Location of Irrigation
Dry regions in the southern Prairies and in the interior of British
Columbia have severe moisture deficits at some time during most
summers. Dry areas are also more prone to long-term drought conditions
as well. These areas (especially southernmost Alberta) hold most
of the one million hectares of irrigated cropland in Canada. The
map clearly shows this pattern. Data on the map is data compiled
for the 1996 Census of Agriculture.
Figure 1 shows that Alberta accounts for 60% of the total irrigated
area. The relatively large figures for Ontario and Quebec reflect
the use of irrigation for certain areas of high-value crops (such
as fruits and vegetables).
[D] Click for larger version, 3 KB Figure 1. Distribution of Irrigated Land in Canada (late 1990s)
Irrigation often makes agriculture possible where it would not
otherwise exist. The on-going benefits to irrigation include:
- increased stability of production
- giving the potential for production of a wider range of high-value
crops
- allowing intensification of production
Irrigation Systems
The peak design flow rate of an irrigation system varies according
to climate, crops, and soil conditions. The amount of water that
needs to be withdrawn for irrigation varies annually; it depends
mainly on two factors:
- winter precipitation
- weather and soil moisture conditions during the growing season
In areas such as southwestern Saskatchewan, spring runoff determines
the amount of water available for irrigation during the following
summer. Temperature, the amount and timing of rainfall, wind, and
evaporation all influence the need for supplemental water for optimum
plant growth.
Water use for larger irrigation projects is often licensed by the
province in which they are located, as a means of controlling total
withdrawals from a water source and minimizing the potential for
conflicts among users. The licence stipulates the maximum volume
of water that can be withdrawn in a year. The licensed amount is
often considerably greater than that withdrawn in an average year.
The expansion of irrigated area depends on both soil characteristics
and a secure supply of water of suitable quality. Some provinces
require irrigators to undertake a soil water compatibility study
before approving irrigation plans.
To limit competition with other water users, irrigators, private
industry, governments, and researchers have cooperated to introduce
greater efficiencies in the way irrigation water is stored, conveyed,
and applied in the field. For example:
- Irrigation headworks, main canals, and whole distribution systems
are renovated to minimize water loss.
- Irrigators are encouraged to switch from less-efficient gravity
systems to more-efficient sprinkler systems or to highly efficient
drip or trickle systems.
- Some irrigators are converting saline land back to dryland.
("Salinization" is the accumulation of salts in the
land as water evaporates from it; "dryland farming"
has farming practices adapt to low rainfall by leaving some land
fallow in some years).
- Governments and industry are conducting research and demonstration
projects to develop refinements to irrigation systems that are
more energy efficient while more effectively irrigating crops.
- Water meters are being used at the district and farm levels
to measure water use and to charge for water based on consumption.
Environmental Concerns of Irrigation
Irrigation can have both positive and negative effects on the environment.
Potential positive environmental benefits are:
- Impoundments and canals can provide increased fish habitat and
greater recreational opportunities.
- Brush and weeds along canals can provide cover and nesting habitat.
Potential negative environmental effects include:
- Reservoir construction can cause flooding of forest and riparian
habitat (habitat along the riverbank).
- Flooding can destroy historic sites.
- Water-level fluctuation can destroy the habitat waterfowl other
water-dependent creatures.
- Alteration of the rate of flow, and the quantity and quality
of water can affect downstream water uses.
- Sediment can build up behind reservoirs.
- As pesticides and fertilizers are used in greater quantities
on irrigated land as opposed to use on dryland farming, there
is an increased risk of contamination of groundwater and streams.
- An increased risk of salinization of water in some areas where
salts present in subsoil.
|