Water as a resource

1
Water

• Water as a resource
• Water is the most important resource studied in
  this course as it is the only one that is
  essential for human survival.
• Water is the commonest substance on Earth it
  exists on land, in the atmosphere and in the
  oceans and lakes.
• It occurs in different states solid (ice),
  liquid (water) and as gaseous water vapour.
• Water may be pure, or it may contain dissolved
  substances, particularly salts oceans, lakes
  and ground water.
• The term Water Resource usually applies to
  fresh water i.e. with low content of dissolved
  solids, suspended solids or biological
  substances.
• Fresh water constitutes only a few of this
  total water. In some places it is very scarce.

2
Water

• Renewable resource
• Water differs from most other resources in that
  it is renewable driven in the Hydrological Cycle
  by the energy of the sun and by gravity.

3
Water

• Renewable resource
• Rainfall globally is irregular or seasonal so its
  renewability is not instantaneous. Rain on
  mountain tops in remote areas may not be
  available for human consumption for days or
  years.
• Extremes causes drought and desertification or
  flooding.
• Modern Water Usage
• The typical amount of water used at subsistence
  levels in developing countries is 20-40 litres
  per person per day, while in industrialised
  nations, it is 500 l/p/d.
• Agriculture - 69 of world water usage. Industry
  - 23.
• Water is used to produce energy energy is
  needed to produce water. Given enough energy,
  fresh water resources can be created from
  seawater. 300 Mjoules of energy will produce 1
  cubic metre of fresh water.

4
Water

• Using water in different ways
• Water is an important resource for Transport on
  seas, rivers, lakes and canals. Of the 3,200km
  of canals in Britain, very few are now used
  commercially, e.g. coal to power stations.
• Abstractive
• Water is temporarily lost as a resource.
  Domestic, irrigation, industrial, cooling (1
  lost to evaporation).
• Non-Abstractive
• Water is used without changing its path or
  quality. Hydroelectric, transport, recreation.

5
Water

• Science of Water
• Water has some peculiar but essential properties.
• Hydrogen bonding
• Hydrogen bonding is similar to methane, but water
  freezes at 0oC and boils at 100oC while methane
  freezes at -184oC and boils at -162oC. The
  difference is in the bonding (polar), which is
  much stronger on water
• Energy properties
• The energy stored, as water changes phase from
  ice to water to steam, is a major factor in
  distributing the energy from the Sun
• Water has a high heat capacity (ability to store
  heat) due to the large number of hydrogen bonds,
  so it heats and cools slower than many
  substances. Consequently, large water bodies
  affect local climate and weather.

6
Water

• Science of Water
• Density properties
• A VITAL property of water is that ice floats!
• If this property were not present, ice would sink
  to the bottom of lakes, rivers and seas, and
  eventually the whole body of water would freeze,
  removing oxygen and killing life. It also allows
  vertical mixing of oxygen and nutrients.
• Solvent properties
• Water is a very good solvent. Polar liquids
  dissolve polar solids like NaCl and mixes
  completely with polar liquids like alcohol. Its
  ideal for transporting nutrients through the
  organic tissues.
• Conversely, because it is a good solvent it is
  easily polluted.
• Water will NOT mix with non-polar liquids like
  oil or fat.

7
Water

• The Water Cycle
• Water moves on, over and through the earth in a
  continuous cycle driven by the sun and gravity.
• This water cycle (Hydrological Cycle) involves
  water as a liquid, solid and gas, which move in
  different ways around the cycle. The total water
  in the cycle remains virtually constant.
• Meteoric water
• fresh atmospheric water, which condenses in lakes
  and rivers and ground water .
• Saline water
• seawater in oceans, seas and some lakes.
• Small amounts of magmatic waters (volcanic) and
  formation waters (held in sediments) can be added
  - both are usually saline.

8
Water

• The Water Cycle cont..
• Storage in the Hydrosphere
• The hydrosphere includes those parts of the earth
  that are mainly water, e.g. oceans. Ice caps,
  lakes, rivers are all temporary natural
  reservoirs in the water cycle.
• Atmosphere contains 15 x 103km3 of water
  (reservoir)
• The worlds lakes contain large volumes but ½ are
  saline 80 of the freshwater occurs in only 40
  large lakes (Great Lakes).

9
Water

• The Water Cycle cont..
• Precipitation
• The atmosphere is one of the smallest reservoirs,
  but is the most important source of water.
  Rising air and water vapour expands (decrease in
  pressure) and cools _at_ 1oC per 100m in altitude.
• As air cools it condenses to form droplets 0.001
  0.1mm Precipitation occurs when water droplets
  reach 1mm or when ice crystals form.
• The net effect of the water cycle is to transfer
  40x103 km3 of fresh water from the oceans to the
  land each year by precipitation.

