EarthSoft Featured in Lake and Reservoir Managment Case Study
March 4, 2010
Lake and Reservoir Management
Managing the lakes of the Rotorua District, New Zealand
Noel Burns, John McIntosh and Paul Scholes, Lakes Consulting, PE/175 Hurstmere Rd, Takapuna, 0622, New Zealand, Environment Bay of Plenty, 5 Quay St., Whakatane, New Zealand
Burns N.M., McIntosh J., Scholes P. 2009. Managing the lakes of the Rotorua District, New Zealand. Lake Reserv. Manage. 25:284–296.
In 2005, Burns, McIntosh and Scholes described strategies to manage the Rotorua Lakes using lake monitoring together with designated baseline Trophic Level Index values established for each lake. Continued monitoring has revealed that 9 of the 12 Rotorua Lakes have Trophic Level Index values in excess of their baseline values. Action Plans have been drawn up for the remediation of these damaged lakes that specify the excess nutrient loading to each lake and propose actions for the decrease of these loadings. Nutrient loading to various lakes has been decreased by upgrading waste treatment facilities, dosing tributary streams with alum, diverting an enriched tributary flow directly into the outflow channel of a lake, precipitating in-lake phosphorus with PhoslockTM and zeolite additions, and removal of macrophyte biomass from a lake and planting an artificial wetland at the entry point of a tributary to a lake. Where data are available, the results of these actions are explored. The similarities between the management system for the Rotorua lakes with the management systems used for two American and European lakes are described. Key words: action plans, trophic level criteria, water quality criteria, trophic level indexes
The twelve Rotorua Lakes lie in the middle of the North Island of New Zealand in what is know as the Central Volcanic Plateau (Fig. 1) and vary widely in character. The beauty of the lakes, together with the interesting geothermal features of the region, have resulted in the Rotorua District being one of the most important national tourist and sport fisheries area of New Zealand. The region also supports a significant amount of successful farming and forestry. The sustainable management of the Rotorua Lakes is the legal responsibility of the Environment Bay of Plenty (EnvBOP) Regional Council.Water quality of the Rotorua Lakes began to change in the early 1900s soon after European settlement of their catchments. A program of routine monitoring of the lakes was started in 1990 by EnvBOP and intensified in 1999 when strategies to halt the deterioration of all the lakes were put into place by EnvBOP (described in detail in Burns et al. 2005). Statutory legislation supporting this management strategy is contained in EnvBOP’s Water and Land Plan (W&LP). This article is a sequel to the previous article (Burns et al. 2005) and describes the strategies, their implementation, their refinement with time and some results of the actions that have been taken.
The Rotorua Lakes are considered to be a national resource in NewZealand.Widespread public concern about the degradation of many of these lakes prompted an investigation and report by the New Zealand arliamentary Commissioner for the Environment (2006). His report endorsed the strategy for restoration of the Rotorua Lakes and led to the signing of a Memorandum of Understanding between the Crown (New Zealand Government) and the Rotorua Lakes Strategy Group, consisting of the Te Arana Lakes Trust, the Rotorua District Council and EnvBOP (EnvBOP 2007a). The Memorandum endorsed the use of the Trophic Level Index (TLI) system together with the TLI targets included in the W&LP. Subsequent to the signing of this agreement, the New Zealand government agreed to pay NZ$72 million toward the estimated cost of NZ$144 million for the planned remedial work to improve the damaged lakes. In 2006, the Government of New Zealand signed an agreement with the TeArawa Maori Trust Board transferring legal title to the Rotorua lakebeds to the local Maori people, while protecting public access, as a partial redress for past actions against the Maori people. This does not currently change EnvBOP’s management role.
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