Restoration of River Pools in the Avon Catchment

Assessment of the ecological impacts of sediment removal at Gwambygine Pool, Katrine Pool and Reserve Pool

Looking after all our water needs

Unpublished report to Wheatbelt NRM Department of Water September 2011

Department of Water 168 St Georges Terrace Perth Western Australia 6000 Telephone +61 8 6364 7600 Facsimile +61 8 6364 7601 www.water.wa.gov.au

September 2011

This work is copyright. You may download, display, print and reproduce this material in unaltered form only (retaining this notice) for your personal, non-commercial use or use within your organisation. Apart from any use as permitted under the Copyright Act 1968, all other rights are reserved. Requests and inquiries concerning reproduction and rights should be addressed to the Department of Water.

Disclaimer

This document has been prepared by the Department of Water. Any representation, statement, opinion or advice expressed or implied in this report is made in good faith and on the basis that the Department of Water and its employees are not liable for any damage or loss whatsoever which may occur as a result of action taken or not taken, as the case may be in respect of any representation, statement, opinion or advice referred to herein. Professional advice should be obtained before applying the information contained in this document to particular circumstances.

Acknowledgements

Shepherd Chipfunde, Project Officer – Department of Water (Northam), would like to thank the following for their contribution to this project:

Michael Allen, Dr Timothy Storer, Bernard Kelly and Martin Revell – Department of Water, for project management and support.

Dr Timothy Storer, Gillian White, Lynette Galvin, and Kelli O'Neill – Department of Water (Water Science Branch), for assistance in project design and their continued support.

Department of Water (Northam) staff for assistance during field surveys.

Terry Brooks – Department of Water (Northam), for analysis and comments on bathymetry and fish data.

Duane Joubert and Joanne Gregory – Department of Water (Water Information Branch), for the provision of hydrographic and water quality data.

Dr Karin Strehlow (Murdoch University) for the identification of macroinvertebrates samples.

For more information about this report, contact Department of Water (Northam) – (08) 9690 2600

Cover photograph: Reserve Pool following sediment removal Restoration of river pools in the Avon catchment

Contents Contents ...... iii Shortened forms ...... v Summary ...... vi 1 Introduction...... 1 1.1 The Avon River Basin ...... 1 1.2 Managing Avon River pools...... 3 1.3 Objectives ...... 4 Sediment removal at Gwambygine Pool ...... 4 River health assessments ...... 4 1.4 Rationale: multi-parameter assessment approach ...... 4 1.5 Background of study sites ...... 5 Gwambygine Pool ...... 5 Katrine Pool ...... 7 Reserve Pool ...... 8 2 Sampling strategy and methods ...... 9 2.1 Water quality sampling and analysis methods ...... 10 2.2 Collecting and sorting macroinvertebrates samples ...... 12 2.3 Fish and crayfish sampling ...... 13 2.4 Site assessment and data recording ...... 14 2.5 Bathymetry survey methods ...... 14 2.6 Timeline for investigation and reporting ...... 15 3 Results ...... 16 3.1 Gwambygine Pool...... 16 Pool bathymetry ...... 16 Water quality ...... 18 Macroinvertebrates ...... 18 Fish and crayfish ...... 20 3.2 Katrine Pool ...... 23 Pool bathymetry ...... 23 Water quality ...... 25 Macroinvertebrates ...... 25 Fish and crayfish ...... 27 3.3 Reserve Pool ...... 28 Pool bathymetry ...... 28 Water quality ...... 30 Macroinvertebrates ...... 31 Fish and crayfish ...... 32 4 Discussion ...... 34 4.1 Pool bathymetry ...... 34 4.2 Water quality ...... 34 Turbidity ...... 34 Salinity ...... 36 pH ...... 37 Dissolved oxygen ...... 35 Temperature ...... 34 4.3 Macroinvertebrates ...... 39

Department of Water iii Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

4.4 Fish and crayfish ...... 41 Gwambygine Pool ...... 41 5 Evaluation...... 44 5.1 Project outcomes ...... 44 5.2 Project limitations...... 44 5.3 Potential future benefits of sediment removal ...... 45 Channel dynamics and sedimentation ...... 45 Macroinvertebrates ...... 45 Fish and crayfish ...... 45 5.4 Recommendations and conclusion ...... 47 Glossary ...... 48 References ...... 50 Figures

Figure 1- Gwambygine channel following sediment excavation (90m cross section) ...... 16 Figure 2 - Gwambygine channel following sediment excavation (150m cross section) ...... 17 Figure 3 - Gwambygine channel following sediment excavation (210m cross section) ...... 17 Figure 4 - Katrine Pool following sediment excavation (100 m cross-section) ...... 24 Figure 5 - Katrine Pool following sediment excavation (200 m cross-section) ...... 24 Figure 6 - Katrine Pool following sediment excavation (300 m cross-section) ...... 24 Figure 7- Feeding groups found at Katrine Pool on 14 October 2010 ...... 27 Figure 8 - Reserve Pool following sediment removal - 25 m cross-section ...... 29 Figure 9 - Reserve Pool following sediment removal - 75 m cross-section ...... 29 Figure 10 - Reserve Pool following sediment removal - 125 m cross-section...... 30 Figure 11- Feeding groups found at Reserve Pool on 27 October 2010 ...... 32 Figure 12 - Potential effects of increased turbidity (from Dunlop et al 2005) ...... 38 Figure 13 – Potential benefits of sediment removal and restoration at Avon Pools ...... 46

Tables

Table 1 Median water quality indicators at Gwambygine Pool during 2007 and 2008 ...... 7 Table 2 Median water quality indicators at Katrine Pool during 2006 and 2007 ...... 8 Table 3 Laboratory analytical methods ...... 11 Table 4 Summary of fish species found during September 2010 survey ...... 20 Table 5 Summary of fish species found during June 2011 survey ...... 22

______iv Department of Water Restoration of river pools in the Avon catchment

Shortened forms AHD Australian Height Datum ANZECC & Australian and New Zealand Environment Conservation Council and ARMCANZ Agriculture and Resource Management Council of Australia and New Zealand ARMA the former Avon River Management Authority AWC the former Avon Waterways Committee AWRC the former Australian Water Resources Council DEC Department of Environment and Conservation DO dissolved oxygen DON dissolved organic nitrogen FARWH Framework for the Assessment of River and Wetland Health FRP filterable reactive phosphorus

NH3-N/NH4-N ammonia as nitrogen NMI National Measurement Institute

NOx-N nitrite and nitrate as nitrogen NRM natural resource management NWC National Water Commission SRP soluble reactive phosphorus SWIRC South West Index of River Condition TDS total dissolved solids TKN total Kjeldahl nitrogen TN total nitrogen TON total oxidised nitrogen TP total phosphorus TSS total suspended solids WIN water information (database) WRC the former Water and Rivers Commission

Department of Water v Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

Summary In 2010, the Department of Water received funding from Wheatbelt NRM to remove sediment from Gwambygine Pool. In addition, funding was provided to undertake a study of the impacts of sediment removal on the ecological health of Gwambygine, Katrine and Reserve pools. This included monitoring water quality (focusing on temperature and dissolved oxygen), physical form features and aquatic biota before and after sediment removal. To undertake the assessment, the Department of Water used the South West Index of River Condition, a suite of indicators and associated sampling techniques developed specifically for south-west Western Australian rivers. These indicators were modified where necessary to reflect the specific characteristics of the river pool environment. One of the limitations in assessing the ecological response to sediment removal was the short timeframe available to undertake the assessments. Ecological assessments were conducted in October 2010 at Katrine and Reserve Pool (post sediment removal only) and September 2010 and June 2011 at Gwambygine Pool, before and after sediment removal. As monitoring data is not available for either Katrine or Reserve Pool before sediment removal, it is not possible to make observations regarding potential impacts of sediment removal for these pools. This project has therefore focussed upon considering the ecological health of these pools following sediment removal. Excavation of Gwambygine Pool occurred in October and November 2010. The increase in hydrological capacity due to the excavation of sediment from each of the pools was significant, with approximately 8 000 m3 of sediment removed from Gwambygine as part of this project and 32 000 m3 and 10 000 m3 previously removed from Katrine and Reserve Pool respectively. The larger storage capacity of the pools increased their ability to act as a drought refuge for aquatic fauna. Water quality monitoring was available for Gwambygine Pool before and after sediment removal. Based upon the limited data available, results were within expected seasonal ranges for the pool. It is recommended that longer duration monitoring be undertaken to better understand the impact of sediment removal on water quality. A total of five native fish/crayfish species were recorded at Gwambygine, three at Katrine and four at Reserve Pool. The dominant fish species recorded were the western hardyhead and the Swan river goby; both estuarine species that have been noted as having colonised large inland areas of the Avon catchment. This change in distribution has been associated with secondary salinisation of the main channel. Sampling at Reserve Pool recorded one nightfish and three western pygmy perch. The nightfish is now largely absent from the Avon catchment and the western pygmy perch is known from only one site east of the Darling Scarp, and on the Dale River. This reduction in distribution is considered to be at least partially attributed to the

______vi Department of Water Restoration of river pools in the Avon catchment

salinity tolerances of these species being exceeded. The persistence of both species at Reserve Pool highlights the need to maintain or improve water quality in the Dale River and protect the pool itself. The presence of large numbers of fish at each of the pools following sediment removal is an encouraging result. The diversity of macroinvertebrates families present varied from three at Gwambygine to ten at both Reserve and Katrine pools. All of the macroinvertebrate families identified at Katrine Pool and Reserve Pool appear to be relatively common, having also been identified in other Avon River or Dale River pools during previous studies. In addition, the majority of the families identified at both pools have also been noted as being either tolerant or very tolerant of poor water quality. To assess the impact of sediment removal on macroinvertebrates at Gwambygine Pool, it was proposed that pre-sediment removal baseline data would be used from a previous study by DEC in 2007/08. This data would then be compared to macroinvertebrate data obtained using the AUSRIVAS macroinvertebrate sampling protocol as part of the ecological assessment following sediment removal. However, during the course of the project it became evident that there were significant differences in methodology and as a consequence an assessment of the impact of sediment removal would not possible. Following discussion with Wheatbelt NRM, it was decided that DEC would be approached to undertake additional sampling in 2011/12 to replicate the more detailed DEC methodology, and gain a better understanding of the ecological response of the invertebrate community to sediment removal.

Department of Water vii

Restoration of river pools in the Avon catchment

1 Introduction 1.1 The Avon River Basin

The Avon River provides natural drainage for the extensive Avon River Basin which stretches from Dalwallinu in the north, Southern Cross in the east and Lake King in the south east – a total area of approximately 120 000 km2, larger than the state of Tasmania. The Avon discharges into the Swan-Canning estuary near Perth. Map 1 shows the location of the Avon River Basin and its sub-catchments. Downstream from the Yenyening Lakes, the main channel of the Avon River was originally braided, with many small channels interweaving between vegetated islands, and a number of deep, shady pools. The Avon has been altered due to clearing of the catchment for agriculture and establishment of towns adjacent to the river. More significantly, the riverbed was modified during the River Training Scheme which was undertaken between 1958 and 1972. This involved removal of channel vegetation and debris to widths of up to 60 m in some places, ripping of the river bed to induce erosion (to create a deeper watercourse) and removal of minor bends in the river. The river was trained from Deepdale Pool, downstream of Toodyay, to as far upstream as Aldersyde. The purpose of the scheme was to reduce flooding in towns and on farms in the floodplain. However, from an ecological perspective, the associated increase in streamflow velocity resulted in sediment mobilisation and the subsequent filling of river pools. The key river management issues identified for the main channel of the Avon River include: flooding and floodplain management, channel erosion, bank stability and sedimentation of river pools, declining water quality through increased salinisation, algal blooms in river pools and the Swan-Canning estuary, and riparian vegetation condition, including the impacts of fire, salinity and weeds.

