HomeMy WebLinkAboutLAURIE SUBDIVISION PUD, 2ND FILING - FINAL - 44-89E - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT•
REVISED DRAINAGE & EROSION REPORT
Submitted for
Final Approval
of
LAURIE SUBDIVISION SECOND FILING
6.4 ACRES LOCATED IN THE
NE 1/4, S3, T 6 N, R 69 W
CITY OF FORT COLLINS, COUNTY OF LARIMER
STATE OF COLORADO
Prepared for
Dr. William Musslewhite
5001 S. Shields Street
Fort Collins, CO 80526
November 14, 1991
Jack Johnson Company
1910 Prospector Avenue
Suite 200
Park City, Utah 84060
(801) 645-9000
TABLE OF CONTENTS
I. DRAINAGE
A.
Scope and References . . . . . . . . . . . . . . 1
B.
Zoning . . . . . . . . . . . . . . . . . . . . . 1
C.
Historic Site Conditions . . . . . . . . . . . . 1
D.
Proposed Site Conditions . . . . . . . . . . . . 2
E.
Existing Topography . . . . . . . . . . . . . . . 2
F.
Contributing Runoff from Upstream Areas . . . . 2
G.
Continuity to Existing Drainages . . . . . . . . 3
H.
Hydrology Study . . . . . . . . . . . . . . . . 4
I.
Street Encroachment . . . . . . . . . . . . . . 5
J.
Street Flow . . . . . . . . . . . . . . . . . . 6
K.
Rip Rap Length . . . . . . . . . . . . . . . . . 8
II. EROSION
A. Wind and Rain Erosion Control . . . . . . . 9
B. Erosion Hazard . . . . . . . . . . . . . . . . 9
C. Erosion Control During Construction . . . . . .10
D. Revegetation Methodology . . . . . . . . . . . .lo
i
0
LIST OF TABLES AND FIGURES
TABLES
1. Hydrology Study - Existing Conditions
2. Hydrology Study - Post -Developed Conditions
3. Culvert Calculation Worksheet
4. Entrance Loss Coefficients
5. Rainfall Performance Standard Evaluation
6. Effectiveness Calculations
7. Effectiveness Calculations
8. Effectiveness Calculations
FIGURES
1. Vicinity Map
2. Rainfall Intensity Curves
3. Flow in Triangular Gutter
4. Reduction Factor for Allowable Gutter Capacity
5. Headwater Depth for Concrete Pipe culverts with Inlet Control
6. Critical Depth Circular Pipe
7. Head for Concrete Pipe Culverts Flowing Full
S. Erosion Protection at Circular Conduit Outlet
9. Expansion Factor for Circular Conduits
10. Conduit Outlet Erosion Protection
11. Flow Path Diagram
12. Pavement and Disturbed Areas
ii
I. DRAINAGE
A. Scope and References
This report references the Preliminary Drainage Report already
completed by Foundation Engineering, Loveland Co., and
submitted to the City of Fort Collins. A copy of the
aforementioned report is attached. Amendments to this report
are in response to Planning Department letters of July 17, and
October 16, and the comments on the Revised Drainage & Erosion
Report submitted by the Jack Johnson Company on August 5, 1991
which comments on the necessary revisions to be made for final
approval. A revegetation methodology is also outlined. This
preliminary drainage report and revegetation methodology along
with the Erosion Control and Grading Plan and General
Landscape Plan identify the erosion control methods to be
used in establishing and maintaining a natural open space
within the project site.
B. Zonincr
The property is currently zoned RE, Estate Residential
District. The proposed 8 lot subdivision lots have a minimum
size of 17,325 square feet.
C. Historic Site Conditions
The site is rectangular and contains approximately 6.47 acres.
The Pleasant Valley and Lake Canal passes through the adjacent
property to the north with a lateral of that ditch that
flowing through the site. The lateral belonging to the
Applewood Estates Irrigation Company. Also associated with
the Canal is a ravine that has been created by the overflow
discharge of the Canal. The overflow crosses the property near
the center, flowing from North to South. East of the lateral
the property slopes to the East and has either been native
grasses and sagebrush or more recently irrigated pasture. The
property to the West of the lateral has not been irrigated and
remains native grasses and sagebrush.
1
D. Proposed Site Conditions
The site when fully developed will have 8 homes, the extension
of Wooded Creek Court, and a private drive to lots 5,6,7, and
8. The Applewood Estates irrigation ditch will be piped
through the project and under Wooded Creek Court. As shown
on the grading plan the slope of the 18 inch pipe is 1.5%, and
with outlet control the pipe has a flow capacity of
approximately 4.5 cfs thus providing adequate capacity. A
block has been included on the master utility plan for
Approval by the Applewood Estates Irrigation Company.
