HomeMy WebLinkAbout217 W. TRILBY RD. - PDP - PDP120006 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPRELIMINARY DRAINAGE REPORT
For: 217 West Trilby Road
Fort Collins, CO 80526
Prepared For:
AFFORDABLE ROOFING, LLC
217 West Trilby Road
Fort Collins, CO 80526
February 29, 2012
Project No. AFFORD-1G2A01-03-304
Prepared By:
Landmark Engineering Ltd.
3521 West Eisenhower Boulevard
Loveland, CO 80537
February 29, 2012
Mr. Glen Schlueter & Wes Lamarque
Storm Water Department
City of Fort Collins
700 Wood Street
Fort Collins, Colorado 80521
RE: 217 W. Trilby ; Affordable Roofing Inc.
Dear Mr. Schlueter & Mr. Lamarque,
Enclosed you will find Landmark Engineering’s completed Preliminary Drainage Report for the 217 W.
Trilby (Affordable Roofing) PDP submittal. This report, along with the Overall Utility Plans, exhibits the
hydrology calculations necessary to show that the storm flows generated above and within this project’s
limits are handled by the proposed on-site drainage system and the proposed detention facilities. There
are two items of note that are usually commented on, which I felt should be briefly discussed. The first
item is detention within parking lots. I briefly spoke with Wes on the phone prior to this submittal and
we discussed the limit of detention elevation in parking areas. In finding that a maximum of one foot (1’)
was allowed, I made use of this ability in pond 2 and pond 4, since detention was difficult on this flat site.
I was still able to achieve one foot (1’) of freeboard in the ponds and one foot (1’) clearance below the
building finished floor elevations. The second item involves the detention pond release locations. In the
past we’ve seen that, even though with detention we reduce flow rates during the 100-year storm event,
comments seem to come back pertaining to sign off by ditch companies or historic water stakeholders.
For this project, I have informed the Owners to speak with the North Louden Ditch people because
they have a good relationship with them and have even improved the Ditch on their property due to
erosion and plant overgrowth. There has been a Ditch signature line incorporated on the cover of the
Utility Plans. With that, I believe that the major challenges of drainage aspects have been addressed.
We look forward to your favorable consideration of our Preliminary Drainage Report and aim to
address any comments during our final submittal process. If you have any questions or concerns, please
do not hesitate to contact me at the above phone number or by email at timh@landmarkltd.com.
Sincerely,
LANDMARK ENGINEERING, LTD.
Tim Halopoff, PE
Senior Civil Engineer
Enclosure
Cc: File
Page i
TABLE OF CONTENTS
Table of Contents ............................................................................................................................ i
Engineer’s Certification Block......................................................................................................... ii
General Description and Location ................................................................................................. 1
Site Description and Location ..................................................................................................... 1
Site Soils...................................................................................................................................... 1
Storm Drainage Criteria ................................................................................................................. 2
Hydrologic Criteria...................................................................................................................... 2
Hydraulic Criteria........................................................................................................................ 2
Drainage Basins, Historic and Proposed Runoff............................................................................. 3
Historic Basins............................................................................................................................. 3
Developed Basins ........................................................................................................................ 4
Stormwater Pollution Prevention................................................................................................... 5
Temporary Erosion Control......................................................................................................... 5
Permanent Erosion Control ......................................................................................................... 5
Summary & Conclusions................................................................................................................. 5
References....................................................................................................................................... 6
Appendices...................................................................................................................................... 7
Site & Soil Descriptions and Characteristics........................................................................... A-1
Proposed Rational & Detention Pond Calculations................................................................. A-2
Sleeve w/ Drainage Plans……………………………………………………………………Sleeve
Page ii
ENGINEER’S CERTIFICATION BLOCK
I hereby certify that this Preliminary Drainage Report for 217 W Trilby, Fort Collins, CO 80526
was prepared by me (or under my direct supervision) for the owners thereof and meets or
exceeds the criteria of the City of Fort Collins Stormwater Design Standards.
________________________________________
Timothy J. Halopoff, PE
Registered Professional Engineer
State of Colorado No. 37953
Page 1
GENERAL DESCRIPTION AND LOCATION
SITE DESCRIPTION AND LOCATION
217 W. Trilby is located in the NORTHEAST QUARTER OF SECTION 14, TOWNSHIP 6
NORTH, RANGE 69 WEST OF THE 6TH P.M., CITY OF FORT COLLINS, COUNTY OF
LARIMER, STATE OF COLORADO. More specifically, 217 W. Trilby is a 2.485 ac. piece of
property that is currently used as a residence and a large open yard, but is zoned LMN and will
support office uses on the east & west side of the property once subdivided.
