HomeMy WebLinkAboutCDP 14-16; SMITH SWITZER IMPROVEMENTS; HYDROLOGY STUDY; 2014-11-13CVf 14 - ly
HYDROLOGY STUDY
41.22 Sunnyhill•Drive
Second Dweffi, g Unit
Prepared for
Lynn Smith & Heidi Switzer
4120 Sunnyhill Drive.
Carlsbad, CA 92008
Prepared By,.
John P. Strohminger Engineering
3588 Gorge Place
Carlsbad, CA 92010
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Date: November 13., 2014
No. C55187 ') "
6/30/1,15
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John P. StrThniinger 55187 Date
TABLE OF CONTENTS
Project Description .3
ExistingCondition ........................................................................ ....................................... 3
ProposedCondition ....................... . ................... . .................................................. . .............. 3
SoilCharacteristics ............................................................ . ......... ........................................ 3
RationalMethod Description...........................................................................................................4
HydrologyAnalysis ......................................................................................................................... 5
WaterQuality ................................................................... .............................................. . ..... . ............ 6
Selection of Source Control BMPs......................................................................................6
Hydromodification and IMP Design............................... .................................................................6
References.......................................................................................................................................7
Attachments:
Vicinity Map
Existing Condition Hydrology Calculations & Exhibit
Proposed Condition Hydrology Calculations & Exhibit
Stormwater Standards Questionnaire (City Document E-34)
1.0 Project Description
The Sunnyhill Drive project site is located on a 0.49 acre parcel in the City of Carlsbad fronting
Sunnyhill Drive. Sunnyhill Drive is a public street that connects with Tamarack Avenue to the
north and MacArthur Avenue to the south. Proposed improvements consist of a second dwelling
unit, a retaining wall, and a brow ditch. The proposed improvements will disturb 0.07 acres. The
site is located on APN 207-082-02, The legal description is Lot 79 of Map 2825. Attachment I
shows the Vicinity Map.
1.01 Existing Condition
The existing site contains a single family residential home, driveway, and attached garage.
Stormwater drains onto the site from the residential neighbor to the east (0.44 acres). There is no
cross lot drainage from the north or south. The stormwater runoff from the site drains directly
onto Sunnyhill Drive and into a sump inlet in the street at the north west corner of the property.
Before leaving the site the existing runoff is treated in one of two NPDES facilities located in the
property's front yard. These were constructed in 2010 as part of an improvement project to add a
garage and additional living space in the existing residence.
The existing impervious area of the project parcel from the house and driveway is 16%.
1.02 Proposed Condition
The proposed condition will intercept flows from the east with a retaining wall and ditch system.
This will direct flows around the proposed second dwelling unit toward the existing NPDES
facilities in the front yard. The proposed improvements will disturb 0.07 acres.
The additional impervious area of the project parcel is 3.6%.
1.03 Soil Characteristics
The following soil group definitions come from Technical Release 55 (TR-55) by the United
States Department of Agriculture:
Group A soils have low runoff potential and high infiltration rates even when thoroughly wetted.
They consist chiefly of deep, well to excessively drained sand or gravel and have a high rate of
water transmission (greater than 0.30 in/hr).
Group B soils have moderate infiltration rates when thoroughly wetted and consist chiefly of
moderately deep to deep, moderately well to well drained soils with moderately fine to
moderately course textures These soils have a moderate rate of water transmission (0.15-0.30 in/
hr).
Group C soils have low infiltration rates when thoroughly wetted and consist chiefly of soils
with a layer that impedes downward movement of water and soils with moderately fine to fine
texture. These soils have a low rate of water transmission (0.05-0.15 in/hr).
Group D soils have high runoff potential. They have very low infiltration rates when thoroughly
wetted and consist chiefly of clay soils with a high swelling potential, soils with a permanent
high water table, soils with a clay pan or clay layer at or near the surface, and shallow soils over
nearly impervious material. These soils have a very low rate of water transmission (0-0.05 in/hr).
The conservative approach is assuming Group D soils for the site.
2.0 Rational Method Description
The rational method, as described in the 2003 San Diego County Hydrology Manual, was used to
generate surface runoff flows, which were then used to size the drainage facilities.