The ravine created by the overflow from The Pleasant Valley
and Lake Canal will be culverted under the private drive with
the existing channel left undisturbed above the culvert and
riprap will be added below the culvert. A second culvert will
be added under the private drive to allow for historic off -
site storm water to continue on to the ravine.
E. Existing Topography
See the Landscape, Erosion Control,Master Utility Plan, or
Figure 1. for the Existing Topography.
F. Contributing Runoff From Upstream Areas
As can be seen from Figure 1., runoff from upstream areas is
not very extensive. The ridge line and slopes to the North
and West of the site direct flows to either Shields Street or
Fossil Creek.
Runoff from the areas above The pleasant Valley and Lake Canal
that would historically flow to the site are now diverted by
that structure. By far the most significant flow from off -
site areas is the flow possibly occurring from the overflow
2
•
structure at the head of the ravine on The Pleasant Valley
and Lake Canal. Attached to this report is a letter from that
company certifying that the structure will allow 30 c.f.s.
(cubic feet per minute) maximum to flow into the ravine.
G. Continuity to Existing Drainages
All off -site storm waters and/or irrigation water will be
routed under the proposed street and private drive such that
all flows will continue along the same existing drainage as
prior to development.
3
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H. Hydrology Study
1. Storm Frequency and Intensities
For R-E Zoned property (Estate Residential) the City of
Fort Collins Storm Drainage criteria call for an initial
storm frequency of 2 years and a major storm frequency of
100 years.
2. Composite Runoff Coefficients
The specified Rational Runoff Coefficients from the City
of Fort Collins Storm Drainage Criteria by zoning
classification are as follows:
Unimprovedareas ...........................0.20
Unimproved Areas - Slope > 7.0% . . . . . . 0.25
Residential: Estate Residential ............0.45
Composite analysis Runoff Coefficients for the 8
residential lots in post developed conditions are
calculated as follows:
Area
impervious Lawns Lawns
Unimproved
Composite
C = 0.95 C = 0.15 C = 0.20
C = 0.20
licit
(Roofs,Drives) (Aver 2 to 7%) (Steep > 7%)
value
(sq. ft.) (sq.ft.) (sq.ft.)
(sq.ft.)
1
9300 2000 500
13000
0.48
2
3850 0 0
17000
0.34
3
9300 2000 500
27400
0.37
4
27900 3000 4500
56000
0.43
5
3470 0 0
43000
0.25
6
27900 3000 4500
34700
0.50
Offsite Areas:
Off site
Area
A
B
C
4
Unimproved Composite
C = 0.20 licit
0.20 0.20
0.25 0.25
0.25 0.25
•
•
Area
Slope
Composite
of Basin
"Cos
%
Value
1
0.87
0.48
2
10.8
0.34
3
19.3
0.37
4
10.5
0.43
5
15.4
0.25
6
14.7
0.50
Area
Slope
Composite
of Basin
locos
A
9.0
0.20
B
14.0
0.25
C
15.0
0.25
TIME OF CONCENTRATION
ON -SITE
AREAS
Length
Frequency
Time of
Time of
of Basin
Adjustment
Concentration
Concentration
feet
Factor
TC , 2 Year
TC , 100 Year
230
1.0/1.25
16.8 min.
16.0 min.
250
1.0/1.25
10.2 min.
8.2 min.
140
1.0/1.25
5.5 min
5.3 min.
370
1.0/1.25
11.0 min.
8.4 min.
140
1.0/1.25
7.8 min.
6.5 min.
170
1.0/1.25
5.4 min.
4.7 min.
OFF -SITE AREAS
Length
Frequency
Time of
Time of
of Basin
Adjustment
Concentration
Concentration
400
1.0/1.25
16.2 min
15.3 min.
275
1.0/1.25
10.0 min.
9.2 min.
450
1.0/1.25
10.9 min.
10.2 min.
See pages 7 and 8 for Hydrology Calculations.
5
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TABLE 2. Hydrology Study - Post -Developed Conditions
I. Street Encroachment
In accordance with Table 4-1 of the City of Fort Collins
"Storm Drainage Design Criteria & Construction Standards", the
initial storm runoff shall not top the curb for the 'Local'
streets in the Laurie Subdivision.
Theoretical Gutter Capacity:
Q= 0. 56 Z S 1 /2 y8/3
n
S = Channel Slope = 0.01 ft/ft
Q = Theoretical Gutter capacity, cfs
y = Depth of flow @ face of gutter, 4-3/4" = 0.396 ft
n = Roughness coefficient, 0.016
Z = Reciprocal of Cross slope, 1/.02 = 50 ft/ft
Q = 0.56 50 0.011/2 0.3968/3 = 14.8 cfs
0.016
Using a reduction factor from Figure 4-2 for 1% slope = 0.8
Q = 14.8 * 0.8 = 11.84 cfs Flow for one gutter
J. Street Flow
Assume a 7"/hour maximum rain fall rate = 0.00194"/second
= 0.000162 ft/sec
Street Area = length = 150 ft
width = 36'
cul-de-sac = 35 ft radius
= 150 x 36 + pi*radius2 = 5400 +(3.1417 * 352)
= 9248 sq. ft.
