Peak Runoff Control - Waituna
Most agricultural contaminants in waterways (such as sediment, phosphorus, and E. coli) are mobilised and enter the stream during rainfall events that result in overland flow (surficial runoff).
This research project is funded by Living Water (DOC/Fonterra Partnership) and being undertaken by Land and Water Science with the primary aim of determining the most effective areas in the catchment where mitigations could reduce this issue. This is being achieved through connecting the physiographic science approach at the catchment scale, and a hydrological assessment at the paddock scale. This information will be combined to inform the best locations for controlling contaminant losses through the construction of peak runoff control structures.
Contaminant transport pathways derived from the physiographic science and water convergence at the paddock scale.
Outputs of this project include identifying where the structures could be placed, what the structures should look like, and different monitoring options to quantify their effectiveness. The primary aim of the structures is to slow the rate at which water leaves the landscape. By holding back the runoff, any contaminants suspended in the water settle out before it is slowly released back in to the stream. A secondary benefit is the reduction of stream power downstream, which reduces the potential of stream bank erosion adding more contaminants as well as mobilising contaminants already settled on the stream bed (in the substrate/mud).
Following the project, Living Water will use this information to choose an appropriate sub-catchment of Waituna to trial the structures. Farmers will then be approached to see if they would like Living Water to build and test these structures. After their construction, the effectiveness of each structure will be assessed to understand whether they are both individually and collectively making a difference.