Ecological water requirements of the Lower De Grey River Department of Water Looking after all our water needs 168 St Georges Terrace, Perth, Western Australia Environmental water report series PO Box K822 Perth Western Australia 6842 Phone: 08 6364 7600 Report no. 20 Fax: 08 6364 7601 June 2012 www.water.wa.gov.au 3053–30–0612 Ecological water requirements of the Lower De Grey River Department of Water Environmental water report series Report no. 20 June 2012 Department of Water Disclaimer 168 St Georges Terrace This document has been published by the Perth Western Australia 6000 Department of Water. Any representation, Telephone +61 8 6364 7600 statement, opinion or advice expressed or Facsimile +61 8 6364 7601 implied in this publication is made in good National Relay Service 133 677 faith and on the basis that the Department www.water.wa.gov.au of Water and its employees are not liable for any damage or loss whatsoever which © Government of Western Australia may occur as a result of action taken or not taken, as the case may be in respect of any June 2012 representation, statement, opinion or advice referred to herein. Professional advice should be obtained before applying the information This work is copyright. You may download, contained in this document to particular display, print and reproduce this material in circumstances. unaltered form only (retaining this notice) for your personal, non-commercial use or use within your organisation. Apart from any use This publication is available at our website as permitted under the Copyright Act 1968, <www.water.wa.gov.au> or for those with all other rights are reserved. Requests and special needs it can be made available in inquiries concerning reproduction and rights alternative formats such as audio, large print, should be addressed to the Department or Braille. of Water. ISSN 1833-6582 (print) ISSN 1833-6590 (online) ISBN 978-1-921789-78-6 (print) ISBN 978-1-921789-79-3 (online) Acknowledgements This report was prepared by Robyn Loomes from the Department of Water’s Environmental Water Planning section. The author acknowledges the input and comments provided by Mike Braimbridge, Michelle Antao, Rob Donohue, Ben Drew and Fiona Lynn. Contents Ecological water requirements of the Lower De Grey Summary vii 1 Introduction 1 1.1 Purpose of this document 1 1.2 Study area 3 2 Groundwater-dependent ecosystems 10 2.1 Groundwater-dependent ecosystems in the De Grey study area 10 2.2 Hydro-ecological linkages 13 3 Approach to determining ecological water requirements 17 3.1 Overview 17 3.2 Linkages 17 3.3 How we determined hydrological thresholds 18 3.4 Recharge classes 18 3.5 Site selection 19 4 Ecological water requirements 21 4.1 Developing the ecological water requirements 21 4.2 Recharge classes 31 4.3 Environmental water requirement summary 35 Appendices 39 Shortened forms 57 Glossary 58 References 60 iii Ecological water requirements of the Lower De Grey Figures Figure 1 Map showing the lower De Grey River EWR study area 2 Figure 2 Total monthly discharge for the Coolenar Pool gauging station on the De Grey River (1975–2010) 4 Figure 3 River flow analysis showing months of flow and years of low flow (<10 per cent average annual flow) 5 Figure 4 Geological cross-section of lower De Grey River study area 6 Figure 5 Depth to groundwater at selected bores across the study area 6 Figure 6 Bore data recorded across the De Grey River area since 1974, x represents data points 8 Figure 7 Location of Coolenar Pool gauging station, EWR pools, monitoring bores and the Namagoorie borefield 9 Figure 8 EWR sites and estimated depth to groundwater on the lower De Grey River 12 Figure 9 Pool levels and percentiles for (a) Coolenar Pool, (b) J96 Pool, (c) Homestead Pool and (d) Makanykarra Pool 22 Figure 10 Water depth percentiles and 0.45 m depth across pool cross-sections at (a) J96, (b) Homestead and (c) Makanykarra pools 24 Figure 11 Water depth percentiles and 1.5 m depth across pool cross-sections at (a) J96, (b) Homestead and (c) Makanykarra pools 27 Figure 12 Groundwater levels and percentiles at (a) bore 7/04, (b) bore U1, (c) bore 6/04 and (d) bore 9/04 30 Figure 13 Wet season flow probability distributions (1975–2011) 32 Figure 14 Mean and absolute groundwater levels for each recharge class at (a) bore 7/04, (b) bore U1, (c) bore 6/04 and (d) bore 9/04 33 Figure 15 Mean and absolute pool levels for each recharge class at (a) Coolenar Pool, (b) J96 Pool, (c) Homestead Pool and (d) Makanykarra Pool 34 iv Ecological water requirements of the Lower De Grey Figure A1 (a) Coolenar Pool and bore 7/04, (b) J96 Pool and bore 3/04 (c) Homestead Pool and bore 9/04, (d) Makanykarra Pool and bore 6/04 and (e) Bulgarene Pool and bore 8/04 40 Figure B1 Relationship between total magnitude of wet season flow and groundwater levels at bores (a) U1, (b) 7/04, (c) 9/04 and (d) 6/04 42 Figure B2 Relationship between wet season river stage height and groundwater levels at bores (a) U1, (b) 7/04, (c) 9/04 and (d) 6/04 42 Figure B3 Relationship between duration of wet season river flow events and groundwater levels at bores (a) U1, (b) 7/04, (c) 9/04 and (d) 6/04 43 Figure B4 Relationship between duration of wet season no-flow events and groundwater levels at bores (a) U1, (b) 7/04, (c) 9/04 and (d) 6/04 43 Figure C1 (a) Bores U1 and 3/04, (b) Bores 9/04 and T2 and (c)Bores 6/04 and U1 44 Figure D1 J96 Pool (a) 5th percentile, (b) 20th percentile, (c) 50th percentile 45 Figure D2 Homestead Pool (a) 5th percentile, (b) 20th percentile, (c) 50th percentile 45 Figure D3 Makanykarra Pool (a) 5th percentile, (b) 20th percentile, (c) 50th percentile 46 Figure F1 Location of additional groundwater-dependent ecosystems 48 Figure F2 Cuttangunah Well groundwater levels and percentiles 49 Figure F3 Elevation across transect between Cuttangunah Well (left) and Triangle Pool (right) 50 Figure F4 Bore H2 groundwater levels and percentiles 51 Figure F5 Elevation across transect between bores H1 (left) and H2 (right) 52 Figure F6 Bore 12 depth to groundwater and percentiles 52 Figure F7 Bore F1 depth to groundwater and percentiles 53 v Ecological water requirements of the Lower De Grey Tables Table 1 Major river flows in the Pilbara region 4 Table 2 Hydro-ecological linkages of river pool and riparian vegetation ecosystems of the lower De Grey River 14 Table 3 River pools and associated bores 20 Table 4 Historic pool-level percentiles and seasonal variations 23 Table 5 Aquatic macrophyte habitat water depth requirements as historic percentile pool depths, pool levels and frequency and duration of levels 25 Table 6 Deep pool habitat water depth requirements as historic percentile pool depths, pool levels and frequency and duration of levels 28 Table 7 Groundwater level/depth requirements as historic percentile levels, depth to groundwater and frequency and duration of levels 31 Table F1 Historic groundwater level/depths 53 vi Summary Ecological water requirements of the Lower De Grey Ecological water requirements (EWRs) are The De Grey alluvial aquifer is recharged the water regimes required to maintain directly from infiltration of water through dependent ecosystems at a low level of risk the riverbed. Groundwater ecosystems (WRC 2000). EWRs are a key part of the water dependent on the aquifer are river pools, allocation process, which also considers the riparian vegetation and aquifer ecosystems social and cultural requirements of the water (stygofauna). The water requirements of resource and its consumptive demand. We stygofauna are poorly understood and also use EWRs in operating strategies and to hence they are not considered specifically help set licence conditions for proponents in this report. We have focused on four sites wishing to abstract water. representative of river pools and riparian vegetation across the study area. The Pilbara groundwater allocation plan will set allocation limits for the lower De Grey In previous studies of alluvial aquifers in the River alluvial aquifer. The Water Corporation’s Pilbara, hydro-ecological linkages have existing De Grey borefield (Namagoorie), been used to describe how groundwater which supplies water to the Port Hedland maintains biodiversity and ecological water supply scheme, is located in this processes and to define hydrological aquifer. This document supports the thresholds. To determine the EWRs this study allocation plan by describing the EWRs for uses a combination of these hydrological groundwater-dependent ecosystems of the thresholds and thresholds based on lower De Grey alluvial aquifer. statistical analyses of local hydrological data. To meet the EWRs we have set water- level criteria that reflect the varying water To set EWRs that reflect seasonal conditions, availability conditions experienced in the we considered different water availabilities. Pilbara region, rather than rigid criteria. These are presented as percentile thresholds. This will ensure that a natural water regime, Water availability conditions have been reflecting dry and wet periods, will be defined as: maintained. The De Grey River is intermittent – it flows after rainfall from summer cyclones • drought conditions: pool or and autumn thunderstorms. Compared with groundwater levels <5th percentile other Pilbara rivers, flow is reliable and has been recorded in all but one of the past • dry conditions: pool or groundwater 36 years. In addition, the De Grey’s mean levels <20th percentile annual flow from 1974 to 2010 (1342 GL) • average/above-average conditions: is an order of magnitude higher than the pool or groundwater levels >50th region’s next largest rivers – the Ashburton percentile.