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Mangrove and saltmarsh surface elevation dynamics in relation to environmental variables in Southeastern |

Kerrylee Rogers University of Wollongong

Rogers, Kerrylee, Mangrove and saltmarsh surface elevation dynamics in relation to environ- mental variables in Southeastern Australia, PhD, School of Earth Environmental Sciences, University of Wollongong, 2004. http://ro.uow.edu.au/theses/653

This paper is posted at Research Online. http://ro.uow.edu.au/theses/653

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Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

CHAPTER TWO THE SETTING

2.1 Introduction This study focuses on saline coastal wetlands within Southeastern Australia. This includes mangrove and saltmarsh habitats geographically distributed between the NSW-Queensland border and coastal Victoria. Study sites were selected according to criteria detailed in this chapter. Study site descriptions are provided, with particular reference to factors that may influence mangrove and saltmarsh distribution and surface elevation dynamics, such as climate and sea-level rise.

2.2 Site Selection Criteria Sites were selected on the basis of four criteria. Since the observed trend of mangrove encroachment of saltmarsh (Saintilan and Williams 1999, 2000) is largely limited to Southeastern Australia, sites were selected from a number of regions throughout temperate Southeastern Australia. Study sites covered 7 catchments and 12 individual locations and approximately 1 800 km of coastline (Figure 2.1 Table 2.1).

Secondly, sites were included from a number of representative geomorphic settings, as described by Roy et al. (2001) (Table 2.1). These settings incorporate geological properties, morphology, and environmental factors such as salinity and sediments to express their structure and function and aid coastal management. Five main groups were recognised; bays (I), tide-dominated (II), wave-dominated estuaries (III), intermittent estuaries (IV) and freshwater bodies (V). Since mangrove and saltmarsh vegetation generally occur abundantly in tide-dominated estuaries and wave-dominated estuaries, these estuary types have been included in this study. While bays in do not tend to support large areas of mangrove and

Kerrylee Rogers 19 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

saltmarsh, primarily due to the wave-activity on the eastern coastline, bays in Victoria experience less wave-activity and support mangrove habitats that are among the most productive communities of coastal Victoria (Champion 1974) and diverse saltmarsh habitats (Adam 1990). Therefore, four sites in Western Port Bay have been included to represent the bay estuary group. In addition, Roy et al. (2001) identified 13 estuary types, with ocean embayments (1), drowned estuaries (3) and barrier estuaries (5) specifically represented in this study. Estuary type, along with stage of infilling and development impacts are all considered to be important modifiers of estuarine ecology. It is anticipated that this classification will aid comparisons between estuaries.

Sites were also chosen on the basis of the degree of interest and involvement of local management agencies. It was anticipated that this research would provide information to catchment, estuary and coastal management committees, government agencies and coastcare groups relevant to the management of mangrove and saltmarsh communities. In particular, Western Port Bay, Hawkesbury , and have been included because of enthusiastic support from local management groups.

Finally, where possible, sites of international, national or state significance have been selected. Island is a RAMSAR listed wetland. The wetlands of Currambene Creek, Cararma Inlet and French Island are located in marine parks and are protected under the NSW Marine Parks Act (1997) and the Victorian National Parks (Marine National Parks and Marine Sanctuaries) Act (2002). The wetlands at Rhyll are administered under the Philip Island Nature Park and the wetlands of Quail Island are classified as a Nature Conservation Reserve and protected under the Victorian Crown Land (Reserves) Act (1978). Homebush Bay, lies within the jurisdiction of Olympic Park Authority and protected under the NSW Authority Act (2001), thereby having specific planning policies that detail their management and conservation. Ukerebagh Island, Kooragang Island, Minnamurra River, Currambene Creek and Cararma Creek are designated SEPP 14 wetlands under the NSW Environmental Planning and Protection Act (1979).

Kerrylee Rogers 20 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.1: Locality map of study sites.

Table 2.1: Study sites, their geomorphic setting and significance. * From Roy et al. 2001.

Kerrylee Rogers 21 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

2.3 Site Descriptions

2.3.1 Ukerebagh Island, Tweed River Ukerebagh Island is located on the Tweed River, near the border of NSW and Queensland, some 860 km north of Sydney (153o33’E, 28o10’S, Figure 2.2). The main arm of the Tweed River is approximately 60 km long and the tidal limit is located 2 km upstream from Murwillumbah (DIPNR 2004). The Tweed River system, incorporates the Tweed River channel, Terranora Creek, Bilambil Creek, , Terranora Broadwater and Cobaki Broadwater. Ukerebagh Island is located approximately 1.5 km south of the Tweed River entrance and is enclosed by Terranora Inlet, the Tweed River channel and Ukerebagh Passage.

