Soils of the - Agriculture and Agri-Food Canada

DEWDNEY SOILS (DW)
Location and Extent : Dewdney soils occur mainly near Hatzic, on Nicomen Island and in the Matsqui Valle y
with scattered areas elsewhere on the floodplain of the Fraser River. There are about 110 ha of pure map unit s
and 810 ha of soil complexes dominated by Dewdney soils . The complexes are mainly with Page, Matsqui ,
Fairfield and Monroe soils .
Topography and Elevation : The topography of Dewdney soils is mostly gently to moderately undulatin g
with slope gradients less than 5 percent . The soils are usually either slightly depressional or occupy lowe r
landscape positions when related to adjacent, better drained Monroe and Matsqui soils and lie slightly higher
than the more poorly drained Page soils . Elevations range between 5 and 15 m above sea level .
Parent Material and Texture : Dewdney soils have developed from 20 to 50 cm of medium-textured, stone -
free Fraser River floodplain deposits (laterally accreted) overlying sand . Surface and subsurface textures are
usually silt loam, occasionally varying to loam or very fine sandy loam . The subsoil is mostly medium or fin e
sand, sometimes containing finer textured lenses .
Soil Moisture Characteristics : Dewdney soils are imperfectly drained and moderately pervious . Surfac e
runoff is slow to moderate . Water holding capacity is high in the upper, silty pay, but low in the subsoil . Th e
watertable fluctuates with the level of the Fraser River and also rises temporarily during periods of heavy rainfall .
General Soil Description : Dewdney soils have a silty, cultivated surface about 20 cm deep which is ver y
dark brown and friable . It is underlain by about 10 cm of weakly leached, grayish-brown or yellowish-brown ,
friable, silty material containing a few, reddish or yellowish mottles . This, in turn, is underlain by about 15 cm of
grayish-brown, silty material in which some illuvial clay has accumulated and is firm when moist and breaks t o
hard, blocky clods when dry . It also contains common, reddish or yellowish mottles . Below about 40 cm depth ,
variably coloured, loose, medium or fine sand or alternating silty and sandy lenses occurs . Reaction varies from
medium acid in the surface to slightly acid in the subsoil . Casts and other evidence of earthworm activity are
prevalent in the upper soil layers . Soil classification is Gleyed Eluviated Melanic Brunisol .
Commonly Associated Soils : Fairfield, Monroe, Matsqui and Page soils are frequently closely associate d
with Dewdney soils, either in soil complexes or in adjacent map polygons . Fairfield soils are similar to Dewdney
soils except that the silty surface capping over sand is more than 50 cm thick . Monroe soils differ from Dewdney
soils by also having a silty capping more than 50 cm thick, in addition to being moderately well drained . Matsqu i
soils are texturally similar to Dewdney soils but differ by being well drained . Page soils differ by being poorl y
drained .
Vegetation : Most areas of Dewdney soils are cleared and cultivated . Uncleared areas support mainl y
deciduous trees and shrubs including black cottonwood, red alder, vine and bigleaf maple, willow, cascara ,
salmonberry and blackberry as well as scattered western red cedar, coast Douglas-fir and Sitka spruce .
Rooting, except for some minor limitations caused by the slight clay accumulation in the subsurface, i s
essentially unrestricted to at least 75 cm depth .
General Land Use Comments : (1) Dewdney soils are valuable agricultural soils . Most crops can be
grown productively although droughty conditions may develop during the latter parts of most growing seasons ,
unless irrigation is used . Small individual areas and intermingling with other soils causes difficulties fo r
management as individual soil units . (2) Rather low bearing strengths may cause subsidence problems if heav y
structures are constructed on these soils . Basements and other excavations will probably contain water durin g
periods when the watertable is high . Septic tank efficiency also suffers during these periods . (3) Growth o f
black cottonwood and similar species is very high . Limited plot data indicates wood production by blac k
cottonwood to be between 18 and 21 m 3/ha/yr.
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