The objective of the Lower Waikato Waipa Control Scheme is to provide flood protection to rural agricultural land in the Waipa and Lower Waikato valleys and to provide protection for the towns of Te Kuiti, Otorohanga and Huntly. A large component of the existing scheme is in the Lower Waikato Management Zone.
The limiting design flood is the one percent Annual Exceedance Probability (AEP) event (100 year recurrence interval), except for specific areas where a lower standard of protection was adopted for economic or other reasons.
An additional objective was incorporated into the scheme works subsequent to the Tongariro Power Development. This objective aimed to offset the effects of increased river levels due to the additional water diverted into the Waikato River as a result of this scheme. These works are known as the Tongariro Offset Works.
Protection is achieved by a combination of the following:
Since it was constructed, the Scheme has been successful in achieving its objectives and continuation of the service is justified because:
The Lower Waikato Waipa Control Scheme was originally funded on the basis of 75 percent from Government subsidy, 12.5 percent from sand royalties and 12.5 percent from landowner contributions that were advanced in the form of loans which will be repaid in 2003.
Project Watershed maintenance costs for the scheme include depreciation, which will be used to fund annual refurbishment works
The Asset Management Plan for the scheme notes that the overall benefit cost ratio for ongoing management and maintenance of the scheme is 8. All sections of the scheme apart from the Mangawara section have a benefit cost ratio well in excess of one. For these sections the high benefit cost ratio shows that continued maintenance of the scheme works is sustainable. The Mangawara section works have a benefit cost ratio of 1.2 which indicates that this part of the scheme is economically viable. However, the relative benefits are not as great as for other parts of the scheme.
For Deroles, studies demonstrated sufficient economic benefit that the landowner agreed to the Council’s construction and operating funding proposals.