Piako River flood protection scheme
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Much of the Hauraki Plains and Piako catchment lies below sea level, which means flooding can occur from a combination of river flows, rainfall and tidal effects.
The Piako River drains into a large lowland catchment – about 1590 square kilometres – into the Firth of Thames and historically experienced frequent, slow-draining floods that caused prolonged inundation of land and towns such as Ngātea, Turua and Kerepehi.
Large-scale drainage and flood control efforts started in the early 1900s, with the core of the modern scheme built during the 1960s to 1970s to protect people, homes, roads and productive farmland.
The scheme is not designed to a uniform standard, with protection levels ranging from a 50% annual exceedance probability (AEP), which is often called a “1 in 2-year flood”, up to a 1% AEP (1-in-100-year flood event), depending on location and land use.
The scheme was agreed to by the communities, who benefit and mostly pay for it via targeted rates.
The scheme is operated as part of an integrated flood system, including the Waihou Valley flood protection scheme.
Much of the Hauraki Plains lies below sea level, which means flooding can occur from a combination of river flows, rainfall and tidal effects.
An asset rationalisation project near the mouth of the Piako River, which saw three floodgates decommissioned and replaced with one, included the creation of deep water refuges for aquatic wildlife, safe fish passage for tuna/eels and a new 10-hectare habitat for resident and migratory shorebirds.