USC FloodStudyUpdate Report - Flipbook - Page 260
Pipes were connected to downstream pipes to ensure continuity of each branch to the outlet.
In some cases, the outlet was not defined and the most likely outlet location was chosen,
taking pipe sizes from the most downstream pipe available.
Pipe were checked and adjusted to ensure consistent pipe sizes (downstream pipes were the
same size or larger than upstream pipes), including assigning reasonable pipe sizes to those
where data was missing.
Pipe polylines were reversed to be drawn from upstream to downstream, where this was not
already the case in the stormwater database.
Invert levels of outlets (where they were not provided) were obtained from the LiDAR data.
Invert levels of pipes (where they were not provided) were taken to be the ground level (from
LiDAR) minus 1.35 m (the average depth to pipe obverts where invert levels were available),
minus the pipe diameter or height.
.
Grated pits (determined by inspection of the November 2018 aerial imagery) were assigned a
size based on an approximate measurement of the grate from the aerial image (where they
were not provided).
Kerb inlet pit lintels (where they were not provided) were assumed to be 1.8 m wide (the
approximate average lintel width where data was provided).
Kerb inlet pits that were not located close to the gutter (within approximately 1 m) were moved
to the gutter (and actual pit location if it could be seen on the aerial imagery) to ensure that
pits drain the flows that will be within the gutter in TUFLOW.
A total of 2,922 pipes and 2,796 pits were included in the TUFLOW model to represent the stormwater
network. Typically the source of the data and any modifications to the data have been included in the GIS
files in a comment field.
In addition to the street stormwater network, the low flow outlets of urban detention basins also typically
consist of pits and basins. These were also represented in the TUFLOW model. Many of the basins have
complicated multi-level outlets to maximise detention of water for different storm events. Where the
information was available from DA drawings, these outlets have been represented in the TUFLOW model.
For all design events, a blockage factor of 50% has been applied to all pits, with pipes having no blockage.
4.7. Culverts and Bridges
Culverts were included in the TUFLOW model as 1D elements where they were 450 mm in diameter and
greater. The parameter values for the culverts were based on the geometrical properties of the structure
(circular or rectangular). There are a number of arch culverts within the study area and these were
represented in the TUFLOW model by calculating a width-height relationship. Depending on the source of
information, invert levels were obtained from topographic survey (undertaken for the previous flood study),
DA design drawings, or estimated based on the LiDAR road levels and a depth of cover. Typically, the
source of the information is included in the GIS file in a comment field. A blockage factor of 50% was
applied to all culverts with a maximum opening (width or height) of less than 1 m and 20% blockage applied
to those structures greater than or equal to 1 m. For some large key structures, the ARR 2019
(Reference 1) blockage methodology has been applied to determine AEP dependent blockage factors.
WMAwater Pty Ltd
118112: 201030_USC_Regional_Model_User_Guide_Final: 30 October 2020
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