Lower Waitaki Hydrogeology
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Lower Waitaki Hydrogeology Report No. R15/54 ISBN 978-0-478-15216-6 (print) 978-0-478-15217-3 (web) Lower Waitaki Hydrogeology Report No. R15/54 ISBN 978-0-478-15216-6 (print) 978-0-478-15217-3 (web) Hisham Zarour April 2016 Report No. R15/54 ISBN 978-0-478-15216-6 (print) 978-0-478-15217-3 (web) 200 Tuam Street PO Box 345 Christchurch 8011 Phone (03) 365 3828 Fax (03) 365 3194 75 Church Street PO Box 550 Timaru 7940 Phone (03) 687 7800 Fax (03) 687 7808 Website www.ecan.govt.nz Customer Services Phone 0800 324 636 Lower Waitaki hydrogeology Summary Background: The Canterbury Regional Council (Environment Canterbury) and the Waitaki catchment communities have embarked on water quality limit setting process as part of the Canterbury Water Management Strategy (CWMS). This joint venture is aimed at producing a sub-regional chapter in the Land and Water Regional Plan (LWRP). Objective: This report provides baseline information on the current state of the groundwater resource quantity and flow (hydrogeology) in the lower Waitaki catchment to inform the collaborative sub-regional planning process. This information is important for the development and analysis of future water and land management scenarios. What we did: I undertook a desktop study with limited field reconnaissance. I synthesised and analysed data from various sources to draw a picture of the current state of groundwater quantity and flow in the lower Waitaki area. What we found: The lower Waitaki area has a dry climate in New Zealand terms. Irrigation is required during summer to maintain crops. Surface water delivered to farms through lined and unlined races meets most irrigation demand. Border dyke is an important irrigation method in the area. The aquifer system is composed of unconsolidated gravelly alluvial sediments infilling valleys and covering floodplains. The aquifer system is relatively thin and groundwater is shallow. Therefore, about two-thirds of the active wells are less than 10 m deep, and more than three-quarters are no deeper than 20 m. More than a quarter of the area’s wells are used for public and domestic water supply, about one quarter for stock, and the rest of the wells are used for various purposes such as dairy supply and irrigation. There are fewer groundwater abstraction consents in the area and the consented volumes are small compared to the rest of Canterbury. The area’s groundwater system is highly connected with surface water. On average, groundwater loses about 54 million cubic metres per year to the lower Waitaki River surface water system. However, this represents less than 0.5% of the river’s total flow. Wetlands and springs are found on the lower terraces at the toe of higher terraces. Many of these emerge as a result of increased groundwater recharge from irrigation, which has raised the water table. Groundwater flow velocities in the area are high, so changes in land use in areas underlain by aquifers will likely result in measurable and noticeable changes in the quality of groundwater and connected surface waters within 1–5 years. What it means: In the lower Waitaki catchment, land use changes can affect groundwater and surface water quantity and quality fairly quickly. Local water table mounding and increased spring and seepage flow can occur as a result of increased irrigation. On the other hand, more efficient irrigation and water delivery systems may cause wetlands to shrink and spring flows to drop. Similarly, modernisation of irrigation practices may result in lower dilution (i.e. higher concentrations) of contaminants such as nitrate in groundwater. The contribution of groundwater losses to surface waterways represents a small fraction of the total flow in the lower Waitaki River (less than 0.5%). Nonetheless, groundwater losses to surface water are critical to smaller systems such as Waikākahi Stream and Whitneys Creek, both in terms of quantity and quality. This makes careful consideration of groundwater quantity and quality an integral requirement to environmental management planning in the area. Environment Canterbury Technical Report i Lower Waitaki hydrogeology ii Environment Canterbury Technical Report Lower Waitaki hydrogeology Table of contents Summary ................................................................................................................ i 1 Introduction ................................................................................................ 1 1.1 Legal and planning framework ................................................................................. 1 1.2 Report scope and coverage ..................................................................................... 4 2 Methodology and concurrent related work ............................................. 4 3 Previous work ............................................................................................ 6 3.1 Geology .................................................................................................................... 6 3.2 Hydrogeology ........................................................................................................... 6 3.3 Groundwater quality and age ................................................................................... 6 3.4 Groundwater recharge and allocation limits ............................................................. 7 4 The study area ........................................................................................... 7 4.1 Extent, definition and main characteristics ............................................................... 7 4.2 Water resources and values ..................................................................................... 7 4.3 Climate ..................................................................................................................... 8 4.4 Physiography and surface water drainage pattern ................................................... 8 4.5 Geology .................................................................................................................. 10 4.5.1 Basement rock ........................................................................................... 10 4.5.2 Late Cretaceous strata .............................................................................. 14 4.5.3 Paleogene–Neogene strata ....................................................................... 14 4.5.4 Late Quaternary deposits .......................................................................... 15 4.6 Structural geological setting ................................................................................... 16 4.7 Springs and wetlands ............................................................................................. 16 4.8 Surface water hydrology ......................................................................................... 17 4.9 Soil .......................................................................................................................... 19 4.10 Land use ................................................................................................................. 19 4.11 Irrigation infrastructure ........................................................................................... 20 5 Hydrogeology ........................................................................................... 24 5.1 Hydrostratigraphy and groundwater occurrence .................................................... 24 5.2 Groundwater wells .................................................................................................. 26 5.3 Hydrogeological parameters .................................................................................. 31 5.4 Groundwater levels and flow directions.................................................................. 31 5.4.1 Concepts .................................................................................................... 31 5.4.2 Groundwater flow in the study area ........................................................... 31 5.5 Groundwater recharge and discharge .................................................................... 33 5.6 Effects of topography on groundwater flow ............................................................ 33 5.7 Groundwater flow velocity, travel time and residence time .................................... 34 5.8 Groundwater-surface water interaction .................................................................. 34 Environment Canterbury Technical Report iii Lower Waitaki hydrogeology 5.8.1 Waitaki River and main tributaries ............................................................. 34 5.8.2 Coastal streams ......................................................................................... 38 5.8.3 Wetlands, ponds and springs .................................................................... 39 5.9 Groundwater use and abstraction consents ........................................................... 39 5.10 Hydrological budget and groundwater system summary ....................................... 42 6 Conclusion ............................................................................................... 45 7 Acknowledgements ................................................................................. 45 8 References ............................................................................................... 45 Appendix A Rainfall calculations maps ................................................. 50 Appendix B Subdivision of the Quaternary and