Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 8601
Title: Thornton Creek restoration:  baseline project effectiveness monitoring, 2012-2013
Author/Editor: S. A. Morley, Jason E. Hall, Joshua W. Chamberlin, K. Hanson
Publication Year: 2013
Publisher: National Marine Fisheries Service
Contracting Agency: City of Seattle Department of Public Utilities, Seattle, Washington
Contract Number: MOU DA2012-23
Abstract:

Seattle Public Utilities (SPU) is preparing to construct two urban floodplain reconnection projects in the Thornton Creek watershed of northeast Seattle in 2014.  To evaluate project performance, the utility contracted with the U.S. Fish and Wildlife Service (USFWS) to collect pre-project physical and biological baseline data from 2005 to 2009.  In 2012, the National Oceanographic and Atmospheric Administration (NOAA) was brought in by SPU to collect additional biological baseline data and to develop a postproject monitoring plan that includes evaluation of new hyporheic design elements.

            Data collection by NOAA has been identical to previous USFWS monitoring for periphyton, benthic invertebrates, and fish density.  Sampling in 2012 differed from earlier years by focusing less on physical habitat, expanding upon fishmovement surveys, and adding collection of invertebrate drift and fish diet samples.  This report summarizes data collected by NOAA during 2012-2013 and provides updates on existing pre-project monitoring results collected by USFWS from 2006 to 2009. 

            The overall biological health of Thornton Creek is poor: scores for the benthic index of biotic integrity (BIBI) range from poor to very poor and diatom assemblages are composed of a relatively high proportion of species tolerant of nutrient enrichment.  In the lower watershed, the invasive New Zealand Mud Snail Potamopyrgus antipodarum dominated benthic assemblages.  Both drift and diet samples were comprised largely of aquatic insects and crustaceans, with smaller contributions from the riparian zone.

            The fish community of Thornton Creek is dominated by cutthroat trout Oncorhynchus clarki, at relatively high densities compared to other Puget Sound lowland streams.  Resident trout in Thornton Creek exhibited high rates of site fidelity:  of the 1,051 fish tagged by NOAA, 75% remained in the watershed and 88% were detected within 100 m of their tagging reach. 

            Future biological monitoring should include evaluation of hyporheic invertebrate and microbial assemblages. These samples can be collected by pumping water from piezometers installed within project treatment and control reaches. Hyporheic sampling should also occur at forested reference streams for regional data context.  There is still a short window to collect hyporheic data prior to project construction in 2014. 

            While SPU’s approach to floodplain reconnection is innovative and holds promise for restoring watershed processes at the reach level, it is also largely untested.  We strongly recommend that a minimum of 35 years of postconstruction surface and hyporheic data be collected in order to adequately evaluate project effectiveness, and to help select and guide the design of future floodplain projects across the City of Seattle. 

Description:

Technical report contracted by Seattle Public Utilities that summarizes pre-project biological monitoring of two Thornton Creek floodplain restoration projects.

Files:
Theme: Habitats to Support Sustainable Fisheries and Recovered Populations
Foci: Develop effective and efficient habitat restoration and conservation techniques.
Characterize relationships between habitat and ecosystem processes, climate variation, and the viability of organisms.