HomeMy WebLinkAboutCT 2018-0002; AVIARA APRTMENTS; DRAINAGE REPORT - LAUREL TREE LANE STREET WIDENING; 2022-03-25D:\76582 Aviara Apts\13 Reports\Hydrology\East _ Laurel\Aviara East DRAINAGE REPORT, 2022-0429.docx ii
TABLE OF CONTENTS
Vicinity Map ....................................................................................................................................1
1. ......... Scope of Report................................................................................................................... 2
2. ......... Existing Condition .............................................................................................................. 2
3. ......... Project Description .............................................................................................................. 3
4. ......... Methodology ....................................................................................................................... 3
4.1 Design Criteria .......................................................................................................................................... 3
4.2 Soils ........................................................................................................................................................... 3
4.3 Runoff Coefficient (C-Factors) .................................................................................................................. 3
4.4 Rainfall ...................................................................................................................................................... 4
4.5 Time of Concentration ............................................................................................................................... 4
4.6 Peak Flow Rates ........................................................................................................................................ 4
5. ......... Hydrology ........................................................................................................................... 4
6. ......... Proposed Inlet ..................................................................................................................... 6
7. ......... Conclusion .......................................................................................................................... 6
REFERENCES
EXHIBITS
Hydrology, Inlet Sizing & Hydraulics Calculations
Inlet Sizing
APPENDIX
Websoil Survey
San Diego County June 2003 Hydrology Manual Excerpts
Carlsbad Inlet Sizing
DRAINAGE MAPS
EXISTING DRAINAGE EXHIBIT ......................................................................... Map Pocket #1
PROPOSED DRAINAGE EXHIBIT ...................................................................... Map Pocket #2
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Vicinity Map
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1. Scope of Report
The scope of this report is limited to the work along the Aviara Apartments West frontages
within the public right-of-way.
The Laurel Tree Lane widening includes pavement widening, curb & gutter, and sidewalk
(frontage improvements will also include multiple Tree Wells and a fill slope along onto the
future Aviara East project). Additional miscellaneous improvements and replacements along
Aviara Parkway frontage for both the Aviara West and Aviara East projects.
A separate SWQMP report (SB&O, Inc. dated March 2022) was prepared above work. Separate
Drainage reports will be prepared for the Aviara West & East sites.
2. Existing Condition
The projects are located south of Palomar Airport Road, east of Interstate 5 and west of El
Camino Real and north of Poinsettia Lane, in the City of Carlsbad. The Aviara Apartment sites
are located on the East and West sides of Aviara Parkway, north of Laurel Tree Lane
intersection, and southwest of Encinas Canyon Creek. The East site is vacant, and the West site
was previously developed with a warehouse building, paved parking lot and two paved
driveways.,
Laurel Tree Lane is partially improved, with the north (project) frontage limited to an asphalt
berm without sidewalk. Surface discharge is primarily overland from the center of the paved
street to the asphalt berm on the north side, then easterly along the berm to an asphalt spillway,
which discharges northeasterly toward the Canyon de las Encinas watercourse.
Aviara Parkway is fully improved along the length of the project frontages with full width
pavement, curb & gutter, contiguous sidewalk and a raised median. There are curb return
improvements at the Laurel Tree Lane intersection, and at the 2 driveway entries along the
Aviara West frontage. Aviara Parkway slopes south to north toward Palomar Airport Road, with
surface runoff directed from the median out to the curb & gutter to curb inlets located on either
side of the street, approximately 300 feet north of the Avaia Apartment sites (about 100’ south of
Palomar Airport Road intersection)
The Aviara East site drains northerly toward Canyon de las Encinias with the northwesterly
portion of the site intercepted by a headwall and storm drain connected to the culvert under
Aviara Parkway.
See Existing Drainage Exhibit in Map Pocket #1.
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3. Project Description
Laurel Tree Lane will be widened and improved along the project frontage of Aviara East site.
The work will extend from the curb return at Aviara Parkway easterly to match the full width
street improvements near the cul-de-sac terminus (approximately 60 feet east of the Aviara East
site). A driveway for the future Aviara East site will be provided.
Additional work is proposed along the Aviara Parkway frontage of both the West and East sites
as follows;
· upgrade pedestrian ramps at the Aviara West project entry at Laurel Tree Lane
intersection.
· Reduce width of existing northerly driveway for the West site
· new driveway entrance for the Aviara East site Apartments.
· replace raised median with pavement for left turn lane pocket
· landscaping on West frontage.
