Metro has many wetlands in its portfolio, and water management is an important tool that scientists use to keep them healthy. People often ask why we can’t let all of them flood naturally. There are three main reasons: dams, development and invasive plants.
Let’s use Metro’s Smith and Bybee Wetlands Natural Area in North Portland as an example.
The Columbia River basin has more than 130 dams for hydropower, navigation and irrigation, and they have changed the way the river flows. For example, the river’s peak flow is only 42 percent of its historic level. This means less water is available to wetlands in the river’s floodplain, including Smith and Bybee.
Development has filled many wetlands. Construction of dikes and levees along the Columbia River and the Columbia Slough has limited the flow of water into Smith and Bybee.
Invasive plants alter systems. Reed canarygrass has modified wetland systems throughout the Pacific Northwest. This “cool season” grass grows in early spring before native plants emerge. Native wetland plants at Smith and Bybee are adapted to spring flood events known as freshets. These “warm-season” plants emerge months later, after freshets would recede. By the time the native plants emerge, the canarygrass is well established and out-competes them.
At Smith and Bybee, we use a water control structure to flood canarygrass, ensure adequate water in wetlands for winter waterfowl and provide off-channel habitat for juvenile salmon seeking refuge from winter floods. We draw down water after canarygrass is weakened and gradually expose mudflats around the large, shallow wetlands. This allows plants to emerge according to their internal clocks, while providing mudflats for migrating shorebirds in summer. Water management is designed to support floodplain forests, emergent wetlands, mudflats and remnant ponds to maintain diverse, healthy habitats.
How do we know it’s working? In partnership with Portland State University, Metro brings in graduate students to conduct detailed monitoring of plant responses to water management at Smith and Bybee. Reed canarygrass covered 49 percent of the area in 2003, when we began monitoring and installed the water control structure.
By fall 2016, work done by our third student found the reed canarygrass covered less than 18 percent. Our management has been successful in reducing this invasive plant.
In addition to controlling invasive reed canarygrass, the water control structure enables us to ensure an adequate supply of water in winter and spring. In a changing climate, where snowmelt is expected to occur weeks earlier by mid-century, we can retain water in the wetlands later into spring and early summer to accommodate the needs of fish, wildlife and plants. Water management might become even more important in future decades and might serve as a bridge during the transition as plants and animals struggle to adapt to rapidly changing conditions.
Water management at Smith and Bybee is just one way that Metro uses science to restore and maintain the land in our care. See for yourself with a visit to Smith and Bybee Wetlands to walk the trails or look for turtles.