Hydrology Group5
Hydrology Group5
Hydrology Group5
IN A CHANGING WORLD
Water Allocation
The amount of water made available to users, including both out of stream users(e.g.
irrigation, town water supply) and instream environmental use (e.g. amenity values,
supporting aquatic populations).Water allocation in a resource management context is about
how to ensure fair and equitable distribution of the water resource between groups of
stakeholders.
1. Fresh water is a finite and vulnerable resource, essential to sustain life, development and
the environment.
2. Water development and management should be based on a participatory approach,
involving users, planners and policy makers at all levels.
3. Women play a central part in the provision, management and safeguarding of water.
4. Water has an economic value in all its competing uses and should be recognised as an
economic good.
c) Demand management
Using water more efficiently requires knowledge of where water losses occur (leakage) and
plans on how to promote water efficiency.
1. ICM recognises the catchment (or river basin) as the appropriate organising unit for
understanding and managing water-related biophysical processes in a context that includes
social, economic and political considerations;
VEGETATION CHANGE
This is a hydrological impact of vegetation cover change, a subject that Bosch and Hewlett
(1982) review in considerable depth.They conclude that the greater the amount of
deforestation the larger the subsequent streamflows will be, but the actual amount is
dependent on the vegetation type and precipitation amount
LAND DRAINAGE
Land drainage is a common agricultural improvement technique in areas of high rainfall and
poor natural drainage.In an area such as the Fens of Cambridge shire, Norfolk and
Lincolnshire in England this has taken the form of drains or canals and an elaborate
pumping system, so that the natural wetlands have been drained completely.The result of
this has been the utilization of the area for intensive agricultural production.At the smaller
scale, land drainage may be undertaken by farmers to improve the drainage of soils.
This is a common practice throughout temperate regions and allows soils to remain relatively
dry during the winter and early spring.The most common method of achieving this is through
a series of tile drains laid across a field that drain directly into a water course (often a ditch)
Traditionally tile drains were clay pipes that allowed water to drain into them through the
strong hydraulic gradient created by their easy drainage towards the ditch.
Modern tile drains are plastic pipes with many small holes to allow water into them.Tile
drains are normally laid at about 60 cm depth and should last for at least fifty years or
more.The aim of tile and mole drainage is to hold less water in a soil.This may have two
effects on the overall hydrology. It allows rapid drainage from the field, therefore increasing
the flashy response (Le rapid rise and fall of hydrograph limbs) in a river.At the same time
the lack of soil moisture may lead to greater infiltration levels and hence less overland flow.
SALINATION
Salination is an agricultural production problem that results from a buildup of salt compounds
in the surface soil.Water flowing down a river is almost never pure', it will contain dissolved
solids in the form of salt compounds.These salt compounds are derived from natural sources
such as the weathering ofsurface minerals and sea spray contained in rainfall.When water
evaporates the salts are left behind, examples are salt lakes such as in Utah, central
Australia, and the Dead Sea in the Middle East.The same process leads to salinity in the
oceans.Salination of soils occurs when there is an excess of salt rich water that can be
evaporated from a soil.The classic situation for this is where river-fed irrigation water is used
to boost agricultural production in a hot, dry climate.The evapotranspiration of salt rich
irrigation water leads to salt compounds accumulating in the soil, which in turn may lead to a
loss of agricultural production as many plants fail to thrive in a salt-rich environment.
GROUNDWATER DEPLETION
In many parts of the world there is heavy reliance on aquifers for provision of water to a
population. Not all groundwater is recharged so readily. Many aquifers have built up their
water reserves over millions of years and receive very little infiltrating rainfall on a year by
year basis. The use of this water at high rates may lead to groundwater depletion, a serious
long-term problem for water management.
URBANIZATION
The continuing rise in urban population around the world makes it an important issue to
consider under the title of change. There is no question that urban expansion has a
significant effect on the hydrology of any river draining the area. Initially this may be due to
climate alterations affecting parts of the hydrological cycle. The most obvious hydrological
impact is on the runoff hydrology, but other areas where urbanization may have an impact
are point source and diffuse pollution affecting water quality, river channelization to control
flooding, increased snow melt from urban areas and river flow changes from sewage
treatment.
RIVER CHANNELISATION
It is a common practice to channelise rivers as they pass through urban areas in an attempt
to lessen floods in the urban environment. Frequently, although not always, this will involve
straightening a river reach and this has impacts on the streamflow.