HomeMy WebLinkAboutRP 92-10A; BLUE WATER GRILL CARLSBAD; HYDROLOGY & LOW IMPACT DEVELOPMENT (LID) REPORT FOR BLUE WATER GRILL (BWG) CARLSBAD; 2016-05-25RECEIVED
AUG 182016
LAND DEVELOPMENT
ENGINEERING
HYDROLOGY & LOW IMPACT DEVELOPMENT
(LID) REPORT
FOR
Blue Water Grill (BWG) Carlsbad
417 Carlsbad Village Drive
Carlsbad, CA 92008
May 25, 2016
~(4EXP3
..
I7
2/i
I
Prepared For:
( Richard Staunton
Bluewater Carlsbad, L.P.
417 Carlsbad Village Drive
Carlsbad, CA 92008
Project No 20150047.01
Prepared by: Josh Bauer
Checked by: John Cruikshank
P.E. No. C50792
John M. Cruikshank Consultants, Inc.
Tel: 310-241-6550 Fax: 310-833-6555 411 N. Harbor Boulevard, Suite 201, San Pedro, CA 90731 www.jmc-2.com
AP qz-Io,4
417 Carlsbad Village Drive
TABLE OF CONTENTS
1. INTRODUCTION
2. HYDROLOGY ANALYSIS
3. METHODOLOGY
4. HYDROLOGY I LACDPW CALCULATIONS
Hydrology Calculations: 50-Year Design Storm Flow Rate (050)
LID Hydrology Calculations: Design Capture Volume (DCV)
B. BMP Design Calculations: Tree Well (SD-1) and Infiltration Basin (INF-1)
5. HYDROLOGY / SITE MAPS
6. LID NARRATIVES
7. APPENDIX
Vicinity Maps
San Diego County 50-year 6-hour Isopluvial Map
San Diego County 50-year 24-hour Isopluvial Map
Table 3-1: Runoff Coefficients for Urban Areas
Table 3-2: Max. Overland Flow Length and Initial Time of Concentration
Figure 3-1: Intensity-Duration Design Chart
Figure 3-3: Rational Formula - Overland Time of Flow Nomograph
Figure B.i-1: 85th Percentile 24-hour Isopluvial Map
County of San Diego Hydrology Manual Soil Hydrologic Groups
BMP Maintenance Criteria
Hydrology & LID Report
417 Carlsbad Village Drive
1. INTRODUCTION
This report is a Hydrology and Low Impact Development (LID) study for the
proposed addition to the existing restaurant at 417 Carlsbad Village Drive, in the City
of Carlsbad, California.
The project site is located at 33°9'33.05"N and 117020'55.90"W at the end of
Carlsbad Village Drive about 1600 FT east of the Pacific Ocean in the City of
Carlsbad, CA. The 0.19-acre project site is comprised of one legal parcel located on
the south side of Carlsbad Village Drive, east of the railroad tracks, west of State
Street and addressed as 417 Carlsbad Village Drive. The project site is located
within Land Use District 1, Carlsbad Village Center, of the Village Master Plan, and
is located within the Village Segment of the coastal zone.
Proposed redevelopment includes the addition of 2,049 sf of interior restaurant
space and 1,202 sf outdoor dining area along with improved walkway/ADA access
and site drainage. Overall site drainage conveyance will remain the same in both the
pre- and post- construction conditions.
2. HYDROLOGY ANALYSIS
The existing site has an area of approximately 12,994 sf with 12,407 sf (95%)
consisting of impervious surfaces. The proposed project will redevelop and/or add
8,755 sf of impervious and is calculated to be 70.5% of the total construction area in
the post-development condition therefore requiring the entire site to be treated with
structural BMPs. To accomplish this, two tree wells (BMP-1) are being added to the
new outdoor patio area and a new 300 sf underground infiltration tank (BMP-2) will
be installed under the redeveloped parking area. Overall, the drainage pattern of the
existing site is being maintained. The only change is the addition of the BMPs to
reduce the amount of water leaving the site through existing city storm drains. The
only storm water that could potentially leave the site will do so through overflow lines
at both the tree wells and infiltration tank. Finally, the existing off-site tributary area
of 11,500 SF will produce run-on that must pass through the new structural BMPs,
so this run-on is being accounted for with overflow devices and have been sized for
the 50-year storm event.
The new outdoor patio of 1,202SF will be treated with two tree wells in the dining area
and the remainder of the site, including the redeveloped parking area, will be treated with
a 300 SF underground Ecorain infiltration system.
Overall, total flow (Q) based on the 50-yr 6-hr rainfall of 2.3-inches yields a total
stormwater flow of 050 = 2.97 CFS for the 0.56 acre area. For Low Impact
Development (LID) purposes, the 851h percentile rainfall event was analyzed to
calculate a design capture volume (DCV) of 15.24 CF for the two proposed tree
wells and 350.5 CF for the 300 SF infiltration basin.
Hydrology & LID Report
417 Carlsbad Village Drive
3. METHODOLOGY
The methods utilized to determine the potential run-off for a study area is based
upon record information that has been collected by both the City of Carlsbad and the
San Diego County Department of Public Works Flood Control Section.
