US Army Corps of Engineers
Los Angeles District

Assessment of Riparian Ecosystem Integrity (2000)


Baseline Ecosystem Integrity

The Assessment of Riparian Ecosystem Integrity (2000) involved conducting a baseline assessment of riparian ecosystem integrity in watersheds under current conditions by dividing the riparian ecosystems into assessment units or “riparian reaches” and assessing each riparian reach using a suite of indicators of ecosystem integrity. Establishing baseline conditions allows for a comparison between riparian ecosystem assessment units under current condition, and for a comparison of riparian ecosystem integrity under current and future conditions. Such comparisons will guide the decision-making process concerning future development projects by ensuring avoidance and minimization of impacts to these resources, both individually and cumulatively.

Hydrologic, water quality, and habitat integrity were identified as three quantities of interest, or assessment “endpoints” to represent riparian ecosystem integrity. The selection of these endpoints follows directly from the mandate in Section 101(a) of the Clean Water Act to “…restore and maintain the chemical, physical, and biological integrity of the Nation’s waters”:
  • Baseline Habitat Integrity: 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: 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: 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):