Department of Water 1 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

Map 1 Avon River basin and subcatchments

2 Department of Water Restoration of river pools in the Avon catchment

1.2 Managing Avon River pools

Avon River pools were identified as priority assets in the Avon Natural Resource Management Strategy, on the basis of their social and ecological values (Avon Catchment Council 2005). In an otherwise dry landscape, they function as a drought refuge and breeding area for aquatic fauna. Socially, river pools were once used for recreation in the form of swimming, boating and fishing, and were also a valuable water resource for early settlers who relied on the Avon River for drinking water and watering stock. The ecological and social values of the pools are now threatened by sedimentation, salinisation and eutrophication. The Avon River originally had more than 26 major pools, some of which were more than 10 m deep. Of these, seven were noted as being completely filled following a study in 2007 and more are likely to fill within the next few years (Advanced Choice Economics and Viv Read & Associates 2007, Department of Water 2007). Over the past few years the Department of Water has worked in partnership with local government, community groups and private landowners to restore priority river pools identified in the Assessment of the status of river pools in the Avon catchment report (Department of Water 2007). The pools were prioritised based on ecological, social and economic values. Although the ecological value of Avon River pools is recognised, little is understood about the complex ecology of individual pools. For the purpose of prioritising the pools, a pool was recognised as being ecologically significant if it has one or more of the following: significant depth to retain water and provide habitat during summer months, foreshore vegetation capable of sustaining a variety of terrestrial fauna, located adjacent to a reserve (Department of Water 2007). Other considerations in prioritising pools for restoration included: the level of community support, ease of access (for large dredging or excavation machinery and proximity to main roads), protection of downstream assets and sediment type. Preference for sediment removal is given to pools that have coarse sands. The rehabilitation of the river pools aims to restore the pools as near to their natural state as possible. Management options for the pools may include removal and disposal of accumulated sediment, installing sediment traps (such as riffles) to minimise infill, stabilising unconsolidated channel sediment with vegetation, fencing and revegetation of the surrounding riparian zone, monitoring and maintenance. In 2010 the Department of Water received funding from Wheatbelt NRM Inc. to remove sediment from Gwambygine Pool, which is located approximately 13 km south of York on the Avon River. In addition, funding was provided to assess the impact of sediment removal on the ecological health at Gwambygine Pool, as well as Katrine Pool and Reserve Pool (on the Avon River and Dale River respectively) which had been previously excavated.

Department of Water 3 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

1.3 Objectives

Sediment removal at Gwambygine Pool

The objectives for undertaking sediment removal at Gwambygine Pool were: To improve ecosystem health – assessed in terms of structure (e.g. species composition, biodiversity, food web structure, water quality) and function (e.g. nutrient cycles, rates of primary production and respiration). To enhance the social values of the pool, and provide increased opportunities for recreation.

River health assessments

The main aim of this project is to evaluate the ecological impacts of sediment removal at Gwambygine, Katrine and Reserve pools. As this project commenced after sediment had been removed from Katrine and Reserve Pool, it was not possible to evaluate the ecological condition of these pools before sediment was removed. This project has therefore focussed upon the ecological health of these pools following sediment removal. For Gwambygine Pool, an assessment was able to be undertaken pre and post sediment removal. The specific objectives of the project were: To assess changes in water quality resulting from sediment removal, primarily because of the increase in depth of the pools. To characterise changes in habitat complexity and availability due to sediment removal. To monitor a range of aquatic fauna (fish, crayfish and macroinvertebrates) and assess any impacts on ecological health that may be related to sediment removal.

1.4 Rationale: multi-parameter assessment approach

The assessment for this project used the South West Index of River Condition (SWIRC) and associated sampling techniques that were developed specifically for south-west Western Australian rivers (Storer et al 2011a, b). SWIRC is a suite of indicators which includes the following four themes: water quality, riparian vegetation, physical form and aquatic biota (macroinvertebrates and fish/crayfish). This multi-parameter assessment approach determines the ecological health by encompassing a direct assessment of the likely effects of sediment removal, including:

4 Department of Water Restoration of river pools in the Avon catchment

provision of a drought refuge for aquatic fauna through the creation of a permanent (or semi-permanent) water source, increased habitat diversity through the provision of a greater range of water depths and water chemistry conditions, and through the submergence of more and varied habitat (e.g. large wood and banks) and, improved ecosystem integrity (described in terms of structure and function). To date, there has been one previous assessment of the ecological benefits of sediment removal from the Avon River pools (Department of Water 2011, unpublished report). This study was undertaken at Sandy Pool located on the Avon River approximately 5.5 km downstream of the Yenyening Lakes confluence. Although the results of the study were inconclusive in demonstrating the ecological impacts of sediment removal, they have provided baseline information for future monitoring and evaluation. Prior to this, monitoring and evaluation following sediment removal have involved photographic records, estimating the volume of sediment removed from pools, and pool bathymetry surveys before and after sediment removal. 1.5 Background of study sites

Gwambygine Pool

Gwambygine Pool is located in the Shire of York, adjacent to Gwambygine Pool Conservation Reserve (Crown Reserve 8125), approximately 13 km south of York (see Map 2). It is one of the few Avon River pools remaining in good condition (Department of Water 2007). The river banks are well vegetated with dominant overstorey native species – Casuarina obesa (swamp sheoak) and Eucalyptus rudis (flooded gum), and a reduced woody shrub layer of Melaleuca sp. The pool is approximately 1 km long and has a maximum depth of 4 m, making it the deepest Avon River pool upstream of York (WRC and ARMA, 2001a). Gwambygine Pool has been a key focus for the River Conservation Society (RCS) which is based in York. Projects initiated for the pool by the RCS include: fencing and revegetation of the foreshore and channel upstream of the pool, biological surveys, vegetation condition assessments, water quality monitoring and bird surveys. A biological survey completed by the RCS between January 1996 and June 1997 has provided useful information on the aquatic fauna of the pool. Gwambygine Pool was also included in an aquatic invertebrates survey of Avon and Dale river pools conducted by the Department of Environment and Conservation (DEC) during 2007 and 2008 (Pinder 2009).

Department of Water 5 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

Map 2 Location of Katrine, Gwambygine and Reserve pools

6 Department of Water Restoration of river pools in the Avon catchment

Management of sedimentation Sediment in Gwambygine Pool consists of silt/clay throughout the pool and medium coarse sand in the upstream section (Davies et al. 1997). Sediment has been removed from the pool with a long reach excavator on three occasions. In May 1996, 8 300 m3 of sediment was removed, and in May 1999 another 4 060 m3 was extracted (WRC and ARMA, 2001a). In 2010, the Department of Water received funds from the Wheatbelt NRM Inc.; a further 8 000 m3 of sediment was excavated from Gwambygine Pool.

Water quality monitoring In 2007, Gwambygine Pool was incorporated into the Avon River catchment water quality and nutrient monitoring program managed by the Department of Water and funded by the Avon Catchment Council (now Wheatbelt NRM Inc.). The Gwambygine Pool sampling site (AWRC reference – 6151157) is located on the Avon River downstream of the pool at Gwambygine Road East bridge, for ease of access. The surrounding land use is broad acre farming with a small park located upstream of the pool. The results from two years of monitoring (2007–08) are summarised in Table 1. Table 1 Median water quality results - Gwambygine Pool during 2007 and 2008

Year TN (mg/L) TP (mg/L) TDS (mg/L) TSS (mg/L) pH DO (mg/L) 2007 1.5 (16) 0.044 (16) 7322 (16) 3.0 (16) 8.1 (16) 9.10 (16) 2008 1.2 (18) 0.030 (18) 9204 (18) 3.0 (18) 8.3 (18) 9.30 (18)

Note: The numbers in brackets indicate the number of samples collected.

Katrine Pool

Katrine Pool is located in the Shire of Northam, adjacent to Viveash Reserve (Crown Reserve 39381) – a popular picnic area between the townships of Northam and Toodyay (see Map 2). This section of the river was subject to the River Training Scheme. In 1996, the former Avon River Management Authority (ARMA) appointed consultants Jim Davies & Associates Pty Ltd and Ecoscape Pty Ltd to undertake a study of the channel and pools of the Avon River between Yenyening Lakes in the east and the Avon Valley National Park in the west. Although the survey data is dated, it has provided a source of information for Katrine Pool and the other river pools surveyed. The 1996 study revealed high levels of sediment deposition in Katrine Pool with two- thirds of the pool volume filled with coarse sand. At the time, the total volume of sediment present was estimated to be 62 000 m3 (Davies et al. 1997). When surveyed in 1996, Katrine Pool was 280 m long, less than half its length (640 m) recorded in 1960. Similarly, the average depth of the pool had reduced from 3.96 m, in 1955, to 1.96 m in 1996 (WRC & AWC 2002b).

Department of Water 7 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

Management of sedimentation In 2001, 3 800 m3 of sediment was excavated from Katrine Pool for use in construction of the Great Eastern Highway By-pass in Northam. In 2009, Department of Water organised the removal of approximately 20 000 m3 of coarse sediment using two excavators and a truck. A further 12 000 m3 was excavated during the 2010–11 summer. The sediment storage site was located adjacent to the pool on a reserve vested with the Shire of Northam.

Water quality monitoring The Katrine Bridge sampling site (AWRC reference – 6151155) is located on the Avon River at the downstream end of Katrine Pool. The site was originally established in 2006 to assess the effects of the Northam wastewater treatment plant on the downstream environment. The results from two years of monitoring (2006–07) are summarised in Table 2. Table 2 Median water quality results - Katrine Pool during 2006 and 2007

DO Year TN (mg/L) TP (mg/L) TDS (mg/L) TSS (mg/L) pH (mg/L) 2006 1.35 (14) 0.027 (14) 12 346 (14) 4.5 (14) 8.7 (14) 11.7 (13) 2007 1.60 (15) 0.051 (15) 8 496 (15) 10.0 (15) 8.4 (15) 11.4 (15)

Note: The numbers in brackets indicate the number of samples collected. Measurement and analysis of nutrient concentrations conducted at Katrine Pool have identified elevated nutrient concentrations, particularly during summer months.

Reserve Pool

Reserve Pool is located on the Dale River adjacent to a conservation reserve vested with the Shire of Beverley (Crown Reserve 8125), approximately 15 km south-west of the Beverley townsite (see Map 2). The Dale River joins the Avon River approximately 10 km downstream of Beverley, delivering relatively fresh water to the Avon River system. Unlike the Avon River, the Dale River was not affected by the river training scheme and the basic structure of pools linked by braided channels is still present. The banks and riparian zone at Reserve Pool are well vegetated, with Eucalyptus rudis (flooded gum), Eucalyptus wandoo (wandoo), Melaleuca sp. and Juncus krausii (shore rush) being the dominant native species. The pool is approximately 300 m long, with a maximum depth in excess of 5 m recorded in the downstream end which has not been affected by sedimentation. Reserve Pool was excavated during July 2009 and there is no previous water quality monitoring data recorded for the pool.

