Suiattle Watershed Analysis Chapter 3 Findings, Synthesis, and Recommendations
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Suiattle Watershed Analysis Chapter 3 - Findings, Synthesis, and Recommendations Table of Contents Chapter 3 - Findings, Synthesis, and Recommendations ......i Introduction ........................................................................................................1 Aquatic Ecosystem Findings ............................................................................1 Water Quality, Hillslope Processes, and Hydrology ...................................1 Aquatic Habitat and Fish Species.................................................................4 Terrestrial Ecosystem Findings........................................................................5 Vegetation.......................................................................................................5 Air Quality .......................................................................................................7 Wildlife.............................................................................................................7 Human Use Findings .........................................................................................9 Timber Management and Special Forest Products.....................................9 Road Infrastructure ........................................................................................10 Communities...................................................................................................12 Recreation.......................................................................................................12 Skagit Wild and Scenic River........................................................................14 Heritage...........................................................................................................15 Synthesis and Recommendations....................................................................15 Aquatic Ecosystem ........................................................................................16 Terrestrial Ecosystem....................................................................................18 Human Uses....................................................................................................20 Chapter 3 Figures Figure 3-1 Aquatic Areas of Concern 24 Figure 3-2 Wildlife Areas of Concern 25 Figure 3 Vegetation Areas of Concern 26 Figure 3-4 Recreational Areas of Concern 27 Chapter 3 - Table of Contents Suiattle Watershed Analysis Introduction Synthesis is the process the watershed analysis team used to identify and evaluate links between the physical and biological functions, processes and uses in the analysis area. Synthesis considers all domains (aquatic, wildlife, vegetation, and recreation) and identifies where overlaps and conflicts occur so that the analysis team can discover opportunities and resource constraints in the watershed. Synthesis was conducted by having each resource area identify areas of concern and findings discovered through the assessment. These concerns and findings were then displayed on a working map so that overlaps, interactions, and potential conflicts could be identified and discussed as a group. This chapter lists the major findings by resource area and then presents the recommendations developed by assessing opportunities and needs in light of resource constraints and management goals for the analysis area. Aquatic Ecosystem Findings Water Quality, Hillslope Processes, and Hydrology Findings • The lower Suiattle River valley and mouths of tributary streams were covered with very fine clay deposited in lakes (lacustrine) caused by ice dams that blocked the Skagit and Sauk Rivers during the last glaciation. As the glaciers on Glacier Peak receded, coarse glacial outwash material was deposited over the lacustrine clay. These strata develop unique soil structural and textural characteristics that influence soil drainage properties and produce unstable hillslopes and river terraces. This is clearly evident where Road 26 traverses the high Suiattle River terrace. The road surface is irregular and in some areas the face of the terrace is actively failing. • Glaciers also filled in hillslope hollows with glacial drift material. These hollows are also very unstable. Glacial drift is common within the inner gorges in Grade/Big, Buck, Downey, and Sulphur Creeks. Drift is less common in Straight, Lime, Miners and Milk Creeks. • Glacier Peak eruptions generated dozens of lahars (mudflows) that inundated the valley floor. These lahar deposits infilled valleys and covered the lacustrine and glacial outwash deposits. Subsequent erosion by streams results in steep inner gorges at the mouths of smaller streams and deep terraces along the mainstem Suiattle River. The inner gorge slopes and terraces are prone to failure due to the high and variable pore pressures caused by the layered coarse and fine deposits. A characteristic chronic river terrace failure is near MP 6 on Road 26. Chapter 3 – Findings, Synthesis, and Recommendations, Page 1 Suiattle Watershed Analysis • Erosion of lahar deposits on Glacier Peak by Chocolate Creek causes flushes of fine sediment during the summer months. Often the quantity of sediment is sufficient to make the lower Suiattle, Sauk and Skagit Rivers very turbid, and may inhibit fish spawning and foraging. These sediments deposit in slow and backwater areas where it reduces the quality of aquatic habitat. Therefore, clear water, low gradient tributaries are important for providing high value refugia for salmonids during these turbid times. • The Straight Creek fault runs through Straight Creek and captures the Suiattle River from Straight Creek to Big Creek. The Suiattle River has downcut more at the fault and has exposed and destabilized lacustrine sediment deposits. • S8 soils (known to be prone to mass wasting) are common throughout the area mapped within the lower Suiattle River watershed, and cause major maintenance problems for roads. S8 soils were not mapped in the Glacier Peak Wilderness area, but do exist. • Recent glacial retreat has exposed large areas of bedrock in the upper Suiattle River watershed. Extensive rock outcrop and talus slopes, a high proportion of steep slopes, and a high stream density result in rapid (flashy) runoff. But snow avalanching has diminished. • A low amount of the prominent rain-on-snow zone and large area within the highland precipitation zone make this watershed less prone to rain-on-snow floods. The October 2003 flood was not a typical rain-on-snow event because a snow pack had not developed. Melt from the highland zone and glaciers contributed to the record flood peaks of the 2003 flood. • The current vegetation disturbance for the analysis area is very low. Most subwatersheds have a low vegetation disturbance level, with the exception of the Lower Suiattle/Tenas Creek subwatershed that contains a high proportion of private land. The highest disturbance levels for the analysis area were from large, stand replacing fires around 1300, 1508, and 1701. A large area of the Suiattle valley, from Lime Creek downstream, burned in 1834. Rain- on-snow effects from timber harvest and roads were greatest in the 1970s and 1980s in Grade, Tenas, Conrad, and All Creeks, and the mainstem below Downey Creek. Chapter 3 – Findings, Synthesis, and Recommendations, Page 2 Suiattle Watershed Analysis • Clearcut harvesting occurred up to the 1980s included cutting up to the stream banks in areas of the lower watershed. This affected the river terraces along the Suiattle mainstem and tributaries such as All, Conrad, Grade, Big, Straight, Circle, and a number of small, unnamed channels. While much of the rest of the analysis area has mature trees lining the channels for shade, bank stability, and large wood recruitment, these other areas are missing some of these attributes. (The lower potion of the Suiattle River has had timber harvest into the 1990’s, and there are active sales in the 2000’s on private lands. Only portions of the following streams -- All Cr., Conrad, Grade, Big, Straight, Circle, etc. had trees cut to the stream. • Only seven percent of the streams are two percent gradient or less. The best spawning and rearing fish habitat is in the low gradient streams. One third of streams two percent gradient or less are also Stream Class 1. Forty-three percent are Class 1 or 2 streams. While the percentage is small, there are still 67 miles of valuable habitat represented by the Class I and 2 streams two percent gradient or less. These stream reaches are also in the portion of the watersheds where forest management has occurred. • Where non-forest or shrub vegetation coincides with highly erosive soils, there is heightened concern for streambank erosion. There are approximately 125 miles of stream channel in the Suiattle analysis area where this situation occurs. Most of these miles are in the Miners Creek and Suiattle River Headwaters subwatersheds, where streams have cut through the volcanic ash depositions. There are another 21 miles of erosive soils and sapling vegetation, most of which is in Circle and Big Creeks and the Lower Suiattle River/Tenas Creek subwatersheds. • Road failures are a concern. Unstable, steep slopes and avalanche chutes adjacent to roads increase the probability of debris plugging road drainage features and resulting in road failure. Roads constructed on inner gorge landforms are at especially high risk of failure resulting in debris flows with high coarse sediment delivery directly to streams. • Roads are not being maintained to standards due to a