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

2

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?

3

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.

4

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

5

6

7

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?

8

9

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.

10

11

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

12

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.

13

14

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

15

16

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

17