HomeMy WebLinkAboutCamacho ResidenceONSITE HYDROLOGY REPORT
FOR
CAMACHO RESIDENCE
Fontana, CA
Prepared for:
J & L Engineering and Land Development
112 East Third Street
Rialto, CA 92376
(909) 421-8909
December 17, 2008
Prepared by:
R bert M. Beers*
370 W. Sixth Street, S
San Bernardino, CA
(951) 317-2041
PE
uite 210
92401
12/18/08
Onsite Hydrology Report
INTRODUCTION
The following report and calculations were prepared to analyze the 10 & 100 -year storm runoff
from the development of three single-family residential lots in the City of Fontana. The three
residential lots are located on approximately 0.35 acre, located on the south side of I-210 Foothill
Freeway.
SITE BACKGROUND
The proposed single-family residential development is located on the south side of Highland
Avenue westerly of Oleander Avenue, and southerly of the I-210 Foothill Freeway. The site was
rough graded several years ago. In the existing condition, the site drains to southwesterly away
from Highland Avenue.
The soil type for the area is Type A per "Hydrologic Soils Group Map for Southwest A Area"
SBCFCD Figure C-13.
METHODOLOGY
Subareas were determined based on the proposed grading of the site. A link -node model was
created for each subarea, with flow path length and elevations shown for the upstream and
downstream nodes for the subarea. Peak 10 & 100 -year flow rates were determined for each
subarea using the CivilDesign Corporation "SB" rational method hydrology software. The
results of those calculations are shown on the site hydrology map included with this report.
Separate maps for the existing and developed condition are included with this report.
ANALYSES/DISCUSSION
Rational method hydrology calculations have been prepared for the development of the future
homes. The site is proposed to be rough graded to create building pads for three future single-
family residential buildings located at 15749, 15755, & 15765 Highland Avenue.
In the existing condition, onsite surface flows go to the rear of the lots to the southwest, and are
collected in a drainage swale along the southerly property line and conveyed towards Knox
Avenue. In the developed condition, a retaining wall will be built along the southerly property
line, and the site will be filled to re -direct the onsite drainage to flow northerly to the front of the
lots onto Highland Avenue, and those flows thence go westerly to Knox Avenue.
The existing and developed condition 10 & 100 -year discharges are summarized below:
Existing
Condition
Existing
Condition
Developed
Condition
Developed
Condition
Area (Ac.)
Q (cfs)
Area (Ac)
Q (cfs)
10- ear 0.346
0.74
0.346
0.93
100 -year 0.346
1.28
0.346
1.47
CONCLUSION
Based on the calculations and proposed grading, onsite flows can be conveyed to suitable points
of disposal (Highland Avenue), and the proposed development will not adversely impact offsite
property.
Existing Condition Calculations
San Bernardino County Rational Hydrology Program
(Hydrology Manual Date - August 1986)
CIVILCADD/CIVILDESIGN Engineering Software, (c) 1989-2005 Version 7.1
Rational Hydrology Study Date: 12/18/08
------------------------------------------------------------------------
Existing Condition - 100 year flow rates
Camacho Residence - 15749, 15755, 15765 Highland Avenue
Fontana, CA
Program License Serial Number 4005
------------------------------------------------------------------------
********* Hydrology Study Control Information **********
------------------------------------------------------------------------
Rational hydrology study storm event year is 100.0
Computed rainfall intensity:
Storm year = 100.00 1 hour rainfall = 1.520 (In.)
Slope used for rainfall intensity curve b = 0.6000
Soil antecedent moisture condition (AMC) = 3
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 10.000 to Point/Station 20.000
**** INITIAL AREA EVALUATION ****
UNDEVELOPED (poor cover) subarea
Decimal fraction soil group A = 1.000
Decimal fraction soil group B = 0.000
Decimal fraction soil group C = 0.000
Decimal fraction soil group D = 0.000
SCS curve number for soil(AMC 2) = 67.00
Adjusted SCS curve number for AMC 3 = 84.60
Pervious ratio(Ap) = 1.0000 Max loss rate(Fm)= 0.290(In/Hr)
Initial subarea data:
Initial area flow distance = 218.000(Ft.)
Top (of initial area) elevation = 1493.800(Ft.)
Bottom (of initial area) elevation = 1490.100(Ft.)
Difference in elevation = 3.700(Ft.)
