Groundwater is the water that soaks into the ground from rain and can be stored beneath the ground. Groundwater floods occur when the water stored beneath the ground rises above the land surface. The Historic Groundwater Flood Mapshows the observed peak flood extents caused by groundwater in Ireland. This map was made using satellite images (Copernicus Programme Sentinel-1), field data, aerial photos, as well as flood records from the past. Most of the data was collected during the flood events of winter 2015 / 2016, as in most areas this data showed the largest floods on record.The map is a vector dataset. Vector data portray the world using points, lines, and polygons (area). The floods are shown as polygons. Each polygon has info about the type of flood, the data source, and the area of the flood.The flood extents were calculated using data and techniques with various precision levels, and as such, it may not show the true historic peak flood extents.The Winter 2015/2016 Surface Water Flooding map shows fluvial (rivers) and pluvial (rain) floods, excluding urban areas, during the winter 2015/2016 flood event, and was developed as a by-product of the historic groundwater flood map.The map is a vector dataset. The floods are shown as polygons. Each polygon has info about the type of flood, the data source, and the area of the flood.The flood extents were made using remote sensing images (Copernicus Programme Sentinel-1), which covered any site in Ireland every 4-6 days. As such, it may not show the true peak flood extents.

Collection of flood and inundation maps over Queensland at various scales 1893-1974, these show flood levels and probable inundation areas at various flood heights. A number of the map series include key maps.

Note: Each CSV in this series includes basic metadata about each map in the series and a URL to access a high resolution scan of each map.

Historic Flood Map is a GIS layer showing the maximum extent of all individual Recorded Flood Outlines from river, the sea and groundwater springs and shows areas of land that have previously been subject to flooding in England. Records began in 1946 when predecessor bodies to the Environment Agency started collecting detailed information about flooding incidents, although we may hold limited details about flooding incidents prior to this date. This dataset differs from the Recorded Flood Outline dataset in that it contains only those flood outlines that are 'considered and accepted' if the following criteria are met:photographic/video evidence with the location referencedrecorded flood levels with the location referencedevidence that the outline represents the time of peak water level (for example date / time stamped photo)evidence that the source of flooding is from rivers, the sea or groundwater and not surface water/overland runoff. The absence of coverage by the Historic Flood Map for an area does not mean that the area has never flooded, only that we do not currently have records of flooding in this area. It is also possible that the pattern of flooding in this area has changed and that this area would now flood under different circumstances. The Historic Flood Map will take into account of the presence of defences, structures, and other infrastructure where they existed at the time of flooding. It will include flood extents that may have been affected by overtopping, breaches or blockages. Flooding shown to the land and does not necessarily indicate that properties were flooded internally. The Historic Flood Map consists of spatial data only.

This story map highlights what the Nebraska Silver Jackets Team has created: an interactive web map that showcases past and ongoing flood mitigation projects across the state. The goal of the map is to create an online location where communities can learn what mitigation projects have been funded, the different grants available, and the array of possible funding partners for all kinds of mitigation projects. The story map includes background information about flood mitigation and describes the data collection process. There is also a how to guide for using the interactive map with widget icons and their descriptions. There is other valuable information including FEMA videos and ways to submit mitigation projects the initial data gathering process may have missed.

(Note: Updated inundation maps for 1:2 to 1:1000 floods are available from Alberta Environment and Parks (2020). The new draft maps can be viewed here: https://floods.alberta.ca/?app_code=FI&mapType=Draft) These inundation maps show whether a property is at risk for various sized river floods. The size of flood shown on this map has a 1/5 or a 20% chance of occurring in any year. The three distinct types of inundation shown on the maps are: o Inundation - Area flooded overland due to riverbank overtopping. o Isolated - Low lying areas that will not be wet from riverbank overtopping, but may experience groundwater seepage or stormwater backup. o Protected - Area protected by a permanent flood barrier. The flood areas shown are based on Alberta Environment and Parks most recent (2020) inundation maps. There is uncertainty inherent in predicting the effects of flood events, and this uncertainty increases for floods with less than a 1% chance of occurrence in any year. Any use of this data must recognizing the uncertainty with regards to the exact location and extent of flooding. More information on flood mapping for Calgary is available at https://calgary.ca/flood For Calgary's River Flood story, see: https://maps.calgary.ca/RiverFlooding/

