The study area of the Hawkesbury Floodplain Risk Management Study & Plan comprises all of the Hawkesbury River and its immediate surrounds that fall within the Hawkesbury Local Government Area. It extends from Agnes Banks/Yarramundi in the south to Wisemans Ferry in the north, representing a river distance of approximately 83 km and an area of some 220 km2 subject to inundation in the Probable Maximum Flood (PMF). The main area of focus is for the area from Agnes Banks/Yarramundi to Wilberforce, including the flood?prone communities of Richmond and Windsor (see Figure 1.2). The Hawkesbury?Nepean catchment covers about 22,500 km2 and is one of the largest of all coastal rivers in New South Wales (see Figure 1.3). It includes extensive grazing areas in the south?west and large National Parks in the Blue Mountains to the north?west. Urban development in the catchment area includes towns such as Goulburn and Lithgow and outer suburbs of western Sydney including Camden and Penrith (ERM Mitchell McCotter, 1995). More than 40% of the total Hawkesbury?Nepean catchment – about 9,000 km2 – is upstream of Warragamba Dam. Half of this area comes from the Wollondilly River. The Warragamba River joins the Nepean River 3.5 km below the dam. The Grose River is a major tributary which joins the Nepean at Yarramundi, after which the Nepean is known as the Hawkesbury. Whilst the Grose has a catchment of only 650 km2, it drains a high rainfall area and can have a significant effect on flooding at Windsor. In particular, it can cause flood levels to rise quickly in the early part of major storms (ERM Mitchell McCotter, 1995). The catchment area at the Windsor gauge is about 12,800 km2. South Creek joins just downstream of the Windsor gauge. Whilst its catchment area of 640 km2 is virtually the same as the Grose, it receives less rainfall and thus has less impact on Hawkesbury River flooding. At Lower Portland the Hawkesbury is joined by the Colo River, which drains an area of 4,640 km2 (ERM Mitchell McCotter, 1995). The Colo can influence flooding in the Hawkesbury River depending on the movement of flood producing rainfall over the Hawkesbury and Colo River catchments. The Colo has a shorter response time to rainfall and as shown in the 1978 flood, it can have a large impact on Hawkesbury River levels, particularly downstream of Sackville. A study of the joint probabilities of floods originating from the Hawkesbury and the Colo has been carried out (AWACS, 1997). AWACS found that the 100 year design flood levels in the Hawkesbury downstream of the Colo confluence were relatively insensitive to the assumed Colo contributions. Nevertheless in some events, flooding in the Hawkesbury River within the lower portions of the study area can be significantly influenced by the Colo subject to the spatial and temporal distribution of the rainfall. When measured in 2000, the Hawkesbury River was subject to tidal influence up to Yarramundi Bridge (MHL, 2005). However, the limit of tidal influence is rarely constant. There are short?term cyclical changes in response to the ever?changing ocean tides, and changes over long time spans according to both natural processes and artificial disturbance. Sand extraction in the vicinity of the limit of tidal influence in the Hawkesbury River is reported to have caused the tidal limit to move a further 10 km upstream over the 20th century (Estuaries Branch, 2010). RECOMMENDATIONS The Floodplain Risk Management Plan (FRMP) showing the preferred floodplain risk management measures for the Hawkesbury study area is presented in this chapter. The recommended measures have been selected from the range of measures discussed in Chapter 6, after an assessment of each measure’s impact on flood risk, as well as consideration of environmental, social, and economic factors. The recommended measures are presented in Table 9.1. The principal components of the Plan are presented below according to priority, which is assessed on the basis

A 17-page overview of the purpose and methods used for developing the flood study.

