The existing 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. In conjunction with extensive native and exotic forest cover, these existing works provide a high level of protection to the present catchment and to Lake Taupo.
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. The emphasis in this zone is on riparian areas, since this reflects the nature of the erosion risk in the pumice land zones and the fact that extensive protection works are in place in many of the hill country areas.
Field surveys have identified a further 131 km of waterways either actively eroding or with high erosion potential. For hill country erosion, assessment of Land Use Capability units for the zone shows that 13 percent of the zone or 36,694 ha of pastoral land classified as between Land Use Capability classes 6 and 8e is considered at risk.
Under Project Watershed, it is proposed that 90 km of this riparian erosion be treated to achieve the sediment reduction. This riparian length is an estimation of the primary areas at risk which were not included in the earlier scheme. The Liaison Subcommittee has agreed these planning assumptions. The gaps in the present coverage, and the proposed new work include key catchments on the western side of the Lake and in the north east. A small amount of lakeshore protection work has also been included in the proposal.
Without the new works there is likely to be an increase of sediment transported into Lake Taupo from its tributaries. As well as affecting farm production, this could reduce the amenity values associated with the high water quality of Lake Taupo, such as trout fisheries, swimming, tourism and water sports.