The basic equation: Q = CiA
C = runoff coefficient (varies with surface)
i = Intensity (in/hr)
A = Area (acres)
The 6 hour and 24 hour rainfall isopluvial maps are found in the 2003 San Diego County
Hydrology Manual. Adjusted P6 calculations can be found on the spreadsheets in Attachments 2
and 3 along with the Rational Method routing calculations. Initial travel time calculations (Ti) are
based on the overland flow equation given in Figure 3-3 of the County's Hydrology Manual and
is limited to the maximum overland flow length in Table 3-2 of the County's Hydrology Manual.
Travel time calculations between nodes are calculated via manning's equation or by the Kirpich
equation as expressed in the County's Hydrology Manual. Travel time values are then entered
into the spreadsheet under Tt. Confluences are done by spreadsheet and are labeled by the node
number where the confluence occurs. Each outfall point is shown on the existing and proposed
condition hydrology exhibits with the flow rate (Q) at that particular location.
4
3.0 Hydrology Analysis
The table below summarizes the pre- and post-construction 100-year flows. The outfall points
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are shown on the Existing and Proposed Drainage Exhibits included in this report.
Description A (ac) Q (cfs)
Existing 100-Yr Node #104 Outfall 015 1.5
Existing 100-Yr Node #112 Outfall 0.18 0.5
Total 0.93 2,0
Proposed 100-Yr Node 0203 Outfall 0.76 1.5
Proposed 100-Yr Node #212 Outfall 0.17 0.5
Total 0.93 2.0
Table I Summary of existing and proposed storniwater runoff.
The total pre-development 100 year flow is 2.0 cfs. The total post-development 100 year flow is
2.0 cfs. The lack of change in runoff would be attributed to the stormwater routing in the
proposed condition.
4.0 Water Quality
The project is subject to the standard stormwater requirements per the completed storm water
standards questionnaire. The project is not a priority project and is therefore not required to
submit a Stormwater Management Plan (SWMP).
4.01 Selection of Source Control BMPs
Source control BMPs are selected by using the "Sources and Source Control BMP Checklist"
provided in Appendix I in the City's Stormwater Manual. Appendix 1 explains that applicable
controls and operational BMPs shall be listed in a table within the narrative and incorporated in
the project design. The following shows the required table:
Potential Sources
of Runoff
Pollutants
Permanent Source Control BMPs Operational Source
Control BMPs
Thai landscape plans will accomplish all of the
allowing:
Preserve existing native trees, shrubs, and ground
over to the maximum extent possible.
Minimize irrigation and runoff, to promote surface
Landscape/Outdoor infiltration where appropriate, and to minimize the use
f fertilizers and pesticides that can contribute to
Maintain landscaping using
Pesticide Use tormwater pollution.
minimum or no pesticides.
Use pest-resistant plants, especially adjacent to
ardscape.
I. Select plants appropriate to site soils, slopes,
climate, sun, wind, rain, land use, air movement,
ecological consistency, and plant interactions.
Table 2 Source Control BMP selection table.
5.0 Hydromodification and IMP Design
This project is exempt from hydromodification requirements since the project is not a priority
project.
6.0 References
City of Carlsbad Engineering Design Manual by the City of Carlsbad
San Diego County Drainage Design Manual by the County of San Diego, May 2005.
San Diego County Hydrology Manual by the County of San Diego, June 2003.
Urban Hydrology for Small Watersheds TR-55 by the United States Department of
Agriculture, June 1986.
Low impact Development Handbook by the County of San Diego, December 31,
2007.
Water Quality Control Plan for the San Diego Basin by the California Regional Water
Quality Control Board San Diego Region, April 25, 2007.
Stormwater Best Management Practice Handbook by California Stormwater Quality
Association, September 30, 2004.
7
Attachment 1
VICINITY WAD
NOT TO SCALE
Vrs
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5cc/c: 1 inch = 40
Symbol
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John P. Strohmiger En SHEET 1 OF 1
C:\Proj3\4120 Sunny Hill Drive
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Pre-Development Hydrology 4120 Sunnyhill Drive, Carlsbad, Ca, 92008, November 13, 2014, John P Strohrninger Engineering
Nodes Incr. Total Soil Land C tncr. Total Flow Slope Over- kirpich Manning Te I .Q=IA Notes
Area Area Op Use C*A C*A Path, % land Ti Ti mm, in/hr. Q, cfs.
ac. ac. ft. Ti, mm. mm. cum.
mm . ..