Slope = 0.01697 s(%)= 1.70
TC = k(0.525)*[(length"3)/(elevation change)]"0.2
Initial area time of concentration = 10.223 min.
Rainfall intensity = 4.395(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for area (Q=KCIA) is C = 0.841
Subarea runoff = 1.278(CFS)
Total initial stream area = 0.346(Ac.)
Pervious area fraction = 1.000
Initial area Fm value = 0.290(In/Hr)
End of computations, Total Study Area = 0.35 (Ac.)
The following figures may
be used for a unit hydrograph study of the same area.
Note: These figures do not consider reduced effective area
effects caused by confluences in the rational equation.
Area averaged pervious area fraction(Ap) = 1.000
Area averaged SCS curve number = 67.0
San Bernardino County Rational Hydrology Program
(Hydrology Manual Date - August 1986)
CIVILCADD/CIVILDESIGN Engineering Software, (c) 1989-2005 Version 7.1
Rational Hydrology Study Date: 12/18/08
------------------------------------------------------------------------
Existing Condition - 10 year flow rates
Camacho Residence - 15749, 15755, & 15765 Highland Avenue
Fontana, CA
Program License Serial Number 4005
------------------------------------------------------------------------
********* Hydrology Study Control Information **********
------------------------------------------------------------------------
Rational hydrology study storm event year is 10.0
Computed rainfall intensity:
Storm year = 10.00 1 hour rainfall = 1.020 (In.)
Slope used for rainfall intensity curve b = 0.6000
Soil antecedent moisture condition (AMC) = 2
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 10.000 to Point/Station 11.000
**** INITIAL AREA EVALUATION ****
UNDEVELOPED (poor cover) subarea
Decimal fraction soil group A = 1.000
Decimal fraction soil group B = 0.000
Decimal fraction soil group C = 0.000
Decimal fraction soil group D = 0.000
SCS curve number for soil(AMC 2) = 67.00
Pervious ratio(Ap) = 1.0000 Max loss rate(Fm)= 0.578(In/Hr)
Initial subarea data:
Initial area flow distance = 218.000(Ft.)
Top (of initial area) elevation = 1493.800(Ft.)
Bottom (of initial area) elevation = 1490.100(Ft.)
Difference in elevation = 3.700(Ft.)
Slope = 0.01697 s(%)= 1.70
TC = k(0.525)*((length"3)/(elevation change))'0.2
Initial area time of concentration = 10.223 min.
Rainfall intensity = 2.949(In/Hr) for a 10.0 year storm
Effective runoff coefficient used for area (Q=KCIA) is C = 0.724
Subarea runoff = 0.738(CFS)
Total initial stream area = 0.346(Ac.)
Pervious area fraction = 1.000
Initial area Fm value = 0.578(In/Hr)
End of computations, Total Study Area = 0.35 (Ac.)
The following figures may
be used for a unit hydrograph study of the same area.
Note: These figures do not consider reduced effective area
effects caused by confluences in the rational equation.
Area averaged pervious area fraction(Ap) = 1.000
Area averaged SCS curve number = 67.0
Hydrology Legend
,o Node Number – –
1493.8 Elevation
– — — – Flowpath
L = 218' Flowpath length
Q.= 100 -year flow rate
Q1.= 10 -year flow rate
Tc 1N = 10 -year time of concentration
Tc10o= 100 -year time of concentratiorflIGHT OF
Soil Type A
Cover = undeveloped poor
10 -year 1 -hour intensity = 1.02 it
100 -year 1 -hour intensity = 1.52
Slope of Intensity Curve = 0.60
Onsite Area = 0.346 Acre (15,09
IN THE COUNTY OF SAN BERNARDINO, STATE OF CALIFORNIA
Existing Condition Hydrology Map
2""'
,A93:
i
HIGHLAND AVENUE
_ N 89°49'00' E _
N 89°49'-- E — — —
1 1p93 8
N 89°49'00' E 55.52' —
I
1 4GHT OF WAY
PROPERTY LINE
1�
I \\ I
\\ PROPERTY LINE
PROPERTY LIN \
AD
Nj
12a"fs 1q9"''
CIA
'0 22R`t���u�es \\
�Ga 10p2 m �\
' Jc,ra
N 89°49'00' E 6000' — N 89 x9.00" E
__— N !19°4900' 55.58'
•EW
PROPE60.00'
RTY LINE PROPERTY LINE `!•PROPERTY LINE
15745
15747
GRAPHIC SCALE
10' 0' 10' 20' 30'
I inch - io n
( IN tzar )
—1492
i
mepdvatee�ngglrroer sgnln Mese plan Is responsible mr assunng Me aauracy
devepubmty o<the des�gn hereon in the event of Mscreparicles arlsl�g after
County approval or tlu4ig c0nsbuctbn, Me IF-- IRaarshell ba responsible
I., detarmlMn9 an accaptabb sdunon and r.Wsbg the Plans for app—I by
NO WORK SHALL BE DONE ON THIS
BITE UNTIL BELOW AGENCY IS NOTIFIED
OF INTENTION TO GRADE OR EXCAVATE.
