Wetland Mapping and Classification of the Kenai Lowland, AlaskaMike Gracz Karyn Noyes Phil North Gerald Tande 21 March 2008
We classified and mapped 350,811 acres of wetlands over a 809,370 acre project area at a scale of 1:24,000 on the Kenai Lowlands, Alaska (43% of the land surface). Wetlands are not always obvious. Wetlands present unique construction challenges. Septic systems, basements, foundations and roads are expensive to construct correctly on wetlands, even without considering effects on water movement and quality, neighbors, and habitat. However, if these other effects are not considered, the cost of future repairs becomes expensive. Many US towns and cities would jump at the opportunity to turn the clock back to where we are, and do things right, from the start.
Despite population growth on the Kenai Peninsula, most lowland wetlands are relatively pristine. Few watersheds have greater than about 5% impervious surface cover (roofs, roads, lawns and parking lots), the threshold that caused impairment to stream habitat, and chemistry in an Anchorage study (Ourso and Franzel, 2003). The Kenai Peninsula continues to change however, and nearly 10,000 privately owned, vacant parcels of less than ten acres are located on wetlands (figure 1). With increased human activity impacts to wetlands are inevitable. Twenty percent of the wetlands within the City of Homer have already been filled. Maintenance of valuable wetland functions requires careful management in order to avoid the mistakes that have required costly correction elsewhere.
Because wetlands do provide valuable functions that are expensive to fix if ignored, activities on wetlands are regulated under the Clean Water Act. Intuitively, we may think that wetlands are areas where standing water is present year-round. But, generally speaking, any spot where the water table is within a foot of the surface for more than about two weeks of the growing season falls under the jurisdiction of the Army Corps of Engineers and their wetland permitting authority under the Clean Water Act. This means that sites with big trees can still be classified as wetlands. Some landowners have found this out the hard way- they were ready to build, then discovered that soil needed to be hauled away and fill brought in because, although the area did not appear to be wet, excavation revealed otherwise. Those hauling costs have stopped or slowed more than one project. Because wetlands are not always obvious, a map was needed.
Before this project was begun, no complete, accurate wetland map was available. The first step to making a wetland map is to name, or classify, wetlands. Batten et. al. (1978) named Alaskan coastal wetlands using plant criteria, but they were limited to wetlands influenced by tidewater. Rosenberg (1986) named wetlands with regards to bird use near the mouth of the Kenai River. His classification covers a limited area near the mouth of the Kenai and Kasilof rivers. A more recent effort built a Hydro-Geomorphic Model (HGM) for two classes of wetlands, River Proximal and Slope, in the lower Kenai River watershed. This model applies to a limited area, and describes just two classes of wetlands.
The only available map for the entire lowlands, produced by the US Fish and Wildlife Service's National Wetlands Inventory, is incomplete and contains numerous mapping errors. Additionally its classification names our wetlands in a general, national context. While this is useful for national purposes, a more locally scaled map was needed.
In 1999, a locally scaled classification and mapping project was begun. Since wetlands are controlled by their position on the landscape (geomorphology) and the amount of water that moves through them (hydrology), a classification was developed to name wetlands to reflect local landscapes and water levels. This locally tailored classification should lead to a map that can predict valuable wetland functions. The final map was finished in 2004.
The classification is in two parts, the first is based on plant occurrence and abundance and the second is based on local "ecosystems". The ecosystem names incorporate dominant landscape features. Each ecosystem is further divided into groups using water table depth. The groups are combined to make wetland names. The classification and map has been used to assign habitat functions for three key wetland animals: coho, sandhill cranes, and caribou.
Wetlands were mapped using stereo-paired aerial photography in the office, and then extensive field visits over a period of four years. Not all wetlands could be visited, and some wetlands are more difficult to map than others. Interpreting where the boundary between spots with a water table within a foot of the surface for two weeks of the growing season meets a spot with a deeper water table can be difficult on the ground, let alone using aerial photographs in the office. Many tools, including the National Wetland Inventory and the recent National Resources Conservation Service Soils map and data were used, and many difficult spots were checked on the ground.
The majority of wetlands on the Kenai Lowlands are obvious vast peatlands (bogs, muskeg, and fens). Nonetheless, other wetlands, especially those mapped as "SL" and "WU", are less obvious and typically on the margin with uplands. Those wetland boundaries should be examined closely if a project is contemplated. "SL" wetlands are Lutz Spruce Discharge Slopes. These spots often occupy the wetland / upland boundary, so should be examined in the detail needed at a specific site for a specific project. Wetlands mapped as "WU" are in Wetland/Upland Complexes. These complexes are areas where wetlands and uplands mix at a scale too fine to map using our aerial photographs. This map unit indicates that wetland conditions are likely over at least a third of the area, but upland conditions are also found within the complex. Again, these sites should be examined in the detail needed at a specific site for a specific project.
Interactive Wetland Map on the Web
The wetland map is available to anyone with a web browser and internet connection. The Kenai Borough supports an Internet Map Server (IMS), where these wetlands can be viewed along with parcel lines and other useful information. Here is a brief description on how to use the IMS: after reading the introductory page (click on page to go there), and accepting the disclaimer to continue, wait for the program to retrieve the initial map data. Then use the "Zoom to:" drop-down menu, at the upper right of the window to pick a locality, such as Kachemak City or Kasilof. Once you are re-directed to your chosen locality, you can zoom in further by clicking on the "Zoom In" tool along the left margin of the window. Use that tool to click and hold to draw a rectangle around a specific area of interest. After you have zoomed to an area of interest you can turn on the wetlands layer by clicking in the square box next to Wetlands, under Hydrography, on the right. Then make the wetlands layer active, by clicking the round circle (radio button). Then use the hotlinks tool on the left, shaped like a lightning, bolt to click on a wetland; URL links will display in the lower frame. Click on one link to visit a general description of the wetland, with soils, plant, and water table information; or the other to view photo of the site, if it has been visited. The FAQ on the initial page provides a helpful description of the many other tools available over the IMS.
We hope this information will assist prospective and current landowners when they make decisions affecting resources beyond their boundaries.
Click below for more detail on any aspect of this project.
Download final shapefile (v3. 14.6Mb- In ArcView 9.x you'll need to point to the layer's data source, under 'properties', 'source' to view the full legend). Metadata. Includes Seward wetlands, complete Habitat Function fields and a full 283 element legend covering both Seward and the Lowlands.
Download a QuickGuide to Kenai Wetland Ecosystems and Mapping Units: zipped html (1.1Mb), or zipped Word 2000 format (799 Kb).
SEWARD WETLAND MAPPING PROJECT
|Contact: Mike Gracz Kenai Watershed Forum PO Box 15301 Fritz Creek, AK 99603||
21 March 2008 12:38