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Project: Identification of Discharges in Areas of Special Biological Significance (ASBS)

Background and Objectives

In the mid-1970s, 34 offshore areas along the coast of California were designated as areas of special biological significance (ASBS), requiring protection by the State Water Resources Control Board (SWRCB). Fourteen of these ASBS are located in the Southern California Bight. According to the 2001 California Ocean Plan, no wastes can be discharged into ASBS. Discharges must be located outside the area of influence of ASBS to ensure maintenance of natural water quality conditions. ASBS are classified as State Water Quality Protections Areas (SWQPAs) in the California Public Resources Code.

Despite the designation of SWQPAs as a protected resource, little is known about the presence and types of discharges that occur in these areas. In southern California, the SWRCB has permitted two discharges into these areas under Ocean Plan exceptions: treated wastewater discharges into the San Clemente Island SWQPA, and a desalination brine discharge into the San Nicolas Island SWQPA. Prior to this survey, though, no substantial information existed regarding other point and nonpoint sources in SWQPAs.

This project documented the numbers and types of discharges into each of the 14 southern California SWQPAs. It was the first survey of its kind to identify which sources potentially contribute discharges into these areas.


This study was completed in 2004.


The 14 southern California SWQPAs were surveyed by foot or boat between March 2001 and February 2003 (Figure 1). All discharges within approximately 100 m of the high tide line were documented. The position of each discharge was recorded at the downstream end using a Leica® GS50 backpack global positioning system (GPS) or a Magellan® Color Trak handheld GPS. Discharge width was measured, or estimated when direct access was not possible.

Figure 1. Map of ASBSs in southern California (SA = Sub-Area).

For the purposes of this project, an anthropogenic discharge was defined as a location where a discernable volume of water from an anthropogenic source is released directly into (or immediately adjacent to) the marine environment of a SWQPA. Anthropogenic discharges were classified into the following categories:

1) Wastewater point sources
2) Municipal/industrial storm water point sources (serving multiple properties and likely operated/maintained by a municipality or other government entity)
3) Small storm drain point sources (primarily serving individual residential or commercial properties (or small clusters of those properties))
4) Nonpoint sources (piers; vessel mooring fields; sheet flow from parking lots, roads, stairways, and ramps; wastewater leach fields; anthropogenic erosion/gully formation; military ordinance testing; and rock quarries)

An "outlet" was defined as any naturally occurring water body that drains into or immediately adjacent to a SWQPA, including perennial streams (or their estuaries), ephemeral streams, and naturally occurring gullies in coastal bluffs and cliffs. After post-processing and checking the data for quality assurance, the data were mapped in ArcView 3.2a®.


This first study of SWQPAs in southern California identified a large number of discharge structures. However, this number could have been an overestimate, reflecting the difficulty of legally defining what constitutes a discharge. Identifying obvious discharges (such as pipes and cement culverts) was straightforward, but identifying other conveyances that do not often have associated flows (such as stairs and pathways) was more problematic. Some of these discharge sources were not large collection devices, but rather structures that only slightly enhanced runoff. Since the goal of this study was to determine the types and numbers of discharges into these areas, all conveyances that could lead to discharges into these areas were included.

While inclusion of all structures that discharge into SWQPAs may have led to an overestimate of discharges, other study design elements could have caused an underestimate of discharges into these areas. First, most surveying was completed during periods of little or no rain, preventing visibility of some discharge flows that may have been covered with sand or vegetation. Few drainages were flowing at the time the survey was conducted. Second, only discharges within 100 m upstream of the high tide line were surveyed, which excludes other discharges further inland. Third, many private homes were located within the survey area, which required conducting the survey from a distance to avoid trespassing.

The largest number of discharge conveyances consisted of small storm drains. A single large entity was not identified as being directly responsible for these discharges. Instead, these small storm drains were installed mostly by developers or homeowners to drain individual properties. These smaller drains were primarily located along the mainland, where population size and development has grown in the surrounding areas since the inception of the SWQPAs.

Although any waste discharges from the identified conveyances are illegal, the large numbers of discharge structures identified may present a regulatory problem, in that it may be unrealistic to demand complete removal of paved pathways or flood control structures from heavily developed areas. Further study of existing conditions is recommended. While identifying actual and potential sources of waste discharge, this study does not answer the questions: 1) Is natural water quality being maintained? and 2) Are beneficial uses being protected? Therefore, a study is recommended to determine whether discharges are impacting water quality and beneficial uses in the SWQPAs, and if they are, what the extent of the impact is. An assessment of existing monitoring data on water quality and benthic communities would be valuable in determining the general status of water quality in SWQPAs, and in identifying any specific problem discharges that need to be addressed promptly. These questions will be examined during the Bight'08 ASBS study.


This project was conducted in collaboration with the State Water Resources Control Board.


For more information on Identification of Discharges in Areas of Special Biological Significance (ASBS), contact Shelly Moore at (714) 755-3207.
This page was last updated on: 9/8/2011