Kapiti Coast groundwater resource investigation Catchment hydrogeology and modelling report Catchment hydrogeology and modelling report investigation resource Kapiti Coast groundwater The Greater Wellington Regional Council promotes Quality for Life by ensuring our environment is protected while meeting the economic, social and cultural needs of the community For more information contact the Greater Wellington Regional Council: Follow the Wellington October 2014 Wellington office Regional Council GW/ESCI-T-14/92 PO Box 11646 Manners Street Wellington 6142 [email protected] 04 384 5708 www.gw.govt.nz Kapiti Coast groundwater resource investigation Catchment hydrogeology and modelling report Mark Gyopari (Earth in Mind Ltd) Doug Mzila (Greater Wellington Regional Council) Brydon Hughes (Liquid Earth Ltd) For more information, contact the Greater Wellington Regional Council: Wellington GW/ESCI-T-14/92 PO Box 11646 ISBN: 978-1-927217-51-1 (print) ISBN: 978-1-927217-52-8 (online) T 04 384 5708 F 04 385 6960 October 2014 www.gw.govt.nz www.gw.govt.nz [email protected] Report prepared by: D Mzila Senior Environmental Scientist Brydon Hughes Mark Gyopari Report reviewed by: H Middlemis Principal Groundwater Engineer Report approved for release by: G Sevicke-Jones Manager, Environmental Science Date: December 2014 DISCLAIMER This report has been prepared by Environmental Science staff of Greater Wellington Regional Council (GWRC) and as such does not constitute Council policy. In preparing this report, the authors have used the best currently available data and have exercised all reasonable skill and care in presenting and interpreting these data. Nevertheless, GWRC does not accept any liability, whether direct, indirect, or consequential, arising out of the provision of the data and associated information within this report. Furthermore, as GWRC endeavours to continuously improve data quality, amendments to data included in, or used in the preparation of, this report may occur without notice at any time. GWRC requests that if excerpts or inferences are drawn from this report for further use, due care should be taken to ensure the appropriate context is preserved and is accurately reflected and referenced in subsequent written or verbal communications. Any use of the data and information enclosed in this report, for example, by inclusion in a subsequent report or media release, should be accompanied by an acknowledgement of the source. The report may be cited as: Gyopari M, Mzila D and Hughes B. 2014. Kapiti Coast groundwater resource investigation: Catchment hydrogeology and modelling report. Greater Wellington Regional Council, Publication No. GW/ESCI-T-14/92, Wellington. Contents 1. Introduction 1 1.1 Background: Proposed regional water allocation framework 1 1.2 Study objectives 1 1.3 Report structure 2 2. Hydrogeology of the Kapiti Coast 3 2.1 Geology 3 2.1.1 Tectonic setting 3 2.1.2 Geological history 5 2.2 Hydrostratigraphy 12 2.3 Groundwater management 12 2.3.1 Otaki groundwater zone 14 2.3.2 Te Horo groundwater zone 14 2.3.3 Waikanae groundwater zone 14 2.3.4 Raumati groundwater zone 14 3. Raumati groundwater zone 16 3.1 Raumati zone geology 17 3.2 Raumati zone hydrogeology 19 3.2.1 Hydraulic properties 20 3.2.2 Groundwater/surface water interaction 20 3.2.3 Groundwater levels 22 3.3 Raumati zone conceptual hydrogeological model 22 4. Waikanae groundwater zone 25 4.1 Waikanae zone geology 26 4.2 Waikanae zone hydrogeology 33 4.2.1 Hydraulic properties 34 4.2.2 Groundwater Levels 36 4.2.3 Groundwater/surface water interaction 43 4.2.4 Recharge and discharge 46 4.3 Waikanae zone summary 47 5. Te Horo groundwater zone 52 5.1 Te Horo zone geology 53 5.2 Te Horo zone hydrogeology 56 5.2.1 Hydraulic properties 57 5.2.2 Groundwater levels 58 5.2.3 Groundwater-surface water interaction 61 5.3 Summary 64 6. Otaki groundwater zone 68 6.1 Otaki zone geology 69 6.2 Otaki zone hydrogeology 72 6.2.1 Hydraulic properties 72 6.2.2 Groundwater/surface water interaction 74 6.2.3 Groundwater levels 77 6.3 Summary 79 7. Kapiti Coast groundwater model 84 7.1 Groundwater modelling purpose and objectives 84 7.2 Numerical model construction 84 7.2.1 Model code selection 84 7.2.2 Model complexity 84 7.2.3 Model domain delination 85 7.2.4 Model design, grid design 85 7.3 Translation of the conceptual model 86 7.4 Boundary conditions 89 7.4.1 External model boundaries and offshore extension 89 7.4.2 Rivers, streams and drains 89 7.5 Rainfall recharge calculation 91 7.5.1 Methodology 91 7.5.2 Climate data 91 7.5.3 Soils mapping and properties 92 7.5.4 Recharge zone delineation 93 7.5.5 Soil moisture balance parameters and calculation 96 7.5.6 Recharge model outputs 97 7.5.7 Recharge model verification 99 7.6 Groundwater abstraction 101 7.6.1 Simulation of garden irrigation abstraction – Waikanae/Paraparaumu 101 7.6.2 Calculation of consented groundwater abstraction 105 7.6.3 Calculated groundwater abstraction in the Kapiti Coast 106 7.7 Hydraulic properties 107 7.7.1 Hydraulic conductivity zonation 108 7.7.2 