HomeMy WebLinkAboutCT 2018-0004; The Seaglass; Drainage Study The SeaGlass; 2019-08-26 (3)DRAINAGE STUDY
THE SEAGLASS
CT2018-0004, GR2019-0025
DWG #: 519-2A
APN: 451-613-36
2646 STATE ST.
CARLSBAD, CA 92008
Prepared By:
_________________________________________________________
John A. Van Ryn, P.E. RCE 80667 EXP: 3-31-21
Pasco Laret Suiter & Associates, Inc.
535 N. Highway 101, Suite A
Solana Beach, CA 92075
Prepared for:
2646 SEA GLASS LLC.
7922 DAGGET ST.
San Diego, CA 92111
August 26, 2019
DRAINAGE STUDY – THE SEAGLASS AUGUST 2019
TABLE OF CONTENTS
1. INTRODUCTION ................................................................................................................................... 4
1.1 Project Description ........................................................................................................................ 4
1.2 Existing Conditions ........................................................................................................................ 4
1.3 Proposed Conditions .................................................................................................................... 4
2. METHODOLOGY .................................................................................................................................. 6
2.1 Rational Method............................................................................................................................ 6
2.2 Runoff Coefficient ......................................................................................................................... 6
2.3 Rainfall Intensity ............................................................................................................................ 6
2.4 Tributary Areas .............................................................................................................................. 6
3. CALCULATIONS/RESULTS ................................................................................................................... 6
3.1 Pre & Post Development Peak Flow Comparison ...................................................................... 6
3.2 Detention ....................................................................................................................................... 6
3.3 Storm Water Quality ..................................................................................................................... 8
4. CONCLUSION ....................................................................................................................................... 8
Appendix 1 ....................................................... Pre & Post Project Hydrology Calculations
Appendix 2 .......................................................... Existing and Proposed Drainage Exhibits
Appendix 3……………………………………………………………..Sump Pump Details
DRAINAGE STUDY – THE SEAGLASS AUGUST 2019
Figure 1 Vicinity Map
DRAINAGE STUDY – THE SEAGLASS AUGUST 2019
1. INTRODUCTION
Project Description
The project is located at 2646 State St. in Carlsbad California. The site exists today as a single lot
with one vacant residential building. The project proposes the demolition of the existing residential
building and constructing a new 8 unit residential condominium. The project will divide the property
into 8 airspace condominium lots via a parcel map.
The project is designed in accordance with the San Diego County Hydrology Manual dated June
2003 and complies with the Regional Water Quality Control Board Region 9 MS4 Permit, Order No.
R9-2015-0100. The project does not propose work adjacent regulated waters therefore 401 and 404
permits are not applicable.
Existing Conditions
The 0.25 acre project site is delineated into one drainage area (DMA) because all drainage is conveyed
to one discharge location. The site relatively flat and sheets flows drainage in a southwesterly direction
towards State Street, therefore the southwest most corner of the site is considered the most downstream
edge of the DMA. Storm water then collects and is conveyed in the street gutter of State St. in a
southeasterly direction approximately 190 feet where it is picked up by a public storm drain inlet
located on the east side of State St. The storm continues in the 36” RCP public storm drain north
westerly in State St and ultimately discharges to the Buena Vista Lagoon. The existing single family
dwelling roof drains to the adjacent ground and then sheet flows to State St. The roof area of the
existing house makes up the existing impervious area located on the project site which is approximately
580 square feet. The impervious area of the existing site is 580 square feet or 5% of the site. The peak
storm water run-off was calculated using the rational method equation (Q=CiA). The precipitation
volume of 2.50 inches was used for design consideration according to the San Diego County 100yr 6hr
Isopluvial Map. A 6.6 in/hr intensity was determined from the San Diego County Hydrology Manual
Figure 3-1 assuming the minimum allowable time of concentration of 5 minutes because the site is
relatively small. This resulted in a peak pre-project run-off of Q= 0.63 CFS using a weighted runoff
coefficient of 0.38 based on the existing impervious area.
