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Project: Effect of Hydromodification on Beneficial Uses

Background and Objectives

Hydromodification can result in degradation of streams and associated loss of beneficial uses, such as habitat for fish and wildlife, stock watering, fire protection, and recreation. The physical effects of hydromodification (e.g., channel incision and widening) have been well documented, but the effects of hydromodification on beneficial uses, particularly in-stream biota, have received less attention. Ultimately, physical alterations can alter a stream habitat as much as, or more than, poor water quality. Habitat degradation may be particularly pronounced in the case of direct hydromodification effects like addition of in-stream structures (e.g., bank armoring or drop structures). Application of well-established biologically-based assessment tools may help to discern whether management targets are being met in hydromodified streams.

Arroyo Seco showing undercutting of the armored bank (left side of photo) and some scour

The goal of this project was to explore potential biological metrics that can be used to measure the direct impact of hydromodification on beneficial uses.


This project was initiated in 2010 and completed in 2011.


This project included three main tasks. The first was an inventory of channel modifications in the Los Angeles Region. Next, select study sites found to experience direct hydromodification underwent an assessment of biological condition. Researchers lastly performed a restoration case study to determine if the measured biological metrics would respond to stream restoration actions.


• Most study sites exhibited localized channel morphology changes in the armored stream segments. In general, armored segments were flatter (i.e., lower gradient), and contained more and deeper pools with fewer riffles. These flow conditions were also associated with increased sediment deposition.

• Both benthic macroinvertebrate and algal taxa exhibited mechanistic responses to the physical effects of armoring, but sample size and differences among sites made it difficult to draw definitive conclusions. The data suggest that species- or functional group-level metrics may be more sensitive tools than integrative indices of biotic integrity (IBIs) for identifying local effects.

• Neither physical nor biological effects appeared to be propagated to downstream segments.


This project was conducted in coordination with the University of California, Berkeley; University of California, Los Angeles; California State University, Stanislaus; and California State University, Northridge.

For more information on Effect of Hydromodification on Beneficial Uses, contact Eric Stein at (714) 755-3233.
This page was last updated on: 2/27/2012