The Tweed River catchment (1 114 km2) lies primarily on alluvial flood plains. The catchment is surrounded by the Tertiary aged McPherson Range and Lamington Plateau, consisting primarily of volcanics (GA 2004).

The Tweed River catchment exhibits sub-tropical climate characteristics, with mean maximum daily temperatures at nearby Murwillumbah of 29.6oC and mean daily minimum temperatures of 8.5oC. Mean monthly rainfall ranges between 40.5 mm and 230.9 mm, with rainfall being significantly high in the warmer months of November to May (BOM 2004a).

All catchments within the study, including the Tweed River, are subject to the effects of El Niño and La Niña cycles (BOM 2004b). The Southern Oscillation Index (SOI) is used to indicate El Niño episodes. Negative SOI values are typically accompanied by warming of the central and eastern tropical Pacific Ocean, a decrease in the strength of the Pacific Trade winds and a reduction in rainfall over eastern and northern Australia. The last El Niño event occurred in March 1997 to April 1998 (Figure 2.3). The SOI was negative during the study period, commencing in March 2002, with positive values being evident in December 2003 (BOM 2004b).

Kerrylee Rogers 22 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.2: Location of the Tweed River and Ukerebagh Island.

Kerrylee Rogers 23 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.3: Southern Oscillation Index (SOI) since January 1995. Note the negative values since March 2002 (BOM 2004b).

Since March 2002 to November 2003, rainfall averaged approximately 30% less than mean monthly rainfall (Figure 2.4) at Murwillumbah. Some months, such as July 2002, exhibit an almost absence of rainfall (BOM 2004c).

Figure 2.4: Total monthly precipitation, and 5-month mean precipitation since January 2000 and monthly average precipitation since 1972 recorded at Murwillumbah weather station (BOM 2004c).

Kerrylee Rogers 24 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

The Tweed River has undergone a number of morphological changes that have been focussed in the estuarine regions. The most significant changes include training of the river entrance, dredging of the river and its and the Tweed River Sand Bypass Project. Dredging of the Tweed River began in the 1870’s and the river entrance was trained in 1904. Dredge spoil was deposited on Ukerebagh Island in the late 1950’s and early 1960’s (Druery and Curedale 1979).

The Tweed River Entrance Sand Bypassing Project, Environmental Impact Statement/Impact Assessment Study (EIS/IAS) predicts very small tidal changes directly attributed to entrance improvements as a result of the operation of the Tweed River Entrance Sand Bypass Project (Hyder 1997). The EIS/IAS predicts that a deeper river entrance condition would result in a slight increase in spring tidal range of about 5 cm at the Letitia 2A tide gauge near the of the Tweed River and Terranora Inlet. However, to date monitoring, by Manly Hydraulics Laboratory, of the tidal data shows that there has been no significant change in tidal conditions that can be contributed to the operation of the sand bypassing system. The annual spring tidal ranges at Letitia 2A for June 2001 to June 2003 have not exceeded the EIS/IAS predictions (Floyd 2001, Floyd 2002 and pers comm. 2003).

Sea-level was estimated to have decreased by 0.22 mm yr-1 for the past 24 years at nearby Brisbane (Mitchell et al. 2000). Water levels have been recorded near the Tweed River entrance at the Letitia Spit since December 1987 (Figure 2.5). Over this period water levels have decreased at a rate of 0.40 mm yr-1. Over the study period of November 2000 to December 2003, water level decreased at a rate of 0.47 mm yr-1 (MHL 2004a).

Kerrylee Rogers 25 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.5: Mean water level measured at the Letitia 2A tide gauge near the mouth of the Tweed River (MHL 2004a). Sea-level has decreased over the past 16 years at a rate of 0.40 mm yr-1. Sea-level has decreased between November 2000 and December 2003 at a rate of 0.47 mm yr-1.

Like most catchment areas in Southeastern Australia, the Tweed River catchment has been substantially impacted since European settlement, including clearing for rural and urban land uses. Pressey and Griffith (1987) estimated that 90% of coastal lowland vegetation in the Tweed catchment has been cleared for urban development. Heap et al. (2001) defined the catchment as modified with less than 65% of the catchment remaining in its natural state. The Tweed Shire Council (2002) State of the Environment Report estimated that 51.3 % of the local government area is non- bushland, while bushland accounts for 47.9%.

