Waikato River Water Take Proposal
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WAIKATO RIVER WATER TAKE PROPOSAL Lower Waikato River Bathymetry Assessment Changes Consequent to Development for Watercare Services Ltd December 2020 R.J.Keller & Associates PO Box 2003, Edithvale, VIC 3196 CONTENTS EXECUTIVE SUMMARY ....................................................................................................................... 4 1. INTRODUCTION ........................................................................................................................ 5 2. SUMMARY AND CONCLUSIONS ................................................................................................ 8 2.1 INTRODUCTION .......................................................................................................................... 8 2.2 “NATURAL” VARIABILITY IN FLOW RATES ........................................................................................ 8 2.3 HISTORICAL CHANGES IN BATHYMETRY ........................................................................................... 9 2.4 HYDRO DAM DEVELOPMENT ........................................................................................................ 9 2.5 SAND EXTRACTION ..................................................................................................................... 9 2.6 LOWER WAIKATO FLOOD PROTECTION ......................................................................................... 10 2.7 LAND USE CHANGES ................................................................................................................. 10 2.8 SEDIMENT REMOVAL THROUGH ADDITIONAL WATER TAKE .............................................................. 11 2.9 CONCLUSIONS.......................................................................................................................... 11 3. REVIEW OF DEVELOPMENT IN THE WAIKATO RIVER ............................................................... 12 4. “NATURAL” VARIABILITY IN FLOW RATES IN LOWER WAIKATO RIVER.................................... 15 4.1 ANALYSIS OF FLOW RECORDS BETWEEN 1963 AND 2020 ............................................................... 15 4.2 FUTURE TRENDS ....................................................................................................................... 18 5. HISTORICAL CHANGES IN BATHYMETRY IN THE LOWER WAIKATO ......................................... 23 5.1 INTRODUCTION ........................................................................................................................ 23 5.2 BATHYMETRY CHANGES AND ANALYSIS IN MOBILE BED RIVERS ......................................................... 23 5.3 LOWER WAIKATO RIVER - AVAILABLE DATA................................................................................... 28 5.4 ANALYSIS OF LOWER WAIKATO RIVER DATA .................................................................................. 28 5.5 DISCUSSION ............................................................................................................................ 29 6. HYDRO DEVELOPMENT ........................................................................................................... 31 6.1 THE HYDRO DAMS .................................................................................................................... 31 6.2 EFFECT OF THE HYDRO DAMS ON RIVER MORPHOLOGY ................................................................... 32 7. SAND EXTRACTION ................................................................................................................. 33 7.1 AVAILABLE DATA ...................................................................................................................... 33 7.2 EFFECT OF SAND EXTRACTION ON BATHYMETRY ............................................................................. 36 7.2.1 Mercer Extraction and Downstream Mean Relative Depth ............................................ 36 7.2.2 Tuakau Extraction and Downstream Mean Relative Depth............................................ 37 7.2.3 Tuakau and Puni Extraction and Upstream Mean Relative Depth ................................. 38 7.2.4 Pukekawa Extraction and Upstream and Downstream Mean Relative Depth ............... 40 7.2.5 Pukekawa Sand Extraction Effect on Local Bathymetry ................................................. 41 7.2.6 General Discussion .......................................................................................................... 45 8 LOWER WAIKATO FLOOD PROTECTION .................................................................................. 46 Page 2 of 110 8.1 INTRODUCTION ........................................................................................................................ 46 8.2 LOWER WAIKATO FLOOD PROTECTION SCHEME DESCRIPTION .......................................................... 46 8.3 INFLUENCE OF LOWER WAIKATO FLOOD PROTECTION SCHEME ON WATER LEVELS AND BED LEVELS ........ 48 9 LAND USE CHANGES ............................................................................................................... 49 9.1 INTRODUCTION ........................................................................................................................ 49 9.2 EFFECT ON RIVER FLOWS ........................................................................................................... 49 9.3 EFFECT ON SEDIMENT YIELD ....................................................................................................... 50 10 SEDIMENT REMOVAL THROUGH ADDITIONAL WATER TAKE................................................... 51 11 EFFECT OF PROPOSED ADDITIONAL WATER TAKE IN CONTEXT ............................................... 52 12 REFERENCES............................................................................................................................ 56 APPENDIX A – GRAPHS OF X-SECTION PROFILES AND CHANGES IN MEAN RELATIVE DEPTH ............ 58 APPENDIX B – DETAILED GRAPHS OF X-SECTION PROFILES, CROSS-SECTIONAL AREA AND CHANGES IN MEAN RELATIVE DEPTH LOCAL TO PUKEKAWA SAND EXTRACTION ZONE ....................................... 93 Page 3 of 110 EXECUTIVE SUMMARY This review has examined those changes that may actually be occurring in the Lower Waikato River as a consequence of development, and what the river may look like in the future. Within this context, the effect of the proposed additional water take of up to 150,000 m3/d net is examined. A number of review elements evolved as being important to understanding how development has affected the hydrology and bathymetry of the Waikato River and how these may continue to be affected into the future. These elements include “natural” variability in flow rates, historical changes in bathymetry, hydro development, sand extraction, flood protection, and land use changes. The proposed take has been considered in the context of each type of development, and also cumulatively in the context of all types of development together. In reviewing the changes that have occurred within the Lower Waikato River, it is clear that the impact of the proposed 150,000 m3/d water take at the Watercare intake site is negligible within the context of both individual and cumulative development changes that have occurred and will continue into the future. Page 4 of 110 1. INTRODUCTION Watercare Services Limited (“Watercare”) is a lifeline utility providing water and wastewater services to a population of 1.7 million people in Auckland. Its services are vital for life, keep people safe and help communities to flourish. More specifically, Watercare is the council-controlled organisation of Auckland Council responsible for municipal water supply within Auckland, and the provider of bulk water supply services to Pokeno and Tuakau in the Waikato District1. Watercare supplies approximately 440,000 cubic metres of water per day (“m3/day”) on average across the year, derived from a range of sources and treated to the Ministry of Health Drinking Water Standards for New Zealand 2005 (revised 2018). Watercare’s three main water supply sources are:2 • Water storage lakes in the Hūnua and Waitākere ranges; • A groundwater aquifer in Onehunga; and • The Waikato River. The exact proportion supplied from each source varies daily, depending on a range of factors including the levels in the storage lakes, forecast rainfall, treatment plant capacity, and maintenance requirements. In December 2013, Watercare applied to the Waikato Regional Council (“WRC”) for resource consents to authorise abstracting an additional 200,000 m3/day of water from the Waikato River, a new water intake structure and discharges from a new water treatment plant. Since that time, Watercare’s water take application (and the associated applications) have been on hold while the WRC processes and determines other applications to take water from the Waikato River Catchment that were lodged before Watercare’s application. During the period from late 2019 through to mid-2020, the Auckland region experienced one of the most extreme drought events in modern times with rainfall for the period between January and May 2020 being approximately 30% of what would normally be expected for that period. At Watercare’s recommendation, in May 2020 Auckland Council imposed water use restrictions in Auckland for the first time since the early 1990s. Watercare also took additional steps to improve security of supply during the drought by exercising emergency powers under section 330 of the 1 Under a bulk supply agreement with Waikato District.