4.106.3. Grading and paving. Construction plans shall indicate how the site grading or drainage system will manage all surface water flows to keep water from entering buildings. Examples of methods to manage surface water include, but are not limited to, the following:
1. Swales
2. Water collection and disposal systems
3. French drains
4. Water retention gardens
5. Other water measures which keep surface water away from buildings and aid in groundwater recharge.
COMMENTARY
Purpose:
This section provides protection from unintended entry of surface water and requires construction plans to show how surface water will be managed. Site design and proper installation of drainage systems will help builders protect structures from the dangers of flooding or subsurface water infiltration. This is especially important in areas where setbacks or obstacles interfere with proper surface drainage.
Examples of Acceptable Methods of Implementation and/or Compliance:
Develop and implement control methods to address ground water flow both above and below the surface to ensure water flow away from the building.
Channel rain gutter discharge away from the building during large or intense rain events.
Builders should consider site design mimicking water flows similar to the natural environment.
Additional design strategies that can be considered are:
Ø Sloped ground surfaces
Ø Properly placed drains
Background:
During large rain events the ground can become saturated causing runoff and/or ponding in low- lying areas, which can cause water to migrate into buildings. It is critically important to channel rain gutter discharge away from the building during these events. Builders should consider site design that mimics water flows similar to the natural environment and incorporate methods as described in this section.
In order to keep a site well-drained and stable, designers and contractors should consider both storm water from the roof and rainwater penetrating into the area around the site. Ground water can flow above or below the surface. Control methods should be developed and implemented which allow for both types of ground water flow to ensure water can continually flow away from the building.
Frequently Asked Questions
Q: Do local storm water ordinances need findings and filing?
A: Sometimes. It is best to check with a specific local municipality about the local ordinance adoption process and required resolutions, findings and filings. Local charters typically address procedures for adopting, amending and rescinding ordinances. Ordinances typically require or prohibit certain actions under specified circumstances and include statements of intent, findings, specific actions required or prohibited, and an adoption clause. Approved ordinances are subsequently incorporated into the county or city codes.
The State Water Resources Control Board (SWRCB), Municipal Storm Water Permitting Program, regulates storm water discharges from municipal separate storm sewer systems (MS4s). Although not a formal finding, changes in local ordinances helpful to or enhancing the local storm water program will need to be reported in the local agency’s annual report to the SWRCB.
Q: CALGreen Section 4.106.2 requires storm water drainage and retention during construction. Does this requirement apply year-round even though construction will occur during non-rainy season months?
A: No. This section provides three methods for complying with this section. The third method involves compliance with a local lawfully enacted storm water management ordinance. In addition, the local enforcing agency has discretion to determine whether these measures are needed based on the potential for storm water impacts during the construction period of the project. However, if there is potential for construction to be postponed or to be extended beyond the initial planned construction phase, the local enforcing agency may consider requirements for storm water drainage and retention as permit requirements for the project.
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