All land use and building permit applications for new structures or additions to
existing structures in Nipomo are required to have drainage plan approval before the
permit can be issued. The drainage plan must provide for the retention of storm
water runoff on the same site as the building. This requirement applies to projects
within the area shown on the attached map, unless the County Engineer determines
that the building site will neither experience nor create drainage problems. Drainage
plans must be prepared and will be processed as required by Sections 22.05.040
through 22.05.050 of the Land Use Ordinance.

Drainage Plan Requirements. Any new structure built should be safe from flooding.
Drainage shall be retained on-site.

Drainage Plan Review. When reviewing drainage plans submitted by applicants, the
Engineering Department will use the following guidelines for site drainage and for
sizing and locating retention basins:

1. Drainage basin capacity: For planning purposes and site layout: the required
   volume of the basin in cubic feet will be generally determined by dividing the
   total square footage of impervious surfacing on the lot by three.
2. Drainage basin and construction specifications: Where required, drainage and
   retention basins shall be designed and constructed in accordance with the
   following standards.

• Recessed planters and drainage basins shall not exceed 2-feet in depth.
• Side slopes of drainage basins must be planted to minimize erosion and
  shall be no steeper than 3:1
• Retention basins that cannot be readily accommodated on a lot will
  require submittal of an engineered drainage plan. 

Addition to Existing Buildings. Approval of permits for additions to existing buildings
shall require the installation of retention basins to handle the actual drainage flow
created by the impervious area being added. If the impervious area being added is
more than 25% of the existing impervious area on the site, a basin shall be provided
to accept runoff for the total impervious area on the site including existing building
structures and flatwork.