The Taylors Road Retarding
Basin covers an area of 16 hectares, and is designed to provide attenuation and
treatment for a number of local catchments. The Basin flows from Lyndhurst Drain
and along the upgraded Eastern Contour Drain channel. Because of its location
within Melbourne Water’s Lyndhurst Drainage Scheme, it needs to meet Melbourne
Water’s ‘Deemed to Comply’ design criteria. Richard Sosenko – a Civil Engineer
with Dalton Consulting Engineers – spoke to 12d about the challenges of meeting
these criteria, and how he and his team achieved compliance with the help of 12d
In order to provide optimal water treatment, Retarding
Basins are designed to have varying depths with different planting bands. One of
the biggest challenges in designing a retarding basin of this nature is to get
the correct mix of depths in accordance with Melbourne Water criteria:
Shallow Marsh Zone (Natural Water Level to -0.15m)
• Deep Marsh Zone (-0.15m
• Submerged Marsh Zone (-0.35m to -0.7m)
• Open Water Zone
This process requires a number of iterations to ensure a
minimum area of 80% is achieved for shallow and deep marsh, known as the
macrophyte zone (main water body).
Given the size of the job, it was
important that a stable, quick and dynamic platform was used to ensure outputs
could be done quickly (due to the repetitive nature). To assist with approval
from Melbourne Water, it was important that the final outputs could be generated
and shared in a client friendly format. In addition, because of safety and
maintenance issues, it was important that minimum batter slopes were achieved
within the Retarding Basin area.
Natural Water Level (NWL) TIN was created at a fixed height of RL6.5 as
calculated from flood analysis. The proposed retarding basin (RB) TIN was then
created by producing 3D strings to model the sediment ponds (1.5m max depth
below NWL), inlet pools (1.5m max depth below NWL), and intermediate pools (1.2m
max depth below NWL) based on batter slopes, as specified in Melbourne Water’s
design criteria. The depth between the NWL TIN and the RB TIN was analysed, and
depth faces/colouring outputted to both plan and perspective views to illustrate
to Melbourne Water the different zone depths. Depth contours were also outputted
based on these different zones/depths, and the plan area of these depth contours
calculated to show the overall percentage of depths for each zone.
slope analysis (set with minimum and maximum crossfalls) was then run on the RB
TIN to show any grades within the macrophyte zone that were flatter than 1 in
150. This quickly identified areas where the batters required remodelling.
Due to the number of design amendments and iterations, the above process
(retriangulating TINs, depth colouring/FACES, slope analysis, etc
.) was written
as a chain and re-run each time the RB TIN was updated.
12d Model software was integral to DCE's achieving compliance on the Taylors
Road Retarding Basin project.
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