Information for this study has been obtained from The City of Carlsbad BMP Design
Manual (February 16, 2016) for LID analysis and from The San Diego County
Hydrology Manual (June 2003).
Both the 50-year design storm frequency, and 85" percentile rainfall event were
adopted to calculate run-off flow rates for this project. After analysis it was
determined that the 85" percentile storm produced a total depth of 0.58 inches per
Figure B.1-1 of the City of Carlsbad BM Design Manual.
Hydrology & LID Report
417 Carlsbad Village Drive
4. HYDROLOGY CALCULATIONS
A. Hydrology Calculations: 50-Year Design Storm Flow Rate (Q50)
Based on the 50-year 6-hour maximum rainfall of 2.3-inches utilizing The County of
San Diego Hydrology Manual, the total maximum design flow rate is 2.97 cfs and
calculated as shown on the following pages.
Hydrology & LID Report
San Diego County Hydrology Manual Date: June 2003
Section: WB
Page: 30f70
WB.2 WORKBOOK EXAMPLES FOR HYDROLOGY MANUAL SECTION 3.0
RATIONAL METHOD AND MODIFIED RATIONAL METHOD
WB.2.1 Rational Method
(Reference Hydrology Manual Section 3.3)
The following example details the application of the RM for a single-family residential
subdivision to calculate the peak flow entering an inlet in the storm drain system. In this
example, the 100-year storm event is used. In this example, the soil type (determined from
the soils maps in Appendix A of the Hydrology Manual) is uniform across all subareas and is
Figure WB.2-1 shows the drainage map for this example.
1tyPSoi 1Y96 = Iq IS fV S SOIL nAPe 'B' :3 used t1
Flow across the initial subarea CC)I CU
First, consider the initial subarea, nodes 0101 to 0102 in Figure WB.2-1.
C = 9I2 (read from Table 3-1 of the Hydrology Manual for single-family
residential, 4.3 dwelling units per acre U/A] or less, type D soil)
A01010102 = 0.4 acres = 1;q94 MO (° z )'ii s O,~ acres
(CA) = 0.24' 0o.c)
L = 220 feet (estimated total flow length after development with house, driveway,
garage, etc.) Use 70 feet maximum per Table 3-2 of the Hydrology Manual.
332'-329.5' S = = 0.011 or 1.1% slope (typical value for graded residential lot) 220, S: 40 1:5 otc\
You can neglect the travel time for the remaining 150 across the pad since it will be small
with respect to T1
Ti = 8.5 rpinutes (Figure 3-3 of the Hydrology Manual)
3.03 mn1e <5'0 (V(\) '• T 1 S'D mukeS
WB-3
San Diego County Hydrology Manual
Date: June 2003
Section: WB
Page: 5of70
5.0 min
Using C fill in the worksheet provided in Figure 3-1 of the Hydrology Manual. Use the
isopluvial maps (Appendix B of the Hydrology Manual) to read the precipitation over a 6-
hour period (P6) and precipitation over a 24-hour period (P24) for the site. With the adjusted
P6 value determined from the worksheet (Figure 3-1 of the Hydrology Manual), fmd the
intensity, 1100. For this example, let P6 = 2.8 inches, and P24 = 4.5 inches. P6 is within 45%
to 65% of P24; therefore, the adjusted P6 = 2.8 inches. so. y. Lenomvlal
P6 = 36ches I. -b" 2V24
IZo = 5/21n/hr &.Ot ifr so
Q0102 = (CA)I = 0.2).4'2) = i/(fs O.Mq
Flow from point 0 1 0210ro 0103 n 10,- on i T
tU 4t4 ,Sa.*1Q c*cefe sv.4e The next step is to determine Tt for the length between point 0102 and 0103. The
watercourse is a gutter and to calculate Tt it is necessary to know the water velocity, V, in the
gutter. However, because the gutter is not a closed conduit, and flow from the subarea is
being added, determination of Tt is an iterative process. To find V, assume an average Q
over the watercourse (discharges for small watersheds typically range from
2 to 3 cfs per acre, depending on land use, drainage area, slope, and rainfall intensity). This
is accomplished using the following method:
. Estimate QAVG and slope, SAVG, to determine V. Estimate qavg as 2.5 cfs/acre.
Assume QAVG = Q0102 + ((qavg)(AoI020I03)/2)
QAVG = 1.1 cfs + ((2.5 cfs/acre)(1.8 acres)/2) 3.4 cfs
329.5'- 326.8'
SAVG = = 0.01 = 1% 285'
From Figure 3-6 of the Hydrology Manual, use QAVG and slope, SAVG, to determine
V.
V = 2.4 fps
WB-5
417 Carlsbad Village Drive
B. LID Hydrology Calculations: Design Capture Volume (DCV)
Based on the 85th percentile storm event utilizing The City of Carlsbad BMP Design
Manual and the infiltration rate of 1.45 in/hr given by the project soils report, the
design capture volume (DCV) for the two proposed tree wells is 15.24 CF and the
DCV for the proposed Ecorain infiltration basin is 350.50 CF. Please see the
following pages for LID hydrology calculations and the following section 'C' for BMP
(tree well and infiltration basin) calculations.
