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Snohomish County Area, Washington
<br />flight. A seasonal perched water table is at a depth of
<br />J to 36 inches from January to March.
<br />Urban land is areas that are covered by streets,
<br />buildings, parking lots, and other structures that obscure
<br />or alter the soils so that identification is not possible.
<br />The Alderwood soil in this unit is used mainly for
<br />parks, building sites, lawns, gardens, and woodland.
<br />The main limitations of the Alderwood soil for
<br />homesites and septic tank absorption fields are the
<br />depth to the hardpan and the seasonal perched water
<br />table. Onsite waste disposal systems often fail or do not
<br />function properly during periods of high rainfall. Drainage
<br />is needed if buildings with basements and crawl spaces
<br />are constructed. Topsoil needs to be stockpiled during
<br />site preparation and subsequently used to cover the
<br />exposed material. Additions of fertilizer and peat are
<br />desirable prior to seeding grass for lawns.
<br />This map unit is in capability subclass IVe.
<br />6—Alderwood-Urban land complex, 8 to 15 percent
<br />slopes. This map unit is on till plains. Areas are irregular
<br />in shape and are 25 to 100 acres in size. The native
<br />vegetation is mainly conifers and hardwoods. Elevation is
<br />50 to 550 feet. The average annual precipitation is about
<br />40 inches, the average annual air temperature is about
<br />50 degrees F, and the average frost -free season is 170
<br />to 190 days.
<br />This unit is about 60 percent Alderwood gravelly sandy
<br />'-am and about 25 percent Urban land. The components
<br />!his unit are so intricately intermingled that it was not
<br />,..actical to map them separately at the scale used.
<br />Included in this unit are small areas of Everett and
<br />Indianola soils on terraces and outwash plains, Kitsap
<br />soils on terraces and terrace escarpments, and Ragnar
<br />soils on outwash plains. Included areas make up about
<br />15 percent of the total acreage.
<br />The Alderwood soil is mode: •ately deep and
<br />moderately well drained. It formed in glacial till. Typically,
<br />the surface layer is very dark grayish brown gravelly
<br />sandy loam about 7 inches thick. The upper part of the
<br />subsoil is dark yellowish brown and dark brown very
<br />gravelly sandy loam about 23 inches thick. The lower
<br />part is olive brown very gravelly sandy loam about 5
<br />inches thick. A weakly cemented hardpan is at a depth
<br />of about 35 inches. Depth to the hardpan ranges from
<br />20 to 40 inches.
<br />Permeability of the Alderwood soil is moderately rapid
<br />above the hardpan and very slow through it. Available
<br />water capacity is low. Effective rooting depth is 20 to 40
<br />inches. Runoff is slow, and the hazard of water erosion
<br />is slight. A seasonal perched water table is at a depth of
<br />18 to 36 inches from January to March.
<br />Urban land consists of areas that are covered by
<br />streets, buildings, parking lots, and other structures that
<br />obscure or alter the soils so that identification is not
<br />possible.
<br />The Alderwood soil in this unit is used mainly for
<br />ks, building sites, lawns, and woodland.
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<br />The main limitations of the Alderwood soil for
<br />homesites and septic tank absorption fields are the
<br />depth to the hardpan and wetness because of the
<br />seasonal perched water table. Drainage is needed if
<br />buildings with basements and crawl spaces are
<br />constructed. Onsite sewage disposal systems often fail
<br />or do not function properly during periods of high rainfall.
<br />Topsoil needs to be stockpiled during site preparation
<br />and subsequently used to cover the exposed underlying
<br />material. Additions of fertilizer and peat are desirable
<br />prior to seeding grass for lawns.
<br />This map unit is in capability subclass IVe.
<br />7—Bellingham silty clay loam. This very deep, poorly
<br />drained soil is in depressional areas. It formed in
<br />alluvium and lacustrine sediment. Areas are regular in
<br />shape and are about 2 to 25 acres in size. The native
<br />vegetation is mainly grass and sedges. Elevation is 50 to
<br />800 feet. Slope is 0 to 3 percent. The average annual
<br />precipitation is about 45 inches, the average annual air
<br />temperature is about 50 degrees F, and the average
<br />frost -free season is 160 to 180 days.
<br />Typically, the surface layer is very dark gray silty clay
<br />loam about 9 inches thick. The subsoil to a depth of 60
<br />inches or more is mottled, gray and olive silty clay.
<br />Included in this unit are small areas of Terric
<br />Medisaprists, very poorly drained organic soils, Norma
<br />soils along upland drainageways, Kitsap and Pastik soils
<br />on terraces, and Bellingham soils that have been
<br />drained. Included areas make up about 10 percent of the
<br />total acreage.
<br />Permeability of this Bellingham soil is slow. Available
<br />water capacity is high. Effective rooting depth is limited
<br />by a seasonal high water table that is at a depth of 0 to
<br />about 12 inches from November to June. Runoff is very
<br />slow, and the hazard of water erosion is slight. Ponding
<br />occurs from November to June.
<br />This unit is used for pasture, woodland, urban
<br />development, and wildlife habitat.
<br />This unit is s::ited to pasture if the excess water on the
<br />surface is removed. Tile drains or open ditches can be
<br />used if suitable outlets are available. Grazing when the
<br />soil in this unit is wet results in compaction of the
<br />surface layer, poor tilth, and reduced infiltration. Use of
<br />proper stocking rates, pasture rotation, and restricted
<br />grazing during wet periods helps to keep the pasture in
<br />good condition. Proper grazing practices, weed control,
<br />and fertilizer are needed for maximum quality of forage.
<br />This unit is suited to red alder. On the basis of a 50-
<br />year site curve, the mean site index is 83. The mean
<br />annual increment at culmination (CMAI) for red alder at
<br />age 40 is 89 cubic feet per acre. Among the trees of
<br />limited extent on this unit are Douglas -fir, bigleaf maple,
<br />western redcedar, and western hemlock. Among the
<br />common forest understory plants are trailing blackberry,
<br />western swordfern,' imbleberry, salmonberry, and
<br />„uckleberry.
<br />The main limitation for the harvesting of timber is soil
<br />wetness, which limits the use of equipment to dry
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