Rainfall/sec = (0.000162 * 9248) = 1.50 cfs from street
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Offsite area 'A' = 9.27 cfsl
Onsite
area '1'
= 1.97
cfs
Street
flow
= 1.50
cfs
Total
flow
=12.74
cfs
Total flow in both gutters = 12.74 cfs Encroachment is OK.2
1See Figure 11
2The private drive has no gutters and the flow uphill from the
road is in the ditch. See the hydrology report for offsite and
onsite flow rates.
7
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� r.a. o, • o• . o•
002
001
Figure 4-t
NONOGRAPH FOR FLOW IN TRIANGULAR GUTTERS
(From U.S. Dept. of Commerce, Bureau of Public Roads, 1965)
FIGURE 3. Flow in Triangular Gutters
U
F— 0 3
Q
~ 02
LJ h
W LFF
0
Fox
MAY 1984
DESIGN CRITERIA
7
A
Cr
o .6
LA-
Q
z 5
0
U
w .4
Cr
3
7
0
0
C-s:06
F=08
.I
z -0.4%
F=0.5
I
I
BELOW
4LLOW48LE
STREET
I
MINIMUM
GRAOE
2 4 6 8 10 12 14
SLOPE OF GUTTER (%)
Figure 4-2
REDUCTION FACTOR FOR ALLOWABLE GUTTER CAPACITY
Apply reduction factor for applicable slope to the theoretical gutter capacity to obtain
allowable gutter capacity.
(From: U.S. Dept. of Commerce, Bureau of Public Roads, 1965)
FIGURE 4. Reduction Factor for Allowable Gutter Capacity
MAY 1984 DESIGN CR!TE
i
OPEN CHANNEL FLOW
MANNINGS EQUATION Q= 1.49 x R 2/3 x S ,/zx A
n
Q = Flow Rate, cfs
R = Hydraulic radius, A/P
S = Slope, feet/feet
A = Cross sectional flow area, feet
z
n = Roughness coefficient
TYPICAL CHANNEL CROSS SECTION
where:
Note: Side slopes are shown and calculated 0 2:1
2 H , side slopes. From contours and site data the cross—
section as shown approximates the open channel.
31
A=3H+2Hz
R = AREA/WETTED SURFACE = 3H + 2H2 /(3 + 4.47H)
Note: Roughness coefficients are from the City of Fort Collins Storm Drainage Criteria
and Construction Standards.
OPEN CHANNEL FLOW RATES
FLOWRATE DEPTH SLOPE ROUGHNESS AREA VELOCITY LOCATION
Q H S n A V
51.07 cfs 1.55' 5.0% 0.060 9.547 sq.ft. 5.35 fps TOTAL LEAVING RAVINE
42.11 cfs 1.41' 5.0% 0.060 8.206 sq/ft. 5.13 fps A80VE 48" CULVERT
As shown above the velocity in the open channel is not supercritical. The use of
2:1 sideslopes is used due to the side slopes of the existing channel having slopes of
2:1 or greater.
0
OPENFLOW.DWG
•
RIPRAP CHANNEL FLOW
1.49 x R
z/3 1/z
MANNINGS EQUATION Q= n x S x A
Q =Flow Rate, cfs
R = Hydraulic radius, A/P
S = Slope, feet/feet
A = Cross sectional flow area, feet
Z
n = Roughness coefficient
TYPICAL CHANNEL CROSS SECTION
where:
Note: Side slopes are shown and calculated 0 2:1
H side slopes. From contours and site data the cross—
section as shown approximates the open channel.
3'--t
A=3H+2HZ
R = AREA/WETTED SURFACE = 3H + 2H2/(3 + 4.47H)
Note: Roughness coefficients are from the City of Fort Collins Storm Drainage Criteria
and Construction Standards.
RIPRAP LINED OPEN CHANNEL FLOW RATES
FLOWRATE DEPTH SLOPE ROUGHNESS AREA VELOCITY
Q H S n A V
42.11 cfs 1.15, 5.0% 0.0395 6.095 sq.ft. 6.91 fps
SUBCRITICAL FLOW
INV = 5046
H w = 34'
SEE FIG. 5
ROAD C.L.
