PHYSICAL MEASUREMENTS OF GROUNDWATER CONTRIBUTIONS TO A LARGE LAKE by Nicole Jean Pyett B.Sc. (Hons), University of British Columbia, Canada, 2010 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE COLLEGE OF GRADUATE STUDIES (Environmental Sciences) THE UNIVERSITY OF BRITISH COLUMBIA (Okanagan) September 2015 © Nicole Jean Pyett, 2015 Abstract Population increases and climate change are expected to increase water stress in the semi‐arid Okanagan Valley in the Interior of British Columbia. Groundwater discharge from the largest unconsolidated aquifer system in the Okanagan Valley to Okanagan Lake was directly measured between September 2011 and August 2013. Seepage meter measurements (331) and gradient calculations (73) were used to measure flow from the Kelowna aquifers in an effort to constrain groundwater values in a basin‐scale water‐balance model constructed to inform water use and planning decisions within the Okanagan Valley. The complexity of the subsurface environment in the Kelowna area led to the construction of a 2‐D MODFLOW transect to provide a sensitivity analysis of the percentage of total flow captured within the study area using a reasonable range of hydraulic conductivity values for the known confining and confined layers. Forty‐two MODFLOW scenarios estimated 26% ‐ 100% of the total flow from the Kelowna aquifers to Okanagan Lake was captured within the study area. Long‐term station seepage meter measurements showed a large range of annual variability with flux measurements which ranged from 10‐11 to 10‐9/10‐8 m3/m2/s. A substantial reduction in flows observed within the study area between study year one (4.1 x 105 m3) and study year two (2.9 x 105 m3) was potentially due to anthropogenic water extractions. The annual groundwater discharge estimate of 3.7 x 105 m3 found flow from the Kelowna aquifers to be less than one percent of some previous estimates and likely less than seven percent of the volume being extracted from upgradient aquifers. Long‐term provincial potentiometric monitoring indicated groundwater pumping rates have likely exceeded recharge in some Kelowna aquifers for the past 34 years. Other studies using modelling and geochemistry have suggested groundwater pumping is inducing recharge from adjacent fluvial water bodies in some areas. The low discharge from the Kelowna aquifers to Okanagan Lake suggests cautious groundwater extraction rates need to be established in the Kelowna area to ensure the groundwater system can continue to support both human and environmental water needs. ii Preface Interim study results were published as: Pyett, N. and Nichol, C. (2013). Physical measurements of groundwater contributions to a large lake. Conference proceedings from GeoMontreal: 66th Canadian Geotechnical Conference & 11th Joint CGS/IAH‐CNC Groundwater Conference. The paper is included in its entirety as Appendix G. The conference organisers, the Canadian Geotechnical Society (CGS), retain no copyright to the papers reproduced in the conference proceedings. The text in the paper was wholly written by N. Pyett with editing contributions from C. Nichol. No sections of the paper have been fully reproduced within the thesis but portions of the background material (e.g. groundwater/surface water interactions) have been integrated into the thesis document. Figure 1 from Pyett & Nichol (2013) was created by C. Nichol but was not reused in the thesis. Figure 2 was a previously published figure (Roed and Greenough, 2004) which benefitted from overlays completed by C. Nichol. This figure was reused as thesis Figure 2.11 (with permission from C. Nichol and the copyright holder of the original figure). Results released in Pyett and Nichol (2013) were based only on data collected in the first year of a two year research project. The initial understanding of the results discussed within the paper were expanded on and clarified throughout Chapters 4 and 5 of the thesis document. iii Table of Contents Abstract........................................................................................................................................... ii Preface ........................................................................................................................................... iii Table of Contents .......................................................................................................................... iv List of Tables ................................................................................................................................ viii List of Figures ................................................................................................................................. ix Acknowledgements ....................................................................................................................... xii CHAPTER 1: INTRODUCTION .......................................................................................................... 1 1.1 Objectives ...................................................................................................................... 2 1.2 Research Value .............................................................................................................. 3 1.3 Thesis Format ................................................................................................................ 3 CHAPTER 2: BACKGROUND ............................................................................................................ 7 2.1 Literature Review .......................................................................................................... 7 2.1.1 Patterns of Groundwater Discharge in Large Water Bodies ................................. 7 2.1.1.1 Sediment heterogeneity ............................................................................ 7 2.1.1.2 Shoreline profile shape .............................................................................. 8 2.1.1.3 Changes in regional hydraulic gradient ..................................................... 9 2.1.2 Methods in Groundwater/Surface Water Interactions....................................... 10 2.1.2.1 Physical methods ..................................................................................... 11 2.1.2.2 Thermal methods ..................................................................................... 12 2.1.2.3 Chemical methods ................................................................................... 13 2.1.2.4 Biological methods ................................................................................... 14 2.1.2.5 Numerical modelling ................................................................................ 14 2.1.2.6 Water‐balance estimations ...................................................................... 14 2.1.2.7 Sampling design and results reporting .................................................... 15 2.2 Site Background .......................................................................................................... 16 2.2.1 Study site ............................................................................................................. 16 2.2.2 Climate ................................................................................................................. 16 2.2.3 Hydrology ............................................................................................................ 17 iv 2.2.4 Geology ................................................................................................................ 18 2.2.5 Hydrogeology and Groundwater/Surface Water Interactions ........................... 19 2.2.6 Patterns of Groundwater Discharge ................................................................... 21 2.3 Approach ..................................................................................................................... 22 2.3.1 Application of Previous and Historical Approaches to the Kelowna Site ........... 22 2.3.2 Approach Proposed for the Kelowna Groundwater Discharge Study ................ 23 CHAPTER 3: METHODS ................................................................................................................. 37 3.1 Gradient Methods ....................................................................................................... 37 3.1.1 Shoreline Vertical Flux Calculations ................................................................... 37 3.1.2 Large Scale Horizontal Flux Calculations ............................................................ 37 3.2 Seepage Meters .......................................................................................................... 38 3.2.1 Long‐Term Stations ............................................................................................. 38 3.2.2 Cluster Measurements and Transects Parallel to the Shore .............................. 39 3.2.3 Control Measurements ...................................................................................... 40 3.2.4 Method Comparison Trials ................................................................................. 40 3.2.5 Transects Perpendicular to the Shore ................................................................ 41 3.2.6 Point Measurements .......................................................................................... 41 3.3 Overall Flow Calculation ............................................................................................