10289 quivas street thornton, colorado final drainage report · 2017. 1. 20. · landmark towers...

Prepared For:

Larry H. Miller

LHM Thornton

Landmark

Towers

10289 Quivas Street

Thornton, Colorado

Anderson, Wahlen & Associates, Inc.

2010 North Redwood Road

Salt Lake City, Utah 84116

Phone: (801) 521-8529

Fax: (801) 521-9551

Project #: 14-116

Date: December 27, 2016

Final Drainage Report

1/17/2017

December 30, 2016

City of Thornton, Colorado

Engineering Department

Re: Final Drainage Report

To Whom It May Concern:

AWA is submitting this Final Drainage Report for the LHM Thornton Landmark Towers project

located at 10289 Quivas Street, Thornton, Colorado.

This report includes, pre-development conditions and peak release rates as well as post-

development peak release rates for this site. In addition this report provides mitigation options

and detention per City standards and regulations. All calculations included in this report follow

the City of Thornton – Standards and Specifications Manual which references the Urban

Drainage and Flood Control District (UDFCD) Manual Volumes 1, 2, and 3.

If you have any questions regarding this report, please feel free to contact me, Arverd Taylor, at

[email protected]

Sincerely,

Arverd Taylor

Project Manager

Responsible Party Certification

“________ hereby certifies that the sewer and water systems for Landmark Towers will be constructed

according to the design presented in this report. I understand that the City of Thornton does not and

shall not assume liability for the sewer and water system designed and/or certified by my engineer. I

understand that the City of Thornton reviews utility plans, but cannot, on behalf of Landmark Towers,

guarantee that final utility design review will absolve ________ and/or their successors and/or assigns of

future liability for improper design. I further understand that approval of the Plat and/or Development

Permit does not imply approval of my engineer’s utility design.”

Attest:

“I hereby certify that this report (plan) for the Final Utility Design of Landmark Towers was

prepared by me (or under my direct supervision) in accordance with the provisions of the City of

Thornton Standards and Specifications for the Design and Construction of the Public and Private

Improvements for the Responsible Parties thereof. I understand that the City of Thornton does

not and shall not assume liability for utilities designed by others.”

XRegistered Pro fession al En g ineer

State of Co lo rado No. ____________________

XName of Respon sib le Party

XNotary Pu b lic

XAuth orized Sign atu re

Table of Contents GENERAL LOCATION MAP ............................................................................................................................. 1

PROPERTY LOCATION & DESCRIPTION ......................................................................................................... 2

PROPERTY LOCATION ................................................................................................................................ 2

DESCRIPTION OF PROPERTY ..................................................................................................................... 2

DRAINAGE BASINS AND SUB-BASINS ............................................................................................................ 2

MAJOR BASIN AND SUB-BASIN DESCRIPTION .......................................................................................... 2

DRAINAGE DESIGN CRITERIA ........................................................................................................................ 3

REGULATIONS ........................................................................................................................................... 3

DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS ...................................................................... 3

HYDROLOGICAL CRITERIA ......................................................................................................................... 3

DRAINAGE FACILITY DESIGN ..................................................................................................................... 4

HYDRUALIC CRITERIA ................................................................................................................................ 6

CONCLUSION ................................................................................................................................................. 6

APPENDICES .................................................................................................................................................. 7

REFERENCES .................................................................................................................................................. 8

1

GENERAL LOCATION MAP

Landmark Towers: 10289 Quivas Street

Thornton, Colorado

2

PROPERTY LOCATION & DESCRIPTION

PROPERTY LOCATION

The proposed property is a Portion of the Northwest Quarter of Section 16, Township 2 South, and

Range 68 West of the 6th P.M. City of Thornton, County of Adams, in the State of Colorado. The address

of the site is 10289 Quivas Street, Thornton, Colorado.

The 6.55 acre site is currently undeveloped. The property is bound on the north by a Five Star Collision

Center-Auto Repair shop, to the east by Quivas Street, to the south by residential housing and a

developed commercial lot, and to the west the Alpine Glen Veterinary Clinic.