C.L. = 5062.15
4' DIA. RCP CULVERT
S = 5.00% L
LOCATION
OUTLET OF 48' CULVERT
AFTER STILLING POND
HYDRAULIC JUMP
SUPERCRITICAL FLOW SUSCRITICAL FLOW
VEL = 18.8 cfs VEL = 6.91 fps
INV = 5041
CULVERT FLOW RATE (FLOWING PARTIALLY FULL)
FLOWRATE DEPTH SLOPE ROUGHNESS AREA VELOCITY
Q H S n A V
42.11 cfs 0.94' 5.0% 0.012 2.24 sq.ft. 18.8 fps
1.15'
d so = 9' _j
8'
ROCK DIA. O STILLING POND
= 12' MIN.
LOCATION
INSIDE 48' CULVER
AT CULVERT OUTLET
0
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TABLE 3. Culvert Calculation Worksheet
0 - •
leo
168
156
144
132
120
108
96
84
72
U1
W
S
U
Z_
Z 60
C 54
Cr
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U 42
U.
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W
33
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30
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CHART 10
8,000 EXAMPLE (Z) (3)
6.
6,000 0.42 lace*$ (3.5 1a11 6.
5,000 0.120 cts 5
4,000 i MM
6.
5.
0 too
3,000 (1) 2.s 0.8
5'
4.
4.
(2) 2.1 7.4
2,000 (3) 2.2 7.7
•
4•
3.
40 is tsar
3'
3.
1,000
900
600
2
2
500
400
300 E*� /
I.S
1.5
N
/ Q
1.5
v
200
_
/ W
/ Q
0
o
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100 Z
Q
so z
1.0
a
x
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60 W
1.0
50 mw SCALE ENTRANCE Q
1.0
p TYPE
mts t
.9
9
r � �•
30 Severe ad"
I'
20 (2) ?'.. ae"* *No al"' W
(3) Greow
pajacti��-
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e
7
rw Jr �'w ? �
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6 To sss scale (2) of (3) project
5 1Nrizestally to 64614 (1)' MN1
4 •ss atreltat 1aclfeN Ila* terawll
0 ss� 0 ocelot, or reverse ss
3 illustrated.
2
1.0
.6
.6
s
s
.s
L 12 HEADWATER DEPTH FOR
HEADWATER SCALES 2153 CONCRETE PIPE CULVERTS
REVISED MAY 1964 WITH INLET CONTROL
9VRGAU 0r RJOLIC ROA07 JAM 1943
i81
FIGURE 5. Headwater Depth for Concrete Pipe Culverts with Inlet Control
OCHART 4
6
I—
W
W
tL 4
V
Q
U
I
12
H
6
4
DISCHARGE-0-CFS
de
CANNOT EXCEED TOP OF PIPE
H
7
H
W
6 W
u
v
2
S ~
a
W
O
J
Q
600 700 H00 900 1000 u
DISCHARGE -0 -CFS
U
�■■■■�■■■■■■■�
�vvv�vm
M1MEN 0
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MEN MEMO�H���
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DES goo���� �EXCEEDC CANNOT ..
F IPE
■■0,9■■■■■■■ ■
�rinMOENM������
DISCHARGE- 0-CFS
BUREAU OF PUBLIC ROODS
JAN.1964 CRITICAL DEPTH
CIRCULAR PIPE
184
FIGURE 6. Critical Depth Circular Pipe
0 1 0
TABLE 12 - ENTRANCE LOSS COEFFICIENTS
Outlet Control, Full or Partly Full Entrance head loss
H4 - k. V2
2Q
Type of Structure and Design of ntrancc
Projecting from fill, socket end (groove -end)
Projecting from fill, sq. cut end . •
Headwall or headwall and wingwalls
Socket end of pipe (groove -end)
Square -edge . . • '
Rounded (radius - 1 / 12D)
Mitered to conform to fill slope r��
$eVe1Ca eageS, ».J vi
Side -or slope -tapered inlet
Pine or Pice Arch Corruinud Metal
0.2
0.5
0.2
0.5
0.2
0.7
0.2
02
0.9
Projecting from fill (no hcadwall) • • . ' 0.5
Headwall or headwall and wingwalls square -edge . . 0.7
Mitered to conform to fill slope, paved or unpaved slope 0.5
'End -Section conforming to fill slope • • • ' . . 0.2
Beveled edges, 33.70 or 45" bevels . . • • ' ' . ' ' 0.2
Side -or slope -tapered inlet . ' • ' ' _
1*43m;1FU
Headwall parallel to embankment (no wingwalls) 0.5
Square -edged on 3 edges
Rounded on 3 edges to radius of 1/12 barrel 0.2
dimension, or beveled edges on 3 sides
Wingwalls at 300 to 75° to barrel 0.4
Square -edged at crown . . . . • • • • . .
