Hydraulic Assessment 29 August 2024

To maintain the integrity of the spillway and prevent any potential obstructions or weakening of the structure, it is required to trim or remove
tree roots that have encroached upon the existing spillway area. Uncontrolled growth of vegetation can undermine the structural soundness
of the spillway, reducing its effectiveness and increasing the risk of overtopping. Regular maintenance should be conducted to ensure that
the spillway remains clear and fully operational at all times.

The design of the spillway should incorporate a minimum base width of 1 meter to effectively handle the expected flow of water. Additionally,
the spillway should have side batters with a minimum slope of 1:2 (vertical to horizontal). This ensures structural stability and facilitates the
safe passage of water through the spillway during peak discharge events. The maximum level of the spillway overflow should be 111.24 m
AHD, to ensure the 1m dry freeboard is maintained.

3.2.1.2 Spillway Channel Protection
It is proposed to incorporate dumped rock into the spillway and channel outlets to prevent erosion as a result of concentrated lateral flow
through the spillway. The principal design features and adopted rock protection of the downstream channel is summarised below for two
options:

     (1) Maintain the existing channel profile with 1m base width; and

     (2) Widen the base of the channel to 2m width – the purpose of widening the base is to reduce the required d50 and dumped rock
         thickness.

Table 3.5: Spillway Channel Design Parameters

 Parameter                                                                          Result

 Design Discharge                                                                   2.88 m3/s


 Batter Slopes                                                                      1H:2V


 Longitudinal Grade                                                                 10 %


 Option 1 – Maintain 1m base width

 D50 Rock Dimension                                                                 500


 Dumped Rock Thickness                                                              1000


 Option 2 – Increase base width to 2m

 D50 Rock Dimension                                                                 300


 Dumped Rock Thickness                                                              600

Energy dissipation at the outlet of the spillway channel is provided by a batter chute outlet structure. The rock pad has been designed to
control soil erosion adjacent to the outlet and to dissipate the flow energy, with parameters informed by the TUFLOW hydraulic model
results.

Table 3.6: Rock Pad Design Parameters

 Parameter                                                                          Result

 Velocity of Flow into Outlet Structure                                             5.0 m/s


 Depth of Approach Flow                                                             0.30 m


 Mean Rock Size, d50                                                                400 mm




38 BARINA COURT, POMONA I BBNE00000_0020-REP-001-0                                                                                            10