Recorded Flood Outlines is a GIS layer which shows all our records of historic flooding from rivers, the sea, groundwater and surface water. Each individual Recorded Flood Outline contains a consistent list of information about the recorded flood.

Records began in 1946 when predecessor bodies to the Environment Agency started collecting detailed information about flooding incidents, although we may hold limited details about flooding incidents prior to this date.

The absence of coverage by Recorded Flood Outlines for an area does not mean that the area has never flooded, only that we do not currently have records of flooding in this area.

It is also possible that the pattern of flooding in this area has changed and that this area would now flood or not flood under different circumstances.

The Recorded Flood Outlines take into account the presence of defences, structures, and other infrastructure where they existed at the time of flooding. It includes flood extents that may have been affected by overtopping, breaches or blockages.

Any flood extents shown do not necessarily indicate that properties were flooded internally.

A companion dataset Historic Flood Map contains a subset of these Recorded Flood Outlines which satisfy a certain criteria.

Abstract

This dataset and its metadata statement were supplied to the Bioregional Assessment Programme by a third party and are presented here as originally supplied.

Polygon data delineating modelled statistical flood extent with an Average Recurrence Interval (ARI) of 100 years. For historical/actual flood extents, refer to 'Historic_extent' layer. Also known as the 1 in 100 year flood layer, it is used, among other things, in the creation of 'Land Subject to Inundation' areas as used in Planning Scheme Zones. The 1 in 100 year data is not restricted. This data is part of a group of layers depicting a range of statistical ARI extents. Current layers include 5, 10, 20, 30, 50, 100, 200, 500, 1000 year intervals, each in a separate dataset. The layer called EXTENT_PMF represents areas of 'probable maximum flood' and is also part of this group. The data is statistically derived using hydrological models, historic flood extents and heights.

Purpose

Mainly used for municipal planning and risk assessment. The EXTENT_100Y_ARI layer is deemed the most appropriate to use for determining areas at risk of flooding. This layer directly inputs into the Land Subject to Inundation overlay. (LSIO)

Dataset History

Lineage: Primary

Positional Accuracy: Precision: 5m to 100m Initial data, flagged as 'modified = 20000101' varies in accuracy, and should be treated with caution, particularly at scales less than 1:25,000. Data with 'modified' values later than 20000101 are quite accurate and mostly sourced from flood studies. This data is suitable to use at township and parcel level. Reliability field provides clues to the accuracy, where a value of 1 is best and 3 is worst.

Attribute Accuracy: Attributes are verified and should be accurate. Overall reliability of the source material is indicated in RELIABILITY field, where 'HIGH' is good and 'LOW' is poor quality source information.

Logical Consistency: Attributes are consistent with other related layers e.g. flood height contours

Data Source: Flood data dates back to mid 1800s and historically has been predominantly located in DNRE Floodplain Management. Some data is located in Water Authorities.

Completeness: Floodplain Management Unit mapping conventions on definitions of flood mapping height data will be followed.

Additional Metadata: Recommend liaison with Floodplain Management Unit to clarify use of this layer

Refer to mapping reports for each major data capture effort to be kept at DNRE Floodplain Management Unit.

