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
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© 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
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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)
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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
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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).
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2.3 ECOLOGICAL PROCESSES IN ESTUARY - FISH MIGRATION The following table lists all fish (native species and species introduced for recreation) occurring and threatened species likely to occur in the Inglis-Flowerdale catchment that require estuarine habitat (DPIWE, 2003b; IFS, 2007).
Table 2. List of fish species occurring in the Inglis-Flowerdale Catchment and their biological requirements in relation to low flow periods and estuary processes (Koehn and O’Connor, 1990; IFS, 2007) Common Name Scientific name Migration Requirements /Note s Native species Australian Bass Macquaria Larvae/juveniles migrate upstream from estuaries novemaculeata October-April; Adults spawn in estuary in winter Tasmanian smelt Retropinna tasmanica Uncertain, maybe spawns in estuary during spring Tasmanian whitebait Lovettia sealii Adults spawn in Lowland estuarine reaches in early spring Blackfish Gadopsis marmoratus No apparent migration Spotted galaxias Galaxias truttaceus Larvae washed to sea in winter; Juveniles migrate from sea October-December Climbing galaxias Galaxias brevipinnis Same as G. truttaceus Short-finned eels Anguilla australis Brown elvers upstream migration from estuary October-January; Silver Eels downstream migration to sea October- May Tupong (Freshwater Pseudaphritis urvilii Downstream migration to spawn in estuaries Flathead) autumn-winter Larvae stay in estuaries for 9 months Short-headed Mordacia mordax Downstream migration to sea August-November; lampreys Upstream migration to spawn August-December Pouched lampreys Geotria australis Similar to M. mordax Common jollytails Galaxias maculatus Same as G. truttaceus; Adults spawn in estuary early autumn Introduced species for Recreation Sea-run brown trout Salmo trutta Adults spawn upstream in March-August Threatened species likely to occur Australian grayling Prototroctes maraena Adults migrate upstream in October-December then larvae migrate to sea in the early year; Juveniles will return to freshwater 6 months later
This species is listed as vulnerable under the Environment Protection and Biodiversity Conservation (EPBC) Act 1999
The main key threat to fish species requiring migration (diadromous and anadromous) between the freshwater reaches of the rivers and streams that flow into the estuary appears to be the addition of barriers limiting migration, particularly during low flows (DPIW, 2003b).
The EPBC Listed Australian grayling is diadromous, meaning it requires summer flows to fulfil biological requirements of larvae migrating from upper reaches to the sea during early summer (December) (IFS, 2007). DPIWE (2003a) has documented the occurrence of Australian grayling in the Inglis catchment, however, only downstream of the weir. This rock weir was constructed at the upper end of the estuary to stop salt water encroachment on key water diversions (see Figure 1, located between Site 1 in the FLOWS assessment and the Bass Highway). The weir may have restricted this species from upstream migration (see Figure 2). The original weir has been modified with the crest being lowered and the
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downstream slope having a lower grade. These modifications may have facilitated migration back into the catchment in recent years. Presently, there is insufficient data to conclusively deduce that this species is present upstream of the weir nor comment on the population dynamics of the remaining migrating fish species occurring in the catchment.
Overall, it appears unlikely that reduced summer flows could significantly alter estuarine flushing and water quality or the estuarine salinity gradient. However, it has the potential to impact on diadromous fish migration. It is recommended that the rock weir at the upper extent of the estuary be reviewed, and if necessary modified to allow fish to pass, particularly under the minimum flows specified in the Water Management Plan.
Figure 2 Rock weir at upstream extent of tidal influence. Flow is about 600 ML/day (flow at Moorleah is 300 ML/day 5/6/2007) – recommended minimum flow is 43 ML/day which is based on both Inglis and Flowerdale low flows.
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3. Hydrology
This section outlines the hydrology of the streams with significant direct inflows into the Inglis estuary. These streams have been identified as Inglis River, Big Creek and Camp Creek. The minor tributaries of Big and Camp creeks flow directly into the estuary at Wynyard (Figure 1) and are ungauged. Therefore, the hydrological analysis has been determined based on analysis of licences and the DPIW hydrologic model of the Inglis - Flowerdale system.
3.1 LICENSES All consumptive water use in Tasmania requires a licence to extract water from a waterway. DPIW has included all licences for the Inglis Flowerdale system in the Inglis – Flowerdale hydrologic model with each licence being allocated to a subcatchment of the model. The licence data from this model was matched up with the results from the WIMS (Water Information Management System) database to determine whether a licence was a direct take or storage licence. Analysis of the licences is given in Table 3.
Table 3 Summary of licences for Camp and Big Creeks. Licences have been categorised according to surety (S) and whether they allow summer diversions (summer) or winter diversion only (winter). An explanation of the different surety’s in the Inglis-Flowerdale catchment is provided in the Water Management Plan
Grand Stream Direct Take Storage Total S 5 S 6 Total S 1 S 5 S 6 Total Inglis - Flowerdale Summer 956 6241 7196 1179 5 23 1207 8403 Winter 5 0 5 384 1417 390 2191 2196 Total 961 6241 7201 1563 1422 413 3398 10599
Big Creek Summer 192 9 201 23 9 6 38 239 Winter 9 9 75 583 222 879 888 Total 201 9 210 97 592 229 917 1127
Camp Creek Summer 86 81 167 1 2 3 169 Winter 2 2 69 217 170 456 458 Total 88 81 169 69 220 170 459 628
3.2 FLOW REGIME The DPIW model was run under current (full use of licences) and natural (i.e. no extractions) conditions. The model results (Table 4, Figure 3 and Figure 4) show that the impact on the flow regime from these water systems is small. This result is expected considering that the mean annual flow is much greater than the licensed volumes.