The project improvements maintain the existing drainage patterns and avoid diversion.
See Proposed Drainage Exhibit in Map Pocket #2.
4. Methodology
4.1 Design Criteria
Drainage systems will be designed in accordance with the City of Carlsbad’s “Engineering
Standards,” Chapter 5. The Rational Method, as defined in the San Diego County Hydrology
Manual (June 2003 edition), is used to calculate peak flow rates for 6-hour 100-year storm
events. (See Appendix)
4.2 Soils
The soil mapping for the Laurel Tree Lane portion of the site is hydrologic soil classification
Type “A.” Regional geologic mapping by Kennedy and Tan (2005 and 2007).
4.3 Runoff Coefficient (C-Factors)
The runoff coefficients used for this project, according to the San Diego County Hydrology
Manual (2003) Table 3-1, includes the following;
Surface Condition % Impervious Runoff Coefficient
for Soil Type “A”
Impervious 100 0.87
Pervious 0 0.20
Intermediate impervious areas will be prorated using values from Table 3-1.
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4.4 Rainfall
Rainfall intensities are calculated using the rainfall totals from the County 6-Hour and 24-Hour
Isopluvial Maps as follows;
Storm
Event
6-Hour
Rainfall
(in)
24-Hour
Rainfall
(in)
Ratio
P6/P24
Adjusted
P6
(in)
100-Year 2.7 4.4 61% 2.7
See Appendix for Isopluvial Maps and Figure 3-1 to determine the adjusted 6-hour rainfall.
4.5 Time of Concentration
Rainfall intensities were calculated using times of concentration in accordance with the
procedures noted in the June 2003 Hydrology manual. This includes the limitations as noted in
Table 3-2, which restricts the initial overland times of concentration (To) based upon the Land
Use / Density (% Impervious) and slope. For impervious areas (streets) the initial time of
concentration are extremely short, ranging from 2.3 to 2.7 minutes (slopes 5% to 2% range).
The remaining travel time is based upon the gutter length and average velocity. Velocity is
based upon flow velocities estimated using the Gutter & Roadway Discharge Velocity Chart for
curb and gutter, and a V shaped channel for the existing Apshalt Berm (6” Type “A” Asphalt
Dike w/ 1:2 batter and the 2% street crossfall). The time of concentration is the sum of the
overland flow and travel time in the gutter.
4.6 Peak Flow Rates
Peak flow rates are estimated using the Rational Method (Q=CIA). Rainfall intensities are based
upon the following formula;
I = 7.44 P6 Tc-.645
Where;
P6 is the adjusted 6-hour rainfall total (inches) for a given storm frequency.
Tc is the time of concentration (minutes) at the design location in the drainage system.
Note: When calculating intensity, the minimum Tc is 5 minutes.
5. Hydrology
The Laurel Tree Lane pavement and sidewalk addition will increase both the total and
impervious area tributary to the inlet east of the Aviara East site. The peak flow rates for the
100-year 6-hour storm are estimated as follows;
EXISTING HYDROLOGY – LAUREL TREE LANE
Basin
Area
(sf)
Area
(ac)
%
Impervious
C
C x A
Tc
(min)
I100
(in/hr.)
Q100
(cfs)
E1 10,090 0.232 100
E2 5,491 0.126 0
Existing 15,581 0.358 64.8 0.66 0.236 5.0 7.11 1.68
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POST DEVELOPMENT HYDROLOGY – LAUREL TREE LANE
Basin
Area
(sf)
Area
(ac)
%
Impervious
C
C x A
Tc
(min)
I100
(in/hr.)
Q100
(cfs)
E1 10,090 0.232 100
P1 8,712 0.200 100
Proposed 18,802 0.432 0.87 0.376 5.0 7.11 2.67
Existing 1.68
Increase 0.99
The above hydrology calculations show an increased peak flow rate from the Laurel Tree Lane
widening and sidewalk addition to be 0.99 cfs. The proposed peak flow ignores the abstraction
and potential mitigation by the tree wells.
Detailed hydrology and hydraulic calculations are provided in Exhibit “A”.
The remaining Aviara Parkway work areas will have limited increases in increases in 100-year
peak flow rates due to limited increases in total impervious areas, summarized as follows;
ID & Scope of Work
P2 Remove & replace impervious areas (pedestrian ramps and cross gutter).
P3 Reduce driveway width – replace with landscaping & walkway,
P5 Replace paved median with road paving,
P6 Add landscaping to existing pervious area – west side of Aviara Parkway.
