Relatively little scientific research or monitoring has occurred in the Pacific Northwest or elsewhere on the biological effectiveness of restoration efforts in heavily urbanized watersheds. With the overarching goal of improving ecological health of its urban creeks, the City of Seattle is testing innovative approaches to stormwater management. We report here on four years of pre-project monitoring data collected over 2006-2009 for one such technique: Natural Drainage Systems (NDS).

This low-impact development approach is designed to modify the quantity, quality, and timing of stormwater delivery to creeks and other water bodies. Seattle Public Utilities has proposed a large-scale NDS within the Pipers Creek basin of North Seattle that will treat approximately 60% of the Venema Creek sub-basin. The focus of NOAAs research effort has been to develop appropriate monitoring parameters and collect baseline data to evaluate the effectiveness of this major restoration action. Our selection of study parameters was guided by specific project goals and includes measures of physical habitat, contaminant loading, and in-stream biota.

We found that the biological health of Pipers Creek is poor compared to forested streams in the Puget Sound region, but comparable to other urban streams in the City of Seattle. The fish community is dominated by cutthroat trout Oncorhynchus clarki; scores for the benthic index of biological integrity (B-IBI) range from very poor to poor; and diatom assemblages are composed of a relatively high proportion of species tolerant of high nutrient levels, organic enrichment, and sedimentation.

Despite poor stream health, densities of cutthroat trout in three of our five study reaches were higher than many urban streams and approaching densities of cutthroat found in natural streams. This may be due to the migratory nature of cutthroat trout, as about half these fish were detected migrating from our study area to lower Piper Creek or Puget Sound.

Results from heavy metal sampling were inconsistent. Zinc concentrations in soil, black fly larvae, and mayfly nymphs collected from Pipers Creek study reaches were significantly higher than for forested streams. We did not detect any differences in copper concentrations between urban and non-urban streams.

We hypothesize that in-stream biological health will improve relative to current baseline conditions following Venema NDS implementation, with treated reaches beginning to more closely resemble forested conditions. Based on statistical power analyses, we recommend that post-project monitoring focus on rate and taxonomic composition metrics rather than simple density measurements. Given the City of Seattles considerable investment of restoration funds towards NDSs, it is critical that post-project data be collected so as to explicitly test these hypotheses. Metal concentrations in soil, periphyton, and benthic invertebrate taxa.