Lagoon Management

Lagoon management update - October 2023

Rainfall during July, August and September elevated the water levels at Waituna Lagoon. In the past the Lake Waituna Control Association has held a consent that allowed it to mechanically open the lagoon when specific triggers were reached. This consent has expired, so there is currently no consent in place that would allow a mechanical opening of the lagoon.

Concerned parties associated with the lagoon have been looking to Environment Southland to fill this void and respond to rising water levels.

Section 330 of the Resource Management Act allows for undertaking ‘emergency works’ (to mechanically open the lagoon) if any of the following apply:

1. an adverse effect on the environment which requires immediate preventive measures; or
2. an adverse effect on the environment which requires immediate remedial measures; or
3. any sudden event causing or likely to cause loss of life, injury, or serious damage to property

Environment Southland staff monitored and assessed the situation. However, the threshold for meeting the requirements of Section 330 are high, and it was determined that the recent situation did not meet the level required under the Act. If it was decided to use Section 330 emergency works, this means actions could be taken immediately, however it still requires a consent to be granted retrospectively for those works.

Lagoon opening consent application process – indicative timeline

Here is an indicative timeline for the consent application.

It is important to note that the criteria and the decision making for the use of Emergency Works under the Resource Management Act to open the lagoon are significantly different to any criteria and decision making associated with any consent conditions that may be granted. So, just because certain levels were used as benchmarks for undertaking a mechanical opening of the lagoon (under the previous consent), these are not benchmarks for considering the same action under Emergency Works powers.

Waghorn Road Bridge

Concerns were raised recently about the integrity of the Waghorn Road Bridge due to it being submerged for some time. We have confirmed with Southland District Council that they hold no concerns for the structural safety of the bridge.

Once the levels drop, the work to upgrade the bridge can commence.

Water quality information on LAWA (Land, Air, Water Aotearoa)

Environment Southland monitors sites in the Waituna Creek and Mokotua Stream. Results for the water quality indicators we measure are available on the LAWA website, and provide an assessment of current state and trend over the 5, 10 or 15 year period. By clicking on the indicator you’re interested in, you can few all the results for a particular period.

Mokotua Stream catchment - https://www.lawa.org.nz/explore-data/southland-region/river-quality/mokotua-stream/mokotua-stream-at-awarua/

Waituna Creek catchment - https://www.lawa.org.nz/explore-data/southland-region/river-quality/waituna-creek/

When emergency works might be actioned

While the recent situation didn’t trigger Section 330 emergency action, staff have drafted several scenarios in which Environment Southland would consider the use of emergency works. The following are some scenarios/triggers when Environment Southland would assess the situation against the 330 criteria, and consider the use of emergency works.

Considerations

1. Three years have passed since the Waituna Lagoon was last opened (either naturally or artificially). If ecological advice demonstrated risk to biodiversity, an opening to take immediate preventative measures to avoid that effect may be justified.
2. An extensive bloom of algae or cyanobacteria that may have wider, adverse ecological impacts.
3. The sediment build-up or changes to the sediment composition that was so significant it posed a threat to the ecological health of the lagoon.
4. One or more nutrients reach critical levels whereby there is an increased risk to the severity of algal blooms or water chemistry becomes harmful or toxic.
5. Ruppia density exceeds and is having an adverse effect on the ecological and cultural health of the lagoon.
6. Dissolved oxygen saturation reaches levels that pose a threat to the ecological health of the lagoon. This may be super-saturation or hypoxic/anoxic.
7. If the forecast water level is likely to cause ongoing serious damage to critical property or infrastructure

Please note, consideration would also be given to the safety of any potential opening before any action was taken. Consideration will also be given to the potential ecological effects of an opening, including the duration it will remain open.

Each situation must be considered on a case by case basis. Reaching a trigger level does not guarantee any action will be taken. Any decision will also take into consideration the longer term effects of opening the lagoon, and timing.

Lake Waituna opening consent application 2021/22

The existing permits that provide for openings of Waituna Lagoon expired in early 2022.

Lake Waituna has been periodically opened to the sea by artificial means since 1908. The initial openings were to aid game fish passage and since 1958 the primary purpose of the openings has been to aid land drainage. Lake openings also enable the flushing of nutrients and sediment and aid native fish passage. The Lake has generally been opened about once a year, usually when the lake level gets to 2m above sea level. The existing permits (in place until decisions are made about the opening consent) include resource consent conditions that determine when the Lake can be opened at different times of year, including specific water levels.

View the existing (pre-2022) coastal permit.

Ongoing work on to improve the ecological health of Lake Waituna and its catchment led to the formation of the Whakamana Te Waituna Charitable Trust. The Trust has implemented a number of initiatives including a programme of work within the Waituna catchment focused on improving the health of the lagoon and ensuring the rural community thrives. Part of this work programme has focused on relieving the pressure on farm land from high lagoon levels by creating a landward buffer.

In 2020/21, the Trust initiated a workstream to develop an opening regime for the Waituna Lagoon that supports ecological health and cultural values. This involved reviewing the current consent conditions and considering a broad range of ecological and cultural values associated with the lagoon. A Technical Assessment has been prepared that assesses the effects of openings and makes recommendations on a new opening regime based on ecological and cultural values. The Technical Assessment recommends an opening level of 2.5 metres as well as provisions to open the lagoon to facilitate fish passage and for flushing excessive nutrients.

Read the Technical Assessment here.

Read a summary of the Technical Assessment here.

Te Rūnanga o Awarua and the Department of Conservation lodged a resource consent application for replacement permits. The primary purpose of the application is to establish a new opening regime focused on the ecological health and cultural values of Waituna Lagoon.