The future use of the site (2.485 ac.) entails subdividing the existing lot into 3 lots and
dedicating additional Trilby Right-of-Way (0.083 ac.). The existing residence will remain on the
new Lot 1, consisting of 0.222 ac. There will also be 2 lots created for the purpose of
constructing 2 office buildings complimented by garage structures. Lot 2 (0.693 ac.), will be
located on the east side of the North Louden Ditch and will support a new office development
with a footprint of 4,200 s.f. The remainder of the existing property will become Lot 3 (1.487
ac.) and will support an office containing a 6,000 s.f. footprint.
The site generally slopes from the southwest to the northeast with slopes ranging between
2.8% and 11.0%. The property is generally covered with sparse native grasses. The North
Louden Ditch traverses the property from the southeast corner to the northwest corner,
flowing northwest and ultimately flowing into a corrugated metal pipe and crossing W. Trilby.
The westerly portion of the property (proposed Lot 3) receives a small area of off-site flow
(2.450 ac.) from the southwest and together with the on-site Lot 3 flows, accumulate a total
area of 2.937 ac., which currently already drains to two points on the ditch. On the east side of
the ditch, which is where the residence is located, 0.740 ac. drains east to two existing sumps
on the east property line. Ultimately, the historic flow from the residence half of the property
(proposed Lot 1 & 2) flow to the neighboring property on the east side. The small portions of
land on the extreme north of both sides of the ditch drain to the south roadside borrow ditch
on Trilby.
SITE SOILS
The 217 West Trilby site consist of loams including: Fort Collins Loam, Thedalund Loam and
Wiley Silt Loam. Fort Collins Loam (Classification #36), having 3-5% slopes, generally has a
combined surface layer thickness of approx. 20 inches. Runoff is moderate, and the hazards of
wind and water erosion are moderate. Thedalund Loam (Classification #108), having 3-9%
slopes, occasionally has a surface layer of clay loam and small areas of Kim, Cushman, and
Midway soils. Runoff is medium, and the hazard of erosion is moderate. Wiley Silt Loam
(Classification #119), having 3-5% slopes, occasionally has a subsurface layer of silt loam or
loam. Runoff is medium, and the hazard of erosion is medium.
All of the loams on this site are classified as being in the Type B hydrologic group. According
to USDA/Natural Resource Conservation Group, the earth on-site has a moderate infiltration
rate when thoroughly wet. These soils consist chiefly of moderately deep or deep, moderately
well drained or well drained soils that have a moderately fine texture to moderately coarse
texture. These soils also have a moderate rate of soils transmission.
Supporting figures can be found in the Appendix, page A-1.
Page 2
STORM DRAINAGE CRITERIA
This preliminary report was prepared to meet or exceed the City of Fort Collins storm water
criteria. The City of Fort Collin’s Storm Drainage Design Criteria and Construction Manual
(with all current 2011 Revisions)(FCSDDCCM) and the Urban Drainage Flood Control
District’s (UDFCD) Drainage Criteria Manual (USDCM) Volumes 1, 2 and 3 were referenced as
guidelines for this design.
HYDROLOGIC CRITERIA
The rational method was performed to calculate the peak runoff rates for each basin.
Weighted percent imperviousness and weighted runoff coefficients were calculated for each
basin using USDCM Tables RO-3 and RO-5 based on Natural Resources Conservation Service
(NRCS) Type B hydrologic soil classification and surface characteristics of each basin. The time
of concentration was calculated using USDCM Equation RO-3 and the intensity was calculated
using the corresponding storm rainfall depth and USDCM Equation RA-3. To account for the
City of Fort Collins’ IDF Curve, Coefficient 3 of the UDFCD’s intensity formula was adjusted to
0.7867. The City of Fort Collins area has 2-yr 1-hr rainfall depth of 0.82 inches and a 100-yr 1-
hr rainfall depth of 2.86 inches. These depths do account for the 1997 adjusted rainfall depths.
HYDRAULIC CRITERIA
The hydraulic calculations provided for in this report are limited to Detention Pond
calculations. This report allows us to prove that the system of proposed detention ponds is
able to reduce the 100-year developed condition flows to the 2-year historical release rates;
thereby satisfying the City’s requirements. Once this Preliminary Report is accepted and
approved, hydraulic calculations for storm drain pipe, water quality structures and rip-rap will
be provided within the Final Drainage Report for 217 West Trilby.
The ultimate 217 West Trilby storm drainage system will be designed to convey the minor and
major storm events through the property with the proposed inlets, storm sewer pipes, and
swales for the flows being calculated by this preliminary report. Per the requirements provided
by the City of Fort Collins Storm Drainage Design Criteria and Construction Manual, all inlets
and storm pipes will be designed to convey the 100-year storm flows. During the major storm
event, the developed condition 100-yr storm, the accumulated water depth will be held to a
maximum depth with a minimum of 1’ freeboard to the top of all building foundations.