Dataset Citation

Victorian Department of Environment and Primary Industries (2014) Victoria - 1 in 100 Year Flood Extent. Bioregional Assessment Source Dataset. Viewed 05 October 2018, http://data.bioregionalassessments.gov.au/dataset/6e59ed35-3fde-48e3-8135-eb05263ce4aa.

description: The Digital Flood Insurance Rate Map (DFIRM) Database depicts flood risk information and supporting data used to develop the risk data. The primary risk classifications used are the 1-percent-annual-chance flood event, the 0.2-percent-annual- chance flood event, and areas of minimal flood risk. The DFIRM Database is derived from Flood Insurance Studies (FISs), previously published Flood Insurance Rate Maps (FIRMs), flood hazard analyses performed in support of the FISs and FIRMs, and new mapping data, where available. The FISs and FIRMs are published by the Federal Emergency Management Agency (FEMA).; abstract: The Digital Flood Insurance Rate Map (DFIRM) Database depicts flood risk information and supporting data used to develop the risk data. The primary risk classifications used are the 1-percent-annual-chance flood event, the 0.2-percent-annual- chance flood event, and areas of minimal flood risk. The DFIRM Database is derived from Flood Insurance Studies (FISs), previously published Flood Insurance Rate Maps (FIRMs), flood hazard analyses performed in support of the FISs and FIRMs, and new mapping data, where available. The FISs and FIRMs are published by the Federal Emergency Management Agency (FEMA).

Groundwater is the water that soaks into the ground from rain and can be stored beneath the ground. Groundwater floods occur when the water stored beneath the ground rises above the land surface. The Winter 2015/2016 Surface Water Flooding map shows fluvial (rivers) and pluvial (rain) floods, excluding urban areas, during the winter 2015/2016 flood event, and was developed as a by-product of the historic groundwater flood map. The map is a vector dataset. The floods are shown as polygons. Each polygon has info about the type of flood, the data source, and the area of the flood.The flood extents were made using remote sensing images (Copernicus Programme Sentinel-1), which covered any site in Ireland every 4-6 days. As such, it may not show the true peak flood extents.

This shapefile (polygon feature) contains the boundary of the July 1, 2022 100-Year Storm Flood Risk Zone, one of the layers of the July 1, 2022 100-Year Storm Flood Risk Map. Areas within this boundary are highly likely to experience “deep and contiguous” flooding during a 100-year storm. A 100-year storm is a storm that has a 1% chance of occurring in a given year. “Deep and contiguous flooding” means flooding at least 6-inches deep spanning an area at least the size of an average City block. The 100-Year Storm Flood Risk Zone does not provide the exact depth of flooding at a given location. It also does not show areas in the City that may experience shallower and/or more localized flooding in a 100-year storm. Finally, the 100-Year Storm Flood Risk Zone shows flood risk from storm runoff only. It does not consider flood risk in San Francisco from other causes such as shoreline overtopping and overland inundation from the San Francisco Bay or Pacific Ocean.

In addition to the 100-Year Storm Flood Risk Zone, the 100-Year Storm Flood Risk Map shows:

• “Areas not served by the Combined Sewer and Stormwater Collection System” - showing where data for rainfall driven storm runoff is not available, and where flood risk has not been analyzed. • “Historical Shoreline”, “Historical Creeks”, and “Historical Waterbodies” - historical hydrology layers to illustrate the general topography of low-lying areas in the City. The Horizontal Datum used for the GIS layers is “NAD_1983_2011_StatePlane_California_III_FIPS_0403_Ft_US.”

Notes on Usage

At a minimum, the 100-Year Storm Flood Risk Map is updated by the San Francisco Public Utilities Commission (SFPUC) on an annual basis on or before July 1 to account for any parcel review requests that remove properties from the Flood Zone. To confirm the latest version of the 100-Year Storm Flood Risk Map, check the SFPUC website at https://sfpuc.org/learning/emergency-preparedness/flood-maps to see if the map has been updated since the date of this shapefile or if there have been any parcel review determinations that identify parcels that are no longer part of the 100-Year Flood Risk Zone. The most recent official map, associated documentation, and list of parcels removed from the map from a parcel review process are available at https://sfpuc.org/learning/emergency-preparedness/flood-maps. Please be advised that the parcels listed are no longer considered to be within the 100-Year Flood Risk Zone as a result of the parcel review process. As of July 2022, this list is updated on an ongoing basis. Check the SFPUC website for any changes to this schedule.

