HomeMy WebLinkAboutPD 2021-0033; 3357 ADAMS STREET; DRAINAGE STUDY; 2022-01-09
DRAINAGE STUDY
FOR
3357 Adams St
APN No.: 205-112-2100
Carlsbad, California
GR2021-0030
DWG 533-2A
Engineer:
Trelos Engineering, Inc.
8605 Santa Monica Blvd #73703
West Hollywood, California 90069
P: 760-809-4714
Prepared by: ____________________________________ Date: _________ Michael B Leeper RCE# 83930 Exp. 9-30-23
Original: 10/25/21
2nd Submittal: 12/6/21
3rd Submittal: 1/9/22
1/9/22
TABLE OF CONTENTS
1.0 PROJECT DESCRIPTION ................................................................................................... 1
2.0 PURPOSE ............................................................................................................................ 2
3.0 METHODOLOGY ................................................................................................................. 2
4.0 HYDROLOGY ...................................................................................................................... 2
4.1 Pre-Development Condition ..................................................................................... 2
4.2 Post-Development Conditions ................................................................................. 2
5.0 CONCLUSION ..................................................................................................................... 3
APPENDICES
Appendix A – Reference Charts
Table 3-1 Runoff Coefficients for Urban Areas
Figure 3-1 Intensity- Duration Design Chart
Soil Hydrologic Groups Map
100 Year Rainfall Event – 6 Hours (P6 Rainfall Isopluvials)
100 Year Rainfall Event – 24 Hours (P24 Rainfall Isopluvials)
Appendix B – Pre-Development Hydrology Calculations
Appendix C – Post-Development Hydrology Calculations
EXHIBITS
Exhibits A & B – Pre and Post Development Hydrology Map
1.0 PROJECT DESCRIPTION
The proposed project is a single family home on ~0.45 acres. The project proposes a total of
one single family home and an attached garage. In addition, the project has an existing pool
area. The project access will be provided on Adams. The existing, pre development, site
contains a single family home, driveway and pool area, but will be modeled as undisturbed
natural habitat.
2.0 PURPOSE
The purpose of this study is to determine the peak runoff rates and velocities for the pre-
development and post-development conditions. Comparisons will be made at the same
discharge points for each drainage basin affecting the site and adjacent properties. The
adequacy of existing and proposed conveyance facilities affected by the project will be
determined.
3.0 METHODOLOGY
The Rational Method as outlined in the San Diego County Hydrology Manual, dated June 2003,
was used to determine the runoff flow rate. The 100-year frequency storm event was analyzed
to determine peak runoff rates discharging the site for both the existing and post-development
condition. Precipitation rates of 2.5” (6 hour) and 4.5” (24 hour) were used.
Soil type was determined to be type B from the Soil Hydrologic Groups map (see Appendix A).
The runoff coefficient “C” was determined using Table 3-1 (see Appendix A) using existing and
proposed development type.
Runoff coefficients, “C” are summarized below:
Pre-Development
o Undisturbed Natural Terrain 0.25
Post-Development
o Low Density Residential 0.32
Intensity
I = 7.44 ( P6) (D ^(-.645))
P6 = 2.5”
D= 5 min
I = 8.958 in/Hr
4.0 HYDROLOGY
4.1 Pre-Development Conditions
Currently the site sheet drains from East to West down the existing slope. This sheet flow
leaves the property to the neighboring property to the west.
A pre-development hydrology map delineating basin areas, flow paths, and concentration points
has been prepared and is attached to this report as Exhibit “A”. Pre-development hydrology
calculations can be found in Appendix “B”.
4.2 Post-Development Conditions
The post-development condition will match the pre-development condition, with runoff directed
off of the property on the west side. Water from the SFH pad area will be directed around the
house and disbursed before leaving the property using rip rap to slow the flow and a rip rap
swale to disburse the concentrated flow. Minimal increase in impervious area will help to reduce
any increase in runoff. There is no negative impact to any adjacent properties.
A post-development hydrology map delineating basin areas, flow paths, and concentration
points has been prepared and is attached to this report as Exhibit “B”. Post-development
hydrology calculations can be found in Appendix “C”.
5.0 CONCLUSION
Development of the project site will result in a slight increase in the runoff from the pre-
developed condition due to the minimal increase in impermeable area. Existing flow patterns
will be maintained, with runoff directed towards the neighbor to the west.
The design is consistent with the requirements of the Storm Water Standards, which is based
on the requirements of SDRWQCB Order No. R9-2013-0001 as amended by R9-2015-0001
and R9-2015-0100 (MS4 Permit). The design being proposed and the applicable source control
and site design BMPs proposed to minimize the potentially negative impacts of this project's
land development activities on water quality.
