PRELIMINARY DRAINAGE REPORT FOR

ADOBE VIEW NORTH SUBDIVISION

PRESENTED TO:

The City of Fruita

PREPARED FOR:

Adobe View Development Company LLC. P.O. Box 903

Rangely, CO 81648

PREPARED BY:

Rolland Consulting Engineers LLC 405 Ridges Blvd. Suite A

Grand Junction, CO 81507

April 26, 2016

TABLE OF CONTENTS

I. SITE LOCATION AND DESCRIPTION II. MAJOR BASIN DESCRIPTION III. EXISTING SITE DESCRIPTION AND SOIL GROUP IV. PROPOSED SITE DESCRIPTION V. EXISTING DRAINAGE CONDITIONS

• On-site Flows

• Off-site Flows

• Runoff Calculations

VI. PROPOSED DRAINAGE CONDITIONS

• General Discussion

• Drainage Fee Calculation

• Off-Site Flows and System Impact

• Operation and Maintenance

VII. DESIGN CRITERIA

• General Considerations

• Hydrology

VIII. CONCLUSIONS

APPENDICES A. CALCULATIONS

• RATIONAL METHOD RUNOFF (EXISTING & PROPOSED)

• PIPE, INLET AND STREET CAPACITIES

B. SUPPORTING INFORMATION

• RATIONAL METHOD RUNOFF COEFFICIENTS TABLE

• IDF DATA FOR USE IN THE GRAND VALLEY

FIGURES MAJOR DRAINAGE BASIN MAP ENCLOSURES FINAL DRAINAGE PLAN

CERTIFICATION STATEMENT

This Drainage Report has been prepared under my direct supervision. _______________________ Kent Shaffer, P.E.

I. SITE LOCATION AND DESCRIPTION The project site is located in the SE¼ NE¼ Section 20 T1N, R2W, of the Ute Meridian also known as 965 18 Road in Fruita, Colorado. The proposed project is a 34 lot, residential single family home, subdivision on an approximate 12.05-acre parcel. The lots will be approximately 1/4 to 1/3 acre in size. The proposed project will be named Adobe View North Subdivision.

II. MAJOR BASIN DESCRIPTION The site lies within a 1700 acre basin of the of the Murray drain system (approximately 3,000 ft upstream from the Colorado River) that is the jurisdiction of the Grand Valley Drainage District. (See major drainage basin map). The site is not within a defined 100-year floodplain. Drainage characteristics within the major drainage basin will remain unchanged.

III. EXISTING SITE DESCRIPTION AND SOIL GROUP The site currently consists of a mostly vacant lot with one residential structure and a few small

out buildings. Previously the site was in irrigated agricultural use. According to the ASoil Survey, Grand Junction Area, Colorado, United States department of Agriculture, Soil Conservation Service, issued in November, 1955", the soil type for this site is Sagers Silty Clay Loam (0-2 percent slopes. An SCS Hydrologic Soil Group B was used for run off calculations.

MAJOR DRAINAGE BASIN MAP

V. PROPOSED SITE DESCRIPTION Initial improvements will include: asphalt roadway with concrete curb and gutter. For proposed run-off calculation purposes, it is estimated that approximately 20 percent of each lot area will be impervious in the fully developed condition. The on-site developed surface treatments (and their approximate size) will consist of the items listed below.

$ Building/driveway 1.81 Acres

$ Asphalt/Concrete 2.23 Acres

• Landscaping/Gravel 7.25 Acres

• Bare/ Undisturbed 0.76 Acres 12.05 Acres

V. EXISTING DRAINAGE CONDITIONS On-Site Flows

The site is considered to be one basin that drains from northeast to southwest at an average slope of 0.5 to 1 percent. The Murray Drain flows south along the west site boundary. Site drainage is channeled to the west along the south boundary line to the open Murray drain. Roadside drainage along the west side of Pine Street (east site boundary) generally flows on-site and joins on-site flow to the west. Off-Site Flows

There is a lot line Drain Ditch along the north boundary that intercepts drainage flowing towards the site from the north and channels it west to the Murray Drain. The Raley Drain ditch generally runs near the south boundary of the site and joins the Murray Drain near the SW corner of the site. There is some contributing sheet flow from the lots of Adobe View Subdivision south of the site. Other off-site drainage from the east of the site, primarily River Glen Estates Subdivision, enters the Raley Drain from a pipe crossing under Pine Street. Runoff Calculations

The hydrology and runoff calculations for the existing conditions are presented in spreadsheet format in Appendix A.

VI. PROPOSED DRAINAGE CONDITIONS

General Discussion

The general drainage pattern from east to west is maintained in the proposed drainage basin. Developed Basin A surface runoff will be conveyed to the southwest corner of the site via concrete roadway gutters. Drainage will enter storm drain inlets near the SW corner of the site and be piped into the Murray Drain.

