This data layer is part of a collection of GIS data created for the Okanagan Mainstem Floodplain Mapping Project. Notes below apply to the entire project data set.***Download Size is 12.5 GBGeneral Notes1. Please refer to the Disclaimer further below.2. Please review the associated project reports before using the floodplain maps: Northwest Hydraulic Consultants Ltd. (NHC). 2020. ‘Okanagan Mainstem Floodplain Mapping Project’. Report prepared for the Okanagan Basin Water Board (OBWB). 31 March 2020. NHC project number 3004430. Northwest Hydraulic Consultants Ltd. (NHC). 2021. ‘Okanagan Mainstem Floodplain Mapping Project – Development of CGVD1928 Floodplain Mapping’. Letter report prepared for the Okanagan Basin Water Board (OBWB). 30 March 2021. NHC project number 3006034.Northwest Hydraulic Consultants Ltd. (NHC). 2022. ‘Supplemental to the Okanagan Mainstem Floodplain Mapping Project – Current Operations Flood Construction Levels for Okanagan and Wood-Kalamalka Lakes’. Report prepared for the Okanagan Basin Water Board (OBWB). Final. 16 August 2022. NHC project number 3006613.3. These floodplain mapping layers delineate flood inundation extents under the specific flood events. Tributaries are not included in mapping.4. The mapped inundation is based on the calculated water level. Freeboard, wind effects, and wave effects have been added to the calculated water level where noted.5. Where noted, a freeboard allowance of 0.6 m has been added to the calculated flood water level. It has been added to account for local variations in water level and uncertainty in the underlying data and modelling.6. Where noted, the FCL (or COFCL) included in lake mapping layers includes an allowance for wind setup and wave runup based on co-occurrence of the seasonal 200-year wind event. The wind and wave effects extend 40 m shoreward to delineate the expected limit of wave effects. Beyond this limit the FCL (or COFCL) is based on inundation of the flood event without wave effects. Wave effects have been calculated based on generalized shoreline profile and roughness for each shoreline reach. Site specific runup analysis by a Qualified Registrant may be warranted to refine the generalized wave effects shown, which could increase or decrease the FCL (or COFCL) by as much as a metre.7. Underlying hydraulic analysis assumes channel and shoreline geometry is stationary. Erosion, deposition, degradation, and aggradation are expected to occur and may alter actual observed flood levels and extents. Obstructions, such as log-jams, local storm water inflows or other land drainage, groundwater, or tributary flows may cause flood levels to exceed those indicated on the maps.8. The Okanagan floodplain is subject to persistent ponding due to poor drainage. Persistent ponding is not covered by the flood inundation mapping.9. For flood level maps (water level and inundation extents):a. Layers for each flood scenario describe inundation extents, water surface elevations, and depths.b. The calculated water level has been extended perpendicular to flow across the floodplain; thus mapping inundation of isolated areas regardless of likelihood of inundation; whether it be from dike failure, seepage, or local inflows. Distant isolated areas may be conservatively mapped as inundated. Site specific judgement by a Qualified Professional is required to determine validity of isolated inundation.c. Filtering was used to remove isolated areas smaller than 100 m2. Holes in the inundation extent with areas less than 100 m2 were also removed. Isolated areas larger than 100 m2 are included in GIS data layers and are shown on maps if they are within 40 metres of direct inundation or within 40 metres of other retained polygons.d. Okanagan Dam breach, dam overtopping, or overtopping and breaching of Penticton Beach were not modelled. Inundation downstream of the Okanagan Dam on the left bank floodplain is based on river modelling with the assumption that Okanagan Lake levels will not overtop Lakeshore Drive and adjacent high ground. For the design flood scenarios, inundation mapping on the right bank of the Okanagan River from the Okanagan Dam downstream to the Highway 97 bridge and Burnaby Avenue is based on additional lake and river modelling. For other flood scenarios, river and lake inundation has been mapped separately and has not been integrated on the right bank. Inundation mapping on the right bank is based on river modelling as far as the most upstream modelled river cross section.10. For flood hazard maps (depth and velocity):a. Layers describe flood water depths and velocities. Depths and velocities are based on the maximum values from three modelled scenarios: all dikes removed, left bank dikes removed, and right bank dikes removed. Depths do not include freeboard.b. All hazard layers were modelled with the same parameters and boundary conditions as the design flood.11. Flood modelling and mapping is based on a digital elevation model (DEM) with the following coordinate system and datum specifications: Universal Transverse Mercator Zone 11-N (UTM Zone 11-N), North American Datum 1983 Canadian Spatial Reference System epoch 2002.0 (NAD83 CSRS (2002.0)), Canadian Geodetic Vertical Datum 2013 (CGVD2013), Canadian Gravimetric Geoid model of 2013 (CGG2013). FCL values are presented on the maps in both CGVD2013 and CGVD1928 vertical datums. CGVD1928 values are based on the following specifications: NAD83 CSRS (2002.0), CGVD1928, Height Transformation version 2.0 epoch 1997 (HTv2.0 (1997)). COFCL and COFCL values are presented only in