The boundaries of this zone align with San Francisco parcel boundaries. The user should confirm proper projection or use of the webmap at https://sfpuc.org/learning/emergency-preparedness/flood-maps to properly identify parcels within the flood zone.

North Carolina Effective Flood zones: In 2000, the Federal Emergency Management Agency (FEMA) designated North Carolina a Cooperating Technical Partner State, formalizing an agreement between FEMA and the State to modernize flood maps. This partnership resulted in creation of the North Carolina Floodplain Mapping Program (NCFMP). As a CTS, the State assumed primary ownership and responsibility of the Flood Insurance Rate Maps (FIRMs) for all North Carolina communities as part of the National Flood Insurance Program (NFIP). This project includes conducting flood hazard analyses and producing updated, Digital Flood Insurance Rate Maps (DFIRMs). Floodplain management is a process that aims to achieve reduced losses due to flooding. It takes on many forms, but is realized through a series of federal, state, and local programs and regulations, in concert with industry practice, to identify flood risk, implement methods to protect man-made development from flooding, and protect the natural and beneficial functions of floodplains. FIRMs are the primary tool for state and local governments to mitigate areas of flooding. Individual county databases can be downloaded from https://fris.nc.gov Updated Jan 17th, 2025.

The Flood Mapping Team within NRCan’s Canada Centre for Mapping and Earth Observation (CCMEO) has completed the digitization of these approximately 1400 historical flood events. By scraping publication records for flood event details, they created a publicly available data layer consisting of point data with attributes for flood location, years/seasons, and details. Sources are available for every point. The maps can be a starting point for understanding regional flood trends or for training machine learning models for predicting nation-wide flood risk.CCMEO’s Flood Mapping Team is advancing flood mapping practices in Canada by leading the Flood Hazard Identification and Mapping Program, compiling existing flood hazard data through the National Flood Hazard Data Layer, digitizing historical flood maps, publishing flood mapping guidelines, and researching innovative ways to advance flood mapping practices relating to geomatics. Overall, the modernization of flood mapping practices will help communities understand and manage their flood risk.The point groupings correspond to the locations that were affected by the same event. The inventory of past flooding has been compiled from various public sources and standardized into a common data model. Flooding events for which no location was included in the sources are positioned on the place name of the location affected by the flooding. The event positions do not indicate where the flooding occurred. It should be noted that no consultation was conducted with the various providers and stakeholders of historical flood data. Disparities in content between the various sources result in an inconsistent product. No warranty is given as to the accuracy or completeness of the information provided. The absence of information does not mean that no flooding has occurred.Additional Resources:Historical flood events (HFE) data page on open.canada.caArticle on the historical flood events layerFlood Hazard Identification and Mapping ProgramUpdate Frequency: Ongoing

The Flood Map for Planning (Rivers and Sea) includes several layers of information. This dataset covers Flood Zone 2 and should not be used without Flood Zone 3. It is our best estimate of the areas of land at risk of flooding, when the presence of flood defences are ignored and covers land between Zone 3 and the extent of the flooding from rivers or the sea with a 1 in 1000 (0.1%) chance of flooding each year. This dataset also includes those areas defined in Flood Zone 3. This dataset is designed to support flood risk assessments in line with Planning Practice Guidance ; and raise awareness of the likelihood of flooding to encourage people living and working in areas prone to flooding to find out more and take appropriate action. The information provided is largely based on modelled data and is therefore indicative rather than specific. Locations may also be at risk from other sources of flooding, such as high groundwater levels, overland run off from heavy rain, or failure of infrastructure such as sewers and storm drains. The information indicates the flood risk to areas of land and is not sufficiently detailed to show whether an individual property is at risk of flooding, therefore properties may not always face the same chance of flooding as the areas that surround them. This is because we do not hold details about properties and their floor levels. Information on flood depth, speed or volume of flow is not included. NOTE: We have paused quarterly updates of this dataset. Please visit the “Pause to Updates of Flood Risk Maps” announcement on our support pages for further information. We will provide notifications on the Flood Map for Planning website to indicate where we have new flood risk information. Other data related to the Flood Map for Planning will continue to be updated, including data relating to flood history, flood defences, and water storage areas. Attribution statement: © Environment Agency copyright and/or database right 2023. All rights reserved. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown Copyright and Database Rights 2023 OS AC0000807064.

