Quantifying the Physical and Biological Changes to Lake Illawarra, New South Wales, Due to Entrance Training
Total Page:16
File Type:pdf, Size:1020Kb
University of Wollongong Research Online Faculty of Science, Medicine & Health - Honours Theses University of Wollongong Thesis Collections 2016 Quantifying the Physical and Biological Changes to Lake Illawarra, New South Wales, Due to Entrance Training Caitlain Regena Follow this and additional works at: https://ro.uow.edu.au/thsci University of Wollongong Copyright Warning You may print or download ONE copy of this document for the purpose of your own research or study. The University does not authorise you to copy, communicate or otherwise make available electronically to any other person any copyright material contained on this site. You are reminded of the following: This work is copyright. Apart from any use permitted under the Copyright Act 1968, no part of this work may be reproduced by any process, nor may any other exclusive right be exercised, without the permission of the author. Copyright owners are entitled to take legal action against persons who infringe their copyright. A reproduction of material that is protected by copyright may be a copyright infringement. A court may impose penalties and award damages in relation to offences and infringements relating to copyright material. Higher penalties may apply, and higher damages may be awarded, for offences and infringements involving the conversion of material into digital or electronic form. Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong. Recommended Citation Regena, Caitlain, Quantifying the Physical and Biological Changes to Lake Illawarra, New South Wales, Due to Entrance Training, BEnvSci Hons, School of Earth & Environmental Science, University of Wollongong, 2016. https://ro.uow.edu.au/thsci/138 Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library: [email protected] Quantifying the Physical and Biological Changes to Lake Illawarra, New South Wales, Due to Entrance Training Abstract Estuaries are environmentally, recreationally and economically valuable systems, however they are increasingly becoming the focus of human developments. Estuaries that are intermittently open to the ocean are particularly prone to entrance works (Morris and Turner, 2010). This study aimed to quantify certain physical and biological changes occurring at Lake Illawarra, a trained barrier estuary located on the south coast of New South Wales, Australia, following entrance training in 2007. A combination of entrance morphology mapping using GIS and aerial photography for the years 2007-2016, volume difference calculations of hydrographic survey data collected in 2008 and 2016, the comparison of tidal and flow gauging data collected in 2008, 2012 and 2016, and sediment sampling were used to quantify the physical changes occurring within the entrance at Lake Illawarra. The current extent of mangroves within Lake Illawarra was also mapped. Lateral erosion and bed scour was most severe downstream of the Windang Bridge along the Windang foreshore where lateral erosion exceeding 100 m occurred and scouring down to -7 m to -8 m was evident, both of which were driven by an eastward shift in the thalweg. Upstream of the Windang Bridge, reactivation of the flood-tidal delta saw the progradation of the delta into the lake by over 100 m at several locations, and vertical accretion at the delta lobes of up to 2 m to 3 m. Sediment analysis classified the entrance channel as an area dominated by marine tidal processes. Mangroves cover approximately 8781 m², and since juvenile trees and small trees account for 92% of mangrove extent, it is evident that the majority of mangroves established due to entrance training. These results will assist in the formation of the Coastal Zone Management Plan (CZMP) currently being prepared for Lake Illawarra. The CZMP will need to consider shoreline protection and engineering options to address channel scouring and erosion, particularly at those areas threatening to undermine shoreline developments along the Windang foreshore and Judbowley Point. The encroachment of mangroves into saltmarsh areas, an endangered ecological community in NSW, will also need to be considered by the CZMP. Future studies should seek to quantify how the physical changes occurring at trained barrier estuaries are impacting the ecosystem as a whole. Degree Type Thesis Degree Name BEnvSci Hons Department School of Earth & Environmental Science Advisor(s) Brian Jones Keywords ICOLLs, Breakwaters, barrier estuary, management This thesis is available at Research Online: https://ro.uow.edu.au/thsci/138 1 Environmental Science Program School of Earth and Environmental Sciences Faculty of Science, Medicine and Health The University of Wollongong Quantifying the Physical and Biological Changes to Lake Illawarra, New South Wales, Due to Entrance Training Caitlain Regena A thesis submitted in part fulfilment of the requirements of the Bachelor of Environmental Science in the School of Earth and Environmental Sciences, Faculty of Science, Medicine and Health, University of Wollongong 2016. October 2016 2 The information in this thesis is entirely the result of investigations conducted by the author, unless otherwise acknowledged, and has not been submitted in part, or otherwise, for any other degree or qualification. 3 Acknowledgements Thank you to my supervisor, Brian Jones, for your fantastic help in the field and honest and valuable feedback. Thank you also to Errol McLean, Heidi Brown, Danny Wiecek, Kerrylee Rodgers and Rob Williams for all helping me at different stages of the project. Thank you to the all the academics before me, who left great reading material behind and instilled anticipation and drive in many of us. Above all, thank you to my family and loved ones for your help, laughs and support. 4 Abstract Estuaries are environmentally, recreationally and economically valuable systems, however they are increasingly becoming the focus of human developments. Estuaries that are intermittently open to the ocean are particularly prone to entrance works (Morris and Turner, 2010). This study aimed to quantify certain physical and biological changes occurring at Lake Illawarra, a trained barrier estuary located on the south coast of New South Wales, Australia, following entrance training in 2007. A combination of entrance morphology mapping using GIS and aerial photography for the years 2007-2016, volume difference calculations of hydrographic survey data collected in 2008 and 2016, the comparison of tidal and flow gauging data collected in 2008, 2012 and 2016, and sediment sampling were used to quantify the physical changes occurring within the entrance at Lake Illawarra. The current extent of mangroves within Lake Illawarra was also mapped. Lateral erosion and bed scour was most severe downstream of the Windang Bridge along the Windang foreshore where lateral erosion exceeding 100 m occurred and scouring down to -7 m to -8 m was evident, both of which were driven by an eastward shift in the thalweg. Upstream of the Windang Bridge, reactivation of the flood-tidal delta saw the progradation of the delta into the lake by over 100 m at several locations, and vertical accretion at the delta lobes of up to 2 m to 3 m. Sediment analysis classified the entrance channel as an area dominated by marine tidal processes. Mangroves cover approximately 8781 m², and since juvenile trees and small trees account for 92% of mangrove extent, it is evident that the majority of mangroves established due to entrance training. These results will assist in the formation of the Coastal Zone Management Plan (CZMP) currently being prepared for Lake Illawarra. The CZMP will need to consider shoreline protection and engineering options to address channel scouring and erosion, particularly at those areas threatening to undermine shoreline developments along the Windang foreshore and Judbowley Point. The encroachment of mangroves into saltmarsh areas, an endangered ecological community in NSW, will also need to be considered by the CZMP. Future studies should seek to quantify how the physical changes occurring at trained barrier estuaries are impacting the ecosystem as a whole. 5 Contents 1 Introduction .................................................................................................................................. 13 1.1 Background ........................................................................................................................... 13 1.2 Aims and Objectives .............................................................................................................. 15 2 Literature Review .......................................................................................................................... 16 2.1 Estuaries ................................................................................................................................ 16 2.1.1 Entrance Form and Function ......................................................................................... 16 2.1.2 Barrier Estuaries ............................................................................................................ 16 2.2 Impacts of Entrance Training ................................................................................................ 19 2.2.1 Changing Hydrodynamics and Sediment Movement ................................................... 19 2.2.2 Flood- and Ebb-tidal