Thames Valley diversion channel planting and maintenance programme

Funded: $1.08m
Total cost: $1.8m
Project starts: 2024/25
Project ends: 2026/27

The project includes fencing, drain shaping and planting of drainage channels to address the significant bank erosion and slumping of drains that happened following the 2022/23 floods and heavy rainfall, which resulted in increased vulnerability for the rural communities of Te Aroha, Paeroa, Morrinsville and Matamata. This work will ensure the effective operation of the land drainage network to clear surface water, thereby reducing damage to pasture and crops and reducing overall sediment release into the Piako and Waihou river systems, and ultimately improve the performance of the flood protection scheme. The other benefits of this work will be reduced maintenance requirements and enhanced instream and riparian ecological values.

The council has been undertaking small scale drain planting trials for a number of years. Monitoring of its trial sites and results from others doing similar works show reduced maintenance requirements (weed spraying and mechanical excavation) and improved water quality (greater clarity, cooler temperatures and higher dissolved oxygen levels).

Native sedges (Carex) are chosen as the predominant plant because they:

• bind the banks together and prevent sediment from entering water
• provide shading of the water to suppress nuisance aquatic weeds growth, reduce water temperatures and increase dissolved oxygen concentrations
• minimise nutrient runoff, which helps prevent algal blooms and excessive aquatic weed growth
• grow low and don’t impede access to the drain for necessary maintenance
• grow quickly and are cost effective and easily maintained.