10
Water

• The Water Cycle
• Interception, evaporation transpiration
• Interception precipitation stopped from
  reaching the ground by vegetation and direct
  evaporation to the atmosphere.
• Dependent upon vegetation type density and
  season. 25-35, coniferous forest, 15-25, broad
  leaf, 14-19 from grassland.
• Water reaching the ground becomes part of the
  overland flow which may soak into soil rock or
  evaporate. Rate of evaporation increases with
  temperature and it is linked with humidity.
  The greater the humidity, the less the
  evaporation.
• Vegetation increases the amount of water returned
  to the air by transpiration.

11
Water

• Ground water
• Infiltration
• Precipitation may run off or sink into the
  ground. The rate of infiltration depends on
  PERMEABILITY.
• The water table is the boundary between the
  aeration zone and the saturated zone.

Underground water filtration process, aeration
zone, saturated zone and groundwater.
12
Water

• Ground water
• Groundwater movement
• Water flows in response to pressure gradients
  from high pressure to low pressure.
• The difference in pressure between 2 points at a
  horizontal distance l metres apart on a sloping
  water table difference in height h. The slope
  of the water table is the hydraulic gradient (HG)
  h/ l.
• The speed of ground water movement v relates to
  the hydraulic gradient by Darcys Law
• v K h/ l in metres/second or metres/day,
• K Hydraulic conductivity

13
Water

• Ground water
• Groundwater movement cont..
• Rocks fall into two categories based on their
  hydraulic conductivity (HC), permeable and
  impermeable.
• Permeable rocks have HC of 1m/day or more.
• The flow rate will be a combination of the
  hydraulic gradient and the hydraulic
  conductivity. e.g. Water in rocks with 1m/day HC
  may only move at 3mm/day if the hydraulic
  gradient is low.
• Volume and speed are related by the equation
• Q (quantity of water) Av
• v speed through a section of rock with
  cross-sectional area A.
• Darcys Law can be substituted into this to give
  the volume in terms of HC and HG. Q AK h/l

14
Water

• Ground water
• Porosity
• Porosity is the amount of water a rock can store.
• porosity pore volume x 100 total
  volume
• It is controlled by the grain size, shape,
  sorting, cementation and fracturing.

1 cm
15
Water

• Ground water
• Permeability
• Porosity is how much water can be stored
• Permeability is a measure of properties which
  determine how fast water can flow.
• For rocks to be high permeability they must have
  interconnected pores. Coarser sands and gravels
  are more permeable than silts (due to surface
  tension).

16
Water

• Ground water
• Aquifers
• An aquifer is a rock which is sufficiently porous
  to hold water and permeable enough to allow water
  to flow.
• The best aquifers are unconsolidated sands
  gravels.

17
Water

• Ground water
• Aquicludes are saturated beds, formations or
  group of formations which can neither release
  water from storage nor transmit water through it.
• Acquitards are saturated beds, formations or
  group of formations which yield in insignificant
  quantities of water when compared to aquifers,
  but allow appreciable amount of water leakage.

18
Water

• Ground water
• Aquifers
• Unconfined Aquifer
• Confined Aquifer

19
Water

• Ground water
• Exploration for groundwater
• Use surface geology maps to determine rock types
• Determine porosity permeability
• Identify possible aquifers
• Remote sensing can be used to establish land
  surface characteristics (e.g. vegetation changes)
  which can indicate sub-surface variations.
• The geological structure is important. The
  general dip and any folding will influence the
  direction of flow.
• Fault zones can act as major aquifers.
• Resistivity surveys and investigation boreholes
  are often used in exploration and assessment.

20
Water

• Surface water
• Springs
• Many streams and rivers have springs as their
  source or are fed by them along their courses,
• Most springs are water table springs and can be
  of several different kinds, depending on the
  geology.
• Valley springs
• Ground surface intersects the water table
• Stratum springs
• Downward percolation is interrupted by
  impermeable rock which usually results in a
  spring line.
• Solution channel springs
• Water travelling through limestone re-emerges at
  surface.

21
Water

• Surface water
• River flow
• Throughflow
• Rivers can receive water by throughflow, i.e.
  water which flows in the aeration zone without
  getting below the water table.
• Baseflow
• Baseflow is the groundwater available and depends
  on the topography, geology, vegetation and
  season. It will be low in a catchment area of
  impermeable rocks.

22
Water

• Surface water
• River flow
• Discharge
• This is the volume of water passing through a
  point in a given time.
• Q Av
• Where,Q quantityA cross- sectional area
  v flow rate

23
Water

• Surface water
• Reservoirs
• Reservoirs have been used to store water for
  thousands of years. Most are built to increase
  water supplies, while some are used to generate
  hydroelectric power and others used to regulate
  water flow to prevent flooding.
• Most of Britains reservoirs are DIRECT SUPPLY.
  They store water for steady release by pipeline.
• River regulation reservoirs are built to store
  water for the release to rivers, the rivers being
  used as the mode of transport of water, so pipes
  are not needed.