DESCRIPTION OF PROPERTY

Existing conditions of, the 6.55 acre, site consist primarily of undeveloped land covered by soil and

weeds. The site is relatively flat with the soils containing Platner loam and Ulm loam, corresponding to

soil class C (Web Soil Survey, Appendix I). Existing drainage of the site occurs from the west to the

northeast side of the property. The 6.55 acre site will be constructed in two phases. This report will

account for the full buildout of both phases to adequately size the detention pond.

The proposed project’s land use will be for Vehicle Service and Storage with a majority of the area

consisting of a parking lot. The site will contain a 4,010 square foot building, parking lot, and landscape

area located within the parking lot. A 10.0’ Public Service Utility Easement will be located south of the

proposed parking lot and a 10’ Gas Easement will be located through the north portion of the site

(Appendix II, Civil Sheets - Utility Plan).

DRAINAGE BASINS AND SUB-BASINS

MAJOR BASIN AND SUB-BASIN DESCRIPTION

The site is located within Zone X (unshaded) of the FEMA floodplain, as determined by the Flood

Insurance Rate Map for Adams County, Colorado, Panel 294 and Map Number 08001C0294H, revised on

March 5, 2007 (Appendix III).

The existing drainage for the site consists of overland sheet low to the northeast onto the neighboring

property. After construction all storm water generated onsite will be collected and detained onsite

before being released at a metered rate.

3

The property was separated into 8 different sub-basins. Each sub-basin area was determined based on

site grading and subsequent drainage patterns. Storm water is collected in each sub-basin by catch

basins which ultimately is conveyed to the onsite detention pond. The detention pond has a low flow

trickle channel that drains to an inlet/outlet structure before connecting to a curb drain in Quivas Street

(Utility Plan, Appendix II).

DRAINAGE DESIGN CRITERIA

REGULATIONS

It is not foreseen that there will be any deviations from the criteria. All waterlines, sanitary sewer lines,

storm drain networks, and site improvements shall be constructed per the City of Thornton Standards

and Specifications.

DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS

At this time there are no known utility studies (i.e., utility reports, project master plans, etc.) done for

this site in question, and no adjacent utility studies. All storm water produced on site will be contained

and will not drain to neighboring property.

HYDROLOGICAL CRITERIA

In accordance with the City of Thornton’s Standards and Specifications, the methodologies and design

standards for determining rainfall, runoff conditions, and detention pond sizing for the project are based

on the standards prescribed in the Urban Drainage and Flood Control District (UDFCD), with local revisions

defined in the Standards and Specifications manual.

Rainfall data was gathered from the NOAA precipitation data frequency server based on latitude and

longitude (Appendix IV). The runoff calculation used was the rational method, as was specified within the

UDFCD manual as an acceptable runoff method for sites smaller than 90 acres. This site was divided into

roof area, landscaping and hard surfaces to determine the runoff coefficient. Individual runoff coefficients

of 0.13, 0.85, and 0.9 were used for landscape, roof and impervious surfaces respectively. The overall

calculated peak runoff for the site for the developed phase is approximately 36 cfs (see calculations

below).

4

Site characteristics:

Area: 6.55 acres

Roof: 4,010 sq. ft.

Hard Surfaces: 234,941 sq.ft.

Landscape: 46,527 sq.ft.

Corresponding Runoff Coefficient = 0.77

Time of Concentration (UDFCD Volume 1, Equation 6-5)

�� = �18 − 15 +�

60�24 + 12��=

�� = �� !��ℎ��#

= �$��%��#��## �� #�� %/100

�� = �(�$� �� (�) $��ℎ ��/�� = (��*�ℎ �� (�) $��ℎ ��

�� = �18 − 15�0.82 +1000

60�24�0.82 + 12√0.03= ~ 10 ��#

Rational Method (UDFCD Volume 1)

