Understanding Eiffelton Irrigation’s targeted stream augmentation.
Thesis DisciplineWater Resource Management
Degree GrantorUniversity of Canterbury
Degree NameMaster of Water Resource Management
Eiffelton Community Group Irrigation Scheme (ECGIS) is a small owner-operated irrigation scheme located near the Ashburton Coast of Canterbury. ECGIS is bisected by a number of drainage channels which serve to lower the water table and keep the land suited for agriculture. ECGIS provides water to its members by targeted stream augmentation. This is where groundwater is pumped from bores into the drainage channels which transports the water to members to enable take for irrigation. Despite the length of operation of ECGIS, little is known about it beyond this conceptual understanding establish in consent documents. Thus, the aim of this investigation was to understand operation and operational effects of ECGIS. This was achieved by meeting four objectives.
The first objective was to document the operation of ECGIS and how operational decisions were made. This was achieved by undertaking semi-structured interviews with ECGIS members. ECGIS consists of 4,000 ha of land, 58 km of drains, and 20 production bores. ECGIS pumps water from the production bores into Deals, Windermere and Home Paddock drains to convey water for irrigation to its members. Bores are pumped into the closest drain, except HP1 which is pumped into Windermere Drain. Diversion gates allow transfer of water between these drains to enable the most cost-efficient use of water. Member access to water is proportional to their relative share of land within the ECGIS footprint. More water can be abstracted from the drains than can be supplied by ECGIS production bores, but each drain has a minimum flow rate which must be complied with whenever an ECGIS member is irrigating. The Race Manager and Assistant Race Manager are responsible for the day-to-day operation of ECGIS. Both are ECGIS members. ECGIS management make decisions on which production bores to use and how much flow to divert between the drains based on their understanding of ECGIS; capacity of the production bores, requirements of each irrigator, and the hydrology of the ECGIS area. Management operates to a 20 L/s surplus in provided water to prevent non-compliance. Management recognises that some bores have better yield than others, while some have higher operating costs. Because of these factors, there is no set order in which production bores are used.
The second objective was to understand the hydrological setting of ECGIS and how scheme operation impacts measured parameters. This was addressed by undertaking field investigation on the largest and centremost drain utilised by ECGIS; Windermere Drain. Gauging results showed Windermere Drain increased in flow towards the coast across 2018, while in 2019 flows increased to Surveyors Road and again fell. Highest nitrate-N concentrations were found at the top of ECGIS and in drain water. E. Coli detections were lowest at the top of ECGIS and increased in drain water down-gradient. Data from the top of ECGIS suggests that Windermere Drain gains in its upper to mid reaches, but loses flow from its mid reaches, with rate increasing towards the coast. When predicting the flow in Windermere Drain over the irrigation period in the absence of targeted stream augmentation and without irrigation abstraction there were significant periods of no flow. This suggests ECGIS ensures flow in Windermere Drain where it may otherwise be dry. Water quality parameters were considered relative to the 2018/19 irrigation season. Targeted stream augmentation by ECGIS is understood to have contributed to lower dissolved oxygen, lower electrical conductivity, and lower nitrate-N concentrations in Windermere Drain and shallow groundwater across the 2018/19 irrigation season.
The third objective was to identify values associated with the Hinds Drains, of which the drains used by ECGIS are a part. This was achieved by conducting semi-structured interviews with ECGIS members and individuals that have been involved in Ashburton water management. The most common value associated with the Hinds Drains by ECGIS members was their function as drains and keeping their land farmable. This likely reflected the fact that most interviewees lived within the Hinds Drains area and so benefitted directly from this primary function of the drains. Recreation (e.g. swimming, fishing) was the value most associated with the Hinds Drains by other interviewees. Presence of introduced and native fish was equally valued by ECGIS Members, but introduced fish were less valued by other interviewees. Interviewees were asked what they would like to see the Hinds Drains used for in a ‘perfect world’. Most interviewees identified restoration to provide for native fish. Many interviewees commented that while it would be nice to see greater biodiversity in the area, developing the drainage network to support such things should not come at the expense of their drainage function.
The final objective was to determine how values could be met using an integrated framework. This was achieved by incorporating information obtained to address the previous three. Integrated water management was selected to identify opportunities to enhance drainage and native fish habitat. It was considered that to address both or either of these that efforts should be made to better understand and optimise existing drainage, and to improve riparian management along Windermere Drain.