P4 Replace sidewalk with driveway paving.
P7 Add sidewalk paving at curb return (Laurel Tree widening).
P8 Temporary slope (Aviara East site from Laurel Tree Lane Widening).
ID
Discharge Location Area
(sf)
Impervious
Change (sf)
%
Impervious
C
(Increase)
C x A
Peak
Increase
(cfs)
P2 B: Aviara Gutter (West) - None
P3 B: Aviara Gutter (West) - None
P5 B: Aviara Gutter (West) - None
P6 B: Aviara Gutter (West) - None
P4 C: Aviara Gutter (East) - 200 0 to 100 0.67 0.026 0.022
P7 C: Aviara Gutter (East) - 176 0 to 100 0.67 0.014 0.019
P8 D: Existing Storm Drain 6,698 None
Totals 376 .041
Notes:
1. Runoff increase based upon increase in imperviousness.
2. Due to the small area and dimension of the work areas, a 5-minute time of concentration
was used to determine the Q100 peak runoff increase.
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6. Proposed Inlet
The street widening will require replacement of the existing asphalt spillway. A modified curb
inlet will be used to intercept flows and direct runoff to the existing ditch. Inlet openings in
sump conditions are estimated using a two cfs per lineal foot of opening per Carlsbad City
Standards chapter 5.4.A (excerpt included in Appendix), which requires a minimum opening
width of 2 foot.
The proposed inlet is identical to a Type “B” curb inlet, which would require a 3 feet clear width
to intercept the post development peak flow. The curb height is 6” with a 2” local depression.
The outlet of the modified curb inlet is a rectangular concrete channel at 1% slope, which results
in a discharge velocity of 3.55 fps, which is below 6-10 fps range. A rip rap energy dissipater
with the smallest rock size (No 2 Backing ) has been specified.
See Exhibit “A” for curb inlet and velocity calculations.
7. Conclusion
The calculations show limited increase in the Laurel Tree Lane peak runoff, which occurs at the
proposed curb inlet with rip-rap energy dissipater. The estimated increase is approximately 1
cfs in the event of an extremely short time rainfall event (time of concentration = 5 minutes),
which decreases during longer duration events. Due to the limited change in impervious area,
the Aviara Parkway improvements will result in negligible increases in peak runoff (a maximum
of 0.04 cfs).
The conversion of pervious areas to impervious surfaces, will naturally result in increased runoff
volumes, which addressed by hydromodification mitigation detailed in the project SWMP. The
project improvements will maintain the existing drainage patterns and avoid diversion.
The Laurel Tree Lane and Aviara Parkway improvements are part of the Aviara Apartments
West & East development sites, which hydromodification mitigation and attenuation of the 100-
year peak runoff, resulting in minor reductions in peak discharge.
In consideration of the above, the Laurel Tree Lane and Aviara Parkway project is expected to
have minimal downstream impacts. Therefore, no additional flood control measures are
necessary.
D:\76582 Aviara Apts\13 Reports\Hydrology\East _ Laurel\Aviara East DRAINAGE REPORT, 2022-0429.docx
APPENDIX
References
1. Kennedy, MP., and Tan, SS., 2007, Geologic map of the Oceanside 30' by 60' quadrangle,
California, regional geologic map series, scale 1:100,000, California Geologic Survey Map
No. 2.
2. Kennedy, MP., and Tan, SS., 2005, Geologic map of the Oceanside 30' by 60' quadrangle,
California, regional map series, scale 1:100,000, California Geologic Survey and United
States Geological Survey,
www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm
3. Preliminary Geotechnical Evaluation 9.2 ACRES, APN 212-040-56-00, LAUREL TREE
LANE AT AVIARA PARKWAY, CARLSBAD, SAN DIEGO COUNTY, CALIFORNIA
FOR SUMMERHILL HOMES, JULY 7, 2016.