/ = $��0 �� #

! = ��

1 = �%��*� ��#�2 �� (( �� 3�� 4��( �� ℎ� �� , ��/ℎ� 6 = �� 2 �� #

/ = !16

/ = �0.77�7.13 �/ℎ��6.55 ��# = 36 ��#

DRAINAGE FACILITY DESIGN

Within the Standards and Specifications section 402.12 (Detention Pond Design), the requirement states

“storage volumes must be calculated using the Full Spectrum Detention Pond sizing method.” Based on

the Full Spectrum Detention Volume specifications within the UDFCD manual, three different volumes are

associated with the design of a full spectrum detention facility. These three different volumes are:

1. WQCV (Water Quality Capture Volume)

2. EURV (Excess Urban Runoff Volume)

3. 100-Year Volume

*Calculations using equations from the UDFCD manual can be found below.

5

1. WQCV (UDFCD Volume 3, Equation 3-1)

8/!9 = ��0.911; − 1.191< + 0.78

� = �� #$��3�* �� 8/!9 3�� =>!= 9�(�� 3, ?� (� 3 − 2

1 = 1�$��%��#��## �%/100

8/!9 = 1�0.91�0.82; − 1.19�0.82< + 0.78�0.82 = 0.34 )��#ℎ�3 − ��ℎ�# = 8084��;

2. EURV (UDFCD Volume 2, Equation 12-3)

@�A9B = 1.20C.�D

= �$��%��#��## ��

@�A9B = 1.20�0.82C.�D = 0.969 )��#ℎ�3 − ��ℎ�# = 23,027 ��;

3. 100-Year Volume (UDFCD Volume 2, Equation 12-4)

9C�� = EC[�0.728C.<GD + 0.15�.<GD6% + �0.364C.<DH + 0.381C.<DHI% + �0.306C.<DH

+ 0.402�.<DH!=%]

=100-year 1-hour rainfall depth= 2.69 in. (Standards and Specifications manual, Section 402.1)

Site Soil Classification = 100% Soil C (Web Soil Survey, Appendix I)

9C�� = 2.69[�0.306�0.82C.<DH + 0.402�0.82�.<DH1] = 1.66 )��#ℎ�3 − ��ℎ�# = 39,456��;

The Full Spectrum Detention Volume Specifications method is also designed to reduce the developed

condition 100-year peak discharge to 90% of the pre-developed 100-year peak flow rate. Table 12-5

within Volume 2 of the UDFCD manual denotes that the specified site can utilize the simplified

equations for the detention pond sizing method. Pre-development peak unit discharge rates are based

on NRCS hydrologic soil group, total flow length and general site slope. Based on the characteristics

listed above Table 12-8 of Volume 2 was utilized to determine the pre-development rate to be 1.49 cfs,

corresponding to a 1.34 cfs release rate for the developed site.

Taking into account the release discharge rate of 1.34 cfs from the 100-Year Volume calculation above,

the site requires a total storage volume of 34,632 ft^3 for the 100-year return period. The onsite

6

detention pond has been adequately sized to detain the required storage volume by providing 56,148

ft^3 of storage capacity. Detention and the specified release rate will be accomplished by two orifice

plates. The first orifice, with a 1.4“ diameter, has been sized to release the EURV in 72 hours as per city

requirements. The second orifice, with a 5” diameter, has been sized to release storm water at the

calculated 1.34 cfs. All orifice calculations can be found in Appendix V.

HYDRUALIC CRITERIA

A private pipe network will be constructed onsite to route storm water runoff to the detention pond

before it is released at a metered rate to Quivas Street. All storm drain, sewer, and additional utility

piping shall be installed per manufacturer’s recommendations and shall meet the City of Thornton’s

Standards and Specifications layout in Section 200, 300, and 400.

CONCLUSION

The LHM Thornton site is in compliance with the City of Thornton’s Standards and Specifications manual.

