IntroductionWater is an essential part of our life and is critical for all biological activity. It cycles continually as it moves through the catchment. This circulation is generally referred to as the hydrologic or water cycle.
A catchment is defined physically, not by Shire or other administrative boundaries. Water enters the catchment in the form of rainfall and moves across it through drainage lines, intermittent creeks and small streams to the major river of the catchment, leaving as stream flow or as evapotranspiration. During its journey, water transports eroding soil, nutrients, salt or other contaminants, leaf litter, rubbish, organic matter and other dissolved substances.
Water characteristics and water flow through a catchment is affected by land management practices and may lead to processes such as erosion and salinity (please refer to the "Land" chapter of this kit). As a result water management must always be a consideration of land management across a catchment (an activity in the upper catchment ultimately affects users downstream) and conversely land management must always consider water management.
Water quality
Water quality can be characterised by 3 aspects:
Physical
Turbidity - the "cloudiness" (caused by suspended materials) of the water. High levels of turbidity reduce light penetration, reducing plant growth.
Litter - Smothers plants and animals, reducing light, and so on.
Chemical composition
pH - acidity/alkalinity - Can cause the death of fish and other organisms.
Temperature - Affected by water depth, season and time of day, as well as the amount of shade (vegetation cover). Changes can cause the death of instream organisms.
Conductivity - Measure of the ion concentration in water, which may reflect level of salinity.
Nutrients - e.g. Nitrogen and phosphorus. Nutrients affect the growth of plants and animals within the aquatic ecosystem. High levels can contribute to algal blooms, which may be toxic.
Salinity - The concentration of salt. Rising groundwater levels, often caused by vegetation clearance, and increase salt concentrations in waterways.
Biological composition
Abundance/diversity of organisms A healthy waterway has a diverse range of plants and animals in it. Pollution and degradation can cause the ecosystem to get "out of balance", leading to problems such as algal blooms, and loss of species (e.g. fish).
Source: Department of Natural Resources and Environment, 1999c
- Contact the NRE for more information.