Heavy rainfall occurred across Louisiana during March 8-19, 2016, as a result of a massive, slow-moving southward dip in the jet stream, which moved eastward across Mexico, then neared the Gulf Coast, funneling deep tropical moisture into parts of the Gulf States and the Mississippi River Valley. The storm caused major flooding in north-central and southeastern Louisiana. Digital flood-inundation maps for Cross Lake near the community of Shreveport in Caddo Parish, LA was created by the U.S. Geological Survey (USGS) in cooperation with Federal Emergency Management Agency (FEMA) to support response and recovery operations following a March 8-19, 2016 flood event. The inundation maps depict estimates of the areal extent and depth of flooding corresponding to 7 High Water marks (HWM) identified and surveyed by the USGS following the flood event. First release: November 2016 Revised: September 2017 (ver. 1.1) Additionally, there is a revision history text file called "September_2017_Revisions" available on the main page that explains exactly what changed in the revision.

The objective of this project is to create a story map that highlights and narrates the history of flooding in Chicago. It will map hydrology, rainfall patterns, floods, and income levels. It will draw from this how different socioeconomic regions and neighborhoods differ in flood response and action. This project will be used to justify a possible green bond for flooding mitigation in low income houses in Chicago.

The PHE benchmarks are an important element in the flood risk prevention and information system, as they make it possible to provide a concrete visual and precise element of the threat of major flooding that weighs on a large number of rivers in France. Watch out! The reported historical flood levels are by no means a guarantee that the water level will not rise above. It only testifies to the reality of a prevailing and cyclical risk in the area. To learn more about high water markers and high flood markers, you can visit the major hazards site: Prim.net: link in “Internet Address (URL)”.

