317
© Springer International Publishing AG 2017
C.W. Finkl, C. Makowski (eds.), Coastal Wetlands: Alteration and Remediation,
Coastal Research Library 21, DOI 10.1007/978-3-319-56179-0_10
Chapter 10
Long Term Impacts of Jetties and Training
Walls on Estuarine Hydraulics and Ecologies
Alexander F. Nielsen and Angus D. Gordon
Abstract Data and theory show that the inlets of several large estuaries on
Australia’s eastern seaboard that appeared to be stable within a range of entrance
conditions are demonstrating unstable scouring modes and have been doing so for
decades, if not centuries, since entrance jetties had been constructed. Jetties have
increased the hydraulic conveyance of the entrance channels by removing sand bars
and extraneous littoral currents that impeded ebb tide discharges. Field data comprising comprehensive water level monitoring in the bays, enabling the definition of
tidal planes to a high resolution, have shown that the spring tidal ranges of these
bays has been increasing steadily for decades with high tide planes rising and low
tide planes falling. The field data have indicated that these changes show no signs of
stabilizing and Escoffier analyses have indicated that it could take centuries for
these inlets to reach new stable hydraulic regimes. Implications have included
extensive scour in the entrance channels requiring channel erosion protection works,
subsidence of road bridges, collapse of foreshores including buildings, sedimentation in the bays and on adjacent beaches and permanent changes to fringing marine
ecologies and fisheries. Changes to the distribution of seagrass, saltmarsh and mangrove forests have been observed to coincide with and confirm the expectations of
impacts on marine ecology that could derive from jetty construction. While jetties
have improved flood conveyance significantly the increases in ebb tide velocities
have resulted in navigational hazards for recreational boating.
Keywords Tidal constituents • Amplitude • Phase • Prism • Inlet • Equilibrium area
• Escoffier stability analysis • Jetties • Training walls • Marine ecology
A.F. Nielsen (*)
Advisian WorleyParsons, Sydney, NSW, Australia
e-mail: Lex.Nielsen@Advisian.com
A.D. Gordon
Coastal Zone Management and Planning, North Narrabeen, NSW, Australia
e-mail: sandgus@optusnet.com.au
© Springer International Publishing AG 2017
C.W. Finkl, C. Makowski (eds.), Coastal Wetlands: Alteration and Remediation,
Coastal Research Library 21, DOI 10.1007/978-3-319-56179-0_10
Chapter 10
Long Term Impacts of Jetties and Training
Walls on Estuarine Hydraulics and Ecologies
Alexander F. Nielsen and Angus D. Gordon
Abstract Data and theory show that the inlets of several large estuaries on
Australia’s eastern seaboard that appeared to be stable within a range of entrance
conditions are demonstrating unstable scouring modes and have been doing so for
decades, if not centuries, since entrance jetties had been constructed. Jetties have
increased the hydraulic conveyance of the entrance channels by removing sand bars
and extraneous littoral currents that impeded ebb tide discharges. Field data comprising comprehensive water level monitoring in the bays, enabling the definition of
tidal planes to a high resolution, have shown that the spring tidal ranges of these
bays has been increasing steadily for decades with high tide planes rising and low
tide planes falling. The field data have indicated that these changes show no signs of
stabilizing and Escoffier analyses have indicated that it could take centuries for
these inlets to reach new stable hydraulic regimes. Implications have included
extensive scour in the entrance channels requiring channel erosion protection works,
subsidence of road bridges, collapse of foreshores including buildings, sedimentation in the bays and on adjacent beaches and permanent changes to fringing marine
ecologies and fisheries. Changes to the distribution of seagrass, saltmarsh and mangrove forests have been observed to coincide with and confirm the expectations of
impacts on marine ecology that could derive from jetty construction. While jetties
have improved flood conveyance significantly the increases in ebb tide velocities
have resulted in navigational hazards for recreational boating.
Keywords Tidal constituents • Amplitude • Phase • Prism • Inlet • Equilibrium area
• Escoffier stability analysis • Jetties • Training walls • Marine ecology
A.F. Nielsen (*)
Advisian WorleyParsons, Sydney, NSW, Australia
e-mail: Lex.Nielsen@Advisian.com
A.D. Gordon
Coastal Zone Management and Planning, North Narrabeen, NSW, Australia
e-mail: sandgus@optusnet.com.au