Water resources in the catchment have been well studied.  Over the last 15 years, many studies have dealt with groundwater movements, the groundwater/surface water interface, flow requirements for aquatic species and water allocation. In addition, a large body of research has focussed on the Lake itself, including its water quality, ecological values and cultural values. The following paragraphs summarise many of the available reports on Lake Ellesmere/Te Waihora and its catchment.

Memorandum: Review of climate change modelling for Selwyn/Te Waihora plan (142 kB) 

Recent reports (2010 onwards)

Te Waihora (Lake Ellesmere) water balance modelling: Horrell 2011 (3.6 MB)

Te Waihora/Lake Ellesmere catchment: ecological values and flow requirements: Burrell 2011 (2.8 MB)

The surface water resource of the Lake Ellesmere/Te Waihora catchment: Clark 2011 (4.5 MB)

Modelling of stream discharge and groundwater levels in the Te Waihora/Lake Ellesmere catchment: Williams 2011 (2.4 MB)

Modelling of stream discharge and groundwater levels in the Te Waihora/Lake Ellesmere catchment - Appendices: Williams 2011 (5.1 MB)

Technical review of the effectiveness of the existing groundwater management regime operating in the West Melton Special Zone: Callendar 2011 (10.5 MB)

Groundwater resources in the Te Waihora/ Lake Ellesmere catchment: management issues and options: Williams 2010 (4.5 MB)

Older reports (1999 – 2009)

Vertical flow in Canterbury groundwater systems and its significance for groundwater management: Lough & Williams 2009

The geology of the Canterbury Plains allows groundwater flow vertically across the sedimentary layering structure as there are no laterally extensive impermeable layers. However, resistance to vertical flow is greater than resistance to horizontal flow.The report concludes that pumping from a well at any depth can induce changes in the water levels and storage volumes in the strata throughout the system, not just the aquifer it abstracts from. Deep wells may develop falls in the water table and stream depletion effects more slowly, and over a more wide-spread area. This ultimately changes the recharge to/discharge from the system. The reduction in storage and lowering of the water table in the shallow aquifer will not always equal the abstracted volume if there are other sources of water present, such as surface water. In this case, the depletion of water will be apportioned between groundwater and the hydraulically connected surface water body. A key relationship is that the lower the vertical hydraulic conductivity and the deeper the well, the smaller but more widespread the drawdowns will be in the shallowest aquifer.
Vertical flow in Canterbury groundwater systems and its significance for groundwater management.(pdf 12.13 MB)

Instream habitat and flow requirements for Birdlings, Halswell, Harts and Lee: Brooker and Graynoth 2008

This study provides an assessment of flow regime requirements for particular sites on these four streams. Physical habitat modelling and related techniques were used to assess the effects in flows on in-stream habitat. The approach was applied to discrete reaches of the streams to assess the effects of variations in discharge on the amount of habitat for key fish species. As a consequence, the following minimum residual flows, mostly for brown trout, were recommended:

• 0.3 m³/s for Birdlings Brook at Lochheads Road
• 0.5 m³/s for Halswell River at Ryans Bridge
• 1.25 m³/s for Harts Creek at Timberyard Road
• 1.5 m for Lee River at Brooklands

Habitat flow regime requirements for Birdlings Brook, the Halswell River, Harts Creek, and the Lee River (pdf 4.57 MB)

Instream habitat and flow regime requirements in the Lower Selwyn River: Brooker and Graynoth 2008

Brooker and Graynoth recommend minimum flows for the Lower Selwyn/Waikirikiri (between Meadowbank and ~500 m upstream of Rotopapa) based on in-stream surveys, historical reports and physical habitat modelling that assess effects of changes in flow on physical habitat, fish stocks and fisheries.  Results: brown trout would require a minimum flow of 0.7-1 m³/s at Coes Ford, which likely provides for spawning if maintained in winter. Eels and other native fish are likely provided for at a minimum flow of 0.3 m³/s, with more flow being beneficial. The maintenance of flushing floods and freshes for channel maintenance is recommended to remove fine sediments and habitat creation.
Instream habitat and flow regime requirements in the Lower Selwyn River (pdf 1.84 MB)
 

Evidence in the matter of applications to take and use groundwater in the Rakaia Selwyn groundwater allocation zone: Horrell 2007

