The Lower Waikato Management Zone covers an area of 283,757 ha. The zone represents 20 percent of the total project catchment area. The boundaries of the zone are shown in map 2. Of the total area, 82 percent is in pasture, three percent in production forestry, and 10 percent in native vegetation, scrub and other land uses.
Geologically the area is quite diverse with volcanic materials including tephra accounting for 26 percent of the area. Twenty six percent is made up of alluvial and unconsolidated sediments, greywacke or argillite 22 percent, peat 13 percent and sandstone/mudstone makes up four percent.
The Lower Waikato Waipa Control Scheme is included in the zone.
The Lower Waikato-Waipa Flood Control Scheme is a comprehensive river control scheme designed to provide flood protection and drainage improvements within the flood plains of the lower Waikato and Waipa rivers. The scheme consists primarily of stopbanks, pump stations, floodgates, and main river channel improvement works. Scheme construction was commenced in 1961 and completed in 1982.
The Lower Waikato River is that portion of the Waikato River extending from Ngaruawahia to the Waikato Heads. Above Ngaruawahia, the River is generally confined within a well incised channel. At Ngaruawahia the River becomes wider and slower flowing, and the flood plain is low and wide.
In its natural state, lakes and wetlands dominated the Lower Waikato floodplain. Today much of this land has been drained and brought into agricultural production. Below Tuakau the River widens out and branches into many smaller channels threading their way through a myriad of small islands before entering Maioro Bay, a wide open tidal expanse of water. From Maioro Bay the River exits through the single narrow channel at the Waikato Heads to the Tasman Sea.
The original area of low lying land in the Lower Waikato, comprising the floodplains of the Waikato River and its tributaries and substantial areas of wetland, was approximately 36,400 ha. Approximately 17,200 ha of this is directly protected by existing scheme works including stopbanks, floodgates and pumping stations. An additional 16,500 ha benefits from improvements to the waterways and river channels (including the main channel of the Waikato River) and the Community Works designed to control ponding areas. Within the Mangawara River Valley the scheme provides protection to approximately 8,300 ha of rural land. In addition to protecting pastoral land, the scheme provides protection to the urban settlements of Huntly in the Lower Waikato zone, and Te Kuiti and Otorohanga in the Waipa zone.
Since the original scheme was completed, two significant works are currently being undertaken as extensions to the Lower Waikato Scheme works.
The Deroles Flood Protection Project comprises a stopbank, pump station and gravity outlet. It is designed to protect 117 ha of low farming land within the Deroles property in the vicinity of Lake Whangape from flooding.
The Mercer West Flood Protection Works are proposed flood protection and drainage works on the area of land adjacent to the western bank of the Waikato River between Mercer and Meremere, protecting approximately 356 ha of low-lying flat farmland. The works consist of stopbanks along the Waikato River, a low return bank along the Morrison Drain and five floodgated outlet structures creating three separate compartments - Northern, Morrison Road and Southern. Rating levels are subject to further progress with these works.
After approaches from the landowners, the projects were developed under the capital works programme of the Lower Waikato-Waipa Control Scheme. Recognising direct and wider community benefits associated with the works, Council proposed that the landowners fund 75 percent of the construction costs (approximately $700,000 for Deroles and $1.1m for Mercer West). The remaining 25 percent is to be funded by Council to reflect the local and wider community benefits from the work. Studies demonstrated sufficient economic benefit for the landowners to agree to this proposal, subject to conditions. Landowner approval for Mercer West has not been received to date, and progress is subject to this approval.
The existing scheme is presently managed by several different agencies, including Environment Waikato and the Franklin and Waikato district councils.
The approximate capital value of the components of the Scheme are:
|Franklin District Council }||$24.0m|
|Waikato District Council }|
|Otorohanga District Council||$2.7m|
The following local areas have decided to take responsibility for maintaining their local protection works and have been excluded from Project Watershed for local protection rating at this stage: Whiskey Flats, Horseshoe, Te Kohanga, Onewhero West, Onewhero East, Tuakau and Ohairoa.