The saline coastal wetlands of the Tweed River include both mangrove and saltmarsh areas. The mangrove areas are dominated by Rhizophora stylosa and Avicennia marina, with some Aegiceras corniculatum, Exoecaria agallocha, Brugiera gymnorhiza and Ceriops tagal. The saltmarsh areas are dominated by Sporobolus virginicus, Sarcocornia quinqueflora, Baumea juncea and Juncus krausii (pers. obs.).

Kerrylee Rogers 26 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

2.3.2 Kooragang Island, Hunter River Kooragang Island has an area of 2 560 ha (Buckney 1987) and is located approximately 11 km north of Newcastle and 160 km north of Sydney and lies on the Hunter River estuary (151o48’E, 32o55’S, Figure 2.6). The Hunter River is approximately 300 km long with the entrance being located at the Port of Newcastle. The Hunter River has a relatively large catchment area (22 000 km2) and incorporates , Williams River, North Channel, South Channel, Fullerton Cove, Throsby Creek, Iron Bark Creek and . The tidal limit is located at Oakhampton, some 45 km from the sea (DIPNR, 2004). The main study area is on the Ash Island section of Kooragang Island, which forms part of the Kooragang Wetland Rehabilitation Project.

Quaternary aged alluvial deposits primarily underlie the Hunter River estuary. The lower Hunter Catchment is underlain by Permian aged sandstone, shale, siltstone, tillitic conglomerate, interbedded with coal seams and Carboniferous aged sandstone- mudstone conglomerates, toscanite, dacite and andesite (GA 2004).

The Hunter River catchment exhibits a temperate climate with a mean maximum daily temperature of 25.6oC in January and a mean minimum daily temperature of 8.4oC in July. Mean monthly rainfall ranges between 69.5 mm and 121.9 mm, with rainfall being slightly greater in the months of February to June (BOM 2004a). Between March 2002 and November 2003, rainfall averaged approximately 30% less than mean monthly rainfall (Figure 2.7). Some months, such as January 2003, exhibit rainfall as low as 3.6 mm. Rainfall was not recorded for the months of July 2001 to September 2001 (BOM 2004c).

Kerrylee Rogers 27 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.6: Location of the Hunter River and Kooragang Island.

Kerrylee Rogers 28 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.7: Total monthly precipitation, and 5-month mean precipitation since January 2000 and monthly average precipitation since 1862 recorded at Newcastle Nobbys weather station (BOM 2004c).

Kooragang Island was formed by the deposition of river-borne sediments creating a series of deltaic islands and channels. While non-tidal areas of the islands supported Casuarina and Melaleuca swamp forests or littoral rainforest, the extensive intertidal areas supported mangrove and saltmarsh (Winning 1996). Clearing for agricultural activities removed all the swamp forest and rainforest and created extensive pasture areas by 1954 (Winning 1996). After the island was zoned for heavy industry in 1960 extensive reclamation and construction occurred at the southern extent of the island causing significant morphological changes (Buckney 1987). Substantial intertidal areas were filled for the establishment of factories. The island has also been used for silt deposition from dredging activities in Newcastle Harbour (Maddock 1983). Currently, BlueScope Steel owns much of the island, while the Kooragang Wetland Rehabilitation Project and the NSW National Parks and Wildlife Service manage significant areas of the island.

Long-term sea-level trends, estimated from the Newcastle ocean level gauge and based on 31.6 years of data illustrates that sea-level has increased at a rate of 1.18 mm yr-1 (Mitchell et al. 2000). Long-term water level trends, estimated from the water level gauge at Hexham Bridge and based on 19 years of data indicates that water levels have increased at a rate of 0.33 mm yr-1 (Figure 2.8). Short-term water level

Kerrylee Rogers 29 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting trends over the study period of December 2001 to December 2003 indicate that sea- level has decreased at a rate of 0.55 mm yr-1 (MHL 2004a).

Figure 2.8: Mean water level measured at the Hexham Bridge tide gauge near Kooragang Island, Hunter River. Sea-level has increased over the past 19 years at a rate of 0.33 mm yr-1. Sea-level has decreased between December 2001 and December 2003 at a rate of 0.55 mm yr-1 (MHL 2004a).

According to the 2001 census, the Lower Hunter River houses 470 610 residents within the local government areas (LGAs) of Newcastle, Port Stephens, Maitland, Cessnock and Lake Macquarie. Other councils within the include Dungog, Gloucester, Great Lakes, Merriwa, Muswellbrook, Scone, Singleton and Murrurundi. The catchment is heavily cleared for urban and rural residential development, agricultural activities, coal mining, power generation, heavy industry, shipping, tourism, manufacturing and fisheries (HCMT 2004). By June 1993, 24% of the Newcastle LGA was described as wetlands, 20% residential, 13% waterways, 9% urban bushland, 9% rural, and the remainder used for industrial, commercial, mining and recreational purposes (Newcastle City Council 2003).