Graeme states that flows in lowland streams are declining in the Rakaia-Selwyn groundwater allocation zone due to lower spring flows and lower groundwater tables. These trends are apparent in representative streams. Graeme relates these trends to trends in consented water takes for each stream catchment.
Evidence in the matter of applications to take and use groundwater in the Rakaia Selwyn groundwater allocation zone (pdf 8.74 MB)

Relationships between groundwater pressures and lowland stream flows in the Lake Ellesmere Area: Aitchinson-Earl 2006

The report provides an analysis of measured groundwater pressure and level in association with stream flows in the eastern lowland tributaries of Lake Ellesmere. The findings confirm that the various drains, streams and lowland rivers reflect groundwater pressures in the water bearing strata, with the shallowest strata having the strongest influence.  The report comments that the above relationships can be used to develop threshold pressures for wells at which to cease abstractions in order to maintain flows and in-stream values in adjacent waterways. However, further stream monitoring and analysis are required before stream flows can be used as an indicator for groundwater pressure and to develop an adaptive groundwater allocation system.
Relationships between groundwater pressure and lowland stream flows in the Lake Ellesmere area (pdf 1.16 MB)

The hydrogeology of the Upper Selwyn Catchment - MSc thesis summary: Vincent 2005

The thesis gives a detailed overview of the hydrogeology in the upper Selwyn. Significant surface losses occur in the upper reaches of the river between Coalgate and Bealey Road, and further downstream between Greendale and Dunsandel. Well heads show that the river provides significant recharge to shallow aquifers. Surface flow losses depend on the water table conditions, but also on total flow and duration of flow peaks. The Hororata River gains significantly between Derrets Road and the Selwyn confluence, which is due to numerous springs derived from surface losses in the Selwyn. Spring flow in (mostly depression) springs between Cotons Road and Derrets Road is permanent. Groundwater occurs in three aquifers (unconfined from 0-30 m, semi-confined from 40-85 m and semiconfined/confined deeper than 100 m). Significant leakage occurs between these aquifers. Dominantly rainfall-recharged water was identified in aquifers 1 and 2 north of the Selwyn in the Greendale area. Dominant river-recharge to aquifers 1 and 2 occurs south of the upper Selwyn River/Waikirikiri. Water in aquifer 3 was generally older. Groundwater in all three aquifers generally flows in a south-easterly direction. All aquifers receive significant recharge from the Selwyn River/Waikirikiri.
The hydrogeology of the Upper Selwyn catchment - MSc thesis summary (pdf 19.97 MB)

Mean annual low flow (seven day) and mean flow mapping for the Upper Selwyn River Catchment: Smith 2004

The aim of the report is to determine estimates of mean annual low flow and mean flow for the tributaries of the upper Selwyn river/Waikirikiri (upper Selwyn River/Waikirikiri, Hawkins River, Waianiwaniwa River, Hororata River, Ford Stream, Bush stream, Flagpole Stream, Glendore Stream, Wairiri stream, Boundary Stream). Stream flow gaugings from long time monitoring sites (so called primary sites) and concurrent spot gaugings (so called tertiary sites) were correlated to calculate the relationship between these sites. This was done for low to above mean flow for all sites. Statistical regression analysis was used to calculate the 7DMALF, median and mean flows for each tertiary site using the calculated flow relationship between the primary and tertiary site, and the flow recorded at the primary site. The detailed summary of 7DMALFS and mean flows is presented on page 14.
Seven Day Mean Annual Low Flow Mapping for the Upper Selwyn River Catchment (pdf 3.60 MB) 

Management plan for wetlands on council endowment land at Kaitorete Spit and Ahuriri Reserves: Grove 2004

The report recommends management practices to protect areas of regionally important indigenous wetland vegetation in the Kaitorete and Ahuriri reserves. For Ahuriri, the report recommends the partial removal of cattle from some areas and wetland restoration and fencing in other areas. For Kaitorete Spit, the report recommends a shift to a more deliberate conservation management, the removal of cattle from all shore wetlands, the removal of all stock from several paddocks containing wetland vegetation, the control of woody vegetation, the investigation of different grazing regimes and investigation of options for pest control.
Management plan for wetlands on council endowment land at Kaitorete Spit and Ahuriri Reserves (pdf 5.56. MB)

The surface and groundwater resources of the Little Rakaia Zone (Lee River, Tent Burn and Jollies Brook): Grant 2003

