HomeMy WebLinkAboutResolution No. 14-7484 - Approving & Adopting A Low Impact Development Technical Guidance Manual For Small Site Developments - NPDESRESOLUTION NO. 14-7484
A RESOLUTION OF THE CITY COUNCIL OF THE CITY OF DOWNEY APPROVING
AND ADOPTING A LOW IMPACT DEVELOPMENT TECHNICAL GUIDANCE
MANUAL FOR SMALL SITE DEVELOPMENTS
WHEREAS, the Municipal Separate Storm Sewer System (MS4) Permit (Order No. R-
2012-0175) was adopted by the California Regional Water Quality Control Board, Los Angeles
Region on November 8, 2012, and requires municipalities electing to prepare a Watershed
Management Program to implement Low Impact Development policies; and,
WHEREAS, Low Impact Development or LID is a strategy to improve the quality of
storm water and urban runoff through the implementation of infiltration, bio-treatment,
xeriscaping, and other types of treatment systems to improve the quality of runoff; and,
WHEREAS, at the meeting of the City Council on April 8, 2014, the City Council held a
Public Hearing and introduced an ordinance amending Article V, Chapter 7 of the Downey
Municipal Code as it relates to Storm Water and Urban Runoff Pollution and Conveyance
Controls, to expand the applicability of the existing pollutant source reduction requirements, by
imposing runoff LID strategies on projects that require building, grading, and construction
permits; and,
WHEREAS, the proposed ordinance provides for a lower LID implementation policy for
those projects that result in the creation, addition, or replacement of 800 square feet or more of
impervious surface area but below the upper thresholds of 2,500, 5,000, and 10,000 square feet
depending on the type of development or redevelopment project; and,
WHEREAS, a Technical Guidance Manual for Small Site Developments (Manual)
greater than or equal to the 800 square foot baseline threshold but below the previously detailed
upper thresholds has been prepared and provides easy to follow design templates that include
but are not limited to infiltration of runoff for consideration; and,
WHEREAS, the Manual may require modifications from time to time as may be
necessary to reflect changing conditions.
NOW, THEREFORE, THE CITY COUNCIL OF THE CITY OF DOWNEY DOES
HEREBY RESOLVE AS FOLLOWS:
SECTION 1. The City of Downey Low Impact Development Technical Guidance
Manual for Small Site Developments attached hereto as Exhibit “A“ is hereby approved,
adopted, and ordered filed with the City Clerk.
SECTION 2. The City Council of the City of Downey, California, hereby authorizes and
directs the Director of Public Works and Director of Cornmunity Development to implement the
program for LID strategies for small development sites as described in the City of Downey Low
Impact Development Technical Guidance Manual for Small Site Developments.
SECTION 3. The City Council authorizes the Director of Public Works or his/her
designee to modify elements of the Manual from time to time as may be necessary to reflect
changing conditions that: (1) facilitate its implementation; and (2) maintain the goal of reducing
pollutants in urban runoff; and (3) are consistent with the requirements of the latest MS4 Permit;
and (4) do not substantially increase the cost of implementation
RESOLUTION NO. 14- 7484
PAGE 2
SECTION 4. The City Clerk shall certify to the adoption of this Resolution and shall
cause the same to be published or posted as required by law
APPROVED AND ADOPTED this 22nd day of April
r
mu
ATTEST:
mRM M. JlaERm
City Clerk
I HEREBY CERTIFY that the foregoing Resolution was adopted by the City Council of
the City of Downey at a Regular Meeting held on the 22nd day of April, 2014, by the following
vote, to wit:
AYES:
NOES:
ABSENT:
ABSTAIN :
Council Members: Guerra, Saab, Marquez, Mayor Vasquez
Council Members: None
Council Members: None
Council Members: Brossmer
e;I
bRIA M. JIMENEZ, C'MC
City Clerk
City of Downey
Low Impact Development
Technical Guidance Manual
for Small Site Developments
+ Z + q
APRIL 2014
EXHIBIT “A“
LID Technical Guidance Manual For Small Site Developments
TABLE OF CONTENTS
Section 1 – Introduction 3
1.1 What is LID? ..................................................................................................................................3
1.2 Why is LID being required? ...........................................................................................................3
Project Applicablility .....................................................................................................................4
LID Exemptions..............................................................................................................................7
1.3
1.4
Section 2 – Commonly Asked Questions.......................................................................................................9
Section 3 – Design Guidelines and Specifications............................,.......,...,.............................................. 10
Design Capture Volume............................................................................................................... 10
Flow-Through Planter Box...........................................................................................................11
Vegetated Swale..........................................................................................................................13
Rain Garden................................................................................................................................. 15
"Hollywood" Driveway ................................................................................................................ 17
3.6 Bottomless Trench ...................................................................................................................... 19
Section 4 – References.....................,..,.....,................................,..,,,...........................................................21
