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Overwater Structures and Non-Structural Piling White Paper

Category: Habitat - Guidelines

Date Published: December 2006

Number of Pages: 218

Author(s): Jones & Stokes Associates, Anchor Environmental, L.L.C., R2 Resource Consultants


In 2006 and 2007, WDFW contracted with Anchor Environmental, Herrera Environmental Consultants, Jones & Stokes Associates, and R2 Resource Consultants to develop a series of “white papers” documenting the state of the science on a range of topics related to HPAs. The original white papers were peer-reviewed by a panel of experts outside of WDFW.

In developing the white papers, the consultants were working under specific time, scope, and cost constraints established by WDFW. These constraints were designed to further WDFW's specific goal of building a scientific foundation for a Habitat Conservation Plan for hydraulic projects that receive HPAs.

The white papers provide a solid scientific foundation upon which to build conservation measures for avoiding potential impacts, but they are not an exhaustive review of every potential impact of hydraulic projects. Rather, they reflect WDFW’s goal of establishing a solid scientific foundation for the HCP with limited time and financial resources.

Despite these constraints, WDFW is confident that a large proportion of the current scientific literature has been incorporated into the white papers. As WDFW continues to develop the Habitat Conservation Plan, we will also continue to assess new science, fill data gaps, and listen to the advice of scientists and hydraulic project construction specialists.


In Washington State, activities that use, divert, obstruct, or change the natural bed or flow of state waters require a Hydraulic Project Approval (HPA) from the Washington Department of Fish and Wildlife (WDFW). The purpose of the HPA program is to ensure that such activities do not damage public fish and shellfish resources and their habitats. To ensure that activities conducted under an HPA comply with the Endangered Species Act (ESA), WDFW is preparing a programmatic, multispecies Habitat Conservation Plan (HCP) to obtain an Incidental Take Permit from the U.S. Fish and Wildlife Service (USFWS) and the National Oceanic and Atmospheric Administration (NOAA) Fisheries Service (known as NOAA Fisheries). WDFWfs objective is to avoid, minimize, or compensate for the incidental take of species potentially covered under the HCP resulting from the implementation of permits issued under the HPA authority. In this context, to gtakeh means to harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect or to attempt to engage in any such conduct (16 U.S.C. 1532(19)).

To evaluate the feasibility of and develop a scientific foundation for the HCP, the WDFW has commissioned a series of white papers that will review and summarize the best available science for up to 21 HPA activities that could be included in the HCP.

This white paper addresses the availability of scientific information on two such HPA activities, overwater structures and the installation and removal of non-structural piling. Overwater structures are defined by WDFW as "docks, piers, floats, ramps, wharfs, ferry terminals and other structures that are supported above or float on the water. This includes all structural or supporting pilings. This does not include structures associated with a Marina." Non-structural piling is defined by the WDFW as "individual, non-structural pilings, power poles, transmission lines, conduits, etc. Pilings are driven into the stream, lake, and ocean bed."

The literature review conducted for this white paper identified 12 impact mechanisms associated with the construction and operation of overwater structures and non-structural piling that could potentially affect aquatic species being considered for coverage under the HCP (gpotentially covered speciesh). These mechanisms describe activities and modifications to habitat arising from activities that can be temporary or permanent in duration. The impact mechanisms evaluated in this white paper are:

  • Shading
  • Littoral vegetation
  • Freshwater aquatic vegetation
  • Riparian and shoreline vegetation
  • Noise
  • Water quality
  • Channel hydraulics
  • Littoral drift
  • Substrate modifications
  • Channel dewatering
  • Artificial light
  • Vessel activities

Following a brief description of overwater structures and non-structural piling activities and potential impact mechanisms, the 52 aquatic species being considered for coverage under the HCP are described. Based on this information, the risks of direct and indirect impacts to the potentially covered species or their habitats are discussed. In addition, the potential for cumulative impacts is discussed, and the risk for incidental take of potentially covered species is qualitatively estimated. The white paper then identifies data gaps (i.e., instances in which the data or literature are insufficient to allow conclusions on the risk of take). The white paper concludes by providing habitat protection, conservation, mitigation, and management strategies consisting of actions that could be taken to avoid or minimize the impacts of overwater structures and non-structural piling.