The objective of the report is to map wells and springs, describe the hydrology of the area, and to investigate the hydraulic connection between groundwater and surfacewater as well as the potential for stream depleting effects. There are 243 wells in the area (60 active groundwater consents), most of which are less than 25 m deep. Most are used for irrigation and domestic/stock water. Consents near the coast have abstraction cut-offs to prevent saltwater intrusion.
The surface and groundwater resources of the Little Rakaia Zone (pdf 2.56 MB)

Interactions between the streams and groundwater in the Harts Creek and Birdlings Brook Catchments: Facer 2000

The objective of the report is to describe the two catchments, verify data for all wells, locate all springs, describe the hydrology and investigate the hydraulic connection. Both creeks (and their tributaries) are reliant on flow from springs, and some drains discharge into the tributaries. groundwater fluctuations are small and some wells in the lower catchment are affected by Lake Ellesmere’s water level. Water for irrigation in the catchment is mostly taken from groundwater (570 L/s consented), and some surfacewater (260 L/s consented). There is a high hydraulic connection and surface depletion effects occur, especially if wells are shallow, pump at high rates or are concentrated around an area. A stream care group was established in 1998 with residents and Environment Canterbury members. Key concerns identified by the group are deteriorating water quality and the loss of fish populations in Birdlings brook and the degree of connection between groundwater and surfacewater.
Interactions between the streams and groundwater in the Harts Creek and Birdlings Brook Catchments (pdf 9.66 MB)

Investigation of Wood Creek and its relationship to groundwater in the Lake Ellesmere Catchment: Loris 2000

Preliminary field investigation to evaluate the relationship between the creek, groundwater and local surface waters to determine whether a comprehensive stream depletion investigation is necessary. The creek is spring-fed and dry along most of its course most of the year. Minimal flows are only observed after consistent rainfall over a period of several months or in response to flooding of the Irwell River. Conclusion: the creek is spring-fed and not affected by fluctuations and flooding in the Selwyn River/Waikirikiri. Stream depletion investigation is not required.
 Investigation of Wood Creek and its relationship to groundwater (3.76 MB)

Pilot study of the springs of the Halswell – L2 Catchment: Earl 1998

Field study for Environment Canterbury’s Springs Database. Data gathered in the study is intended to be used to consider stream depletion issues. The study contains:

• location of the catchment’s springs (more than 100 springs, with the potential that some have disappeared due to lower groundwater levels and some are unknown or forgotten).
• classification of springs according to type (mostly artesian and 40 % undetermined – the latter still need examination of well logs).
• morphology (mostly point source and seepage).
• geology (most discharge from mud/silt, sand soils or gravels).
• discharge variability (2/3 permanent, 1/3 intermittent; limited data on discharge obtained).
• chemistry (little ions, low alkalinity).

 Pilot study of the springs of the Halswell / L2 Catchment (1.59 MB)

Quality assurance of well and consent data for the Halswell/L2 Catchment: Rossiter 1997

The objective of the report is to provide the groundwork for stream depletion investigations in the two streams. The report deals largely with quality assurance of well and consent data in 1997. 384 wells were inventoried in the field and information on grid reference, well owner, water use and other well details was obtained. On average around 30 % of the allocated groundwater take was utilised per year (informal survey). There was a lack of awareness amongst consent holders, with only 30 % of the well owners knowing how much they were pumping and the existence of measuring equipment being uncommon. A number of consents had not been transferred to the new owner and a number of wells were used without water permits. Water use was dependent on climate, land use, irrigation system design and economic circumstances, which made quantifying actual groundwater abstractions is a difficult task. 
 Quality assurance of well and consent data for the Halswell / L2 (1.17 MB)

Brown Trout spawning in the Lake Ellesmere (Te Waihora) tributaries, and some surrounding catchments: AEL 1997

The report summarises survey results on trout spawning in the spring-fed tributaries of Lake Ellesmere and the Selwyn River/Waikirikiri mainstream and its spring-fed tributaries. It also compares results to an earlier survey by NCFG in 1980s. The data gathered consists of Redd counts and records of reaches of suitable spawning ground, all of which are plotted on GPS maps.
Brown Trout spawning in the Lake Ellesmere (Te Waihora) tributaries, and some surrounding catchments (pdf 7.48 MB)