3.1
3.2
3.3
3.4
3.5
City of Downey Page 2 of 21 2014
LID Technical Guidance Manual for Small Site Developments
I SECTION 1 – INTRODUCTION
1.1 WHAT IS LID?
UD Stands for: Low Impact Development. It is a stormwater and urban runoff management strategy that
emphasizes conservation and the use of existing natural site features integrated with distributed, small-
scale stormwater and urban IJnoff controls to more closely mimic natural hydrologic patterns in
residential, commercial, and industrial settings.
1.2 WHY IS LID BEING REQUIRED?
The urbanization of Southern California has disrupted the natural flow of stormwater runoff. Rain falling
on roofs now flows into metal or plastic downspouts, then to concrete curbs and gutters along asphalt
roads, then to concrete storm drains, then to concrete river channels, and then finally into estuaries and
the Pacific Ocean.
You can see the problem; rainwater no longer comes into contact with dirt and vegetation. Any
pollutants (heavy metals, bacteria, nutrients, pesticides) that would have previously been naturally
degraded, are now flowing straight out to environmentally sensitive areas.
LID is a new design strategy that helps correct this problem. There are many highly technical manuals for
designing LID systems, some of which are listed in Section 4 herein. The purpose of this guidance manual
is to simplify your design.
[
Typical LID systems include:
• Flow-Through Planter Boxes
• Vegetative Swales
• Rain Gardens
• “Hollywood" Driveways
• Bottomless Trenches
In addition to the LID systems listed above, there are many other acceptable systems such as capture
and re-use (cisterns/rain barrels), green roofs, pewious pavement/pavers, turf block, etc. However, the
design, installation, and subsequent operation and maintenance of these systems can be complex and
should be carefully evaluated prior to being proposed. When using these other systems, a published
design standard shall be followed.
City of Downey Page 3 of 21 2014
LID Technical Guidance Manual for Small Site Developments
1.3 PROJECT APPLICABLILITY
Step 1: Categories.
There are four LID categories. The first step in LID design is to determine which category the project fits
inlo
Category I.Rns4 LID Category.
The project is beyond the scope of this manual and is subject to the provision of the
Municipal Separate Storm Sewer System permit (MS4) issued by the California Regional
Water Quality Control Board. These projects include the following:
a.
b
C.
d.
e.
f.
g.
h
1.
All Development Projects equal to 1 acre or greater of disturbed area that adds
more than 10,000 square feet of Impervious Surface area.
Industrial Parks with 10,000 square feet or more of surface area.
Commercial MaIls with 10,000 square feet or more of surface area.
Retail Gasoline Outlets with 5,000 square feet or more of surface area
Restaurants1 with 5,000 square feet or more of surface area.
Parking Lots with 5,000 square feet or more of Impervious Surface area, or with 25
or more parking spaces.
Streets and roads construction with 10,000 square feet or more of Impervious
Surface area. Street and road construction applies to standalone streets, roads,
highways, and freeway projects, and also applies to streets within larger projects.
Automotive Service Facilities2 with 5,000 square feet or more of surface area.
Projects located in or directly adjacent to, or discharging directly to an
Environmentally Sensitive Area, where the Development will:
(1) Discharge Stormwater Runoff that is likely to impact a sensitive biological
species or habitat; and
(2) Create 2,500 square feet or more of Impervious Surface area
Single-family Hillside Properties.J.
k.Redevelopment Projects:
1.Land disturbing activity that results in the creation or addition or replacement of
5,000 square feet or more of impervious surface area on an already developed
site of one of the Projects identified in this Subsection.