Abstract: This data shows the extent of land that might be flooded by the sea (coastal flooding) and the associated flood depths during a theoretical or ‘design’ flood event with an estimated probability of occurrence, rather than information for actual floods that have occurred in the past. This represents the worst case scenario as any flood defences potentially protecting the coastal floodplain are not taken into account. Flood event probabilities are referred to in terms of a percentage Annual Exceedance Probability, or ‘AEP’. This represents the probability of an event of this, or greater, severity occurring in any given year. These probabilities may also be expressed as the chance or odds (e.g. 200 to 1) of the event occurring in any given year. They are also commonly referred to in terms of a return period (e.g. the 200-year flood), although this period is not the length of time that will elapse between two such events occurring, as, although unlikely, two very severe events may occur within a short space of time. The following sets out the range of flood event probabilities for which coastal flood extent maps were developed, expressed in terms of Annual Exceedance Probability (AEP), and identifies their parallels under other forms of expression. 50% AEP can also be expressed as the 2 Year Return Period and as the 2:1 odds of occurrence in any given year. 20% AEP can also be expressed as the 5 Year Return Period and as the 5:1 odds of occurrence in any given year. 10% AEP can also be expressed as the 10 Year Return Period and as the 10:1 odds of occurrence in any given year. 5% AEP can also be expressed as the 20 Year Return Period and as the 20:1 odds of occurrence in any given year. 2% AEP can also be expressed as the 50 Year Return Period and as the 50:1 odds of occurrence in any given year. 1% AEP can also be expressed as the 100 Year Return Period and as the 100:1 odds of occurrence in any given year. 0.5% AEP can also be expressed as the 200 Year Return Period and as the 200:1 odds of occurrence in any given year. 0.1% AEP can also be expressed as the 1000 Year Return Period and as the 1000:1 odds of occurrence in any given year. The Present Day Scenario is also referred to as the Current Scenario. Present Day Scenario data was generated using methodologies based on historic flood data, without taking account of potential changes due to climate change. The potential effects of climate change have been separately modelled and reported on. Flooding from other sources may occur and areas that are not shown as being within a flood extent may therefore be at risk of flooding from other sources. The flood extent and depth maps are suitable for the assessment of flood risk at a strategic scale only, and should not be used to assess the flood hazard and risk associated with individual properties or point locations, or to replace a detailed flood risk assessment. Lineage: The National Coastal Flood Hazard Maps (NCFHM) 2021 are ‘predictive’ flood maps, as they provide predicted flood extent and depth information for a ‘design’ flood event that has an estimated probability of occurrence (e.g. the 0.5% AEP event), rather than information for floods that have occurred in the past. The maps have been produced at a strategic level to provide an overview of coastal flood hazard in Ireland, and minor or local features may not have been included in their preparation. A Digital Terrain Model (DTM) was used to generate the maps, which is a ‘bare-earth’ model of the ground surface with the digital removal of human-made and natural landscape features such as vegetation, buildings and bridges. This methodology can result in some of these human-made features, such as bridges and embankments, being shown within a flood extent, when in reality they do not flood. It should be noted that the flood extent maps indicate the predicted maximum extent of flooding, and flooding in some areas, such as near the edge of the floodplain area, might be very shallow. The predicted depth of flooding at a given location is indicated on the flood depth maps. The flood depth is displayed as a constant depth over grid squares with a 5m resolution, whereas in reality depths may vary within a given grid square. No post-processing of the flood extent and depth map datasets has been undertaken to remove small areas of flooding that are remote and isolated, small islands within the flooded area, etc. Local factors such as flood defence schemes, structures in or around river channels (e.g. bridges), buildings and other local influences, which might affect coastal flooding, have not been accounted for. Detailed explanations of the methods of derivation, data used, etc. is provided in the NCFHM 2021 Flood Mapping Methodology Report. Users of the maps should familiarise themselves fully with the contents of this report in advance of the use of the maps. Purpose: The data has been developed to inform a national assessment of flood risk that in turn will inform a review of the Preliminary Flood Risk Assessment required to comply with the requirements of the European Communities (Assessment and Management of Flood Risks) Regulations 2010 to 2015 (the “Regulations”) (implementing Directive 2007/60/EC) for the purposes of establishing a framework for the assessment and management of flood risks, aiming at the reduction of adverse consequences for human health, the environment, cultural heritage and economic activity associated with floods.

The "Geological Map of Lower Saxony 1: 50 000 — Early-historical flood events" is a digital dataset of the Geological Map of Lower Saxony 1: 50,000 derived analysis map. Taking into account the age, nature and origin of geological strata, this map identifies areas that were affected by floods in recent geological past, i.e. in the last 11,500 years ago, which was summarised here as an early history. From a geological point of view, these areas are also potentially at risk of flooding in the future, as the natural water balance (e.g. precipitation, above-ground drain) has not changed significantly. Since the early-historical flood events took place mainly in times before human intervention into the landscape (e.g. hydrological protection measures such as dikes and dams, processes of land extraction), such protective measures that exist today are not taken into account in the mapwork. The early-historical flood deposits therefore give an impression of how deep flooding events can penetrate the hinterland in the event of failure of protective measures (e.g. dyke breakage). The map distinguishes between widespread deposits of early-historical flood events (hazard level 1) and “deposits of early-historical flood events in sub-areas, e.g. deposits of early-historical flood events” (hazard level 2)”. In areas with risk level 1, there are widespread deposits that have been disposed of in early-historical flood events (e.g. floodplain deposits in river valleys or marine and brackish water deposits in the coastal area). Failure of any existing protective measures in these areas is highly likely to be flooded. The areas of hazard level 2 are generally higher than those at risk level 1. In some areas, however, early-historical flood deposits can also be found here, sometimes in small areas. Therefore, a flood risk cannot be ruled out in principle for the future. In individual cases, the local geological situation must be assessed. The "Geological Map of Lower Saxony 1: 50 000 — Early-historical flood events" is a digital dataset of the Geological Map of Lower Saxony 1: 50,000 derived analysis map. Taking into account the age, nature and origin of geological strata, this map identifies areas that were affected by floods in recent geological past, i.e. in the last 11,500 years ago, which was summarised here as an early history. From a geological point of view, these areas are also potentially at risk of flooding in the future, as the natural water balance (e.g. precipitation, above-ground drain) has not changed significantly. Since the early-historical flood events took place mainly in times before human intervention into the landscape (e.g. hydrological protection measures such as dikes and dams, processes of land extraction), such protective measures that exist today are not taken into account in the mapwork. The early-historical flood deposits therefore give an impression of how deep flooding events can penetrate the hinterland in the event of failure of protective measures (e.g. dyke breakage).