8 Department of Water Restoration of river pools in the Avon catchment

2 Sampling strategy and methods River health assessments, based on methods developed for the South West Index of River Condition (SWIRC) (Storer et al. 2011a, b), were conducted at Gwambygine Pool, Katrine Pool and Reserve Pool. These methods are compliant with the Framework for the Assessment of Wetland and River Health (FARWH) (NWC 2007a). The SWIRC incorporates assessment of the major components interacting within an aquatic ecosystem, including: catchment disturbance, fringing zone, physical form, water and sediment quality, hydrology and aquatic biota. The SWIRC methods were slightly modified to suit the conditions encountered in river pools. Water quality assessments included in situ measurements of temperature, dissolved oxygen, electrical conductivity and pH. Grab samples were also obtained and the following parameters analysed; total suspended solids, turbidity and nutrient concentrations (organic and inorganic forms of nitrogen and phosphorus). Temperature is an important parameter as it influences the physical, chemical and biological processes in the water. Temperature affects solubility in water, the rates of chemical reactions and the types of organisms that will survive in the water. The differences in temperature in the water column may result in thermal stratification. Oxygen is essential for aerobic metabolism in water. The supply of oxygen is either from the photosynthesis of aquatic plants or directly from the atmosphere. The solubility of oxygen is dependent on temperature and pressure. Salinity will also affect the solubility of oxygen. The environmental values of river pools in the Avon catchment are threatened by salinisation (Department of Water 2007). Knowing the salinity of the water in river pools will help to understand other processes occurring in the pools and how aquatic fauna are affected. Salinity is often expressed as total dissolved solids (TDS), which refers to the residual weight of salts after drying and filtration. Electrical conductivity (EC) is also used as a surrogate for TDS and is a measure of the ability of a solution to conduct an electrical current between two points (ANZECC & ARMCANZ 2000). In-stream salinity also serves as an indicator of other processes occurring in the catchment beyond the river pools. Dissolved and suspended particulate matter will reflect, scatter and absorb light that passes through the water column. The amount of light in the water will affect the rate of photosynthesis which drives primary production and produces oxygen. Turbidity can be used as an indicator of the amount of sediment suspended in the water. Nitrogen (N) and phosphorus (P) are important for the growth and maintenance of plant life in water. As elevated nutrient levels may result in eutrophication, it is important to know the amounts of available (dissolved) and unavailable forms of N and P and their ratios.

Ecological assessments primarily aim to measure the structure and function of biological communities. This principally involves field-based measurements that

Department of Water 9 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

examine changes in the relative abundance and diversity of species, community structure and composition (ANZECC & ARMCANZ 2000). Macroinvertebrates have been selected as the key indicator group for bio-assessment of the health of Australia‟s streams and rivers under the National River Health Program (Schofield and Davies 1996). Bathymetric surveys (measuring pool depth) were also conducted at all three pools. These surveys provide an indication of the shape of the river channel as well as baseline information that can be used in the future to assess sediment influx. 2.1 Water quality

Standard procedures and guidelines were observed at all times during collection, preservation, transportation and analysis of samples. Portable water meters were used to measure temperature, dissolved oxygen, electrical conductivity and pH in situ. The meters were calibrated before and after each round of sampling for quality control purposes. Grab samples were collected in high density polyethylene (HDPE) bottles, at water surface level – while avoiding scum or debris. The bottles were prewashed to avoid contamination of the sample by rinsing the bottle three times with the water to be sampled, before collecting the actual sample. Samples for the analysis of dissolved and/or filterable nutrients were collected by filtering the sample through a 0.45 µm pore diameter cellulose acetate (membrane) filter using a vacuum pump. All samples were carefully labelled giving reference to the date, site name, and analytes. Additional information, measurements and comments were recorded on field observation forms. Samples were stored at temperatures between 1 ºC and 5 ºC to ensure preservation until analysis, and care was taken during transportation by placing into eskies containing ice bricks.

Analysis

Samples were analysed by the National Measurement Institute (NMI) laboratory, accredited by the National Association of Testing Authorities. The samples were analysed for total nitrogen (TN), total phosphorus (TP) and total suspended solids (TSS). The filtered samples were analysed for dissolved organic nitrogen (DON), nitrite and nitrate as nitrogen (NOx-N, TON), Total Kjeldahl Nitrogen (TKN), ammonia/ammonium as nitrogen (NH3-N/NH4-N), soluble reactive phosphorus (SRP, PO4-P). The analytical and sample preservation methods are summarised in below (Table 3).

10 Department of Water Restoration of river pools in the Avon catchment

Table 3 Laboratory analytical methods

Analyte Sample preparation Analytical methods Limits of or preservation reporting mg/L Total nitrogen Unfiltered and chilled NMI (WL 239), persulphate 0.025 in an esky with ice digestion method 4500-N bricks. Stored in the C, (APHA 1998), and the dark cadmium reduction method 4500-NO3-F, (APHA 1998) Total phosphorus Unfiltered andchilled in NMI (WL 239), persulphate 0.005 an esky with ice bricks. digestion method 4500- Stored in the dark PB.5, (APHA 1998) and the ascorbic acid colorimetric method 4500- P E. (APHA 1998) Total suspended Unfiltered andchilled in NMI (WL 126), APHA 1 solids an esky with ice bricks method 2540 (APHA 1998) Nitrite and nitrate Filtered through a 0.45 NMI (WL 239), colorimetric 0.01 as nitrogen (total µm membrane, and method 4500-NO2-B oxidised then chilled in an esky (APHA 1998) and the nitrogen) with ice bricks. Stored cadmium reduction method in the dark 4500-NO3-F, (APHA 1998) Ammonia/ammo Filtered through a NMI (WL 239), (APHA 0.01 nium as nitrogen 0.45 µm membrane, 1998) phenate method and then chilled in an 4500-NH3 G esky with ice bricks. Stored in the dark Soluble reactive Filtered through a NMI (WL 239), ascorbic 0.005 phosphorus 0.45 µm membrane, acid colorimetric method and then chilled in an 4500-P F (APHA 1998) esky with ice bricks. Stored in the dark Dissolved Filtered through a NMI (WL 239) by 0.025 organic nitrogen 0.45 µm membrane, calculation and then chilled in an DON = filtered TN – (total esky with ice bricks. oxidised nitrogen & NH3-N/ Stored in the dark NH4-N) The results were sent to the Department of Water‟s Water Information Branch and stored in the Water Information Systems (WIN) database. Data was extracted from the WIN database and checked for errors before analysis.

Department of Water 11 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

2.2 Macroinvertebrates

Macroinvertebrates samples were collected using the standard AUSRIVAS protocols (Halse et al 2001) at Katrine and Reserve pools and during the second round of sampling at Gwambygine Pool. Channel habitat was sampled using a 250 µm mesh D-framed pond net. Channel habitat is defined as “the central part and margins of the main channel of a stream, without riffles, submerged macrophytes or pool rocks” (Halse et al 2001). Areas of emergent sedges and shrubs along the banks were avoided. Samples were collected by vigorously sweeping the net through the water column using short vertical lifts to disturb the substrate and dislodge any organisms present, then sweeping the net through the suspended substrate to collect the macroinvertebrates. Sample collection is undertaken over 10 m sampling area starting at the downstream end and moving upstream. The samples were processed in the field using a 64 cell box sub-sampler to randomly select cells for sorting. Macroinvertebrates from the randomly selected cells were then picked out from a sorting tray using forceps and pipettes and placed into a sample vial containing 70% ethanol and a field label. The random selection and sorting of cells continued until at least 200 macroinvertebrates were picked and stored in the vial, preserved in alcohol, for identification in the laboratory. Macroinvertebrates were identified to family with the exception of Oligochaetes (worms) and Acarinids (mites) were identified to order.

Photo 1 – Macroinvertebrate sorting at Reserve Pool During the first round of monitoring at Gwambygine Pool, macroinvertebrates were not sampled because the intention was to utilise results collected by Department of Environment and Conservation (DEC) between 2007 and 2008 (Pinder 2009) for pre- sediment removal analysis. Gwambygine Pool was sampled on four occasions

12 Department of Water Restoration of river pools in the Avon catchment

between February 2007 and December 2008. Invertebrates were collected using a 250 µm mesh net with samples taken from the littoral water column, disturbed sediments and aquatic and draped riparian vegetation. Each sample consisted of 60 sweeps (Pinder 2009). 2.3 Fish and crayfish

Fish and crayfish samples were collected using box traps and fyke nets deployed over a 24-hour period during each of the surveys. Fyke nets were set at either end of the pool to catch the fish species migrating into the pool. Rectangular fyke nets were used, with openings 1.05 m wide and 0.75 m high, tail lengths of 3.00 m, and wings 4.00 m long and 0.55 m high. Foam floats were used in the tail of the fyke net to ensure that animals requiring air to breathe (e.g. turtles and water rats) did not drown if they were caught in the traps. Five small box-traps measuring 260 x 260 x 460 mm, with a 3 mm mesh and five large box-traps (470 x 210 x 600 mm) with a 20 mm mesh were set in pool between the fyke nets during each of the surveys. The box traps were baited with chicken pellets in small plastic bait holders approximately 50 mm long and 20 mm wide.

Photo 2 – Fyke net at the downstream end of Katrine Pool

On the second day of each ecological survey the fish were removed from the fyke nets and box-traps and placed into buckets for identification and counting. Collected fish and crayfish were identified to species and the abundances of each fish species found were recorded into the following size classes:

Department of Water 13 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

Fish (mm): 0–20, 20–50, 50–100, 100+ Large Fish (mm): 0–100, 100–200, 200–400, 400+ Crayfish (mm): 0–20, 20–50, 50–76, 76–100, 100+ Native species were returned to the water immediately after counting and exotic species were disposed of in accordance with the feral fish protocols. 2.4 Site assessment and data recording

The site conditions at the time of the surveys were recorded on field sheets. Assessments were made of the following: General characteristics – stream width measurements at the time of the surveys were recorded on cross-sectional diagrams relative to the bankfull width and baseflow. Aquatic habitat – type and proportion of habitat present, stream shading, physical and substrate diversity, sediment deposition, water and sediment characteristics. Physical form – amount of erosion, severity of erosion, bank stability, pollution sources and adjacent land use. Vegetation – presence of riparian vegetation, structure of riparian zone vegetation, presence of exotics and recruitment in the riparian zone and dominant features of adjacent vegetation. Barriers – presence of barriers to fauna movement. 2.5 Bathymetry survey methods

The objective of the bathymetric surveys was to determine the depth of the pools before and after sediment removal and to provide a baseline for monitoring the influx of sediment in the future. A temporary benchmark was established and assigned a height of 10 m at each site. Cross-sections were established 30 m apart at Gwambygine Pool; 50 m apart at Katrine Pool and 25 m apart at Reserve Pool, to include the entire length of each of the pools surveyed, as well as upstream and downstream sections that were undisturbed by the sediment removal process. The survey data (depths, water level, and bed/bank heights) at each cross-section were analysed in relation to the temporary benchmarks. Survey pegs were driven into the ground on the same bank at each of the pools to establish reference points for the surveys. A tape measure was placed across the pool, perpendicular to the banks, with the zero mark of the tape measure on the survey peg. Measurements were recorded for each cross-section to include: top of bank, bank toe, and noticeable change of gradient on riverbed, or at regular intervals across the channel. The surveyed points are identified in terms of metres along the tape measure. A surveyor‟s staff was used to obtain depth readings and a kayak was used to get across the pool in deeper sections.

14 Department of Water Restoration of river pools in the Avon catchment

All measurements were recorded on a survey sheet in the field and recorded on Excel spreadsheets for further analysis in the office. The changes in depth were calculated using reduced levels, as the actual depth of the pool at any time is dependent on water level. The cross-sections were plotted on Excel charts (not to scale) and three representative cross-sections for each pool are displayed in the results section. 2.6 Timeline for investigation and reporting

Table 4 Project timeline

Activity Scheduled Timeline Gwambygine Pool ecological assessment – pre-sediment September 2010 removal Katrine Pool ecological assessment – post sediment removal October 2010 Reserve Pool ecological assessment – post sediment October 2010 removal Gwambygine Pool bathymetry survey – post-sediment April 2011 removal Gwambygine Pool ecological assessment – post-sediment June 2011 removal Report September 2011

Department of Water 15 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

3 Results 3.1 Gwambygine Pool

Pool bathymetry

Bathymetric survey results for three cross-sections are presented in Figures 1–3. The cross-sectional diagrams are representative of the change in channel shape and increase in depth observed between the pre and post-sediment removal surveys.

