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Last updated: 14 December 2011
Related weblink: www.gw.govt.nz
Economic Evaluation of Wairarapa Irrigation Project
Name of Applicant Group: Greater Wellington Regional Council
Contact person: Nigel Corry
Address: PO Box 11646, Wellington 6142
Telephone: 04 802 0334
CIF funding: $264,375
Total project funding: $708,750
Proposed start date: 2009-07
Proposed finish date: 2012-06
The Greater Wellington Regional Council is commencing a formal review of its Regional Freshwater Plan. An innovative approach to the development of RMA planning is required to ensure that sufficient robust science exists to allow for the potential for irrigation proposals – largely by way of water harvesting and storage proposals – to prove viable as a key component of the RMA plan review process. However, sources of water readily available for irrigation – or other purposes - in the Wairarapa are near or at full allocation.
As part of investigating the feasibility of expanding Wairarapa’s existing irrigation infrastructure, a regionally integrated irrigation project will take cognisance of the values and issues pertaining to the catchments’ surface and groundwater resources.
Environmentally responsible management of water within the Wairarapa Valley holds the key to unlocking the valley’s full agricultural potential complemented by the community’s existing rural base.
In particular, challenges are being made to the water allocation provisions of the existing Regional Freshwater Plan as potential irrigators seek water for new proposals, or existing irrigators seek to expand production.
The project therefore seeks to enhance the Regional Council’s understanding of the hydrological and cultural aspects of Wairarapa’s water resource as well as evaluating the economics of an irrigation scheme.
The combination of increased demand for water from agriculture, industry and general population demand now mean that water can no longer be regarded as an infinite resource. In addition, it is predicted that climate change will negatively impact on recharging Wairarapa’s groundwater aquifer for the summer months with less rainfall during winter and spring, along with temperature increases.
For rural land users, access to a reliable water supply is important. If agricultural production is to increase, water must be available at critical times of the year. To achieve this, the water resource needs to be managed in a fully integrated manner, not just periods of low flows and high demand, but also during times of peak flow when water harvesting may be possible.
In addition, the capital cost to establish an irrigation scheme means its imperative to have a detailed understanding of how water interacts within the valley – this project progresses our advancement of that knowledge.
The scope, purpose and objectives of this project, and that relate more specifically to the potential to develop irrigation infrastructure in the Wairarapa, are described below:
The scope of the study includes the water resources of the Wairarapa Valley; groundwater and surface water. The study looks at how these resources might best be utilised to ensure sufficient instream flows exist while at the same time allowing for, and encouraging where appropriate, off line storage and harvesting of water.
The purpose of the study is to better understand the availably of, and demand, for water. It is recognised that this study has the potential to develop the scientific framework for a viable community based irrigation initiative in the Wairarapa which will allow for water storage opportunities to be explored while at the same time providing for the social, environmental and cultural aspirations for the community to be met.
The objective of the study is to ensure that the best use is made of the water resource, taking into account economic productivity but protecting social, cultural and environmental values.
More specifically, the project models and runs scenarios on the linkage between ground and surface water, investigates methodologies for assessing instream ecological values, provides for investigation of iwi environmental and recreational instream values and identifies and quantifies the costs and benefits of an irrigation scheme for the Wairarapa.
Each of the above project components will help inform decisions around the issues of water allocation policy that will play a key role in determining the irrigation potential in the Wairarapa valley.
The focus of this work has been the development of a numerical model that simulates the hydrodynamics of Wairarapa groundwater. The modelling work has been completed with associated technical reports due for publication.
The model has been used to run demand scenarios which has led to proposed management zones and associated water allocation options. These zones take into account the links between surface water and groundwater as simulated by the model. The overall objective of this work is to outline a recommended approach for the management of groundwater/surface water interaction in the Wairarapa as part of Wellington's overall water strategy. The report describing a framework for conjunctive water management for the Wairarapa is due to be presented to Te Upoko Taiao – Natural Resource Management Committee in March 2011. A copy of the report will be released once the committee has approved it.
A report on the instream flow assessment work for the Tauherenikau River is completed apart from the section on iwi values (see Milestone 3). More general methods for assessment of instream flows, generalised habitat models and water quality models have been reviewed for application in the Wairarapa with reports received from Cawthron.
The contract to undertake work on the Iwi consultation on instream values is nearing completion. A literature review has been completed, interviews with kaumatua have taken place, a workshop has been held and a number of significant sites on waterways identified. Field work was carried out in summer 2011 with a report on the project due in March 2011.
Project work and report completed.
The focus of the investigations conducted during the last 4 months has focused on the Wairarapa groundwater model. The actual modelling work has been completed with associated technical reports in the final stage of publication. In terms of scale, each of these reports comprises 300-400 pages for the upper, middle and lower Ruamahanga River catchment respectively.
The model has been used to run demand scenarios which has led to proposed management zones and associated water allocation options. These zones take into account the links between surface water and groundwater as simulated by the model. The overall objective of this work is to outline a recommended approach for the management of groundwater/surface water interaction in the Wairarapa as part of Wellington’s overall water strategy. As the main focus of the report is on the management options that may be considered as part of future policy development the report is primarily intended for a technical/policy audience.
The third and final phase of the investigation therefore describes the management zone work, a framework for conjunctive water management. This phase was the application of the outputs from the first two phases of the project to the development of a management framework to enable sustainable management of the groundwater resources of the Wairarapa Valley. In particular, this work utilised both the conceptual and numerical models developed for the Phase 2 investigations.
The purpose of this phase was to develop recommendations for sustainable groundwater allocation limits as well as the management of individual and cumulative stream depletion effects on hydraulically connected surface water resources resulting from groundwater abstraction. The report is at the final draft stage and is scheduled to be completed late 2010/early 2011
The report on one part of the instream flow assessment work, namely the Tauherenikau River, is completed apart from the section on iwi values. More general methods for assessment of instream flows, generalised habitat models and water quality models have been reviewed for application in the Wairarapa with reports received from Cawthron.
The report investigates flow requirements for sustaining instream values of the river and reviews the appropriateness of existing minimum flow for the river specified under the existing Freshwater Plan.
The contract to undertake work on the Iwi consultation on instream values is underway. The literature review has been completed, interviews with kaumatua have taken place, a workshop has been held and a number of significant sites on waterways identified.
The principal outcome from the last period has been the completion of the technical work on the Wairarapa Groundwater Model Development. This has involved extremely complex work which was tested through a calibration and scenario testing. An independent assessment has been undertaken to ensure the technical integrity of the project which will be used as the basis for a groundwater allocation framework.
Work has commenced on identifying the instream cultural values for Wairarapa streams and rivers. Effectively the background work has been completed to be followed by interfacing through hui. This study will comprise a component of the instream flow assessment also being conducted with the assistance of CIF funding.
The principal milestone achievement has been completion of the Economic Evaluation of the proposed irrigation project i.e. a cost benefit analysis and the economic viability investigation. Overall, it showed that the project is viable from the perspective of all parties namely farmers, the Wairarapa community, plus the entire region. A reasonably conservative set of assumptions was made to ensure that the figures reflected the inherent uncertainties associated with forecasting over 25 years.