2.Where Redevelopment results in an alteration to more than fifty percent of
impervious surfaces of a previously existing development, and the existing
development was not subject to post-construction stormwater quality control
requirements, the entire project must be mitigated.
3 Where Redevelopment results in an alteration of less than fifty percent of
impervious surfaces of a previously existing development, and the existing
development was not subject to post-construction stormwater quality control
1 Standard Industrial Classification (SIC) of 5812
2 Standard Industrial Classification (SIC) of 5013, 5014, 5511, 5541, 7532-7534 and 7536-7539
City of Downey Page 4 o/ 21 2014
LID Technical Guidance Manual for Small Site Developments
requirements, only the alteration must be mitigated, and not the entire
development.
4.Redevelopment does not include routine maintenance activities that are
conducted to maintain original line and grade, hydraulic capacity, original
purpose of facility or emergency redevelopment activity required to protect
public health and safety. Impervious surface replacement, such as the
reconstruction of parking lots and roadways which does not disturb additional
area and maintains the original grade and alignment, is considered a routine
maintenance activity. Redevelopment does not include the repaving of existing
roads to maintain original line and grade.
5. Existing single-family dwelling and accessory structures are exempt from the
Redevelopment requirements unless such projects create, add, or replace
10,000 square feet or more of impervious surface area.
Category 2.Exempt Category.
The project will create, add or replace less than 800 square feet of impervious surface
a rea
Category 3.Small Scale Residential LID Category.
The project is residential, will involve 4 or less dwelling units and will create, add or
replace more than 800 square feet of impervious surface area.
Category 4.Small Scale Commercial/Industrial LID Category.
(
The project will create, add or replace more than 800 square feet of impervious surface
area and wiI! either involve 5 or more dwelling units, a commercial development, or an
industrial development.
Step 2: LID Design Requirements.
For Residential LID Pro}ects (Category 3 above)
•
•
A Residential LID Project must incorporate one or more LID system(s) in the project design. The
system(s) must be shown on the plans submitted to the City.
Include the following statement:
[
As the designer/architect of this project, I have designed the LID system in accordance with the
design criteria of the City of Downey’s LID Technical Guidance Manual for Small Site
Developments,
@ Language describing maintenance activities and indicating the responsible party for such activities
(including signature) must be located on the plans and/or documents submitted to the City. Note:
for ttlose projects creating, adding, or replacing 5,000 square feet or more of impervious surface
area, such language shall be recorded in a Covenant and Agreement recorded with the Los Angeles
County Recorder.
•The disturbed area must drain to the LID system(s). If water is flowing to the LID system from areas
outside the disturbed area, the LID system must be designed accordingly to treat all tributary areas.
In instances where a project cannot treat the runoff from the development area, an equivalent
onsite area may be treated as an alternative, upon approval of the City.
City of Downey Page 5 of 21 2014
LID Technical Guidance Manual for Small Site Developments
Calculations must be included on the plans showing the LID system is adequately sized. For
Residential LID Projects, the BMP(s) size must be a minimum of 4% of the tributary area (see table
below for sizing guidance).I
Tributary Area
(sq. ft.)
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
Minimum BMP Size
(sq. ft.}*
32
36
40
Tributary Area
(sq. ft.)
3100
3200
3300
3400
3500
3600
Minimum BMP Size
(sq. ft.)*
124
128
132
13644
48 140
144
148
152
156
160
164
52
56 3700
3800
3900
4000
4100
4200
4300
4400
4500
4600
4700
4800
4900
5000
60
64
68
72
76 168
172
176
180
184
188
192
196
200
2000
2100
80
84
2200
2300
2400
88
92
2500 100
104
108
112
2600
2700
2800
2900 116
3000 120
*Calculated from 4% of the tributary area.
City of Downey Page 6 of 21 2014
LID Technical Guidance Manual for Small Site Developments
For Commercial/Industrial LID Projects (Category 4 above)
• A Commercial/Industrial LID Project must incorporate one or more LID system(s) in the project
design. The system(s) must be shown on the plans submitted to the City.
• Include the following statement:
As the engineer/architect of record for this project, I have designed the LID system in accordance
with the design criteria of the City of Downey’s UD Technical Guidance Manual for Small Site
Developments.
