Instream barriers and energy
How do instream barriers as a result of energy generation activities potentially influence water resources?
Instream barriers consist of dams, culverts, weirs, and discharge pipes.
Hydro-dams permanently affect water levels and flows along a lake or river, thereby obstructing and redirecting the natural movement of water and the associated mahinga kai, invertebrates, and plants along its length. Large dams prevent the upstream and downstream migration of mahinga kai, such as tuna.
Culverts, weirs, and pipes are used in and around waterways when new power stations are built to provide the infrastructure and transport network needed to access sites such as wind farms and geothermal power plants. Wind farms especially may be located in remote and elevated areas prone to erosion.
Instream barriers alter the natural flow of water which many mahinga kai species rely on to migrate and breed. Altered water flow can also lead to erosion of river banks and disruption of mahinga kai habitats.
Using fish-friendly culverts and maintaining the natural slope of a stream are important for mahinga kai to successfully migrate upstream and downstream. Any instream structures should incorporated designs (modified culverts, wetted margins, and low flow areas) that facilitate fish passage to upstream habitat.
Potential impacts of instream barriers on water quality and mahinga kai
- Prevent migration of fish - barriers prevent mahinga kai, such as īnanga, which form part of the whitebait catch and are not very good climbers, from moving further upstream and accessing otherwise suitable habitats.
- Increase velocity - sustained high water velocity prevents some fish access to upstream habitats.
- Modified channel form - erosion through loss of vegetation after construction leads to scouring and breakdown of stream and river banks, which can eventually change the form of the channel further upstream.
- Modified flow regime - flow changes as stream banks are modified and realigned. This can eventually also lead to changes in the benthic (bottom) structure of the stream/river bed. Coarse substrates such as gravels and boulders are then replaced and covered by sand and silt.
- Loss of species habitat - many mahinga kai species need the protection and habitat provided at upstream sites. Loss of large areas of inaccessible upstream habitat can result in loss of breeding sites and feeding sites.