351
channel, where changes to seagrass distribution and abundance has occurred as a
result of increased tidal velocities causing channel bed scour and accreting flood
tide deltas causing seagrass smothering. The data indicated that the total abundance
of all seagrass throughout the estuary decreased by 57% (from 189.3 to 80.9 ha).
Approximately 64% of this loss was Posidonia and the remaining 36% predominantly Zostera. In this case some of the Posidonia beds were covered as the delta
spread into the bay. Over 33% of the total seagrass loss occurred within the channel
with approximately 72% of that being the loss of Zostera.
Since 1957, throughout most of the Wagonga estuary the mangrove communities
were found to be either stable or expanding with expansion occurring through incursion up-slope into the saltmarsh communities, laterally along the foreshore and
down-slope onto prograding deltas and sandbars (Burrell 2012). The data from
Burrell (2012) showed that the rate of change had increased threefold since the jetties were constructed in 1978 (Fig. 10.33) with the greatest increase occurring in the
upper part of the estuary.
Since 1957, saltmarsh has decreased throughout the estuary. Foreshore reclamation for a caravan park, urbanization and draining of wetlands has accounted for the
most significant loss of saltmarsh within the Inlet (Burrell 2012). Taking into
account those major impacts, the data from Burrell (2012) indicated that the natural
rate of saltmarsh loss increased threefold since the jetties were constructed
(Fig. 10.34).
Fig. 10.32 Change in the extent of seagrass at the entrance to Lake Wagonga 1979–2005 (Duchatel
et al. 2014). Loss of seagrass in the channel has been attributed to channel scour whereas on the
flood tide delta it has been attributed to sand inundation
10 Long Term Impacts of Jetties and Training Walls on Estuarine Hydraulics…
channel, where changes to seagrass distribution and abundance has occurred as a
result of increased tidal velocities causing channel bed scour and accreting flood
tide deltas causing seagrass smothering. The data indicated that the total abundance
of all seagrass throughout the estuary decreased by 57% (from 189.3 to 80.9 ha).
Approximately 64% of this loss was Posidonia and the remaining 36% predominantly Zostera. In this case some of the Posidonia beds were covered as the delta
spread into the bay. Over 33% of the total seagrass loss occurred within the channel
with approximately 72% of that being the loss of Zostera.
Since 1957, throughout most of the Wagonga estuary the mangrove communities
were found to be either stable or expanding with expansion occurring through incursion up-slope into the saltmarsh communities, laterally along the foreshore and
down-slope onto prograding deltas and sandbars (Burrell 2012). The data from
Burrell (2012) showed that the rate of change had increased threefold since the jetties were constructed in 1978 (Fig. 10.33) with the greatest increase occurring in the
upper part of the estuary.
Since 1957, saltmarsh has decreased throughout the estuary. Foreshore reclamation for a caravan park, urbanization and draining of wetlands has accounted for the
most significant loss of saltmarsh within the Inlet (Burrell 2012). Taking into
account those major impacts, the data from Burrell (2012) indicated that the natural
rate of saltmarsh loss increased threefold since the jetties were constructed
(Fig. 10.34).
Fig. 10.32 Change in the extent of seagrass at the entrance to Lake Wagonga 1979–2005 (Duchatel
et al. 2014). Loss of seagrass in the channel has been attributed to channel scour whereas on the
flood tide delta it has been attributed to sand inundation
10 Long Term Impacts of Jetties and Training Walls on Estuarine Hydraulics…