Sediment traps in hill country

The farmers have been involved in riparian fencing and planting but saw a need to try and reduce the sediment load of water channels that appeared during larger rainfall events in small catchment areas on their hill country sheep and beef farms.

This project examined the effectiveness of 3 different sediment traps on three neighbouring properties in the lower Mokau sub-catchment. It found:

• Sediment concentrations tended to increase with the height sampled
• Sediment concentrations were highly variable, but generally decreased between the inflow and the outflow, suggesting that the sediment traps were generally improving water quality
• The sediment trays showed that sediment settled in the base of the trap which means less sediment flowing downstream.
• The farmers faced challenges adapting the riser design to their environment and more work is needed to find a design that works in this environment.
• Maintaining pasture cover within the sediment trap/pond area will help reduce sediment loss even further.