Specific yield and specific storage zones 113 8. Model calibration 114 8.1 Calibration procedure 114 8.2 Minimising non-uniqueness 114 8.3 Calibration evaluation 116 8.4 Preliminary steady-state calibration and mass balance 118 8.4.1 Results 118 8.4.2 Steady state mass balance 120 8.5 Transient calibration 121 8.5.1 Transient calibration set-up 121 8.5.2 Automated calibration (PEST) 121 8.5.3 Calibration targets,observation data processing and weighting 123 8.6 Automated calibration (PEST) 131 8.6.1 Objective function formulation 131 8.6.2 PEST Optimisation results 131 8.6.3 Calibration validation run 135 8.6.4 Discussion: model to measurement head fit 135 8.6.5 Water balance calibration 148 8.6.6 Groundwater management zone water balances 149 8.7 Calibrated parameter values 156 8.7.1 Parameter sensitivity 156 8.8 Summary 159 8.9 Model limitations 159 References 161 Kapiti Coast groundwater resource investigation 1. Introduction 1.1 Background: Proposed regional water allocation framework In May 2011 Greater Wellington Regional Council (GWRC) published a technical report (Hughes and Gyopari, 2010) detailing a proposed methodology for the conjunctive management of groundwater and surface water abstraction in the Wairarapa Valley. The methodology proposed significant modifications to the existing GWRC Regional Freshwater Plan (RFP)1 in the way that the region’s freshwater resources are allocated to ensure that they are sustainable. The new framework proposes a more holistic approach to water resource management and is built on the concept that groundwater and surface water are a single connected resource and must therefore be managed conjunctively. The integration of groundwater and surface water allocation ensures that the cumulative effects of water abstraction remain within sustainable limits as defined by environmental flows in rivers, streams and wetlands. The framework makes provision for the regulation of groundwater pumping in order to mitigate immediate effects on freshwater ecosystems (streams, rivers, springs and wetlands). It also considers the longer-term cumulative effects of groundwater abstraction on the surface water environment on a catchment- wide scale to establish sustainable groundwater allocation limits. 1.2 Study objectives This report details the investigations undertaken to apply the framework for conjunctive water management methodology to the Kapiti Coast. The objectives of investigation are to: Review and revise the conceptual hydrogeology of the Kapiti Coast; Characterise and quantify the flow dynamics and waters balances of the various aquifers; Characterise groundwater and surface water connectivity; Quantify of groundwater abstraction effects on surface water ecosystems; Review and revise groundwater management zones; Estimate the sustainable allocation limits for each zone based upon criteria such as surface water depletion effects and saline intrusion risk; Apply the conjunctive water management framework. (Kapiti Coast groundwater investigation: Proposed framework for conjunctive water management. Greater Wellington Regional Council, GW/ESCI-T-14/103) 1 WRC (1999) 1118059-V5 PAGE 1 OF 162 Kapiti Coast groundwater resource investigation 1.3 Report structure This report comprises the following sections: Chapters 2-6 – The Hydrogeology of the Kapiti Coast: Documentation of a revised conceptual hydrogeological model for the Kapiti Coast. Chapter 7 – Numerical Model Development: Details of numerical modelling undertaken to determine potential groundwater allocation limits for the Kapiti Coast. Chapter 8 – Numerical model calibration and parameter sensitivity analysis PAGE 2 OF 162 1118059-V5 Kapiti Coast groundwater resource investigation 2. Hydrogeology of the Kapiti Coast Characterisation and conceptualisation of the hydrogeology of the Kapiti Coast has drawn upon previous groundwater investigations (e.g. Kampman and Caldwell 1983, WRC 1994, and URS 2004) and an analysis of subsequently available hydrogeological information. The primary objectives of developing a conceptual hydrogeological model for the Kapiti Coast are: To provide a physical basis for the construction of the regional-scale numerical groundwater model described in the following section; and, To assist implementation of the proposed conjunctive water management framework to the groundwater resources. 2.1 Geology The sedimentary sequence underlying the Kapiti Coast comprises a complex assemblage of fluvial and coastal sediments accumulated as a result of geological processes occurring along the western coast of the lower North Island over the past 400,000 years. These processes include significant variations in sedimentation rates and relative sea levels accompanying cyclic variations in climate between cold glacial and temperate interglacial conditions, structural deformation resulting in active uplift in the Tararua Range and development of a large sedimentary basin to the west, as well as altered sediment supply resulting from episodic volcanic eruptions in the central North Island.