Water Storage Development – It’s Time to Act
The variability of water supply from week-to-week, month-to-month, and year-to-year means that many parts of New Zealand have a mismatch between supply and demand in most summer months.
For most parts of Canterbury this hasn’t been an issue for the past two irrigation seasons, but we know well from past drought years that it will be a challenge we’ll face again in future! Climate change projections show the challenge becoming even greater due to increasing water demand, lower river flows in summer months and increasing month-to-month variability.
Strategic water studies over the past twenty years consistently show that water storage is a key strategy to address this water supply reliability problem. Improvements in irrigation efficiency, alone, will not solve it.
One of the Government's goals is to move to higher value land uses that deliver greater export revenue per hectare and per cubic metre of water used (see MPI’s publication “Fit for a Better World”). The sting in the tail of increasing revenue per cubic meter of water used is that the financial loss from water supply shortages increases. Delivering highly reliable water (e.g., 98%) to the primary sector is a critical enabler of moves to higher value land uses — storage is key. On the flip side, maintaining (or reducing) current levels of water supply reliability tends to lock in current land uses.
However, water storage of the scale required is not without controversy. There is a lot of public and political debate about whether New Zealand should build storage to adapt to future climate. The changing regulatory landscape is likely to be a major factor in reducing the primary sector’s access to water, increasing the storage volume needed and the difficulty of securing consents and development finance. Ideal storage sites that are acceptable from all perspectives are challenging to find!
In addition to providing secure water supplies for agriculture and horticulture, water storage developments must focus on delivering multiple long-term benefits to communities and the environment. This must include making provision for environmental flow improvements and community drinking water supplies and may include recreational amenities and flood mitigation.
Given these challenges, designers of storage-based water supply schemes in New Zealand need to take a whole-of-system, strategic approach to their work to ensure that their solutions can deliver long-term farm, community, cultural and environmental benefits. This approach involves understanding local and central government regulations, working through the best available science to find practical options for meeting multiple objectives, and analysing the consequences of foreshadowed changes in regulation and projected changes in climate. Taking this big-picture approach to a project maximises the chances of it proceeding past the design stage. In our opinion, several projects have failed because too much time and money have been spent too soon on detailed dam engineering, without having the fundamental aspects of water supply and demand properly nailed down. Granted, getting the dam design and engineering right is extremely important, but getting the design of the broader water resource system right first will mean that the storage design can be optimised: perhaps the volume of storage required isn’t as big as originally assumed.
Water infrastructure projects take a long time to progress from conceptual design to first water delivery – twenty years would not be unusual. If one started now, water supply may not commence until the 2040s. Climate change projections indicate that we’ll be experiencing severe droughts more frequently by then.
It’s time to take decisive action and get this adaptation journey underway!