The mangrove environment on Kooragang Island is dominated by Avicennia marina, however large numbers of Aegiceras corniculatum are located beneath the Avicennia canopy. The saltmarshes of Kooragang Island are dominated by Sporobolus

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virginicus, with significant areas of Sarcocornia quinqueflora, Juncus krausii and Baumea juncea (pers. obs.).

2.3.3 and Marramarra Creek, Berowra Creek (151o15’E, 33o30’S) and Marramarra Creek (151o03’E, 33o31’S) lie within the Hawkesbury River system, 50 km north of Sydney (Figure 2.9). The Hawkesbury River becomes the upstream. The Hawkesbury River has a large catchment area (21 500 km2) and is NSW largest estuary. The tidal limit is near Yarramundi, 45 km upstream (DIPNR 2004). The Hawkesbury River system incorporates the main tributaries of McDonald River, Redbank Creek, , South Creek, Eastern Creek, Reedy Creek, , Mullet Creek, Patonga Creek, Berowra Creek, Marramarra Creek, and Mangrove Creek. The Berowra Creek and Marramarra Creek catchment has an area of 310 km2. Berowra Creek estuary extends for approximately 23 km in a southerly direction from the Hawkesbury River, while Marramarra Creek extends in a westerly direction for approximately 7 km (Webb et al. 2000).

The lower Hawkesbury River catchment is largely set upon Triassic aged Hawkesbury sandstone that is interbedded with shale and quartz with small volcanics intrusions. Large alluvial deposits underlie the mud basins within the estuarine regions (GA 2004).

The Hawkesbury River catchment exhibits a temperate climate with mean maximum daily temperatures of 26.8oC in January and mean minimum daily temperatures of 6.0oC in July. Mean monthly rainfall ranges between 71.1mm in September and 147.4 mm in March, with rainfall being greater in the months of January to May (BOM 2004a). Between March 2002 and November 2003, rainfall averaged approximately 26% less than mean monthly rainfall (Figure 2.10). Rainfall was as low as 21 mm in October 2002 (BOM 2004c).

Kerrylee Rogers 31 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.9: Location of the Hawkesbury River, Berowra Creek and Marramarra Creek.

Kerrylee Rogers 32 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.10: Total monthly precipitation, and 5-month mean precipitation since January 2000 and monthly average precipitation since 1981 recorded at Peats Ridge weather station (BOM 2004c).

The Hawkesbury River is a drowned river valley estuary created approximately 10 000 to 6 500 years ago by rising sea-levels (Roy et al. 2001). While other areas of the Hawkesbury River have undergone significant alterations since European settlement, there has been little alteration to the morphology of Berowra Creek and Marramarra Creek. Catchment impacts associated with developments, agriculture and bushfire mobilise sediments. Coles (1995) estimated an annual catchment denudation rate of 0.78 t ha-1 for Berowra Creek.

Long-term water level trends, based in 12 years of water level data from the tide gauge at nearby Spencer, indicate that sea-level has risen at a rate of 0.69 mm yr-1 in the Hawkesbury (Figure 2.11). Over the short 8-month study period sea-level rose at a rate of 25.91 mm yr-1 (MHL 2004a).

The Berowra Creek and Marramarra Creek catchments remain largely undisturbed bushland (70%), which is contained within Berowra Valley Regional Park, Muogamarra or (Webb et al. 2000). The majority of the 85 000 population of the catchment exists within the urban and industrial area to the south and east of Berowra Creek (Webb et al. 2000). The remaining area consists of rural and urban land uses.

Kerrylee Rogers 33 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.11: Mean water level measured at the Spencer tide gauge near Berowra Creek and Marramarra Creek, Hawkesbury River. Sea-level has increased over the past 12 years by 0.70 mm yr-1. Sea-level has increased between November 2002 and August 2003 by 25.91 mm yr-1 (MHL 2004a).

The saline coastal wetlands of Berowra Creek and Marramarra Creek consist of mixed forests of Avicennia marina and Aegiceras corniculatum at the seaward edge. Saltmarshes occur immediately behind the mangrove forest or at the seaward edge in the upper reaches of the creeks. Saltmarshes are typically dominated by Juncus krausii with undergrowth of Sarcocornia quinqueflora, Sporobolus virginicus and Samolus repens (pers. obs.).

