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Modifications in the Shoalhaven estuary and the delivery of sediments to the coast in the last 40 years
EP25630
Modifications in the Shoalhaven estuary and the delivery of sediments to the coast in the last 40 years
Submitted on 13 Mar 2017

Rafael Carvalho, Colin Woodroffe
University of Wollongong
This poster was presented at 25th NSW Coastal Conference
Poster Views: 406
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Poster Abstract
The Shoalhaven River is one of the few rivers in NSW to supply significant quantities of sand to the coast at present time. The bulk of
sediment delivery does not occur continuously but rather in pulse events driven by storms and floods that breach the beach berm at
Shoalhaven Heads and modify the estuary and adjacent nearshore. Analysis of aerial photographs and Landsat imagery revealed that the
river mouth at Shoalhaven Heads was open in 1961, 1974-1980, 1988-1994, 1998-1999, 2013-2014 and 2015-2016.

This work presents a series of surveys that started in the 1980’s and included repeated echo-sounding, LiDAR and RTK-GPS data to assess the volumetric change after the reduction in fluvial input imposed by the construction of Tallowa Dam in 1976.

Results show a gradual deposition at Shoalhaven Heads channel and erosion of the Crookhaven channel, with considerable changes in the estuarine and offshore volume over the years. Bathymetric data between 1981 and 2006 indicates that the estuary continued to receive fluvial and marine sediments and a gross accretion of ~1,020,000
m3 occurred between surveys. The estuarine area upstream of the confluence of Berry’s Canal accreted ~2,620,000 m3, whereas the lower end between Shoalhaven Heads and Crookhaven Heads eroded ~1,600,000 m3. During the same period, bathymetric variation in the nearshore indicated a delivery of at least 1,065,000 m3 of sediment to the coast. During the 2013 and 2015 breaching events, a loss of ~ 200,000 m3 and 165,000 m3 of sand occurred from the beach berm adjacent to Shoalhaven Heads, respectively.

These figures seem to be in agreement with the average sediment yield of ~528,000 m3/y for the catchments upstream from Tallowa Dam
and the delivery of ~90,000 m3/y to the estuary in the past 40 years. This study provided the framework for future research and an avenue for management actions, showing a direct application of the conservation of mass to the littoral sediments of the Shoalhaven Coast.Report abuse »
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