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Hydrology for the Environment, Life and Policy

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  • Home > Water and the Environment - Updated: 23-03-2005 9:53 am
    The natural environment, and the biodiversity it contains, is threatened by both water withdrawals and water pollution. We must find a balance between the protection of crucial ecological services and the human need for water. Where there is insufficientwater for both, some consistent quantitative basis for deciding on the value of different water uses must be found. The implicit value of the environment, rather than its immediate economic value, must be included in any analysis.    

    The environment and water policy

    Water and the environment are a recent issue, which is mainly being addressed by developed countries able to fulfil the basic water needs of their population. For example, in California instream flows are legally mandated for preservation of wild and scenic rivers, protection of endangered fish and wildlife species and prevention of saltwater intrusion.

    In any society, the level of environmental protection to be provided will be a matter of political choice and commitment. Developing countries will usually be least able or willing to consider the issue of the water required for environmental protection – their first priority will be taking care of the immediate, basic needs of their population. Efforts should be made to raise the awareness so that these two objectives are not contradictory.

    Environmental economics is a relatively new discipline, which is developing methodologies for valuing the benefits of ecological services provided by nature, but these are notalways included in conventional economic analyses. It is essential that these methodologies are developed and accepted by decision makers so that action is taken to allocate scarce water for the protection of the environment in a cost-effective way. An excellent example is how, in 1976, the environment protection agency of the Rio de Janeiro State was able to save the Baia da Guanabara’s mangroves. This action prompted the enactment of federal legislation for the protection of mangroves throughout Brazil.

    The environment and water management

    Even if it is a truism, it must be reaffirmed that not only people but also the environment – that is, ecosystems – need water. The natural framework of water management is the catchment, which includes not only the aquatic but also the related terrestrial ecosystems. A critical requirement for integrated river-basin management is the introduction of land-use and water planning and management mechanisms that focus at the river-basin scale. The ecological water demands are not always obvious and may be difficult to quantify. They have consequently often been ignored or underestimated in terms of total water demand, but such practices may lead to environmental and social problems. Although all the ecosystems of a basin have to be taken into account for water management, given the limited space available here the stress will be on wetlands and, for large lowland rivers, on the importance of the alluvial floodplain.

    Although wetlands usually occur as small and scattered patches, they occupy approximately 6 per cent of the Earth's surface and contribute about 25 per cent of the net production of the planet’s ecosystems. Beyond this contribution to the Earth’s productivity, wetlands act as natural infrastructures and hydrological regulators. Some of the most important functions of wetlands related to the water cycle are water storage (flow regulation, flow mitigation, groundwater recharge, groundwater discharge), water-quality control (water purification, retention of pollutants, nutrients and sediments) and local climate regulation (rainfall, temperature and evaporation). The wise use of wetlands, and their protection and restoration, could thus be considered a means of sustaining supplies of water for a range of human uses.

    In lowland floodplain systems, engineering works for flood defence, hydropower and water transfer, or dredging, deforestation and intensification of agriculture are the main causes of the decline of river quality, the perturbation of the flow regime, and loss of floodplain forests and wetlands. Most of these modifications have harnessed, straightened, “fossilised” the rivers. Natural lowland rivers are very dynamic hydrosystems, continuously creating and destroying sets of diverse and complex water bodies in their floodplain, which play an important role in the water cycle. “Fossilised” rivers cannot assume these functions. Therefore it is vital to ensure “free space” for rivers to maintain natural dynamics and ecological processes and to encourage wise use of river ecosystems.

    This need does not mean that no embankment, dike or engineering work can be constructed in lowland rivers; but it does mean that we must find a balance between human needs and natural ecosystem functioning.

    The hydrological science contribution

    We still have little or no ability to model and reliably predict the combined effects of multiple land-use changes in operational scale catchments (10000 km2 or larger), or the cumulative effects of such changes over time. This is because, even after 65 years of catchment studies and 35 or more years of process studies and mathematical modelling, too little work has been done on the integrating processes within catchments. Not enough is known about the key processes that combine the various inputs, state variables and modulating processes to generate the output signals of flow and chemistry. We have relied on the integrating nature of the catchment itself, but no studies have been done on how it takes place. The result is that model predictions of the effects of multiple changes are not good enough to be useful, and the interactions and feedbacks of hydrology with the ecosystem and environment remain largely unknown.

    There is a need to identify, describe and model these processes – and models should be tested against real world changes. Pressing issues include the potential impacts on the environment of:

  • population growth
  • industrialisation and pollution
  • land cover/land-use changes
  • species extinction and introduction of new species
  • perceptions and attitudes of society towards the environment

    Research questions include:

    • What role does the environment play in securing water resources?
    • How do we place a value on the “natural” environment?
    • How can we identify the impacts of environmental change on water resources?
    • How do we minimise conflicting environmental and human requirements?
    • What is the effectiveness of environmental law on water resources?

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