Proposed Conditions
The project proposes 8 residential townhome style condominium units. The project also proposes a
pervious paver drive isle and LID landscape areas to reduce the proposed impervious footprint. The
impervious area of the proposed developed site is 8,188 square feet or 75% of the site. The proposed
impervious areas will include concrete walkways and roof tops. The pervious areas will include
landscape areas and a paver drive isle. The post project condition has been delineated by one (1)
drainage area to model the post project condition and the point of compliance (POC) is considered to
be the southwesterly most edge of the project which is consistent with the existing condition. PR-1 is
the on-site condition of the proposed project. All roof runoff and on-site storm water runoff will be
directed to LID landscape areas and pervious paver areas and then outflow via sheet flow to the curb
& gutter of State Street. The roof area will be directed via downspouts towards landscape areas
directly adjacent to the paver drive isle and the peak flows will continue to sheet flow across the
paver drive and discharge from the site in same manner as the existing condition. A small storm
drain sump pump is proposed to collect and outlet the subsurface nuisance water collected by the
DRAINAGE STUDY – THE SEAGLASS AUGUST 2019
pervious pavers that is not able to infiltrate into the sub-surface soil layer. The sump pump will
discharge the sub-surface water out to the street gutter of State St. via a sidewalk under-drain. AThe
sump pump detail and pump curve is provided in Appendix 3 of this report. Another 3” sidewalk
underdrain is proposed along the northerly edge of the site solely to provide a drainage path for the
water collected in the landscape strip and runoff generated from the unit entry landings. The water
will then continue in the street gutter of State St. in same manner as the existing condition. The post
project peak un-detained runoff flow was calculated to be 1.3 CFS using the Rational Method Q=CiA
and a weighted runoff coefficient of 0.76 based on 75% impervious area.
DRAINAGE STUDY – THE SEAGLASS AUGUST 2019
2. METHODOLOGY
The proposed project has been analyzed to determine the peak runoff flow for 100 year, 6 hour rainfall
event using the Rational Method per the San Diego County Hydrology Manual, dated June 2003. The
Runoff Coefficient, C, for the existing and proposed conditions were calculated using a weighted average
of C values from Table 3-1 on page 3-6 in the San Diego Hydrology Manual. The time of concentration
for all existing and proposed drainage areas were calculated using the minimum TC of 5 min which yields
an intensity of 6.6 inches per hour from using the equation on Figure 3-1.
The proposed LID best management practices have been sized and located such that all runoff will be
directed to landscape planters or through pervious areas where feasible before ultimately discharging to the
downstream storm drain system.
2.1 Rational Method
As mentioned above, runoff from the project site was calculated for the 100-year storm events. Runoff was
calculated using the Rational Method which is given by the following equation:
Q = C x I x A
Where:
Q = Flow rate in cubic feet per second (cfs)
C = Runoff coefficient (Determined from Table 2, P. 82, City of San Diego Drainage Design Manual)
I = Rainfall Intensity in inches per hour (in/hr)
A = Drainage basin area in acres, (ac)
Rational Method calculations were performed using the City of San Diego Drainage Design Manual
(Section 1-102.3)
2.2 Runoff Coefficient
The Runoff Coefficient, C, for the existing and proposed conditions were calculated using a weighted
average of C values from Table 3-1 on page 3-6 in the San Diego Hydrology Manual. The weighted average
runoff coefficient is based on the actual impervious area which was calculated to be 0.76 in the post project
condition. See section 3.1.2 in the San Diego County Hydrology Manual.
2.3 Rainfall Intensity
Rainfall intensity was determined using the Rainfall Intensity Duration Frequency Curves from Figure 3-1
in the San Diego County Hydrology Manual, dated June 2003. Based on a 5 min time of concentration, an
intensity of 6.6 inches per hour was determined.
2.4 Tributary Areas
Drainage basins are delineated in the Post-Project Hydrology Exhibit in Appendix 1 and graphically portray
the tributary area for each drainage basin.
