US Army Corps of Engineers
Los Angeles District

Planning Level Delineation (2000)


A planning level delineation of aquatic resources was performed within the San Diego Creek Watershed in Orange County, California. A planning level delineation is defined here as the identification of areas that meet the jurisdictional requirements under Section 404 of the Clean Water Act, but is done at watershed scale and covers regulated water bodies (including aquatic resources regulated under the California Department of Fish and Game 1600 Code) at a high level of accuracy but it is not specific to any one site. Thus, a planning level wetland delineation does not replace the need for a jurisdictional wetland delineation from the Corps of Engineers (COE) permitting program.

The following GIS layers were produced as a result of the Planning Level Delineation:

  • Regulatory Probability Rating Units: A final map for WoUS, including wetlands, was developed by assigning probability ratings for regulatory purposes to the riparian vegetation/hydrogeomophic base map. These designations were made based on the results of the field verification sampling, and by evaluating the hydrology for each geomorphic surface, and its vegetation type. These designations were further evaluated using GIS software to compare their spatial distribution patterns with those of other types (e.g. watersheds, human disturbance and geomorphic surfaces).
  • Hydrogeomorphic Floodplain Units: Geomorphic surfaces mapped in the riparian zones representing several different return intervals were used to inform the Corps' determination of WoUS probability ratings at a watershed scale. Hydrogeomorphic floodplain surfaces mapped included abandoned floodplain/terrace, floodplain, bankfull stream channel, and uplands.
  • Vegetation Species Association Units: Individual vegetation units were sampled at 65 sites to characterize indicators for wetland and non-wetland WoUS. The vegetation units in the riparian areas were then rated in terms of their probability of qualifying as wetland or non-wetland WoUS, which was used to inform final WoUS probability ratings.
  • Mainstem Waterways: These waterways include higher order streams that are associated with riparian ecosystems characterized by two distinct zones: 1) The portion of the riparian ecosystem that is flooded by surface water from the stream channel at least every five to ten years and 2) abandoned floodplains and terraces formed by fluvial processes operating under different climatic or hydrologic regimes.
  • Mainstem Tributaries: These tributaries are ephemeral and intermittent stream types that fall into several different Rosgen stream classes and are generally characterized as steep, entrenched, cascading step/pool streams often in sand and gravel or bedrock and boulder dominated channels.
GIS datasets produced as part of the Planning Level Delineation can be viewed using the map below (best viewed using Chrome or Firefox):