9.000

8.500

8.000

7.500

7.000 Before

6.500 After Reduced Level Level Reduced(m)

6.000

5.500

5.000 0.8m 1.8m 8.0m 10.4m 13.0m 17.0m 21.0m 26.3m Distance across the Channel from the Eastern Bank Survey Peg

Figure 1- Gwambygine channel following sediment excavation (90m cross section)

Figure 1 shows the changes in the shape of the channel resulting from sediment excavation at the 90 m cross-section. Excavation increased depth by a maximum of 2.68 m at this cross-section, the largest for any cross-section, with an average increase in depth of 1.64 m across this section. At the 150 m cross-section, excavation increased depth by an average of 1.16 m across the section, with a maximum increase of 1.64 m as shown in Figure 2 below.

16 Department of Water Restoration of river pools in the Avon catchment

8.500

8.000

7.500

7.000

Before 6.500

After Reduced Level Level Reduced(m) 6.000

5.500

5.000 1.6m 2.3m 8.0m 12.0m 20.7m 21.9m 28.9m 30.5m 34.8m Distance across the Channel from the Eastern Bank Survey Peg Figure 2 - Gwambygine channel following sediment excavation (150m cross section) 8.500

8.000

7.500

7.000

Before 6.500

After Reduced Level Level Reduced(m)

6.000

5.500

5.000 1.6m 3.0m 6.0m 12.0m 17.0m 22.0m 27.0m 32.0m 37.3m Distance across the Channel from the Eastern Bank Survey Peg Figure 3 - Gwambygine channel following sediment excavation (210m cross section)

Department of Water 17 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

The maximum increase in depth at the 210 m cross-section was 2.27 m as shown in Figure 3 above. The survey results show an average increase in depth of 1.08 m at this cross-section. The average increase in depth for the whole pool following sediment removal, based on the survey results was 1.33 m. The volume of Gwambygine Pool increased by about 7 000 m3, using the average change in depth above. The contractor estimated 8 000 m3 of sediment was removed from the pool.

Water quality

The results of water quality sampling on two occasions – before and after sediment removal, at Gwambygine Pool are displayed below. Table 5 shows in situ measurements at the time of sampling on both occasions and Table 6 shows the TSS, turbidity and nutrient concentrations of the grab samples. Table 5 Comparison of in situ measurements

Date Temperature Dissolved Dissolved Electrical pH (° C) Oxygen Oxygen (%) Conductivity (mg/L) (µS/cm) 7/9/10 15.4 11.30 116.6 17 33 8.30 9/6/11 16.2 10.25 107.7 10 12 8.15

Table 6 Comparison of nutrients, TSS and turbidity before and after sediment removal

Date DON NOx-N, TKN TN NH3- TP PO4-P TSS Turbidity

(mg/L) TON (mg/L) (mg/L) N/NH4- (mg/L) {SRP} (mg/L) (NTU) (mg/L) N (mg/L) (mg/L) 7/9/10 0.65 <0.01 0.78 0.79 0.017 0.017 <0.005 3.0 3.0 9/6/11 1.4 <0.01 1.7 1.7 0.043 0.076 0.019 7.0 6.4

Macroinvertebrates

Pre-sediment removal Between February 2007 and December 2008 Department of Environment and Conservation (DEC) undertook sampling of Avon and Dale river pools to assess whether invertebrate communities of river pools within the Avon catchment represented a threatened ecological community. Four pools were included in the study – Wilberforce Pool and Gwambygine Pool (on the Avon River), as well as Mile Pool and Deep Pool (on the Dale River). Gwambygine Pool was sampled on four occasions between February 2007 and December 2008. Sampling at Gwambygine Pool identified 62 macroinvertebrate species from 36 families. Previously, sampling had been undertaken by the River

18 Department of Water Restoration of river pools in the Avon catchment

Conservation Society between January 1996 and June 1997, and 56 macroinvertebrate species were identified.

Post-sediment removal Three macroinvertebrates families were recorded in Gwambygine Pool on 9 June 2011 (Table 7). The macroinvertebrates found were non-biting midges (Chironomidae), biting midges (Ceratopogonidae) and estuary shrimp (Palaemonetes australis) – identified to species level. Macroinvertebrate abundance and composition was very poor at Gwambygine Pool compared to Katrine and Reserve pools (Table 12 and Table 16). Table 7 Summary of macroinvertebrates found at Gwambygine Pool, June 2011

AUSRIVAS Other Functional Taxa Code Description Family details feeding groups Abundance (Other) predators, gathering Biting collectors, QD099999 midges Ceratopogonidae scrapers 8 Non-biting QDAZ9999 midges Chironomidae Other 2 Estuary australis Gathering OT029999 shrimp Palaemonidae sp. collectors 6 Total abundance 16 No. of families 3

The functional feeding groups used to categorise the macroinvertebrates are described as follows: scrapers/grazers, which consume algae and associated material; shredders, which consume leaf litter or other coarse particulate organic matter (CPOM), including wood; gathering collectors, which collect fine particulate organic matter (FPOM) from the stream bed; filtering collectors, which collect FPOM from the water column using a variety of filters; and predators, which feed on other consumers (Naiman and Bilby 2001). A sixth category, other, includes species that are omnivores, or simply do not fit into the categories described above.

Department of Water 19 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

Fish and crayfish

Pre-sediment removal Four native fish species (nightfish, Swan River Goby, western hardyhead and western minnow), a shrimp species and one exotic fish species (mosquitofish) were found in Gwambygine Pool during the river health survey conducted on 15 and 16 September 2010. More than 200 fish and 100 shrimp were found during this first round of sampling (Table 8). The fish fauna was dominated by western hardyhead and mosquitofish. Streamflow velocity at the time of the survey was estimated at 0.08 m/s.

Upstream fyke net Two nightfish (Bostockia porosa), one Swan River goby (Pseudogobius olorum), 11 western hardy head (Leptatherina wallacei), one shrimp (Palaemonetes australia) and one mosquitofish (Gambusia holbrooki) were found in the upstream fyke net. All the fish observed in the upstream fyke net were 20–50 mm long size except for the two nightfish that were recorded in the 50–100 mm size class.

Downstream fyke net Ten western minnow (Galaxias occidentalis) and one nightfish, 50–100 mm in size, were found in the downstream fyke nets. Ten Swan River goby (20–50 mm) were also found, some of which showed evidence of reproduction. Six (0–20 mm) and approximately 100 (20–50 mm) western hardy head were found in the downstream fyke nets. Approximately 75 mosquitofish (50–100 mm) were recorded, some of which showed evidence of reproduction. Approximately 130 shrimp were recorded in both the 0–20 mm and 20–50 mm size classes in the downstream fyke nets.

Box traps No fish were found in the box traps however a small, dry and weathered crayfish exoskeleton with a carapace length of 42 mm was observed on the western bank near the downstream fykes. Table 8 Summary of fish species found at Gwambygine Pool, September 2010

Size class 0–20 20–50 50–100 Evidence of Species mm mm mm reproduction Upstream fyke Nightfish Bostockia porosa 2 Swan River goby Pseudogobius olorum 1 Western hardy head Leptatherina wallacei 11 Mosquitofish Gambusia holbrooki 1 Shrimp Palaemonetes australis 1

20 Department of Water Restoration of river pools in the Avon catchment

Size class 0–20 20–50 50–100 Evidence of Species mm mm mm reproduction Downstream fykes Western minnow Galaxias occidentalis 10 Nightfish Bostockia porosa 1 Swan River goby Pseudogobius olorum 10 Yes Western hardy head Leptatherina wallacei 6 100

Downstream fykes cont. Mosquitofish Gambusia holbrooki ~75 Yes Shrimp Palaemonetes australis ~65 ~65

Photo 3 – Fish captured in the downstream fyke at Gwambygine Pool Post-sediment removal Three native fish species (Swan River Goby, western hardy head and western minnow), a shrimp species and the introduced mosquitofish were found in Gwambygine Pool during the river health survey conducted on 9 and 10 June 2011. A total of 135 fish and 214 shrimp were found during the second survey. All shrimp recorded were in the 0–20 mm size class (Table 9). The fish fauna composition was dominated by the shrimp and the western hardyhead post sediment removal.

Upstream fyke net

Department of Water 21 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

Twelve western minnow were found in the upstream fyke net, 11 of which were 20– 50 mm in size and one of which was in the 0–20 mm size class. Twenty (20–50 mm) and ten (0–20 mm) western hardy head, four mosquitofish (0–20 mm) and six shrimp were found in the upstream fyke net.

Downstream fyke net Eight Swan River goby were found in the downstream fyke nets, seven of which were 20–50 mm in size and one 0–20 mm. Thirty-five western hardyhead were found in the downstream fyke nets, ten of which were in the 0–20 mm size class and 25 in the 20–50 mm size class. Twenty-five mosquitofish and 188 shrimp were recorded in the downstream fyke nets.

Box traps Seven (0–20 mm) and six (20–50 mm) Swan River goby, six hardyhead (20–50 mm), two mosquitofish (0–20 mm) and 20 shrimp were recorded in the box traps. Table 9 Summary of fish species found at Gwambygine Pool during June 2011

Size class Species 0–20 mm 20–50 mm 50–100 mm Upstream fyke Western minnow Galaxias occidentalis 1 11 Western hardyhead Leptathyerina wallacei 10 20 Mosquitofish Gambusia holbrooki 4 Shrimp Palaemonetes australis 6

Downstream fyke Swan River goby Pseudogobius olorum 1 7 Western hardyhead Leptathyerina wallacei 10 25 Mosquitofish Gambusia holbrooki 25 Shrimp Palaemonetes australis 188 Box traps Swan River goby Pseudogobius olorum 7 6 Western hardyhead Leptathyerina wallacei 6 Mosquitofish Gambusia holbrooki 2 Shrimp Palaemonetes australis 20 2

22 Department of Water Restoration of river pools in the Avon catchment

3.2 Katrine Pool

Pool bathymetry

Bathymetric survey results for three of the nine cross-sections are presented in Figures 4–6. The cross-sectional diagrams are representative of the change in channel shape and increase in depth observed between the pre and post-sediment removal surveys. Figure 4 shows the changes in the shape of the channel resulting from sediment excavation at the 100 m cross-section. Excavation increased depth by a maximum of 4.04 m at this cross-section, the largest for any cross-section, with an average increase in depth of 2.26 m across this section. At the 200 m cross-section, excavation increased depth by an average of 1.48 m across the section, with a maximum increase of 2.73 m as shown in Figure 5 below.

6 Before 4 After

0 X Section 1.7m 5.0m 15.0m 25.0m 35.0m 45.0m 54.8m 100m @ Distance across the Channel from the Northern Bank Survey peg

Department of Water 23 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

Figure 4 - Katrine Pool following sediment excavation (100 m cross-section)

6 Before

4 After

0 X Section 1.7m 5.0m 15.0m 25.0m 35.0m 45.0m 54.8m 100m @ Distance across the Channel from the Northern Bank Survey peg

11 Figure 5 - Katrine Pool following sediment excavation (200 m cross-section)

8 Before After

Reduced Level Level Reduced7(m)

5 X Section 3.0m 10.0m 19.0m 31.0m 39.0m 47.0m 300m @ Distance across the Channel from the Northern Bank Survey Peg

Figure 6 - Katrine Pool following sediment excavation (300 m cross-section)

The maximum increase in depth of the 300 m cross-section was 3.27 m as shown in Figure 6 above. The survey results show an average increase in depth of 1.95 m at this cross-section. The average increase in depth for the whole pool following

24 Department of Water Restoration of river pools in the Avon catchment

sediment removal, based on the survey results was 1.45 m. The volume of the surveyed section of Katrine Pool increased by about 30 000 m3, using the average change in depth above. An estimated 2 000-3 000 m3 in addition was removed by the contractor upstream of the surveyed area, making the total volume of sediment removed approximately 32 500 m3. The contractor estimated 32 000 m3 of sediment was removed from the pool.

