References

Sheldon, P. (2005) Earth’s Physical Resources: An Introduction (Book 1 of S278 Earth’s Physical Resources: Origin, Use and Environmental Impact), The Open University, Milton Keynes
Roy, A. (1999) The Cost of Living, Random House Inc, New York

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4 Summary

  1. Many rivers are fed by springs, which occur at points where groundwater reaches the surface. Springs can occur in different geological settings, forming valley springs, stratum springs or solution channel springs.

  2. The water in a river originates from overland flow, from interflow and from baseflow. Baseflow forms a higher proportion of river water in summer than in winter, and in rivers flowing over good aquifers.

  3. River discharg
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3.5 Big dams in the future?

Throughout the 20th century, reservoir construction to improve water resources was considered a key component of development. It was undertaken universally by industrialized nations, and by the later 20th century, increasingly by developing nations, building bigger and bigger dams. More recently the debate over the environmental impact of big dams and their questionable cost-benefit analysis has been universally recognized. In the 1990s the Narmada scheme caused the World Bank to rethink its
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3.4.6 Soil salinization

The change from annual flooding by a river to perennial irrigation that can be provided from a reservoir can cause soil salinization, if salts normally present in the river water accumulate in the soil as the water evaporates. These salts were previously washed away by the flooding, but the reduced supply of water by irrigation leaves them in the soil. The water is taken in by plants, or evaporated by the sun, leaving the salts behind. This causes a decline in crop yields until eventually the
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3.4.5 Sediment loss to agriculture

The trapping of sediment behind dams may also affect agriculture. The Nile Valley, for example, used to flood naturally once a year, and the sediment in the waters was deposited on the land, forming a fertile soil. These floodwaters and the sediment they carry are now trapped behind the Aswan Dam, and artificial fertilizers must be used down river in the valley. Without the yearly supply of sediment in floodwater, the banks of the Nile are eroding downstream of the dam, and the Nile delta is
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3.4.2 Ecological changes

Creation of a reservoir produces ecological changes not only to the area of the reservoir itself, by destroying the natural vegetation, but also upstream and downstream of the reservoir. The gradient of a river upstream of a reservoir may be reduced, so the water will slow down, changing the character of the river, causing deposition of sediment, and changes to the natural vegetation and animal life. Downstream of the reservoir the discharge will change, as well as the sediment load, also aff
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3.4 Environmental effects of reservoir construction

Reservoirs may totally alter the water resources of a country. Before the Aswan Dam was completed in Egypt, more than half of the 8 × 1010 m3 of water that flowed down the River Nile through Egypt each year ran into the sea. Most of the water can now be used in Egypt, mainly for irrigation, and instead of a single annual crop grown after seasonal flooding, more than one crop can be grown each year. However, advantages such as these must be considered in conjunction with
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2 River flow

The total land area drained by a river system, including all its tributaries, is called a river catchment. The water in a river comes not only from direct precipitation, springs and overland flow (i.e. water flowing across the ground surface, excluding that in streams and rivers; this is rare in temperate vegetated areas) but also from the underground flow of water, directly to the river. Part of this underground flow is interflow, that part of infiltration which moves th
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1 Springs

We have seen that where precipitation reaches the ground, some runs off the surface into streams and rivers and some of it infiltrates, passing through the soil. Water that reaches the water table to become groundwater may eventually re-emerge at the surface as springs where the water table intersects the surface. Almost all streams and rivers have springs or seepages as their ultimate source, or are fed by them at various points along their courses.

Artesian springs that are associated
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Learning outcomes

By the end of this unit you should be able to:

  • list the types of springs, and how each type relates to a different geological setting;

  • use hydrographs to distinguish overland flow and interflow from baseflow, and make inferences about the climate of an area;

  • expain how various changes in land use in a river catchment will change the hydrograph of a river;

  • distinguish the different types of reservoir construction, and decide whether a
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Acknowledgements

Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:

The content acknowledged below is Proprietary and used under licence (not subject to Creative Commons licence). See Terms and Conditions.

Figures

Figure 1 Copyr
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8 Summary

  1. The rate at which water infiltrates into the ground depends on the permeability of the rocks and the state of the ground surface. Below the ground surface there is an unsaturated zone which has air in the pore spaces, and a saturated zone which has all the pores filled with water. The water table is the boundary between the unsaturated zone and the saturated zone, and is the level at which water stands in wells. Water below the water table is called groundwa
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7 Aquifers

A layer of rock that is sufficiently porous to store water, and permeable enough to allow water to flow through it, is called an aquifer. Consolidated porous and permeable rocks, for example, sandstone and limestone, can form important and extensive aquifers (e.g. Figure 15). Unconsolidated sands and gravels may also be good
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6 Permeability

It is important to distinguish clearly between porosity and permeability. Porosity is a measure of how much water can be stored in a rock, whereas permeability is a measure of the properties of a rock which determine how easily water and other fluids can flow through it (see Section 4). Permeability depends on the exte
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8.6 Line spectra: Activity 8 Quasar redshifts

Activity 8: Quasar redshifts

Read Peterson section 1.3.5 (pages 16 and 17) by clicking the link below.

1.4 The invisible Sun

Figure 7 shows an image of the Sun, taken when a huge prominence was visible (bottom left). The image was recorded using instruments that are sensitive to ultraviolet radiation rather than visible light, so the colours that you see are ‘false’. They simply indicate different levels of intensity of ultraviolet radiation. The u
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9 Wildebeest migration

The skill of thinking in a scientific way is as much a part of being a scientist as is knowing facts – perhaps more so. In this series of units, you'll not only come across facts about particular techniques, such as radio transmitters and bat detectors, but also the tactics that scientists use to inves
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8.3 Shortage of minerals

You may be familiar with salt licks that are provided for domesticated cattle. In the wild, grass is also often low in minerals (e.g. it has almost no sodium and very little calcium), so grazers may have to go to extraordinary lengths to supplement their diet with additional minerals obtained from the most unlikely places. LoM gives some examples, but the most impressive activity takes place in the caves of Mount Elgon in Kenya [pp. 113–114]. You'll probably recall this spectacular footage
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7 Plant defences

Activity 5

Watch the ‘Plant Predators’ programme from 05.03–12.07 and make notes in answer to the following questions.

(a) In what ways do plants shown in this sequence protect themselves against their predators?

(b) H
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5.2 Pseudo-ruminants

Animals in the third suborder of the Artiodactlya, the pigs, peccaries and (according to most authorities) the hippopotamuses (suborder Suina), use a slight variant on the ruminant method, and are often referred to as pseudo-ruminants. You might like to add this information to your version of Table 2. These animals do have st
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