This project development is not required to obtain approval from the Regional Water Quality
Board under the Federal Clean Water Act section 401 or 404 as the proposed site is not located
within, and does not drain directly to a wetland area. In addition, erosion control mitigation will
protect construction site such that no dredged or fill material will be allowed to run off project
site.
Table 1 – Pre-Development Areas and Flows
Area (ac) Q100
(cfs)
Basin /
Node Pre-Dev Pre-
Dev
Impervious
%
100 .45 0.59 0
TOTAL .45 0.59 0
Table 2 – Post-Development Areas and Flows
Area (ac) Q100
(cfs)
Basin /
Node Post-Dev Post-
Dev
Impervious
%
100 .32 .40 10
200 .13 .23 10
TOTAL .45 .63 10
REFERENCES
San Diego County Hydrology Manual, dated June 2003
APPENDIX A
Reference Charts
Hydrologic Soil Group—San Diego County Area, California
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/25/2021
Page 1 of 436691003669110366912036691303669140366915036691603669100366911036691203669130366914036691503669160468460468470468480468490468500468510468520468530468540468550
468460 468470 468480 468490 468500 468510 468520 468530 468540 468550
33° 9' 38'' N 117° 20' 17'' W33° 9' 38'' N117° 20' 13'' W33° 9' 36'' N
117° 20' 17'' W33° 9' 36'' N
117° 20' 13'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 11N WGS84
0 20 40 80 120
Feet
0 5 10 20 30
Meters
Map Scale: 1:462 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Lines
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Points
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: San Diego County Area, California
Survey Area Data: Version 16, Sep 13, 2021
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jan 24, 2020—Feb
12, 2020
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Hydrologic Soil Group—San Diego County Area, California
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/25/2021
Page 2 of 4
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
MlC Marina loamy coarse
sand, 2 to 9 percent
slopes
B 0.9 100.0%
Totals for Area of Interest 0.9 100.0%
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive
precipitation from long-duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three 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) when
thoroughly wet. These consist mainly of deep, well drained to excessively
drained sands or gravelly sands. These soils have a high rate of water
transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well
drained 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 consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of
water transmission.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell
potential, soils that have a high water table, soils that have a claypan or clay
layer at or near the surface, and soils that are shallow over nearly impervious
material. 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 is
for drained areas and the second is for undrained areas. Only the soils that in
their natural condition are in group D are assigned to dual classes.
Rating Options
Aggregation Method: Dominant Condition
Hydrologic Soil Group—San Diego County Area, California
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/25/2021
Page 3 of 4
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—San Diego County Area, California
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/25/2021
Page 4 of 4
APPENDIX B
Pre-Development Hydrology Calculations
San Diego County Rational Hydrology Program
CIVILCADD/CIVILDESIGN Engineering Software,(c)1991‐2019 Version 9.1
Rational method hydrology program based on
San Diego County Flood Control Division 2003 hydrology manual
Rational Hydrology Study Date: 12/07/21
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
100adams100pre
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
********* Hydrology Study Control Information **********
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
Program License Serial Number 6515
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
Rational hydrology study storm event year is 100.0
English (in‐lb) input data Units used
Map data precipitation entered:
6 hour, precipitation(inches) = 2.500
24 hour precipitation(inches) = 4.500
P6/P24 = 55.6%
San Diego hydrology manual 'C' values used
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 101.000 to Point/Station 102.000
**** INITIAL AREA EVALUATION ****
______________________________________________________________________
Decimal fraction soil group A = 0.000
Decimal fraction soil group B = 1.000
Decimal fraction soil group C = 0.000
Decimal fraction soil group D = 0.000
[UNDISTURBED NATURAL TERRAIN ]
(Permanent Open Space )
Impervious value, Ai = 0.000
Sub‐Area C Value = 0.250
Initial subarea total flow distance = 40.000(Ft.)
Highest elevation = 120.000(Ft.)
Lowest elevation = 116.000(Ft.)