•
•
The project engineer/architect must make sure the safety and soil stability of the LID system is
carefully evaluated prior to its inclusion in the design.
Language describing maintenance activities and indicating the responsible party for such activities
(including signature) must be located on the plans and/or documents submitted to the City. Note:
for those projects creating, adding, or replacing 5,000 square feet or more of impervious surface
area, such language shall be recorded in a Covenant and Agreement recorded with the Los Angeles
County Recorder.
• The disturbed area must drain to the LID system(s). If water is flowing to the LID system from areas
outside the disturbed area, the LID system must be designed accordingly to treat all tributary areas.
In instances where a project cannot treat the runoff from the development area, an equivalent
onsite area may be treated as an alternative, upon approval of the City.
• Calculations must be included on the plans showing the LID system is adequately sized. A calculation
template is shown on the following specification pages. For Commercial/Industrial LID Projects, the
BMP(s) must be sized to treat the entire design capture volume (DCV).
[Step 3: Plan development and submittal.
The LID system(s) design and location must be shown on the plans and submitted to the City. The
standard details herein are available for guidance. Site-specific details following the criteria outlined
herein are also acceptable.
1.4 LIDEXEMPTIONS
Exemptions from LID Requirements. LID requirements do not apply to any of the following:
1. A Development that only creates, adds or replaces less than 800 square feet of impervious surface
a rea;
2.
3.
4.
5.
A Development involving only emergency construction activity required to immediately protect
public health and safety;
Infrastructure projects within the public right-of-way3;
A Development or Redevelopment involving only activity related to utilities such as gas, water,
cable, or electricity services on private property;
A Development involving only resurfacing, re-striping, slurry seal, or other maintenance activities of
permitted parking lots, where the original line and grade, hydraulic capacity, and original purpose of
the facility is maintained;
3 Except for applicable Green Street projects for Transportation Corridors.
City of Downey Page 7 of 21 2014
LID Technical Guidance Manual for Small Site Developments
6. A project involving only exterior movie or television production sets, or facades on an existing
developed site;
7. A project not requiring a City building, grading, demolition or other permit for construction activity.
City of Downey Page 8 of21 2014
LID Technical Guidance Manual for Small Site Developments
SECTION 2 - COMMONLY ASKED QUESTIONS
1. 1 am adding a second story to my house. The existing footprint will remain unchanged, does UD
apply?
No, LID is required only where 800 square feet of soil is being disturbed.
2. 1 will be adding a new 800 square foot room that will replace some of my backyard. Does LID
apply?
Yes, you’ve reached the 800 square foot threshold.
3. 1 will be building a new addition that will be over 800 square feet, but I can’t fit an LID system into
the new addition. Can I create an LID system for an equivalent area of the existing building?
Yes, you can create an LID system for an equivalent area of the existing building.
4. 1 own a business which is concrete and asphalt all around. I am disturbing more than 800 square
feet; however, I cannot find a way to incorporate an LID system. Will LID be required if infeasible?
A waiver for technical infeasibility may be issued by the Director of Public Works, or authorized
representative; however in this situation it is unlikely to be granted. Generally there is always a way
to implement LID requirements.
5. How big do I have to design the LID systems?
On the following pages are design criteria. Generally you have to make the systems big enough to
treat runoff from a 0.75 inch storm.
6. 1 am removing a 1,200 square foot concrete/asphalt pad that is in need of repair and replacing it
with a new concrete pad. Does LID apply?
No, such projects maintaining original line and grade are exempt from LID requirements. Refer to
Section 1.4 of this document for further information.
7. 1 am installing new interior electrical and new plumbing and will have created, added or replaced
more than 800 square feet of impervious surface area. . When the project is finished, the trenches
will be patched to match the existing surrounding surfaces. The existing building will be
unchanged. Will LID apply?
No, utility projects are exempt from LID requirements. Refer to Section 1.4 of this document.
8. My project does not require any permits from the City, does LID apply?
No, only projects requiring City permits need to comply with LID.
9. If at some time in the future I want to change the design of the LID system, can I?
Only with City approval.