CGVD2013.12. The accuracy of simulated flood levels is limited by the reliability and extent of water level, flow, and climatic data. The accuracy of the floodplain extents is limited by the accuracy of the design flood flow, the hydraulic model, and the digital surface representation of local topography. Localized areas above or below the mapped inundation maybe generalized. Therefore, floodplain maps should be considered an administrative tool that indicates flood elevations and floodplain boundaries for a designated flood. A qualified professional is to be consulted for site-specific engineering analysis.13. Industry best practices were followed to generate the floodplain maps. However, actual flood levels and extents may vary from those shown. OBWB and NHC do not assume any liability for variations of flood levels and extents from that shown.Data Sources Design flood events are based on hydrologic modelling of the Okanagan River watershed. The hydraulic response is based on a combination of 1D and 2D numerical models developed by NHC using HEC-RAS software, and NHC SWAN models. The hydraulic models are calibrated to the 2017 flood event and validated to the 2018 flood event; due to limits on data availability the hydrologic model is calibrated using data from 1980-2010. The digital elevation model (DEM) used to develop the model and mapping is based on Lidar data collected from March to November 2018 and provided by Emergency Management BC (EMBC), channel survey conducted by WSP in March, April, and June 2019, and additional survey data. See accompanying report for details NHC (2020).DisclaimerThis document has been prepared by Northwest Hydraulic Consultants Ltd. for the benefit of Okanagan Basin Water Board, Regional District of North Okanagan, Regional District of Central Okanagan, Regional District of Okanagan-Similkameen, Okanagan Nation Alliance for specific application to the Okanagan Mainstem Floodplain Mapping Project, Okanagan Valley, British Columbia, Canada (Ellison, Wood, Kalamalka, Okanagan, Skaha, Vaseux, and Osoyoos lakes and Okanagan River from Okanagan Lake to Osoyoos Lake). The information and data contained herein represent Northwest Hydraulic Consultants Ltd. best professional judgment in light of the knowledge and information available to Northwest Hydraulic Consultants Ltd. at the time of preparation, and was prepared in accordance with generally accepted engineering practices.Except as required by law, this document and the information and data contained herein are to be treated as confidential and may be used and relied upon only by Okanagan Basin Water Board, Regional District of North Okanagan, Regional District of Central Okanagan, Regional District of Okanagan-Similkameen, Okanagan Nation Alliance, its officers and employees. Northwest Hydraulic Consultants Ltd. denies any liability whatsoever to other parties who may obtain access to this document for any injury, loss or damage suffered by such parties arising from their use of, or reliance upon, this report or any of its contents.Data Layer List and Descriptions<!--· River / Lake Model Boundary -River / Lake Model Boundary (NHC): Boundary between Okanagan River and Okanagan Lake modelling and mapping areas for design and flood mapping.Recommended Design Flood (gates open): Ellison, Skaha, Vaseux, and Osoyoos lakeso Lake Shoreline Flood Construction Level (FCL) Zone – Recommended Design Flood with Freeboard and Wave Effect (NHC): Zone defined based on approximate shoreline and the wave breaking boundary plus a buffer; FCLs defined by zone along shoreline; shoreline FCLs take precedence over lake inundation FCLs.o Lake Flood Construction Level (FCL) Zone (Inundation Extent) – Recommended Design Flood with Freeboard (NHC): Design flood inundation extent with freeboard. Design event varies by lake, plus wind setup, plus mid-century climate change; plus freeboard 0.6m.o Lake Inundation Extent – Recommended Design Flood without Freeboard (NHC): Design flood inundation extent without freeboard. Design event varies by lake, plus wind setup, plus mid-century climate change.o Depth Grids§ Ellison Lake Depth – Recommended Design without Freeboard (NHC): ELLISON LAKE: 200-YEAR MID-CENTURY. Design flood depth

Forecasts of flows entering and leaving the Chain of Lakes on the Fox River in northeastern Illinois are critical information to water-resource managers operating the Stratton Dam at McHenry, Illinois. These managers determine the optimal operation of the Stratton Dam at McHenry, Ill., to manage Chain of Lakes pool levels and to help mitigate flooding in the Chain of Lakes system. In 2020, the U.S. Geological Survey (USGS) and the Illinois Department of Natural Resources–Office of Water Resources (IDNR–OWR) began a cooperative study to develop a system to enable engineers and planners to simulate and communicate water-surface elevations and flows and proactively prepare for runoff events forecasted for the Chain of Lakes. The hydraulic model may be helpful to the IDNR–OWR for optimizing the operation of the Stratton Dam and includes the implementation of three newly installed torque-tube crest gates that became operational in 2020. The hydraulic model for the Chain of Lakes was developed using the Hydrologic Engineering Center–River Analysis System (HEC-RAS) program (version 6.5; U.S. Army Corps of Engineers, 2022). The hydraulic model was used to simulate water-surface elevations and flows through the 18.5-miles Chain of Lakes system to 1.7 miles downstream from the Stratton Dam. Five USGS streamgages within