Elevation difference = 4.000(Ft.) Slope = 10.000 %
INITIAL AREA TIME OF CONCENTRATION CALCULATIONS:
The maximum overland flow distance is 100.00 (Ft)
for the top area slope value of 10.00 %, in a development type of
Permanent Open Space
In Accordance With Figure 3‐3
Initial Area Time of Concentration = 7.10 minutes
TC = [1.8*(1.1‐C)*distance(Ft.)^.5)/(% slope^(1/3)]
TC = [1.8*(1.1‐0.2500)*( 100.000^.5)/( 10.000^(1/3)]= 7.10
Rainfall intensity (I) = 5.253(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for area (Q=KCIA) is C = 0.250
Subarea runoff = 0.131(CFS)
Total initial stream area = 0.100(Ac.)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 102.000 to Point/Station 100.000
**** SUBAREA FLOW ADDITION ****
______________________________________________________________________
Rainfall intensity (I) = 5.253(In/Hr) for a 100.0 year storm
Decimal fraction soil group A = 0.000
Decimal fraction soil group B = 1.000
Decimal fraction soil group C = 0.000
Decimal fraction soil group D = 0.000
[UNDISTURBED NATURAL TERRAIN ]
(Permanent Open Space )
Impervious value, Ai = 0.000
Sub‐Area C Value = 0.250
Time of concentration = 7.10 min.
Rainfall intensity = 5.253(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for total area
(Q=KCIA) is C = 0.250 CA = 0.112
Subarea runoff = 0.460(CFS) for 0.350(Ac.)
Total runoff = 0.591(CFS) Total area = 0.450(Ac.)
End of computations, total study area = 0.450 (Ac.)
APPENDIX C
Post-Development Hydrology Calculations
San Diego County Rational Hydrology Program
CIVILCADD/CIVILDESIGN Engineering Software,(c)1991‐2019 Version 9.1
Rational method hydrology program based on
San Diego County Flood Control Division 2003 hydrology manual
Rational Hydrology Study Date: 01/09/22
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
100adams100post
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
********* Hydrology Study Control Information **********
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
Program License Serial Number 6515
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
Rational hydrology study storm event year is 100.0
English (in‐lb) input data Units used
Map data precipitation entered:
6 hour, precipitation(inches) = 2.500
24 hour precipitation(inches) = 4.500
P6/P24 = 55.6%
San Diego hydrology manual 'C' values used
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 101.000 to Point/Station 102.000
**** INITIAL AREA EVALUATION ****
______________________________________________________________________
Decimal fraction soil group A = 0.000
Decimal fraction soil group B = 1.000
Decimal fraction soil group C = 0.000
Decimal fraction soil group D = 0.000
[LOW DENSITY RESIDENTIAL ]
(1.0 DU/A or Less )
Impervious value, Ai = 0.100
Sub‐Area C Value = 0.320
Initial subarea total flow distance = 30.000(Ft.)
Highest elevation = 116.500(Ft.)
Lowest elevation = 114.000(Ft.)
Elevation difference = 2.500(Ft.) Slope = 8.333 %
Top of Initial Area Slope adjusted by User to 10.000 %
INITIAL AREA TIME OF CONCENTRATION CALCULATIONS:
The maximum overland flow distance is 100.00 (Ft)
for the top area slope value of 10.00 %, in a development type of
1.0 DU/A or Less
In Accordance With Figure 3‐3
Initial Area Time of Concentration = 6.52 minutes
TC = [1.8*(1.1‐C)*distance(Ft.)^.5)/(% slope^(1/3)]
TC = [1.8*(1.1‐0.3200)*( 100.000^.5)/( 10.000^(1/3)]= 6.52
Rainfall intensity (I) = 5.552(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for area (Q=KCIA) is C = 0.320
Subarea runoff = 0.178(CFS)
Total initial stream area = 0.100(Ac.)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 102.000 to Point/Station 103.000
**** PIPEFLOW TRAVEL TIME (User specified size) ****
______________________________________________________________________
Upstream point/station elevation = 114.000(Ft.)
Downstream point/station elevation = 107.000(Ft.)
Pipe length = 180.00(Ft.) Slope = 0.0389 Manning's N = 0.013
No. of pipes = 1 Required pipe flow = 0.178(CFS)
Given pipe size = 4.00(In.)
Calculated individual pipe flow = 0.178(CFS)
Normal flow depth in pipe = 1.94(In.)
Flow top width inside pipe = 4.00(In.)
Critical Depth = 2.85(In.)
Pipe flow velocity = 4.24(Ft/s)
Travel time through pipe = 0.71 min.
Time of concentration (TC) = 7.22 min.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 103.000 to Point/Station 103.000
**** CONFLUENCE OF MINOR STREAMS ****
______________________________________________________________________
Along Main Stream number: 1 in normal stream number 1
Stream flow area = 0.100(Ac.)
Runoff from this stream = 0.178(CFS)
Time of concentration = 7.22 min.