Hydrology & LID Report
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods
Worksheet B.2-1. DCV - O\6.Oth' 4o 1 WdIs (C ea )
85th percentile 24-hr storm depth from Figure B.1-1 d= 0 S inches
2 Area tributary to BMP (s) A= 0.016 acres
Area weighted runoff factor (estimate using Appendix
0-10 3 B.1.1 and B.2.1) C= unidess
Z+WS
4 Tree wells volume reduction TCV 2.0 cubic-feet
5 Rain barrels volume reduction RCV cubic-feet
Calculate DCV = -2.O
6 (3630 x C x d x A) - TCV - RCV DCV= cubic-feet
B-10 February 2016
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods
Worksheet B.2-1. DCV - 7
85" percentile 24-hr storm depth from Figure B.1-1 d= 0 SS inches
2 Area tributary to BMP (s) A= OAS S acres
3
Area weighted runoff factor (estimate using Appendix
B.1.1 and B.2.1) C 90 unitless
4 Tree wells volume reduction TCV= - cubic-feet
5 Rain barrels volume reduction RCV= cubic-feet
6
Calculate DCV = 3O(O.'i)(D. (0. IS')
(3630 x C x d x A) - TCV - RCV DCV
351). S
cubic-feet
1 J93S 54 -. 11 6f 1vP4frTj VIA 4 Qj S4: 0.1135 c(C(eS
B-10 February 2016
417 Carlsbad Village Drive
C. BMP Design Calculations: Tree Well (SD-1) and Infiltration Basin (lNF-1)
Hydrology & LID Report
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods
B.4.1 Simple Method -OAO>l ?AU Toe Wells 6 z
Stepwise Instructions:
Compute DCV using Worksheet B.4-1.
Estimate design infiltration rate using Form 1-9 in Appendix I.
Design BMP(s) to ensure that the DCV is fully retained (i.e., no surface discharge during the
design event) and the stored effective depth draws down in no longer than 36 hours.
Worksheet B.4-1: Simple-Sizing Method for Infiltration BMPs
I DCV (Worksheet B.2-1) DCV= tS.V'i cubic-feet
2 Estimated design infiltration rate (Form 1-9 in Appendix K,;= in/hr
3 Available BMP surface area ABip= 32_ sq-ft
Average effective depth in the BMP footprint
(DCV/Aaw)
D.,,,;= 0. 4 feet
5 Drawdown time, T (D *12/I(j ,) T= 3 .R hours
6 Provide alternative calculation of drawdown time, if needed. -3.93 < 3
Y1j4
Notes:
Drawdown time must be less than 36 hours. This criterion was set to achieve average annual
capture of 80% to account for back to back storms (See rationale in Section B.4.3). In order
to usc a diffcrcnt drawdown time, BMPs should be sized using the percent capture method
(Section B.4.2).
The average effective depth calculation should account for any aggregate/media in the BMP.
For example, 4 feet of stone at a porosity of 0.4 would equate to 1.6 feet of effective depth.
This method may overestimate drawdown time for BMPs that drain through both the bottom
and walls of the system. BMP specific calculations of drawdown time may be provided that
account for BMP-specific geometry.
B-18 February 2016
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods
0.4.1 Simple Method -
Stepwise Instructions:
Compute DCV using Worksheet B.4-1.
Estimate design infiltration rate using Form 1-9 in Appendix I.
Design BMP(s) to ensure that the DCV is fully retained (i.e., no surface discharge during the
design cvcnt) and the stored effective depth draws down in no longer than 36 hours.
Worksheet B.4-t Simple Sizing Method for Infiltration BMPs
I DCV (Worksheet B.2-1) DCV= 3W. S cubic-feet
Estimated design infiltration rate (Form 1-9 in Appendix
1)
x' o'= S
3
DcJF 1 Available BMP surface area ABMP sq-ft
Average effective depth in the BMP footprint D g= 1.4 feet
- (DCV/ASMP)
5 Drawdown time, T (D, *12/lCd.) T= 12. 2. hours
6 Provide alternative calculation of drawdown time, if needed.
S% ecn1 VA+ 1.46 x12. : j: IZ2S -45
2SID ahat Z3R34s5
04 —(t( Csa - S
q) o.'1) 2Qh,Zc ()k ,1i.ch
Notes:
Drawdown time must be less than 36 hours. This criterion was set to achieve average annual
capture of 80% to account for back to back storms (See rationale in Section B.4.3). In order
to use a different drawdown time, BMJ?s should be sized using the percent capture method
(Section B.4.2).
The average effective depth calculation should account for any aggregate/media in the BMP.
For example, 4 feet of stone at a porosity of 0.4 would equate to 1.6 feet of effective depth.
This method may overestimate drawdown time for BMPs that drain through both the bottom
and walls of the system. BMP specific calculations of drawdown time may be provided that
account for BMP-specific geometry.