Water quality

Water quality sampling results from Katrine Pool on 14 October 2010 are displayed below. Table 10 shows in-situ measurements at the time of sampling and Table 11 shows the TSS, turbidity and nutrient concentrations of the grab sample. Table 10 In situ measurements at Katrine Pool on 14 October 2010

Date Temperature (° C) Dissolved Electrical pH Oxygen (mg/L) Conductivity (µS/cm) 14/10/10 21.8 6.64 21 600 8.26

Table 11 Nutrient, TSS and turbidity concentrations at Katrine Pool

Date DON NOx-N, TKN TN NH3- TP PO4-P TSS Turbidity

(mg/L) TON (mg/L) (mg/L) N/NH4- (mg/L) {SRP} (mg/L) (NTU) (mg/L) N (mg/L) (mg/L) 14/10/10 1.2 0.028 1.6 1.6 0.22 0.056 0.016 6.0 6.3

Macroinvertebrates

The results of the macroinvertebrates sampling conducted at Katrine Pool on October 2010 are summarised in Table 12 below. A total of 10 families were identified with the family Daphniidae accounting for 50% of the total abundance. Table 12 Summary of macroinvertebrates found at Katrine Pool on 14 October 2010

AUSRIVAS Other Functional feeding Taxa Code Description Family details groups Abundance Non-biting Tanyponidae (sub- midges - family) QDAE9999 sub family (Chironomidae) Predator 18 Pedatory diving QC099999 beetles Dytiscidae adult Predator 3

Department of Water 25 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

AUSRIVAS Other Functional feeding Taxa Code Description Family details groups Abundance Pedatory diving QC099999 beetles Dytiscidae larvae Predator 2 Water Scavenger QC119999 beetles Hydrophilidae adult Predator 1 Zooplankton OH089999 - Ostracods Cyprididae filtering collectors 24 (Other) predators, Biting gathering collectors, QD099999 midges Ceratopogonidae scrapers 7 Non-biting QDAZ9999 midges Chironomidae Other 10 (Other) Shredder, OP020102 Amphipods Ceinidae predators, scrapers 99 OG049999 Water Fleas Daphniidae Scrapers 180 Zooplankton - Benthic Harpacticoida OJ699999 Copepods (Order) filtering collectors 5 Zooplankton OJ199999 - Copepods Calanoida (Order) filtering collectors 9 Long horned (Other) Shredder, QT259999 Caddis Fly Leptoceridae predators, scrapers 1 Total abundance 359 No. of families 10

Summary of the functional feeding groups found at Katrine Pool Ten families and four feeding groups were recorded when Katrine Pool was sampled in October 2010. The macroinvertebrate community was composed of 50% scrapers, 6.5% predators, 11% filtering collectors and 32.5% other.

26 Department of Water Restoration of river pools in the Avon catchment

Katrine Pool 14/10/10

scrapers/grazers shredder predator gathering collectors filtering collectors other

Figure 7- Feeding groups found at Katrine Pool on 14 October 2010

Fish and crayfish

Three species of fish and one species of shrimp were found at Katrine Pool during sampling in October 2010. The two native fish species identified were the Swan River goby and western hardyhead. The introduced mosquitofish was also present in the pool. A large number of freshwater shrimp were found in the upstream fyke and downstream fyke (approximately 1200 in each). The dominant fish species identified in the downstream fyke was the mosquitofish. Large numbers of Swan River goby and western hardyhead were also recorded. The dominant species recorded from the upstream fyke was the western hardyhead. A relatively large number of Swan River goby and a small number of mosquitofish were also recorded. A number of freshwater shrimp and a small number of Swan River goby were captured in the crayfish traps located within the pool itself. Table 13 Summary of fish species found at Katrine Pool – October 2010

Size class

Species 0–20 mm 20–50 mm 50–100 mm Upstream fyke Western hardyhead Leptatherina wallacei ~1500 210 Mosquitofish Gambusia holbrooki 10

Department of Water 27 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

Freshwater shrimp Palaemonetes australis ~1250 Swan River goby Pseudogobius olorum 74 30 Downstream fykes Western hardyhead Leptatherina wallacei ~200 6 Mosquitofish Gambusia holbrooki ~350 Shrimp Palaemonetes australis ~1200 Swan River goby Pseudogobius olorum ~100 20 Box traps Swan River goby Pseudogobius olorum 2 Shrimp Palaemonetes australis 44

3.3 Reserve Pool

Pool bathymetry

Bathymetric survey results for three cross-sections are presented in Figures 8–10. The cross-sectional diagrams are representative of the change in channel shape and increase in depth observed between the pre and post-sediment removal surveys. Figure 8 shows the changes in the shape of the channel resulting from sediment excavation at the 25 m cross-section. Excavation increased depth by a maximum of 1.30 m at this cross-section with an average increase in depth of 0.78 m across this section. At the 75 m cross-section, excavation increased depth by an average of 1.60 m across the section, with a maximum increase of 2.37 m as shown in Figure 9 below.

28 Department of Water Restoration of river pools in the Avon catchment

9.5

8.5

7.5 Series1 7 Series2 6.5 Level Reduced(m)

5.5

5 X 3.5m 6.4m 9.5m 12.5m 18.6m 25.3m 28.8m 31.1m 31.7m Section 25m Distance across the Channel from the Eastern Bank Survey Peg Figure 8 - Reserve Pool following sediment removal - 25 m cross-section

9.5

8.5

7.5

ReducedLevel (m) 6.5 Before 6 After 5.5

5 X Section 75m0.0m 7.5m 13.4m 18.0m 21.5m 25.5m 26.8m 30.4m

Distance across the Channel from the Eastern Bank Survey Peg Figure 9 - Reserve Pool following sediment removal - 75 m cross-section

Department of Water 29 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

9.5

8.5

7.5

6.5 Reduced Level Level Reduced(m) Before 6 After 5.5

5 X Section 2.0m 6.5m 14.0m 26.5m 33.5m 36.5m 125m

Distance across the Channel from the Eastern Bank Survey Peg

Figure 10 - Reserve Pool following sediment removal - 125 m cross-section The maximum increase in depth at the 125 m cross-section was 3.69 m, the largest increase in any cross-section, as shown in Figure 10 above. The survey results show an average increase in depth of 2.12 m at this cross-section. The average increase in depth for the whole pool following sediment removal, based on the survey results was 0.93 m. The volume at Reserve Pool increased by approximately 10 000 m3.

Water quality

Water quality sampling results from Reserve Pool on 27 October 2010 are displayed below. Table 14 shows in situ measurements at the time of sampling and Table 15 shows the TSS, turbidity and nutrient concentrations of the grab sample. Table 14 In situ measurements at Reserve Pool on 27 October 2010

Date Temperature Dissolve Dissolved Electrical pH (° C) Oxygen Oxygen Conductivity (mg/L) (%) (µS/cm) 27/10/10 21.7 7.78 92.0 11 960 7.96

30 Department of Water Restoration of river pools in the Avon catchment

Table 15 Nutrient, TSS and turbidity concentrations at Reserve Pool

Date DON NOx-N, TKN TN NH3- TP PO4-P TSS Turbidity

(mg/L) TON (mg/L) (mg/L) N/NH4- (mg/L) {SRP} (mg/L) (NTU) (mg/L) N (mg/L) (mg/L) 27/10/10 0.51 <0.01 0.67 0.67 <0.01 0.017 <0.005 2.0 3.3

Macroinvertebrates

The results of the macroinvertebrates sampling conducted in October 2010 at Reserve Pool are summarised in Table 16 below. A total of 10 families were identified, with the family Chironomidae accounting for 87% of the total abundance. Table 16 Summary of macroinvertebrates found at Reserve Pool on 27 October 2010

AUSRIVAS Functional feeding Taxa Code Description Family groups Abundance Non-biting midges Tanyponidae QDAE9999 - sub family (Chironomidae) Predator 136 Oligochaete (sub- LO999999 Aquatic worms class) Gathering collectors 1 Zooplankton - OJ399999 Copepods Cyclopoida (Order) Filtering collectors 6 Zooplankton - OJ199999 Copepods Calanoida (Order) Filtering collectors 4 (Other) predators, gathering collectors, QD099999 Biting midges Ceratopogonidae scrapers 13 QDAZ9999 Non-biting midges Chironomidae Other 117 (Other) Shredder, OP020102 Amphipods Ceinidae predators, scrapers 1 OT029999 Estuary shrimp Palaemonidae Gathering collectors 3 QH679999 Backswimmer Notonectidae Predator 1 QH659999 Water boatman Corixidae Predator 7 QO179999 Dragonfly Libellulidae Predator 2 Total abundance 291 No. of families 10

Department of Water 31 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

Summary of the functional feeding groups found at Reserve Pool Ten families from four functional feeding groups were found in Reserve Pool. The macroinvertebrate community was composed of 50% predators, 3.5% filtering collectors, 1.5% gathering collectors and 45% other. This site was sampled once following sediment removal. Reserve Pool 27/10/10

scrapers/grazers shredder predator gathering collectors filtering collectors other

Figure 11- Feeding groups found at Reserve Pool on 27 October 2010

Fish and crayfish

Four species of fish and one species of shrimp were found at Reserve Pool during sampling in October 2010. The three native fish species identified were nightfish, western pygmy perch and western hardyhead. The introduced mosquitofish was also present in the pool. A relatively large number of freshwater shrimp were found in the upstream fyke (> 400). The dominant native fish species identified in the upstream fyke was the western hardyhead. An oblong turtle (Chelodina oblonga) was also captured in the fyke net. Remains of a crayfish were also present (claws only) and it is likely that it had been consumed by the turtle. Only one mosquitofish was found in the downstream fyke. However, this may not be an accurate reflection of the actual number of fish captured in the fyke as a very large number of turtles were also recorded (29). This is likely to have led to predation of other fish that may have been present in the fyke. A number of freshwater shrimp were captured in the box traps set in the pool.

32 Department of Water Restoration of river pools in the Avon catchment

Table 17 Summary of fish species found at Reserve Pool – October 2010

Size class 0–20 20–50 50–100 Species mm mm mm Upstream fyke net Nightfish Bostockia porosa 1 Western hardyhead Leptatherina wallacei 17 Mosquitofish Gambusia holbrooki 19 Shrimp Palaemonetes australis >400 Western pygmy perch Edelia Vittata 3 Downstream fyke net Mosquitofish Gambusia holbrooki 1 Freshwater shrimp Palaemonetes australis 16 1 Crayfish box traps Shrimp Palaemonetes australis 21 13

Photo 4 – Oblong turtles being released from downstream fyke at Reserve Pool

Department of Water 33 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

4 Discussion 4.1 Pool bathymetry

The hydrological capacity of all the pools assessed was significantly increased following sediment removal. This increase in hydrological capacity has enhanced the drought refuge function of Gwambygine, Katrine and Reserve pools during summer months. Sediment removal increased the pools‟ capacities to ameliorate flood flows. It is not yet known if sediment is again infilling Gwambygine, Katrine and Reserve pools, however, pre and post-excavation cross-sectional surveys have been carried out which will enable this to be determined in the future. It is recommended that a cross sectional survey be conducted at least once every two years, at each of the pools. Most of the sediment removed was coarse quartz sand. The high levels of sedimentation present in both Katrine and Gwambygine Pools has been attributed to the River Training Scheme on the Avon River. High levels of sediment deposition at Reserve Pool is likely to be related to extensive land clearing and erosion within the catchment. The removal of sediment will reduce the influx of sediment downstream of the pools and provide permanent and more diverse aquatic habitat. 4.2 Water quality

Temperature

Water temperature varies in response to a range of factors including air temperature, exposure to sunlight, turbidity, groundwater inflows to the water body, water depth and flow in a water body. Riparian vegetation provides shade and traps sediment particles that would otherwise enter the waterway and absorb heat from sunlight. The shade and clarity of the water help to keep the water cool and well oxygenated. The temperature of a water body directly affects many physical, chemical and biological processes. Warm water is more susceptible to eutrophication because photosynthesis and bacterial decomposition occur at faster rates at higher temperatures. Oxygen is less soluble in warmer water and this can affect aquatic life. By contrast, salts are more soluble in warmer water, so temperature can affect the water‟s salinity (Waterwatch Australia Steering Committee 2002). Temperature directly affects the metabolic rate of plants and animals. Aquatic species are able to tolerate a specific range of water temperatures. With extreme changes in temperature, organisms do not function as effectively and become more susceptible to pollution, parasites and diseases, and many organisms will die. By excavating Gwambygine, Katrine and Reserve pools, it is envisaged that temperature variations will be reduced because of the larger volumes of water

34 Department of Water Restoration of river pools in the Avon catchment

present in the pools. Changes in the long-term temperature average may allow different species to establish within the pools. Although it is believed that the larger volumes of water at Gwambygine, Katrine and Reserve pools will prevent rapid changes in temperature, the non-turbulent flow in most months is likely to allow stratification to occur in the pools i.e. varying temperatures from the top to the bottom of the water column, as a result of poor mixing. More consistent temperatures are expected in winter than in drier months because of the relatively uniform mixing of the water in larger flows. Aquatic organisms can experience stress where a temperature change of more than 2 °C occurs in a 24-hour period (Waterwatch Australia Steering Committee 2002). Further monitoring is recommended to assess if temperature variations have reduced as a result of excavating at Gwambygine, Katrine and Reserve pools.

