Depending on your location and what data are available in your area, to create a baseline map of wetlands for VSP planning and implementation, we have provided some key recommendations below. In addition, some areas may need multiple datasets that can be downloaded digitally.
The Washington State Department of Agriculture maybe able to assist with creating GIS maps displaying the intersection of wetlands and agriculture. For assistance, please contact Perry Beale at the Washington Department of Agriculture at email@example.com or 360-951-9098.
- Locations with local inventories: Where available, use wetland inventories and maps that have been completed by local entities. Local efforts may have produced better maps using high-resolution imagery or improved technology than are available at the state or national level. These may be the most complete source of information.
- Western Washington / east slopes of the Cascades without a local inventory: Use the Wetlands Change Analysis Modeled Wetland Inventory maps together with the National Wetlands Inventory (NWI) maps. The NWI may identify smaller wetlands not mapped in the Modeled Wetland Inventory. Also use the National Hydrography Data (NHD) to map streams and other water bodies.
- Other parts of Eastern Washington without a local inventory: Use NWI with National Hydrography Data.
We worked in partnership with NOAA's Coast Change Analysis Program (C-CAP) to carry out the Wetland Change Analysis project. To more accurately map Washington wetlands, C-CAP was used to develop a method to create a Modeled Wetlands Inventory. The inventory is based on a land cover classification using Landsat scenes analyzed according to C-CAP protocol to determine land cover. This involved extracting the wetlands land cover classifications from the overall land cover layer.
NOAA applied the improved wetland layer to previous C-CAP analyses that occurred between 1992 and 2016. C-CAP will use the improved wetland layer for land cover mapping and analyses every five years.
The Modeled Wetlands Inventory:
- Is more accurate than the National Wetlands Inventory for wetlands larger than one acre, especially in agricultural/pasture, forests, and stream corridors.
- Includes a "Potentially Disturbed Wetlands" category for areas that have a high potential to be wetland, but have an observed land cover of "pasture/hay" or "cultivated."
- Can be used for planning purposes and for initial permit review.
- Most wetlands one acre or less in size are not mapped.
- The data are less accurate detecting forested and slope wetlands.
- The inventory identifies areas that have a high potential to be wetlands. Locations of mapped wetlands are approximate due to the medium resolution scale. The absence or presence of a wetland on the map does not mean that the wetland is actually absent or present.
For counties outside the area where Ecology has Modeled Wetlands Inventory data, the land cover in the interior of Washington is available from the National Land Cover Database (NLCD). It is mapped by USGS through Multi-Resolution Land Characteristics Consortium (MRLC).
The National Wetlands Inventory is the only statewide map of wetlands. It was created by the U.S. Fish & Wildlife Service (USFWS) for the entire country using interpretation of aerial photographs at various scales.
In much of Eastern Washington, it is the only wetlands map available. However, USFWS policy is to exclude certain types of "farmed wetlands" from the inventory. There is no record of the types or locations of farmed wetlands excluded from the NWI covering Washington.
- The maps are nearly 40 years old and much has changed.
- As mentioned, certain types of "farmed wetlands" were excluded from NWI mapping.
- Certain wetland habitats are also excluded such as seagrasses or submerged aquatic vegetation. Forested wetlands and wetlands on slopes may either be missed or mapped as smaller than what occurs on the ground.
- A NWI wetlands mapper describes the data limitations.
The National Hydrography Dataset (NHD) is used to show surface water on the national map at a 1:24,000 scale. These data are designed to be used in general mapping and in the analysis of surface water systems such as rivers, streams, canals, lakes, ponds, coastline, dams, and stream gages. The NHD is produced by the U.S. Geological Survey (USGS) and we manage the data for Washington.
This data set can be used to supplement wetland inventories to show how mapped wetlands relate spatially to other surface water bodies.
- To maintain mapping clarity, not all water features are represented, including those using a moderate level of detail.
- They divide their map units by HUC watersheds. However, you can download HUC 4 region and add WRIA boundaries.
Josh Greenberg, PhD. GISP
Washington State NHD Steward