Crown edge rounded to radius of 1 / 12 barrel 0.2
dimension, or beveled top edge
Wingwall at 100 to 250 to barrel 0.5
Square -edged at crown . . • • • • •
Wingwalls parallel (extension of sides) 0.7
Square -edged at crown 0.2
Side -or slope -tapered inlet
'Note: 'End Section conforming to fill slope,' made of either metal or concrete,
are the sections commonly available from manufacturers. From limited hydrau-
lic tests they arc equivalent in. operation to a hgeadwall in baper �in�the r
act swig control.
Superior r end sections,
e lie performance.incot1nTh se atter sections can be
TABLE 4. Entrance Loss Coefficients
•
•
r- 2000
1000
e00
120
600
108
S00
96
400
84
300
1200
72
66
60
W
C)
2
100
W
ZO
2
80%
_
a
H
60
C7
W
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33
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Q
C
2T
30
24
21
20
18
0
CHART 5
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Women 0 OVTIET CULVCRT tLOWIMG r .S 11
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too 8
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0 rz —10
a
HEAD FOR
CONCRETE PIPE CULVERTS
FLOWING FULL ✓
BLOEA, Or "LC *04M J" /943 n = 0.012
FIGURE 7. Head for Concrete Pipe Culverts Flowing Full
0
R. Rip Rap Length
The rip rap length has been calculated using the Urban Storm
Drainage Criteria Manual. Flow through the 48" culvert is
super critical.
D = Pipe Diameter = 4'
Yt = Tail water depth = 1.5'
Q = Flow rate = 42 CFS (See hydrology report)
V = Flow velocity = 5.5 fps (for erosive soils)
Yn = Normal depth of super critical flow in the culvert =
0.93'
Da = (Diameter for super critical flows)= 1/2(D + Yn)
Da = 1/2(4+0.93) = 2.465
Yt/Da = 1.5/2.465 = 0.608
Q/Da1.5 = 42/2.4651.5 = 10.85
From Figure 5-7 type L Riprap is required.
From Table 5-1 Type L Riprap d50 - 9 inches
d50 = g"
Length = (1/ (2 tan X) ) (At/Yt - W)
L = length of protection in feet.
W = Diameter of culvert = 4 feet
Yt/Da = 0.608
Q/D2.5 = 42/42.5 = 1.31
From.Figure 5-9 1/(2 tan) = 6.7
At = Q/V = 42/5.5 = 7.636
Length = (6.7)(7.636/1.5 -4)
r
7.31 feet
NOTE: A minimum riprap length = 3d = 12 feet.
Use 4d = 16 feet of riprap.
10
r 0 •
DRAINAGE CRITERIA MANUAL RIPRAP
Od
K0
Q
'C
M
PEZ.,00000,
11-00
TYPE L
? 4
A 1r
Yt/D
Use Da instead of D whenever flow is supercritical in the barrel.
**Use Type L for a distance of 31) downstream
FIGURE 8. Riprap Erosion Protection at Circular Conduit Outlet
11-15-82
URBAN DRAINAGES FLOOD CONTROL DISTRICT
i
DRAINAGE CRITERIA MANUAL
Xr-
7
0
G = Expansion Angle
h
N
�O
h
Q"
O
1'
a
O
6�
�
.l _2 .3 .4 .5 .6 .7 .8
TAILWATER DEPTH/ CONDUIT HEIGHT, Yt/D
RIPRAP
FIGURE 9. EXPANSION FACTOR FOR CIRCULAR CONDUITS
1 1-15 -82
URBAN DRAINAGE 9 FLOOD CONTROL. DISTRICT
v 0 1
DRAINAGE CRITERIA MANUAL
C7
RIPRAP
't =
FIGURE 10. Conduit Outlet Erosion Protection
Z
O
U
w
O
x
IZ
Z
O
U)
O
lY
W
w
J
O
0
z
O
U
w.
Ld
x
M
U
LL-
11-15-82
URBAN DRAINAGE 3 FLOOD CONTROL DISTRICT
•
•
II. EROSION
A. Wind and Rain Erosion Control
A Performance Standard has been calculated on the following
in Table #5 through Table #8. The erosion control plan and
the grading plan show the methods to control wind and rain
erosion using hay bales and riprap. The landscape plan shows
revegetation to control wind erosion and rain erosion
utilizing a hydraulic mulch with a tacifier on all disturbed
areas.
The site has been divided into 6 subbasins (as in the
hydrology report). A single family housing development is
proposed with an estimate 3 year build -out. The site is
currently rangeland grass with approx. 50% ground cover and
irrigated pasture land.
No overlot grading will take place. Only the areas labeled
as "disturbed areas" in this report (see fig. 12) will be
disturbed. This area encompasses the extension of Wooded
Creek Court, the private drive and cul-de-sac, and the
immediate area surrounding these roads.
