The effects of high lake levels due to climate change on lakeside communities and adjacent land use: Case study: Lake Ellesmere/Te Waihora : A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Water Resource Management at Lincoln University

Abstract

This research aims to assess the effects of sea-level rise on Lake Ellesmere/Te Waihora’s current opening regime and consequently on adjacent land and it’s lakeside communities. The research also aims to assess Lake Ellesmere/Te Waihora’s lakeside communities’ level of preparedness to adapt to these anticipated changes. Unlike other natural hazards that occur abruptly, sea-level rise is incremental and foreseeable, and its effects on coastal areas and communities are expected to occur gradually. Thus, it is crucial to start planning now for future sea-level rise to reduce its adverse impacts on coastal areas and communities. Intermittently closed and open lakes and lagoons (ICOLLs) such as Lake Ellesmere/Te Waihora are vulnerable to the effects of sea-level rise due to their setting within the coastal landscape. The water level of many ICOLLs around the world, including Lake Ellesmere/Te Waihora, are managed by artificially creating a temporary opening through the barrier separating the ICOLL from the sea and inducing premature breakout to protect adjacent land and communities from inundation. The artificial opening is induced when a predefined opening trigger value is reached. The success of the artificial opening is dependent on local sea conditions. As sea levels continue to rise, the continuation of flood management practice in the form of artificial openings for ICOLLs will become challenging due to a decrease in hydraulic gradient between the ICOLL and the sea. Eventually, in order to be able to open Lake Ellesmere/Te Waihora to flow into the sea, the current predefined trigger value will have to increase in height relative to local sea level rise. In the short-term future, this will result in an increase in the risk of temporary inundation of adjacent land. In the long-term future, the increase of the ICOLL artificial opening trigger levels will result in permanent loss of adjacent land and the displacement of communities. A quantitative risk assessment was carried out to determine the effects of sea-level rise on Lake Ellesmere/Te Waihora’s artificial opening trigger levels in the short-term (10 to 30 years) and longer-term (50 to 100 years). This quantitative risk assessment was also able to determine the probable risk of permanent inundation of adjacent land. Geographic Information Systems were used to create contour maps showing the increase in Lake Ellesmere/Te Waihora’s current summer and winter artificial opening trigger levels in response to future sea-level rise. These maps are used to determine who will be affected by increasing amounts of sea level rise. Additionally, a qualitative risk assessment was undertaken to assess the level of preparedness of Lake Ellesmere/Te Waihora’s communities that have been identified to be at risk of inundation as a result of the anticipated increase in the lake’s water levels.