100-101 0.20 0.20:D R2.00.46 0.09 0.091 100, 3.00: 8.8. 1 8.8; 4.76.0.41 Initial Area
101-102 0.25,045 D R 2.0: 0.46,0.12: 021 112 0.7. 95 4.52 0 9 Total flow from east
102-103 0.18 0.63 D R2.010.46 0.061 0.29. 140 . 0.8. .10.31 430.....Sheet flow rear yard
103-104 0.12 0.750 R2.O: 0.46 0.06: 0.351 103: 2.00: 0.2 10.51 4.24 1.5 Grass swalen.035,v7fps
Total Flow at Node 104 I.S.CFS
110-111 0.06.0.06.0 A 2.0 046 003 0.031 100 10 5.8: 5.8: 622 0 2 Initial Area
111-112 0.12 0.180 R2.0 0.46: 0.061 0.08 93 2 . 0.2 6.01 6.094 0.5 Grass swalen.035,.v=7fps
Total Flow at Node 112 0.SICFS . .
lsopluvial Data
P6 = 26 Adjusted P6 26
P24= 45 1 . . . . .
P6/P24= 58%
klrpich 101 to 102 102 to 103
Formula .
L length in feet 1121.
Elevation High 534.2: 523,
Elevation Low 523 506 .
Linmiles 0.02: 0.03:
Delta 11.2':17: . . . . .......... -
Tin minutes 0.7 0.81 .
TE
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SLOPE in feet.per foot -s
0 C) OODC)C)C' PP PPPPPPP PCD 0 p p p p P
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HYDRAULIC RADIUS In feet 4 R
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vELocrrY in feet per sethncl - V
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ROUGHNESS Coothçjent n
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Post-Development Hydrology 4120 Sunnyhitl Dr., Carlsbad, Ca, 92008, November 13, 20141 John P Strohmnger Engineering
Nodes lncr. Total Soil Land C lncr. Total Flow Slop Over- Kirpich Manning Tc I Q=CIA Notes Area Area Gp Use C*A C*A Path, e % land Ti Ti mm, in/hr. Q, cis. ac. ac. ft Ti, min. mm. cum.
mm
100-101 0.20: 0.20 .1) 'R2.0 0.46.:0.09.0.09: 100 3.00 88 88 4.76 04 Initial Area 101-102 0.25 0.45D :A2.00.46 0.12 0.21: 112 0.7 9.51 4.52 J O.9 Total flow from east 200-201 0.04 0.49D .. .R2.0 0.46 i 0.02; 0.23.88: 6.8 0.1 9.6 4.49. 1.0:Concswalen=.015, v=l7fps 201-202 0.15 0.640 :R2M .0.46 0.07-0.29 87. 9.20 0.2 9.8. 4.43 1.3 Grass swalen=.035, v=8.5fps 202-203 0.12 0.76D A 2.0 0.46 0.06 0.35; 103 2... 0.2. 10.0. 4.38 1.5 Grass swale n=.035, v=7fps
:Total Flow at Node lo4: 1.5CFS
,210-211 1 0.02i 002D R20 0.46'r 0.01, 001 53 10 58 5.81 6.22,01 Initial Area 211-212 0 15 0.17;D A 2.0 046 0.07 0.08 130 2 0.3:: 6.1 6.03 0.5. Grass swale n--.035, v=7fps
Total Flow at Node 112 05 CFS
Isopluvial Data:
P6= . Adjusted P6= .26.....; .. . I .. H.. . P24= 45
P6/P24 58% : .
Kirpich 101 to 102
Formula
:.L length infeet 112
Elevation High 534.2
Elevation Low . 523
.Lin miles 0.02.
1DeItaE 11.2
Tin minutes 0.7
• EQUATION: V9R21,• •••
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GENERAL SOLUTION
SOURCE: USD01, FHWA, HDS-3 (1961
F I G U R E
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GENERAL SOLUTION
SOURCE: USDOT, FHWA, HDS-3 (1961)
F. I G U R E.
MannIngs Equation Nomograph 34J
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Attachment 4
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STORM WATER
STANDARDS Development Services
Land Development Engineering
1635 Faraday Avenue
760-602-2750
www.carlsbadca.gov
P -
To address post-development pollutants that may be generated from development projects, the City requires that new development and
significant redevelopment priority projects incorporate Permanent Storm Water Best Management Practices (BMP's) into the project
design per the City's Standard Urban Stormwater Management Plan (SUSMP). To view the SUSMP, refer to the Engineering Standards
(Volume 4, Chapter 2).