Additional erosion protection contributed by the hay bales has
not been used in the calculations, but all 6 subbasins have
performance factors greater than the required 84.45%
11
RAINFALL PERFORMANCE STANDARD EVALUATION
PROJECT:
LAURIE SUBDIVISION
COMPLETED
BY MATTHEW PRICE
---------------------------
DEVELOPED
ERODIBIUTY
Asb
SUBBASIN
---------------------------
ZONE
(cc)
1
MODERATE
0.57
2
MODERATE
0.40
3
MODERATE
0.70
4
MODERATE
2.11
5
MODERATE
1.07
6
MODERATE
1.62
6.47
LB = (230 x 0.57 +
+ 140 x 1.07
SB=(0.87x0.57 +
+ 15.4 x 1.07
PS = USING TABLE 8-
STANDARD FORM 8
DATE: 10-30-91
------
Lsb
--------------
Ssb
Lb
--------------
Sb
PS
(ft)
(7.)
(feet)
(7)
(7.)
230'
0.87%
(See Fig. 10 for L )
250'
10.8%
sb
140'
19.3%
370'
10.5%
140'
15.4%
170'
14.7%
237.25 1 12.43 1 84.45
250 x 0.40 + 140 x 0.70 + 370 x 2.11
+ 170 x 1.621)/6.47 = 237.25'
10.8 x 0.4 0 + 19.3 x 0.70 + 10.5 x 2.11
+ 14.7 x 1.62)/6.47 = 12.43
A (By interpolation) = 84.45
TABLE 5. Rainfall Performance Standard Evaluation
EFFECTIVENESS CALCULATIONS
PROJECT
COMPLETED BY: MATTHEW PRICE
STANDARD FORM B
DATE: 10-30-91
EROSION CONTROL
C—FACTOR
P—FACTOR
METHOD
-------------------------------------------------------------
VALUE
VALUE COMMENT:
ROADS/WALKS
0.01
1.00
WOOD FIBER MULCH
0.06
1.00 To be applied to all
bare
W/ TACKIFIER
ground ® 2 tons/ acre.
ESTABLISHED GRASS
0.08
1.00
r ----
MAJOR
--------------------------------------
PS I SUB AREA
BASIN (%) BASIN (Ac)
CALCULATIONS
---- ---- --------------------------------------------------------
A 84.45 1 0.57
PAVEMENT AREA
= 4500 sq. ft. = 0.103 Ac. (see fig.
12)
BARE GROUND =
DISTURBED GROUND — PAVEMENT
=
6420
sq. ft. — 4500 sq. ft. = 1920 sq.
ft.
=
0.044
Ac. (see fig.
12)
AREA IN PREDEVELOPED
GRASS (Undisturbed)
=
0.57 cc.— 6420/43560 (Disturbed area)
=
0.423
Ac.
WEIGHTED C—FACTOR
_
(0.01
x 0.103 + 0.06 x 0.044
+ 0.08 x 0.423)/0.57
=
0.066
WEIGHTED P—FACTOR
=
(1 —
1 x 0.066) x 100
=
93.4%
EROSION CONTROL
C—FACTOR
P—FACTOR
METHOD
-------------------------------------------------------------
VALUE
VALUE COMMENT:
ROADS/WALKS
0.01
1.00
WOOD FIBER MULCH
0.06
1.00 To be applied to all
bare
W/ TACKIFIER
ground ® 2 tons/ acre.
ESTABLISHED GRASS
0.08
1.00
---- ---- ---- ----
MAJOR PS SUB AREA
--------------------------------------------
CALCULATIONS
BASIN (7) BASIN (Ac)
---- ---- ---- ----
A 84.45 2 0.40
--------------------------------------------
PAVEMENT AREA
= 3850 sq. ft. = 0.088 Ac. (see fig.
12)
BARE GROUND =
DISTURBED GROUND — PAVEMENT
=
8700
sq. ft. — 3850 sq. ft. = 4850 sq.
ft.
=
0.111
Ac. (see fig.
12)
AREA IN PREDEVELOPED
GRASS (Undisturbed)
=
0.40 Ac. — 8700/43560 (Disturbed area)
=
0.200
Ac.