3. CALCULATIONS/RESULTS
3.1 Pre & Post Development Peak Flow Comparison
Below are a series of tables which summarize the calculations provided in the Appendix of this report.
DRAINAGE STUDY – THE SEAGLASS AUGUST 2019
SITE IMPERVIOUS AREA COMPOSITION
TOTAL
IMPERVIOUS
AREA (ACRES)
TOTAL
PERVIOUS
AREA
(ACRES)
TOTAL
PROJECT
AREA (ACRES)
%
IMPERVIOUS
SURFACES
RUNOFF
COEFFICIENT
“C”
Existing 0.01 0.24 0.25 5% 0.38
Propose
d 0.19 0.06 0.25 75% 0.76
Table 1. Runoff Coefficient “C” Comparison
The table above shows the difference in the runoff coefficient, “C”, between the existing and proposed
condition.
EXISTING DRAINAGE FLOWS
DRAINAGE
AREA
DRAINAGE
AREA
(ACRES)
RUNOFF
COEFFICIENT
(C)
Q100
(CFS)
I100
(IN/HR)
EX-1 0.25 0.38 0.63 6.6
Table 2. Existing Condition Peak Drainage Flow Rates
Table 2 above lists the peak flow rates for the project site in the existing condition for the respective rainfall
events.
Table 3. Proposed Condition Peak Drainage Flow Rates
PROPOSED DRAINAGE FLOWS
DRAINAGE
AREA
DRAINAGE
AREA
(ACRES)
RUNOFF
COEFFICIENT
(C)
Q100
(CFS)
I100
(IN/HR)
PR-1 0.25 0.76 1.27 6.6
The table above lists the peak flow rates for the project site for the proposed condition for the respective
rainfall events.
Table 4. Proposed Condition Peak Drainage Flow Rates
PEAK DRAINAGE FLOW COMPARISON
CONDITION
DRAINAGE
AREA
(ACRES)
Q100
(CFS)
V100
(CU-FT)
C
Existing 0..25 0.63 860 0.38
Proposed 0.25 1.27 1731 0.76
DRAINAGE STUDY – THE SEAGLASS AUGUST 2019
Table 4 above shows a comparison between the peak flow rates and precipitation volume for the proposed
condition and the existing condition.
As shown in Table 4, the project does not increase the peak runoff rate or runoff volume for the design
storms analyzed when comparing the pre-project condition to the post-project condition because the
proposed development is consistent with the land use of the existing condition.
3.2 Detention
The project proposes an increase in total impervious area therefore an increase in peak runoff is anticipated
however, the proposed pervious paver section of the drive isle will capture and retain the initial
concentration of storm water runoff. The pre-project and post post-project volume was calculated to show
the proposed increase in runoff volume. The volume captured by the pervious paver section is greater than
the proposed increase in runoff volume therefore adequate detention is provided and as a result the post
project runoff peak will be less than the pre-project condition because the paver section will provide
sufficient detention. See the detention calculation in Appendix 1 that shows the post-project flow is
captured by the pervious paver section.
3.3 Storm Water Quality
The project’s runoff will be treated for storm water quality by site design and source control measures. The
project does not propose greater than 10,000 square feet of impervious surface therefore the project is
classified as a “Standard” Development project according to the Storm Water Standards Questionnaire (E-
34) therefore, permanent treatment control BMPs are not proposed and a Storm Water Quality Management
Plan has not been prepared. Low Impact Design was implemented by locating pervious areas where feasible
to minimize the impervious footprint and to direct storm water runoff towards pervious areas before leaving
the site.
4. CONCLUSION
As discussed previously, the proposed project’s peak runoff flow and volume does not increase in
comparison to the existing condition because of the proposed pervious paver areas capture the additional
volume, therefore, the project will not negatively affect downstream facilities since the overall peak flow
rate will remain the same. The project does not negatively impact adjacent properties. It is my professional
opinion that the storm drain systems as proposed in this report and on the grading plans herein is adequate
to intercept, contain and convey Q100 and will not create negative impacts to the downstream system.