The map distinguishes between widespread deposits of early-historical flood events (hazard level 1) and “deposits of early-historical flood events in sub-areas, e.g. deposits of early-historical flood events” (hazard level 2)”. In areas with risk level 1, there are widespread deposits that have been disposed of in early-historical flood events (e.g. floodplain deposits in river valleys or marine and brackish water deposits in the coastal area). Failure of any existing protective measures in these areas is highly likely to be flooded. The areas of hazard level 2 are generally higher than those at risk level 1. In some areas, however, early-historical flood deposits can also be found here, sometimes in small areas. Therefore, a flood risk cannot be ruled out in principle for the future. In individual cases, the local geological situation must be assessed.

A slow-moving area of low pressure and a high amount of atmospheric moisture produced heavy rainfall across Louisiana and southwest Mississippi in August 2016. Over 31 inches of rain was reported in Watson, 30 miles northeast of Baton Rouge, over the duration of the event. The result was major flooding that occurred in the southern portions of Louisiana and included areas surrounding Baton Rouge and Lafayette along rivers such as the Amite, Comite, Tangipahoa, Tickfaw, Vermilion, and Mermentau. The U.S. Geological Survey (USGS) Lower Mississippi-Gulf Water Science Center operates many continuous, streamflow-gaging stations in the impacted area. Peak streamflows of record were measured at 10 locations, and seven other locations experienced peak streamflows ranking in the top 5 for the duration of the period of record. In August 2016, USGS personnel made fifty streamflow measurements at 21 locations on streams in Louisiana. Many of those streamflow measurements were made for the purpose of verifying the accuracy of the stage-streamflow relation at the associated gaging station. USGS personnel also recovered and documented 590 high-water marks after the storm event by noting the location and height of the water above land surface. Many of these high water marks were used to create twelve flood-inundation maps for selected communities of Louisiana that experienced flooding in August 2016. This data release provides the actual flood-depth measurements made in selected river basins of Louisiana that were used to produce the flood-inundation maps published in the companion product (Watson and others, 2017). Reference Watson, K.M., Storm, J.B., Breaker, B.K., and Rose, C.E., 2017, Characterization of peak streamflows and flood inundation of selected areas in Louisiana from the August 2016 flood: U.S. Geological Survey Scientific Investigations Report 2017–5005, 26 p., https://doi.org/10.3133/sir20175005. First release: February 2017 Revised: April 2017 (ver. 1.1) Additionally, there is a revision history text file available on the main page that explains exactly what changed in the revision.

CFRAM Model Nodes - Current Scenario. Published by Office of Public Works. Available under the license Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 (cc-by-nc-nd).Abstract: This data shows the model nodes, indicating water level only and/or flow and water levels along the centre-line of rivers that have been modelled to generate the CFRAM flood maps. The nodes estimate maximum design event flood flows and maximum flood levels.

