drainage conformance letter - city of thornton · drainage conformance letter lot 1e, skylake...

Astra Engineering LLC

7887 E. Belleview Avenue, Suite 1100, Englewood, Colorado 80111 Ph. 303-475-5691

DRAINAGE CONFORMANCE LETTER

Lot 1E, Skylake Ranch, Amendment #5. City of Thornton, Adams County, State of Colorado

July 27, 2016 Jason O’Shea Development Director City of Thornton City Development Department 9500 Civic Center Drive Thornton, CO 80229-4326 303-538-7295 Re: Skylake Ranch Daycare Dear Mr. O’Shea: This letter is written to state that the drainage patterns and provisions for Skylake Ranch Daycare, Lot 1E, Skylake Ranch Amendment #5, now named “The Learning Experience – Skylake Ranch Plaza” conforms to the “Preliminary Drainage Study for Skylake Ranch,” prepared by CLC Associates, Inc., Greenwood Village, Colorado, August, 2012, (”Preliminary Report”,) and also to the “Final Drainage Report for Skylake Ranch,” Point Consulting LLC, Littleton, CO, June 29, 2016 (“Final Report”. ) The 1.16-acre site is located in the southwest corner of the 11.7-acre overall site at the northwest corner of 119th Avenue and Holly Street. It slopes to the southeast at an average slope of 2.7%, and is covered with native grasses and weeds. Soils are loamy, and of Hydrologic soil type “C.” Most of the site is a rectangular area for the daycare center and parking, with a small dog-leg north to tie the lot into a partially-completed internal drive, via a shared access. Runoff for the site will be carried by storm sewer and as sheet flow towards a regional detention pond to be provided by the owner of the overall development (Skylake Ranch) adjacent to the southwest corner of the site. Peripheral landscape areas facing Holly Street and 119th Avenue drain undetained to the streets at near or less than existing flows, as most of the area will be diverted to the pond. The preliminary report assumed 95% imperviousness for this commercial shopping area. No detention sizing was made to the southern end of the site, and the proposed imperviousness for the TLE site is 57%.

The site was divided into 8 small basins as well as one offsite basin to the northeast, which will be tributary to the site at the north access drive. This will allow that area to drain to the regional detention pond, as planned by the previous master drainage studies. Flowrates for the small basins are shown on the drainage plan and in the calculations in the Appendix of the report. The runoff coefficient for the offsite basin (O1, 0.60 acres) was taken from the values assumed in the Final Report. The onsite sub-basins were labeled starting with “B1” instead of the usual “A” names to avoid confusion with the Final Report, the plan for which is reproduced on this site’s drainage plan According to the Final Report the overall developer for the larger site will construct a private storm sewer system beginning approximately 125’ northeast of the TLE site within the existing access drive for the overall site. The system will continue southwest, turning south just beyond the north corner of the TLE site, with sump inlets on both sides of the access road again. From there it drains south then west along the north edge of the regional pond to an outfall into the pond near the northwest corner of it. Private storm sewer (12” PVC) will extend west to tie into the regional storm at two locations, one from a low point in the shared access drive, and one from a low point in TLE’s parking lot. Sub-basin B1 (0.4 acres of playground, landscape and parking lot drains to a sump inlet near the southeast corner of the parking lot. Sub-basins B2 and B3 consist of half the roof each (0.11 acres each) which will drain north in 6” PVC pipes to tie into the 12” PVC. A 5-foot curb opening inlet will have the capacity for both the 5-year and 100-year storm. (See capacity calculations in the Appendix.) Offsite sub-basin O1 drains east, joining runoff from sub-basin B4 (0.18 acres of parking and landscaping) at the low point in the access drive. A 5-foot curb opening inlet will pick up the 5-year and approximately half of the 100-year storm. Sub-basin B5 (0.08 acres of parking lot and landscape) will drain to the west side of the access drive. A 5-foot curb opening inlet will pick up the 5-year runoff and the 100-year storm, plus potentially the excess 100-year runoff from the east side of the street. Sub-basin C1 (0.07 acres of landscape and sidewalk) along the west side of the site will sheet flow off into the regional pond. Sub-basins D1 (0.18 acres of landscape and sidewalk) will sheet flow off to the south (119th Avenue), and Sub-basin D2 (0.2 acres of landscape) will sheet flow off to Holly Street. The hydraulic grade line analysis was taken from the Final Report, which includes the laterals extending into the site, in order to show how the entire system will work. The Final Report analysis shows the 5-year storm will be contained within the storm system, and there may be some ponding and overflow towards the regional pond,

