2915
60
2.860
4706
0.54
0.50
1794
2912
65
1 2.720
4849
0.54
0.50
1932
2917
70
2.590
4973
0.54
0.49
2070
2903
75
2.480
5101
0.53
0.49
2208
2893
80
2.380
5222
0.53
0.49
2346
2876
85
2.290
5339
0.53
0.49
2484
2855
90
2.210
5455
0.53
0.49
2622
2833
95
2.130
5550
0.53
0.48
2760
2790
100 1
2.060
5650
0.53
0.48
2898
2752
105
2.000
5760
0.52
0.48
3036
2724
110
1.940
5853
0.52
0.48
3174
2679
115
1.890
5961
0.52
0.48
3312
2649
120
1.840
6056
0.52
0.48
3450
2606
'Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
1
Page 1 of 1
959-001 DetentionVolume FAAModified Method.xls
�INORTHERN
ENGINEERING
ADDRESS:
Pum. 97D221.4158
200E College Ave. Suds 10
WERStiE:
PAX; 970221.4159
Fort Collins, Cl
w .nurtwonengmeonng.com
Project Title Geico Office Building
Project Number 959-001
Client Steve Allen
Pond Designation Permeable Paver Detention Area
4964.39 ft
Water quality Volume
384 cu. ft.
100-yr Detention Volume
2917 cu. ft.
Total Pontl Volum
2917 cu. ft.
Date: April 30, 2014
Cates By: C. Snowdon
Paver Volume W
Surface Volume
Volume
Elevation
(8)
Surface
Area (ft')
Incremental
Depth (It)
Incremental
Vol. (R)
Total Vol.
1000%CaPacity(fts)
Total Vol.
400% Caparityfl)
Surface
Area (0')
Incremental
Depth (ft)
Incremental
Vol. (ft)
Total Vol.
(ft')
Total Volume
In)
4,962.40
'A2\iA
N/A
0
0
N/A
N/A
N/A
U
4,962.50
431.56
0.1
15,67
15.67
6.268
N/A
N/A
N/A
0
6.268
4962.60
1,510.75
0.1
91.66
107.32
42.928
N/A
N/A
N/A
0
42.928
.70
2,582.62
0.1
202.29
309.61
123.844
N/A
N/A
N/A
0
123.844
.80
3,437.20
0.1
299.97
609.59
243.836
N/A
N/A
N/A
0
243.836
.90
3,859.56
0.1
364.63
974.22
389.688
N/A
N/A
N/A
0
389.688
.00
3,892.57
0.1
387.61
1361.83
544.732
N/A
N/A
N/A
0
544.732
.10
3,894.39
0.1
389.35
17S1.17
700.468
N/A
N/A
N/A
0
700.468
.20
3,896.22
0.1
389.53
2140.71
856,284
N/A
N/A
N/A
0
856.294
.30
3,898.05
0.1
389.71
2530.42
1012.168
N/A
N/A
N/A
0
2012.168
.40
3,899.87
0.1
389.9
2920.31
1168.124
N/A
N/A
N/A
0
1168.124
_ .50
.60
3,901.70
3,903.53
0.1
0.1
390.08
390.26
3310.39
1324.156
N/A
N/A
N/A
0
1324.156
3700.65
1480.26
N/A
N/A
N/A
0
1480.26
.70
3,905.35
0.1
390.44
4091.1
1636.44
N/A
N/A
N/A
0
1636.44
3,907.18
CIA
390.63
4481.72
1792.688
N/A
N/A
N/A
0
1792.688
3,909.01
3,910.94
0.1
0.1
390.81
390A9
4872.53
1949.012
N/A
N/A
N/A
0
1949.012
5263.53
2105.412
N/A
N/A
N/A
0
2155.412
3,912.66
3,936.32
0.1
0.1
391.18
387,44
5654.7
2261.88
N/A
N/A
N/A
0
2261.88
6042.14
2416.856
N/A
N/A
N/A
0
2416.856
3,608.35
0.1
372.18
6414.32
2565.728
N/A
N/A
N/A
0
2565.728
3,231.89
0.1
341.94
6756.16
2702,464
4,964.40
0.95
N/A
0
2702.464
2,747.45
0.1
298.64
7054.8
2821.92
4,964.50
76.24
0.1
3.86
2825.78
2,223.23
0.1
248.07
7302.87
2921.148
4,964.60
303.69
0.1
19
2940.148
1,S52.02
0.1
187.76
7490.63
2996.252
4,964.70
687.66
49.57
3045.822
1,213.53
0.1
137.93
7628.56
3051.424
4,964.82
1,158.82
i
92.32
3143.744
832.43
0.1
101.7
7730.26
3092.104
4,964.SO
1,717.68
143.83
3235.934
375.39
0.1
58.89
7789.16
3115.664
4,965.00
2,355.38
203.65
3319.31A
ADDRESS: PHONE: 970.221.4158
ENORTHERN NE I 200 S. College Ave. Style 10 w w-north
ENGINEERING Fort Collins, C080524 FAX:970.221.4159 www.northernengmeenng.con'
Project Title Geico Office Building Date: April 30, 2014
Project Number 959-001 Calcs By: C. Snowdon
Client Steve Allen
Pond Designation Permeable Paver Detention Area
Q=CA -EJ11
Q = Release Rate (cfs)
C = Discharge Coefficients (unitless)
A. = Area Allowed of Opening (ft)
g = Gravity (32.2 ft/s2)
Eh = High Water Surface Elevation (ft)
E; = Elevation of Outlet Invert (ft)
Cos 9 2 = -► 0 = 2Cos '
FAII
VR
S=Rl9 A =nRZ-K
RZ % -Sur I
K=
2
H = Height of Opening (in.)