Dissolved oxygen

The concentration of dissolved oxygen (DO) is an important indicator of the health of an aquatic ecosystem. Persistently low DO will harm most aquatic life because oxygen is essential for almost all forms of life. Aquatic animals, plants and most bacteria need it for respiration, as well as for some chemical reactions. Air is one source of dissolved oxygen into the water column. The speed at which oxygen from the air enters and disperses through a water body depends on the amount of agitation at the water surface, the depth of the water body and the rate at which water mixes through the pool. As water temperature rises, oxygen diffuses out of the water into the atmosphere. Aquatic plants and algae are another source of dissolved oxygen. They photosynthesise during daylight and increase DO concentrations around them. Shallow flowing waterways usually have high DO concentrations. In still waters, such as river pools in summer, DO concentrations often vary from the surface to the bottom, with less DO in the deeper, poorly mixed layers. Warm or saline water holds less DO than cold water or freshwater (Waterwatch Australia Steering Committee 2002). DO concentrations change with the seasons, as well as daily, as the temperature of the water changes. When Gwambygine Pool was sampled before and after sediment excavation DO was recorded at 11.30 mg/L and 10.25 mg/L, respectively. Both DO concentrations are classified as oxygenated (8–12 mg/L) when using the Statewide River Water Quality Assessment classification (Department of Water 2004). DO was marginally low (<8.00 mg/L) when Katrine Pool and Reserve Pool were sampled in October 2010 recording 6.64 mg/L and 7.78 g/L respectively. The relatively low readings may be attributable to the warmer October water temperatures, recording 21.8 °C at Katrine Pool and 21.7 °C at Reserve Pool. At DO concentrations below 2.00 mg/L, aquatic fauna and ecosystem processes are severely affected, with fish and macroinvertebrate mortality common (ANZECC & ARMCANZ 2000; Davies1995; Davies et al. 2004; Waterwatch Australia Steering

Department of Water 35 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

Committee 2002). Hunt and Christiansen (2000) indicate that concentrations below 5.00 mg/L will start to have an impact on fish, with most species actively moving away to more oxygen rich waters. They further define „clean‟ water as having a DO concentration greater than 6.50 mg/L. The Waterwatch Australia Steering Committee (2002) suggests that a minimum DO concentration of 5.00–6.00 mg/L is required for fish growth and activity. All DO concentrations recorded at Gwambygine, Katrine and Reserve pools were above this threshold.

Salinity

Salinity is an indicative measure of the total concentration of cations that include sodium, calcium, magnesium, and potassium (Na+, Ca2+, Mg2+, K+), and anions that 2- 2- 2- - include sulphate, carbonate, bicarbonate, and chloride (SO4 , CO3 , HCO3 , Cl ) in solution (ANZECC & ARMCANZ 2000). Salinity may also be expressed as total dissolved solids (TDS) or total soluble salts, which refer to the residual weight of salts after drying and filtration. Measures of TDS closely resemble those of total soluble salts (ANZECC & ARMCANZ 2000). Electrical conductivity (EC) is often used as a surrogate for TDS and total soluble salts and is a measure of the ability of a solution to conduct an electrical current between two points. Conductivity accurately reflects measures of TDS and total soluble salts except at very high salinities where the relationship between total soluble salts and conductivity diminishes and can vary depending on which ions are dominant (Williams and Sherwood 1994). EC at Gwambygine Pool was 17 330 μS/cm (11 230 mg/L TDS) before sediment removal and 10 120 μS/cm (6559 mg/L TDS) after excavation. Salinity was classified as highly saline (10 000–35 000 mg/L TDS) and saline (5 000–10 000 mg/L TDS) on the two occasions sampled. Although this represents a large reduction in salinity levels after sediment removal, it is important to note that seasonal effects are likely to be the primary cause. Pre-sediment removal sampling was conducted in October 2010, following the lowest winter rainfall on record. This would have resulted in reduced streamflow and higher levels of evapo-concentration of salts. The second round of sampling took place in early winter (June 2011) following the first flow of the season which is likely to have resulted in dilution of salinity levels in the pool. Solubility of salts is also directly proportional to temperature hence warmer water is likely to be saltier than cooler water. Katrine Pool and Reserve Pool recorded ECs of 21 000 µS/cm (14 000 mg/L TDS) and 11 960 µS/cm (7751 mg/L TDS), respectively. Katrine Pool was highly saline (10 000–35 000 mg/L TDS) and Reserve Pool was saline (5000–10 000 mg/L TDS) using the Statewide River Water Quality Assessment classification (Department of Water 2004). Maintaining and improving the water quality in these river pools is important because elevated concentrations of salinity (and turbidity) are usually associated with a loss of biodiversity and a decline in the health and integrity of aquatic ecosystems (Dunlop et al 2005).

36 Department of Water Restoration of river pools in the Avon catchment

pH pH is a measure of acidity or alkalinity, calculated as the negative logarithm of the concentration of hydrogen ions in solution(Waterwatch Australia Steering Committee 2002). Values of pH range from 0 (highly acidic) to 14 (highly alkaline). Where water has no net acidity or alkalinity it is said to be neutral and has a pH of 7. All animals and plants are adapted to specific pH ranges, generally between 6.5 and 8.0. If the pH of a waterway is outside the normal range for an organism it can cause stress or even death to that organism (Waterwatch Australia Steering Committee 2002). A wide variety of factors may have an effect on the pH of water. These include the source of the water, rainfall, time of day, water temperature, geology and soils, photosynthesis and respiration, and salinity (Waterwatch Australia Steering Committee 2002). The pH of a water body varies during the course of the day as the balance between photosynthesis and respiration changes with the light intensity and temperature. Inflowing water may affect the pH of a water body and rainfall contributions are usually slightly acidic because of carbon dioxide dissolved in it. pH at Gwambygine Pool and Katrine Pool was alkaline (>8.00), using the Statewide River Water Quality Assessment classification (Department of Water 2004). When Gwambygine Pool was sampled before and after sediment excavation, pH was recorded at 8.30 and 8.15, respectively. pH at Katrine Pool was 8.26 when the pool was sampled after sediment removal, on 14 October 2010. pH above 8.00 is common in this part of the Avon catchment with median pH values greater than 8.00 recorded when Gwambygine Pool and Katrine Pool were monitored between 2006 and 2008 – see Table 1 and Table 2 (Department of Water 2009b). When Reserve Pool was sampled in October 2010 pH was 7.96.

Turbidity

Turbidity is a measure of water clarity or cloudiness and is defined as the optical property of a liquid that causes light to be scattered and absorbed rather than transmitted in straight lines (Bruton 1985). Turbidity results from the scattering of light in water by organic and inorganic particles, however, high turbidities usually are caused by suspended inorganic particles, particularly sediment (Lloyd et al 1987). Figure 12 highlights the potential impacts of turbidity upon aquatic ecosystems. Suspended particles absorb heat hence can result in water temperature rising faster in turbid water than they do in non-turbid water. The concentration of dissolved oxygen is likely to be less in warmer, turbid water since the solubility of oxygen reduces with rising temperature. Sediment-induced turbidity is also likely to decrease primary production, thus reducing the amount of food and oxygen available to aquatic life. Suspended silt particles eventually settle into the spaces between the gravel and rocks on the riverbed and decrease the amount and type of habitat available for creatures that live in those crevices. Reduced abundances of zooplankton and

Department of Water 37 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

macroinvertebrates have been observed in naturally and artificially turbid aquatic systems (Lloyd et al 1987). Suspended particles can clog fish gills, inducing disease, slow growth and, in extreme cases, death (Dunlop et al 2005). Turbidity is also known to influence the way fish feed and breathe, as well as their breeding success (Dunlop et al 2005). Unfortunately, most previous studies on this topic have been conducted overseas, so knowledge about the effects of turbidity on Australian native fish is very limited (The Murray-Darling Freshwater Research Centre 2010).

Figure 12 Potential effects of increased turbidity (from Dunlop et al 2005)

Turbidity at Gwambygine Pool was 3.0 NTU and 6.4 NTU before and after sediment excavation, respectively. These turbidity measurements are considered low (<5 NTU) and moderate (6–10 NTU) when using the Statewide River Water Quality Assessment classification (Department of Water 2004). The difference can be explained by the different flow conditions at the time of sampling, the pre-sediment sampling was done in October when streamflow velocity had receded to 0.08 m/s reducing suspended particulate matter carrying capacity. The post-sediment sampling was done immediately after the first flow for the winter. Turbidity levels are often higher at this time due to the flushing out of particulate matter that has accumulated in the pool and upstream during the dry months. Katrine Pool and Reserve Pool recorded turbidity of 6.3 NTU and 3.3 NTU respectively. Both pools were sampled in October 2010. The Dale River catchment is

38 Department of Water Restoration of river pools in the Avon catchment

less disturbed than the Avon River catchment, with more remnant vegetation to act as a buffer and reduce the amount of sediment entering the system. The Avon River underwent the River Training Scheme as well as extensive clearing in the catchment thus providing more opportunities for sediment mobilisation. 4.3 Macroinvertebrates

It was initially proposed that data obtained during the aquatic invertebrates study conducted by DEC in 2007/08 would be used for pre-sediment removal analysis for Gwambygine Pool (Pinder 2009). This data would then be compared to macroinvertebrates data obtained using the standard AUSRIVAS macroinvertebrate sampling protocols as part of the South West Index of River Condition (SWIRC) assessment, following sediment removal. During the course of the project it became evident that there were significant differences in methodology and data would be incomparable. Following discussion with Wheatbelt NRM Inc., it was decided that it would be beneficial to replicate the DEC methodology to gain a better understanding of the ecological response of the invertebrate community to sediment removal. It was decided that this component of the project would be undertaken by DEC as a separate project. Most of the species identified by DEC at Gwambygine Pool, before sediment was removed, were common and widespread in south-western and southern parts of Australia. In addition, the majority of the species recorded are freshwater species that are noted as being tolerant of increased levels of salinity (Pinder 2009). Results of the DEC study suggest that: Salinisation has probably resulted in a homogenisation of the invertebrate fauna in the Avon River pools with less variation evident between the fauna of the deep pools and the shallower reaches of the channel. In addition to supporting some species that have a preference for the deeper pools on the Avon, the pools are likely to act as drought refuges for a variety of invertebrates that can recolonise the river as flow returns in winter. Due to their tolerance of a range of environmental conditions, the Avon pool invertebrate communities are not considered to be under serious threat. However, sedimentation was identified as an ongoing threat that will require ongoing in-stream and catchment management (Pinder 2009). Post-sediment removal macroinvertebrates sampling was done at Katrine Pool and Reserve Pool. Sediment was most recently removed from Katrine Pool in late 2010 with the removal of 12 000 m3 of sediment. Before this, approximately 20 000 m3 was removed from the pool in 2009 and 3800 m3 in 2001. Sediment was excavated from Reserve Pool in 2009, with the removal of 10 000 m3 of coarse sand. Since sediment had been excavated from both pools before this project began, there is no pre- sediment removal data available for comparison purposes.