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Table 4 Summary of flows and diversions for main waterways entering the Inglis Estuary – flows are current condition flows. Stream Mean annual flow Minimum annual Licenced flow extractions Inglis River 266 000 ML 96 000 ML (2006) 10599 ML Big Creek 21 000 ML 3 200 ML (2006) 1127 ML Camp Creek 12 300 ML 1 740 ML (2006) 628 ML
Big Creek
100.0
90.0
80.0 Current
70.0 Natural
60.0
50.0
40.0 Flow (ML/day) Flow
30.0
20.0
10.0
0.0 0% 20% 40% 60% 80% 100% Percent of modelled flows
Figure 3 Flow duration curve for Big Creek comparing modelled current and natural conditions.
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Camp Creek
100.0
90.0
80.0 Current
70.0 Natural
60.0
50.0
40.0 Flow (ML/day) Flow
30.0
20.0
10.0
0.0 0% 20% 40% 60% 80% 100% Percent of modelled flows
Figure 4 Flow duration curve for Camp Creek comparing modelled current and natural conditions.
3.3 IMPACT OF DIVERSIONS As discussed in Sections 3.1 and 3.2 the volumes of licences are small compared to the mean annual flow. The diversion of flows has not altered the seasonality of the flows into the Inglis estuary so the key triggers for ecological processes will continue to occur at the same time as they would naturally. The major impact of diversions is an increase in the period of low flows caused by diversion for irrigation. The environmental flows set out in the Recommendations Report (Earth Tech 2007c) have taken into account the requirements of the key species and should ensure that the key migratory requirements are maintained. The impact of diversions on higher flows (e.g. summer freshes) will be much less as the response time of the system is short and the rainfall that causes the fresh will also result in a decrease in demand for direct diversions from the system.
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4. Conclusions
Given the limited background information on estuarine processes in the Inglis-Flowerdale estuary, it is unclear how highly modified the estuary is or how tributaries, not analysed in the FLOWS assessment, have impacted on these processes. Overall, it has been determined that the majority of freshwater input into the estuary is from the Inglis-Flowerdale River and that under low flow conditions the volume of tidal flushing is an order of magnitude greater than the freshwater inflows. This will result in a limited estuarine zone (i.e. salinity ranging between fresh and sea water).
The greatest potential impact of the WMP may be the potential of minimum summer flows becoming too low to allow diadromous fish migration at this time. The minimum flows determined in the Flow Recommendations report have been set to achieve the required conditions for fish migration. The rock weir that is located at the upper extent of tidal influence should be assessed and modified as necessary to ensure that fish passage for the diadromous fish that are known, or are expected, to occur in the system can occur for the full range of summer flows (i.e. low flows).
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5. References
DPIW (2006) Waterways Monitoring Report 2006 - Inglis Catchment, Water Assessment and Planning Branch, Department of Primary Industries and Water, Hobart.
DPIWE (2005) Waterways Monitoring Report 2005 - Inglis Catchment, Water Assessment and Planning Branch, Department of Primary Industries Water and Environment, Hobart.
DPIWE (2003a) State of the Rivers Report for the Inglis-Flowerdale Catchment, Technical Report No. WAP 03/12, Water Assessment and Planning Branch, Department of Primary Industries Water and Environment, Hobart.
DPIWE (2003b) Index of River Condition for the Inglis/Flowerdale River Catchment, Water Assessment and Planning Branch, Department of Primary Industries Water and Environment, Hobart.
Earth Tech (2007a) Environmental Flow Determination for the Inglis River – Issues Paper, Unpublished Report to Cradle Coast Natural Resource Management Committee by the Inglis River Environmental Water Requirements Technical Panel.
Earth Tech (2007b) Environmental Flow Determination for the Inglis River – Site Paper, Unpublished Report to Cradle Coast Natural Resource Management Committee by the Inglis River Environmental Water Requirements Technical Panel.
Earth Tech (2008) Environmental Flow Determination for the Inglis River – Recommendation Paper, Unpublished Report to Cradle Coast Natural Resource Management Committee by the Inglis River Environmental Water Requirements Technical Panel.
Edgar, G.J; Barrett, N.S. and Graddon, D.J. (1999). A Classification of Tasmanian Estuaries and Assessment of their Conservation Significance using Ecological and Physical Attributes, Population and Land Use. Marine Research Laboratories - Tasmanian Aquaculture and Fisheries Institute, University of Tasmania
Inland Fisheries (IFS) (2007). http:// www.ifs.tas.gov.au/ifs/IFSDatabaseManager/SpeciesDatabase
Koehn, J. D. and O'Connor, W. G. (1990). Biological Information for Management of Native Freshwater Fish in Victoria. Government Printer, Melbourne.
Ryan, D.A; Heap A.D; Radke, L. and Heggie D.T. (2003). Conceptual Models of Australia’s Estuaries and Coastal Waterways – applications for coastal resource management. Geoscience Australia Record 2003/09
Pierson, W.L; Bishop, K; Van Senden, D; Horton, P.R. and Adamantidis, C.A. (2002). Environmental water requirements to maintain estuary processes. Environmental Flows Initiative Technical Report Number 3. Commonwealth of Australia, Canberra.
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