Seepage into Lake Ellesmere: Ettema & Moore 1995

Aim: to determine the magnitude and spatial distribution of GW seepage into Lake Ellesmere.  An earlier study by Horrell (1992) estimated the seepage flux into the Lake at less than 1 m³/s, noting that it was not a major factor in lake salinity and lake water quality. The authors of this report carried out measurements using seepage meters in summer 94/95. Seepage is thought to be coming most likely from the shallow aquifer (Riccarton formation), from a northerly and north-westerly direction. However, contribution from the deeper aquifer beneath the lake may be substantial.  Findings include that the seepage pattern into the lake is inhomogeneous, with maximum seepage usually occurring within 20 m of the shore. Seepage rates measured varied between 0 and 0.0904 l/min/m² during low groundwater pressure conditions. The average seepage rate was estimated to be 0.014 l/min/m² for the whole study area and 0.016 l/min/m² for the northwest and west lake shore. Average seepage from the south and east were estimated at 0.002 l/min/m². This does not include the known springs in the lake. These seepage rates are estimated to lead to a north / northwest seepage flux into the lake of 0.44 m³/s. Lake level and tidal changes are believed to influence seepage, however, the study has not adjusted the results for these effects.
Seepage into Lake Ellesmere (pdf 4.44 MB)

Electronic copies are not currently available for the following articles

Adaptive management of groundwater in the Rakaia Selwyn groundwater allocation zone -technical and implementation issues: Howard Williams et al 2008

The authors recommend using a recharge-based groundwater method for groundwater management (rather than using groundwater levels as triggers) to restore the flows in spring-fed lowland streams and a continued decline in groundwater tables. The suggested allocation regime is for consent holders to hold a base (fixed) entitlement and an adaptive (variable) entitlement. This method is seen to avoid complications of localised interference effects, it can deal with climate change effects and it allows the prediction of environmental effects from abstractions. Flow in Harts Creek has been used as indicator for modelling the environmental responses to such an adaptive management regime.
 
Reconstruction of a daily flow record along a hydrologically complex alluvial river: NIWA 2008

The article describes and analyses the results of the long term model that has been developed to reconstruct a 22 year record of flows in the Selwyn River/Waikirikiri.  The 60 km long model domain encompasses perennial, ephemeral and intermittent reaches, which are divided into 18 cross-sections along the river main stem. The model results indicate that longitudinal flow patterns can be predicted. However, dry reaches around the Hororata confluence were under-predicted and dry reaches downstream (km 45-49) over-predicted. The model simulates that the mean annual length of dry river channel has increased by 0.6 km/year over the last two decades.

Decreases in low flows in the lower Selwyn River: McKerchar et al 2007

The paper uses multiple linear regression analysis to predicts seasonal low flows at Coes Ford for 1984 -2005. The equation explains more than 90 % of the variance of the flows at Coes Ford. The report concludes that the trend over 22 years of recording is that low flows at Coes Ford have decreased by 32 L/s per year over this period, after the effect of low rainfall has been accounted for. The article rejects the hypothesis that upstream flow and recharge are sufficient to explain variability in Coes Ford flows. The decrease in low flows is consistent with increased water abstractions from groundwater but the analysis is not sufficiently sensitive to identify effects of a low rate of increase in irrigation from 1984 and 1989. Another possible explanation is that the trend in low flows is due to a long-term depletion of groundwater from naturally occurring high levels in the 1950s.

Invertebrate and microbial responses to inundation in an ephemeral river reach in New Zealand - effects of preceding dry periods: Larned et al 2007

The researchers assessed invertebrate and microbial responses to inundation over a range of preceding dry periods in an ephemeral reach of the Selwyn River/Waikirikiri. Indicators used for microbial activity were dissolved oxygen consumption and esterase activity. Sampling sites had been dry for between 1 and 592 days prior to sampling collection.  The study found that taxon richness decreased linearly with dry period length while density decreased exponentially. These patterns indicate that a large number of individuals from desiccation-sensitive taxa liminated soon after flow ceases. A low-density assemblage of a small variety of desiccation-resistant taxa persists during prolonged dry periods. These results indicate that a temporal ecotone exists between an aquatic and a terrestrial ecosystem for about one week after flows cease and a terrestrial system stabilises.