Rainfall intensity = 5.195(In/Hr)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 104.000 to Point/Station 105.000
**** INITIAL AREA EVALUATION ****
______________________________________________________________________
Decimal fraction soil group A = 0.000
Decimal fraction soil group B = 1.000
Decimal fraction soil group C = 0.000
Decimal fraction soil group D = 0.000
[LOW DENSITY RESIDENTIAL ]
(1.0 DU/A or Less )
Impervious value, Ai = 0.100
Sub‐Area C Value = 0.320
Initial subarea total flow distance = 25.000(Ft.)
Highest elevation = 110.500(Ft.)
Lowest elevation = 110.000(Ft.)
Elevation difference = 0.500(Ft.) Slope = 2.000 %
Top of Initial Area Slope adjusted by User to 1.538 %
INITIAL AREA TIME OF CONCENTRATION CALCULATIONS:
The maximum overland flow distance is 85.00 (Ft)
for the top area slope value of 1.54 %, in a development type of
1.0 DU/A or Less
In Accordance With Figure 3‐3
Initial Area Time of Concentration = 11.21 minutes
TC = [1.8*(1.1‐C)*distance(Ft.)^.5)/(% slope^(1/3)]
TC = [1.8*(1.1‐0.3200)*( 85.000^.5)/( 1.538^(1/3)]= 11.21
Rainfall intensity (I) = 3.912(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for area (Q=KCIA) is C = 0.320
Subarea runoff = 0.275(CFS)
Total initial stream area = 0.220(Ac.)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 105.000 to Point/Station 103.000
**** PIPEFLOW TRAVEL TIME (User specified size) ****
______________________________________________________________________
Upstream point/station elevation = 110.000(Ft.)
Downstream point/station elevation = 107.000(Ft.)
Pipe length = 200.00(Ft.) Slope = 0.0150 Manning's N = 0.013
No. of pipes = 1 Required pipe flow = 0.275(CFS)
Given pipe size = 4.00(In.)
NOTE: Normal flow is pressure flow in user selected pipe size.
The approximate hydraulic grade line above the pipe invert is
1.419(Ft.) at the headworks or inlet of the pipe(s)
Pipe friction loss = 4.187(Ft.)
Minor friction loss = 0.232(Ft.) K‐factor = 1.50
Pipe flow velocity = 3.16(Ft/s)
Travel time through pipe = 1.06 min.
Time of concentration (TC) = 12.27 min.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 103.000 to Point/Station 103.000
**** CONFLUENCE OF MINOR STREAMS ****
______________________________________________________________________
Along Main Stream number: 1 in normal stream number 2
Stream flow area = 0.220(Ac.)
Runoff from this stream = 0.275(CFS)
Time of concentration = 12.27 min.
Rainfall intensity = 3.692(In/Hr)
Summary of stream data:
Stream Flow rate TC Rainfall Intensity
No. (CFS) (min) (In/Hr)
1 0.178 7.22 5.195
2 0.275 12.27 3.692
Qmax(1) =
1.000 * 1.000 * 0.178) +
1.000 * 0.589 * 0.275) + = 0.340
Qmax(2) =
0.711 * 1.000 * 0.178) +
1.000 * 1.000 * 0.275) + = 0.402
Total of 2 streams to confluence:
Flow rates before confluence point:
0.178 0.275
Maximum flow rates at confluence using above data:
0.340 0.402
Area of streams before confluence:
0.100 0.220
Results of confluence:
Total flow rate = 0.402(CFS)
Time of concentration = 12.270 min.
Effective stream area after confluence = 0.320(Ac.)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 103.000 to Point/Station 100.000
**** PIPEFLOW TRAVEL TIME (User specified size) ****
______________________________________________________________________
Upstream point/station elevation = 107.000(Ft.)
Downstream point/station elevation = 101.000(Ft.)
Pipe length = 55.00(Ft.) Slope = 0.1091 Manning's N = 0.013
No. of pipes = 1 Required pipe flow = 0.402(CFS)
Given pipe size = 4.00(In.)
Calculated individual pipe flow = 0.402(CFS)
Normal flow depth in pipe = 2.33(In.)
Flow top width inside pipe = 3.95(In.)
Critical depth could not be calculated.
Pipe flow velocity = 7.64(Ft/s)
Travel time through pipe = 0.12 min.
Time of concentration (TC) = 12.39 min.
End of computations, total study area = 0.320 (Ac.)