Additionally, the detention ponds will be designed to detain all onsite flows and maintain 1’ of
freeboard. Since this report shows that there is no change to any of the offsite flows, they will
pass the 100-year offsite flows over the weirs.
All swale and pipe outlets will be protected with riprap. Storm sewer pipe outlets will be
protected using the requirements set by the USDCM for the protection of downstream
conveyance channels and culverts.
Page 3
DRAINAGE BASINS, HISTORIC AND PROPOSED RUNOFF
HISTORIC BASINS
217 West Trilby is an infill development piece of property. As such, the existing and proposed
drainage basins will need to follow the generally accepted principle of releasing the 100-yr.
developed condition storm flow at the same location and magnitude as the 2-yr. historic
condition flow rate. There are offsite areas that flow across the proposed development site.
Referring to the “Existing Drainage Plan” (Appx. - Sht. 1 of 2, included in the sleeve at back),
the following describes the existing condition drainage basins.
Existing Offsite Drainage Basins (OF):
Sub-basin OF1 consist of 1.52 acres that flows northeasterly, across private property
and enters the onsite development property at the northwest corner; where the flow is
conveyed by Basin ON1 to the North Louden Ditch irrigation channel.
Sub-basin OF2 consist of 0.93 acres that flows easterly, across private property and
enters the onsite development property at the southwest corner; where the flow is
conveyed by Basin ON2 to the North Louden Ditch irrigation channel.
Sub-basin OF3 consist of 2.20 acres that flows easterly, across private property and
the storm drainage travels on the south curb and gutter/southerly roadside ditch of
Trilby Road. Along this path, the drainage from Sub-basin OF3 stays north of the
subject development property and for this reason, is excluded from the
hydraulic/detention pond calculations.
Sub-basin OF4 consists of 0.56 acres that flows northeasterly, across private property
and the drainage travels along the south side of the subject property. Along this path,
the drainage from Sub-basin OF4 stays north of the subject development property and
for this reason, is excluded from the hydraulic/detention pond calculations.
Existing Onsite Drainage Basins (ON):
Sub-basin ON1 consists of 0.43 acres that flows easterly, across the northwest ¼ of
the development property, conveying flow from Sub-Basin OF1 and its own flow,
making the total area flowing to the North Louden Ditch at the bottom of ON1 1.95 ac.
Sub-basin ON2 consists of 0.92 acres that flows northeasterly, across the southwest
¼ of the development property, conveying flow from Sub-Basin OF2 and its own flow,
making the total area flowing to the North Louden Ditch at the bottom of ON2 1.85 ac.
Sub-basin ON3 consists of 0.55 acres that flows easterly, across the southeast ¼ of
the development property. This Sub-basin drains to a sump area located midway of the
easterly property line and flows directly to the neighboring property, where it makes its
way back to Trilby’s south borrow ditch.
Sub-basin ON4 consists of 0.23 acres that flows easterly, across the northeast ¼ of
the development property. This Sub-basin drains to a sump area located at the top of
the easterly property line and flows directly to the neighboring property, where it
makes its way to the south borrow ditch at Trilby.
Page 4
DEVELOPED BASINS
The proposed sub-basins have been designed to mimic the historic basins, both on and off-site.
We have achieved proposed sub-basins that are close to the same acreages on-site and have
intentionally designed our sub-basins such that they are exactly the same in the off-site
condition. This has enabled us to simplify the hydrology calculations, thereby simplifying the
detention pond calculations as well. Furthermore, because we have been able to keep the off-
site sub-basins the same for the existing and proposed conditions, we were able to avoid re-
calculating and reiterating the information provided for off-site in the prior section. Referring
to the “Proposed Drainage Plan” (Appx. - Sht. 2 of 2, included in the sleeve at back), the
following describes the proposed condition on-site drainage basins.
Proposed Onsite Drainage Basins (ON):
Sub-basin ON1 consists of 0.43 acres and flows from the pick-up point where Off-site
Sub-basin OF1 enters the site in the northwest. From there, we routed the flow
through a series of two detention ponds connected by a small storm pipe. The two
ponds act as one detention pond. Following the water quality/detention structure, the
flows are released to flow over a rip-rap spreading pad and directed toward the same
swale as the existing condition.
Sub-basin ON2 consists of 0.92 acres and flows from the pick-up point where Off-site
Sub-basin OF2 enters the site in the southwest. From there, we routed the flow down
the back of the parking lot retaining wall in a trickle pan. That pan conveys flows to the
detention pond in the rear of the Lot 3 building. This detention pond is a combined
concrete parking area/reseeded open space. We have shown that the small volume
necessary for detention is kept below 1’ of ponding in any part of the parking area.
