Impact of erosion investigated further

Erosion at the Clay Cliffs at Lake Benmore, near Omarama. The Upper Waitaki Zone Water Management...
Erosion at the Clay Cliffs at Lake Benmore, near Omarama. The Upper Waitaki Zone Water Management Committee has expressed concern about the potential impact of phosphorus on water quality as a result of erosion. PHOTO: SUPPLIED
The potential impact of erosion from the Clay Cliffs on the water quality of Lake Benmore is set to be explored in more detail.

Yesterday, Upper Waitaki Zone Water Management Committee members received a report on the issue after concerns were raised about erosion from the cliffs near Omarama and if it was impacting on water quality, specifically phosphorus levels.

Those concerns were raised a second time at the committee's February meeting, as was whether steps could be taken to try to reduce erosion.

A report compiled by Environment Canterbury Waitaki zone manager Chris Eccleston in response to concerns raised at the November and February meetings said the issue of erosion and any potential impacts on water quality were not new, and there was a "small risk" the amount of phosphorus in the lake would increase.

However, the turbidity, or cloudiness, of the water had not increased in recent years and it was noted that phosphorus levels had decreased over time in the Ahuriri arm of the lake, which the report said "could be related to climatic factors".

Equipment would be employed to monitor water quality in the future, which the report said would "give us a better understanding of the effect of high flow events on lake turbidity and sediment transport".

It was likely the erosion was also happening at other areas in the catchment.

"There is the potential to reduce phosphorus inputs to the Ahuriri River and the lake from a number of other streams in the Ahuriri catchment through the implementation of GMP (good management practice), which would likely be a more cost-effective approach."

According to Land, Air and Water Aotearoa, when phosphorus levels increase to very high levels, the body of water is "likely to experience rapid weed growth or algal blooms which can choke aquatic life and cause long-term damage to the health of a stream, river, or lake".

The issue is scheduled to be discussed in greater detail at the committee's July meeting.

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