2.3.4 Homebush Bay, River Homebush Bay is situated on the , which is the largest river entering Sydney Harbour (Figure 2.12). The catchment area is small (130 km2) and the tidal limit is at the Charles Street Weir in Parramatta, 19 km upstream from the mouth of the river in and 30 km from the coast (DIPNR 2004). The main tributaries to the Parramatta River include Subiaco Creek, , Duck River, Duck Creek, , , Creek and .

Kerrylee Rogers 34 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.12: Location of the Parramatta River, Homebush Bay and Powells Creek.

The Parramatta River, Sydney Harbour and Homebush Bay lie within a valley consisting primarily of Triassic aged Hawkesbury sandstone and sandstones belonging to the Wiannamatta group. The mud basin of Homebush Bay has extensive alluvial deposits suitable for the establishment of swamp habitats (GA 2004).

The Parramatta River catchment exhibits a temperate climate with mean maximum daily temperatures of 28.2oC in January and mean minimum daily temperatures of 6.2oC in July. Mean monthly rainfall ranges between 46.2mm in July and 124.7 mm

Kerrylee Rogers 35 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

in February, with rainfall being greater in the months of January to April (BOM 2004a). Between March 2002 and November 2003, rainfall averaged approximately 28% less than mean monthly rainfall (Figure 2.13). Rainfall was as low as 5.9 mm in September 2003 (BOM 2004c).

Figure 2.13: Total monthly precipitation, and 5-month mean precipitation since January 2000 and monthly average precipitation since 1965 recorded at Parramatta North weather station (BOM 2004c).

Homebush Bay and Powells Creek are tributaries to the Parramatta River, which enters the ocean at Port Jackson. Since the estates of “Newington” and “Home Bush” were handed to the government in the early 1900s, most of the land has remained under the control of state or federal government. Due to the occupation of the site by industries such as an abattoir, brickworks and armaments depot, the site has undergone significant morphological change. The wetland areas were progressively filled and reclaimed and Powells Creek was trained (CSIRO 1996).

Long-term sea-level trends, based on 90 years of sea-level data from the ocean tide gauge at , indicate that sea-level has risen at a rate of 0.91 mm yr-1 in Sydney Harbour between 1915 and 2004 (NTF 2004). Over the four-year study period of February 2000 to January 2004, sea-level has decreased at a rate of 9.52 mm yr-1 (Figure 2.14).

Kerrylee Rogers 36 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.14: Mean sea-level measured at the Fort Denison tide gauge in Sydney Harbour. Sea-level has increased over the past 90 years at a rate of 0.91 mm yr-1. Sea-level has decreased between February 2000 and January 2004 at a rate of 9.52 mm yr-1 (NTF 2004).

The Homebush Bay catchment has been characterised by heavy industry and medium density housing. While the number of industrial sites in the catchment has decreased since the 1970’s, the catchment remains largely highly developed (Taylor et al. 2004).

The saline coastal wetlands at Homebush Bay are Sydney Harbour’s largest remaining mangrove forest and second largest saltmarsh community. The mangrove forest is dominated by Avicennia marina, while the saltmarsh area is dominated by Sarcocornia quinqueflora and supports a number of species that are rare in the Sydney region, including Halosarcia pergranulata, Wilsonia backhousei and Lampranthus tegens. The dominant saltmarsh species are Sarcocornia quinqueflora, Sueada australis and Juncus krausii. The weed species Juncus acutus also occurs in significant numbers (pers. obs.).

2.3.5 Minnamurra River Minnamurra River lies 100 km south of Sydney (150o52’E, 34o39’S, Figure 2.15). The catchment area is small (110 km2) and the tidal limit is near Terragong Swamp, 10 km from the river entrance (DIPNR 2004). The River catchment incorporates the tributaries of Rocklow Creek and Wrights Creek. The Minnamurra River lies at the

Kerrylee Rogers 37 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

southern end of the coastal lowlands and extends for approximately 50km, bounded in the east by the Pacific Ocean and in the west by the .

Figure 2.15: Location of the Minnamurra River and study site locations.

The upper Minnamurra River is set predominantly in rolling hills, with areas of steep terrain. The catchment is underlain by geology belonging to the Shoalhaven group, consisting of Triassic aged sandstone and shale; and Permian aged volcanics and coal

Kerrylee Rogers 38 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

measures. The river flows into extensive floodplains and estuarine wetlands mostly underlain by Quaternary aged alluvium and sands (Wagner 1996).