Initially this questionnaire must be completed by the applicant in advance of submitting for a development application (subdivision,
discretionary permits and/or construction permits). The results of the questionnaire determine the level of storm water standards that
must be applied to a proposed development or redevelopment project. Depending on the outcome, your project will either be subject to
'Standard Stormwater Requirements' or be subject to additional criteria called 'Priority Development Project Requirements'. Many
aspects of project site design are dependent upon the storm water standards applied to a project.
Your responses to the questionnaire represent an initial assessment of the proposed project conditions and impacts. City staff has
responsibility for making the final assessment after submission of the development application. If staff determines that the questionnaire
was incorrectly filled out and is subject to more stringent storm water standards than initially assessed by you, this will result in the return
of the development application as incomplete. In this case, please make the changes to the questionnaire and resubmit to the City.
If you are unsure about the meaning of a question or need help in determining how to respond to one or more of the questions, please
seek assistance from Land Development Engineering staff.
A separate completed and signed questionnaire must be submitted for each new development application submission. Only one
completed and signed questionnaire is required when multiple development applications for the same project are submitted concurrently.
In addition to this questionnaire, you must also complete, sign and submit a Project Threat Assessment Form with construction permits
for the project.
Please start by completing Step I and follow the instructions. When completed, sign the form at the end and submit this with your
application to the city.
STEP I .
TO_E_COMPLETED FOR ALL gj~CTS
To determine if your project is a priority development project, please answer the following questions:
YES NO
Is your project LIMITED TO constructing new or retrofitting paved sidewalks, bicycle lanes or trails that meet
the following criteria: (1) Designed and constructed to direct storm water runoff to adjacent vegetated areas, or
other non-erodible permeable areas; OR (2) designed and constructed to be hydraulically disconnected from
paved streets or roads; OR (3) designed and constructed with permeable pavements or surfaces in
accordance with USEPA Green Streets guidance?
Is your project LIMITED TO retrofitting or redeveloping existing paved alleys, streets, or roads that are
designed and constructed with Green Streets guidance? _in_accordance _the _USEPA
If you answered "yes" to one or more of the above questions, then your project is NOT a priority development project and therefore is
NOT subject to the storm water criteria required for priority development projects. Go to step 4, mark the last box stating "my
project does not meet POP requirements" and complete applicant Information.
If you answered "no" to both questions, then go to Step 2.
E-34 Page 1 of 3 Effective 6/27/13
Am- Ca
ANT 01
STORM WATE.
STANDARDS Development Services
Land Development Engineering
1635 Faraday Avenue
760-602-2750
www.carlsbadca.gov
. '1 ?. ' L'aoM EPCRF4W EDEE JTRC
To determine if your project is a priority development project, please answer the following questions: YES NO
Is your project a new development that creates 10,000 square feet or more of impervious surfaces collectively
over the entire project site? This includes commercial, industrial, residential, mixed-use, and public
development projects on public or private land.
Is your project creating or replacing 5,000 square feet or more of impervious surface collectively over the entire
project site on an existing site of 10,000 square feet or more of impervious surface? This includes commercial,
indutrial,_reeldential,_mixed-usa,_and public development projects on public erpr1 vate land.
Is your project a new or redevelopment project that creates 5,000 square feet or more of impervious surface
collectively over the entire project site and supports a restaurant? A restaurant is a facility that sells prepared
foods and drinks for consumption, including stationary lunch counters and refreshment stands selling prepared
foods and drinks for immediate consumption.
Is your project a new or redevelopment project that creates 5,000 square feet or more of impervious surface
collectively over the entire project site and supports a hillside development project? A hillside development
project includes development on any natural slope that is twenty-five percent or greater.
Is your project a new or redevelopment project that creates 5,000 square feet or more of impervious surface
collectively over the entire project site and supports a parking lot. A parking lot is a land area or facility for the
temporap,'paj*ig or storage of motor vehicles used personally for business or for commerce.
