Transcript Gunnamatta & Gymea Bays Estuary Processes Studies

Gunnamatta & Gymea Bays Estuary Processes
Studies
• Catchment, Bathymetric and Hydrodynamic
Details
• Sediment Processes
• Water Quality Processes
• Ecology Processes
• Processes Interactions
• Management Implications
Gunnamatta Bay Estuary Processes Study
Catchment, Bathymetric and Hydrodynamic Details
• Soils: relatively high erodability
• Topography: moderate to steep slopes
• Landuse: predominantly residential, some
commercial and parklands
Gunnamatta Bay Estuary Processes Study
Sediment Processes
• Infill rates: fluvial deltas now receding
• Infill rates: deeper areas ~ 1mm/yr
• Sediment Quality:Mostly good, except site
3, near Cronulla marina – high PAHs,
Aluminium, Copper, Lead, Zinc and
Mercury
• Marine shoal: minor reworking along
eastern shoreline and erosion off seaward
face, with deposition on landward face
Gunnamatta Bay Estuary Processes Study
Water Quality Processes
• Existing Data: Sometimes high TP and TN,
frequently high FC
• Sources: Catchment runoff, sewer
overflows, possible pollution from
watercraft
• Hydraulic Impacts: Very good tidal flushing
due to proximity to ocean, and high
assimilation capacity due to large resident
volume of bay (4 x annual runoff volume)
Gunnamatta Bay Estuary Processes Study
Ecology Processes
• Presence of noxious seaweed Caulerpa
Taxifolia
• Reduced seagrass extents
• Few areas of remnant bushland
• Exotic weeds (garden escapees)
• Construction of rock / concrete retaining
walls has resulted in loss of aquatic habitat
• Possible filling of former wetland areas
Gunnamatta Bay Estuary Processes Study
Processes Interaction
Catchment Processes
Hydrodynamics
Sediments
Water Quality
Ecology
Gunnamatta Bay Estuary Processes Study
Processes Interaction – Human Impacts
Human Activities
Sediments
Catchment Processes
Ecology
Water Quality
Gunnamatta Bay Estuary Processes Study
Processes Interaction – Conceptual model of interactions
Gunnamatta Bay Estuary Processes Study
Management Directions
• Nutrient and Bacteria loads from sewerage system
overflows / exfiltration
• High concentrations of heavy metals in tributaries
and in surface sediments around Cronulla marina
• Urgent need for WQ monitoring within the bay
itself
• Establishment of Caulerpa Taxifolia and potential
spread to other areas
• Loss of seagrasses over past 50 years and other
terrestrial and aquatic habitat areas
Gymea Bay Estuary Processes Study
Catchment, Bathymetric and Hydrodynamic Details
• Soils: high to extreme erodability
• Topography: moderate to steep slopes
• Landuse: predominantly residential, some
parklands
Gymea Bay Estuary Processes Study
Sediment Processes
• Infill rates: Alkaringa Creek delta still
prograding, Coonong Creek delta now
stable
• Infill rates: deeper areas ~ 0.3mm/yr
• Sediment Quality:All good, only slightly
elevated Lead at surface of Core 1 –
Coonong Creek mouth
• Fluvial deltas: has had impact on residents
adjacent to shoal, as well as Gymea Baths
Gymea Bay Estuary Processes Study
Water Quality Processes
• Data measured for this study: High nutrient and
bacteria levels in both creeks, independent of
antecedent rainfall
• Beachwatch Data: Generally very good in Gymea
Baths for FC
• Sources: Catchment runoff, sewer overflows,
minimal pollution from watercraft
• Hydraulic Impacts: Reasonable tidal flushing (<30
days), and high assimilation capacity due to large
resident volume of bay (~6 x annual runoff
volume)
Gymea Bay Estuary Processes Study
Ecology Processes
• Very small area of seagrass and mangroves due to
steep underwater and intertidal slopes
• Threat from noxious seaweed Caulerpa Taxifolia
due to presence in Gunnamatta Bay
• Few areas of remnant bushland
• Exotic weeds (garden escapees)
• Construction of rock / concrete retaining walls has
resulted in loss of aquatic habitat
Gymea Bay Estuary Processes Study
Processes Interaction
Catchment Processes
Hydrodynamics
Sediments
Water Quality
Ecology
Gymea Bay Estuary Processes Study
Processes Interaction – Human Impacts
Human Activities
Sediments
Catchment Processes
Ecology
Water Quality
Gymea Bay Estuary Processes Study
Processes Interaction – Conceptual model of interactions
Gymea Bay Estuary Processes Study
Management Directions
• Nutrient and Bacteria loads from sewerage system
overflows / exfiltration
• Urgent need for WQ monitoring within the bay
itself
• Possible future establishment of Caulerpa
Taxifolia
• Loss of terrestrial and aquatic habitat areas
• Continued advancement of Alkaringa Ck delta into
the bay