Hydraulic Assessment 29 August 2024

4. CONCLUSION
Engeny have been engaged by Mark Kussrow to prepare a Local Hydraulic Assessment for the existing dam at 38 Barina Court, Pomona. This
hydraulic assessment has addressed the relevant items of Condition 16 and Condition 25 of the Noosa Council development approval for a
Reconfiguration of Lot, which called for a civil/hydraulic RPEQ to evaluate catchment hydrology and design flows, ensuring that the existing
spillway maintains a minimum dry freeboard of 1 m below the embankment crest. The study also examined the need for upgrades to the
existing channel along the embankment toe and identified erosion protection measures for the main spillway discharge channel.

The assessment concluded that:

•   The flows through the dam spillway do not exceed the embankment crest or associated discharge channels in a 1% AEP storm event,
    with the peak 1% AEP flood level in the dam is 112.05 m AHD, which demonstrates flood flows up to the 1% AEP event will not exceed
    the current minimum crest height of 112.24 m AHD.

•   The dam spillway is to be set at a maximum level of 111.24 m AHD to ensure the minimum 1m dry freeboard is achieved below the
    minimum crest elevation (112.24 m AHD). 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).

•   The peak flow depths were within acceptable limits below the embankment crest and spillway channel, with the spillway channel showing
    a peak velocity of 5.0 m/s. To prevent erosion, it is recommended to incorporate dumped rock in the spillway, channel, and outlets, with
    energy dissipation provided by a batter chute outlet structure. A design was provided for two channel options, being:

    –   Option 1 - Maintaining the existing channel base width of 1m and batter slope of 1V:2H; and,

        –   Rock protection = D50 = 500mm and 1000mm thick.

    –   Option 2 - Widening the base width of the channel to 2m to reduce the unit flow rate and d50 rock dimension.

        –   Rock protection = D50 = 300mm and 600mm thick.
•   For both options a rock pad is required at the channel outlet where it transitions into the next flow path. This rock back should be a
    minimum 4.8m long and use D50 = 400mm rock.




38 BARINA COURT, POMONA I BBNE00000_0020-REP-001-0                                                                                           12