Drainage Fee Calculation

The option of a drainage fee payment in lieu of detention has been selected. The fee calculation method is found in the SWMM section 403.4:

$ FEE = B(CD – CH)A0.7

B=$17,058,

Runoff coefficients CD and CH are derived from Table 701 and 702 and figure 703

17,058 (0.52 – 0.35)(12.05) 0.7 = $16,560.29

Off-Site Flows and System Impact

Off-site flow will remain unchanged in the proposed drainage condition. The Raley drain ditch has been piped as a part of the previous Adobe View Subdivision development.

Operation and Maintenance

The piped portion of the proposed drainage system will be located in right-of-way areas to be dedicated to the City of Fruita.

VII. DESIGN CRITERIA General Considerations The 2 year and 100 year runoff rates were calculated for this project using the Rational Formula Method as described in the Mesa County Storm water Management Manual (SWMM) dated January 2008.

The spreadsheet presented in appendix A, lists all parameters for the runoff calculation and detention area sizing. All variables were selected from tools contained in the SWMM and are referenced in Appendix A. No previous drainage studies are known to have been performed for the site

VIII. CONCLUSIONS The runoff calculations for the Adobe View North Subdivision are according to the SWMM. No additional off-site flow will enter the site. The flow path for the developed condition is similar to the existing condition. Release of developed flow will discharge into the Murray Drain undetained. The drainage fee in lieu of detention is the preferred option for this development. C:\PROJECTS\A6216\A6216DRN1.doc

APPENDIX A

RATIONAL METHOD RUNOFF CALCULATIONS

PIPE, INLET AND STREET CAPACITY CALCULATIONS

RO

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NG

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IEW

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UB

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BY

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Tc C

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(Acre

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(L in

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Slo

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rla

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Flo

w (

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To

(Min

ute

s)

Co

nce

ntr

ate

d

Le

ng

th

(Fe

et)

Co

nce

ntr

ate

d

Ve

locity (

F/S

)T

s

(Min

ute

s)

Ch

an

ne

l

Le

ng

th

(Fe

et)

Ch

an

ne

l

Ve

locity (

F/S

)

Tch

an

(Min

ute

s)

(Min

ute

s)

(In

ch

es/H

ou

r)(C

FS

)

His

tori

c F

low

s

Ba

sin

A

2 Y

R1

1.8

8

0.3

21

1.7

6

0.9

30

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0.3

33

00

0.8

26

.01

28

01

.00

21

.34

7.3

0.4

51

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10

0 Y

R1

1.8

8

0.3

81

1.7

60

.95

0.1

20

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30

00

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4.0

12

80

1.0

02

1.3

45

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8.3

4

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ve

lop

ed

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ws

Ba

sin

A1

2 Y

R4

.47

0

.29

4.4

70

.29

18

31

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9.7

90

01

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2.5

32

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0.6

7

10

0 Y

R4

.47

0

.52

4.4

70

.52

18

31

.01

4.1

90

01

.21

2.5

26

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5.3

1

Ba

sin

A2

2 Y

R5

.25

0

.29

5.2

50

.29

18

31

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9.7

91

11

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2.7

32

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0.7

9

10

0 Y

R5

.25

0

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5.2

50

.52

18

31

.01

4.1

91

11

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2.7

26

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6.2

2

Ba

sin

A3

2 Y

R1

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0

.29

1.1

70

.29

11

51

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5.6

78

01

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0.8

26

.50

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0.2

0

10

0 Y

R1

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0

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1.1

70

.52

11

51

.01

1.2

78

01

.21

0.8

22

.02

.54

1.5

4

Ba

sin

A4

2 Y

R0

.76

0

.29

0.7

60

.29

65

1.0

11

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00

1.2

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15

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0.1

7

10

0 Y

R0

.76

0

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0.7

60

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65

1.0

8.4

30

01

.24

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2.6

3.3

41

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Ba

sin

A5

2 Y

R0

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0

.29

0.2

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10

02

.01

1.6

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0.0

6

10

0 Y

R0

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0

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0.2

40

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10

02

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0.4

9

Fo

rmu

las:

Q =

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C =

Ra

tio

na

l m

eth

od

ru

no

ff c

oe

ffic

ien

t, d

ime

nsio

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ss (

Ta

ble

70

1,7

02

,70

3)

i =

ra

infa

ll in

ten

sity in

in

ch

es/h

ou

r (f

orm

ula

se

ctio

n 6

04

)

Tc =

Ove

rla

nd

Flo

w (

To

) +

Sh

allo

w C

on

ce

ntr

ate

d F

low

(T

s)

+ C

ha

nn

el F

low

(T

ch

an

)

To

= 1

.8(1

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)L0

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0.3

3

L=

Le

ng

th o

f flo

w p

lan

e (

30

0' m

axim

um

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S =

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rag

e p

erc

en

t slo

pe

of

the

ove

rla

nd

pla

ne

Ts =

Ls/V

s

Ls =

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ng

th o

f flo

w in

co

nce

ntr

ate

d a

rea

Vs =

Ve

locity in

co

nce

ntr

ate

d a

rea

(fig

ure

"E

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se

d o

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OR

MW

AT

ER

MA

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RC

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00

6

^

APPENDIX B

SUPPORTING INFORMATION