1. Title slide; Irrigation and the Environment.
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2. Traditional irrigation has been sustained in harmony with
the natural environment in many parts of the world for centuries
(Nigeria). |
3. Large-scale “modern” irrigation has over the last century
brought dramatic changes which often lead to environmental
imbalances (Burundi). |
4. Pressure for land causes farmers to clear natural vegetation
from steeply sloping land causing accelerating rates of erosion
(Malawi). |
5. Sediment carried down from a catchment in to a main river
system following a major storm (Nepal). |
6. Sediment deposited in the head reaches of a reservoir reduces
the storage available for scarce irrigation water (Zimbabwe).
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7. The colour of the water passing down the spillway of this
dam shows how much sediment is being carried. |
8. Twin settling basins – the right channel is ready for dredging
while the left channel continues to flow (Indonesia). |
9. Waterlogging resulting from failure of a lined watercourse
(India). |
10. When water drawn from the watertable by capillary action
evaporates, it may leave a deposit of salts in the root-zone
of the soil; a process known as salinisation (Nigeria) |
11. Aquatic weeds can seriously affect the performance of
an irrigation scheme, reducing channel capacities and clogging
structures (Sri Lanka). |
12. Mechanical removal of weeds in the Gezira project is replacing
manual methods which had resulted in most of the labourers
catching schistosomiasis (The Sudan). |
13. Impounding reservoirs may result in drowning large areas
of potentially fertile land. Unless vegetation is cleared
prior to impoundment, the water may become subject to eutrophication
(Sri Lanka). |
14. In its natural state, there is a close interaction between
the water and the sediment transported by a river. Abstraction
of water may therefore have far-reaching effects (Zambia).
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15. Increasing the natural sediment load of a river may result
in an unstable channel from which it will be very difficult
to obtain a continuous supply of water (Kenya). |
16. Researchers surveying the snail population in a night
storage reservoir as part of the ODU’s study of schistosomiasis
transmission in small irrigation schemes (Zimbabwe). |
17. Chemicals can be used to control aquatic vegetation or,
as in this case, to control the snails which harbour the disease
schistosomiasis. Unless used with care, these chemicals may
harm humans, livestock and crops (Kenya). |
18. Migrant labourers required for harvesting often have to
live in poor quality housing where the provision of an adequate
water supply may be difficult (Sudan). |
19. Agro-industry such as this sugar factory may arise in
association with irrigation and produce effluent which affects
water quality downstream (Mozambique |
20. People drawn together into villages on an irrigation scheme
frequently bring livestock with them which may cause degradation
and erosion in the surrounding area (Nigeria). |
21. The provision of a reliable source of water may also encourage
other activities such as fishing or .... |
22. ... duck farming to provide alternative sources of food
and/or income (Philippines). |
23. The rich fisheries and grazing (for both domestic and
wild animals) in this natural flood plain have already been
affected by hydrological changes to generate hydropower and
would be further affected by plans for large-scale irrigation
(Zambia). |
24. Global solutions must be found to problems associated
with the conservation of unique natural habitats and rare
species of flora and fauna (Kenya). |