Underg round Service Alert
REVISIONS
PREPARED UNDER THE UPE O
I�KRoberI
M. Beers
M. Beers
370 W. Sixth Street, Suite 210
San Bemartlln0, CA 92401
IN THE CITY OF FONTANA
Existing Hydrology Map
SHEET NO.
NO. DATE BY DESCRIPTION APPROVED
the County
Call: TOLL FREE
'I–$QQ
422-4133
RE ISTERED CIVIL ENGINEER O. 39405
DATE Dec. 10, 2008 R ISTRATION EXPIRES: 12/ 1/09
(951) 317-2041
for �+
CAMACHO RESIDENCE
15749, 15755, 15765 HIGHLAND AVENUE
OF 2 SHEET
CONTRACTOR AGREES THAT HE I SHE ASSUME SOLE ANDAPPROVED
r CWIS or cONSTRUCTON
� THIS ECT IN DING SnFET' OF ATLPERSONS AND vROPERTYTNT THIS
MR°�iral�,LLAPPL.eGNTN000S-1 AND NOTKL,NITE.TGN�RWL
o rxEHmm RAl.
AN'HE Er H RxARGL[ss Faa.En'n nNouMUAelun
BY:
Z1
SCALE:
=10,
BENCH MARK
FILE NO.
121505
DATE:
DESIGNED BY: DRAWN BY. RM Beers CHECKEDeY:RMBears
DWG ONFO: GRADING LOG #: 000000000
REAL oR A ECEG IN CONNEcrlcn WITH THE PERrcRNANCE or w ON THIS
n R OR eiNGwEeR LwelLlry awslNc rRoe. THE so�NEcucENCEor
THE R
TyyO WORKING DAYS BEFORE YOU DIG
DATE.
Dec. 10, 2008
Dec.10,2008
Developed Condition Calculations
San Bernardino County Rational Hydrology Program
(Hydrology Manual Date - August 1986)
CIVILCADD/CIVILDESIGN Engineering Software, (c) 1989-2005 Version 7.1
Rational Hydrology Study Date: 12/18/08
------------------------------------------------------------------------
Developed Condition - 100 -year flow rates
Camacho Residence - 15749, 15755, & 15765 Highland Avenue
Fontana, CA
Program License Serial Number 4005
------------------------------------------------------------------------
********* Hydrology Study Control Information **********
------------------------------------------------------------------------
Rational hydrology study storm event year is 100.0
Computed rainfall intensity:
Storm year = 100.00 1 hour rainfall = 1.520 (In.)
Slope used for rainfall intensity curve b = 0.6000
Soil antecedent moisture condition (AMC) = 3
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 10.000 to Point/Station 11.000
**** INITIAL AREA EVALUATION ****
RESIDENTIAL(8 - 10 dwl/acre)
Decimal fraction soil group A = 1.000
Decimal fraction soil group B = 0.000
Decimal fraction soil group C = 0.000
Decimal fraction soil group D = 0.000
SCS curve number for soil(AMC 2) = 32.00
Adjusted SCS curve number for AMC 3 = 52.00
Pervious ratio(Ap) = 0.4000 Max loss rate(Fm)= 0.314(In/Hr)
Initial subarea data:
Initial area flow distance = 261.000(Ft.)
Top (of initial area) elevation = 1495.050(Ft.)
Bottom (of initial area) elevation = 1491.390(Ft.)
Difference in elevation = 3.660(Ft.)
Slope = 0.01402 s(%)= 1.40
TC = k(0.374)*L(length"3)/(elevation change)]'0.2
Initial area time of concentration = 8.131 min.
