Volume 1 Report This flood study has been undertaken to determine the flood behaviour in the catchment due to local storm runoff for the 0.5% Annual Exceedance Probability (AEP), 1% AEP, 2% AEP, 5% AEP, 10% AEP, 20% AEP, 50% AEP and 100% AEP flood events and the Probable Maximum Flood (PMF). In accordance with its objectives, the study has determined the nature and extent of flooding through the estimation of design flood flows, levels and velocities. Flood impacts due to storm events in the Brisbane Water estuary are detailed in the Brisbane Water Foreshore Flood Study (2009). In undertaking the flood study, a hydrologic-hydraulic computer model of the major channels and floodplain within the catchment was established and verified against historical flood event observations. The hydraulic model was then used with design rainfall conditions to simulate design flood behaviour in the catchment. The study has defined Provisional Flood Hazard and Hydraulic Categories for the flood affected areas. The objective of this Study is to define the nature of the existing flood behaviour due to local runoff only in the Davistown catchment. To achieve the objectives, the following tasks were undertaken:,

The flood study carried out for Medowie identifies flood liable land for a range of floods and finds that many properties and approximately 20 residences, are likely to be flood liable during the 1% AEP event. Recommendations going forward are as follows: • In some locations existing drains are incapable of carrying 20 – 10% AEP (and in some cases even lower) flows. An example of this is the open drain which passes through Ballet Close from north to south. Enhancing the capacity of these trunk drainage systems should be examined as this may achieve a degree of flood relief for those properties which are exposed to flooding on a regular basis. Such an examination should however ensure that flooding issues are not simply transferred downstream; • Houses in County Close which remain subject to inundation should be closely monitored. It is likely that local flows cause inundation of these low lying properties and minor works by Council may alleviate this circumstance for impacted residents; • More generally there a number of locations where, due to the limited range of design flood behaviour (flood depths do not change markedly for variable AEP), minor works such as bunding could provide good levels of flood protection for individual properties. A good example of this is on Kirrang Drive (western side) where houses are currently impacted by flows from the swale at the front of their properties; • Generally Council needs to recognise the main overland flow paths identified in the study and move to restrict development in these “corridors” in the future; • In order to assess the issue in the CDIA with regard to upstream development potentially increasing flooding downstream of Ferodale Road, satisfactorily answer questions in the CDIA in regard to the impact of proposed development on the wet sequences which often deny property owners of access/enjoyment of their land, Council need to have a water balance type of exercise carried out. This will address the kinds of events which impact on inundation within the CDIA but which do not have any relevance to the definition of peak flood levels. It is noteworthy that during the Management Study process it will also be necessary to ensure mitigation works designed to alleviate flooding liability do not negatively impact on long term inundation for water sequences in the CDIA. The Management Study should consider a range of solutions but ensure that water quality is either maintained or improved; • Council should take care not to raise those sections of roads currently inundated as doing so will directly impact on peak flood levels. This is due to the fact that much of the 1% AEP flow moves over roads rather than through corresponding culverts; and • During the Management Study it is recommended that runs are carried out which examine the impact of removing the pinch which currently exacerbates the duration, extent and magnitude of inundation further upstream in the CDIA; and • Pinch plus pump capacity enhancement runs be carried out. Note unless pinch works are modelled, nothing will be achieved by looking at pumping rate enhancement alone.

Potential Flood areas for all Hobart catchments. METHODOLOGY: Modelled Flood Areas - 2100 1% Annual Exceedance Probability (Modelled areas of all Hobart waterways including Hobart, New Town and Sandy Bay rivulets and minor drainage lines). Additional areas may be subject to flooding. Site specific investigation may be required for each property. DISCLAIMER: This map should be read in conjunction with the Understanding Flood Risk page on the Hobart City Council web site. While all reasonable care has been taken to ensure the accuracy of the information portrayed in this data, its purpose is to provide a general indication of the location of Council services. The information provided may contain errors or omissions and the accuracy may not suit all users. A site inspection and investigation is recommended before commencement of any project based on this data. The Hobart City Council does not warrant that the information contained on this plan is correct and a field survey is to be conducted before the information contained in this plan is relied upon.

The 32km2 Erina Creek catchment is one of the major tributaries entering Brisbane Water at East Gosford (Figure 1). Figure 2 shows a digital terrain image of the study area and Figures 3 to 5 show further detail of the study area. Figure 6 indicates the current land use zones. The Erina Creek Flood Study Review 1990 was completed in 1991 (Reference 1), which utilised information available and current at the time hydrologic and hydraulic models to produce design flood profiles along the lower parts of Erina Creek. The aim of the present study is to update the Erina Creek Flood Study Review 1990 with currently available data, notably the use of airborne laser scanning (ALS) data and more sophisticated hydraulic modelling techniques as well as verification to the June 2007 event. All earlier flood studies of Erina Creek were superseded with completion of the Erina Creek Flood Study Review 1990. WMAwater was engaged by Gosford City Council to undertake the Erina Creek Flood Study Review utilising current technology and data. The information and results obtained from the study will provide a basis for development of targeted stormwater management strategies and a subsequent Floodplain Risk Management Study and Plan. The study was developed in order to meet the primary objective of defining the flood behaviour (50%, 20%, 10%, 5%, 2%, 1%, 0.5%, 0.2% AEP and the Probable Maximum Flood (PMF) design events) along the major tributaries in the Erina Creek catchment. The study area was significantly greater than for the previous 1991 Flood Study. This report details the results and findings of the Flood Study investigations. The key elements include:,

TUFLOW hydraylic models for caclulating flood damages

The U.S. Geological Survey (USGS), in cooperation with Connecticut Department of Transportation, completed a study to improve flood-frequency estimates in Connecticut. This companion data release is a Microsoft Excel workbook for: (1) computing flood discharges for the 50- to 0.2-percent annual exceedance probabilities from peak-flow regression equations, and (2) computing additional prediction intervals, not available through the USGS StreamStats web application. The current StreamStats application (version 4) only computes the 90-percent prediction interval for stream sites in Connecticut. The Excel workbook can be used to compute the 70-, 80-, 90-, 95-, and 99-percent prediction intervals. The prediction interval provides upper and lower limits of the estimated flood discharge with a certain probability, or level of confidence in the accuracy of the estimate. The standard error of prediction for the Connecticut peak-flow regression equations ranged from 26.3 to 45.0 percent (Ahearn and Hodgkins, 2020). The Excel workbook consists of four worksheets. The worksheets provide an overview of how the application works; input and output tables of the explanatory variables and flood discharges, and graphical display of the results; and the computational formulas used to estimate the flood discharges and prediction intervals.