WEIGHTED C—FACTOR
=
(0.01
x 0.088 + 0.06 x 0.111
+ 0.08 x 0.200)/0.40
=
0.059
WEIGHTED P—FACTOR
_
(1 —
1 x 0.059) x 100
=
94.1%
TABLE 6
POST—EFF.DWG
TABLE 6. Effectiveness Calculations
z.F'FECTIVENESS CALCULATIONS
PROJECT
COMPLETED BY: MATTHEW PRICE
STANDARD FORM B
DATE: 10-30-91
EROSION CONTROL C—FACTOR P—FACTOR
METHOD VALUE VALUE COMMENT:
--------------------------------------------------------------
ROADS/WALKS 0.01 1.00
WOOD FIBER MULCH 0.06 1.00 To be applied to all bare
W/ TACKIFIER ground ® 2 tons/acre
ESTABLISHED GRASS 0.08 1.00
MAJOR
BASIN
A
PS
8 4.45
SUB T AREA
BASIN (Ac)
3 0.70
CALCULATIONS
----------------------------
PAVEMENT AREA = 2670 sq. ft. = 0.061 Ac. (see fig. 12)
BARE GROUND = DISTURBED GROUND — PAVEMENT
= 7090 sq. ft. — 2670 sq. ft. = 4420 sq. ft.
= 0.101 Ac. (see fig. 12)
AREA IN PREDEVELOPED GRASS (Undisturbed)
= 0.70 Ac. — 7090/43560 (Disturbed area)
= 0.537 Ac. (see fig. 12)
WEIGHTED C—FACTOR
= (0.01 x 0.061 + 0.06 x 0.101
+ 0.08 x 0.537)/0.70
= 0.071
WEIGHTED P—FACTOR
= (1 — 1 x 0.071) x 100
= 92.9%
EROSION CONTROL EROSION CONTROL EROSION CONTROL
METHOD METHOD METHOD COMMENT:
-------------------------------------------------------------
ROADS/WALKS 0.01 1.00
WOOD FIBER MULCH 0.06 1.00 To be applied to all bare
W/ TACKIFIER ground ® 2 tons/acre
ESTABLISHED GRASS 0.08 1.00
----------------------
MAJOR PS SUB AREA
BASIN (fie) BASIN (Ac)
A 84.45 4 2.11
POST—EF2.DWG
CALCULATIONS
--------------------------------------------
PAVEMENT AREA = 4680 sq. ft. = 0.107 Ac. (see fig. 12)
BARE GROUND = DISTURBED GROUND — PAVEMENT
= 6900 sq. ft. — 4680 sq. ft. = 2220 sq. ft.
= 0.051 Ac. (see fig. 12)
AREA IN PREDEVELOPED GRASS (Undisturbed)
= 2.11 Ac. — 6900/43560 (Disturbed area)
= 1.95 Ac. (see fig. 12)
WEIGHTED C—FACTOR
= (0.01 x 0.107 + 0.06 x 0.051
+ 0.08 x 1.95)/2.11
= 0.076
WEIGHTED P—FACTOR
(1 — 1 x 0.076) x 100
92.4%
TABLE 7
TABLE 7. Effectiveness Calculations
ECTIVENESS CALCULATION
PROJECT STANDARD FORM B
COMPLETED BY: MATTHEW PRICE DATE: 10-30-91
EROSION CONTROL
C—FACTOR
P—FACTOR
METHOD
-------------------------------------------------------------
VALUE
VALUE COMMENT:
ROADS/WALKS
0.01
1.00
WOOD FIBER MULCH
0.06
1.00
W/ TACKIFIER
ESTABLISHED GRASS
0.08
1.00
MAJOR PS
BASIN I (`:)
A T 84.45
SUB
BASIN
5
AREA
(Ac)
1.07
CALCULATIONS
--------------------------------------------
PAVEMENT AREA = 3470 sq. ft. = 0.080 Ac. (see fig. 12)
BARE GROUND = DISTURBED GROUND — PAVEMENT
= 9710 sq. ft. — 3470 sq. ft. = 6240 sq. ft.
.= 0.143 Ac. (see fig. 12)
AREA IN PREDEVELOPED GRASS (Undisturbed)
= 1.07 Ac. — 9710/43560 (Disturbed area)
= 0.847 Ac. (see fig. 12)
WEIGHTED C—FACTOR
= (0.01 x 0.080 + 0.06 x 0.143
+ 0.08 x 0.847)/1.07
= 0.072
WEIGHTED P—FACTOR
(1 — 1 x 0.072) x 100
92.8%.
EROSION CONTROL
C—FACTOR
P—FACTOR
METHOD
-------------------------------------------------------------
VALUE
VALUE COMMENT:
ROADS/WALKS
0.01
1.00
WOOD FIBER MULCH
6.06
1.00
W/ TACKIFIER
ESTABLISHED GRASS
0.08
1.00
MAJOR PS SUB
BASIN (%) BASIN
A 84.45 6
POST—EF3.DWG
----------------------------------------------------
AREA CALCULATIONS
(Ac)
-- — -----------------------------
1.62 PAVEMENT AREA = 9300 sq. ft. = 0.213 Ac. (see fig. 12)
BARE GROUND = DISTURBED GROUND — PAVEMENT
= 14350 sq. ft. — 9300 sq. ft. = 5050 sq. ft.
