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Calming the StormCalming the StormCalming the StormCalming the Storm
Strategies and Tools for Easing the Design and Permitting
Process
Site Evaluation and Constraints
Presented By:
Richard C. Tso, P.E., QSD/PDavid M. Ramsey, PE., QSD/P
Civil Engineering | Structural Design | Development Planning
June 2015
Challenges to LID Implementation
What are some of the things that tend to make LID implementation difficult?
• Not engaging the Civil Engineer early in the planning phase
• Lack of public infrastructure nearby
• Hillside conditions
• Poorly draining soils
• High water table
• Retrofitting developed sites
• Perception that LID is guaranteed to reduce project costs
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Challenges to LID Implementation
Not Engaging the Civil Engineer Early in Planning
• Structures located at the low point of the site
• Insufficient open space provided
• Open space limited to areas immediately adjacent to buildings where storage/infiltration is not advised
• Site layout which precludes any ability to alter site grades for LID
• So what should you do?
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Pre-Project Planning
• Consult with the Civil Engineer prior to the start of any project regarding
storm water requirements.
• After the initial site planning and/or programming by the architect or
planner, consult with a civil engineer regarding storm water treatment
and storage designs.
• Keep in mind that some sites will require accurate and final design
analysis by the civil engineer even in the planning stage due to tight site
constraints and limited real-estate!
• It is important to meet with the city or county staff regarding storm
water design concepts at the early stages of the planning process to
ensure a project is heading on the right track.
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Challenges to LID Implementation
Lack of Nearby Infrastructure for Connection
• Most favored LID facilities require depth, up to 4 feet (bioswales, raingardens)
• Once water goes in, how to get it back out?
• Draining through curb faces is not always possible
• Especially true with tight, in-fill developments where raising the site may not be feasible
• Filling sites isn’t environmentally sensitive and can be expensive, jeopardizing project budgets and desired economic development
• Raising a site can block runoff coming to the site from adjacent properties
• Accounting for off-site run-on can increase project costs (bypass system or larger LID facilities)
• Could be mitigated by use of pumps…as long as local agencies allow them
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Challenges to LID Implementation
Hillside Conditions
• Bioswales don’t work when slope is excessive
• Raingardens should be level to maximize their efficiency
• It can be expensive to create flat areas where the natural terrain does not provide them
• Does it make sense to construct a retaining wall and then intentionally put water behind it?
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Challenges to LID Implementation
Poorly Draining Soils
• How to infiltrate when permeability is near zero (clay or bedrock)?
• Soil strata may require drilling though clay layers to get to more suitable materials
• EPA permit for injection well?
• May require additional detention and treatment area and volumes.
• Design system for multiple storm discharge rates.
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Challenges to LID Implementation
High Water Table
• Ground water cannot be at or above the bottom of an LID facility
• Requires raising the site, or….
• Shallow LID facilities = Larger Footprints
• Larger SF can increase project costs
• Take away usable building or open space
• Create more earthwork & environmental impacts
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Challenges to LID Implementation
Retrofits of Developed Sites
• Parking lot repaving…subject to stormwater regulations or not?
• Most contractors (and owners) likely aren’t even aware there could be a trigger for stormwater compliance if existing pavement is being removed and replaced
• Creating space for LID facilities on existing sites is challenging and can be expensive
• Sometimes requires losing parking spaces which is not always an option.
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Challenges to LID Implementation
Perception that LID Reduces Project Costs
• Digging pits and filling with rock can be expensive• If deep enough, they can require expensive shoring to support pit walls
where sloping excavation isn’t feasible
• Facilities at times require deep concrete side walls to separate “wet” storage areas from adjacent materials that require protection
• Deepening and waterproofing building foundations
• Sleeving utilities penetrating LID facilities
• Up front design costs are higher due to complexity of design
• Plan reviews and approvals can take longer
• Multiple disparate facilities with overflow piping can lead to MORE piping/trenching
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CONTACT:
The earlier our involvement, the greater chance for
project success!
5300 Soquel Avenue, Suite 101
Santa Cruz, CA 95062
Ph. (831) 426-5313
www.iflandengineers.com
Stormwater Specialists:
Richard C. Tso, P.E., QSD/P
David Ramsey, P.E. QSD/P
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