DRAINAGE STUDY – THE SEAGLASS AUGUST 2019
APPENDIX 1
PRE-PROJECT & POST-PROJECT
HYDROLGY CALCULATIONS
THE SEAGLASS
J-3078
8/26/2019
Drainage
Area Area Description
Total
Area
(Ac)
Total Area
(sq-ft)
Total
Impervious
Area (Sq-Ft)% Impervious
%
Pervious
Weighted
Runoff
Coefficient
Peak
Runoff Q:
(CFS)
Peak Runoff
Volume:
(cu-ft)
EX-1 Existing Site 0.25 10878 580 5%95%0.38 0.63 860
BMP
Location Basin Description
Total
Area
(Ac)
Total Area
(sq-ft)
Total
Impervious
Area
(Sq-Ft)% Impervious
%
Pervious
Weighted
Runoff
Coefficient
Peak
Runoff Q:
(CFS)
Peak Runoff
Volume:
(cu-ft)
PR-1A Proposed Site 0.02 822 613 75%25%0.76 0.10 130
PR-1B Proposed Site 0.23 10056 7575 75%25%0.76 1.17 1601
0.25 10878.0 8188.00 75%25%0.76 1.27 1731
Note:
1
Intensity:6.60 in/hr 0.90
Precip:2.50 in 0.35
0.35
Detention Calculation:
Pre-Project Peak Runoff Volume:860 cu-ft
Post-Project Peak Runoff Volume:1601 cu-ft
Delta Peak Runoff Volume (Post - Pre):742 cu-ft
Pervious Paver Area:3820 sq-ft *Proposed Drive Isle
Pavers Section Depth:1.75 ft
Paver Section Void Ratio 0.4
Paver Retention Volume:2674 cu-ft
2674>872 Therefore, Adequate Detention Provided
ON-SITE POST-PROJECT HYDOLOGY
ON-SITE PRE-PROJECT HYDOLOGY
Permeable Pavers
Landscape
Impervious
Runoff Coefficient100 Yr Storm at 5 Min TC
TOTAL
J:\Active Jobs\3078 THE SEAGLASS\CIVIL\REPORTS\HYDROLOGY\3078-DRN.xlsx
THE SEAGLASS
J-3078
8/26/2019
J:\Active Jobs\3078 THE SEAGLASS\CIVIL\REPORTS\HYDROLOGY\3078-DRN.xlsx
Hydraflow Table of Contents 3078-DETENTION.gpw
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2018 by Autodesk, Inc. v2018.3 Monday, 08 / 26 / 2019
Watershed Model Schematic......................................................................................1
Hydrograph Return Period Recap.............................................................................2
100 - Year
Summary Report.........................................................................................................................3Hydrograph Reports...................................................................................................................4Hydrograph No. 1, Manual, PAVER INFLOW..........................................................................4
Hydrograph No. 2, Reservoir, PAVER OUTFLOW...................................................................5
Pond Report - PAVER STORAGE.......................................................................................6
1
2
1
Watershed Model SchematicHydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2018 by Autodesk, Inc. v2018.3
Project: 3078-DETENTION.gpw Monday, 08 / 26 / 2019
Hyd.Origin Description
Legend
1 Manual PAVER INFLOW
2 Reservoir PAVER OUTFLOW
Hydrograph Return Period Recap
2
Hyd.Hydrograph Inflow Peak Outflow (cfs)Hydrograph
No.type hyd(s)Description