B-18 February 2016
Appendix I: Forms and Checklists
10 t,ncl LWiAA) 'O.wi'
dEG2y L' "" lI I
Factor Category Factor Description Assigned
Weight (,w)
Factor
Value(v)
Product (p)
p=wxv
Soil assessment methods 0.25
Predominant soil texture 0.25
A Suitability
Assessment
Site soil variability 0.25
Depth to groundwater / impervious
layer 0.25
Suitability Assessment Safety Factor, SA =EP
Level of pretreatment! expected
sediment loads 0.5
B Design Redundancy! resiliency 0.25
Compaction during construction 0.25
Design Safety Factor, SR = Ep
Combined Safety Factor, S g i= SA x SB (.4
Observed Infiltration Rate, inch/hr,
(corrected for test-specific bias)
Design Infiltration Rate, in/hr. K, = / S1031 I ,1$ /Iir
Supporting Data
Briefly describe infiltration test and provide referencc to tcst forms:
rSr 4'TrlCHep u EWT VnTeD ozfo/1
"GEOTECHNICAL INVESTIGATION, PROPOSED BUILDING EXPANSION AND PARKING
IMPROVEMENTS, BLUE WATER GRILL RESTAURANT, 417 CARLSBAD VILLAGE DRIVE
CARLSBAD, CALIFORNIA" BY SMS GEOTECHNICAL SOLUTIONS, INC.
1-7 February 2016
417 Carlsbad Village Drive
5. HYDROLOGY I SITE MAPS
Hydrology & LID Report
6. LID NARRATIVES
Peak Storm Water Runoff Discharge Rates - The design capture volume
(DCV), based on 0.58-inches of rainfall (the 85 th percentile storm event) was
calculated as 15.24 CF for the two proposed tree wells and 350.5 CF for the
300 SF infiltration basin. Based on 50-yr 6-hr storm frequency, the total flow
rate for post-construction conditions is calculated to be 2.97 cfs.
Conserve Natural Areas - 90% of the subject site be developed into
hardscape structures and surfaces. The rest will be allocated for landscape /
planter areas.
Minimize Storm Water Pollutants of Concern - The possible pollutants that
could be found on a new project would be oil, grease, sediments, and
fertilizers. The general pre-development drainage patterns will remain. The
proposed stormwater conveyance system has been designed to minimize the
introduction of site runoff pollutants by utilizing the landscape/planter areas,
and permeable pavement designed to collect sediment, debris, metals and
hydrocarbons from stormwater runoff.
Protect Slopes and Channels - If applicable, sloped areas will be vegetated
with native or drought tolerant vegetation to prevent erosion.
Provide Storm Drain System Stenciling and Signage - You (as project owner)
must stencil "NO DUMPING - DRAINS TO OCEAN" at all storm drain inlets
and catch basins, install signs and prohibitive language and/or graphical icons
to prohibit illegal dumping at public access points, and maintain these items.
Properly Design Outdoor Material Storage Areas - Outdoor material storage
should be maintained within a sandbagged. "storage area' that blocks
construction material from draining from the site.
Properly Design Trash Storage Areas - Trash storage area should be placed
within the property and construction trash shall be picked up and placed in
commercial trash bins daily during construction.
Design Standards for Structural or Treatment Control BMPs - The proposed
engineered system is designed to capture, process, and utilize runoff water.
The system helps reduce storm water quantity. by providing landscape
irrigation and filters out contaminants that would otherwise run off into storm
drains. This improves water quality, reduces runoff velocity and volume, and
can encourage groundwater recharge.
Provide Proof of Ongoing BMP Maintenance - The standard maintenance for
a catch basin, pump, and planter box system requires routine inspection at
least four times per year and inspection after major storm events to detect
any cleaning or maintenance issues. Rain gutters must also be inspected and
cleaned at least two times per year to address clogging and associated
drainage problems. In addition, adequate mosquito control measures must be
implemented to avoid stagnant water issues.
ProDerly Design to Limit Oil Contamination and Perform Maintenance - The
project owners must treat to remove oil and petroleum at the construction
parking area and provide maintenance of the treatment system in order to
ensure proper project compliance.
Hazardous Waste Management - Many of chemicals used on site can be
hazardous materials which become hazardous waste upon disposal. These
wastes may include 1) paints and solvents; 2) petroleum products such as
oils, fuels and grease; 3) herbicides and pesticides. The following steps will
help reduce storm water pollution from hazardous wastes.
Use the entire product before disposing of the container.
Do not remove the original product label; it contains important safety and
disposal information. Follow all of manufacture's instructions.
Do not over-apply herbicides and pesticides. Prepare only the amount
needed. Follow the recommended usage instructions. Apply surface
dressings in several smaller applications, as opposed to one large
application, to allow time for infiltration and to avoid excess material being
carried off-site by runoff. Do not apply these chemicals just before it rains.
People applying pesticides must be certified in accordance with federal and
state regulations.