The Minnamurra river catchment has a temperate climate with mean maximum daily temperatures of 25.1oC in January and February, and mean minimum daily temperatures of 8.4oC in July. Mean monthly rainfall ranges between 75.2 mm in September and 144.9 mm in March. Rainfall is greatest in the months of January to June (BOM 2004a). While rainfall measurements were not recorded for the period of August 2002 to December 2002, it is evident that prior to August 2002, total monthly rainfall and 5-month mean rainfall was significantly less than the average rainfall recorded at Kiama bowling Club since 1897 (Figure 2.16) (BOM 2004c).

Figure 2.16: Total monthly precipitation, and 5-month mean precipitation since January 2000 and monthly average precipitation since 1897 recorded at Kiama Bowling Club weather station (BOM 2004c).

The Minnamurra River is described as a triple barrier estuary (Roy 1984, Ryan 1992, Roy et al. 2001). The entrance to the river is located at the southern end of a coastal embayment (Watkinson 1998) and is protected from high wave-energy by Stack Island, creating an environment suitable for the establishment of mangrove and saltmarsh. Since sea-level reached its present level approximately 6 500 years ago, the

Kerrylee Rogers 39 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

estuary has undergone little morphological change aside from the deposition of terrigenous sediments within the estuary.

Long-term sea-level trends, based on 19-years of data from the water-level gauge in nearby , indicate that sea-level has decreased at a rate of 0.47 mm yr-1 (Figure 2.17, MHL 2004a). Ocean-level data from the tide gauge in nearby indicates that over the past 19 years, sea-level has decreased at a rate of 1.16 mm yr-1 (NTF 2004). Over the 23-month study period, based on data from the water level gauge at Macquarie Rivulet, sea-level has decreased at a rate of 6.17 mm yr-1 (MHL 2004a).

Figure 2.17: Mean sea-level measured at the Macquarie Rivulet water-level gauge. Sea-level has decreased over the past 19 years at a rate of 0.47 mm yr-1. Sea-level has decreased between August 2001 and September 2003 at a rate of 9.52 mm yr-1 (MHL 2004a).

The Minnamurra River catchment lies within the local government areas of Shellharbour City Council and Kiama Municipal Council. Both councils carry out waste disposal adjacent to Rocklow Creek causing significant nutrient addition and groundwater contamination. The Minnamurra estuary is surrounded almost entirely by residential landuse, while some sand mining does occur on the northern side of the catchment. The upper Minnamurra River is used heavily for rural landuse, however a

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significant portion of the catchment is within Budderoo National Park or classified as natural forest (Watkinson 1998).

The Minnamurra River supports a number of large natural saline coastal wetlands and freshwater wetlands. The saline coastal wetlands consist primarily of mangrove forests of Avicennia marina and Aegiceras corniculatum. Saltmarshes are typically dominated by Sporobolus virginicus and Sarcocornia quinqueflora, with significant Samolus repens, Sueada australis and Juncus krausii populations. At higher elevations saltmarsh graduates into Casuarina forests that are underlain with upper saltmarsh species such as Zoysia macrantha and Sporobolus virginicus (pers. obs.).

2.3.6 Cararma Inlet and Currambene Creek, Jervis Bay Cararma Inlet (150°49’27”E, 35°0’57”S) and Currambene Creek (150°40’28”E, 35°2’38”S) both enter Jervis Bay, located 180 km south of Sydney (Figure 2.18). The Jervis Bay catchment area is relatively small (410 km2) and the main tributaries to the bay include Cararma Inlet, Currambene Creek, Callala Creek, Bib Bib Creek and Moona Moona Creek (DIPNR 2004). Cararma Inlet has a small catchment area (3 km2), primarily draining the saline coastal wetlands and is located in the northeast corner of Jervis Bay. Currambene Creek is the largest to Jervis Bay with a catchment of 165 km2 and lies on the northwestern boundary of Jervis Bay.

Jervis Bay is primarily set upon Permian aged quartz sandstone, siltstone and conglomerates from the Shoalhaven group, while the estuarine regions of the tributaries of Currambene Creek and Cararma Inlet are underlain by alluvial deposits ideal for mangrove and saltmarsh establishment (GA 2004).

The Jervis Bay catchment has a temperate climate with mean maximum daily temperatures of 23.9oC in February and mean minimum daily temperatures of 9.2oC in July. Mean monthly rainfall ranges between 79.5 mm in September and 134.2 mm in May, with rainfall being greater in the months of January to July (BOM 2004a). Between March 2002 and November 2003, rainfall averaged approximately 16% less than mean monthly rainfall (Figure 2.19). Rainfall was as low as 7.1 mm in July 2002 (BOM 2004c).

Kerrylee Rogers 41 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.18: Location of Jervis Bay, Cararma Inlet and Currambene Creek.