City of Downey Page 9 of 21 2014
LID Technical Guidance Manual for Small Site Developments
SECTION 3 - DESIGN GUIDELINES AND SPECIFICATIONS
3.1 DESIGNCAPTUREVOLUME
The Design Capture Volume (DCV) is required to design the flow through planter box, vegetated swale,
rain garden, and any other volume-based LID system.
DCV Equation:
1
DCV (/t:3) = C x d x 4 x 43560 x=
With:
C = (0.75 x Impervious area) + 0.15
d = Design Storm Depth (assume 0.75 inch unless otherwise known)
A = Tributary /Irea
The guidelines provided below must be followed when designing LID for your project. Standard drawings
for each LID are included for reference.
City of Downey Page 10 of 21 2014
LID Technical Guidance Manual for Small Site Developments
3.2 FLOW-THROUGHPLANTERBOX
\
LI
;
•I !
g
Figure 1: Flow-through planter box (http://lateameffort.blogspot.com).
Design criteria for a flow-through planter box include the following:
• Minimum design drawdown time = 48 hours (surface); 72 hours (total)
• Factor of safety = 2
• Max ponding depth = 18 inches
• Soil depth = 2 feet (3 preferred)
• Slotted PVC pipe (2 inches Minimum) within 6 inches (minimum) of bottom of facility
• The area (width * length) must equal a minimum of 4% of the tributary area
• Flows may outlet to a curb drain, rain garden, or equivalent
• Cover must be dense, wet, and dry tolerant vegetation
City of Downey Page 11 of 21 2014
LID Technical Guidance Manual for Small Site Developments
DOWN
SPOUT
M
OVERFLOW a
SPLASH
BLOCK
1.5' PONDING DEPTH
MAX.SEE
NOTE 1 -3” MULCH
2’ MIN.
AMENDED
SOIL
VARIES
}}{-4.25’
MIN.T
FILTER FABRIC
e
@R
E
(OPTIONAL;
NOTE 5)
l’ MIN.
GRAVEL
SLOTTED PVC PIPE
(2” MIN, 6“ MAX)
6“ THICK
IMPERVIOUS
MATERIAL
BOTTOM
(OPTIONAL,
NOTE 7)
GENERAL NOTES:
1.
2.
3.
4.
5.
6.
7.
DENSE. WET AND DRY TOLERANT VEGETATION.
PONDED WATER MUST DRAIN WITHIN 72 HOURS TO PREVENT
VECTOR BREEDING.
IF NEEDED. MULTIPLE PIPES MAY BE USED.
THE PLANTER BOX AREA (WIDTH + LENGTH) MUST EQUAL A
MINIMUM OF 4% OF THE TRIBUTARY AREA+
FILTER FABRIC AVAILABLE AT LOCAL HARDWARE STORES.
FLOWS MAY OUTLET TO A CURB DRAIN, RAIN GARDEN, OR
EQUIVALENT.
IMPERVIOUS BOTTOM LAYER IS ONLY REQUIRED IF THE BMP IS
LOCATED LESS THAN 8 FEET FROM THE BUILDING FOUNDATION OR
IN CASES WHERE THE SOILS ARE NOT SUITABLE FOR INFILTRATION
(1.E. CONTAMINATED SITES).
REVISIONSIcITY OF DOWNEY PUBLIC WORKS DEPT
LID–FLOW THROUGH PLANTER BOX
City of Downey Page 12 of 21 2014
LID Technical Guidance Manual for Small Site Developments
3.3 VEGETATED SWALE
Figure 2: Vegetated Swale (Downey, CA).
Design criteria for a vegetated swale include the following:
• Design flow velocity $ 1 ft/sec.
• Side slopes shall not exceed 3:1 (H:V).
• Slope in flow direction 1% (min) to 6% (max).
• Minimum bottom width = 1 foot
• Minimum swale length = 15 feet
• Max ponding depth = 5 feet
• Soil depth = 2 feet min
Minimum design drawdown time = 48 hours (surface); 72 hours (total)
• The area (width * length) must equal a minimum of 4% of the tributary area
• Cover must be dense, wet, and dry tolerant vegetation
•
City of Downey Page 13 of 21 2014
LID Technical Guidance Manual for Small Site Developments
SEE NOTE 1
FILTER FABRIC
(OPTIONAL,
NOTE 4)
1’ MIN
GRAVEL 1 ’ MIN
BOTTOM
WIDTH IMPERMEABLE
LAYER
(CONDITIONAL, NOTE 5)
GENERAL NOTES:
1.
