Design and Construction of Bioretention Areas Calming the Storm Resource Conservation District of Santa Cruz County June 25, 2015 Melanie Mills, PLA Cannon
City of Spokane; AHBL, Inc. What is Bioretention? High Performance Landscape 2
City of Atascadero, Casey Patterson LA What is Bioretention? Engineered landscape area that mimics the hydrology of a native landscape evapotranspiration storage infiltration 3
City of Atascadero, Casey Patterson LA What is Bioretention? Small scale, decentralized throughout the project site 4
City of Paso Robles, Cannon What is Bioretention? Focus on capturing, treating, and retaining small storms 5
Can you do Bioretention? Bluegreenbuilding.com Native soils Steep slopes High groundwater Existing polluted soils Proximity to drinking water wells (100 ) Existing buildings/foundations Space constraints City of Portland, Kevin Robert Perry City of Seattle, SvR 6
What really makes it Bioretention? 7
Bioretention Areas Depressed planting area Open bottom Receives stormwater Has special soil mix Allows stormwater to be retained Stormwater infiltrates to the native soil Has specially selected plants 8
Bioretention: 2 Basic Design Types 9
High Point Community, SvR Design Sloped-sided Bioretention Rain garden or linear shape Edge transition achieved w/ planting surface Landscape condition differs 10
Flat Bottom (planter) Bioretention Requires more structure at edges Edge considerations for pedestrian interface (curb) One landscape condition 11
Cannon Bluegreenbuild.org Bioretention Design Elements Facility Dimension/Design Hard Infrastructure Soil Media & Aggregate Landscape 12
Standard Details & Specifications There are many bioretention details available - designers need to use what s technically up-to-date and consistent with regulations. 100 BIORETENTION DESIGN NOTES 1. Overflow structure required for in-line systems without overflow bypass, Detail 140. 2. Provide spot elevations on civil plans (TBSM, OE, GIE, IE). See Detail 120. 3. Edge condition will vary for new and retrofit projects. Curb details may be modified for project by civil and geotechnical engineers. 4. If check dams are needed, see Concrete Check Dam Detail 131. 5. If Caltrans Class 2 Permeable is not available, substitute Class 3 Permeable with an overlying 3" deep layer of 3/4" (No. 4) open-graded aggregate. CONSTRUCTION NOTES 1. Scarify subgrade before installing bioretention area aggregate and BSM. 2. Compact each 6" lift of BSM with landscape roller or by lightly wetting. If wetting, allow to dry overnight before planting. 3. Never work within bioretention area limits during rain or under wet conditions. 4. Keep all heavy machinery outside bioretention area limits. 6. Bioretention Soil Media (BSM) specification per BASMAA Soils for Biotreatment or Bioretention Facilities. 7. Plant Selection per LIDI Plant Guidance for Bioretention Areas Technical Assistance Memo (TAM). 8. Mulch (optional) per LIDI Plant Guidance for Bioretention Areas TAM. Grading to allow for specified soil and mulch depths while achieving finished elevations per civil plans. 9. Locate energy dissipation cobble only as specified in inlet details - avoid decorative use. LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS detail number Municipality Department Name Bioretention Area Planter 100 Standard Details Design Specifications
Standard Details and Specifications Correct facility dimensions and materials 14
Design: Side Slope Grades 3:1 max (needs shelf) 4:1 recommended 15
Design: Curb Cut Inlets Inlet design has evolved Plans must provide details A A PERSPECTIVE VIEW Correct spacing PLAN VIEW Include energy dissipation BIORETENTION DESIGN NOTES 1. For use with stormwater facilities with flat bottoms. 2. Provide spot elevations on plans (TBSM, OE, GIE, IE). See Detail 100. 3. Refer to municipal standard drawings and match gutter pan of adjacent curb and gutter. SECTION A-A CONSTRUCTION NOTES 1. After construction place sand bags at gutter openings to keep storm flows from entering facility until vegetation is established. LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS detail number Curb Cut Inlet for Planters 120 Municipality Department Name 16
Design: Energy Dissipation 17
Design: Cobble Energy Dissipation Extend down sides of sloped-sided Avoid excessive or decorative use 18
City of Portland, Environmental Services City of Paso Robles, Cannon Design: Check Dams Needed when there is longitudinal slope 19
Cannon Design: Overflow Structures Raised overflow Beehive or CB Typically connected to storm system 20
Design: Aggregate & Soil 21
Source: Cannon Design: Aggregate Storage Layer No filter fabric Specified aggregates limit migration of fine material 22
City of Spokane; AHBL, Inc. What is Bioretention? High Performance Landscape 23
Design: Bioretention Soil Media (BSM) Plans must include a BSM specification 24
Design: Plants Aesthetics Habitat Treatment Air Pollution Carbon Sequestration Reduces Heat Island 25
Design: Plants Central Coast Zone A Plant List 26
Plant Selection 27
City of Atascadero, Casey Paterson LA Design: Trees Side slopes typically http://www.southwesturbanhydrology.com/ Separated 28
Design to Construction Bioretention design, methods, and materials may still be new to contractors - clear communication is crucial. Required pre-bid and pre-con meetings 29
Construction LID features often look like conventional features What are key differences for contractors and developers to understand? 30
Cannon Construction: Protection Review protection requirements of LID features -protect from compaction -sedimentation -pollutants After Planting During Construction 31
Construction: Grading Make sure contractors are aware of grading design and intended routing of stormwater 32
bluegreenbldg.org Construction: Elevations Adjacent surface Gutter inlet elevation Top of curb Overflow elevation Finished grade in facility 33
Construction: Elevations Incorrect design elevations or construction adjustments can negate stormwater functionality 34
Cannon LIDI Construction: Atypical Elements Review project plans and details for atypical design elements 35
Construction: Sequencing Reduce protection costs by excavating for LID features after adjacent construction is complete 36
Construction: Bioretention Soil Media Confirm soil and aggregate quantities with delivery tickets Review project soil compaction procedures Avoid mixing soils types: native vs. imported Do not work soils if they are wet 37
Construction: Landscape Plant installation must accurately match plans Ensure final grades are maintained after planting and mulch installation 38
Cannon Construction: Plant Substitutions Avoid substitutions to ensure function is not impacted Contractors may need to seek out new suppliers for appropriate plants 39
Cannon Construction: Plant Establishment Plants need to be sufficiently established before facility goes on-line. 40
Construction: Landscape Materials Clarify type of top dressing for bioretention areas to avoid floating material Minimize decorative use of river rock
Construction: Irrigation Drought tolerant approach 2 to 3 years for establishment/supplemental during extreme conditions Clarify understanding and hand watering if no irrigation Proper application rates Avoid overwatering BSM sandy soils Prevent potential discharges if underdrain system 42
Design and Construction Resources centralcoastlidi.org 43
Design & Construction Guidance 44
Construction Guidance 45
Melanie Mills 805.503.4532 melaniem@cannoncorp.us