By Tom Dean, Zach Ferdaña, Jacques White and Curtis Tanner

The sub-estuaries of Puget Sound — the major river deltas — have suffered a collective 80% loss of tidal marsh habitats in the past 150 years. In order to restore balance, function and health to this ecosystem and natural resources, People for Puget Sound, a nonprofit regional environmental group has been developing protocols to systematically look for opportunities to reverse this loss by restoring salt marsh and other estuarine intertidal habitats.

The Skagit Estuary Restoration Assessment has two goals. The first is to identify the extent of habitat loss in the Skagit River estuary. The second is to identify and prioritize areas that would be appropriate for restoring estuarine habitat.

This study is not a restoration plan, but rather the ecological basis for developing a restoration plan. Any site-specific restoration plan will have to combine this assessment with social, cultural and economic values and activities in the Skagit River delta and drainage. Development of a delta restoration plan will ultimately be accomplished through coordination and adoption by an open, community-based organization like the Skagit Watershed Council.

Through this study, we have developed a simple system of looking at the physical landscape to sensibly prioritize restoration goals based on the historic estuary. We designed this system with the ultimate goal of applying it to all rural river deltas in the Puget Sound basin.

While restoration of Puget Sound's estuaries is essential for the survival of chinook and other wild salmon, it also provides myriad benefits for birds and wildlife as well as for human recreation and enjoyment of nature. In addition to improving opportunities to catch fish and hunt or view wildlife, restored tidal wetlands provide areas for flood waters to disperse. Various programs and tax laws can provide financial incentives for landowners to engage in restoration of the historic estuarine processes and functions.

Study Location
The Skagit River and its drainage basin encompass a rich history of natural processes and human development. From its headwaters in the North Cascade range to its extensive delta in Skagit County, the Skagit watershed is the largest that drains to Puget Sound. The Skagit was once home to one of the largest runs of wild chinook salmon in Puget Sound, with thousands of fish returning each year, but by 1999 the number of returning wild spawning spring chinook had dropped to 471 fish.

Intensive land modification, primarily logging and draining of lowlands for agriculture, began around 1860. The Skagit River delta was one of the first in Puget Sound to be converted from tidal wetlands to agriculture. A vast and densely vegetated wetland, including a complex system of channels and sloughs extending from the shoreline into the upland forest, was cleared and drained. This made the delta inaccessible or inhospitable to the fish and wildlife that had adapted to those habitats over many centuries.


The Historic Estuary
In order to identify candidate areas for restoration, we needed a better picture of the historic conditions. No survey of the pre-diked delta exists, so we estimated historic conditions by looking at relics of historic sloughs on aerial photos (1993 orthophotos) and comparing them to the U.S. Geological Survey topographic quadrangle maps (photo-revised 1968). Since blind sloughs are carved and/or maintained by tidal drainage, they are a good indication of the historic upper extent of tidal influence. The upper extent of the Skagit's historic blind sloughs describe a line very close to the USGS five-foot contour, which is very close to the highest extent of tidal flooding in the main stem of the Skagit River.
The lightly shaded area shown on Map 1 closely represents an area that was under daily tidal influence before the dikes were built. Because the greatest loss of tidal wetlands in the Skagit has occurred in vegetated wetlands, Map 1 estimates only those areas (tidal mudflats are not included). Of course, not all of this area would have been flooded each day or all year. But the entire area would have been classified as wetland by modern standards, and the sloughs and wetlands would have been accessible to juvenile salmon as rearing habitat.
Map 1 shows that the historic extent of vegetated tidal wetlands for the Skagit was approximately 25,766 acres, and the current extent is 1,941 acres. This means that the Skagit delta has lost approximately 23,825 acres of estuary habitat — more than 37 square miles, or 93% of historic coverage. The Skagit estuary was certainly the largest in Puget Sound, and was of a scale comparable to all other Puget Sound estuaries combined. This finding is consistent with the river’s relatively large flow and historical accounts of the Skagit’s impressive chinook runs.

The Survey Area
Our estimate of the historic estuary stops at +14.4 feet, but two major blind sloughs cross this line. For this reason, and because tidal surges in the main stem extend at least to Mt. Vernon, we decided to extend our region of study from +9.4 to +19.4 feet tidal elevation — about ten feet above mean high tide.
This elevation range provided us with a survey area that would include a variety of vegetated tidal wetlands from emergent marsh to scrub/shrub and forested. This range eliminates the functioning tidal wetlands seaward of the dikes. We excluded from the survey areas above +19.3 feet because tidal influence above this elevation is minimal and largely confined within the main stem of the Skagit River — even historically.
We used a Geographic Information System (GIS) running ARC/INFO and ArcView software to characterize and analyze the region. We converted all the data to grid coverages with a quarter acre cell size to run the analysis.

Prioritizing Areas for Estuary Restoration
Since Puget Sound Chinook salmon were placed on the endangered species list in 1999, many resource managers have been struggling with the question of how to prioritize restoration efforts. The following set of criteria was developed to tackle this question for rural estuaries, based on attributes of landscape ecology and ease of restoration. The criteria are designed to identify the specific areas needed by fish, while at the same time focusing on those areas where humans and fish can live side-by-side.

A scoring system was developed that layered and summed these characteristics to achieve an overall score for each quarter acre cell in the study area. A more detailed description of the process is given on People for Puget Sound’s website, www.pugetsound.org/blueprints/skagit_main.html.

Discussion
The survey area was divided into four categories of priority. Since most of the criteria are water-based, it is not surprising that the high priority areas are associated with the two main stems, the distributary channels, and blind sloughs, which are the current and historic salmon migration routes and rearing areas. The analysis does not suggest, however, that restoration of fish passage is adequate in and of itself. The majority of the highest priority shading covers areas adjacent waterways, so any slough passage restoration should be accompanied by adjacent and connected wetland restoration. Just as with farming, the amount of food produced and entering the estuarine food web is directly related to the amount of vegetated marsh area.

From a cost perspective, projects that could restore areas between fingers of channels or sloughs would be less expensive, as they would allow restoration with less dike modification. These kinds of opportunities show most abundantly at the mouth of the South Fork.

The second-highest priority areas are more focused on large blocks of land adjacent to major stems and channels. Again, this highlights the need for large areas to be restored as the foundation of the chinook salmon food web. From a cost perspective, one very large project would be cheaper than a number of smaller projects. Of course, most of these large areas are currently farmed and contain residences, so any restoration activity would have to be conducted with the cooperation and compensation of the landowners.

The results of this analysis should also be viewed in light of current restoration activity both up stream and in the estuary. The most recent estuary restoration effort has been at the mouth of the South Fork at Deepwater Slough. Since juvenile salmon migrating down stream must commit to one fork or the other, this suggests that the North Fork would present the next area of greatest need for restoration. Most of the effort in the watershed to date has been focused on restoring and re-connecting spawning habitat up stream, which will increase the amount of juveniles moving down stream and looking for rearing habitat. Over time, it will be necessary to restore enough rearing habitat in the delta to assure that upstream efforts actually result in increased numbers of returning spawners.