16 November 2010 When the well runs dry, we know the true value of water

Recently there has been a strong growth in demand from the agricultural sector in New Zealand to use fresh water for commercial uses such as irrigation.

Professor Ross Cullen, Dr Edward Hearnshaw and Professor Ken Hughey of Lincoln University have undertaken a study to determine the impact that the dam on the Opuha River in South Canterbury has on the river and its catchment.

Professor Cullen says improved understanding of the impacts of water use is particularly topical in Canterbury.

“Irrigation is extremely valuable to agricultural production and can help generate three times the income of non-irrigated farms,” he says. “Around 70 percent of the country's irrigated area is in Canterbury, and the region's high level of evaporation through its dry summers means even more water is required than in other agricultural areas.

“Our research uses an ecosystem service benefits model to investigate what impact the dam and water use has on the ecosystem and what benefits have been derived.”

Professor Cullen says water projects are typically evaluated using cost benefit analysis, but many ecosystem service benefits (the direct and indirect benefits people obtain from ecosystems) are difficult to value and include in cost benefit studies.

“There is a growing appetite for understanding the full range of values gained from human manipulation of water resources. Typically, the approaches used have separate economic, social and environmental analyses, which do not allow an easy summary of the overall merit of projects,” he says.

The Ecosystem Services Model, on the other hand, examines provisioning (for example, food), regulating (for example, water purification) and cultural services (for example, recreation) to assess economic impacts.

Professor Cullen says the research team wanted to make all ecosystem services explicit and quantifiable so they can be accounted for in the evaluation of water use projects. “We want to provide insights for decision makers into the effects of human manipulation on the land for economic purposes,” he says. “This requires the development of a comprehensive set of indicators for ecosystem services to determine the true impact of water use on rivers.

“Existing ecosystem service reviews have often lacked definitive outcomes because they lacked the indicators needed to gauge the effects of projects such as dams. Once a comprehensive set of indicators is developed, you can begin to look at establishing an ecosystem service index to help quantify changes to the ecosystem services,” he says.

Professor Cullen says the Opuha Dam proved the perfect site to test the possibility of listing and quantifying ecosystem services after Environment Canterbury approached Lincoln University to conduct research into the impact the dam had on the river.

The Opuha-Opihi catchment is prone to hot summers, and water extraction by the Levels Plains Irrigation scheme frequently resulted in a dry riverbed in summer, which stranded fish and halted irrigation.

The degradation of the river and low river flows led to the Opuha Dam being constructed in 1998. It was created to store spring run-off water from the mountains which can then be released in summer and autumn to maintain minimum flows and allow continuous irrigation throughout the dry months.

As well as its water storage role, the lake created by the dam provides recreational benefits such as fishing, boating and rowing and also generates a small amount of hydro electricity.

“The first step in the research project was to assess what ecosystem services the river and its catchment provided before dam construction. We then hypothesised what changes we expected to see once a dam was built and tested these hypotheses,” he says.

The research team sought data for a range of indicators to determine the impact of the Opuha Dam on 17 ecosystem services. A wide range of indicators were used, including salmon spawning numbers, water temperature, and gravel extraction. Pre-dam and post-dam data were compared to evaluate impacts.

Professor Cullen says it is well known that the dam has led to significant increases in agricultural output because more water is available for irrigation. The research has also shown there have been three major impacts from the Opuha Dam.

“The dam has created Lake Opuha, changed the river flow regime, and provided more water for consumptive uses,” he says. “This has resulted in a cascade of changes in ecosystem services.

“The change in summer flows means the river no longer dries up and this has been favourable for recreational trout and salmon fisheries, but there has been a reduction in the number of flushing flows. This has changed the river from a braided to a largely single-channelled form. The lack of flushing flows has also increased the risk of in-stream contamination, particularly as water quality has fallen due to land use intensification and reduced the amount and quality of habitat for native birds.” he says.

The results of the study have been published in a report to Environment Canterbury band is publicly available at http://www.canterburywater.org.nz/downloads/ecosystemservices-review-the-opihi-river-case.pdf.

Further developments of the ecosystem services approach are underway.

Project: Ecosystem services review of water projects

Researchers: Professor Ross Cullen, Dr Edward Hearnshaw, Professor Ken Hughey

Funder: Environment Canterbury