DoC calls to protect river flows

Department representatives say plan must reflect ecosystems' adaptation to high and low flows.

Department representatives say plan must reflect ecosystems' adaptation to high and low flows.

THE Department of Conservation has urged district planners to take into account the natural flow of rivers when they are setting water limits, as a way to maintain healthy freshwater ecosystems.

During a hearing on water quantity issues in the proposed freshwater plan DoC representatives told the panel river ecosystems have adapted to naturally occurring high and low flows, and this must be reflected in the plan.

Adam Canning, a freshwater ecology researcher, said such natural “flow variability” was essential to the life-supporting capacity and ecosystems in freshwater, yet it was increasingly disrupted by human activity, largely via water abstraction, barriers, deforestation and climate change.

Certain species live between the rocks, yet during low flow sediment can build up in these areas and they need larger-than-normal flows to flush it out.

Any measures that would steady the flows of rivers, especially those with slow flow, could prevent sediment build up from flushing away and affect the ecosystems.

“Flushes and floods are essential for maintaining habitat in rivers, especially slow flowing rivers,” said Mr Canning.

Many native fish species, including eels and five whitebait species, rely on river flows for migration and reproduction. The flow needs to be continuous and connect with the sea for them to complete their lifecycles.

High flow increases dissolved oxygen in the river and decreases rock slime (periphyton) build-up.

Mr Canning suggested a new definition of measuring mean annual low flow (MALF) in the plan, the lowest average water flow over a seven consecutive day period in the year.

In the proposed plan MALF measures only the water flowing through a river, without taking into account diverted water, such as that taken for irrigation.

DoC has requested a “naturalised” MALF instead, one that would include “all known takes of water from the waterbody to estimate naturalised flow”.

Forest and Bird made a similar request in its written submission on the issue.

A “naturalised” MALF would increase the amount set as a “minimum flow” for a river.

Mr Canning supported the plan’s suggestion to set minimum flows at 90 percent of MALF.

The panel questioned DoC over how they could measure “naturalised” MALF, how reliable a figure would be and the time and costs of implementing such a system.

THE Department of Conservation has urged district planners to take into account the natural flow of rivers when they are setting water limits, as a way to maintain healthy freshwater ecosystems.

During a hearing on water quantity issues in the proposed freshwater plan DoC representatives told the panel river ecosystems have adapted to naturally occurring high and low flows, and this must be reflected in the plan.

Adam Canning, a freshwater ecology researcher, said such natural “flow variability” was essential to the life-supporting capacity and ecosystems in freshwater, yet it was increasingly disrupted by human activity, largely via water abstraction, barriers, deforestation and climate change.

Certain species live between the rocks, yet during low flow sediment can build up in these areas and they need larger-than-normal flows to flush it out.

Any measures that would steady the flows of rivers, especially those with slow flow, could prevent sediment build up from flushing away and affect the ecosystems.

“Flushes and floods are essential for maintaining habitat in rivers, especially slow flowing rivers,” said Mr Canning.

Many native fish species, including eels and five whitebait species, rely on river flows for migration and reproduction. The flow needs to be continuous and connect with the sea for them to complete their lifecycles.

High flow increases dissolved oxygen in the river and decreases rock slime (periphyton) build-up.

Mr Canning suggested a new definition of measuring mean annual low flow (MALF) in the plan, the lowest average water flow over a seven consecutive day period in the year.

In the proposed plan MALF measures only the water flowing through a river, without taking into account diverted water, such as that taken for irrigation.

DoC has requested a “naturalised” MALF instead, one that would include “all known takes of water from the waterbody to estimate naturalised flow”.

Forest and Bird made a similar request in its written submission on the issue.

A “naturalised” MALF would increase the amount set as a “minimum flow” for a river.

Mr Canning supported the plan’s suggestion to set minimum flows at 90 percent of MALF.

The panel questioned DoC over how they could measure “naturalised” MALF, how reliable a figure would be and the time and costs of implementing such a system.

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