Heavy damage from summer floods has highlighted the need for ongoing protection works, as well as demonstrating the benefits provided by earlier protection works.
Environment Waikato needs to find $270,000 from its reserves to cover the cost of damage from severe flooding over the summer.
Last week’s Operations Committee heard that two intense electrical storms over two days in mid-January caused considerable flooding and damage to Environment Waikato scheme assets and private property. The damage occurred from Te Aroha to Paeroa, Thames Valley’s drainage area, Te Puru, Tararu, Karaka, Hape, mid Kauaeranga and Mangakirikiri tributaries.
In the Te Aroha-Paeroa catchments the electrical storm on the evening of Friday, January 11 produced more than 150mm of rain in Te Aroha. Waihou Valley Scheme works performed very well, especially on urban streams, although there was substantial damage in the Mangaiti catchments.
The severe storm the next day was an exceptional event causing extensive damage to both Waihou Valley Scheme works and private property. Rainfall figures of 170mm in the mid-Tararu catchment and in the lower Kauaeranga of 142mm in three hours were far more than the 100-year return period of 95mm in three hours for Thames.
The cost of damage to the Tararu Stream amounted to $200,000, but even though the damage was considerable and damage to private property was distressing, without the protection works further severe damage would have occurred, acting Group Manager Bob Priest said.
The works protecting the central business area of Thames performed very well and no property damage was identified. Damage to the scheme works in the Mangakirikiri and Kauaeranga was widespread.
About the same time a similar downpour occurred in the Waitoa/Elstow/Springdale area, with more than 75mm recorded over two to three hours. There was widespread flooding of several hundred hectares including roads, sheds and other assets. Most had cleared by Monday, with flood pumps operating until Tuesday, January 15.
Total damage to the various streams from these events amounted to $70,000.
The Committee also heard details of four earlier floods in December, which was the wettest on record in many parts of the Region, and followed a wet November. Many floods were caused by isolated thunderstorms, rapidly raising river levels.
Lake Taupo levels increased rapidly and the lake needed to be lowered as quickly as possible without causing flooding in the Lower Waikato. Environment Waikato worked closely with other agencies to manage the risk. The Waikato River also flowed brown following severe scouring above Cambridge.
The Committee heard that several initiatives had been taken as a result of the events, with a number of issues to be addressed under Project Watershed.