Do not clean brushes or rinse paint containers into the dirt, street, gutter,
storm drain, or stream. "Paint out" the brushes as much as possible. Rinse
water-based paints into the sanitary sewer. Filter and reuse thinners and
solvents. Dispose of excess oil-based paints and sludge as hazardous
waste.
Hazardous materials and wastes should be stored in covered containers and
protected from vandalism.
Place hazardous waste containers in secondary containment.
Arrange for regular waste collection before containers overflow.
I certify under penalty of law that this document and all attachments were
prepared under my jurisdiction or supervision in accordance with a system designed
to assure that qualified personnel properly gather and evaluate the information
submitted. Based on my inquiry of the person or persons who manage the system or
those persons directly responsible for gathered the information, to the best of my
knowledge and belief, the information submitted is true, accurate, and complete.
I am aware that there are significant penalties for submitting false information,
including the possibility of fine and imprisonment for knowing violations.
Name
Position/Title i€Z.-T Egz waw
Date
Signatu'
7. APPENDIX
Vicinity Maps
San Diego County 50-year 6-hour Isopluvial Map
San Diego County 50-year 24-hour Isopluvial Map
Table 3-1: Runoff Coefficients for Urban Areas
Table 3-2: Max. Overland Flow Length and Initial Time of Concentration
Figure 3-1: Intensity-Duration Design Chart
Figure 3-3: Rational Formula - Overland Time of Flow Nomograph
Figure B.1-1: 85th Percentile 24-hour Isopluvial Map
County of San Diego Hydrology Manual Soil Hydrologic Groups
BMP Maintenance Criteria
lass'
NOT TO SCALE
SITE MAP
Bluewater Grill
RP 92-10(A) / CDP 92-08(A)
BMP Inspection/Maintenance _____________________
Reponsible Inspection! Maintenance Minimum Frequency of BMP Party(s) Activities Required Activities
MAINTENANCE INDICATOR
ACCUMULATION OF SEDIMENT, LITTER, OR DEBRIS; STANDING
WATER IN TREE-WELLS FOR LONGER THAN 96 HOURS
FOLLOWING A STORM EVENT
TREE WELL (SD-1) OWNER MAINTENANCE ACTION
MAKE APPROPRIATE CORRECTIVE MEASURES SUCH AS
INSPCTING / UNCLOGGING ORIFICE OPENING, ADJUSTING
IRRIGATION SYSTEM, REMOVING OBSTRUCTIONS OF DEBRIS OR
INVASIVE VEGETATION, CLEARING UNDERDRAINS (WHERE
APPLICABLE), OR REPAIRING / REPLACING CLOGGED OR
COMPACTED SOILS.
MAINTENANCE INDICATOR
ACCUMULATION OF SEDIMENT, LITTER, OR DEBRIS IN ECORAIN
INFILTRATION OWNER INFILTRATION BASIN AND PRE-TREATMENT DEVICE AT CATCH
TANK (INF-1) BASIN
MAINTENANCE ACTION
REMOVE AND. PROPERLY DISPOSE ACCUMULATED MATERIALS.
MAINTENANCE INDICATOR
STANDING WATER IN SUBSURFACE INFILTRATION GALLERY FOR
LONGER THAN 96 HOURS FOLLOWING A STORM EVENT
ECORAIN MAINTENANCE ACTION
INFILTRATION OWNER THIS CONDITION REQUIRES INVESTIGATION OF WHY
INFILTRATION IS NOT OCCURRING. IF FEASIBLE, CORRECTIVE TANK (INF-1) ACTION SHALL BE TAKEN TO RESTORE INFILTRATION (E.G.
FLUSH FINE SEDIMENT OR REMOVE AND REPLACE CLOGGED
SOILS). BMP MAY REQUIRE RETROFIT IF INFILTRATION CANNOT
BE RESTORED. IF RETROFIT IS NECESSARY, THE CITY ENGINEER
SHALL BE CONTACTED PRIOR TO ANY REPAIRS OR
RECONSTRUCTION.
Appendix E: BMP Design Fact Sheets
E.2 SD-1 Tree Wells
MS4 Permit Category
Site Design
Manual Category
Site Design
Applicable Performance
Standard
Site Design
Primary Benefits
Volume Reduction
Tree Wells (Source: County of San Diego LID Manual - EOA, Inc.)
Description
Trees planted to intercept rainfall and runoff from impervious areas can be used as storm water quality
management measures that provide additional benefits beyond those typically associated with trees,
including energy conservation, air quality improvement, and aesthetic enhancement. Typical storm
water management benefits associated with trees include:
Treatment of storm water - Storm water from impervious area should be directed the tree
wells. Trees provide treatment through uptake of nutrients and other storm water pollutants
(phytoremediation) and support of other biological processes that break down pollutants..