the study area (Nippersink Lake at Fox Lake, USGS station 05548000; Fox River at Johnsburg, USGS station 05548500; Fox River at Miller Bridge near McHenry, USGS station 05549400; Fox River near McHenry, USGS station 05549500; Fox River (Tailwater) near McHenry, USGS station 05549501; U.S. Geological Survey, 2023) were used as reference points for model calibration and the water-surface elevations from each of these five USGS streamgages were used as an initial condition for the model simulation. This hydraulic model was calibrated to three runoff events (April–May 2022 [April 23–May 3], September 2022 [September 9–26], and March 2023 [February 28–March 15]) that incorporated the design specifications and observed gate operations of the Stratton Dam; furthermore, this hydraulic model simulated a validation event (January–February 2024 [January 28–February 22, specifically]) and a substantial flooding event during July 2017. The July 2017 event predated the torque-tube crest gate installation but nevertheless tested the performance of the model for such a substantial event. The model simulation results were a good fit to observed records at USGS streamgages with simulated peak water-surface elevations within −0.36 to 0.15 feet and peak flow −236 to 50 cubic feet per second. This data release contains a zip file that includes HEC–RAS model run files used in the calibration of the Chain of Lakes hydraulic model along with model performance and calibration metrics. References Cited: U.S. Army Corps of Engineers, 2022, HEC–RAS—River analysis system: U.S. Army Corps of Engineers software release, accessed October 15, 2023, at https://www.hec.usace.army.mil/software/hec-ras/download.aspx. U.S. Geological Survey, 2023, USGS surface-water data for the Nation, in USGS water data for the Nation: U.S. Geological Survey National Water Information System database, accessed May 13, 2024, at https://doi.org/10.5066/F7P55KJN. [Surface-water data directly accessible at https://waterdata.usgs.gov/nwis/sw.]

The study determined the flooding areas of the Dordogne and the Rhue in the crossing of the municipality of Bort-les-Orgues by hydrogeomorphological approach to the natural areas and by a hydraulic approach on the areas with stakes (urbanised areas crossed by the Dordogne up to the confluence with the Rhue and the area of the aid centre by the work of the Willow bordered by the Rhue). The mapping from this study replaces the mapping of the flooding area of the Dordogne established in 2000 only on the Plantade sector. The hydrogeomorphological study is a naturalistic approach based on the morphology and sedimentology of the alluvial plain. It makes it possible to identify the different river beds shaped by past floods (minor, medium, major, or even exceptional) in order to map the ordinary river bed, very frequent flood areas (annual return, here marnage zone of the hydro dam holding), frequent (return from 5 to 15 years) and exceptional (higher water). The hydraulic approach seeks to reproduce the reference flood by integrating flood and flow parameters. The reference flood for the Dordogne is the 1944 flood with an estimated return period of 150 years; for the Rhue the reference flood is the estimated centennial flood. Hydraulic modelling was carried out using Hec-ras (EU) software

Within large-river ecosystems, floodplains serve a variety of important ecological functions. A recent survey of 80 managers of floodplain conservation lands along the Upper and Middle Mississippi and Lower Missouri Rivers in the central United States found that the most critical information needed to improve floodplain management centered on metrics for characterizing depth, extent, frequency, duration, and timing of inundation. These metrics can be delivered to managers efficiently through cloud-based interactive maps. To calculate these metrics, we interpolated an existing one-dimensional HEC-RAS hydraulic model for the Middle Mississippi River, which simulated water surface elevations at cross sections spaced (<1 kilometer) to sufficiently characterize water surface profiles along an approximately 800 kilometer stretch upstream from the confluence with the Mississippi River over an 80-year record at a daily time step. To translate these water surface elevations to inundation depths, we subtracted a merged terrain model consisting of floodplain LIDAR and bathymetric surveys of the river channel. We completed these calculations for an 800 kilometer stretch of the Missouri River, spanning from Rulo, Nebraska to the river's confluence with the Mississippi River. Analyzed areas include the entirety of the Mississippi River floodplain, with the exception of the St. Louis metropolitan area in which analysis was constrained to currently unleveed areas only. This approach resulted in a 29,000+ day time series of inundation depths across the floodplain using grid cells with 30 meter spatial resolution. This dataset presents 14 metrics for each of two scenarios, one using a baseline timeseries of stages from the HEC-RAS simulation and one using a timeseries of stages adjusted to account for removal of existing levees from the floodplain. These metrics are calculated on a per pixel basis and encompass a variety of temporal criteria generally relevant to flora and fauna of interest to floodplain managers, including, for example, the average number of days inundated per year within a growing season. We also include the base elevation layer that we generated to calculate depth of inundation from interpolated water-surface elevations.