Sub-basin ON3 consists of 0.45 acres and flows from the high points on the bermed
areas east of the North Louden Ditch and will flow directly into the new native/low
water tolerant grassed detention pond located in the rear of the proposed building on
future Lot 2. From there, we routed the flow down a trickle pan and through the water
quality/detention structure. Following the water quality/detention structure, the flows
are released to flow over a rip-rap spreading pad and directed toward the same swale as
the existing condition.
Sub-basin ON4 consists of 0.29 acres and flows from the high points on the bermed
areas east of the North Louden Ditch and into a trickle pan that crosses the parking
lot/fire truck turn-around toward the north east corner of the property. Once the
flows are conveyed to the northeast corner, they are terminated into a retaining wall
that allows the detention pond to have the appropriate 1’ of freeboard. This detention
pond is a combined concrete parking area/reseeded open space. We have shown that
the small volume necessary for detention is kept below 1’ of ponding in any part of the
parking area.
In conclusion, the detention pond elevations created by the waters calculated in the
Appendices will be discussed in the following section entitled “Summary and
Conclusions”.
Page 5
STORMWATER POLLUTION PREVENTION
TEMPORARY EROSION CONTROL
A temporary erosion control plan is to be implemented for the site during construction.
Temporary erosion control measures include, but are not limited to, slope and swale
protection provided by the use of erosion control wattles/sediment control logs, silt fence
placed around areas of disturbance, construction vehicle tracking pads at entrances, designated
concrete truck washout basins, designated vehicle fueling areas, inlet protection, etc. All
temporary erosion control measures are to be removed after they are deemed unnecessary.
PERMANENT EROSION CONTROL
Permanent erosion control measures include, but are not limited to, the constructed
detention/water quality pond, riprap pads placed for culvert outlet protection, seeding and
mulch placed to enable and established vegetative growth, etc. Long-term maintenance of these
erosion control measures shall be the responsibility of the owner of the property.
A general erosion control plan will be included with the Final Development Plan, Utility Plan set
and in the appendix of the Final Development Plan Drainage Report. Ultimately before
construction of this project, a more detailed erosion control plan will need to be performed
within the Storm Water Management Plan that must be submitted to the State of Colorado and
the City of Fort Collins.
SUMMARY & CONCLUSIONS
To summarize the flow rates and detention pond characteristics, we have shown calculations as
per the City’s requirements for Preliminary Drainage reports in section “A-2, Proposed
Rational and Detention Pond Calculations”. For the required detention pond release rates, we
calculated the 2-year historic on-site flows for contributing basins and reduced that flow by the
area of development contributing to the pond. The remaining areas are left undisturbed. We
then used the modified Detention Pond Calculator “FAA12” (Fater, Judish & Li; 1998) to
calculate the required pond size, to which the volume calculated for Water Quality, was then
added. The weir size was calculated using the 100-year storm flows from both the historic off-
site and developed on-site, which assumes that the outlet structure is completely clogged.
Pond 1 was calculated to need 0.022 acre-feet of volume and 0.030 acre-feet is provided. Pond
2 was calculated to need 0.165 acre-feet and 0.169 acre-feet is provided. Pond 3 was calculated
to need 0.010 acre-feet and 0.106 acre-feet is provided. Pond 4 was calculated to need 0.07
acre-feet and 0.070 acre-feet is provided. All of the weir sizes account for the 100-year flows
that enter the respective detention ponds.
In conclusion, all of the City of Fort Collins hydrology calculations were performed using the
required methods and all of the 217 Trilby Project drainage amenities, meet or exceed the
necessary drainage feature requirements. Furthermore, this preliminary drainage report and
the complimenting Overall Utility Plans show appropriate grading, permanent landscaping,
riprap, and on-site construction facilities (e.g. storm pipes, inlets, etc.) that will be calculated
hydraulically and discussed in the Final Drainage Report and on it’s accompanying Maps.
Page 6
REFERENCES
1. Urban Storm Drainage Criteria Manual (Volumes 1, 2, and 3), Urban Drainage and Flood
Control District, June 2001.
2. Storm Drainage Criteria Manual and Construction Standards, City of Fort Collins Storm
Water Utility, City of Fort Collins, Colorado, Updated January, 1997.