during the 100-year storm. Complete analysis of the ponding and over flow will have to be completed when the design of the offsite storm system by others is finalized Conclusion The regional pond west of the proposed site will provide detention and water quality improvement for the impervious areas of the site. It is being designed concurrently by Point Consulting, LLC, Littleton, Colorado. We believe the drainage provisions for the proposed development of the “The Learning Experience – Skylake Ranch Plaza” (Skylake Ranch Daycare,) Lot 1E, Skylake Ranch Amendment #5, is in substantial conformance with the approved preliminary drainage study, and the Final Drainage Report, currently under review. Sincerely, Connie Ellefson, P.E. Astra Engineering, LLC 303-523-3664

DND Properties, LLC hereby certifies that the drainage facilities for The Learning Experience, Skylake Ranch, 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 drainage facilities designed and/or certified by my engineer. I understand that the City of Thornton reviews drainage plans but cannot, on behalf of DND Properties, LLC, guarantee that final drainage design review will absolve DND Properties, LLC 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 drainage design. Attest: ______________________________ DND Properties, LLC ___________________________ ______________________________ Notary Public Authorized Signature "I hereby certify that this report (plan) for the final drainage design of The Learning Experience, Skylake Ranch 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 Public and Private Improvements for the Responsible Parties thereof. I understand that the City of Thornton does not and shall not assume liability for drainage facilities designed by others _________________________________________ Registered Professional Engineer State of Colorado No. 23371

Astra Engineering Inc.The Learning Center

Thornton, CO 7/26/2016

Proposed Composite Coefficients of Runoff

Site 1.11 acres 48400


Cover type Area (sf) Imperviousness

Landscape 17,479 2%

Roof 10,000 90%

Playground 5,206 75%Concrete 15,715 90%

48,400

Proposed Imperviousness I= 56.6%

B1 0.40 acres 17211Proposed Composite Coefficients of Runoff


Landscape 10,830 2%Roof 0 90%

Playground 5,206 75%Concrete 1,175 90%

17,211


c5 = 0.30

c100= 0.57

B2 and B3 are all roof I = 90%

c5 = 0.75

c100= 0.83



Landscape 460 2%Roof 0 90%

Playground 0 75%

Concrete 7,250 90%

7,710


c5 = 0.68

c100= 0.79



Landscape 400 2%

Roof 0 90%

Playground 0 75%

Concrete 2,920 90%

3,320

Proposed Imperviousness

I= 79.4%

c5 = 0.63

c100= 0.74

C1 0.07 acres 3156Proposed Composite Coefficients of Runoff


Landscape 1,846 2%

Roof 0 90%

Playground 0 75%

Concrete 1,310 90%

3,156


c5 = 0.34

c100= 0.58

D1 0.18 acres 7642



Landscape 6,882 2%Roof 0 90%

Playground 0 75%Concrete 760 90%

7,642

Proposed Imperviousness

I= 10.8%

c5 = 0.22

c100= 0.53

STANDARD FORM SF - 1TIME OF CONCENTRATION

PROJECT: Thornton TLEDATE: 7/26/2016 tc = ti + tt

INITIAL / OVERLAND TRAVEL TIME tc CHECK FINAL REMARKS

TIME (ti) (tt) (URBANIZED BASINS) tc

BASIN AREA C5 LENGTH SLOPE ti LENGTH SLOPE VEL. tt COMP.TOTAL

LENGTHtc=(l/180)

+10DESIGN. Ac Ft % Min Ft % FPS Min tc (Ft) Min Min

(2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

Use 5.0 minutes for all proposed basins

CALCULATED BY: CLE STANDARD FORM SF -2 PROJECT: TLE

DATE: 7/26/2016 STORM DRAINAGE SYSTEM DESIGN Thornton

(RATIONAL METHOD PROCEDURE) DESIGN STORM: 5 YR MAJOR STORM: 100YR

DIRECT RUNOFF TOTAL RUNOFF STREET PIPE TRAVEL TIMED

ES

IGN

P

OIN

T

AR

EA

D

ES

IGN

AR

EA

(A

C)

RU

NO

FF

C

OE

FF

tc

(MIN

)

C .