= 0.116 Ac. (see fig. 12)
AREA IN PREDEVELOPED GRASS (Undisturbed)
= 1.62 Ac. — 14350/43560 (Disturbed area)
= 1.29 Ac. (see fig. 12)
WEIGHTED C—FACTOR
= (0.01 x 0.213 + 0.06 x 0.116
+ 0.08 x 1.29)/1.62
= 0.069
WEIGHTED P—FACTOR
(1 — 1 x 0.069) x 100
93.1 %
TABLE 8
TABLE 8. Effectiveness Calculations
u
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B. Erosion Hazard
The greatest erosion potential is within the existing ravine
through the center of the project. The area which has the
most active erosion will be stabilized by the placement of
fill for the road across the ravine at this location. Prior
to construction, erosion will be minimized along the ravine
by pre -placement of straw bales near the ravine and the
smaller drainage to the east. (See Erosion Control and
Grading Plan) After construction is complete, additional
erosion along the ravine will be controlled by riprap, rock
and revegetation. (See Revegetation Methodology below)
Other new possible erosion areas will be exposed by the cuts
and fills of the private road which will be controlled by
strategic placement of bales until revegetation and permanent
erosion control takes place.
C. Erosion Control During Construction
As shown on the Erosion Control and Grading Plan straw bales
will be placed to minimize erosion during construction. The
48" culvert placed in the ravine should be constructed during
a low flow period to reduce erosion. Riprap will also be
placed as shown on the Erosion Control and Grading Plan to
reduce erosion at both the inlet and outlet of both the
Culvert #1 and the Culvert #2. All construction will conform
to The City of Fort Collins Erosion Control Reference Manual.
D. Revegetation Methodoloc7y
1. General
The area of the site that will be disturbed by the
construction of the private drive and by other utility
construction, i.e., culverts, will be revegetated. (See
the General Landscape Plan for the extent of this area.)
This revegetation will mitigate the visual impact of the
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disturbed areas and will provide erosion control. The
revegetated plantings will have a natural appearance by
being placed in tree and shrub groupings scattered randomly
throughout the disturbed area. Grasses will be utilized
to cover the ground plane. This revegetation process will
use native plant material to fit with the existing plant
material on the site.
In addition to erosion control though plantings of native
plant material, soil tackifiers will be used in the grass
seeding process to halt wind and water erosion. Also,
erosion control blankets will be used as necessary on steep
slopes to ensure establishment of grass seeding.
2. Process
a) Earthwork
In the initial cutting of the road grade, all topsoil
will be stripped and stockpiled to be used in the final
grading as an over layer for planting. Placement of
topsoil will be laid at a minimum depth of 4 inches.
b) Soil Stabilization Method
Soil Tackifier
Soil tackifier should be placed on disturbed areas with
the hydroseed grass mixture as recommended by the
tackifier manufacturer.
Erosion Control Blankets
Erosion control blankets should be used where required
and installed as recommended by the manufacturer.
c) Bank Stabilization
The stream bank is to be stabilized at points of inlet
and outlet of culverts and other existing areas
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requiring stabilization. This stabilization is to be
accomplished by placing boulders of varying sizes in
unstable areas and by placing riprap at the inlet and
outlet points of culverts. Extent and amount of riprap
and boulder placement to be determined at the time of
final design.
d) Revegetation
1) Plant Relocation
Existing plant material identified as being in areas
to be disturbed are to be tagged. Of the trees and
shrubs tagged, those which are of a size and
condition suited for transplanting are to be
transplanted to a location identified on site by the
project landscape architect in coordination with City
Forester. Trees too large to transplant will be
placed on site in the open space as deadfall for
wildlife habitat.
2) Proposed Trees and Shrubs
Existing plant material will be enhanced by proposed
tree and shrub plantings. The proposed plant
material to be used is identified on the general
landscape plan. The proposed plant material will be
native to the site and located in such a manner to
create a natural appearance.
3) Grasses
All areas disturbed by construction shall be seeded
by a grass mixture as recommended by the City of Fort
Collins. The seed mixture shall be as specified on
the General Landscape Plan. The method of seed
planting shall be the Hydroseed Method.
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3. Maintenance
The maintenance of the areas of revegetation will be
performed by the contractor during construction and until
accepted as complete by the owner and City officials. The
contractor is to guarantee all planting for the period of
one year after substantial completion. The contractor
whenever notified by the owner of City official shall
immediately place in satisfactory condition in every
instance any of such guaranteed work. After substantial
completion and acceptance, maintenance of the revegetated
area shall be by the homeowner's association.
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