Department of Water 39 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

Sampling following sediment removal at Katrine Pool found species from ten macroinvertebrate families. A large proportion of the macroinvertebrates found at the pool were from either from the Daphniidae family (water fleas) and categorised as scrapers within the functional feeding group, or from the Ceinidae family (a type of amphipod) which includes shredders, predators and scrapers. A long horned caddisfly larvae (Ocetis sp.) was found at Katrine Pool. The caddisfly species was from the Leptoceridae family which is one of the largest families of caddisfly found throughout Australia. Caddisfly larvae have been noted as being sensitive or moderately tolerant to reduced water quality (Waterwatch Australia Steering Committee 2002). Sampling following sediment removal at Reserve Pool revealed species from 11 macroinvertebrate families. The majority of the individuals found at Reserve pool were from the Chironomidae family (non-biting midges). Larval chironomids are noted as being widespread in south western wetlands with greatest abundances found in nutrient enriched or slightly saline wetlands (Jones et al 2009). Nutrient concentrations in Reserve Pool at the time of sampling were 0.67 mg/L TN (moderate) and 0.017 mg/L TP (low) and streamflow was saline (7 751 mg/L TDS) (Department of Water 2004). The feeding habit of chironomid larvae varies between species, with species from the sub-family Tanypodinae being generally predatory and other species being largely herbivorous, consuming plant detritus and algae (Jones et al 2009). A dragonfly larvae was found at Reserve Pool (from the Libellulidae family). Dragonfly larvae have been noted as being sensitive or moderately tolerant of poor water quality (Waterwatch Australia Steering Committee 2002). All of the families of macroinvertebrate identified at Katrine Pool and Reserve Pool appear to be relatively common, having also been identified in other Avon River or Dale River pools during the DEC study (Pinder 2009, Jones et al 2009). Almost all of the families identified at both pools have been noted as being either tolerant or very tolerant of poor water quality. Based upon the available macroinvertebrate sampling data it is not possible to evaluate the impact of sediment removal at Katrine Pool or Reserve Pool. However, further macroinvertebrate sampling is proposed at Gwambygine Pool to replicate monitoring undertaken by DEC prior to sediment removal. It is anticipated that this will provide a better understanding of the impact of sediment removal on macroinvertebrates at this pool. In addition, probable improvements in ecological health are discussed further in the section 5.3.

40 Department of Water Restoration of river pools in the Avon catchment

4.4 Fish and crayfish

Gwambygine Pool

The first round of fish and crayfish sampling was undertaken in September 2010 where five fish species were recorded: western minnow, nightfish, western hardyhead, Swan River goby and the introduced mosquitofish. The western minnow (Galaxias occidentalis) is the most common and widespread of the freshwater fishes endemic to the south western corner of Australia. It spawns following the onset of winter rains when it moves into small tributaries and feeder streams of rivers and wetlands to spawn among flooded vegetation Morgan et al (2009) The nightfish (Bostockia porosa) is found in clear or tannin-stained water of rivers, usually near the cover of rocks, aquatic plants or woody debris. It feeds at night on crustaceans, small fishes and aquatic insects, and spawns in small side creeks after winter rains (Morgan et al (2009) The Swan River goby (Pseudogobius olorum) and the western hardyhead (Leptatherina wallacei) are noted as being the most commonly encountered estuarine species in the rivers and lakes of south-western Australia. Their range has increased substantially due to the elevated salinities now found in many south west rivers due to extensive land clearing Morgan et al (2009) . The Swan River goby is common and abundant throughout its extensive range and predominantly spawns in spring and autumn. The western hardyhead is also very abundant throughout its range (Morgan et al 2009) . The mosquitofish (Gambusia holbrooki) is an introduced pest species which is widespread in south-western Australia often occurring in very high numbers. Mosquitofish breeding is triggered by increases in water temperature and daylight hours and occurs in either late summer/early autumn or spring. In pre-sediment removal sampling there was evidence of reproduction with gravid (live or egg bearing) female mosquitofish and Swan River goby. Although no crayfish were found in either survey there was a crayfish carapace located on the bank near the downstream fyke net during the first round of sampling. Four species of fish were recorded in June 2011 following the removal of sediment. The two dominant species of fish identified were the western hardyhead (Leptatherina wallacei) and mosquitofish (Gambusia holbrooki). Low numbers of western minnow (Galaxias occidentalis) and Swan River goby (Pseudogobius olorum) were recorded. The nightfish was not recorded. The presence of a number of fish species in the pool following sediment removal is a positive result, particularly given that the first opportunity to undertake sampling was in the winter following sediment removal when it was anticipated that fish activity may be lower than in the warmer months. The results from both ecological surveys are positive and provide an indication of the capacity of the aquatic fauna to recover following sediment removal.

Department of Water 41 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

As a consequence of the removal of 8 000 m3 of sediment, the hydrological capacity of the pool has been greatly increased. This increase in hydrological capacity would have enhanced the drought refuge function of Gwambygine Pool for the summer of 2010–11. Sediment excavation increased the depth of the upper reaches of the pool and subsequently provided additional habitat diversity. Sampling in winter and spring demonstrated that more fish were moving upstream than downstream. The spring sample identified fish that were in breeding condition. The river pools would have been the only breeding habitat available for use by these fish when the river ceased to flow later in the spring. This highlights the importance of river restoration projects that provide habitat and refuge for aquatic fauna.

Katrine Pool

As sediment had been removed from the pool before this project began, there is no fish data pre-sediment removal available for comparison purposes. Three species of fish were recorded in October 2010 following the removal of sediment. The two dominant species of fish identified in the downstream fyke were the western hardyhead (Leptatherina wallacei) and mosquitofish (Gambusia holbrooki). Morgan et al (2009) have identified that both the estuarine Western hardyhead and Swan River goby have now colonised large inland areas of the Avon catchment. This change in distribution, which now includes much of the salinised main channel of the Avon River and the Mortlock River, has been associated with secondary salinisation of the main channel. Western hardyhead was the dominant species recorded with a large numbers (~1710) moving downstream into the pool. A large number of freshwater shrimp (Palaemonetes australis) a euryhaline shrimp (tolerant of a wide range of salinities) found in south-west Australian rivers and estuaries were also recorded during sampling. This species is known to be highly tolerant of saline conditions and are often found in both fresh and estuarine waters. They have been recorded in salinities up to 25 000 mg/L (Smith 2009). The presence of such a large number of fish in the pool following sediment removal is a positive result. The diversity of fish species is low, but other factors including water quality (salinity in particular) have been identified as the cause of low diversity in the Avon River (Morgan et al 2009). As a consequence of the removal of up to 32 000 m3 of sediment, the hydrological capacity of the pool has been greatly increased. This increase in capacity has enhanced the drought refuge function of Katrine Pool over the summer of 2010–11, when the lowest rainfall on record resulted in extremely low water levels. Sediment excavation has significantly increased the depth of the upper reaches of the pool and also increased habitat diversity. Due to the limitations of the current sampling program it is recommended that further biological sampling of the pool be undertaken to better evaluate the impact of sediment removal upon fish and crayfish fauna.

42 Department of Water Restoration of river pools in the Avon catchment

Reserve Pool

As sediment had been removed from the pool before this project began, there is no fish data pre-sediment removal available for comparison purposes. Four species of fish were recorded in October 2010 following the removal of sediment. The two dominant species of fish identified were the western hardyhead (Leptatherina wallacei) and mosquitofish (Gambusia holbrooki). Nightfish and western pygmy perch were recorded at low numbers at this site. Morgan et al (2009) note that the nightfish are now largely absent from the Avon catchment and the western pygmy perch is known from only one site east of the Darling Scarp, also on the Dale River. This reduction in distribution is considered to be at least partially attributed to the salinity tolerances of these species being exceeded. The persistence of both species at Reserve Pool highlights the need to maintain or improve water quality in the Dale River and protect the pool itself. Large numbers of freshwater shrimp (Palaemonetes australis) were also recorded in the pool. The presence of a number of fish species in the pool following sediment removal is a positive result. As a consequence of the removal of up to 10 000 m3 of sediment, the hydrological capacity of the pool has been greatly increased. This increase in capacity has enhanced the drought refuge function of Reserve Pool over the summer of 2010–11, when the lowest rainfall on record resulted in extremely low water levels. Sediment excavation has significantly increased the depth of the upper reaches of the pool and also increased habitat diversity. Due to the limitations of the current sampling program it is recommended that further biological sampling of the pool be undertaken to better evaluate the impact of sediment removal upon fish and crayfish fauna.

Department of Water 43 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

5 Evaluation With limited data obtained within the project timeframe, it was only possible to undertake a preliminary assessment of the impact of sediment removal on the ecological health of Gwambygine, Katrine and Reserve pools. In assessing the results of monitoring it is important to note that sediment removal addresses only one of the threatening processes that impact upon river pools in the Avon catchment. Other factors include degradation of the riparian zone through erosion, grazing and weed infestation, and increased salinity and nutrient levels. 5.1 Project outcomes

The ecological impact of the excavation of sediment from Gwambygine, Katrine and Reserve pools has been assessed and the following outcomes have been identified: Removal of 8 000 m3 of sediment from Gwambygine Pool has created a deeper pool that provides drought refuge for aquatic fauna. A better understanding of the ecology of Gwambygine, Katrine and Reserve pools and the macroinvertebrate and fish communities present has been developed. Obtained monitoring data that provides a better understanding of the water quality in Gwambygine, Katrine and Reserve pools following sediment removal. Obtained important baseline data which will enable the ecological response of Gwambygine, Katrine and Reserve pools to be further evaluated in the future, should funding become available. 5.2 Project limitations

The major limitation of the project was the limited amount of time (less than 12 months) that was available to observe and monitor the ecological response of Gwambygine Pool following sediment removal. This meant that monitoring was undertaken in different seasons, with the first round of sampling completed in spring and the second round in early winter following sediment removal. The influence of seasonality on macroinvertebrate and fish species richness and abundance is recognised and this could well account for differences noted in the results obtained. In addition, Katrine Pool and Reserve Pool were both only sampled once and there is no previous data (before sediment removal) to use for comparison purposes. Should funding become available, sampling should be repeated at least once a year during similar conditions – about the same time of the year to enable the impacts associated with sediment removal to be evaluated.

44 Department of Water Restoration of river pools in the Avon catchment

5.3 Potential future benefits of sediment removal

The improvement of the ecological health of Gwambygine, Katrine and Reserve pools depends on an integrated approach to managing a range of issues. Sediment removal is an important strategy to improve the ecological health of these pools. However, improved ecological health also requires that other complimentary management strategies are implemented to improve water quality, protect and restore riparian vegetation and prevent erosion. This includes activities such as fencing and revegetation of the riparian zone and managing impacts from within the catchment to minimise nutrient and sediment loads into the river system upstream. It is anticipated that a range of ecological benefits will become apparent over the long term following sediment removal at Gwambygine, Katrine and Reserve pools. As part of this project a conceptual model has been developed to highlight the potential future benefits of sediment removal (Figure 13).

Channel dynamics and sedimentation

Based on the current understanding of the Avon system, it is likely that sedimentation will continue to be a management issue under the prevailing flow and sediment regime. If this assumption and the initial interpretation of field assessments are correct, there is likely to be the threat of on-going sedimentation in the channel. This can be managed through an integrated approach to managing soil erosion in the broader catchment, reducing bank erosion and controlling in-stream sediment movement.