Jervis Bay estuary is described as a coastal embayment; however, the tributaries of Currambene Creek and Cararma Inlet are both barrier estuaries (Roy et al. 2001). Cararma Inlet has remained relatively geomorphologically stable since the last sea- level transgression. However Currambene Creek has undergone significant morphological changes. Numerous meanders, that are still evident, show the different locations the creek has flowed since 1832 (Wilton 2002). In particular, a meander at Wollamia, west of the entrance, was cut-off just over 100 years ago and Shoalhaven City Council and NSW Public Works constructed a rock groyne at the entrance in the 1980s (Wilton 2002).

Kerrylee Rogers 42 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.19: Total monthly precipitation, and 5-month mean precipitation since January 2000 and monthly average precipitation since 1965 recorded at Parramatta North weather station (BOM 2004c).

Long-term sea-level trends, based on 10 years of data from the ocean tide gauge at Creswell, on the shores of Jervis Bay, indicate that sea-level has increased at a rate of 4.12 mm yr-1 (Figure 2.20). Over the three-year study period of February 2001 to February 2004 at Currambene Creek, sea-level has decreased at a rate of 27.48 mm yr-1. Over the 24-month study period of August 2001 to August 2003 at Cararma Inlet, sea-level decreased at a rate of 34.93 mm yr-1 (MHL 2004b).

While the Currambene Creek catchment has been developed for agricultural and rural residential land uses, much of the catchment remains relatively untouched. The lower estuarine section of Currambene Creek, including Huskisson is relatively urbanised. In contrast the catchment of Cararma Inlet remains relatively natural and was described as pristine (>90% natural cover remaining, Heap et al. 2001).

Kerrylee Rogers 43 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.20: Mean sea-level measured at the Creswell ocean tide gauge. Sea-level has increased over the past 10 years at a rate of 4.12 mm yr-1. Sea-level has decreased at Currambene Creek over the study period of February 2001 to February 2004 at a rate of 27.48 mm yr-1. Sea-level has decreased at Cararma Inlet over the study period of August 2001 to August 2003 at a rate of 34.93 mm yr-1 (MHL 2004b).

The saline coastal wetlands of Jervis Bay are significant and were included in the Directory of Important Wetlands in Australia (ANCA 1996, pp. 94-96). In the mangrove habitats, Avicennia marina and Aegiceras corniculatum form forests at the shoreward edge. Saltmarsh communities dominated by Sarcocornia quinqueflora, Samolus repens, Sporobolus virginicus, Sueada australis, Juncus krausii and Baumea juncea occur at higher tidal elevations. The saltmarsh at Cararma Inlet is also heavily dominated by Sclerostegia arbuscula, which is nearing its northern most limit at this location. Significant populations of Wilsonia backhousei, which is classified as vulnerable under the NSW Threatened Species Conservation Act (1995), also occur at Cararma Inlet. The terrestrial boundaries at Currambene Creek and Cararma Inlet are frequently colonised by Casuarina glauca, Melaleuca and Eucalyptus forests (pers. obs., Saintilan and Wilton 2001).

Kerrylee Rogers 44 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

2.3.7 French Island, Kooweerup, Quail Island and Rhyll, Western Port Bay Western Port Bay (38o21’00”S, 145o13’00”E), Victoria, Australia, lies east of Melbourne (Figure 2.21). Western Port Bay was classified as a coastal embayment (Roy et al. 2001). Due to the positioning of Phillip Island at the mouth of the bay, the waters of the bay are protected from the winds in Bass Strait and remain relatively calm. Western Port Bay provides a suitable environment for mangrove and saltmarsh development. The study site of French Island is the largest island off the coast of Victoria and is located in the centre of Western Port Bay (38°23’S, 145°18’E). French Island has an area of 17 410 ha, with 11 000 ha being national park. Kooweerup is located at the head of Western Port Bay (38°12’45”S, 145°22’40”E) and primarily consisted of over 100 000 ha of swamp until drainage began in the 1860’s. Quail Island is a nature conservation reserve located approximately 9 km southwest of Tooradin (38°13’20”S, 145°18’28”E). The study site at Rhyll is located on Phillip Island (38°27’53”S, 145°17’57”E), which is a relatively small island (10 000 ha) and is positioned at the mouth of Western Port Bay.

The geology of Western Port Bay is complex, particularly on the western boundary and along the Mornington Peninsula. However, each of the study sites primarily lies on relatively young Holocene aged alluvial deposits, lagoon and swamp deposits and Pleistocene Aeolian dune deposits. Phillip Island is also set upon Tertiary aged volcanics; while French Island is set upon Tertiary aged sandstone, siltstone and conglomerates (GA 2004).

