US Army Corps of Engineers
Los Angeles District

Baseline Habitat Integrity for the SDC Watershed SAMP


Baseline Ecosystem Integrity

The Riparian Ecosystem Restoration Plan (2004) for the San Diego Creek Watershed defined linear corridors ("riparian reaches") of variable width that occur along perennial, intermittent, and ephemeral streams that exhibit distinctive geomorphic features and vegetation communities in response to periodic exchange of surface and ground water between the stream channel and adjacent areas. Riparian reaches were defined as discrete segments of the mainstem, bankfull stream channel, and the adjacent riparian ecosystem that were relatively homogenous with respect to geology, geomorphology, channel morphology, substrate type, vegetation communities, and cultural alteration.

Each riparian reach unit was assessed using a suite of indicators that represent physical, chemical, and biological factors influencing riparian ecosystem integrity at the three spatial scales: the riparian reach, the local drainage (area contributing to tributary, groundwater, and overland flow that directly enters the riparian reach), and the drainage basin (area contributing to mainstem inflow from upstream of a riparian reach). Indicators were scaled to a reference condition and then combined into indices for hydrologic, water quality, and habitat integrity:
  • Baseline Habitat Integrity Index: Riparian ecosystems with habitat integrity exhibit the quality and quantity of habitat necessary to support and maintain a balanced, integrated, adaptive biological system having the full range of characteristics, processes, and organisms at the site specific, landscape, and watershed scales that historically characterized riparian ecosystems in the region. Several factors were considered in selecting indicators of habitat integrity including the spatial extent and quality of riparian habitat, the “connectedness” of riparian habitats at the riparian reach and drainage basin scales, and the spatial extent and quality of upland habitat in the landscape adjacent to riparian ecosystems.
  • Baseline Hydrologic Integrity Index: Hydrologic integrity was defined as exhibiting a range of frequency, magnitude, and temporal distribution of stream discharge along with a concomitant surface and subsurface interaction with the floodplain that historically characterized riparian ecosystems in the region. In the arid southwest, this translates into seasonal intermittent, ephemeral, or low flow periods, with annual bankfull discharges superimposed on a background of episodic, and often catastrophic, larger magnitude floods that inundate historical terraces.
  • Baseline Water Quality Integrity Index: Water quality integrity was defined as exhibiting a range of loading in the pollutant categories of nutrients, pesticides, hydrocarbons, and sediments that are similar to those that historically characterized riparian ecosystems in the region. Assessing changes in the range of loading in each pollutant category can be determined directly by comparing data on current loading with data on historical loading when such data is available. While there is some historical and recent monitoring data available for a limited number of stations in the watershed, little or no loading data is available at the riparian reach scale. Consequently, the assessment of water quality integrity was based on indicators of drainage basin and riparian reach characteristics that have been shown to influence water quality integrity.
Final scores for baseline habitat, hydrologic, and water quality integrity for each riparian reach can be viewed using the map below (best viewed using Chrome or Firefox) :