Functionality Enhancement of The Nature Conservancy's Tide Gate Optimization Decision Support Tool

Estuaries are exceedingly valuable for the biodiversity they harbor and the ecosystem services they provide to resident and migratory species. Despite their enormous importance and value to both biodiversity and humans, estuaries represent some of the most de-graded habitats and continue to be stressed by threats from human activities on the ocean, on land, and in freshwater.
Over time thousands of acres on the Oregon Coast have been drained, and infrastructure—such as tide gates, levees, and channels—has been built to control the tide, reduce flooding, and drain the land. This infrastructure supports the use of roads, buildings, and productive working lands. But it can also prevent salmon, lamprey, and other aquatic species from accessing the historical streams and floodplains that are vital for their foraging, spawning, refuge, and rest, as well as transition zones between freshwater and marine ecosystems.
Much of the tide gate infrastructure along the West Coast is reaching its maximum life expectancy. A challenge facing landowners interested in replacing their tide gates is that new devices are expensive. Modern construction materials, coupled with the sophisticated designs necessary to meet current fish passage regulations, are not affordable to many landowners. At the same time, government agencies and private organizations interested in conservation and wildlife, such as salmon, are eager to help upgrade and modernize tide gate infrastructure.
The Nature Conservancy (TNC) is interested in solutions that allow for the productive use of coastal lands while providing access to habitats needed for wildlife to thrive. Over the past few years, TNC has taken a widely used fish passage optimization model (O’Hanley 2014) and applied it in a new and innovative way to assist tide gate removal and replacement decisions.
After the initial test runs in the Coquille and Coos estuaries, TNC sought to further develop the tool to add functionality beyond fish habitat gains and provide more information to a larger set of stakeholders in sup-port of tide gate decision-making. In this white paper, TNC describes the information-gathering step to learn about stakeholder interests, the investigation to identify relevant spatial datasets to support additions to the tool, and the enhancements added to provide a useful decision-planning tool to a range of stakeholders.

Both NOAAs and the Oregon State coho recovery plans list juvenile access to floodplains (connectivity and complexity) as the #1 limiting factor for recovery of the species on the Oregon coast. Fish able to access estuaries to feed and rest, grow larger than the fish that are rearing in the rivers without access. These same fish entering the sea at larger sizes have a better chance of survival and a better chance of returning home to spawn.

The tide gate optimization decision support tool can inform which tide gates along the Coast of Oregon are key for maximizing fish passage and habitat gains for four anadromous fish species while simultaneously prioritizing the use of limited funds.