The Western Port Bay catchment has a temperate climate with mean maximum daily temperatures of 24.4oC in February and mean minimum daily temperatures of 7.0oC in July. Mean monthly rainfall ranges between 42.8 mm in February and 79.1 mm in June, with rainfall being greater in the months of April to October (BOM 2004a). Between March 2002 and November 2003, rainfall averaged approximately 22% less than mean monthly rainfall (Figure 2.22). Rainfall was as low as 10.8 mm in February 2003 (BOM 2004c).

Kerrylee Rogers 45 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.21: Location of Western Port Bay, French Island, Kooweerup, Quail Island and Rhyll.

Western Port Bay evolved after the land around it persisted following Holocene marine submergence. It remains largely as a marine system rather than an estuarine system, with only a few inflowing streams. Much of the northern region, now known as Kooweerup, remained as swamp following submergence, however, has since been drained and reclaimed for agricultural use (Bird 1986). While significant changes in the extent of fringing mangroves and sandy shoreline have been recorded since 1842, the shoreline has remained largely unchanged (Bird and Barson 1975).

Long-term sea-level trends, from the tide gauge at Williamstown in nearby Port Phillip Bay indicate that sea-level has risen at a rate of 0.26 mm yr-1 over the past 32 years (Mitchell et al. 2000). Based on 10 years of data from the ocean tide gauge at Stony Point, on the shores of Western Port Bay, sea-level has increased at a rate of 2.66 mm yr-1 (Figure 2.23). Over the three-year study period of October 2000 to November 2003, sea-level has decreased at a rate of 4.05 mm yr-1 (NTF 2004).

Kerrylee Rogers 46 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

Figure 2.22: Total monthly precipitation, and 5-month mean precipitation since January 2000 and monthly average precipitation since 1882 recorded at Phillip Island weather station (BOM 2004c).

Figure 2.23: Mean sea-level measured at the Stony Point ocean tide gauge. Sea-level has increased over the past 11 years by 2.66 mm yr-1. Sea-level has decreased between October 2000 and November 2003 by 4.05 mm yr-1 (NTF 2004).

The Western Port Bay catchment is well-developed for rural and agricultural land uses with small residential communities located primarily around the western shore of the bay and on Phillip Island. Approximately 50% of French Island is national park and protected from development, while the remaining portion of the island is used for grazing and horticulture (Vic DPI 2004). The majority of the lands immediately surrounding Kooweerup is used for grazing and horticulture, with minimal natural

Kerrylee Rogers 47 Mangrove and Saltmarsh Surface Elevation Dynamics in Chapter Two: Relation to Environmental Variables in Southeastern Australia The Setting

vegetation cover remaining. Quail Island is entirely protected as a nature reserve, however may be severely impacted by the agricultural activities occurring in the Kooweerup and Tyabb regions surrounding the island. Rhyll, located on Phillip Island, has a well-developed catchment consisting almost entirely of grazing and horticulture, and little natural vegetation cover. Significant residential development has occurred in the nearby townships of Cowes and Rhyll.

The saline coastal wetlands of Western Port Bay primarily comprise of mangrove forests and saltmarsh plains. Avicennia marina is the only mangrove species occurring south of Merimbula, New South Wales and is close to its southern limit in Corner Inlet (38o48’00”S, 146o21’30”E, Hogarth 1999). The saltmarsh plains are floristically rich, supporting approximately 30 species, including a number species endemic to this region (pers. obs.).

2.4 Conclusions In summary, the sites chosen reflect a number of geomorphological settings and catchment development. Sites have also been selected that are regionally, nationally or internationally significant. Inclusion of sites of different geomorphology and catchment development assisted with interpretation of comparisons of results between sites. It was anticipated that the inclusion of sites on the basis of the degree of interest and involvement of local management agencies would enhance interest in this research and aid in its continuation past the completion of this thesis. It was hoped that community groups would continue with monitoring so that strong trends can be identified and that sedimentation and elevation trajectories would be useful for predicting the outcome of these environments.

The overall average sea-level trend for Australia was estimated to be rising at a rate of 0.30 mm yr-1 (Mitchell et al. 2000). Sea-level trends have not consistently risen throughout Australia or at individual study sites. The study sites of Ukerebagh Island and Minnamurra River exhibit long-term declines in sea-level, however, the overall trend was for long-term sea-level at study sites to rise at a mean rate of 0.40 mm yr-1.

Kerrylee Rogers 48