A

(AC

)

I

IN /

HR

Q

(CF

S)

tc

(M

IN)

SU

M C

. A

(A

C)

I

IN /

HR

Q

(CF

S)

SLO

PE

(%

)

ST

RE

ET

F

LOW

(CF

S)

DE

SIG

N

FLO

W(C

FS

)

SLO

PE

(%

)

PIP

E

S

IZE

LEN

GT

H

(F

T)

VE

LOC

ITY

(FP

S)

tt

(M

IN)

REMARKS

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)

5-year 1 B1 0.40 0.30 5.0 0.12 4.66 0.56

2 +B2 0.11 0.75 5.0 0.08 4.66 0.38 5.0 0.20 4.66 0.94

3 +B3 0.11 0.75 5.0 0.08 4.66 0.38 5.0 0.29 4.66 1.33

4 O1* 0.60 0.68 5.0 0.41 4.66 1.90 *c factor assumed in Point Consulting report

5 +B4 0.18 0.68 5.0 0.12 4.66 0.57 5.0 0.53 4.66 2.47

6 +B5 0.08 0.63 5.0 0.05 4.66 0.23 5.0 0.58 4.66 2.71

7 C1 0.07 0.34 5.0 0.02 4.66 0.11

8 D1 0.18 0.22 5.0 0.04 4.66 0.18

9 D2 0.02 0.16 5.0 0.00 4.66 0.01

100-yr

B1 0.40 0.57 5.0 0.23 9.12 2.08

+B2 0.11 0.83 5.0 0.09 9.12 0.83 5.0 0.32 9.12 2.91

+B3 0.11 0.83 5.0 0.09 9.12 0.83 5.0 0.41 9.12 3.74

O1* 0.60 0.83 5.0 0.50 9.12 4.54 *c factor assumed in Point Consulting report

+B4 0.18 0.79 5.0 0.14 9.12 1.30 5.0 0.64 9.12 5.84

+B5 0.08 0.74 5.0 0.06 9.12 0.54 5.0 0.70 9.12 6.38

C1 0.07 0.58 5.0 0.04 9.12 0.37

D1 0.18 0.53 5.0 0.10 9.12 0.87

D2 0.02 0.52 5.0 0.01 9.12 0.09

Project:

Inlet ID:

Gutter Geometry (Enter data in the blue cells)

Maximum Allowable Width for Spread Behind Curb TBACK = 2.0 ft

Side Slope Behind Curb (leave blank for no conveyance credit behind curb) SBACK = ft/ft

Manning's Roughness Behind Curb (typically between 0.012 and 0.020) nBACK = 0.013

Height of Curb at Gutter Flow Line HCURB = 6.00 inches

Distance from Curb Face to Street Crown TCROWN = 13.0 ft

Gutter Width W = 2.00 ft

Street Transverse Slope SX = 0.020 ft/ft

Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft) SW = 0.083 ft/ft

Street Longitudinal Slope - Enter 0 for sump condition SO = 0.000 ft/ft

Manning's Roughness for Street Section (typically between 0.012 and 0.020) nSTREET = 0.013

Minor Storm Major Storm

Max. Allowable Spread for Minor & Major Storm TMAX = 13.0 13.0 ft

Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX = 6.0 12.0 inches

Allow Flow Depth at Street Crown (leave blank for no) check = yes

MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm

MAJOR STORM Allowable Capacity is based on Depth Criterion Qallow = SUMP SUMP cfs

ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm)

(Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread)

Enter Your Project Name Here

Inlet 1-B1

Copy of UD-Inlet_v4.03, Inlet 1-B1 7/24/2016, 3:09 PM

Design Information (Input) MINOR MAJOR

Type of Inlet Type =

Local Depression (additional to continuous gutter depression 'a' from 'Q-Allow') alocal = 3.00 3.00 inches

Number of Unit Inlets (Grate or Curb Opening) No = 1 1

Water Depth at Flowline (outside of local depression) Ponding Depth = 4.6 4.6 inches

Grate Information MINOR MAJOR

Length of a Unit Grate Lo (G) = N/A N/A feet

Width of a Unit Grate Wo = N/A N/A feet

Area Opening Ratio for a Grate (typical values 0.15-0.90) Aratio = N/A N/A

Clogging Factor for a Single Grate (typical value 0.50 - 0.70) Cf (G) = N/A N/A

Grate Weir Coefficient (typical value 2.15 - 3.60) Cw (G) = N/A N/A

Grate Orifice Coefficient (typical value 0.60 - 0.80) Co (G) = N/A N/A

Curb Opening Information MINOR MAJOR

Length of a Unit Curb Opening Lo (C) = 5.00 5.00 feet

Height of Vertical Curb Opening in Inches Hvert = 6.00 6.00 inches

Height of Curb Orifice Throat in Inches Hthroat = 6.00 6.00 inches

Angle of Throat (see USDCM Figure ST-5) Theta = 63.40 63.40 degrees

Side Width for Depression Pan (typically the gutter width of 2 feet) Wp = 2.00 2.00 feet

