Drainage Guidelines for Single Family Dwellings

County of Santa Cruz Public Works Department
701 Ocean Street - Room 410
Santa Cruz, CA 95060

DRAINAGE REQUIREMENTS FOR SITE PLANS

To be approved, proposed building projects must conclusively demonstrate that:

• The site is being adequately drained.
• Site runoff will be conveyed to the existing downstream drainage conveyance system or other safe point(s) of release.
• The project will not adversely impact roads and adjacent or downslope properties.

More specifically, an adequate site plan will typically include the following:

• Topographic information, such as existing and proposed ground elevations or labeled contour lines, particularly as such information pertains to the existing and proposed pathways of runoff.
• Specific drainage features, such as existing and proposed curbs, natural drainage channels, creeks, dikes, ditches, swales, rain gutters, splash blocks, storm drain inlets and pipe systems, french drains, driveway culverts, energy dissipators, etc.
• The methods by which stormwater runoff from roofs and other new impervious areas--such as driveways, walkways and patios--will be conveyed away from structures to safe points of release. Use arrows to depict pathways of runoff.
• Clear indication of where the stormwater runoff will go when it leaves the site. Any unusual conditions within the affected drainage courseway (such as evidence of erosion or flooding) must be noted. In some cases Public Works staff will request a more detailed drainage analysis or the approval of an appropriate professional, such as a geotechnical and/or a civil engineer, on behalf of the applicant. For projects requiring offsite work, analyses and plans shall be completed by a licensed civil engineer.
• For drainage plans involving new developments and additions over 500 square feet: Projects within GROUNDWATER RECHARGE or WATER SUPPLY WATERSHED ZONES are required to limit runoff release to predevelopment rates. This generally requires an engineered drainage plan involving retention of concentrated runoff with sizing calculations based on site soil infiltration rates and a geotechnical engineer’s assessment of slope stability. Runoff and percolation rates should be reported in cubic feet per second.

STORM DRAINAGE ZONE FEES

The drainage impact of a proposed project depends, in part, on how much land area is to be made impervious by addition of covered structures and paved areas including buildings, driveways, walkways, patios and concrete decks. Projects within Storm Drainage Zones of the Santa Cruz County Flood Control and Water Conservation Districts are subject to an impervious area fee based on the net increase in impervious area. Baserock-covered driveway areas are considered impervious and are subject to regular Storm Drain Zone fees unless they are less than 4 inches thick, in which case fees are assessed at 50% the normal rate.

To receive credit for previously permitted impervious areas being removed, replaced or modified, applicants may submit evidence of existing impervious area; evidence may be gathered from available sources (e.g., assessor’s records, dated aerial photos, prior building permits). Drainage review staff will use plans, maps, and other information in department files to ascertain the accuracy of submitted plans. These materials are available through the County Surveyor and are regularly consulted by applicants and their agents, professionals and the public at large.

Note: To expedite drainage plan review and fee calculation, please conform to the following labeling conventions on site plans: All impervious area to be added by the proposed project should be highlighted or hatched on the site plan and labeled “N” for new. Any pre-existing impervious areas should be labeled “E” for existing. Existing impervious area to be removed should be labeled “E, TO BE REMOVED.”

LET US HELP

Drainage division staff can assist you with drainage plans.
Please contact us at:

Drainage Division
County of Santa Cruz Public Works Department
701Ocean Street - Room 414
SantaCruz, CA 95060
(831)454-2160