Canopy Interception of rainfall — tree surfaces (roots, foliage, bark, and branches) intercept,
evaporate, store, or convey precipitation to the soil before it reaches surrounding impervious
surfaces
Reduced erosion - trees protect denuded area by intercepting or reducing the velocity of rain
drops as they fall through the tree canopy
Increased infiltration - soil conditions created by roots and fallen leaves promote infiltration
lvpical tree well system components include:
Directing runoff from impervious areas through a drainage opening into a tree well planting
area
Trees of the appropriate species for site conditions and constraints
Available growing space based on tree species, soil type, water availability, surrounding land
E-15 February 2016
Appendix E: BMP Design Fact Sheets
uses, and project goals
Optional suspended pavement design to provide structural support for adjacent pavement
without requiring compaction of underlying layers
Optional root barrier devices as needed; a root barrier is a device installed in the ground,
between a tree and the sidewalk, intended to guide roots down and away from the sidewalk in
order to prevent sidewalk lifting from tree roots.
Optional tree grates; to be considered to maximize available space for pedestrian circulation
and to protect tree roots from compaction related to pedestrian circulation; tree grates are
typically made up of porous material that will allow the runoff to soak through.
Optional shallow surface depression for ponding of excess runoff
Optional planter box drain
Design Adaptations for Project Goals 1
Site design BMP to provide incidental treatment. Tree wells primarily functions as site design
BMPs for incidental treatment. Benefits from tree wells are accounted for by adjustment factors
presented in Appendix B.2. Trees as a site design BMP are only credited up to 0.25 times the DCV
from the project footprint (with a maximum single tree credit volume of 400 ft3).
Storm water pollutant control BMP to provide treatment. Applicants are allowed to design trees
as a pollutant control BMP and obtain credit greater than 0.25 times the DCV from the project
footprint (or a credit greater than 400 ft3 from a single tree). For this option to be approved by the
City Engineer, applicant is required to do infiltration feasibility screening (Appendix C and D) and
provide calculations supporting the amount of credit claimed from implementing trees within the
project footprint. The City Engineer has the discretion to request additional analysis before approving
credits greater than 0.25 times the DCV from the project footprint (or a credit greater than 400 ft'
from a single tree).
fbesign Criteria and Considerations 1
Tree Wells must meet the following design criteria and considerations. Deviations from the below
criteria may be approved at the discretion of the City Engineer if it is determined to be appropriate:
Siting and Design Intent/Rationale
Tree species is appropriately chosen for the
development (private or public). For public Proper tree placement and species rights-of-ways, city planning guidelines and selection minimizes problems such as zoning provisions for the permissible species pavement damage by surface roots and and placement of trees are consulted. A list of poor growth.
trees appropriate for site design are provided in
Appendix E.20
E-16 February 2016
Appendix E: BMP Design Fact Sheets
Siting and Design Intent/Rationale
Location of trees planted within private
development follows city landscape guidelines.
Building setback, utility alignments, vehicle and
pedestrian line of sight are considered in tree
selection and placement.
Location of trees planted along public streets
follows city requirements and guidelines.
Vehicle and pedestrian line of sight are
considered in tree selection and placement.
Unless otherwise approved by the City
Engineer the following minimum tree
separation distance is suggested:
Roadway safety for both vehicular and
pedestrian traffic is a key consideration
for placement along public streets.
Minimum 0 Improvement distance to
Tree Well
Traffic Signal, Stop sign 20 feet
Underground Utility lines
(except sewer) 5 feet
Sewer Lines 10 feet
Above ground utility
structures (Transformers, 10 feet
Hydrants, Utility poles, etc.)
Driveways 10 feet
Intersections (intersecting
curb lines of two streets) 25 feet
Underground utilities and overhead wires
are considered in the design and avoided or Tree growth can damage utilities and
circumvented. Underground utilities are routed overhead wires resulting in service
0 around or through the planter in suspended interruptions. Protecting utilities routed
pavement applications. All underground through the planter prevents damage and
utilities are protected from water and root service interruptions.
penetration.
E-17 February 2016
Appendix E: BMP Design Fact Sheets
Siting and Design Intent/Rationale
Suspended pavement designs provide
structural support without compaction
Suspended pavement design was developed of the underlying layers, thereby
where appropriate to minimize soil compaction promoting tree growth.
and improve infiltration and filtration Recommended structural cells include U capabilities. poured in place concrete columns, Silva
Suspended pavement was constructed with an Cells manufactured by Deeproot Green
approved structural cell. Infrastructures and Stratacell and
Stratavault systems manufactured by
Citygreen Systems.
A minimum soil volume of 2 cubic feet per
square foot of canopy projection volume is
The minimum soil volume ensures that
there is adequate storage volume to
allow for unrestricted
evapotranspiration.
A lower amount of soil volume may be
U provided for each tree. Canopy projection area allowed at the discretion pf the City
is the ground area beneath the tree, measured Engineer if certified by a landscape
at the drip line, architect or agronomist. The retention
credit from the tree is directly
proportional to the soil volume provided
for the tree.
Establishing Amended Soil regains
greater storm water functions in the tree
wells, provides increased treatment of
Amended soil layer for tress shall be a pollutants and sediments that result from
minimum of three feet deep and extend at least development and habitation, and
twelve inches in all directions of the root ball D minimizes that need for some
when planted. The length and width must landscaping chemicals, thus reducing
ensure the appropriate volume for the species pollution through prevention.
and site. For more details on Amended Soil, refer
to Appendix E in County of San Diego
BMP Design Manual.