24
Water

• Surface water
• Sites for reservoirs
• Dam a river valley
• Factors to be considered
• Adequate supply of high quality water
• Minimal environmental effects
• Elevation providing natural flow using gravity
• Watertight base sides
• No geological hazards due to rock
  instability/earthquakes
• Suitability of site (general)
• Superficial deposits
• Peat should be removed
• Clays can be useful

25
Water

• Surface water
• Dams Gravity Dams
• Two types are commonly used which are
  fundamentally different ways of withstanding the
  PRESSURE of water.
• This system depends on its own weight to
  withstand deformation and movement.
• Usually made up of selected unconsolidated
  material such as clay or broken rock, these are
  called earth dams. They usually have an
  impermeable clay cone, to reduce seepage through
  the dam. The sides are usually covered by broken
  blocks rock or concrete to reduce erosion by rain
  or waves.
• Gravity dams can also be built entirely piled
  masonry or concrete. The largest in Britain, the
  Kielder Dam is an earth dam- e.g. Aswan High Dam.

26
Water

• Surface water
• Dams Gravity Dams
• Aswan High Dam, shown below, is a rock filled
  gravity dam, 1.2km long. It incorporates an
  upstream cofferdam (A) and a downstream cofferdam
  (B).

27
Water

• Surface water
• Dams Wall Dams
• Wall dams are usually only built in narrow
  valleys when a relatively high dam is needed.
  They must be strong and impermeable and are
  usually constructed of masonry or concrete. Their
  strength is often increased by making them convex
  (toward the reservoir) or with buttresses on the
  down riverside. E.g. Hoover Dam on the Colorado
  River

28
Water

• Surface water
• Dams Environmental effects
• Change of land use. Generally agriculture to
  reservoir. In the case of Aswan 6000 km2 needed.
  Kielder covers around 10.5 km2 and is the largest
  in Europe.
• Ecology. Ecological changes happen not only near
  the reservoir but also upstream and downstream.
  Down stream sedimentation is also changed and
  annual flooding may cease.
• Dam Failure. Dams may collapse releasing large
  volumes of water downstream onto habituated or
  cultivated land.
• Sediment filling. The lifetime of reservoirs can
  vary greatly many last over 1000 years, more
  usually 50. This is due to sedimentation build up
  and the reduction of water capacity.

29
Water

• Surface water
• Dams Environmental effects
• Sediment filling cont... Lake Mead, Colorado has
  had its capacity halved since 1935. This is less
  important in Britain as rivers are smaller and
  carry less sediment.
• Derwent reservoir has 1 capacity reduction in
  60 years.
• Sediment loss to agriculture. Trapped sediment
  behind the dams is effectively lost to
  agriculture use. E.g. Aswan
• Soil salination. Perennial irrigation can cause
  soil salination as salts normally present in the
  river water accumulate in the soils. These salts
  were previously washed away by annual river
  flooding. This causes a decline in crop yields
  and eventually the soil becomes useless for
  agriculture

30
Water

• Surface water
• Dams Environmental effects
• Inducted earth quakes. Rare but have been
  recorded in China. Some of these are over 100m
  deep, often earthquake-affected areas L Marathon
  Greece, L. Mead USA, Kariba Zimbabwe, L. Nasser
  Egypt.

31
Water

• Water quality
• Natural waters
• Total dissolved solids (TDS) composition
• Rainwater, seawater, river water and groundwater
  differ widely in their concentrations of TDS and
  chemical composition as shown below. N.B. the
  different scales used!

32
Water

• Water quality
• Natural waters
• Total dissolved solids (TDS) composition
• Groundwater limestone granite

33
Water

• Water quality
• Natural waters
• Water Hardness
• Hardness in water is mainly due to the presence
  of ions of the elements Ca, Mg Fe. They cause
  scum scaling, and react with soap forming
  insoluble compounds and preventing the soap from
  lathering.
• The extent of hard water in Britain tends to
  follow a North to South-East gradient the
  softest water is in Scotland, N England Wales
  and the hardest in E Anglia and SE England.
  There is a similar trend for mortality from
  cardiovascular disease! Soft water High CV
  rate. EU has set level of minimum hardness for
  drinking water.

34
Water

• Water quality
• Water Pollution
• Water quality in England Wales. Water may be
  polluted by discharges (sewage works), overflow
  (farmland) or incidents (rupture of farm slurry
  tank).

35
Water

• Water quality
• Water Treatment
• The quality of water required depends on the
  intended use. Drinking water needs quality
  standards different from those for industrial or
  irrigation water. The World Health Organisation
  and the European Community have set water quality
  standards.
• In recent years, the nitrate concentration in
  surface and groundwater is some areas of the UK
  has been increasing and is now above EU
  acceptable levels with associated health risks.
  To treat would be too expensive, so new boreholes
  have been sunk, water of high levels is blended
  with low-levels, and more control on the use of
  fertilizers in farmland to control the nitrates
  getting into the water.