Water take and thermal
How may thermal energy generation activities influence water resources?
Water is the second most important resource used in thermal energy production, after fuel. Some of the water used is converted to steam which drives the generator producing the electricity. However, most of the water is used to remove heat from the condenser cooler. The condenser cooling water is abstracted from rivers located near thermal power plants. Water is circulated to absorb the heat. The water can then be either returned to the water body from where it was extracted, or cooled using air contact and evaporation in a cooling tower.
When natural seasonal flow variations are interrupted by taking water from streams, rivers, and lakes, extreme care must be taken to maintain the amount of water needed to support healthy ecosystems. The amount of water needed is called environmental flow, which considers maximum and minimum flow levels to support a healthy ecosystem. Failure to provide an environmental flow can have serious consequences for water quality and mahinga kai.
Impacts of water take (abstraction) on water quality and mahinga kai
- Changes in flow - changes in water levels and flow variability alters available mahinga kai habitat and the invertebrates they feed on.
- Reduction in habitat - a decrease in water levels reduces habitat for fish and can impact feeding and spawning success.
- Reduction in specialist habitats - a decrease in water levels reduces flow to riparian wetlands, backwaters, and intermittent streams.
- Decreases in species abundance and diversity - aquatic species have developed life history strategies in direct response to natural flows; for example, diadromous fish species migrate up and down the river at various times of the year and rely on preferred velocities and depths.
- Changes in sediment accumulation - flow reduction affects movement and deposition of sediments in streams and rivers.
- Changes in water quality parameters - for example, turbidity and temperature levels can increase with reduced flows in rivers.
- Increases in algae accumulation - algae respond to changes in temperature and nutrients, which are likely to increase with reduction of flow, especially during summer months.