The calculated developed site has a peak runoff of 46 cfs generated onsite. This 46 cfs peak runoff is

calculated prior to detention and a metered outfall from the site. The detention pond has been sized

using Full Spectrum Detention Specifications method outlined in the UDFCD manual. Equations utilized

within the UDFCD manual calculated a 100-year volume of 39,456 cubic feet, a WQCV volume of 8,084

cubic feet, and a EURV volume of 23,027 cubic feet. A release rate for the developed site was calculated

to be 1.34 cfs. This release rate requires a storage volume of 34,632 cubic feet, which is adequately

stored in the designed detention pond, which has 56,148 cubic feet of storage capacity. Detention will

be accomplished by the use of two orifice plates. The first orifice, with a 1.4“ diameter, has been sized to

release the EURV in 72 hours as per city requirements. The second orifice, with a 5” diameter, has been

sized to release storm water at the calculated 1.34 cfs. All flows larger than the detention basin will be

directed to Quivas Street before flooding the building or neighboring properties.

7

APPENDICES

APPENDIX I – WEB SOIL SURVEY (SOIL CLASSIFICATION)

APPENDIX II – CIVIL SHEETS

APPENDIX III – FEMA FLOOD MAP

APPENDIX IV – NOAA RAINFALL DATA

APPENDIX V – ORIFICE CALCULATIONS

8

REFERENCES

City of Thornton (2012, October). City of Thornton – Standards and Specifications. Retrieved from

https://cityofthornton.net/government/citydevelopment/Pages/standards-specifications.aspx

Urban Drainage and Flood control District (2016, January). Urban Storm Drainage Criteria

Manual – Volume 1. Retrieved from http://udfcd.org/volume-one


Manual – Volume 2. Retrieved from http://udfcd.org/volume-two


Manual – Volume 2. Retrieved from http://udfcd.org/volume-three

United States Department of Agriculture, Natural Resources Conservation Service (n.d.). Web Soil

Survey. Retrieved from https://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx

FEMA (n.d.). FEMA Flood Map Service Center. Retrieved from http://msc.fema.gov/portal

APPENDIX I WEB SOIL SURVEY (SOIL CLASSIFICATION)

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Hydrologic Soil Group

Hydrologic Soil Group— Summary by Map Unit — Adams County Area, Parts of Adams and Denver Counties, Colorado(CO001)

Map unit symbol Map unit name Rating Acres in AOI Percent of AOI

PlC Platner loam, 3 to 5percent slopes

C 5.7 85.6%

UlD Ulm loam, 5 to 9 percentslopes

C 1.0 14.4%

Totals for Area of Interest 6.7 100.0%

Description

Hydrologic soil groups are based on estimates of runoff potential. Soils areassigned to one of four groups according to the rate of water infiltration when thesoils are not protected by vegetation, are thoroughly wet, and receiveprecipitation from long-duration storms.

The soils in the United States are assigned to four groups (A, B, C, and D) andthree dual classes (A/D, B/D, and C/D). The groups are defined as follows:

Group A. Soils having a high infiltration rate (low runoff potential) whenthoroughly wet. These consist mainly of deep, well drained to excessivelydrained sands or gravelly sands. These soils have a high rate of watertransmission.

Group B. Soils having a moderate infiltration rate when thoroughly wet. Theseconsist chiefly of moderately deep or deep, moderately well drained or welldrained soils that have moderately fine texture to moderately coarse texture.These soils have a moderate rate of water transmission.

Group C. Soils having a slow infiltration rate when thoroughly wet. These consistchiefly of soils having a layer that impedes the downward movement of water orsoils of moderately fine texture or fine texture. These soils have a slow rate ofwater transmission.

Group D. Soils having a very slow infiltration rate (high runoff potential) whenthoroughly wet. These consist chiefly of clays that have a high shrink-swellpotential, soils that have a high water table, soils that have a claypan or claylayer at or near the surface, and soils that are shallow over nearly imperviousmaterial. These soils have a very slow rate of water transmission.

If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter isfor drained areas and the second is for undrained areas. Only the soils that intheir natural condition are in group D are assigned to dual classes.