3. “Hydrologic Group Rating for Larimer County Area, Colorado”, USDA-Natural Resources
Conservation Service, National Cooperative Soil Survey. Web Soil Survey URL:
http://websoilsurvey.nrcs.usda.gov. [July 21, 2010]
Page 7
APPENDICES
Site & Soil Descriptions and Characteristics (A-1)
Proposed Rational & Detention Pond Calculations (A-2)
Existing & Proposed Drainage Plans (Sleeve)
Page A-1
SITE & SOIL DESCRIPTIONS AND CHARACTERISTICS
Page A- 2
PROPOSED RATIONAL & DETENTION POND CALCULATIONS
100 Year
This is to convert % imp. to a C value
100-year (must insert % imp. and C pervious).
ft
3
acre-ft.
'C' value 0.55 1179.3 0.0271
'C' * 1.25 0.6875
Area 0.3 acres Modified Modified
Release Rate 0.28 M. FATER D. JUDISH C. LI
5/95 Nov-97 Nov-98
DETENTION POND SIZING
TIME TIME INTENSITY Q 100 Runoff Release Required Required
cum 100 year Volume Cum total Detention Detention
(mins) (secs) (in/hr) (cfs) (ft^3) (ft^3) (ft^3) (ac-ft)
0 0 0 0.00 0 0.0 0.0 0.0000
5 300 9.950 2.05 615.6563 84.0 531.7 0.0122
10 600 7.720 1.59 955.35 168.0 787.4 0.0181
15 900 6.520 1.34 1210.275 252.0 958.3 0.0220
20 1200 5.600 1.16 1386 336.0 1050.0 0.0241
25 1500 4.980 1.03 1540.688 420.0 1120.7 0.0257
30 1800 4.520 0.93 1678.05 504.0 1174.1 0.0270
35 2100 4.080 0.84 1767.15 588.0 1179.2 0.0271
40 2400 3.740 0.77 1851.3 672.0 1179.3 0.0271
45 2700 3.460 0.71 1926.788 756.0 1170.8 0.0269
50 3000 3.230 0.67 1998.563 840.0 1158.6 0.0266
55 3300 3.030 0.62 2062.294 924.0 1138.3 0.0261
60 3600 2.860 0.59 2123.55 1008.0 1115.6 0.0256
65 3900 2.720 0.56 2187.9 1092.0 1095.9 0.0252
70 4200 2.590 0.53 2243.588 1176.0 1067.6 0.0245
75 4500 2.480 0.51 2301.75 1260.0 1041.8 0.0239
80 4800 2.380 0.49 2356.2 1344.0 1012.2 0.0232
85 5100 2.290 0.47 2408.794 1428.0 980.8 0.0225
90 5400 2.210 0.46 2461.388 1512.0 949.4 0.0218
95 5700 2.130 0.44 2504.081 1596.0 908.1 0.0208
100 6000 2.060 0.42 2549.25 1680.0 869.3 0.0200
105 6300 2.000 0.41 2598.75 1764.0 834.8 0.0192
110 6600 1.940 0.40 2640.825 1848.0 792.8 0.0182
115 6900 1.890 0.39 2689.706 1932.0 757.7 0.0174
120 7200 1.840 0.38 2732.4 2016.0 716.4 0.0164
125 7500 1.790 0.37 2768.906 2100.0 668.9 0.0154
130 7800 1.750 0.36 2815.313 2184.0 631.3 0.0145
135 8100 1.710 0.35 2856.769 2268.0 588.8 0.0135
140 8400 1.670 0.34 2893.275 2352.0 541.3 0.0124
145 8700 1.630 0.34 2924.831 2436.0 488.8 0.0112
150 9000 1.600 0.33 2970 2520.0 450.0 0.0103
155 9300 1.570 0.32 3011.456 2604.0 407.5 0.0094
160 9600 1.540 0.32 3049.2 2688.0 361.2 0.0083
165 9900 1.510 0.31 3083.231 2772.0 311.2 0.0071
170 10200 1.480 0.31 3113.55 2856.0 257.6 0.0059
175 10500 1.450 0.30 3140.156 2940.0 200.2 0.0046
180 10800 1.420 0.29 3163.05 3024.0 139.1 0.0032
185 11100 1.400 0.29 3205.125 3108.0 97.1 0.0022
190 11400 1.380 0.28 3244.725 3192.0 52.7 0.0012
195 11700 1.360 0.28 3281.85 3276.0 5.8 0.0001
200 12000 1.340 0.28 3316.5 3360.0 -43.5 -0.0010
205 12300 1.320 0.27 3348.675 3444.0 -95.3 -0.0022
210 12600 1.300 0.27 3378.375 3528.0 -149.6 -0.0034
215 12900 1.280 0.26 3405.6 3612.0 -206.4 -0.0047
220 13200 1.260 0.26 3430.35 3696.0 -265.7 -0.0061
100 Year
This is to convert % imp. to a C value
100-year (must insert % imp. and C pervious).
ft
3
acre-ft.
