Brisbane Water Plan of Management - Gosford City Council - NSW ...

The Committee at its first meeting, met and resolved to extend its name to the Brisbane
Water Plan of Management and Catchment Management Committee so that the context
in which it was carrying out its work was not lost.
In the Committee, Sub-Committees, and Task Group meetings, the open Committee
system was used with the Committee only being confined to appointed members when
confidential matters had to be discussed. Visitors were encouraged at all other times and
input was always taken from persons or organisations who had contributions to make.
Representatives from Government Authorities were also co-opted to assist where their
expertise and in all cases the spirit of involvement was excellent.
(iii)
Detailed Technical Studies
The Committee found that it was necessary to arrange for some detailed technical studies
particularly in the area of the current depth of Brisbane Water to enable it to determine the
rate of sedimentation and whether the channels in Brisbane Water had substantially
changed over the years of human settlement. A request was made of the previous Public
Works Department of the NSW Government as to whether such a study could be carried
out. Funding was granted to assist in carrying out this study.
The water depth studies had shown that a large number of hydrographic surveys had
been carried out at intervals throughout Brisbane Water but most of these studies related
to minor projects either proposed or carried out over the previous 50 years or so.
Fortunately, an extensive hydrographic survey had been carried out of Brisbane Water in
1901 which had used very carefully planned and detailed survey control and an excellent
coverage of the depth of Brisbane Water and its bays and tributaries. The study designed
for the Brisbane Water Plan of Management Committee's work was to carry out a similar
extensive study of all the depths of Brisbane Water and then compare these depths with
the depths that had been determined in 1901. This work was carried out using the latest
electronic measuring devices and the resulting work was compared with the 1901 work by
comparing cross sectional data from the two studies between known fixed points and
observing the differences in depths that were found. Comparisons of the accuracy of the
different work were made.
It was found that there is little difference in the depth of Brisbane Water between the two
studies except in the areas where the sediments within the channels have been dredged
or have been moved by the fast running tidal current. This finding was contrary to the
belief of many of the Committee members as there has been a general feeling that the
centre of Brisbane Water is considerably shallower than it was many years ago, however
the documentary evidence is quite conclusive.
A further technical study called the Brisbane Water Environmental Study was carried out
to determine the water quality and the quality of the sediments in Brisbane Water. Whilst
this study did not address the main issues of the Stage 1 work, it was seen as an
essential background study to the Stage 2 work and should be carried out at an early
time. A study was required over an extended period to get the full knowledge of the
seasonal variations in water quality. The work on the sediments was necessary to tie in
with the sediment studies being carried out as detailed above. The water quality work
was designed to carry out sampling and testing to show whether there was a profile or
gradation of water quality from the outlet of Brisbane Water to the upper reaches of the
various major tributaries of Brisbane Water and was designed to enable the Committee or
later Committees to be able to determine where further works should be targeted to
overcome any problems that might be found. The sediment studies also enable an
examination of the nutrient levels in the bed of Brisbane Water and was also was able to
Brisbane Water Plan of Management - July 1995
Page viii