San Diego County Rational Hydrology Program
CIVILCADD/CIVILDESIGN Engineering Software,(c)1991‐2019 Version 9.1
Rational method hydrology program based on
San Diego County Flood Control Division 2003 hydrology manual
Rational Hydrology Study Date: 12/07/21
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
200adams100post
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
********* Hydrology Study Control Information **********
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
Program License Serial Number 6515
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
Rational hydrology study storm event year is 100.0
English (in‐lb) input data Units used
Map data precipitation entered:
6 hour, precipitation(inches) = 2.500
24 hour precipitation(inches) = 4.500
P6/P24 = 55.6%
San Diego hydrology manual 'C' values used
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 201.000 to Point/Station 200.000
**** INITIAL AREA EVALUATION ****
______________________________________________________________________
Decimal fraction soil group A = 0.000
Decimal fraction soil group B = 1.000
Decimal fraction soil group C = 0.000
Decimal fraction soil group D = 0.000
[LOW DENSITY RESIDENTIAL ]
(1.0 DU/A or Less )
Impervious value, Ai = 0.100
Sub‐Area C Value = 0.320
Initial subarea total flow distance = 110.000(Ft.)
Highest elevation = 109.000(Ft.)
Lowest elevation = 97.850(Ft.)
Elevation difference = 11.150(Ft.) Slope = 10.136 %
INITIAL AREA TIME OF CONCENTRATION CALCULATIONS:
The maximum overland flow distance is 100.00 (Ft)
for the top area slope value of 10.14 %, in a development type of
1.0 DU/A or Less
In Accordance With Figure 3‐3
Initial Area Time of Concentration = 6.49 minutes
TC = [1.8*(1.1‐C)*distance(Ft.)^.5)/(% slope^(1/3)]
TC = [1.8*(1.1‐0.3200)*( 100.000^.5)/( 10.136^(1/3)]= 6.49
Rainfall intensity (I) = 5.568(In/Hr) for a 100.0 year storm
Effective runoff coefficient used for area (Q=KCIA) is C = 0.320
Subarea runoff = 0.232(CFS)
Total initial stream area = 0.130(Ac.)
End of computations, total study area = 0.130 (Ac.)
EXHIBITS A & B
Pre and Post Development Maps
3357 ADAM STREETAPN 205-112-21>>>>>0.10EL.120.0EL.116.0>>>>>>>>>>>>>>>>>>>>>>>>>>EL.97.850.358605 Santa Monica Blvd, Suite 73703West Hollywood, CA 90069P: 760-809-4714DATE: Dec 07, 21 10:34pm by:MLFILE:D:\Dropbox (MLE)\Trelos\Projects\2021\3357 Adams St\Hydrology\CAD\3357 Adams Pre.dwgHYDROLOGY MAPPRE-DEVELOPMENTEXHIBIT 'A'HYDROLOGY MAP3357 ADAMS STREET3357 ADAMS STREETLEGEND100-YEAR FREQUENCY DISCHARGE (CFS)FLOW PATH>MAJOR BASIN BOUNDARYNODEBASIN AREA (ACRES)10-YEAR FREQUENCY DISCHARGE (CFS)2-YEAR FREQUENCY DISCHARGE (CFS)POINT OF CONCENTRATION - NODESUB-BASIN BOUNDARY 0.00TRELOS ENGINEERING, INC.SCALE:
PLPLPLPLPLPLPLPLPLPLPLWWWWWSSSSSSSSSSGGGGGG*********
****3357 ADAM STREETAPN 205-112-210.10EL.116.5EL.101.00.13>>>0.22>>>>>>>>>>>>>>>>>>>>>>>EL.107.0EL.109.0EL.97.85>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>EL.114.0>>>>>>>>>>>>>>>>>>>>>>>>>>>>>EL.110.5EL.110.08605 Santa Monica Blvd, Suite 73703West Hollywood, CA 90069P: 760-809-4714DATE: Jan 09, 22 1:34pm by:MLFILE:D:\Dropbox (MLE)\Trelos\Projects\2021\3357 Adams St\Hydrology\CAD\3357 Adams Post.dwgHYDROLOGY MAPPOST-DEVELOPMENTEXHIBIT 'B'HYDROLOGY MAP3357 ADAMS STREET3357 ADAMS STREETLEGEND100-YEAR FREQUENCY DISCHARGE (CFS)FLOW PATH>MAJOR BASIN BOUNDARYNODEBASIN AREA (ACRES)10-YEAR FREQUENCY DISCHARGE (CFS)2-YEAR FREQUENCY DISCHARGE (CFS)POINT OF CONCENTRATION - NODESUB-BASIN BOUNDARY 0.00TRELOS ENGINEERING, INC.SCALE: