Inglis Estuary – Direct Inflow

INGLIS - FLOWERDALE WATER MANAGEMENTPLAN INGLIS ESTUARY – DIRECT INFLOW Inglis-Flowerdale WMP –Direct Inflow from Streams into Estuary Inglis – Flowerdale Water Management Plan Inglis Estuary – Direct Inflow from Streams Earth Tech Project Number 6307009 Earth Tech Oracle Number 102537 Document History: REVISION ISSUE DATE AUTHOR CHECKED APPROVED NUMBER 10.1.2008 - K Cousins B Dyer B Dyer 7.3.2008 1 K Cousins F Dyer F Dyer Environment Group Earth Tech Engineering Pty Ltd ABN 61 089 482 888 Head Office 71 Queens Road Melbourne VIC 3004 Tel +61 3 8517 9200 All Rights Reserved. No part of this document may be reproduced, transmitted, stored in a retrieval system, or translated into any language in any form by any means without the written permission of Earth Tech Engineering Pty Ltd. Intellectual Property Rights All Rights Reserved. All methods, processes, commercial proposals and other contents described in this document are the confidential intellectual property of Earth Tech Engineering Pty Ltd and may not be used or disclosed to any party without the written permission of Earth Tech Engineering Pty Ltd. © Earth Tech Engineering Pty Ltd 2007 Inglis-Flowerdale WMP –Direct Inflow from Streams into Estuary Contents 1. Introduction ....................................................................................................... 1 2. Estuarine processes ......................................................................................... 2 2.1 Overview of Inglis Estuary Condition .................................................................. 2 2.2 Estuarine Flushing .............................................................................................. 3 2.3 Ecological processes in Estuary - Fish Migration ................................................ 4 3. Hydrology .......................................................................................................... 6 3.1 Licenses ............................................................................................................. 6 3.2 Flow regime ........................................................................................................ 6 3.3 Impact of diversions ............................................................................................ 8 4. Conclusions ...................................................................................................... 9 5. References ...................................................................................................... 10 A BETTER TOMORR OW made possib le 1. Introduction This report is an assessment of the Inglis estuary and is a supporting document in the development of the Inglis-Flowerdale Water Management Plan (WMP) for the Cradle Coast Natural Resource Management (CCNRM) Committee. The report will examine the potential impacts on the estuary associated with the adoption of the proposed WMP, focusing on the effects of summer low flows. These potential impacts will be discussed in reference to the following areas: key estuarine processes, current estuary condition, fish species requiring migration (diadromous and anadromous) and freshwater input (from associated diversions or from key inflows in the catchment). Only key inflows into the estuary will be discussed in this report, and they have been determined to be from the Inglis River, Big Creek and Camp Creek (Figure 1). DPIWE (2005) defines Camp Creek as flowing into the mouth of the estuary but it has been included in this analysis for completeness. In addition to this, Camp Creek has been heavily modified with the lower reaches altered to concrete channels. It is assumed from this observation that there is minimal estuarine area in the mouth of Camp Creek. Where relevant, the report will also make recommendations on any likely actions that are both associated with the WMP and may also impact on the estuary. Figure 1. Location of the Inglis Estuary, indicating the key inflows of Big Creek and Camp Creek. The modified rock weir is located near Site 1 of the FLOWS assessment (Earth Tech, 2007b) A BETTER TOMORR OW made possib le 1 2. Estuarine processes The Inglis estuary has various classifications as a result of state and federal assessments of Tasmanian estuaries but it is commonly classified as a wave dominated delta (Edgar et al. , 1999). This can mean that freshwater input into this type of estuary may be relatively high and, as such, catchment activities can have a large influence on the condition of the estuary (Ryan et al., 2003). Therefore, restricted flows may affect the estuary in summer by resulting in complete or partial closure of the mouth (Pierson et al. , 2002), although this has not been reported in the Inglis River estuary. Generally, restricted flows have the potential to: • obstruct diadromous fish and crustacean migration; • alter estuarine flushing and water quality; and • alter the estuarine salinity gradient. An overview of the Inglis estuary condition and attributes aims to assess if the aforementioned disturbances are likely to occur if summer flows are restricted in the Inglis catchment. 2.1 OVERVIEW OF INGLIS ESTUARY CONDITION Edgar et al. (1999) initially classified the condition of the Inglis estuary as severely modified. It was later reclassified as highly modified as the catchment is dominated by moderate levels of human activities, rather than input from the urbanised tributaries (DPIW, 2006). Edgar et al. (1999) provides only a general understanding and description of the current condition of the Inglis-Flowerdale catchment due to the broad-scale nature of the classification and reliance on dated information (Table 1). Table 1. Summary of condition report for the Inglis-Flowerdale catchment (DPIW, 2006) Area approx. 505 kms 2 (Estuarine Catchment Area) 6.0 km (Estuarine Drainage Area) 2 0.30 kms (Estuarine Area) 6.6 km (Perimeter) 2.2 m (Tidal Range) Conservation Management Priority Very High Relative Representativeness Moderate Biophysical class • Large mesotidal river estuaries located along the north coast Special Values • Phylogenetically distinct fauna species: Ornithorynchus anatinus (platypus) • Threatened fauna species: Prototroctes maraena (Australian grayling) • Priority fauna species: Lovettia sealli sp. nov. A. (Tasmanian whitebait, northern stock) • Priority fauna species: Nycticorax caledonicus (rufous night heron) Condition Poor Land Tenure Security Low A BETTER TOMORR OW made possib le 2 This limitation in background data has hindered determining if the current ecological processes are likely to be impacted by reduced environmental flows. Therefore, for the purpose of this report, Earth Tech have collated all available information on the Inglis estuary to estimate current condition, current uses and likely impacts from limited freshwater inputs in summer 1. A summation of the relevant physical attributes and uses within the estuary are: • The area of the Inglis estuary stretching from the Inglis River at the Bass Highway to the mouth of the estuary (Pers comm , Martin Huzzey, Department of Primary Industries and Water) (Figure 1); • The estuary is relatively small in comparison to other estuaries in northwest Tasmania (Edgar et al ., 1999); • There are no saltmarshes in the catchment, which can be typical of a riverine estuary • Big Creek is the only major tributary flowing into the estuary that was not studied in the FLOWS assessment (Earth Tech, 2007b); • Threatened migratory fish species are likely to be present in the catchment (refer to Table 2); • The catchment has high social values related to recreational fishing of estuarine dependent species - Tasmanian whitebait, Australian salmon and brown trout (refer to Table 2). 2.2 ESTUARINE FLUSHING Earth Tech has compared the estuary tidal volume with freshwater low flow volume to determine the extent of estuarine flushing during summer. The estuarine tidal volume was estimated based on a surface area and tidal range to calculate a volume. For an estuarine area of 0.3km 2, and a hypothetical low tidal range of 1 m, the volume per tide is 300 000 m 3. DPIWE (2006) indicates that the tidal range within the Inglis estuary is in the order of 2.2 m thus the volume per tide is 660 000 m 3. With two tides per day the estimated daily tidal flushing of the estuary in the range of 600 and 1300 ML (1 ML = 1000 m3). It should be noted that this analysis is a simplified one, and does not consider the local tidal hydraulics. Given the estimated volume of tidal flushing the contribution of freshwater from the Inglis- Flowerdale system to the estuary in low flow periods (43ML/day 2) is estimated to be in the range of 3% to 7%. This indicates that the Inglis estuary will be dominated by seawater during low flow periods. It should be recognised that this analysis has not considered other contributing tributaries, however, freshwater flows into the estuary are expected to be dominated by those that have been analysed in this study. Overall, it appears that during periods of low flow in the Inglis River the area of saltwater - freshwater interaction for the Inglis estuary would be limited to the section of the Inglis River, in the vicinity of the Bass Highway. 1 Assessment was limited to summer low flows as this is the period when extraction is greatest 2 43ML is derived from 26ML (Inglis River: reaches 1 and 2) and 17ML (Flowerdale River: reach 3). A BETTER TOMORR OW made possib le 3 2.3 ECOLOGICAL PROCESSES IN ESTUARY - FISH MIGRATION The following table lists all fish (native species and species introduced for recreation)

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