2.
3.
4.
5.
DENSE. WET AND DRY TOLERANT VEGETATION.
PONDED WATER MUST DRAIN WITHIN 72 HOURS TO PREVENT VECTOR
BREEDING.
THE BOTTOM AREA (WIDTH + LENGTH) MUST EQUAL A MINIMUM OF 4%
OF THE TRIBUTARY AREA.
FILTER FABRIC AVAILABLE AT LOCAL HARDWARE STORES.
AN IMPERMEABLE LAYER MUST BE USED IF THE BMP IS LOCATED LESS
THAN 8 FEET FROM THE BUILDING FOUNDATION OR IN CASES WHERE THE
SOILS ARE NOT SUITABLE FOR INFILTRATION (1.E. CONTAMINATED SITES,
HIGH GROUNDWATER, LOW INFILTRATION RATES, ETC.).
CITY OF DOWNEY PUBLIC WORKS DEPT
LID–VEGETATED SWALE
City of Downey Page 14 of 21 2014
LID Technical Guidance Manual for Small Site Developments
3.4 RAINGARDEN
Figure 3: Rain Garden (http://www.prairiefirenewspaper.com/2009/04/rain-gardens).
Design criteria for a rain garden include the following:
• Minimum design drawdown time = 48 hours (surface); 72 hours (total)
• Factor of safety = 2
• Maximum ponding depth = 18 inches
• Minimum ponding depth = 8 inches
• Soil depth = 2 feet minimum (3 preferred)
• if downspout is directed to rain garden, slope must be 2% minimum
• Cover must be dense, wet, and dry tolerant vegetation
• The bottom of the rain garden should be no less than 10 feet from the groundwater table
City of Downey Page 15 of 21 2014
LID Technical Guidance Manual for Small Site Developments
DOWN
SPOUT
PURPOSES SLOPE
VARY
FOR AESTHETIC
CAN
BUILDING
SPLASH
BLOCK
PONDING
8“ MIN.
18” MAX.2% MIN
SLOPE
NATIVE
SOIL
FOUNDATION
MIN 8’ OR AS
DETERMINED BY
GEOTECHNICAL ENGINEER
'3” MULCH
SEE NOTE 3 & 6
GENERAL NOTES:
1.
2.
3.
4.
5.
6.
DENSE, WET AND DRY TOLERANT VEGETATION.
PONDED WATER MUST DRAIN WITHIN 72 HOURS TO PREVENT
VECTOR BREEDING.
BIORETENTION SOIL DEPTH 2’ MINIMUM (3’ PREFERRED).
THE RAIN GARDEN AREA (WIDTH # LENGTH) MUST EQUAL 4% OF
THE TRIBUTARY AREA.
THE BorroM OF THE RAIN GARDEN SHOULD BE NO LESS THAN 10’
FROM THE GROUNDWATER TABLE.
AN IMPERMEABLE BOTTOM IN CONJUNCTION WITH UNDERDRAINS
MUST BE USED iF THE BMP IS LOCATED LESS THAN 8 FEET FROM
THE BUILDING FOUNDATION OR IN CASES WHERE THE SOILS ARE
NOT SUITABLE FOR INFILTRATION (I.E. CONTAMINATED SITES, HIGH
GROUNDWATER. LOW INFILTRATION RATES, ETC.).
REVISIONSICITY OF DOWNEY PUBLIC WORKS DEPT
LID–RAIN GARDEN
City of Downey Page 16 of 21 2014
LID Technical Guidance Manual for Small Site Developments
3.5 "HOLLYWOOD" DRIVEWAY
n + = { Pbt, qI+H /,_ +( B +4.
Figure 4: "Hollywood Driveway" (http://www.apartmenttherapy.com)
Design criteria for a "Hollywood" Driveway include the following:
• Recommended spacing between ribbons is 5 to 7 feet (may vary depending on expected traffic)
• Ribbon width = 2 feet minimum
• Ribbon thickness = 6 inches minimum (with mesh or rebar)
• Ribbons should drain outward from the center of crown
• Center strip should include an irrigation line
City of Downey Page 17 of 21 2014
LID Technical Guidance Manual for Small Site Developments
DRAiN FRC)ivi
CENTER OUTWARD
CROWN)(%” IN 1
MIN, 5’ O,C
MAX. 7’ O.C
(NOTE 1)
2’ MIN
4’ MAX
(NOTE 1)PERVIOUS
(NOTE 4)
SURFACE
GENERAL NOTES:
1.