(origin)1-yr 2-yr 3-yr 5-yr 10-yr 25-yr 50-yr 100-yr
1 Manual -------------------------------------------------------1.270 PAVER INFLOW
2 Reservoir 1 -------------------------------------------------0.000 PAVER OUTFLOW
Proj. file: 3078-DETENTION.gpw Monday, 08 / 26 / 2019
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2018 by Autodesk, Inc. v2018.3
Hydrograph Summary Report
3
Hyd.Hydrograph Peak Time Time to Hyd.Inflow Maximum Total Hydrograph
No.type flow interval Peak volume hyd(s)elevation strge used Description
(origin)(cfs)(min)(min)(cuft)(ft)(cuft)
1 Manual 1.270 5 240 1,371 ------------------PAVER INFLOW
2 Reservoir 0.000 5 n/a 0 1 35.61 1,371 PAVER OUTFLOW
3078-DETENTION.gpw Return Period: 100 Year Monday, 08 / 26 / 2019
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2018 by Autodesk, Inc. v2018.3
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2018 by Autodesk, Inc. v2018.3 Monday, 08 / 26 / 2019
Hyd. No. 1
PAVER INFLOW
Hydrograph type = Manual Peak discharge = 1.270 cfs
Storm frequency = 100 yrs Time to peak = 240 minTime interval = 5 min Hyd. volume = 1,371 cuft
4
0 50 100 150 200 250 300
Q (cfs)
0.00 0.00
1.00 1.00
2.00 2.00
Q (cfs)
Time (min)
PAVER INFLOW
Hyd. No. 1 -- 100 Year
Hyd No. 1
Hydrograph Report
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2018 by Autodesk, Inc. v2018.3 Monday, 08 / 26 / 2019
Hyd. No. 2
PAVER OUTFLOW
Hydrograph type = Reservoir Peak discharge = 0.000 cfs
Storm frequency = 100 yrs Time to peak = n/aTime interval = 5 min Hyd. volume = 0 cuftInflow hyd. No.= 1 - PAVER INFLOW Max. Elevation = 35.61 ft
Reservoir name = PAVER STORAGE Max. Storage = 1,371 cuft
Storage Indication method used.
5
0 50 100 150 200 250 300
Q (cfs)
0.00 0.00
1.00 1.00
2.00 2.00
Q (cfs)
Time (min)
PAVER OUTFLOW
Hyd. No. 2 -- 100 Year
Hyd No. 2 Hyd No. 1 Total storage used = 1,371 cuft
Pond Report 6
Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2018 by Autodesk, Inc. v2018.3 Monday, 08 / 26 / 2019
Pond No. 1 - PAVER STORAGE
Pond Data
Contours -User-defined contour areas. Conic method used for volume calculation. Begining Elevation = 35.07 ft. Voids = 67.00%
Stage / Storage Table
Stage (ft)Elevation (ft)Contour area (sqft)Incr. Storage (cuft)Total storage (cuft)
0.00 35.07 3,820 0 00.25 35.32 3,820 640 6400.50 35.57 3,820 640 1,2800.75 35.82 3,820 640 1,9191.00 36.07 3,820 640 2,5591.25 36.32 3,820 640 3,1991.50 36.57 3,820 640 3,8391.75 36.82 3,820 640 4,4792.00 37.07 3,820 640 5,118
Culvert / Orifice Structures Weir Structures
[A][B][C][PrfRsr][A][B][C][D]
Rise (in)= 3.00 0.00 0.00 0.00
Span (in)= 3.00 0.00 0.00 0.00
No. Barrels = 1 0 0 0
Invert El. (ft)= 35.07 0.00 0.00 0.00
Length (ft)= 10.00 0.00 0.00 0.00
Slope (%)= 2.00 0.00 0.00 n/a
N-Value = .013 .013 .013 n/a
Orifice Coeff.= 0.60 0.60 0.60 0.60