Flood event probabilities are referred to in terms of a percentage Annual Exceedance Probability, or ‘AEP’. This represents the probability of an event of this, or greater, severity occurring in any given year. These probabilities may also be expressed as odds (e.g. 100 to 1) of the event occurring in any given year. They are also commonly referred to in terms of a return period (e.g. the 100-year flood), although this period is not the length of time that will elapse between two such events occurring, as, although unlikely, two very severe events may occur within a short space of time.

The following sets out a range of flood event probabilities for which fluvial and coastal flood maps are typically developed, expressed in terms of Annual Exceedance Probability (AEP), and identifies their parallels under other forms of expression: 10% (High Probability) Annual Exceedance Probability which can also be expressed as the 10 Year Return Period and as a 10:1 odds of occurrence in any given year. 1% (Medium Probability - Fluvail/River Flood Maps) Annual Exceedance Probability which can also be expressed as the 100 Year Return Period and as 100:1 odds of occurrence in any given year. 0.5% (Medium Probability - Coastal Flood Maps) Annual Exceedance Probability which can also be expressed as the 200 Year Return Period and as 200:1 odds of occurrence in any given year. 0.1% (Low Probability) Annual Exceedance Probability which can also be expressed as the 1000 Year Return Period and as 1000:1 odds of occurrence in any given year.

The Present Day Scenario is also referred to as the Current Scenario. Present Day Scenario data was generated using methodologies based on historic flood data, without taking account of potential changes due to climate change. The potential effects of climate change have been separately modelled and reported on.

Data has been produced for the 'Areas of Further Assessment' (AFAs), as required by the EU 'Floods' Directive [2007/60/EC] and designated under the Preliminary Flood Risk Assessment, and also for other reaches between the AFAs and down to the sea that are referred to as 'Medium Priority Watercourses' (MPWs). River reaches that have been modelled are indicated by the CFRAM Modelled River Centrelines dataset.

Flooding from other reaches of river may occur, but has not been mapped, and so areas that are not shown as being within a flood extent may therefore be at risk of flooding from unmodelled rivers (as well as from other sources).

The purpose of the Flood Maps is not to designate individual properties at risk of flooding. They are community-based maps.

Lineage: Fluvial and coastal flood map data is developed using hydrodynamic modelling, based on calculated design river flows and extreme sea levels, surveyed channel cross-sections, in-bank / bank-side / coastal structures, Digital Terrain Models, and other relevant datasets (e.g. land use, data on past floods for model calibration, etc.).

The process may vary for particular areas or maps. Technical Hydrology and Hydraulics Reports set out full technical details on the derivation of the flood maps.

For fluvial flood levels, calibration and verification of the models make use of the best available data, including hydrometric records, photographs, videos, press articles and anecdotal information. Subject to the availability of suitable calibration data, models are verified in so far as possible to target vertical water level accuracies of approximately +/-0.2m for areas within the AFAs, and approximately +/-0.4m along the MPWs.

For coastal flood levels, the accuracy of the predicted annual exceedance probability (AEP) of combined tide and surge levels depends on the accuracy of the various components used in deriving these levels i.e. accuracy of the tidal and surge model, the accuracy of the statistical data and the accuracy for the conversion from marine datum to land levelling datum. The output of the water level modelling, combined with the extreme value analysis undertaken as detailed above is generally within +/-0.2m for confidence limits of 95% at the 0.1% AEP. Higher probability (lower return period) events are expected to have tighter confidence limits.

Purpose: The data has been developed to comply with the requirements of the European Communities (Assessment and Management of Flood Risks) Regulations 2010 to 2015 (the “Regulations”) (implementing Directive 2007/60/EC) for the purposes of establishing a framework for the assessment and management of flood risks, aiming at the reduction of adverse consequences for human health, the environment, cultural heritage and economic activity associated with floods....