'C' value 0.83 6595.2 0.1514
'C' * 1.25 1
Area 0.64 acres Modified Modified
Release Rate 0.31 M. FATER D. JUDISH C. LI
5/95 Nov-97 Nov-98
DETENTION POND SIZING
TIME TIME INTENSITY Q 100 Runoff Release Required Required
cum 100 year Volume Cum total Detention Detention
(mins) (secs) (in/hr) (cfs) (ft^3) (ft^3) (ft^3) (ac-ft)
0 0 0 0.00 0 0.0 0.0 0.0000
5 300 9.950 6.37 1910.4 93.0 1817.4 0.0417
10 600 7.720 4.94 2964.48 186.0 2778.5 0.0638
15 900 6.520 4.17 3755.52 279.0 3476.5 0.0798
20 1200 5.600 3.58 4300.8 372.0 3928.8 0.0902
25 1500 4.980 3.19 4780.8 465.0 4315.8 0.0991
30 1800 4.520 2.89 5207.04 558.0 4649.0 0.1067
35 2100 4.080 2.61 5483.52 651.0 4832.5 0.1109
40 2400 3.740 2.39 5744.64 744.0 5000.6 0.1148
45 2700 3.460 2.21 5978.88 837.0 5141.9 0.1180
50 3000 3.230 2.07 6201.6 930.0 5271.6 0.1210
55 3300 3.030 1.94 6399.36 1023.0 5376.4 0.1234
60 3600 2.860 1.83 6589.44 1116.0 5473.4 0.1257
65 3900 2.720 1.74 6789.12 1209.0 5580.1 0.1281
70 4200 2.590 1.66 6961.92 1302.0 5659.9 0.1299
75 4500 2.480 1.59 7142.4 1395.0 5747.4 0.1319
80 4800 2.380 1.52 7311.36 1488.0 5823.4 0.1337
85 5100 2.290 1.47 7474.56 1581.0 5893.6 0.1353
90 5400 2.210 1.41 7637.76 1674.0 5963.8 0.1369
95 5700 2.130 1.36 7770.24 1767.0 6003.2 0.1378
100 6000 2.060 1.32 7910.4 1860.0 6050.4 0.1389
105 6300 2.000 1.28 8064 1953.0 6111.0 0.1403
110 6600 1.940 1.24 8194.56 2046.0 6148.6 0.1412
115 6900 1.890 1.21 8346.24 2139.0 6207.2 0.1425
120 7200 1.840 1.18 8478.72 2232.0 6246.7 0.1434
125 7500 1.790 1.15 8592 2325.0 6267.0 0.1439
130 7800 1.750 1.12 8736 2418.0 6318.0 0.1450
135 8100 1.710 1.09 8864.64 2511.0 6353.6 0.1459
140 8400 1.670 1.07 8977.92 2604.0 6373.9 0.1463
145 8700 1.630 1.04 9075.84 2697.0 6378.8 0.1464
150 9000 1.600 1.02 9216 2790.0 6426.0 0.1475
155 9300 1.570 1.00 9344.64 2883.0 6461.6 0.1483
160 9600 1.540 0.99 9461.76 2976.0 6485.8 0.1489
165 9900 1.510 0.97 9567.36 3069.0 6498.4 0.1492
170 10200 1.480 0.95 9661.44 3162.0 6499.4 0.1492
175 10500 1.450 0.93 9744 3255.0 6489.0 0.1490
180 10800 1.420 0.91 9815.04 3348.0 6467.0 0.1485
185 11100 1.400 0.90 9945.6 3441.0 6504.6 0.1493
190 11400 1.380 0.88 10068.48 3534.0 6534.5 0.1500
195 11700 1.360 0.87 10183.68 3627.0 6556.7 0.1505
200 12000 1.340 0.86 10291.2 3720.0 6571.2 0.1509
205 12300 1.320 0.84 10391.04 3813.0 6578.0 0.1510
210 12600 1.300 0.83 10483.2 3906.0 6577.2 0.1510
215 12900 1.280 0.82 10567.68 3999.0 6568.7 0.1508
220 13200 1.260 0.81 10644.48 4092.0 6552.5 0.1504
100 Year
This is to convert % imp. to a C value
100-year (must insert % imp. and C pervious).
ft
3
acre-ft.