Hydrologic Soil Group—Adams County Area, Parts of Adams and Denver Counties, Colorado LHM - Thornton

Natural ResourcesConservation Service

Web Soil SurveyNational Cooperative Soil Survey

12/26/2016Page 3 of 4

Rating Options

Aggregation Method: Dominant Condition

Component Percent Cutoff: None Specified

Tie-break Rule: Higher

Hydrologic Soil Group—Adams County Area, Parts of Adams and Denver Counties, Colorado LHM - Thornton

Natural ResourcesConservation Service

Web Soil SurveyNational Cooperative Soil Survey

12/26/2016Page 4 of 4

APPENDIX II - CIVIL SHEETS (UTILITY PLAN)

APPENDIX III FEMA FLOOD MAP

APPENDIX IV - NOAA RAINFALL DATA

NOAA Atlas 14, Volume 8, Version 2 Location name: Thornton, Colorado, USA* Latitude: 39.8825°, Longitude: -105.0079°

Elevation: 5520.06 ft** * source: ESRI Maps

** source: USGS

POINT PRECIPITATION FREQUENCY ESTIMATES

Sanja Perica, Deborah Martin, Sandra Pavlovic, Ishani Roy, Michael St. Laurent, Carl Trypaluk, Dale Unruh, Michael Yekta, Geoffery Bonnin

NOAA, National Weather Service, Silver Spring, Maryland

PF_tabular | PF_graphical | Maps_&_aerials

PF tabular

AMS-based point precipitation frequency estimates with 90% confidence intervals (in

inches/hour)1

DurationAnnual exceedance probability (1/years)

1/2 1/5 1/10 1/25 1/50 1/100 1/200 1/500 1/1000

5-min2.89

(2.24-3.72)4.15

(3.22-5.36)5.26

(4.04-6.80)6.88

(5.18-9.41)8.24

(6.06-11.4)9.73

(6.90-13.7)11.3

(7.72-16.4)13.6

(8.93-20.2)15.5

(9.84-23.1)

10-min2.12

(1.64-2.72)3.04

(2.36-3.93)3.85

(2.96-4.98)5.03

(3.80-6.88)6.04

(4.43-8.32)7.13

(5.05-10.0)8.30

(5.65-12.0)9.98

(6.53-14.8)11.4

(7.21-16.9)

15-min1.72

(1.34-2.22)2.48

(1.92-3.19)3.12

(2.41-4.05)4.10

(3.09-5.60)4.91

(3.60-6.76)5.79

(4.11-8.16)6.75

(4.59-9.75)8.12

(5.31-12.0)9.24

(5.86-13.7)

30-min1.21

(0.942-1.56)1.74

(1.35-2.25)2.19

(1.69-2.84)2.86

(2.16-3.90)3.42

(2.51-4.71)4.02

(2.85-5.66)4.68

(3.18-6.75)5.60

(3.67-8.29)6.36

(4.03-9.46)

60-min0.746

(0.580-0.960)1.08

(0.834-1.39)1.36

(1.05-1.76)1.77

(1.33-2.41)2.11

(1.55-2.90)2.48

(1.75-3.48)2.87

(1.95-4.14)3.43

(2.24-5.07)3.88

(2.46-5.77)

2-hr0.443

(0.348-0.564)0.642

(0.502-0.818)0.809

(0.630-1.04)1.05

(0.800-1.42)1.25

(0.928-1.70)1.47

(1.05-2.04)1.70

(1.17-2.42)2.03

(1.34-2.96)2.29

(1.47-3.37)

3-hr0.319

(0.252-0.403)0.461

(0.363-0.584)0.580

(0.455-0.738)0.753

(0.575-1.01)0.895

(0.667-1.21)1.05

(0.754-1.44)1.21

(0.836-1.71)1.44

(0.957-2.09)1.63

(1.05-2.37)

6-hr0.189

(0.151-0.236)0.268

(0.214-0.336)0.335

(0.265-0.422)0.431

(0.333-0.568)0.510

(0.384-0.679)0.594

(0.432-0.808)0.684

(0.478-0.954)0.811

(0.545-1.16)0.913

(0.596-1.31)

