There are some areas of the Upper Waipa catchment where additional protection is considered appropriate. The requirement for new works has been identified by means of the estimation process for soil conservation discussed in section 8. Proposals include treatment of eroding hill country areas, particularly in upper reaches of key catchments, steps made toward stabilising the Tunawaea landslide area, and riparian protection within the main channels and other priority sub catchments.
It is proposed that 496 km of stream banks in the zone be treated. This riparian length includes 298 km of waterways that are either actively eroding or have high erosion potential plus a further 198 km included for practical reasons.
Land use capability assessments for the Upper Waipa catchment show a total of
7841 ha which can be classified for erosion risk potential as severe. It is estimated that 10 percent of this erosion has been treated. It is proposed to treat a further 20 percent of the hill country type erosion. Treatment would take the forms of open pole planting or the fencing, retirement and planting of severely eroding areas.
The proposals to stabilise the Tunawaea landslide area have been brought forward as requested by the Subcommittee. The issue of purchasing land to be retired in the area, as recommended, has not yet been considered by Council.
The landslide and damming of the Tunawaea Stream occurred in 1991 and the dam failed during a minor flood event in 1992. As a result of this natural event, the landslide area has continued to provide a heavy sediment load into the Waipa River during rainfall events, and the debris from the landslide has continued to affect the Waipa River channel and valley floor upstream of Toa Bridge.
The Upper Waipa Strategy identified that significant works were required to stabilise the landslide environs and the debris in the valley floor, and Project Watershed was to provide a mechanism that would fund the necessary work.
The costs for managing the Tunawaea landslide and its downstream effects have to date been included in both Project Watershed’s soil conservation and river improvement works. Managing the landslide area and the downstream debris is better considered as a single, separate project, as the soil conservation works and river improvement works have the same purpose, and in this area will include a mixture of the same types of work.
In addition, the issues relating to the area of the Tunawaea landslide and debris are considered to be different from the normal soil conservation and river improvement works, as there is more catchment and Regional benefit and less local benefit from the proposed works.
Accordingly, a separate funding policy has been developed for the soil conservation and river control works from the Tunawaea landslide downstream to the Toa bridge.
In the Middle Waipa catchment the existing Waitomo Catchment Control Scheme is well documented in the Asset Management Plan. The level of service and associated justification has been agreed with the community and affected landowners. A range of benefits result from the scheme. These include saved loss from erosion, farm management benefits (stock shelter and shade, paddock subdivision), reduction in stock losses, production forestry returns and protection of farm and community infrastructure (farm access and local roading). Landowners and the local community primarily benefit.
Other benefits to the Middle Waipa catchment include water quality protection, aesthetic enhancement and resource protection. There are a range of beneficiaries, including the local and wider communities. In particular, commercial tourism interests operating in the immediate Waitomo area benefit.
There are some areas where additional protection is considered appropriate. The requirement for new works has been identified by means of the estimation process for soil conservation discussed in section 8. Proposed new works include protecting the steeper areas of this zone at risk from surface erosion, and riparian protection in identified key sub catchments within the zone.
It was initially proposed that 1084 km of stream banks in the middle Waipa catchment be treated. This riparian length includes 494 km of waterways that are either actively eroding or have high erosion potential plus a further 590 km included for practical reasons. The priority streams identified include the Waitomo, Turitea, Puniu and Mangapiko.
Land use capability assessments for the middle Waipa catchment show a total of 8718 ha which can be classified for erosion risk potential as severe. It is estimated that 15 percent of this erosion has been treated. It was proposed to treat a further 15 percent of the severe hill country type erosion. Works may take the forms of open pole planting, and the fencing and planting of the most erodable areas.
However the (former) Middle Waipa Liaison Subcommittee considered that soil conservation works implementation should be discussed in further detail on a subcatchment basis, and supported the concept of pilot studies to demonstrate the nature of the proposal in the first instance. The estimate therefore assumes only a low level of work for the initial five year period. The work will be reviewed after that time.