We have had consultants do a very good job assessing how we keep the barway open , prevent flooding  and a number of secondary future potential issues relating to climate change. I truly believe that once the main issue is climate change then the whole of Austraila will be in difficult times and our trouble will seem insignificant. So my purpose in making my submission to the consultants was to emphasize that we need solutions that are cost effective and can be implemented.

Monday, November 10, 2025
Topic: Comment on the Scamander River
Adaptation Pathways.

I have mentioned at public meetings the importance of the
connection of the Scamander River to Henderson Lagoon.
Nowhere in the summaries I have seen has this pathway been
given due consideration. This is why I am now doing just that as
I consider its usefulness should be reinstated as number 1 in the
no regret options.
To recap there was a side rivulet which entered the Scamander
River just east of the playground. Water entering this conduit
would flow south entering marshy ground and eventually
reaching Henderson Lagoon. Halfway along Dune Street this
rivulet is still visible. It was noted at Community meetings that
small rowing boats could traverse this passageway when it was
flowing.
When the break wall was built in the early 90’s the connection
was broken and obviously its importance was lost.
The advantage of this passageway is that it did not suffer from
the ingress of sand as occurs with the
mouth of the Scamander River and
hence was always there as a conduit.
Furthermore it locked in position of
the Scamander river towards the levee
bank in front of the playground.
Looking at the sketch provided above
you can just see that for about 600m
from the river the rivulet flows
through marsh land. The implication
of this is that it needs the river to rise
in order to make this connection. This
is exactly what happened in past times
before the break wall was installed.
Why is this rivulet so important? You
could ask yourself these questions and the
answer is simple. This
rivulet only flows when
the river mouth is blocked
and the water in the
catchment rise.
At present the Scamander
mouth is closing far more
than when the extended
break wall was still intact.

Figure 2 the old rivulet-remnant near playground
Figure 1 map of rivulet near mouth
of Scamander River
This so called break wall was never a real levee and surprisingly
it did the job well. The hydraulic reasons for this are not well
understood. But one feature that stood out is that the barway
never moved south of this breakwall until it was breached.
The Scamander River closes when the river flows drop. In these
circumstances the ingress of windborne and tidal flow sands
block the mouth. This will happen when the catchment doesn’t
provide enough water during outgoing tidal flows.
Once the river mouth closes it remains closed with the only
mechanism being to mechanical open it or wait for flooding
rains. It must be remembered too that the sands blocking the
mouth can continue to accumulate sand and be well over a metre
high.
When the mouth is closed the water levels in the upper reaches
starts to rise slowly
depending on freshwater
flows from the catchment of
the Scamander and Avenue
rivers. Without a significant
rain event it never catches up
with the ingress of sand at the
mouth. Eventually this can
lead to the entire saltwater
catchment being over a metre
higher than in the normal
flow condition.
This in turn means that
salt and salty water is
Figure 3 dead trees and eroded banks up the river
affecting the vegetation along the river and killing it. ( there is
also the likelihood of the banks being affected by the regular
opening and closing of the mouth mechanically).
If the rivulet was still available then when the river rose it
would flow into the Henderson lagoon catchment.
As I have already said without a significant rainfall event, flows
into the catchment at this time drop. With the rise in the river
levels and the rivulet open then waters would flow to Henderson
lagoon and no further rises in the catchment levels would occur.
This would eliminate those necessary mechanical openings now
occurring in these periods of low flows. It would also have the
added advantage of flushing the Henderson lagoon upper
reaches and giving added flows to its outlet.
The saltwater catchment of the Scamander river is at least 150
ha. With a water rise of say 1 metre this is equivalent to 1500
megalitres. ( this is a optimistic figure as quite a lot of the
measured catchment area is marsh land and therefore above
ground at lower catchment levels) Even this may seem to be a
lot of water but with heavy rain events catchment flows in
excess of 4000 Ml./day have been recorded. However the
dynamics of the river should be looked at more closely during
rain free days.( eg over 200 days were recorded over a 10 year
period of with flows less than 40ML/day ) .
When the river has risen and a mechanical opening becomes
necessary the barway width widens rapidly and water flows are
impressive. However after just a few days the levels of water in
the catchment have dropped and tidal flows once again
predominate. It is in this scenario that sand continues to
accumulate in the bridge area before the barway closes again.
It is for this reason too that barway openings should be
minimized and would be if the rivulet is operating.
.
In conclusion the number 1 priority in my opinion is reestablish
this rivulet. The rivulet at the upper end appears to have been
blocked by the development of the Surfclub.
Quite often outside significant rainfall events the average runoff
into the catchment is less than 50 megalitres a day. Taswater
useage is less than 1 megalitre a day so it is not significant. 50
megalitres a day can easily be handled by this rivulet. There is
no direct danger to the houses in Dune Street directly being
caused by the operation of the rivulet.
However a flooding situation towards Dune Street will always
exist if there is a significant rainfall event and the barway was
closed. In such circumstances the river would still overflow the
banks and run towards Henderson lagoon. This result is
independent of the presence or otherwise of the rivulet and has
already been observed.
It should be noted too that significant rainfall events of short
duration quickly return to low catchment flows less than 200
megalitres per day.(perhaps a week). Complex and continuing
heavy rains are a different matter.
An analysis of catchment flows shows that in the last 10 years .
daily flows were less than 50ML/day for over 235 days. The
average flow rate during this period was only 14Ml/day.
Conclusion:
The rivulet needs to be repaired and reopened. Takeoff levels
and gradient need to be surveyed so that flows only occur when
river rises. Catchment levels if the barway is closed will only
rise to the entrance of the rivulet and remain constant. If the
barway is open then the level will drop based on tidal situation
and rivulet will stop flowing.
The barway will not need mechanical opening as catchment
levels won’t change once rivulet is flowing. The barway will
only need opening if an impending serious rain event is likely.
Damage to the banks and fauna in the upper reaches of the
Scamander river catchment will be prevented and flushing of the
upper reaches of Henderson lagoon will occur.
Calculations are available for these conclusions
Regards Denis Buchanan
.