The U.S. Geological Survey (USGS), in cooperation with the Fond du Lac Band of Lake Superior Chippewa (FDLB), Minnesota, analyzed the hydrologic and hydraulic conditions within the Stoney Brook watershed. The Stoney Brook watershed covers an area of 100.8 square miles in Carlton and St. Louis counties with most of the watershed within the Fond du Lac Reservation. Wild rice, which is harvested by the FDLB, naturally grows in the lakes on the Fond du Lac Reservation and is susceptible to damage from increased water-levels after substantial rainfall events. Channel modifications and frequency rainfall events were simulated to assess lake level conditions that could mitigate potential damages to the wild rice yields. The channel modifications were also used to evaluate options for improving conveyance and floodplain storage in the watershed. The study area consists of 77.9 square miles of the watershed with the downstream boundary located 2.4 miles downstream from the USGS streamgage Stoney Brook at Pine Drive near Brookston, Minn. (USGS station 04021520; U.S. Geological Survey, 2023). A hydrologic model was used to simulate precipitation runoff and outflow hydrographs from delineated subwatersheds in the Stoney Brook watershed. A two-dimensional hydraulic model was used to simulate streamflows, volume accumulation, lake water-levels, and inundation duration and depths. The hydrologic model was developed using Hydrologic Engineering Center–Hydrologic Modeling System (HEC–HMS) computer program (version 4.3; U.S. Army Corps of Engineers, 2022) for the simulation of single rainfall events. A total of 14 subwatersheds were used in the HEC–HMS model to represent the 77.9 square mile study area within the Stoney Brook watershed. The HEC–HMS model was calibrated using streamflow time series from the USGS streamgage Stoney Brook at Pine Drive near Brookston, Minn. (USGS station 04021520; U.S. Geological Survey, 2023) to two high-flow events: April 21–30, 2008, and June 19–July 1, 2012. The calibrated HEC–HMS model used 24-hour duration design rainfall events consisting of precipitation frequencies of 1-, 2-, 5-, and 10-year recurrence intervals (100-, 50-, 20-, and 10-percent annual exceedance probabilities) for the simulation of channel modification alternatives in the hydraulic model. The hydraulic model was developed using Hydrologic Engineering Center–River Analysis System (HEC–RAS) computer program (version 6.4.1; U.S. Army Corps of Engineers, 2023). The HEC–RAS model was calibrated using streamflow time series from the USGS streamgage Stoney Brook at Pine Drive near Brookston, Minn. (USGS station 04021520; U.S. Geological Survey, 2023) to two high-flow events: April 21–30, 2008, and June 19–July 1, 2012. Channel modification alternatives were developed in the HEC–RAS model as terrain modifications and were intended to improve flow conveyances and storage and wetland coverage within the floodplain. These terrain modifications include breaches in the bank spoils, reconnecting the original channel to Stoney Brook, and clearing the original channel of soil deposition and debris. The HEC–HMS with HEC–RAS scenarios were simulated using flows from 1-, 2-, 5-, and 10-year recurrence interval (100-, 50-, 20-, and 10-percent annual exceedance probabilities) precipitation events distributed over a 24-hour duration. The HEC–RAS model was used to determine differences in hydraulic characteristics such as: peak water-surface elevations in the lakes, peak flows, volume accumulation, and inundation durations and depths. This data release contains a zip file that includes the HEC–HMS and HEC–RAS model run files, model performance and calibration metrics, and model outputs used in this study. References Cited: U.S. Army Corps of Engineers, 2018, Hydrologic Engineering Center Hydrologic Modeling System HEC–HMS 4.3. User’s Manual: U.S. Army Corps of Engineers software release, accessed October 10, 2022, at https://www.hec.usace.army.mil/software/hec-hms/downloads.aspx. U.S. Army Corps of Engineers, 2023, HEC–RAS—River analysis system version 6.4: U.S. Army Corps of Engineers software release, accessed October 2, 2023, at https://www.hec.usace.army.mil/software/hec-ras/download.aspx. U.S. Geological Survey, 2023, USGS surface-water data for the Nation, in USGS water data for the Nation: U.S. Geological Survey National Water Information System database, accessed October 2, 2023, at https://doi.org/10.5066/F7P55KJN. [Surface-water data directly accessible at https://waterdata.usgs.gov/nwis/sw.]