12-hr0.116

(0.094-0.143)0.160

(0.129-0.199)0.197

(0.158-0.245)0.251

(0.196-0.326)0.294

(0.224-0.387)0.341

(0.251-0.458)0.391

(0.276-0.538)0.461

(0.313-0.650)0.517

(0.341-0.734)

24-hr0.071

(0.058-0.087)0.098

(0.079-0.119)0.119

(0.096-0.146)0.149

(0.117-0.191)0.174

(0.133-0.224)0.199

(0.148-0.263)0.226

(0.161-0.305)0.262

(0.180-0.365)0.292

(0.195-0.409)

2-day0.041

(0.034-0.050)0.057

(0.047-0.069)0.070

(0.057-0.085)0.087

(0.069-0.109)0.100

(0.077-0.126)0.113

(0.084-0.146)0.126

(0.091-0.168)0.145

(0.100-0.197)0.159

(0.107-0.220)

3-day0.030

(0.025-0.036)0.041

(0.034-0.049)0.049

(0.040-0.059)0.060

(0.048-0.075)0.069

(0.054-0.087)0.078

(0.059-0.101)0.088

(0.063-0.116)0.100

(0.070-0.136)0.110

(0.075-0.151)

4-day0.024

(0.020-0.028)0.032

(0.026-0.038)0.038

(0.031-0.046)0.047

(0.037-0.058)0.053

(0.042-0.067)0.060

(0.046-0.077)0.067

(0.049-0.088)0.077

(0.054-0.104)0.084

(0.057-0.115)

7-day0.015

(0.013-0.018)0.020

(0.017-0.024)0.024

(0.020-0.028)0.029

(0.023-0.035)0.032

(0.026-0.040)0.036

(0.028-0.046)0.041

(0.030-0.053)0.046

(0.033-0.062)0.051

(0.035-0.068)

10-day0.012

(0.010-0.014)0.015

(0.013-0.018)0.018

(0.015-0.021)0.021

(0.017-0.026)0.024

(0.019-0.030)0.027

(0.021-0.034)0.030

(0.022-0.039)0.034

(0.024-0.045)0.037

(0.026-0.049)

20-day0.008

(0.007-0.009)0.010

(0.008-0.011)0.011

(0.009-0.013)0.013

(0.011-0.016)0.014

(0.012-0.018)0.016

(0.012-0.020)0.017

(0.013-0.022)0.019

(0.014-0.025)0.021

(0.015-0.028)

30-day0.006

(0.005-0.007)0.007

(0.006-0.009)0.009

(0.007-0.010)0.010

(0.008-0.012)0.011

(0.009-0.013)0.012

(0.010-0.015)0.013

(0.010-0.017)0.015

(0.011-0.019)0.016

(0.011-0.020)

45-day0.005

(0.004-0.005)0.006

(0.005-0.007)0.007

(0.006-0.008)0.008

(0.007-0.009)0.009

(0.007-0.010)0.010

(0.008-0.012)0.010

(0.008-0.013)0.011

(0.008-0.014)0.012

(0.009-0.016)

60-day0.004

(0.004-0.005)0.005

(0.004-0.006)0.006

(0.005-0.007)0.007

(0.006-0.008)0.008

(0.006-0.009)0.008

(0.006-0.010)0.009

(0.007-0.011)0.010

(0.007-0.012)0.010

(0.007-0.013)

1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of annual maxima series (AMS).

Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a given duration and annual exceedance probability) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values.

Please refer to NOAA Atlas 14 document for more information.

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APPENDIX V - ORIFICE CALCULATIONS

Q=CdAo(2gh)^1/2 Q=CdAo(2gh)^1/2

Flow (Q) = 0.09 Flow (Q) = 1.34

Head (h) = 3 Head (h) = 4

Cd= 0.62 Cd= 0.62

Area (in^2)= 1.50 Area (in^2)= 19.39

Dia (in) = 1.38 Dia (in) = 4.97

*Use 1.4" Diameter * Use 5" Diameter

EURV - 72 Hour

(100 Year Event) Total 100 Year Event

Orifice Calculations

10289 quivas street thornton, colorado final drainage report · 2017. 1. 20. · landmark towers...

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