waituna landscape

Reducing Contaminants Using Peak Run Off Control Structures

Biofilters

About the project

High intensity rainfall events (peak run-off events) are when most contaminants get washed into rivers and streams damaging healthy freshwater environments. Scientific studies have shown that by reducing peak run-off, there are correlating reductions in suspended solids (61-94 percent), nitrogen (45-91 percent), and phosphorus (47-88 percent) (Finland, Marttila and Kløve 2010; Marttila and Kløve, 2009). There are also reductions in bank erosion and improvements to downstream aquatic habitat conditions (Marttila, 2010).

 In 2012 scientists from AgResearch identified the potential for different types of drainage to decrease nitrogen and phosphorus losses to Waituna Lagoon. Part of this study looked at Peak Runoff Control (PRC) structures as an alternative option.

The lack of demonstrated success of peak run-off controls (PROCs) at catchment scale is the most likely barrier preventing their widespread adoption. We want to test peak run-off controls within a sub-catchment of Waituna Lagoon as a way of determining if they would be effective at reducing contaminant levels at a catchment scale.

Secondary objectives are to:

  • demonstrate how to use a catchment model to locate ideal sites for interventions
  • design small, cost effective, scalable structures that can be used to reduce peak flow
  • gather evidence of how effective peak run off controls are at improving water quality

The peak run-off controls project is being managed by Living Water with input from Land and Water Science Limited - who helped generate the placement model and Geosolve - who designed the peak run-off control structures. This project is part of the borader Whakamana Te Waituna project.

PROC structures are most effective when used across an entire landscape. Living Water used a hydrological model to identify where best to locate peak run-off controls in the Waituna sub-catchment.

A small, wooden structure has been designed to reduce peak flows at approximately 30 sites. These structures allow water to build up behind them when drains are running and let the water out in a consistent, controlled manner.

This approach will be first trialled in Waituna’s Carrans Creek area. 30 PROC structures will be installed and monitoring set up  to determine if this is a suitable approach for the whole Waituna catchment.

Nicki Atkinson

Nicki Atkinson

Impact & Partnerships Manager
Cain Duncan

Cain Duncan

Fonterra Sustainable Dairying Advisor
Potential peak runoff control structure design
wairua detention bund

Benefits

  • Reduction of contaminants in receiving environments
  • Improved water quality in local waterways

Progress

  • Interactive map and hydrological modelling completed Dec 2018
  • Sub-catchment and 30 sites identified
  • Monitoring programme developed

What's next

  • Contstruct and install PROC structures Sept-Dec 2019
  • Monitor effectiveness and report findings (2020)
  • Case study to be written

More info and graphics of Peak Run-off Control Structures

PROC drone shot