Flood Study Overview, Flood Study Report, 12 technical volumes, 4 map book volumes, Engagement Outcomes Report

Digital flood-inundation map libraries for two reaches that comprise 14.8 miles of the Little and Big Papillion Creeks in Omaha, Nebraska were created by the U.S. Geological Survey (USGS) in cooperation with the Papio-Missouri River Natural Resource District. The flood-inundation maps, which can be accessed through the USGS Flood Inundation Mapping Program website at https://www.usgs.gov/mission-areas/water-resources/science/flood-inundation-mapping-fim-program, depict estimates of the areal extent and depth of flooding corresponding to selected water levels (stages) at the USGS streamgages Little Papillion Creek at Irvington, Nebr. (station 06610750), Little Papillion Creek at Ak-Sar-Ben at Omaha, Nebr. (station 06610765), and Big Papillion Creek at Q Street at Omaha, Nebr. (station 06610770). Near-real-time stages at these streamgages may be obtained from the USGS National Water Information System database at https://doi.org/10.5066/F7P55KJN or from the National Weather Service Advanced Hydrologic Prediction Service at https://water.weather.gov/ahps/. Flood profiles were computed using hydraulic models for two different stream reaches that comprised 14.8 miles of stream length of the Little and Big Papillion Creeks in Omaha. The models were calibrated by adjusting roughness coefficients to best represent the current (2022) stage-streamflow relation at the streamgages within the study reach. The hydraulic models were then used to compute water-surface profiles at 1-foot (ft) stage intervals at selected stage ranges to represent various flooding scenarios at the streamgages in the reach. The simulated water-surface profiles then were combined using a geographic information system with a digital elevation model, which had a 10-ft grid to delineate the area flooded and water depths at each stage. Along with the inundated area maps, polygon shapefiles of areas behind the levees were created to display the uncertainty of these areas if a levee breach were to occur. These 'areas of uncertainty' files have '_breach' appended to the file names in the data release. The availability of these maps, along with information regarding current stage from USGS streamgages, will provide emergency management personnel and residents with information that is critical for flood response activities such as evacuations and road closures, as well as for post-flood recovery efforts.

Hydrological model outputs for all design events.

The final report provides a comprehensive summary of the project's objectives, data collection and review, methodology, key flood modelling results, consequences of flooding on the community and conclusions.

Volume 1 and Volume 2

Digital flood-inundation maps for a 2.4-mile reach of the Schoharie Creek in North Blenheim, New York, were created by the U.S. Geological Survey (USGS) in cooperation with the New York Power Authority. The flood-inundation maps, which can be accessed through the USGS Flood Inundation Mapping Science web site at https://fim.wim.usgs.gov/fim/, depict estimates of the areal extent and depth of flooding corresponding to selected water levels (stages) at the USGS streamgage on the Schoharie Creek near North Blenheim, NY (station number 01350212). Flood profiles were computed for the stream reach by means of a two-dimensional implicit finite volume hydraulic model. The model was calibrated using the active (as of April, 2021) stage-discharge ratings at two USGS streamgages on the Schoharie Creek (Schoharie Creek near North Blenheim, NY [01350212] and Schoharie Creek at North Blenheim, NY [01350180]) and documented high-water marks in the study reach from the floods of August 28, 2011, January 19, 1996, and April 4, 1987. The hydraulic model was used to compute 13 water-surface profiles for flood stages at 1-foot (ft) intervals referenced to the streamgage datum and ranging from 14 ft, or near bankfull, to 26 ft, which is the highest whole-foot-increment on the stage-discharge rating for the streamgage. The simulated water-surface profiles were then combined with a geographic information system digital elevation model (derived from light detection and ranging data having a 0.52-ft vertical accuracy and 3.3-ft horizontal resolution) to delineate the area flooded at each stage. This data release contains five child items: (1) the field survey points used in model development; (2) the hydraulic model used to develop the inundation maps, and the (3) depth grids, (4) inundation polygons, and (5) water surface elevation grids from the model output.

Richmond Valley Flood Study 2023 - spatial mapping outputs. This zip folder contains post processed model outputs for the design floods (5%, 5%CC, 2%, 2%CC, 1%, 1%CC, 0.2%, 0.2%CC & PMF), covering- ~peak flood height (mAHD) - (ASC) ~peak flood depth (m) - (ASC) ~peak velocity (m/s) - (ASC) ~flood hazard (H1-H6) - (ASC) ~peak flood vectors - (TAB & SHP) ~flood islands (TAB & SHP) ~Flood Planning Levels (1%CC AEP + 500mm) (TAB & SHP) ~Roads with Flood Levels (mAHD)