Macroinvertebrates

The in-channel effects of a deeper and permanent water body during the dry season will be beneficial and contribute to improved ecological health, provided water quality is maintained or improved. Habitat structures are likely to increase at various depths of the pool through the deposition and accumulation of organic matter, and establishment of aquatic plants. As a result, more macroinvertebrate species are likely to colonise the pool in increased abundance.

Fish and crayfish

As a consequence of sediment removal, there is a greater volume of water at Gwambygine, Katrine and Reserve pools which has increased the wetted area and provided more habitat for aquatic fauna such as fish and crayfish. The proportion of deeper areas has increased and this is likely to enable larger populations of fish to persist in the pools. The water quality, particularly salinity and turbidity, will have a major effect on the species and populations the system will support.

Department of Water 45 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

Conceptual model – Benefits of sediment removal and restoration in Avon river pools

Figure 1413 – PotentialConceptual benefits model of ofsediment the benefits removal of sediment and restoration removal at and Avon restoration Pools at Avon Pools

46 Department of Water Restoration of river pools in the Avon catchment

5.4 Recommendations and conclusion

The assessments completed at Katrine, Reserve and Gwambygine pools have provided an improved understanding of the ecological condition of each pool. The ability of the assessments to determine the impact of sediment removal from the pools was limited by the short timeframe available to undertake the project. As a consequence, there are a number of issues that need clarification and further investigation before ecological benefits can be clearly identified. These are related to the need for long term monitoring to better understand the impacts of sediment removal on fish and macroinvertebrate communities, and water quality. To gain a more detailed understanding of the ecological health of Gwambygine, Katrine and Reserve pools and their response to sediment removal it is recommended that; Future ecological assessments of river pool response to sediment removal need to be replicated over a longer time frame with sampling conducted during the same seasons. Sampling for a minimum of 2 years following sediment removal is suggested. Additional monitoring of the ecological response to sediment removal from Gwambygine, Katrine and Reserve pools is recommended. Further monitoring of the pools will also contribute to the development of integrated management strategies that will address issues such as degradation of the riparian zone, poor water quality and erosion management. Additional macroinvertebrate monitoring at Gwambygine Pool is recommended, using the same methodology utilised by DEC in 2007/08 (Pinder 2009) to provide a better understanding of the ecological response to sediment removal. Ongoing monitoring of water quality occurs at Gwambygine, Katrine and Reserve pools and other priority sites on the Avon River. This will assist in identifying water quality trends and provide a better understanding of seasonal variability and the relationship between sediment removal and water quality in river pools. This should include 24 hr logging of DO and temperature to evaluate daily fluctuations and stratification in the pools. It is also recommended that natural resource management activities within the Avon River catchment that improve water quality and river health are undertaken in priority areas. This includes revegetation of riparian zones, erosion control, fencing of waterways and riparian zones and implementation of best management practices for agriculture.

Department of Water 47 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

Glossary

Acid, acidic See pH.

Algae Algae are a diverse group of aquatic plants containing chlorophyll and other photosynthetic pigments. Many are microscopic (often being single cells) but some can be large, including the large seaweeds. They grow as single cells or aggregations of cells (colonies).

Algal bloom A „bloom‟ is the rapid excessive growth of algae, generally caused by high nutrient levels and favourable climatic conditions. Blooms can result in de-oxygenation of the water when the algae die, leading to the death of aquatic flora and fauna.

Alkaline See pH.

Anoxic, anoxia Deficiency of oxygen in the water.

Aquatic Living in, growing in or frequenting water.

Basin The area drained by a river and its tributaries(see catchment).

Biochemical oxygen BOD is the amount of oxygen taken up by micro-organisms that demand (BOD) decompose organic waste matter in water. It is therefore used as a measure of the amount of certain types of organic pollutant in water. A high BOD indicates the presence of a large number of micro-organisms, which suggest a high level of pollution.

Catchment The area of land which intercepts rainfall and contributes the collected water to surface water (streams, rivers, wetlands) or groundwater.

Confluence Where a tributary joins a river.

Dissolved oxygen (DO) The concentration of oxygen dissolved in water or effluent.

Ecosystem A biological community and its physical environment, and the interrelationships and dependencies that occur between the organisms and their environment.

Eutrophication Eutrophication is a natural process of accumulation of nutrients leading to increased aquatic plant growth in lakes, rivers, harbours and estuaries. Human activities contributing fertilisers and other high nutrient wastes can speed up the process, leading to algal blooms and deterioration in water quality.

48 Department of Water Restoration of river pools in the Avon catchment

Evapoconcentration The concentration of a solute in water due to the loss of water by evaporation to the atmosphere.

Natural resource The ecologically sustainable management of the land, water, air management (NRM) and biodiversity resources for the benefit of existing and future generations.

Nutrient enrichment Over-enrichment of water by dissolved nutrients, particularly nitrates and phosphates, which leads to excessive growth of aquatic plants (see algal bloom and eutrophication).

Nutrient load The amount of nutrient reaching the waterway over a given time (usually per year) from its catchment area.

Nutrients Nutrients are minerals dissolved in water, particularly inorganic compounds of nitrogen (nitrate and ammonia) and phosphorus (phosphate) which provide nutrition (food) for plant growth. Total nutrient levels include the inorganic forms of an element plus any bound in organic molecules. pH pH is a measure of acidity (the negative logarithm of hydrogen ion concentration) in water in which pH 7 is neutral, values above 7 are alkaline and values below 7 are acid.

Phytoplankton Microscopic (up to 1–2 mm in diameter) free-floating or weakly mobile aquatic plants (e.g. diatoms, dinoflagellates, chlorophytes, blue-green algae).

Remnant vegetation The parts of the natural vegetation still existing after major change to the environment

Runoff Water that flows over the surface from a catchment area, including streams

Salinity The measure of total soluble (or dissolved) salt, i.e. mineral constituents in water

Sediment Sand, clay, silt, pebbles and organic material carried and deposited by water or wind

Turbidity Muddiness or opaqueness of water due to suspended particles in the water causing a reduction in the transmission of light

Department of Water 49 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

References Advanced Choice Economics and Viv Read & Associates 2007, Review of the economic viability of sediment extraction from the Avon River pools (draft), Department of Water, Perth, Western Australia. ANZECC & ARMCANZ 2000, Australian and New Zealand guidelines for fresh and marine water quality, Australia and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra, Australian Capital Territory. APHA 1998, Standard methods for the examination of water and wastewaters, 20th edition, American Public Health Association, Washington. Avon Catchment Council 2005, The Avon Natural Resource Management Strategy. The Regional Natural Resource Management Strategy for the Avon River Basin, Avon Catchment Council, Western Australia Beatty, S, Rashnavidi, M, Morgan, D, & Lymbery, A 2008, Salinity tolerances of native freshwater fishes of the Blackwood River, Centre for Fish & Fisheries Research, Murdoch University report to South West Catchments Council. Bruton, M.N. 1985, „The effects of suspensoids on fish‟, Hydrobiologia, vol. 125, pp. 221–241. Davies, J, Rogers, A, Sim, D, Kaesehagen, D & Orifici, R 1997 Avon River Survey 1996 Volume 5 Avon River Pool Survey, Avon River Management Authority, Northam, Western Australia. Davies, PM 1995, „Ecosystem processes: A direct assessment of river health‟, in MUys (ed.) Classification of rivers and environmental health indicators, Water Research Commission, Pretoria, Republic South Africa. Davies, P, Cook, B, Rutherford, K & Walshe, T 2004 Managing high in-stream temperatures using riparian vegetation, River Management Technical Guideline No. 5, Land and Water Australia, Canberra, Australian Capital Territory. Department of Water 2004, Statewide river water quality assessment 2004, Department of Water, Perth, Western Australia. Department of Water 2007, Assessment of the status of river pools in the Avon catchment, Department of Water, Perth, Western Australia. Department of Water 2009a, Field sampling guidelines: A guideline for field sampling for surface water quality monitoring programs, Department of Water, Perth, Western Australia. Department of Water 2009b, Avon River catchment water quality and nutrient monitoring program for 2008, Department of Water, Perth, Western Australia. Department of Water 2011, Restoration of Sandy Pool: An assessment of the ecological impacts of sediment removal at Sandy Pool, Department of Water, Northam, Western Australia.

50 Department of Water Restoration of river pools in the Avon catchment

Dunlop, J, McGregor, G & Horrigan, N 2005, Potential impacts of salinity and turbidity in riverine ecosystems. Characterisation of impacts and a discussion of regional target setting for riverine ecosystems in Queensland, The State of Queensland, Australia Halse, S, Smith, M, Kay, W, Scanlon, M & Cocking J 2001, AUSRIVAS in Western Australia, Manual for use of AusRivAS Models for assessing river health in Western Australia, Department of Conservation and Land Management, Perth, Western Australia. Hunt, RJ & Christiansen, IH 2000, Dissolved oxygen information kit, A CRC Sugar Technical Publication, CRC for Sustainable Sugar Production, Townsville, Queensland. Jones, S, Francis, C, Leung, A & Pinder, A 2009, Aquatic invertebrates and waterbirds of wetlands in the Avon region, Department of Environment and Conservation, Bentley, Western Australia. Lloyd, DS, Koenings, JP, & Laperriere, JD, 1987. „Effects of Turbidity in Fresh Waters of Alaska‟, North American Journal of Fisheries Management, January, Vol. 7, No. 1 : pp. 18-33. Morgan, DL, Beatty SJ, & Sarre GA, 2009. “Ascending the Avon: Fishes of the Northam Pool, and the Swan‐Avon Catchment”, Centre for Fish & Fisheries Research Murdoch University, South St Murdoch, Western Australia Naiman, RJ & Bilby, RE (Eds.), River Ecology and Management: Lessons from the Pacific Coastal Ecoregion, Springer Verlag, New York. NWC 2007a, Australian Water Resources 2005. Assessment of river and wetland health: a framework for comparative assessment of the ecological condition of Australian Rivers and Wetlands, National Water Commission, Canberra, Australian Capital Territory. Pinder, A 2009, Aquatic invertebrate communities in Avon and Dale river pools. Report to Species and Communities Branch, Department of Environment and Conservation, Perth, Western Australia. Schofield, NJ & Davies, PE 1996, 'Measuring the health of our rivers' , Water, vol. May/June, pp. 39-43. Smith, KA 2009, Development of fish larvae and zooplankton as indicators of ecosystem health in the Swan-Canning Estuary, Final report to Swan River Trust, Department of Fisheries, Western Australia. Storer, T, White, G, Galvin, L, O‟Neill K, van Looij, E & Kitsios, A 2011a, The Framework for the Assessment of River and Wetland Health (FARWH) for flowing rivers of south-west Western Australia: project summary and results, Final report, Water Science Technical Series, report no. 39, Department of Water, Western Australia.

Department of Water 51 Assessment of the ecological impacts of sediment removal at Gwambygine, Katrine & Reserve pools

Storer, T, White, G, Galvin, L, O‟Neill K, van Looij, E & Kitsios, A 2011b, The Framework for the Assessment of River and Wetland Health (FARWH) for flowing rivers of south-west Western Australia: method development, Final report, Water Science Technical Series, report no. 40, Department of Water, Western Australia. The Murray-Darling Freshwater Research Centre 2010, Effects of the decommissioning of Lake Mokoan on fish community structure in the Broken River, The Murray-Darling Freshwater Research Centre – Fact sheet – M/BUS/292, Version 1, Feb 2010 Water and Rivers Commission and Avon River Management Authority 2001a, Gwambygine Pool management plan, Water resource management series, report no. 27, Water and Rivers Commission, Perth and Avon River Management Authority, Northam, Western Australia. Waterwatch Australia Steering Committee 2002, Waterwatch Australia national technical manual, module 4 – physical and chemical parameters, Environment Australia, Canberra, Australian Capital Territory. Williams, WD, & Sherwood, JE 1994, „Definition and Measurement of Salinity in Salt Lakes‟, International Journal of Salt Lake Research, vol. 3, pp. 53–63.

52 Department of Water