On the Country Hour…
- Talk about no new dams in NSW welcomed by Inland Rivers Network – July 2018
The Environmental Impacts of Dams
Large water storages in NSW inland river systems have caused major changes to the ecological function and health of rivers and floodplain environments.
When the timing, frequency and magnitude of flooding events are altered, the ecosystem suffers because animal, fish, plant and invertebrate species have evolved to respond to such events for their long term survival.
Rivers are connected in 3 ways:
- Upstream and downstream connectivity: this is connectivity from the headwater to the floodplain. This connectivity is needed for the movement of nutrients, food and animals along the river. Major disruptions to this connectivity are dams and barriers
- Lateral connectivity: this is the connectivity between the river and the floodplain. This connectivity is important because rivers are able to gain food and nutrients and allows for vital breeding processes to occur. Levees, barriers and lack of flow reduce connectivity and damage the river and biodiversity.
- Vertical connectivity: this is connectivity between surface water and groundwater. Over extraction is major threat to surface-groundwater connectivity.
‘Dams change the chemical, physical, and biological processes of river ecosystems. They alter free-flowing systems by reducing river levels, blocking the flow of nutrients, changing water temperature and oxygen levels, and impeding or preventing fish and wildlife migration.’ Dams – Are They Worth a Dam?
Seasonality of water delivery
The capture of snowmelt and high rainfall events in large water storages prevents the movement of natural flow volumes through river systems in the season in which they occur. Early spring inflows, autumn and winter events are generally stored for summer use.
The release of water from large storages to deliver irrigation orders in the hotter, drier summer climate has significantly altered the natural flow regimes of rivers and interfered with breeding cycles of native plants and animals.
Loss of natural flow regime
Large water storages capture the top of drought breaking flood waters, thus preventing downstream wetlands, billabongs and other floodplain ecosystems from receiving the full benefit of climatic change from dry to wet.
The river systems often suffer prolonged and unnatural drought sequences.
Large storages tend to capture all the medium flows. The variability of natural flows and benefits provided are lost to riverine ecology.
The release of water from large storages in the form of constant base flows to provide basic rights and stock and domestic supplies are unseasonal and remove the natural drying sequences that occur in unregulated river systems.
Water quality impacts
Large water storages have a major impact on water quality both within the storage and downstream. Cold water pollution is caused by the release of water from the bottom of the storage. Changes to water temperature in rivers impacts on fish habitat eg more than 100 km Macquarie River downstream of Burrendong Dam is impacted by thermal pollution. This has an influence on threatened fish populations such as silver perch.
Deoxygenation of water is caused by the trapping of nutrient-laden sediments behind the dam. This reduces the storage volume and increases the cycle of eutrophication or oxygen depletion. This results in increased plant and algal growth, bacterial decomposition that consumes oxygen and release of phosphorous that nourishes further algal growth. Deoxygenated or ‘dead’ water releases from water storages have a major impact on downstream ecosystems and fish habitat.
Blue green algal blooms are caused by high levels of nutrients and surface water temperature in water storages. Water released from dams can seed downstream river reaches with blue green algae outbreaks eg releases from Windamere Dam on the Cudgegong River. Although this dam has a variable off-take the blue green algal blooms can be so deep that cold water has to be released to manage downstream toxic algal pollution. The Glennies Creek Dam built in the same period also has major problems with blue green algae, as does Seaham Weir on the Williams River in the Hunter. Any new water storages are likely to produce toxic blue green algae blooms. These have major health impacts on humans, livestock and wildlife coming into contact or consuming polluted water.
Salinity levels in water storages can increase through the capture of first flow flushes from dryland salinity affected areas. Irrigation activities are known to increase water tables and salinity levels in catchment areas. This is particularly known to happen with irrigation in arid areas.
Changes to river channels
The regulation of rivers through capturing of flood events and the unnatural releases from large water storages has caused major changes to riverine geomorphology. The release of high flows in dry times and sudden drops in river height has caused bank slumping.
This increases erosion and turbidity and changes the stability of river channels.
Degradation of water dependent vegetation and fauna populations
The long-term impacts of changes to river function and health has caused a loss of species that have evolved around the variability of flow heights, volumes and velocities. Changes have occurred to floodplain habitats such as wetlands, billabongs and ephemeral lakes. These provide breeding and feeding grounds for a large number of birds, reptiles, amphibians, fish and plant species. The loss or degradation of these areas has caused a significant drop in population and extent of native water dependent species.
Any additional large water storages in inland NSW will cause a further decline in natural river flows.
Natural flows in rivers allow for:
- Fish, bird and plant survival by providing an essential breeding and feeding habitat – Woodland and aquatic plant growth
- The connectedness of river channels with floodplains, wetlands and other freshwater areas for food and nutrient cycling
- Riparian vegetation survival that depends on the groundwater that surrounds rivers and streams
- The survival of the ecologies of estuaries that depend on the flows of freshwater streams and aquifers
- Renewal of groundwater reserves
The current level of water storage in NSW has caused significant environmental damage. A range of significant water reforms have been instigated to address these problems. The consideration of increasing the impacts of water storage is not a sustainable option.
Brokered by the World Bank and the World Conservation Union (IUCN), the World Commission on Dams (WCD) was established in May 1998 in response to the escalating local and international controversies over large dams. It was mandated to:
review the development effectiveness of large dams and assessed alternatives for water resources and energy development; and develop internationally acceptable criteria, guidelines and standards for the planning, design, appraisal, construction, operation, monitoring and decommissioning of dams.
The WCD identified various issues relating to dams and large water storages as outlined in the following quotes from the Executive Summary:
‘Dams fundamentally alter rivers and the use of a natural resource, frequently entailing a reallocation of benefits from local riparian users to new groups of beneficiaries at a regional or national level.’
‘In too many cases an unacceptable and often unnecessary price has been paid to secure those benefits, especially in social and environmental terms, by people displaced, by communities downstream, by taxpayers and by the natural environment.’
‘Lack of equity in the distribution of benefits has called into question the value of many dams in meeting water and energy development needs when compared with the alternatives.’
‘The evidence of success and failure we present in this report provides the best rationale why the ‘business as usual’ scenario is neither a feasible nor a desirable option.’
‘Demand management, reducing consumption,recycling and supply and endues efficiency measures all have significant potential to reduce pressure on water resources in all countries and regions of the world.’