Polder Management
Type of Development
Restoration, Reconnection
Topography
Baylands
Longevity
Long Term
Environment
Natural Habitat
Maintenance
Low
Cost
Dependent on scale and current use.
Overview
Polders are human-impacted low lying marshes and mudflats that are surrounded with levees that cut off flows from the Bay and the upper watershed. The lack of water and sediment flow from the watershed and Bay to the polders causes compaction, low amounts of oxygen, low nutrient flows, lack of vegetation, and leaves polders extremely vulnerable to the impacts of rising tides. Managing polders can include adjusting levees by filling– both through natural sedimentation buildup and direct placement of sediment– and dredging, in order to restore the bayland to its original topography. Restoring polders protects shores from tidal erosion and sea level rise and reconnects the baylands to the greater watershed. Each polder along the Santa Clara County Bay divide is used for a different purpose, thus polder management has different meanings in each case. Some are connected to salt ponds, while some are connected to marshes and mudflats. Water and sediment regulation are needed for each polder, but the amount at which it is needed will vary greatly.
Function
Polders connect ecosystems, reduce flooding, control sediment loads, and provide a habitat for birds, as well as native flora and fauna.
Benefit
Reconnecting polders to tidal flats, marshes and mudflats will allow sediment flow to naturally elevate land and decompact the land. Elevated, strong land will slow tides and reduce erosion risks of rising sea levels. Decompacted land has higher storage capacity for water.
Dependency
Hydrologic system, the reconstruction and reconnection of adjacent ecosystems and the greater watershed. Land ownership and fill permits should be considered.
Development Considerations
Polder management should include connection points to existing natural and engineered systems and ecosystems. Development considerations include the degree to which polder revitalization efforts connect to these systems– namely whether dikes should be added or removed to protect the area further or reintegrate it into the surrounding ecosystem. For example, adding sediment often requires a large dredging project, which can be avoided with warping and levee lowering which gradually introduces sediment, and also avoids catastrophe during levee failures.
Environmental Considerations
Changing polders will have great impacts on surrounding areas and if done correctly, polder management should restore surrounding ecosystems.
Maintenance Consideration
There is little to no maintenance required as long as the hydrologic system is adequately restored and there is a regular sediment flow. However, without this reconnection there is a need to continue a sediment supply until the ecosystem can sustain itself. While other maintenance is not required, tracking of progress is valuable for future projects.
Cost Considerations
Dependent on scale and current use.