The Selwyn River of New Zealand - A benchmarking system for alluvial plain rivers: NIWA 2007

The report introduces NIWA’s long-term research programme on the Selwyn River/Waikirikiri. It gives a detailed overview of the river’s characteristics, including its perennial, intermittent and ephemeral reaches. The report also describes the river’s response to different weather events and groundwater / surfacewater interactions in its gaining and losing reaches. Complete flow loss occurs in four contiguous reaches: a 2.5 km long perennial losing reach where the river enters the Plains, a 35 km long ephemeral-losing reach on the Plains, followed by a 8 km long intermittent-gaining reach and a 15 km perennial-gaining reach that ends at Te Waihora. These reaches have distinctive flow regimes that reflect variations in runoff and input to/losses from groundwater. In the losing reach, rising groundwater levels following runoff events are apparent. In the gaining reach, some high surfacewater flows precede rising groundwater levels, at other times surfacewater lag behind rising groundwater levels. There are high correlations between flow recorders and wells between 5 and 10 km from the river.

Evidence in the Lynton Dairy case: Horrell 2007

The evidence describes the flow measurements in the Irwell River and Selwyn River/Waikirikiri. It presents an explanation for an apparent decrease in low flows and whether this is a natural phenomenon or a result of increased water allocation.  The evidence analyses 5 different causes of this phenomenon: 

1. reduced flows from upper catchment,
2. reduced groundwater recharge from rainfall in the upper catchment,
3. reduced groundwater recharge from rainfall in the lower catchment,
4. more severe summer droughts, and
5. increased water allocation.  

Lake Ellesmere/Te Waihora lower tributaries minimum flows. Report on the views and local knowledge of the advisory groups: Consensus Environmental Consulting 2003

The report contains the information gathered through the consultation process for the Ellesmere catchment. It provides an overview of local knowledge and views, including documentation from public meetings, advisory group meetings, original submissions from residents and a record of meetings and other procedural matters. 

Estimates of mean annual low flows for Lake Ellesmere tributaries and streams in the Little Rakaia Zone: 2003

The purpose of the report is to establish the ‘natural’ low flows of the lake tributaries and the Little Rakaia Zone. This investigation establishes a 7DMALF for each tributary. These are intended to help the expert panel develop minimum flow recommendations for the Lake Ellesmere tributaries. 30 locations of spot flow measurements were naturalised with regard to upstream abstractions, groundwater and surfacewater and 5 long-term primary sites (long-term monitoring sites). A number of assumptions about abstractions, drainage and seepage were made to arrive at the assumed ‘natural’ flow of the tributaries.

The surface and groundwater resources of the catchment of the Te Waikekewai Creek: Smith 2001

The report notes that the creek is important as a food source associated with Taumutu Marae. Much of the bed is permanently dry due to good drainage in the upper catchment. There are direct contributions to its flow from water races, which are a significant percentage of its total flow. There is a direct spring contribution in its flowing reaches. As part of the study, relevant springs were mapped according to Environment Canterbury’s springs database. Wells in the catchment were quality assured to Environment Canterbury standards in Environment Canterbury’s database.

Effects of irrigation on groundwater recharge between the Rakaia and Selwyn Rivers: Evans 1999

The thesis investigates the relationship between irrigation and groundwater recharge between the Rakaia River and Selwyn River/Waikirikiri, south of Highway 1. It finds that border dyke irrigation, although only a small contribution to groundwater recharge in the study area, results in a marked increase in groundwater levels downstream (up to 6 m directly below irrigation channels, with a dispersion rate of ~0.7 m/km) due to the application of large volumes over a short time on a confined area. As a result, irrigation efficiency is only 8-13 %. Spray irrigation produces ten times less recharge than border dyke irrigation, with irrigation efficiencies varying between 25-90 % depending on soil moisture content.

The Natural Resources of Lake Ellesmere (Te Waihora) and its catchment: Environment Canterbury 1996

This comprehensive report gives a complete overview of the catchment. The chapters cover the physical description of the catchment, land and water use, groundwater and surface water hydrology, water quality, Tangata Whenua, biodiversity, fisheries and recreation.

Ellesmere – A critical area – Resource investigation: Department Lands and Survey 1982

The report describes Lake Ellesmere in terms of the following components:

• physical resources (geomorphology, wetlands, soils)
• biological resource (wetland productivity, flora and Fauna, scientific values)
• cultural values (Maori and European)
• recreational values (Fishing, Bird shooting, boating, passive activities)
• commercial (fishing, agriculture)
• lake level control (stabilisation of levels and stopbanking)
• historical and current attitudes (tenure, public access).