Part Four: Managing flood risk

• the legislation relevant to flood risk management
• principles for managing future flood risk
• options for managing future flood risk
• challenges in managing future flood risk.

Relevant legislation

The two main pieces of legislation relevant to climate change and flood risk management are the Resource Management Act 1991 (RMA) and the Civil Defence Emergency Management Act (CDEM) 2002.

The RMA requires regional authorities to control the use of land for the avoidance or mitigation of natural hazards. Territorial authorities are required to control the actual or potential effects of the use, development or protection of land, including for the purpose of avoiding or remedying natural hazards. The Resource Management (Energy and Climate Change) Amendment Act 2004 further requires local authorities to have particular regard to the effects of climate change.

The CDEM Act is another key piece of legislation for flood risk management. The Act primarily focuses on the sustainable management of hazards, resilient communities and on ensuring the safety of people, property and infrastructure in an emergency. The CDEM Act recommends an approach based on risk reduction, readiness, response and recovery.

Although risk reduction is primarily achieved through proactive planning as required by the RMA and the CDEM Act, other relevant legislation for climate change and flood risk management includes the Building Act 2004, the Local Government Act 2002 and the Soil Conservation and Rivers Control Act 1941.

Principles for managing future flood risk

Local government operates under a range of principles that are set out in the legislation described above or that have evolved through good practice and case law. The following principles should also be incorporated into all aspects of planning and decision-making about managing flood risk exacerbated by climate change.

• Take a precautionary approach: a precautionary approach to decision-making means you take into account the level of risk, use existing knowledge and account for uncertainties. The principle implies there is a social responsibility to minimise the exposure of your community to harm as much as possible when scientific investigation has found a plausible risk. A precautionary approach should be used when making planning decisions that relate to new development as well as to changes to existing development. Full information on climate change effects may not be available at the time of decision-making, particularly when there is a high level of uncertainty and where decisions are effectively irreversible. A precautionary approach is particularly relevant where there are effects of low probability but potentially high impact (eg, the effects of infrequent but high flood levels in developed flood plain areas).
• Use flexible or adaptive management options: these are options implemented incrementally or as small steps over time, responding to new information and adjusting management gradually, rather than acting in one step. Monitoring is an important part of these approaches and they are good for handling uncertainty, as management is adjusted over time. Being flexible means you do not have to fully implement an option at a single time. Instead, you implement the option in phases and monitor the situation so you know when each additional phase should be implemented.
• Use no-regrets options: these will deliver benefits that exceed their costs whatever the extent of climate change. These should always be implemented where they exist. For instance, if you are already experiencing weather-related problems, then cost-effective actions to deal with them should be no regret options. No regret options are particularly suitable for the near term as they can deliver obvious and immediate benefits, and can provide experience on which to build further actions.
• Use low-regrets options: these have relatively low costs and seek to maximise the return on investment when certainty of the associated risks is low. Ensuring that any changing rainfall patterns are taken into account early in the process of maintaining or improving infrastructure is an example of a low regrets option.
• Avoid making decisions that will make it more difficult for you or others to manage climate change flood risks in the future: this involves not locking in options that limit further adaptation in the future.
• Use progressive risk reduction: new developments should not be exposed to, nor increase, flood risk over their intended lifetime. For existing developments the level of risk should be progressively reduced.
• Adopt an integrated, sustainable approach to the management of flood risk: this approach aims to consider a wide range of perspectives to decision-making that contributes to the environmental, cultural, social and economic well-being of people and communities.

Options for managing future flood risk

Managing present-day and future risk from flooding through policy development, planning and resource consenting involves a combination of risk-avoidance and risk-reduction activities.

For already developed sites, a wider mix of mechanisms for avoiding, reducing and managing flood risk can be useful. The treatment options could be a combination of avoiding risk where possible, controlling risk through structural or legislative measures, transferring risk through insurance, accepting risk, emergency management planning, warning systems, and communicating risk (including residual risk) to affected parties. When planning new development, infrastructure and services to avoid flood hazards over their intended lifetime, the most effective and sustainable approach is to take a precautionary approach.

While the range of options available to manage flood risk is likely to be the same in the future, the mixture of options you choose to use may be influenced by how climate change will affect flooding in a particular location. For example, climate change could potentially exacerbate your existing flood risk and this may alter your flood management priorities into the future, change your community’s acceptability or tolerability of flood risk or mean that you choose different flood risk management options. In practice, you are likely to consider a range of factors to determine the most appropriate treatment options, such as through cost−benefit analysis and community consultation. Some possible options for managing flood risk are outlined below.

