STUDY FINDINGS - Swamp/Fishery Creeks System The most significant flooding of the Swamp/Fishery Creeks system over the last 50 years occurred in February 1990 and June 2007. Detailed investigations and modelling undertaken for this study has shown that the June 2007 flood was larger or rarer than the design 100 year ARI event, and that it was substantially rarer in the vicinity of Abermain. The analysis shows that the June 2007 event was in the order of a 200 year ARI flood at Abermain and slightly rarer (i.e., or larger) than a 100 year ARI event at Weston. This event led to inundation of large areas of the adjoining floodplain of Swamp Creek and significant property damage at Abermain and Weston, and in between. The modelling of design events up to the 100 year ARI flood shows that flooding of Swamp Creek is most severe between the Kline Street Bridge and the Government Road Bridge crossings, with significant overbank inundation occurring during floods of the magnitude of the 20 year ARI event. A number of properties are flooded in this area in events of this severity, particularly in the vicinity of the Fourth Street Bridge crossing (refer to Figure 18). Water depths in the vicinity of the houses along the right bank of the Fourth Street Bridge crossing are estimated to be up to 0.8 metres in the 100 year ARI flood and mean velocities are in the order of 0.5 m/s. Flooding at Abermain can also be severe, as evidenced by the June 2007 event. Floodwaters from the upper catchment are concentrated in the main channel of Swamp Creek which is flanked by residential development that extends along both banks the William Street and the Cessnock Road bridges. The flood modelling results show that this reach of Swamp Creek experiences steeper flood surface gradients than further downstream. As a result, there is greater potential for flood damage and risk to life due to the high energy flow regime that can occur during major flooding. Downstream of Loxford, Wentworth Swamps provide a massive flood storage area which has the capacity to hold a volume of nearly 11 million cubic metres in a design 100 year ARI event. This storage serves to provide significant attenuation of flows carried by Swamp Creek and reduces the impact of these flows before they discharge into Wallis Creek. Therefore, it is important that the Wentworth Swamps storage be retained so that flooding downstream in the Louth Park and South Maitland area is not exacerbated. - Wallis Creek Flooding due to catchment runoff (with no fresh in the Hunter) is generally retained within the defined floodplain downstream to Buttai Lagoon. Further downstream, in the Louth Park area, floodwaters are controlled by local levees and spillways. These spillways are overtopped in the 1% AEP local catchment runoff event. However, flooding of the lower Wallis Creek Valley can be influenced by backwater flooding from the Hunter River. That is, the worst flooding conditions downstream from John Renshaw Drive typically occur when flooding of Wallis Creek occurs concurrently with flooding of the Hunter River. Modelling has shown that when a flood of 20 year recurrence or rarer occurs in the Hunter River, levees around Maitland within the Lower Hunter Flood Mitigation System, will overtop and begin to fill backwater storages. As these backwater storages fill, floodwaters back-up in a southerly direction along Wallis Creek, generating higher flood levels than would occur in local catchment events. Historical flood records indicate that a peak flood level of 10.3 mAHD was recorded during the 1955 flood at Victoria Bridge, which is near the current site of the Wallis Creek flood gates. A peak level of 6.2 mAHD was recorded at the Trappaud Road Bridge crossing of Wallis Creek in 1977. As a result, peak 100 year recurrence flood levels along Wallis Creek are generated by the occurrence of coincident Hunter River flooding. As shown in Figures 22 to 30, these backwater effects extend almost upstream to John Renshaw Drive. - RECOMMENDATIONS - Swamp/Fishery Creeks System  Undertake a floodplain management study for Abermain and Weston aimed at investigating planning and structural options that could be implemented to reduce flood damages incurred by property owners adjacent to the creek. Potential structural flood damage reduction options (in order of provisional priority) include: (i) creek improvements such as vegetation clearing, channel de-silting and channel realignment; (ii) construction of on-line flood control dams or retarding basins in the upper catchment of Swamp Creek; (iii) modification to existing off-line storages such as Hebburn Reservoir so as to increase their flood storage capacity; (iv) upgrading of bridge waterway areas for bridge crossings; and, (v) installation of levees along the creek banks. It should be noted that a preliminary assessment of potential structural flood management options is being undertaken concurrently with the finalisation of this report. This assessment includes the consideration of the flood mitigation benefits that would be afforded by channel vegetation clearing, channel lowering (dredging) and increased off-line flood storage (Hebburn Reservoir). The findings from this preliminary option assessment are to be documented in a separate report which will inform any future Floodplain Risk Management Plan that is developed for the villages of Abermain and Weston. Potential non-structural measures that could be implemented to minimise flood damage (in order of provisional priority) include: (i) House raising. (ii) Property buy back scheme. (iii) Flood proofing of flood affected buildings (iv) Planning controls that:  Set minimum habitable floor levels based on the flood hazard  Modify land-use zonings upstream of the perceived flood problem to ensure that future development is not incompatible with flooding and that future development does not worsen flooding in downstream areas (v) Provide flood evacuation routes. (vi) Undertake flood awareness campaigns and develop a suitable flood warning system.  Re-commission the water level gauge recorder (Station No 210053) located at Horton Road, Kurri Kurri, so that a continuous record of the water levels of future floods can be recorded and used to generate a discharge hydrograph for Swamp Creek, which in turn can be used to calibrate further hydrodynamic modelling, as required. - Wallis Creek System  Undertake a floodplain management study for the Buchanan Area aimed at determining planning controls that could be implemented to manage potential future development that may be promoted on or adjacent to the floodplain as a consequence of the F3 Extension to Branxton.  Installation of a pluviograph within the Wallis Creek catchment to provide a continuous record of rainfall for use in assessing the severity of future floods and the significance of rainfall distributions to flood behaviour. It is suggested that the pluviograph be located around Mulbring to provide a realistic measure of average rainfall patterns.  Re-commission the water level gauge recorder located along Wallis Creek at Richmond Vale, so that a continuous record of the water levels of future floods can be recorded and used to generate a discharge hydrograph for Wallis Creek, which in turn can be used to calibrate further hydrodynamic modelling, as required.