2.
3.
4.
5.
MAXIMUM WIDTH AND SPACING ARE RECOMMENDED AND MAY VARY
DEPENDING ON EXPECTED TRAFFIC.
DRIVEWAY RIBBONS SHOULD BE AT LEAST 2 FEET IN WIDTH.
DRIVEWAY RIBBONS SHOULD BE AT LEAST 6 INCHES THICK WITH MESH
OR REBAR.
PERVIOUS SURFACE INCLUDES; VEGETATION (GRASS), WIDELY SPACED
INTERLOCKING PERVIOUS PAVERS. AND GRAVEL.
DRIVEWAY RIBBONS SHALL BE CONCRETE. TRAFFIC RATED PAVERS.
BRICK, OR EQUIVALENT MATERIAL.
REVISIONsICITY OF DOWNEY PUBLIC WORKS DEPT
LID–HOLLYWOOD DRIVEWAY
City of Downey Page 18 of 21 2014
LID Technical Guidance Manual for Small Site Developments
3.6 BOTTOMLESSTRENCH
Figure 5: Bottomless trench (http://www.cob.org/services/environment/water-quality/).
Design criteria for a Bottomless Trench include the following:
• Trench width = 24 inches (across driveway)
• Trench depth = 18 inches
• Bottom 8 inches of the trench must be filled with crushed rock
• Trench must be at least 12 inches from back of sidewalk (or edge of pavement in the case of no
sidewalk)
• Longitudinal width = 6 inches (along driveway)
• Frame and grate must be pedestrian safe
City of Downey e 2014
LID Technical Guidance Manual for Small Site Developments
PEDESTRIAN SAFE
FRAME & GRATE
(SEE NOTE 9)3'
/ DIMENSIONS
VARY (NOTE 7)
REBARtoP & BOTTOM
CRUSHED ROCK
CRUSHED
W/FILTER
ROCK
CLOTH SECTION A OPTIONAL PERFORATED
PIPE TO ADJACENT LAWN
GRATE
/al
@
MIN. 24“
NOTE 7
PLAN VIEW
GENERAL NOTES:
1.
2.
3.
4.
5.
6.
7.
TRENCH SHOULD BE 24" WIDE (ACROSS DRIVEWAY) X 18" DEEP.
PRECAST MAY BE USED.
FILTER CLOTH MUST BE PLACED IN THE TRENCH EXTENDING 12” VERTICAL.
BOTTOM 8“ OF THE TRENCH MUST BE FILLED WITH CRUSHED ROCK.
DIMENSIONS DETERMINED BY GRATE FRAME DIMENSION. USE FRAME AS A FORM.
MUST BE APPLIED AT LEAST 12” FROM BACK OF SIDEWALK OR EDGE OF
PAVEMENT IN THE CASE OF NO SIDEWALK.
MINIMUM LONGITUDINAL WIDTH (MEASURED ALONG DRIVEWAY) OF FRAME & GRATE
IS EQUAL TO 6“ WITH %” SLOT OPENINGS. ALHAMBRA FOUNDRY IRON OR EQUAL.
REVISIONS ICI TY OF DOWNEY PUBLIC WORKS DEPT
LID–BOTTOMLESS TRENCH
City of Downey Page 20 of 21 2014
LID Technical Guidance Manual for Small Site Developments
SECTION 4 – REFERENCES
The Los Angeles County Low Impact Development Standards Manual at:
http://dpw.lacounty.gov/wmd/dsp_Low ImpactDevelopment.cfm
The City of Los Angeles Low Impact Development Best Management Practices Handbook at:
http://lacitysan.org/wpd/Siteorg/program/UD/lidintro.htm
Please note that the City of Downey’s LID ordinance takes precedent in the event of any inconsistencies
with any outside references.
City of Downey Page 21 of 21 2014