Clogging Factor for a Single Curb Opening (typical value 0.10) Cf (C) = 0.10 0.10

Curb Opening Weir Coefficient (typical value 2.3-3.7) Cw (C) = 3.60 3.60

Curb Opening Orifice Coefficient (typical value 0.60 - 0.70) Co (C) = 0.67 0.67

Low Head Performance Reduction (Calculated) MINOR MAJOR

Depth for Grate Midwidth dGrate = N/A N/A ft

Depth for Curb Opening Weir Equation dCurb = 0.22 0.22 ft

Combination Inlet Performance Reduction Factor for Long Inlets RFCombination = 0.59 0.59

Curb Opening Performance Reduction Factor for Long Inlets RFCurb = 1.00 1.00

Grated Inlet Performance Reduction Factor for Long Inlets RFGrate = N/A N/A

MINOR MAJOR

Total Inlet Interception Capacity (assumes clogged condition) Qa = 2.9 2.9 cfs

Inlet Capacity IS GOOD for Minor and Major Storms(>Q PEAK) Q PEAK REQUIRED = 0.6 2.1 cfs

INLET IN A SUMP OR SAG LOCATION

CDOT Type R Curb Opening

H-VertH-Curb

W

Lo (C)

Lo (G)

W o

WP


Override Depths

Copy of UD-Inlet_v4.03, Inlet 1-B1 7/24/2016, 3:09 PM

Project:

Inlet ID:




















Thornton TLE

Inlet 2 - O1 + B4

UD-Inlet_v4.03, Inlet 2 - O1 + B4 7/24/2016, 4:09 PM




























MINOR MAJOR


WARNING: Inlet Capacity less than Q Peak for Major Storm Q PEAK REQUIRED = 2.5 5.8 cfs

Warning 5: The width of unit is greater than the gutter width.



H-VertH-Curb

W

Lo (C)

Lo (G)

W o

WP


Override Depths

UD-Inlet_v4.03, Inlet 2 - O1 + B4 7/24/2016, 4:09 PM

Project:

Inlet ID:




















Thornton TLE

Inlet 3 - B5

Copy of UD-Inlet_v4.03 - Inlets 2 and 3, Inlet 3 - B5 7/27/2016, 9:08 PM




























MINOR MAJOR


Inlet Capacity IS GOOD for Minor and Major Storms(>Q PEAK) Q PEAK REQUIRED = 0.2 0.5 cfs



H-VertH-Curb

W

Lo (C)

Lo (G)

W o

WP


Override Depths

Copy of UD-Inlet_v4.03 - Inlets 2 and 3, Inlet 3 - B5 7/27/2016, 9:08 PM

60

18

9

3

0

45

30

SCALE: 1" = 30'

5221

5220

5220

5225

5217

5218

5222

5224

5222

5217

5218

5219

5224

5221

5223

52235224

5225

5218521952205221

5221

5220

20

22

18

19

20

21

19

21

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21

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2221

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22

22

21

22

22

22

21

2221

20

21

REGIONAL DETENTION POND(BY OTHERS)

18"STORM (BY OTHERS)

LINE 1

LINE 2

1' CHASE SECTION

B1

0.40

.30

.57

B2

0.11

.75

.83

B3

0.11

.75

.83

O1

0.60

.68

.83

C1

0.07

.34

.58

21

D2

0.02

.16

.52

D1

0.18

.12

.53

B4

0.18

.68

.79

B5

0.08

.63

.74

5' TYPE R INLET 1

Q5=0.6 CFS

Q100=2.6CFS

5' TYPE R INLET 3

Q5=0.2 CFS

Q100=0.5 CFS

5' TYPE R INLET 2

Q5=2.5 CFS

Q100=5.8CFS

C-VALUES FROM POINT

CONSULTING REPORT

5. C.O.INLET

(BY OTHERS)

FL. 21.20

INV IN(NE):

18.40

INV

OUT(S):18.20

18" [email protected]%

(BY OTHERS)

18" [email protected]%

(BY OTHERS)

5. C.O.INLET

(BY OTHERS)

FL. 21.18

INV IN(N): 18.07

INV OUT(S):17.87

REGIONAL DETENTION POND

(BY OTHERS) - SEE ABOVE

RIGHT

4

6

3

2

1

8

7

9

5

AREA TRIBUTARY TO

STORM SEWER BY

OTHERS

5-YR ASSUMED* Q = 2.4 CFS5-YR ACTUAL Q = 0.6 CFS100-YR ASSUMED* Q = 6.6 CFS100-YR ACTUAL Q = 2.1CFS

* ASSUMED BY POINTCONSULTING (SEE BELOW.)