Is your project a new or redevelopment project that creates 5,000 square feet or more of impervious surface
collectively over the entire project site and supports a Street, road, highway freeway or driveway? A street,
road, highway, freeway or driveway is any paved impervious surface used for the transportation of
automobiles, trucks, motorcycles, and other vehicles.
Is your project a new or redevelopment project that creates or replaces 2,500 square feel or more of
impervious surface collectively over the entire site, and discharges directly to an Environmentally Sensitive
Area (ESA)? "Discharging Directly to" includes flow that is conveyed overland a distance of 200 feet or less
from the project to the ESA, or conveyed in a pipe or open channel any distance as an isolated flow from the /
project to the ESA (i.e. not commingles with flows from adjacent lands) *
Is your project a new development that supports an automotive repair shop? An automotive repair shop is a
facility that is categorized in any one of the following Standard Industrial Classification (SIC) codes: 5013,
5014, 5541, 7532-7534, or 7536-7539.
Is your project a new development that supports a retail gasoline outlet (RGO)? This category includes RGO'S
that meet the following criteria: (a) 5,000 square feet or more or (b) a project Average Daily Traffic (AUT) of
100 or more vehicles per day.
is your project a new or redevelopment project that results in the disturbance of one or more acres of land and
are expected to generate pollutants post construction?
11.1s your project located within 200 feet of the Pacific Ocean and (1) creates 2,500 square feet or more of
impervious surface or (2) increases impervious surface on the property by more than 100/o?
If you answered "yes to one or more of the above questions, you ARE a priority development project and are therefore subject to
implementing structural Best Management Practices (BMP's) in addition .to implementing Standard Storm Water Requirements such
as source control and low impact development BMP's. A Storm Water Management Plan (SWMP) must be submitted with your
application(s) for development. Go to step 3 for redevelopment projects. For new projects, go to step 4 at the end of this
questionnaire, check the "my project meets PDP requirements" box and complete applicant information.
If you answered no" to all of the above questions, you ARE NOT a priority development project and are therefore subject to
implementing only Standard Storm Water Requirements such as source control and low impact development BMP's required for all
development projects. A Storm Water Management Plan (SWMP) is not required with your application(s) for development. Go to step! 4 at the end of this check the "my does PDP questionnaire, project not meet requirements" box and complete applicant information.
E-34 Page 2 of 3 Effective 6/27/13
Development Services
Land Development Engineering
1635 Faraday Avenue
760-602-2750
www.carlsbadca.gov
project result in the creation or replacement surface in an amount of
I_, -.4I \F
YES NO
If you answered "yes," the structural BMP's required for Priority Development Projects apply only to the creation or replacement of
impervious surface and not the entire development. Go to step 4, check the "my project meets POP requirements" box and
complete applicant Information.
If you answered "no," the structural BMP's required for Priority Development Projects apply to the entire development. Go to step 4,
check the "my project meets POP requirements" box and complete applicant Information.
srEP4
CHECK TI-IE ARPRO?IATE BOX AND C61ETE APPLQANT INFQRtATiQN
U My project meets PRIORITY DEVELOPMENT PROJECT (POP) requirements and must comply with additional stormwater
criteria per the SUSMP and I understand I must prepare a Storm Water Management Plan for submittal at time of application.
I understand flow control (hydromodification) requirements may apply to my project. Refer to SUSMP for details.
My project does not meet POP requirements and must only comply with STANDARD STORMWATER REQUIREMENTS per
the SUSMP. As part of these requirements, I will incorporate low impact development strategies throughout my project.
Applicant Information and Signature Box
Address: 4tzL ttNN)'Hl Li— D..
Applicant Name:J j
Applicant Signature:
Accessor's Parcel Number(s):
Applicant Title: E1
Date:
This Box for City Use Only
City Concurrence:
* Environmentally Sensitive Areas include but are not limited to all Clean Water Act Section 303(d) impaired water bodies; areas
designated as Areas of Special Biological Significance by the State Water Resources Control Board (Water Quality Control Plan for the
San Diego Basin (1994) and amendments): water bodies designated with the RARE beneficial use by the State Water Resources
Control Board (Water Quality Control Plan for the San Diego Basin (1994) and amendments); areas designated as preserves or their
quivalent under the Multi Species Conservation Program within the Cities and County of San Diego; and any other equivalent
environmentally sensitive areas which have been identified by the Copermittees.
E-34 Page 3 of 3 Effective 6127/13