Environment Waikato will be closely monitoring the impact of pine-pasture conversions in Waikato River catchments above Lake Karapiro, due to concerns that this will significantly increase flood risks downstream.
An Environment Waikato report finds there are potential implications for flood protection works in the Lower Waikato. With increased water flows due to the conversion of pine plantations to pasture in the upper Waikato River catchment, this is likely to impact downstream resulting in reduced protection standards for stopbanks.
For example, in assessing the impact of the proposed Wairakei Pastoral conversions, the report estimates that up to 33 per cent of the freeboard in the lower Waikato for a 100-year storm may be lost. This means floods would more frequently overtop the stop banks and flood productive farmland.
“Given that only the Wairakei Pastoral proposed conversions are assessed in this report, Environment Waikato considers these findings as a minimum level of impact,” said Environment Waikato's chairman Jenni Vernon.
“The effects of the private and Carter Holt Harvey conversions would be additional, but have not yet been comprehensively evaluated.”
Implications of the report’s findings
The report raises significant issues for a number of Environment Waikato's work programmes, including Project Watershed, flood risk management, policy review for land use above Karapiro and civil defence requirements.
Environment Waikato will now be conducting a comprehensive review of the implications of the impact on flood risk. Once that review is completed, Environment Waikato will look at a range of issues, including options such as whether to introduce new regulations or adjust its Project Watershed rates to ensure flood risks are managed appropriately.
“In the interim, we will advocate to those district councils where the land use change is known to be occurring or proposed (for example Taupo, Rotorua and South Waikato districts) that they take into account the findings in this report when exercising their function to control the use of land for the avoidance or mitigation of natural hazards.”