R = Inner Radius of Outfall Pipe (in.)
A = Top of Plate to Center of Pipe (in.)
S=Arc Length of Open Area (in.)
A, = Area of Opening (ins)
6 = Angle of Plate on Pipe to Center Pipe (radians)
2-1/4 in
Q = 0.92 cfs
C = 0.605
Eh = 66.25 ft
Ei = 63.06 ft
0.106095 ft2
15.27765 in'
ADDRESS:
NORTHERN
PHONE: 970221.4158
WEBSrtE:
200 S. College Ave. Suite 10
E N G I N E E R I N G Fort Collins. C080524
FAA: 970.221.4159
www.northernengineenng.rom
Project Title
Geico Office Building
Date:
April 30, 2014
Project Number
959-001
Calcs By:
C. Snowdon
Client
Steve Allen
Pond Designation Permeable Paver Detention Area
Q = Release Rate (cfs)
C = Discharge Coefficients (unitless)
A. = Area Allowed of Opening (ft)
g = Gravity (32.2 ft/s`)
Eh = High Water Surface Elevation (ft)
El = Elevation of Outlet Invert (ft)
Ec = Elevation of Outlet Centroid (ft)
Circular Orifice
Orifice Size (in.) 4 - 1/4 in.
Area (in') 14.22 sq-in
Q, - - . 0.89 cfs
Rectangular
Orifice
4 - 3/4 in.
Orifice Width (in.)
3 in.
Area (in2)
14.22 sci-in
Q
0.89 cfs
C = 0.65
E„ = 66.25 ft
E; = 63.06 it
E, = 63.24 ft Circular
E, = 63.26 ft Rectangular
10.09875 ft`
14.219970 In
P
Required Water
Quality Storage Provided Water
Basin ID (ac-ft) Quality (ac-ft)
'
B 383.814 0.009
1
1
1
I�
Pond Spillway Pond Volume
■
North ernEngineering.com // 970.221.4158
■ NORTHERN ADDRESS: PHONE: 970.221.4158 wEBSITE:
ENGINEERING 200 S. College Ave. Suite to g g
Fort Collins, CO 80524 FAX: 970.221.4159 www.northernen ineerin com
Project Title
Project Number
Client
Pond Designation
Geico Office Building
959-001
Steve Allen
Permeable Paver Detention Area
Date: April 30, 2014
Calcs By: C. Snowdon
WQCV=a0.91i'-1.19i2+0.78i to 12hr -
a = 0.8
WQCV = Watershed inches of Runoff (inches) i = 51.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) MWQCV = 0.167 in
Water Quality Capture Volume
0.45
a 0.4
L
c 0,35
a 0.3
s
m` 0.25
3 0.2
> 0.15
V
0.1
3
0.05
0
- 6 h,
U h,
14 hr
40 h,
0
0 0 a a in m v 0 io 0
0 0 0 0 0 0 0 0 0 0 0
Total Imperviousness Ratio (i = 1.4100)
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
V=Il
rWQ12 V ) 0.53 ac
0.0088 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
1.2 = 20%Additional Volume (Sediment Accumulation)
I
I
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. NorthernEngineering.com // 970.221.4158
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INorth ernEngineering.com /1 970.221.4158
NORTHERN
' ENGINEERING
Geico Office Building
A comprehensive Erosion and Sediment Control Plan (along with associated details) will be included
' with the final construction drawings. It should be noted, however, that any such Erosion and
Sediment Control Plan serves only as a general guide to the Contractor. Staging and/or phasing of
the BMPs depicted, and additional or different BMPs from those included may be necessary during
' construction, or as required by the authorities having jurisdiction.
It shall be the responsibility of the Contractor to ensure erosion control measures are properly
maintained and followed. The Erosion and Sediment Control Plan is intended to be a living
document, constantly adapting to site conditions and needs. The Contractor shall update the
location of BMPs as they are installed, removed or modified in conjunction with construction
activities. It is imperative to appropriately reflect the current site conditions at all times.
The Erosion and Sediment Control Plan shall address both temporary measures to be implemented
' during construction, as well as permanent erosion control protection. Best Management Practices
from the Volume 3, Chapter 7 — Construction BMPs will be utilized. Measures may include, but are
not limited to, silt fencing along the disturbed perimeter, gutter protection in the adjacent roadways
and inlet protection at existing and proposed storm inlets. Vehicle tracking control pads, spill
' containment and clean-up procedures, designated concrete washout areas, dumpsters, and job site
restrooms shall also be provided by the Contractor.
' Grading and Erosion Control Notes can be found on Sheet CS2 of the Utility Plans. The Utility
Plans at final design will also contain a full-size Erosion Control Plan as well as a separate sheet
dedicated to Erosion Control Details. In addition to this report and the referenced plan sheets, the
Contractor shall be aware of, and adhere to, the applicable requirements outlined in any existing
Development Agreement(s) of record, as well as the Development Agreement, to be recorded prior
to issuance of the Development Construction Permit. Also, the Site Contractor for this project will
' be required to secure a Stormwater Construction General Permit from the Colorado Department of
Public Health and Environment (CDPHE), Water Quality Control Division — Stormwater Program,
before commencing any earth disturbing activities. Prior to securing said permit, the Site Contractor
' shall develop a comprehensive Stormwater Management Plan (SWMP) pursuant to CDPHE
requirements and guidelines. The SWMP will further describe and document the ongoing activities,
inspections, and maintenance of construction BMPs.
r,
Preliminary Erosion Control Report
W I NORTHERN
ENGINEERING
Geico Office Buildi
Preliminary Erosion Control Report