The minimum tributary area ensures that
DCV from the tributary area draining to the the tree receives enough runoff to fully
U tree is equal to or greater than the tree credit utilize the infiltration and
volume evapotranspiration potential provided. In
cases where the minimum tributary area
is not provided, the tree credit volume
E-18 February 2016
Appendix E: BMP Design Fact Sheets
Sithzg and Design Intent/Rationale
must be reduced proportionately to the
actual tributary area.
Inlet opening to the tree that is at least 18
inches wide.
Design requirement to ensure that the
runoff from the tributary area is not
bypassed.
Different inlet openings and drops in
grade may be allowed at the discretion of
A minimum 2 inch drop in grade from the inlet the City Engineer if calculations are
to the finish grade of the tree. shown that the diversion flow rate
Grated inlets are allowed for pedestrian
circulation. Grates need to be ADA compliant
and have sufficient slip resistance.
(Appendix B.1.2) from the tributary area
can be conveyed to the tree. In cases
where the inlet capacity is limiting the
amount of runoff draining to the tree,
the tree credit volume must be reduced
proportionately.
[Conceptual Design and Sizing Approach for Site Design I
Determine the areas where tree wells can be used in the site design to achieve incidental
treatment. Tree wells reduce runoff volumes from the site. Refer to Appendix B.2. Document
the proposed tree locations in the SWQMP.
When trees are proposed as a storm water pollutant control BMP, applicant must complete
feasibility analysis in Appendix C and D and submit detailed calculations for the DCV treated
by trees. Document the proposed tree locations, feasibility analysis and sizing calculations in
the SWQMP. The following calculations should be performed and the smallest of the three
should be used as the volume treated by trees:
a. Delineate the DMA (tributary area) to the tree and calculate the associated DCV.
b. Calculate the required diversion flow rate using Appendix B.1.2 and size the inlet
required to covey this flow rate to the tree. If the proposed inlet cannot convey the
diversion flow rate for the entire tributary area, then the DCV that enters the tree
should be proportionally reduced.
For example, 0.5 acre drains io the tree and the associated DCV is 820 W. The
required diversion flow rate is 0.10 ft/s, but only an inlet that can divert 0.05
ft3/s could be installed.
Then the effective DCV draining to the tree = 820 ft3 * (0.05/0.10) = 420 ft3
c. Estimate the amount of storm water treated by the tree by summing the following:
E-19 February 2016
Appendix E: BMP Design Fact Sheets
Evapotranspiration credit of 0.1 * amount of soil volume installed; and
Infiltration credit calculated using sizing procedures in Appendix B.4.
E-20 February 2016
Appendix E: BMP Design Fact Sheets
E.8 INF-1 Infiltration Basin
MS4 Permit Category
Retention
Manual Category
Infiltration
Applicable Performance
Standard
Pollutant Control
Flow Control
Primary Benefits
Volume Reduction
Peak Flow Attenuation
lie • .-. -
Photo Credit: http.//www. storm waterpartners. corn/facilities/basin. html
Description
An infiltration basin typically consists of an earthen basin with a flat bottom constructed in naturally
pervious soils. An infiltration basin retains storm water and allows it to evaporate and/or percolate
into the underlying soils. The bottom of an infiltration basin is typically vegetated with native grasses
or turf grass; however other types of vegetation can be used if they can survive periodic inundation
and long inter-event dry periods. Treatment is achieved primarily through infiltration, filtration,
sedimentation, biochemical processes and plant uptake. Infiltration basins can be constructed as linear
trenches or as underground infiltration galleries.
Typical infiltration basin components include:
Inflow distribution mechanisms (e.g., perimeter flow spreader or filter strips)
Energy dissipation mechanism for concentrated inflows (e.g., splash blocks or riprap)
Forebay to provide pretreatment surface ponding for captured flows
Vegetation selected based on basin use, climate, and ponding depth
Uncompacted native soils at the bottom of the facility
Overflow structure
E-35 February 2016
Appendix E: BMP Design Fact Sheets
MAINTENANCE ACCESS
OVERFLOW STRUCTURE -
A C-
' \• .------ 1 -' - ' A *
*1 • • \ /' • • •l • • • •T • •'4\ •
"f" * 11. • \*j* ', • Ii • • • I. •
c • + + ;• +1 i. Jr • •+ • • • •+ + ;•• •\+
O%SLOPE(RECOMMENDED) *
Al
3:1 MAX.