• Take an integrated catchment management approach to managing flood risk where you consider a range of perspectives across a catchment, in contrast to a piecemeal approach that separates land management from water management.
• Use planning-based tools such as regional policy statements, zoning and rules in regional and district plans, resource consent processes and conditions, urban development/growth strategies, asset management and planning, strategic catchment-based management and the development of flood hazard management plans. Preparing for Climate Change has a useful checklist for considering climate change in local government plans.
• Use non-regulatory methods such as guidelines and codes of practice (eg, that promote appropriate design specifications for stormwater management systems), siting and designing buildings to minimise risk, or risk transference through insurance.
• Use soft engineering solutions for more natural flood risk management. This involves maintaining or restoring the natural river and coastal features and processes with the aim of slowing down the flow of water and storing water along catchments. By restoring natural land and water processes, natural flood management techniques can directly contribute to reducing flood risk to people and property, and provide additional benefits such as conservation of biodiversity, habitat protection and improved water quality and amenity. Natural flood management can also be used in combination with hard engineering solutions.
• If necessary, consider hard engineering solutions or structural treatment options (eg, stopbanks), which aim to reduce the frequency of occurrence of a hazard by modifying the hazard itself through structural or built measures. Hard engineering solutions should be considered after natural flood management solutions have been looked at. This is because natural solutions can be more sustainable in the long term, are cheaper to maintain and can provide additional benefits to local communities. Examples of structural treatments include upstream storage of floodwaters, stopbanks and floodwalls, erosion protection methods, floodways and deviation channels, and household/business flood protection measures.
• Increase public awareness of flood risk through making available, and/or facilitating and supporting, educational material, hazard maps, websites, public talks and meetings. Providing information and raising awareness of flood risk is an approach that can be used to support other methods for managing flood risk. There are also ways of raising public awareness through statutory mechanisms, such as incorporating hazard and risk information in regional and district plans, and in other planning documents (eg, long-term council community plans, strategic plans and possibly annual plans). Providing information on hazard risks alone does not always influence people’s decision-making on purchasing property, or their behaviour and choices when living within at-risk areas.

Issues for managing flood risks

In considering the principles and options for managing flooding there are some significant challenges in achieving effective flood risk reduction. Climate change may further complicate some of these challenges including how to deal with residual risk, the acceptability of risk, dealing with uncertainties and providing appropriate levels of service from your infrastructure to your community.

Identifying residual risk

Residual risk is the risk remaining after risk reduction measures have been put in place. Residual risk may be related to failure of the risk reduction measures, parts of the community that do not benefit from the risk reduction measures proposed, or risks from events that exceed the design standards of the structural risk-reduction options. Climate change may increase the amount of residual risk you need to manage over time. Examples of options for managing residual risk include insurance, emergency management planning, warning systems and community education.

Acceptability of risk

It is important not to confuse the cost of flood risk treatment with determining the acceptability or tolerability of flood risk. Just because a community may not want to, or cannot afford to, reduce the flood hazard through the use of an engineering solution does not necessarily make the risk acceptable. Other treatment options should be considered, such as planning controls or risk transference through insurance. In some cases, managed retreat might be appropriate.

Dealing with uncertainty

Flood risk assessments and climate change science will always have a level of uncertainty associated with projections for how climate change will affect natural processes such as sea-level rise and rainfall. Other aspects of the risk assessment also contain uncertainties, including those due to limited data, hydrological flow estimation and fragility of infrastructure. A precautionary approach requires action based on our current understanding of the effect of climate change on flood risk. From time to time you may need to reconfirm that your infrastructure will perform in the future climate as described in the Hutt River case study. In the end you will need to take action and identify adaptable solutions based on a combination of advice from the best expertise and information available at the time balanced with council funding and planning processes and priorities.

Level of service

Another important part of the risk evaluation stage is reaching agreement through community consultation and engagement on the minimum levels of service that you and your community want from your infrastructure. Many local authorities define minimum levels of service for new development, and some define intervention levels for existing development. The flood risk assessment process will enable local authorities to decide whether they will be able to maintain these levels of service under climate change, or whether it will be acceptable to reduce minimum levels of service over time. When considering whether the levels of service should be allowed to be reduced in the future, inter-generational equity should be considered. This will help ensure that decision-making is not unfairly burdening future generations with flood risk that will be unacceptable to them.