5-YR ASSUMED* Q = 2.8 CFS5-YR ACTUAL Q = 2.7 CFS (PIPE)100-YR ASSUMED* Q = 6.2 CFS100-YR ACTUAL Q = 6.4CFS(PIPE)

5-YR ASSUMED* Q = 1.4 CFS5-YR ACTUAL Q = 2.5 CFS100-YR ASSUMED* Q = 3.1 CFS100-YR ACTUAL Q =5.8 CFS

Q5=2.6CFSQ100=3.7CFS

A

0.90

0.45

BASIN DESIGNATION

AREA IN ACRES

5-YEAR RUNOFF COEFFICIENT

100-YEAR RUNOFF COEFFICIENT

DIRECTIONAL FLOW ARROW

DETENTION AREA

EXISTING CONTOUR

PROPOSED CONTOUR

PROPOSED SPOT ELEVATION

0.45

DRAINAGE LEGEND

DRAINAGE BOUNDARY

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DATE:

DRAWN:

CHECKED:

ROGUE PROJECT NO.:

04.26.2016

CLE

TRC

2015.36

SHEET:

© 2016 Rogue Architecture, Inc.

4100Wadsworth Boulevard

Suite 300Wheat Ridge

CO 80033720•599•3330 - P303•987•2304 - X

25528 Genesee Trail RoadGolden, CO 80401

OWNER:

1. G.C. MUST PROVIDE & INSTALL ALL PRODUCTSPER PLANS. ONLY SUBSTITUTED PRODUCTS NEEDTO BE SUBMITTED TO THE ARCHITECT FORAPPROVAL. UNAPPROVED SUBSTITUTIONS WILLBE REPLACED AT THE EXPENSE OF THE G.C.

2. VERBAL REPRESENTATION HAS NO VALUE ANDALL REQUESTS TO CHANGE ANY PRODUCTS ORSPECIFICATIONS PER PLANS, MUST BESUBMITTED IN WRITING TO THE ARCHITECT &T.L.E. FOR APPROVAL.

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DATE: ISSUE:TLE REVIEW03.02.201695% TLE REVIEW SET04.08.2016

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100% FINAL REVIEW SET04.26.2015CONSTR. REV. #107.15.2016 1

THE LEARNING EXPERIENCE

CONSTRUCTION PLANS

FROM: "FINAL DRAINAGE REPORT FOR SKYLAKERANCH," POINT CONSULTING LLC," LITTLETON, COJUNE 29, 2016

1 OF 1

DRAINAGE PLAN

FINAL DRAINAGE PLAN

SCALE: 1" = 40'

SCALE: 1" = 70'

WORK SHALL BE CONSTRUCTED TO CITY OF THORNTONSTANDARDS AND SPECIFICATIONS. THIS APPROVAL ISFOR CONFORMANCE TO THESE STANDARDS ANDSPECIFICATIONS AND OTHER CITY REQUIREMENTS. THEDESIGN AND CONCEPT REMAINS THE RESPONSIBILITY OFTHE PROFESSIONAL ENGINEER OR LANDSCAPEPROFESSIONAL.

SUMMARY RUNOFF TABLE

DESIGN POINT CONTRIBUTING CONTRIBUTING 5-YR 100-YR BASIN(S) AREA RUNOFF RUNOFF

(acres) (cfs)

1 B1 0.40 0.56 2.08

2 +B2 0.11/0.51 0.38/0.94 0.83/2.91

3 +B3 0.11/0.62 0.38/1.33 0.83/3.74

4 O1 0.60 1.90 4.54

5 +B4 0.18/.78 0.57/2.47 1.30/5.84

6 +B5 0.08/.86 0.23/2.71 0.54/6.38

7 C1 0.07 0.11 0.37

8 D1 0.18 0.18 0.87

9 D2 0.02 0.01 0.09

drainage conformance letter - city of thornton · drainage conformance letter lot 1e, skylake...

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