'C' value 0.49 1378.5 0.0316
'C' * 1.25 0.6125
Area 0.45 acres Modified Modified
Release Rate 0.48 M. FATER D. JUDISH C. LI
5/95 Nov-97 Nov-98
DETENTION POND SIZING
TIME TIME INTENSITY Q 100 Runoff Release Required Required
cum 100 year Volume Cum total Detention Detention
(mins) (secs) (in/hr) (cfs) (ft^3) (ft^3) (ft^3) (ac-ft)
0 0 0 0.00 0 0.0 0.0 0.0000
5 300 9.950 2.74 822.7406 144.0 678.7 0.0156
10 600 7.720 2.13 1276.695 288.0 988.7 0.0227
15 900 6.520 1.80 1617.368 432.0 1185.4 0.0272
20 1200 5.600 1.54 1852.2 576.0 1276.2 0.0293
25 1500 4.980 1.37 2058.919 720.0 1338.9 0.0307
30 1800 4.520 1.25 2242.485 864.0 1378.5 0.0316
35 2100 4.080 1.12 2361.555 1008.0 1353.6 0.0311
40 2400 3.740 1.03 2474.01 1152.0 1322.0 0.0303
45 2700 3.460 0.95 2574.889 1296.0 1278.9 0.0294
50 3000 3.230 0.89 2670.806 1440.0 1230.8 0.0283
55 3300 3.030 0.84 2755.974 1584.0 1172.0 0.0269
60 3600 2.860 0.79 2837.835 1728.0 1109.8 0.0255
65 3900 2.720 0.75 2923.83 1872.0 1051.8 0.0241
70 4200 2.590 0.71 2998.249 2016.0 982.2 0.0225
75 4500 2.480 0.68 3075.975 2160.0 916.0 0.0210
80 4800 2.380 0.66 3148.74 2304.0 844.7 0.0194
85 5100 2.290 0.63 3219.024 2448.0 771.0 0.0177
90 5400 2.210 0.61 3289.309 2592.0 697.3 0.0160
95 5700 2.130 0.59 3346.363 2736.0 610.4 0.0140
100 6000 2.060 0.57 3406.725 2880.0 526.7 0.0121
105 6300 2.000 0.55 3472.875 3024.0 448.9 0.0103
110 6600 1.940 0.53 3529.103 3168.0 361.1 0.0083
115 6900 1.890 0.52 3594.426 3312.0 282.4 0.0065
120 7200 1.840 0.51 3651.48 3456.0 195.5 0.0045
125 7500 1.790 0.49 3700.266 3600.0 100.3 0.0023
130 7800 1.750 0.48 3762.281 3744.0 18.3 0.0004
135 8100 1.710 0.47 3817.682 3888.0 -70.3 -0.0016
140 8400 1.670 0.46 3866.468 4032.0 -165.5 -0.0038
145 8700 1.630 0.45 3908.638 4176.0 -267.4 -0.0061
150 9000 1.600 0.44 3969 4320.0 -351.0 -0.0081
155 9300 1.570 0.43 4024.401 4464.0 -439.6 -0.0101
160 9600 1.540 0.42 4074.84 4608.0 -533.2 -0.0122
165 9900 1.510 0.42 4120.318 4752.0 -631.7 -0.0145
170 10200 1.480 0.41 4160.835 4896.0 -735.2 -0.0169
175 10500 1.450 0.40 4196.391 5040.0 -843.6 -0.0194
180 10800 1.420 0.39 4226.985 5184.0 -957.0 -0.0220
185 11100 1.400 0.39 4283.213 5328.0 -1044.8 -0.0240
190 11400 1.380 0.38 4336.133 5472.0 -1135.9 -0.0261
195 11700 1.360 0.37 4385.745 5616.0 -1230.3 -0.0282
200 12000 1.340 0.37 4432.05 5760.0 -1328.0 -0.0305
205 12300 1.320 0.36 4475.048 5904.0 -1429.0 -0.0328
210 12600 1.300 0.36 4514.738 6048.0 -1533.3 -0.0352
215 12900 1.280 0.35 4551.12 6192.0 -1640.9 -0.0377
220 13200 1.260 0.35 4584.195 6336.0 -1751.8 -0.0402
100 Year
This is to convert % imp. to a C value
100-year (must insert % imp. and C pervious).
ft
3
acre-ft.
