Soil Formations: Geologic Classes and Characteristics - Geotechnical Engineering Investigation - page 501

TABLE 7.4
Typical Drainage Patterns for Various Soil Types and Formations a

Geologic Condition Predominant Drainage Geologic Condition Predominant Drainage

Pattern Pattern

Sand sheets, terraces No surface drainage

Clayey soils b Young till plains,

uplifted
peneplains
with impervious
soils Deranged with ponds

Fine dendritic and swamps

Clay-sand mixtures c Old till plains,

thick

Medium dendritic Medium dendritic

Sandy soils, some cohesion, Loess

porous clays d

Coarse dendritic Pinnate and dendritic

Coastal plains, mature Lake beds,

with questas floodplains

Coarse parallel Meandering with oxbow

lakes

Alluvial fans Permafrost regions

Radial braided Thermokarst

Sheet wash, coalescing
alluvial fans

Parallel braided

a

Drainage patterns given in terms of coarse, medium, and fine textures are for humid climate conditions. Arid
climates generally produce a pattern one level coarser.

b

Coarse: First-order streams over 2 in. (5 cm) apart (on map scale of 1:20,000) and carrying relatively little runoff.

c

Medium: First-order streams ¼ to 2 in. (5 mm to 5 cm) apart.

d

Fine: Spacing between tributaries and first-order stream less than ¼ in. (5 mm).

Mode of Occurrence
As an integral part of the rock mass, the surface expression of residual soils relates to the
rate of rock decay and the effects of differential erosion, and therefore generally reflects the
parent rock type and the original landform (peneplain, mountainous, etc.) as described in
Section 6.7.3.