Soil Management Handbook - Ministry of Agriculture and Lands

Detailed information is provided in the publication,
B.C. Agricultural Drainage Manual.
3.6 Drainage in Upland Soils
Most upland soils are moderately well or well
drained. However, soils that occur in depressional
areas, or have compact slowly permeable layers close
to the surface, are poorly to very poorly drained.
Springs may also be present in upland sites, therefore,
they should/could be intercepted with underdrains to
remove wet spots. If the land is sloping, saturated
soils will not hold additional water and surface runoff
and soil erosion will occur. Uncontrolled soil erosion
can bring about substantial, permanent damage to
many upland soils, so that soil productivity and
manageability are greatly reduced and the livelihood
of the land user is threatened. Refer to Section 3.3,
Soil Management for Erosion Control, for more
information on erosion control in upland areas.
Generally, perforated plastic drain tiles should be
placed across the field contour between a 0.2/100 and
0.4/100 grade. The laterals should feed into
non-perforated mainlines running down slope. A
mainline grade should not exceed 5%. The mainlines
should discharge into concrete or plastic junction
boxes (sumps) before the water is discharged from the
field. To discharge water from the junction boxes off
the field, a flexible polyethylene pipe can be used.
This pipe should be anchored or buried and discharge
into rip rap in a stream or ditch bottom. Refer to the
B. C. Agricultural Drainage Manual for more
information.
3.6.1 Generalized Soil Drainage Guide
This guide presents guidelines for drainage and is a
supplement to the B.C. Agricultural Drainage
Manual which deals with detailed design procedures.
It was developed based upon many years of practical
experience in the Fraser Valley. The aim is to help in
the identification of drainage requirements without
the need of having to go through the detailed
investigations described in the Drainage Manual.
The basis of this guide is a set of generalized soil
profiles or soil categories which are distinctly
different in regard to drainage and soil management
requirements, see Table 16 (pages 60 to 61).
Drainage requirements were formulated for each soil
category, see Table 17 (page 62).
Since the recommendations of this guide are based on
average conditions and generalized soil profiles, it is
possible that, on occasion, site specific conditions are
at variance with those for which the guidelines were
formulated. It is for this reason, that caution must be
used in applying the recommendations. Only through
on-site investigation, can the necessary information
for completely accurate drainage recommendations be
provided.
3.7 Salt Affected Soils
Soils containing sufficient soluble salts to impair their
productivity are considered to be either saline or
sodic. The major salt constituents of saline or sodic
soils are sodium, calcium, magnesium, potassium,
carbonates, sulphates and chlorides. In semi-arid and
arid regions, like the Okanagan, deep percolation of
rain water does not occur frequently enough to leach
salts. Any leaching that does occur is usually only
local and a result of irrigation, so salt removal is held
to a minimum. Salt movement may result in a
concentration of salts in "seeps" or salt affected areas
within a field particularly where shallow till or glacial
lacustrine soils overlie calcareous bedrock.
Salinity is usually caused by natural processes. Salts
in the groundwater may become concentrated in the
plow layer when water evaporates from the surface,
leaving the salts behind.
Salinity may also develop from the application of
salty irrigation water applied to poorly drained or
undrained land. Repeated applications of excessively
high fertilizer rates, without crop use or leaching, can
also lead to salinity. Salt affected soil are classified
into three groups:
E.C E.S.P pH
1. Saline >4 15 >8.5
2. Non-Saline-Alkali or sodic 15 >8.5
E.C. = Electrical Conductivity, dS/m
E.S.P. = Exchangeable Sodium Percent
58 Soil Management Handbook – Okanagan-Similkameen Valleys