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Restoring Hydrology: Breaking Down Tidal Barriers
For decades, coastal and river wetland habitat in the United States has been seriously degraded as a result of the complete or partial blockage of water flow by levees, dikes, and causeways. NOAA is focused on restoring the hydrology of wetland habitat along coasts and rivers by removing or fixing blockages beneath road crossings and breaching dikes and levees.
Estuarine ecosystems are created by the natural ebb and flow of seawater interacting with freshwater. The location, salt content, volume, exchange, temperature, and velocity of water, as well as flooding frequency, all influence coastal ecosystems and the way they function. Floodplains and off-channel river wetlands are also dependent on the flow of water, sediment, and nutrients from the river and nearby land. Some habitat types are more sensitive to changes in hydrology, often resulting in dramatic changes in the ecosystem. Others will shift slowly and perhaps will not be noticeable to the untrained eye.
Estuarine and river wetlands are vital rearing, feeding, and refuge habitat for many commercially and recreationally important fish and a number of threatened and endangered species. These wetlands are also important for flood control and recreation. When degraded by blocked hydrology, coastal and river wetlands are no longer able to provide these essential functions.
Hydrologic Restoration at a Glance
NOAA restoration specialists are:
- Working to restore the flow of water to coastal systems, floodplains, and habitat along rivers.
- Identifying the habitats where hydrologic restoration can make the most impact and where restoration can last the longest in the face of sea level rise and other pressures.
- Developing national goals and best management practices for restoring hydrology to coastal and river wetland systems.
Changing Tides—Examples of the Hydrology Breakdown
Hydrology is the dynamic processes of water within an environment. This includes the sources, timing, amount, and direction of water movement. Below and in the photo gallery are examples of hydrological impacts on different types of habitat.
Open water/ Soft Bottom. When water bodies once open to the ocean’s tides are blocked, they often degrade into a lagoon. These lagoons are less able to sustain species that thrive in the dynamic salt water conditions of the typical tidal marsh and promote bacteria and other life that can harm many naturally occurring fish and plant species.
Tidal marshes. Tidal wetlands have been degraded by pollutants, urban runoff, invasive species, and dredging for shipping or recreation. These wetlands are also lost when they are drained for agriculture and urban development or diked for flood control or other purposes. With the absence of tides, the wetland or tidal marsh eventually gives way to different habitat types altogether.
Seagrass. Seagrasses typically grow in shallow coastal waters, including protected bays and inlets, but they are often fragmented into patches from boats, dredging, and coastal development. In addition, water diversions, dams, sea level rise, changes in salt content of the water, increased erosion and sedimentation rates, and changes in temperature and water quality can adversely affect seagrass habitat.