Rainfall intensity = 5.042(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for area (Q=KCIA) is C = 0.844
Subarea runoff = 1.472(CFS)
Total initial stream area = 0.346(Ac.)
Pervious area fraction = 0.400
Initial area Fm value = 0.314(In/Hr)
End of computations, Total Study Area = 0.35 (Ac.)
The following figures may
be used for a unit hydrograph study of the same area.
Note: These figures do not consider reduced effective area
effects caused by confluences in the rational equation.
Area averaged pervious area fraction(Ap) = 0.400
Area averaged SCS curve number = 32.0
San Bernardino County Rational Hydrology Program
(Hydrology Manual Date - August 1986)
CIVILCADD/CIVILDESIGN Engineering Software, (c) 1989-2005 Version 7.1
Rational Hydrology Study Date: 12/18/08
------------------------------------------------------------------------
Developed Condition - 10 -year flow rates
Camacho Residence - 15749, 15755, & 15765 Highland Avenue
Fontana, CA
Program License Serial Number 4005
------------------------------------------------------------------------
********* Hydrology Study Control Information **********
------------------------------------------------------------------------
Rational hydrology study storm event year is 10.0
Computed rainfall intensity:
Storm year = 10.00 1 hour rainfall = 1.020 (In.)
Slope used for rainfall intensity curve b = 0.6000
Soil antecedent moisture condition (AMC) = 2
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 10.000 to Point/Station 11.000
**** INITIAL AREA EVALUATION ****
RESIDENTIAL(8 - 10 dwl/acre)
Decimal fraction soil group A = 1.000
Decimal fraction soil group B = 0.000
Decimal fraction soil group C = 0.000
Decimal fraction soil group D = 0.000
SCS curve number for soil(AMC 2) = 32.00
Pervious ratio(Ap) = 0.4000 Max loss rate(Fm)= 0.391(In/Hr)
Initial subarea data:
Initial area flow distance = 261.000(Ft.)
Top (of initial area) elevation = 1495.050(Ft.)
Bottom (of initial area) elevation = 1491.390(Ft.)
Difference in elevation = 3.660(Ft.)
Slope = 0.01402 s(%)= 1.40
TC = k(0.374)*[(length'3)/(elevation change)]"0.2
Initial area time of concentration = 8.131 min.
Rainfall intensity = 3.384(In/Hr) for a 10.0 year storm
Effective runoff coefficient used for area (Q=KCIA) is C = 0.796
Subarea runoff = 0.932(CFS)
Total initial stream area = 0.346(Ac.)
Pervious area fraction = 0.400
Initial area Fm value = 0.391(In/Hr)
End of computations, Total Study Area = 0.35 (Ac.)
The following figures may
be used for a unit hydrograph study of the same area.
Note: These figures do not consider reduced effective area
effects caused by confluences in the rational equation.
Area averaged pervious area fraction(Ap) = 0.400
Area averaged SCS curve number = 32.0
Hydrology Legend
10 Node Number
95.1,' Elevation
Flowpath
L = 261' Flowpath Length
Q = 100 -year flow rate
Q = 10 -year flow rate
Tc = 100 year time of concentration
Tc = 10 year time of concentration
Soil Type A
Cover =
10 -year intensity = 1.02 in/hr
100 -year intensity - 1.52 in/hr
Slope of Intensity Curve = 0.60
Onsite Area = 0.346 acre (15,091 sf)
Note: add 1400' to elevations shown
IN THE COUNTY OF SAN BERNARDINO, STATE OF CALIFORNIA
Developed Condition Onsite Hydrology Map
GRAPHIC SCALE
10' 0' 10' 20' 30'
1 1mE - 10 R
( Di Fun
NO WORK SHALL BE DONE ON THIS REVISIONS PREPARED UNDE TH SU I OF: SHEET NO.