Multi-Stage = n/a No No No
Crest Len (ft)= 8.00 0.00 0.00 0.00
Crest El. (ft)= 37.00 0.00 0.00 0.00
Weir Coeff.= 2.60 3.33 3.33 3.33
Weir Type = Broad ---------
Multi-Stage = Yes No No No
Exfil.(in/hr)= 0.000 (by Wet area)
TW Elev. (ft)= 0.00
Note: Culvert/Orifice outflows are analyzed under inlet (ic) and outlet (oc) control. Weir risers checked for orifice conditions (ic) and submergence (s).Stage / Storage / Discharge Table
Stage Storage Elevation Clv A Clv B Clv C PrfRsr Wr A Wr B Wr C Wr D Exfil User Totalftcuftftcfscfscfscfscfscfscfscfscfscfscfs
0.00 0 35.07 0.00 ---------0.00 ---------------0.0000.25 640 35.32 0.00 ---------0.00 ---------------0.0000.50 1,280 35.57 0.00 ---------0.00 ---------------0.0000.75 1,919 35.82 0.00 ---------0.00 ---------------0.0001.00 2,559 36.07 0.00 ---------0.00 ---------------0.0001.25 3,199 36.32 0.00 ---------0.00 ---------------0.0001.50 3,839 36.57 0.00 ---------0.00 ---------------0.0001.75 4,479 36.82 0.00 ---------0.00 ---------------0.0002.00 5,118 37.07 0.29 oc ---------0.29 s ---------------0.294
DRAINAGE STUDY – THE SEAGLASS AUGUST 2019
APPENDIX 2
EXISTING & PROPOSED
DRAINAGE EXHIBITS
DRAINAGE STUDY – THE SEAGLASS AUGUST 2019
APPENDIX 3
SUMP PUMP DETAIL
&
PUMP CURVE
EFFLUENT PUMPS
MYERS® ME3 SERIES
PUMP PERFoRMaNcE
Capacity gallons per minute Total head in metersTotal head in feetCapacity liters per minute
40
30
20
10
0010203070506040
0 150 25010050200
12
10
8
6
4
2
0
ME
3
H
1
/
3
H
P
ME
3
F
1
/
3
H
P
3
SAFDIE RABINESARCHITECTS43215CDBASUBMITTAL / REVISIONSIssue DateScaleNo.DateSRA Project Number01Description06/10/19BUILDING PERMIT SUBMITTAL02030408/02/19BUILDING PERMIT RESUBMITTAL171308/02/2019925 FORT STOCKTON DRIVE, SAN DIEGO, CA 92103P: (619) 297-6153 / F: (619) 299-6072www.safdierabines.comSeaGlassNEW CONSTRUCTIONOWNER2646 Sea Glass LLC7922 DAGGET ST.SAN DIEGO, CA 921111(949) 369-3966APPLICANTPROPHET SOLUTIONS, INC5845 AVENIDA ENCINAS, SUITE 138CARLSBAD, CA 92008C: (858) 334-9490 / O: (760) 999-2146CIVIL ENGINEERPASCO LARET SUITER & ASSOCIATES535 NORTH HIGHWAY 101, SUITE ASOLANA BEACH, CA 92075(858) 259-8212LANDSCAPE ARCHITECTMcCULLOUGH LANDSCAPE ARCHITECTURE, INC.703 16TH STREET, SUITE 100,SAN DIEGO, CA(619) 296-3150STRUCTURAL ENGINEERPATTERSON ENGINEERING, INC.928 FORT STOCKTON DRIVE #201SAN DIEGO, CA 92103(858) 605-0937MECHANICAL / PLUMBING ENGINEERBTA ENGINEERING, INC.9845 ERMA RD, SUITE 204SAN DIEGO, CA 92131(858) 715-6601ELECTRICAL ENGINEERNEDC, INC.3103 FALCON ST. SUITE JSAN DIEGO, CA 92103(619) 278-0078SOILS ENGINEERGEOSOILS, INC.5741 PALMER WAYCARLSBAD, CA 92010(760) 931-0915LAND SURVEYORK&S ENGINEERING, INC.7801 MISSION CENTER COURT, SUITE 100SAN DIEGO, CA 92108(619) 296-5565S A F D I E R A B I N E SA R C H I T E C T S2646 STATE STREET, CARLSBAD, CA 92008APN: 203-101-20-00PLUMBINGDETAILSP8.1