4. County of San Diego Hydrology manual, 2002 Edition.
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EXHBIT A
Calculations
Hydrology
Inlet Sizing
Hydraulics
LAUREL TREE LANE HYDROLOGYBASINLOCATIONIMPERVIOUSAREACC x ALoSoToLgSgVgTgTcI100Q100Discharge(%)(AC)(ac)(ft)(%)(min)(ft)(%)(fps)(min)(min)(in/hr)(cfs)LocationE1 LAUREL TREE LANE - EXISTING 100.0% 0.232 E2 LAUREL TREE LANE - EXISTING 0.0% 0.126 EXISTING100.0% 0.358 0.660 0.236 35 5.6% 1.38 472 2.3 2.24 3.51 4.89 7.11 1.68 ABASINLOCATIONIMPERVIOUSAREACC x ALoSoToLgSgVgTgTcI100Q100Discharge(%)(AC)(ac)(ft)(%)(min)(ft)(%)(fps)(min)(min)(in/hr)(cfs)LocationE1 LAUREL TREE LANE - EXISTING 100.0% 0.232 P3 LAUREL TREE LANE - ADD 100.0% 0.200 POST DEVELOPMENT100.0% 0.432 0.870 0.376 37 5.6% 1.42 468 2.3 3.2 2.44 3.86 7.11 2.67 ADifference0.074 0.139 2.0 -4.0 1.0 -1.1 (1.03) 0.99D:\76582 Aviara Apts\13 Reports\SWQMP\East _ Laurel\ProjectData-OFFSITE.xlsx Hydrology
Curb Inlet Sizing - Laurel Tree Lane
Q = 0.67 hL(2gd)^0.5 Orifice Option
Q=2.67 cfs
Curb Height 8.00 in
Curb Opening Height (h)4.80 in
Curb Opening Height (h)0.40 ft
Curb Opening Length (L)3 ft
Effective Depth (Do)0.188 ft
g 32.17 fps/s
Qcapacity 2.80 cfs
Effective Depth d0= (y+a)-h/2 Sin(theta)
y 3.36 depth of flow in adjacent gutter
a 2 curb inlet depression (in)
h/2 Sin(theta)3.1 in
d0= 2.26 in
d0= 0.188 ft
Q = CwLwd^1.5 Weir Flow
Q=2.72 cfs
Cw 3.0
Lw (Opening)3 ft
D (flow depth)0.45 ft
Q required 2.671
Curb Height 8.00 in
Curb Opening Height (h)4.80 in
Curb Opening Height (h)0.40 ft
Clear Opening Size Used 3 ft
D:\76582 Aviara Apts\13 Reports\SWQMP\East _ Laurel\ProjectData-OFFSITE.xlsx Hydrology Range A85..I91
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APPENDIX
Websoil Survey
County of San Diego Hydrology Manual Excerpts
City of Carlsbad Standards
PLANNING ENGINEERING SURVEYING
3990 Ruffin Road, Suite 120
San Diego, Ca. 92123
858-560-1141
858-560-8157 Fax
BASIN LOCATION DESCRIPTION NET AREA NETAREA IMPERVIOUSPERVIOUS IMPERVIOUSDISCHARGE
(SF)(AC)(SF)(SF)(%)LOCATION
E1 LAUREL TREE LANE - EXISTING PAVING TO REMAIN 10,090 0.232 10,090 8,712 100.0%A
E2 LAUREL TREE LANE - EXISTING PERVIOUS AREA BEHINDBERM 5,491 0.126 - 5,491 0.0%A
TOTAL 15,581 0.358 10,090 14,203 64.8%A
PLANNING ENGINEERING SURVEYING
3990 Ruffin Road, Suite 120
San Diego, Ca. 92123
858-560-1141
858-560-8157 Fax
BASIN LOCATION DESCRIPTION NET AREA NET AREA IMPERVIOUSPERVIOUS IMPERVIOUS DISCHARGE
(SF)(AC)(SF)(SF)(%)LOCATION
P1 LAUREL TREE LANE STREET WIDENING 8,712 0.200 8,712 -100.0%A
P2 AVIARA PKWY - MAIN DRWY WEST R&R RAMP & GUTTER - - - - -B
P3 AVIARA PKWY - SECONDARY ENTRYWEST REDUCE DRWY / ADDWALK - - - - -B
P5 AVIARA PKWY - MEDIAN RAISED MEDIAN TO PAVING - - - - -B
P6 AVIARA PKWY - WEST ADD LANDSCAPING - - - - -B
P4 AVIARA PKWY - DRWY ENTRY EAST ADD DRWY PAVING 200 0.005 200 -100.0%C
P7 LAUREL TREE WIDENING @ RETURN ADD SIDEWALK 176 0.004 176 -100.0%C
P8 AVIARA EAST - LAUREL TREE R/W SLOPE MODIFICATION 6,698 0.154 - 6,698 0.0%D
- -
E1 LAUREL TREE LANE - EXISTING PAVING TO REMAIN 10,090 0.232 10,090 -100.0%A