The ptivetee Irwa:rsignin mase pane Hresponatbb for assuring the&—mr SITE UNTIL BELOW AGENCY IS NOTIFIED p�°F RObeft M. Fieers IN THE CITY OF FONTANA
rq aaaevtad`iydthe tlesg h«eon. In the evam of at «ePandesarislzf. OF INTENTION TO GRADE OR EXCAVATE. NO. DATE BY DESCRIPTION APPROVED (f,
County approval or dw*g Com,h lipn, me private engineer shall ire respon.4Ne 4,p S M �, 370 W. Sixth Street Suite 210
f« tleter,NNng an eccepmhle sdumn and reNsing tna plane far approval M OB RT M. BEERS F,a San Bernardino, CA 92401
Underground Service Alert 3 2� Developed Condition
the Count' DATE: Dec 18, 2008 REGISTTRATIONiEXPIREI E�R3N .39405 rc Onsite Hydrology Map
Call: TOLL FREE ph 39405 OF SHEET
aESoRACREESTw.T „e ISNE Assu„E sotE Aro caa�EtE APPROVED BY: °f'°°E J+'+aL SCALE: BENCHMARK:
EaH�epmro„aaanEeo~al.a„aaealaaTHE �aEn -NET--N : . CAMACHO RESIDENCE FILE NO.
« E A„D RRaRERTY: TItATTH a -1 _4300
RE-RE%iiwisiw :wrmrwwsurtu�io rur of u„nEoro „o„ru,� CMV 1"=10'
woAa„a MnT„.Tr„Ea«.ra�Eraae„wteErE„a„aE„„,III „F �� 15749, 15755, 15765 HIGHLAND AVENUE 2+�D5
tato THE OWNER MD THE ENcI„EER lwun—E RR -ANY ANDa LL,_
422-4133 Q''Cµ.\ DATE:
THE—AELLxeEv�iric coa weiTmAwsine rRora r„E so�riEcucENCE s TWO WORKING DAYS BEFORE Y00 DIG DESIGNED BY: PETER RAMEY DRAWN BY: PETER RAMEY CHECKED BY: DATE: Dec. 18, 2008 Dea 78, 2008 DWG ONFO: GRADING LOG #:000000000
TME OWNER OR ENOMEE0.
Reference Materials
SAN BERNARDINO COUNTY
HYDROLOGY MANUAL
-12 ye
111
U.rfii
•"ire"' -} f - y�� �` ® � Ig��
'� _ _� S"'• 1 Ali
• a. c.o�,o ed�tou• _I,F Vic_==__
. v��� wwvora.o..nn. _z,v-_ •It �..e�nu
SCALE REDUCED BY 1/2 HYDROLOGIC SOILS GROUP MAI
G -L16 r Mu"t L-1
8-11 F IGURE 0 -'.
W
R
R W 04W .
}`rY {ti'SyT - -
�. `R2W .. RIW
RIE R2E
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.1017,
FY
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y
BEF
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19 .....
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PL1N0 .�
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_ ••
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ONT IOa-•'
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lis
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'- 1
1
REDL MD
r
RIE
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I RSIDE
••
.- — /
— _ _— .—
._ �-_ _ _ R4W—_j
_ R3
R2W
_ RI_
-___-
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/
SAN BERNARDINO C
FICT
s
R5W:
\
REDUCED DRAWING
SCALE I'- 4 MILES
VALLEY AREA
001/TETALS
Y.- 10 YEAR I HOUR
' SAN BERNARDINO COUNTY
.s
.w.n..o
R 8 W
R 7 W •••
................
6
R HYDROLOGY MANUAL
Dart suu ri,t .a Oa4.e w
............ ....•'
IROL'—o R[CI r r TATIO of INC" F%1
rrrrrY r.ir .,o. a .. rx
8-11 F IGURE 0 -'.
g -Ip FIGURE 8-4
Curve (1) Numbers of Hydrologic Soil -Cover Complexes For Pervious Areas -AMC D
Quality of
Soil Group
Cover Type (3)
Cover (2)
NATURAL COVERS -
Barren
78
86
91
93
(Rockland, eroded and graded land)
Chaparral, Broadleaf
Poor
33
70
80
83
(Manzonita, ceanothus and scrub oak)
Fair
40
63
73
81
Good
31
37
71
78
Chaparral, Narrowleaf
Poor
71
82
88
91
(Chamise and redshank)
Fair
33
72
81
86
Grass, Annual or Perennial
Poor
67_
71_
Fair
SO
69
79
84
Good
38
61
74
80
Meadows or Cienegas
Poor
63
77
83
88
(Areas with seasonally high water table,
Fair
31
70
80
84
principal vegetation is sod forming grass)
Good
30
38
71
78
Open Brush
Poor
62
76
84
88
(Soft wood shrubs - buckwheat, sage, etc.)
Fair
46
66
77
83
Good
41
63
73
81
Woodland
Poor
43
66
77
83
(Coniferous or broadleaf trees predominate.