'C' value 0.82 2741.8 0.0629
'C' * 1.25 1
Area 0.29 acres Modified Modified
Release Rate 0.161 M. FATER D. JUDISH C. LI
5/95 Nov-97 Nov-98
DETENTION POND SIZING
TIME TIME INTENSITY Q 100 Runoff Release Required Required
cum 100 year Volume Cum total Detention Detention
(mins) (secs) (in/hr) (cfs) (ft^3) (ft^3) (ft^3) (ac-ft)
0 0 0 0.00 0 0.0 0.0 0.0000
5 300 9.950 2.89 865.65 48.3 817.4 0.0188
10 600 7.720 2.24 1343.28 96.6 1246.7 0.0286
15 900 6.520 1.89 1701.72 144.9 1556.8 0.0357
20 1200 5.600 1.62 1948.8 193.2 1755.6 0.0403
25 1500 4.980 1.44 2166.3 241.5 1924.8 0.0442
30 1800 4.520 1.31 2359.44 289.8 2069.6 0.0475
35 2100 4.080 1.18 2484.72 338.1 2146.6 0.0493
40 2400 3.740 1.08 2603.04 386.4 2216.6 0.0509
45 2700 3.460 1.00 2709.18 434.7 2274.5 0.0522
50 3000 3.230 0.94 2810.1 483.0 2327.1 0.0534
55 3300 3.030 0.88 2899.71 531.3 2368.4 0.0544
60 3600 2.860 0.83 2985.84 579.6 2406.2 0.0552
65 3900 2.720 0.79 3076.32 627.9 2448.4 0.0562
70 4200 2.590 0.75 3154.62 676.2 2478.4 0.0569
75 4500 2.480 0.72 3236.4 724.5 2511.9 0.0577
80 4800 2.380 0.69 3312.96 772.8 2540.2 0.0583
85 5100 2.290 0.66 3386.91 821.1 2565.8 0.0589
90 5400 2.210 0.64 3460.86 869.4 2591.5 0.0595
95 5700 2.130 0.62 3520.89 917.7 2603.2 0.0598
100 6000 2.060 0.60 3584.4 966.0 2618.4 0.0601
105 6300 2.000 0.58 3654 1014.3 2639.7 0.0606
110 6600 1.940 0.56 3713.16 1062.6 2650.6 0.0608
115 6900 1.890 0.55 3781.89 1110.9 2671.0 0.0613
120 7200 1.840 0.53 3841.92 1159.2 2682.7 0.0616
125 7500 1.790 0.52 3893.25 1207.5 2685.8 0.0617
130 7800 1.750 0.51 3958.5 1255.8 2702.7 0.0620
135 8100 1.710 0.50 4016.79 1304.1 2712.7 0.0623
140 8400 1.670 0.48 4068.12 1352.4 2715.7 0.0623
145 8700 1.630 0.47 4112.49 1400.7 2711.8 0.0623
150 9000 1.600 0.46 4176 1449.0 2727.0 0.0626
155 9300 1.570 0.46 4234.29 1497.3 2737.0 0.0628
160 9600 1.540 0.45 4287.36 1545.6 2741.8 0.0629
165 9900 1.510 0.44 4335.21 1593.9 2741.3 0.0629
170 10200 1.480 0.43 4377.84 1642.2 2735.6 0.0628
175 10500 1.450 0.42 4415.25 1690.5 2724.8 0.0626
180 10800 1.420 0.41 4447.44 1738.8 2708.6 0.0622
185 11100 1.400 0.41 4506.6 1787.1 2719.5 0.0624
190 11400 1.380 0.40 4562.28 1835.4 2726.9 0.0626
195 11700 1.360 0.39 4614.48 1883.7 2730.8 0.0627
200 12000 1.340 0.39 4663.2 1932.0 2731.2 0.0627
205 12300 1.320 0.38 4708.44 1980.3 2728.1 0.0626
210 12600 1.300 0.38 4750.2 2028.6 2721.6 0.0625
215 12900 1.280 0.37 4788.48 2076.9 2711.6 0.0622
220 13200 1.260 0.37 4823.28 2125.2 2698.1 0.0619
225 13500 1.240 0.36 4854.6 2173.5 2681.1 0.0615
230 13800 1.220 0.35 4882.44 2221.8 2660.6 0.0611
235 14100 1.210 0.35 4947.69 2270.1 2677.6 0.0615
240 14400 1.200 0.35 5011.2 2318.4 2692.8 0.0618
Required detention
Page 1
225 13500 1.240 0.34 4613.963 6480.0 -1866.0 -0.0428
230 13800 1.220 0.34 4640.423 6624.0 -1983.6 -0.0455
235 14100 1.210 0.33 4702.438 6768.0 -2065.6 -0.0474
240 14400 1.200 0.33 4762.8 6912.0 -2149.2 -0.0493
Required detention
Page 1
225 13500 1.240 0.79 10713.6 4185.0 6528.6 0.1499
230 13800 1.220 0.78 10775.04 4278.0 6497.0 0.1492
235 14100 1.210 0.77 10919.04 4371.0 6548.0 0.1503
240 14400 1.200 0.77 11059.2 4464.0 6595.2 0.1514
Required detention
Page 1
225 13500 1.240 0.26 3452.625 3780.0 -327.4 -0.0075
230 13800 1.220 0.25 3472.425 3864.0 -391.6 -0.0090
235 14100 1.210 0.25 3518.831 3948.0 -429.2 -0.0099
240 14400 1.200 0.25 3564 4032.0 -468.0 -0.0107
Required detention
Page 1