Otago Regional Council chief executive Sarah Gardner considers the impact on water quality from land use in this week’s Protecting our Water series.
Otago is home to some of New Zealand’s most renowned waterways, including pristine, snow-fed alpine lakes and roaring mountain rivers.
We know water quality is excellent in these mountainous areas, which are predominantly covered in native vegetation. But as rivers and streams travel down valleys and into more populated areas, water quality is impacted by land use.
This year, the Ministry for the Environment released its Environment Aotearoa report, which brought together environmental reporting across multiple domains for the first time.
The report shows that “changes to the vegetation on our land are degrading the soil and water”.
Native forest today covers only a quarter of our country, where it used to cover 80%, and 40% of our land cover is now pasture. These changes have occurred to support farming and the development of urban centres and infrastructure.
Land use changes have resulted in more soil being washed into our waterways, smothering aquatic environments, reducing our capacity for flood flows and affecting flora and fauna.
So what can we do as a region? We know many land users in Otago are already using a “best practice” approach to reducing sediment loss, including:
Best-practice winter grazing
Select paddocks that are well away from waterways.
Graze stock in the lower, damper areas of paddocks last, to reduce sediment runoff from these areas.
Graze animals from top to bottom on sloping land so any sediment is trapped by lower-lying crops and stays on your land.
Consider back-fencing so stock cannot stir up areas that have already been grazed.
Use troughs for stock water.
Controlling rural sediment run-off
Create a wide buffer strip of long grass or low vegetation between grazing paddocks and waterways, and also in gullies or swales. Sloping land needs a wider buffer strip than flat land.
Create a sediment trap such as a pit in the ground or cut-offs into paddocks. Slowing the water down allows the sediment to drop out.
Put hay bales or silt cloth in place to trap sediment where there is potential for run-off. It is best to have many smaller measures on the way down the catchment rather than relying on one at the end.
Clean out drains or irrigation races when they are empty.
Think about preventing run-off from high-traffic areas such as gateways, lanes, culverts, crossings, troughs and baleage feeders.
Sediment management in urban environments, in particular earthworks for new developments
Ensure a sediment control plan is in place.
Minimise soil disturbance and keep it away from waterways.
Keep sediment from entering waterways or storm-water drains (only drain rain).
Stabilise soil and surfaces and protect steep slopes.
Although these ideas could take time and money, in the long run they provide savings as they keep valuable nutrients from being washed away and reduce the need for channel cleaning and maintaining the capacity of flood protection and drainage.