SIDE
SLOPES
'- RIPRAP FOR ENERGY
DISSIPATION
MAINTENANCE ACCESS
BERM t. VEGETATED SIDE
SLOPES AND BOTTOM
PLAN
NOT TO SCALE
OVERALL BASIN:
LW RATIO? 2:1
MIN. 2% OF
TRIBUTARY AREA
BERM
/ r MIN. V FREEBOARD
MAINTENANCE ACCESS -
MAINTENANCE I I OVERFLOW STRUCTURE
ACCESS SURFACE L---RIPRAP
-------------[PONDING
INFLOW PIPE - - -- r fl, ,s • .Yfl,
EXISTING UNCOMPACTED OUTLET PIPE
PERVIOUS SOILS
SECTION A-A'
NOT TO SCALE
Typical plan and section view of an Infiltration BMP
Design Adaptations for Project Goals I
Full infiltration BMP for storm water pollutant control. Infiltration basins can be used as a
pollutant control BMP, designed to infiltrate runoff from direct rainfall as well as runoff from adjacent
areas that are tributary to the BMP. Infiltration basins must be designed with an infiltration storage
volume (a function of the surface ponding volume) equal to the full DCV and able to meet drawdown
time limitations.
Integrated storm water flow control and pollutant control configuration. Infiltration basins can
E-36 February 2016
Appendix E: BMP Design Fact Sheets
also be designed for flow rate and duration control by providing additional infiltration storage through
increasing the surface ponding volume.
!Design Criteria and Considerations 1
Infiltration basins must meet the following design criteria. Deviations from the below criteria may be
approved at the discretion of the City Engineer if it is determined to be appropriate:
Siting and Design Intent/Rationale
Placement observes geotechnical
recommendations regarding potential Must not negatively impact existing site O hazards (e.g., slope stability, landslides, geotechnical concerns. liquefaction zones) and setbacks (e.g.,
slopes, foundations, utilities).
Selection and design of basin is based Must operate as a full infiltration design and
0 on infiltration feasibility criteria and must be supported by drainage area and in-situ appropriate design infiltration rate (See infiltration rate feasibility findings. Appendix C and D).
Finish grade of the facility is S 2% (0% Flatter surfaces reduce erosion and 0 recommended). channelization with the facility.
Settling forebay has a volume? 25% of A forebay to trap sediment can decrease facility volume below the forebay frequency of required maintenance. overflow.
Prolonged surface ponding reduce volume
available to capture subsequent storms.
0 Infiltration of surface ponding is limited The applicant has an option to use a different
to a 36-hour drawdown time. drawdown time up to 96 hours if the volume
of the facility is adjusted using the percent
capture method in Appendix B.4.2.
Minimum freeboard provided is 21 Freeboard minimizes risk of uncontrolled 0 foot. surface discharge.
Gentler side slopes are safer, less prone to
E] Side slopes are = 3H:IV or shallower, erosion, able to establish vegetation more
quickly and easier to maintain.
Inflow and Overflow Structures
E-37 February 2016
ft
Appendix E: BMP Design Fact Sheets
Siting and Design Intent/Rationale
Inflow and outflow structures are Maintenance will prevent dogging and ensure accessible by required equipment (e.g., proper operation of the flow control D vactor truck) for inspection and structures. maintenance.
Inflow velocities are limited to 3 ft/s or
less or use energy dissipation methods High inflow velocities can cause erosion, scour U (e.g., riprap, level spreader) for and/or channeling.
concentrated inflows.
Overflow is safely conveyed to a
downstream storm drain system or
U discharge point. Size overflow structure
to pass 100-year peak flow for on-line
basins and water quality peak flow for
off-line basins.
Planning for overflow lessens the risk of
property damage due to flooding.
[Conceptual Design and Sizing Approach for Storm Water Pollutant Control
To design infiltration basins for storm water pollutant control only (no flow control required), the
following steps should be taken:
Verify that siting and design criteria have been met, induding placement and basin area
requirements, forebay volume, and maximum slopes for basin sides and bottom.
Calculate the DCV per Appendix B based on expected site design runoff for tributary areas.
Use the sizing worksheet (Appendix B.4) to determine if full infiltration of the DCV is
achievable based on the infiltration storage volume calculated from the surface ponding area
and depth for a maximum 36-hour drawdown time. The drawdown time can be estimated by
dividing the average depth of the basin by the design infiltration rate. Appendix D provides
guidance on evaluating a site's infiltration rate.
rConceptua: Design and Sizing Approach for Storm Water Pollutant Treatment and Flow Control 1
Control of flow rates and/or durations will typically require significant surface ponding volume, and
therefore the following steps should be taken prior to determination of storm water pollutant control
design. Pre-development and allowable post-project flow rates and durations should be determined as
discussed in Chapter 6 of the manual.
1. Verify that siting and design criteria have been met, including placement and basin area
requirements, forebay volume, and maximum slopes for basin sides and bottom.
E-38 February 2016
L
Appendix E: BMP Design Fact Sheets
Iteratively determine the surface ponding required to provide infiltration storage to reduce
flow rates and durations to allowable limits while adhering to the maximum 36-hour
drawdown time. Flow rates and durations can be controlled using flow splitters that route the
appropriate inflow amounts to the infiltration basin and bypass excess flows to the
downstream storm drain system or discharge point.
If an infiltration basin cannot fully provide the flow rate and duration control required by this
manual, an upstream or downstream structure with appropriate storage volume such as an
underground vault can be used to provide additional control.
After the infiltration basin has been designed to meet flow control requirements, calculations
must be completed to verify if storm water pollutant control requirements to treat the DCV
have been met.
E-39 February 2016