Fair
36
60
73
79
Canopy density is at least 30 percent.)
Good
23
33
70
77
Woodland, Grass
Poor
37
73
82
86
(Coniferous or broadleaf trees with canopy
Fair
44
63
77
82
density from 20 to 30 percent)
Good
33
38
72
79
URBAN COVERS_:
Residential or Commercial Landscaping
Good
32
36
69
73
(Lawn, shrubs, etc.)
Turf
Poor
39
74
83
87
(Irrigated and mowed grass)
Fair
44
63
77
82
Good
33
38
72
79
AGRICULTURAL COVERS -
Fallow
77
86
91
94
(Land plowed but not tilled or seeded)
SAN BERNARDINO COUNTY CURVE NUMBERS
FOR
HYDROLOGY MANUAL PERVIOUS AREAS
C-6 Figure C-3 0 of 2)
_J L
Curve (I) numbers of Hydrologic Soil -Cover Complexes For Pervious Areas -AMC 11
Quality of
Soil Group
Cover Type (3)
Cover (2)
AGRICULTURAL COVERS (Continued)
Legumes, Close Seeded
(Alfalfa, sweetclover, timothy, etc.)
Poor
Good
66
3E
77
72
93
81
E9
E3
Orchards, Evergreen
(Citrus, avocados, etc.)
Poor
Fair
37
44
73
63
S2
77
U
E2
Good
33
38
72
79
Pasture, Dryland
Poor
69
79
86
E9
(Annual grasses)
Fair
49
69
79
E4
Good
39
61
74
90
Pasture, Irrigated
(Legumes and perennial grass)
Poor
Fair
SE
44
74
63
S3
77
E7
E2
Good
33
38
72
79
Row Crops
(Field crops - tomatoes, sugar beets, etc.)
Poor
Good
72
67
31
7E
98
E3
91
E9
Small grain
(Wheat, oats, barley, etc.)
Poor
Good
63
63
76
73
94
93
99
E7
Notes:
I. All curve numbers are for Antecedent Moisture Condition (AMC) II.
2. Quality of cover definitions:
Poor -Heavily grazed, regularly burned areas, or areas of high burn potential. Less than
50 percent of the ground surface is protected by plant cover or brush and tree canopy.
Fair -Moderate cover with 30 percent to 75 percent of the ground surface protected.
Good -Heavy or dense cover with more than 75 percent of the ground surface protected.
3. See Figure C-2 for definition of cover types.
SAN BERNARDINO COUNTY
HYDROLOGY MANUAL
C-7
CURVE NUMBERS
FOR
PERVIOUS AREAS
Figure C-3 (2 of 2)
ACTUAL IMPERVIOUS COVER
Land Use (1)
Natural or Agriculture
Public Park
School
Single Family Residential: (3)
2.5 acre lots
1 acre lots
2 dwellings/acre
3-4 dwellings/acre
5-7 dwellings/acre
8-10 dwellings/acre
More than 10 dwellings/acre
Multiple Family Residential:
Condominiums
Apartments
Mobile Home Park
Commercial, Downtown Business
or Industrial
Notes:
Range -Percent
0 - 0
10 - 25
30 - 50
Recommended Value
For Average
Conditions -Percent (2)
0
15
40
5 -
15
10
10 -
25
20
20 -
40
30
30 -
50
40
35 -
55
50
,0 .
70
- 60-=--- -.._
65 -
90
80
45 -
70
65
65 -
90
80
60 -
85
75
80 - 100
90
1. Land use should be based on ultimate development of the watershed. Long
range master plans for the County and incorporated cities should be reviewed
to insure reasonable land use assumptions.
2. Recommended values are based on average conditions which may not apply to
a particular study area. The percentage impervious may vary greatly even on
comparable sized lots due to differences in dwelling size, improvements, etc.
Landscape practices should also be considered as it is common in some areas
to use ornamental gravels underlain by impervious plastic materials in place of
lawns and shrubs. A field investigation of a study area shall always be made,
and a review of aerial photos, where available, may assist in estimating the
percentage of impervious cover in developed areas.
3. For typical equestrian subdivisions increase impervious area 5 percent over the
values recommended in the table above.
SAN BERNARDINO COUNTY ACTUAL IMPERVIOUS COVER
FOR
HYDROLOGY MANUAL DEVELOPED AREAS
C-8 Figure C-4