Category Archives: Projects

Bay of Plenty River Water quality: State and Trends

River Lake has been working with Bay of Plenty Regional Council to complete a report on the state and trends of water quality in Bay of Plenty rivers.

Over the ten year period 2009 to 2018 the Bay of Plenty river monitoring sites have shown overall worsening trends for total phosphorus (TP), dissolved reactive phosphorus (DRP) and nitrate (NNN); but overall improving trends for absorbance (A440), total ammonia (NH4-N) and electrical conductivity.

The trend results are shown in the graphs below:

River water quality trends 2009-2018
River water quality trends 2009 – 2018
The proportion of BOP river monitoring sites with improving trends (PIT) for selected variables.

The full report can be downloaded from here:

Otamakaokao Awatapu Lagoon Restoration

Awatapu Lagoon restoration planting, October 2019.

River Lake is supporting the Otamakaokao Kaitiaki Trust to restore the mauri of Awatapu Lagoon, Whakatane . We are starting with riparian planting. So far this spring 2019, 45 community volunteers have helped plant 2500 wetland plants and install a small floating nursery.

This project is a partnership between Otamakaokao Kaitiaki Trust and Halo Whakatane. It is supported by the Bay of Plenty Regional Council Environmental Enhancement Fund.

Awatapu 2019: The first wetland plants in the ground.
Awatapu planting day, October 2019

Palmerston North City Wastewater Treatment Plant

Manawatu at Totara Road WWTP discharge, facing upstream.

River Lake has been working with Palmerston North City Council for many years to help understand and reduce the effects of the Tōtara Road wastewater treatment plant (WWTP).

We have undertaken monitoring  of aquatic macroinvertebrates, periphyton, water quality, and diurnal fluctuation in dissolved oxygen. We have also undertaken investigations and experiments to understand river processes.

Learn about the role of nutrients in driving excessive periphyton growth in the Manawatu River, and how periphyton mine phosphorus from fine sediment captured within their mats. Click the link below:

In 2017 PNCC initiated a Best Practical Option (BPO) review of how to improve the treatment and disposal of wastewater in the future. River Lake is part of a team assisting with this process.

Here is our 2019 experimental setup to assess what concentrations of nitrogen are required to control periphyton growth in the Manawatu River.

Periphyton growth experiment, Manawatu 2019

Phosphorus loads to Lake Rotorua

 What is the phosphorus load to Lake Rotorua and how much comes from human activity?

River Lake revised estimates of P loads to Lake Rotorua to account for groundwater catchment areas, geothermal inputs and long-term average loads.

This work contributed to the Science Review required by Plan Change 10 of the Bay of Plenty Regional Water and Land Plan (RWLP).

Read the report here:

Hamill KD 2018. Anthropogenic Phosphorus Load to Rotorua Review and Revision. Prepared for Bay of Plenty Regional Council by River Lake Ltd

Kaituna River Mixing Study

River Lake studied the mixing of diagonal drain pump station with the lower Kaituna River. We used Rhotomine dye WT to understand how well the pump station discharge mixed across the Kaituna River before the intake for the new diversion to Maketū Estuary.

The work was done for Bay of Plenty Regional Council rivers and drainage team.

Rhodamine WT dye entering the Kaituna River from the Diagonal Drain pump station, 2.3 km upstream from the river mouth (9 Nov 2017). Photo by Andy Belcher.
Lower Kaituna River facing towards Maketū Estuary. The borrow pits are visible on the true right of the river. At this location discharges from Diagonal Drain had mixed across 50% to 70% of the river, depending on the tide (9 November 2017). Photo by Andy Belcher.

Kaituna River re-diversion

The Ongatoro/Maketū estuary is a shallow, inter-tidal estuary located north of Te Puke. In 1957 the Kaituna River was diverted directly to sea and the influence of the river on the estuary was dramatically reduced. This resulted in accelerated in-filling from the
flood tide delta, loss of mussel beds, loss of wetlands and sea grass, algal accumulations and changes in the benthic fauna. The project sought to re-divert more of the river back into the estuary to improve the ecology and mauri.

River Lake provided science and planning input for the application to re-divert the Kaituna River back to the Ongatoro/Maketū Estuary. Keith co-ordinated and led the science input related to water quality and ecology. He jointly prepared a gap analysis,  undertook investigations, prepared AEE reports relating to water quality and ecology and presented at the Consent Hearing and the the Environment Court.

Water quality and biota are strongly influenced by internal nutrient loads (e.g. sediments). An important part of the investigations was to quantify the likely internal loads compared to external loading predicted by the hydro-dynamic model. This involved measuring oxygen regimes and mapping algal accumulations.

View River Lakes Assessment of Effects for the Project here:  Kaituna Maketu current state aquatic

Waituna Lagoon Guidelines

River Lake contributed to the Lagoon Technical Group (LTG) and Catchment Technical Group (CTG) advising Southland Regional Council on interventions to protect and restore Waituna Lagoon.

Waituna Lagoon is a highly valued, large brackish coastal lagoon and a wetland of international importance (Ramsar site). Ruppia (seagrass) is a key stone species central to the ecological functioning, of the lagoon. It is threatened by nuisance filamentous algae, sedimentation, an an opening regime that can increase salinity when the seagrass is germinating.

Our work included:

  • Analysing water quality state and trends;
  • Assessing the risk of the lagoon ‘flipping’ to a dirty water state;
  • Contributing the the development of lagoon guidelines with quality targets for lagoon health, and  management options.

Find the report here: Waituna lagoon Guidelines