Objective: Demonstrate how to develop coastal flooding visualizations and share them with coastal property owners for understanding the causes of flooding hazards such as storms or lake levels and changes related to future climate conditions.
Authors: Jeffrey D. Stone, Association of State Floodplain Managers; Sam Johnson, Consultant
Publication Date: October 30, 2013
Revision Date: May, 2016
Update Note: This case study has been reviewed, and the information presented here remains current and accurate. Additional information has been added regarding the "Lake Level Viewer," an analysis and visualization tool for understanding the impact of lake level fluctuations.
The 1973 Nor’easter storm (see “Nor’Easter Coastal Storm Flooding on Green Bay”) caused coastal flooding on Green Bay resulting in property damage for both Brown County and the City of Green Bay. While this storm occurred during a period of higher lake levels, even during low lake level periods, coastal storms can produce extreme water levels and storm surge as further documented for the winter storms of 1990 and 2009 during lower lake level periods (Jensen et al., 2012; Melby et al., 2012).
High waves and storm surge can affect property owners on the coast and even further into the coastal watershed. Periods of great shoreline damage and property loss due to erosion or flooding are related more to times of high wave power than to times of peak water levels. (Keillor, 2003)
This case study describes the process of using visualization tools like CanVis and the Lake Level Viewer to show the impacts of coastal flooding. CanVis is a visualization program that can be used to "see" potential impacts from coastal development or changes in Great Lakes water levels resulting from storms or long-term fluctuations. Water levels are influenced by short-term factors such as wind-driven waves resulting from storms, or by long-term climatic factors like evaporation, precipitation, temperature and ice cover. These short- and long-term factors are described along with links to additional resources in the next section.
The Lake Level Viewer for the Great Lakes (2014) incorporates detailed elevation data so that users can visualize lake level changes ranging from six feet above to six feet below historical long-term average water levels in the Great Lakes. The Viewer is quite useful for understanding the extent of shoreline and inland impacts by showing potential flooding at a given water level. The Viewer was created to help communities make smart planning decisions for zoning restrictions and infrastructure (e.g., marinas, intake pipes), encourage sustainability, and restore and conserve natural habitats. Water levels are shown as they would appear during calm conditions, and the data and maps illustrate the scale of potential flooding or land exposure at a given water level (not the exact location). City planners, floodplain managers, tribes, business owners, and other users can download the data, and may also access services for more in-depth analyses. For additional reference to the Lake Level Viewer see the "Understanding Section" below.
Brown County and the City of Green Bay, the county seat, are located at the mouth of the Fox River—one of the largest northward-flowing rivers in the United States—which empties into the south end of Lake Michigan's Green Bay. The bay is approximately 100 miles long with an average depth of about 35 ft. The south-end of the bay is low-lying with relatively flat relief, which sets up conditions for possible damages from Nor’easter-type storms. Additionally, if coastal storm surges capable of pushing water up into the Lower Fox and East Rivers are coupled with heavy rainfall, the flood risk potential increases.
Understanding the Elements of Coastal Floods
Coastal flooding is primarily caused by storm surge and waves but many other factors have an influence. On Great Lakes shorelines, flooding is dependent on local lake levels, which vary primarily as a result of natural processes, but also do include human influences. Future climate conditions and variability may cause more intense storms with heavier rainfall while also impacting lake levels through increased evaporation or decreased ice cover through winter months (Angel and Kunkel, 2010; Lofgren, 2011).
By understanding these factors and the natural processes associated with coastal flooding, we collect much of the information needed to answer the question: What information do you need to visualize coastal flood risk in your community?
The three (3) major factors that cause coastal flooding on the Great Lakes are:
Storms, Storm Surge & Waves
The intensity and duration of a storm strongly influence storm surge wave heights and power, and in turn, determines how much damage the waves may cause at the shoreline. Wave power is determined primarily by wind speed, duration and the open water distance (fetch).
Great Lakes Water Level Dashboard
Courtesy of: NOAA GLERL
Great Lakes water levels vary due to climatic conditions that affect the entire drainage basin – historically lake levels vary from season to season, over several years, or over multiple decades. A wide variety of interconnected factors control water levels including precipitation, temperature, evaporation, ice cover and more that will change as climate changes in the region. And, while nature controls the water levels on the Great Lakes, humans do influence it.Read more...
Great Lakes Lake Level Viewer
Courtesy of: NOAA OCM
The Great Lakes Water Level Dashboard provides an interactive viewer to explore historic and future projections of water levels for the Great Lakes. For individuals who are interested in visualizing lake level fluctuations, NOAA has created a Lake Level Viewer for the Great Lakes basin. This tool allows users to visualize where inundation would occur if water levels in the great lakes were to increase by up to 6 feet and how the coastline would change if water levels declined by as much as 6 feet.
Historic Water Level Data from the
Green Bay Gage Station
Courtesy of: NOAA NOS
Alternatively, current and historic water levels for the Great Lakes or more specific to the Green Bay gage (NOS Station #9087079) may be obtained via tables and reports. FEMA Base Flood Elevation (BFE) values developed as part of the Flood Insurance Rate Map (FIRM) can be found via the Flood Mapping (FEMA) layer in the Brown County Map Portal or simply in the effective Digital FIRMs for Brown County, WI (fees may apply) when downloaded from FEMA’s Map Service Center.
The coastal flood modeling process used to establish BFEs helps in understanding how lake levels, waves and wind are used to establish where wave impacts and flood inundation will occur – essentially describing how for instance; the flood hazard line is drawn on FEMA’s Flood Insurance Rate Maps (FIRMs). FEMA has initiated a coastal analysis and mapping study to produce updated Digital Flood Insurance Rate Maps (DFIRMs) for coastal counties around the Great Lakes. To learn more, visit the Great Lakes Coastal Flood Study website.
Shore Characteristics and Elevations
The nearshore and beach slopes greatly affect waves, which subsequently influence their impacts on flooding and erosion. Wide beaches with a gentle slope help protect structures or habitat behind the beach by helping to reduce the wave power before reaching them. Gentle slope in the offshore or nearshore can also reduce wave power, while the opposite condition of deeper water close to the water’s edge allows more wave power to reach the shore potentially causing flooding and/or erosion.
The Visualization Process
CanVis photo visualizations can help show coastal property owners the impact of different coastal flooding hazards resulting from storms and fluctuating lake levels.
Specific instruction and online training can be found in the Support tab of the NOAA Digital Coast CanVis page and in the User’s Guide, accessible via the Help menu in CanVis. Explore the guidance documents Using CanVis for Visualizations and Height and Horizon Calculations and training videos on the website.
The general process for creating visualizations is shown below along with links to locally-relevant data and resources for completing the work. A detailed tutorial is currently being developed and will be provided via linked pages and downloadable as a separate document.
1. Get photos.
Obtain or take photos of the shoreline area by specific parcels/lots (GPS-enabled camera is suggested), and gather as much information about the photo (focal lengths, distances, object heights) as you can. Photos taken perpendicular to the subject area at an elevation at or above the maximum water level you wish to simulate will work best, as will those that contain flat surfaces such as seawalls (and other reference objects) against which alternate water levels will be measured or applied.
Example images (2)
Record high lake levels and FEMA Base Flood Elevations (BFEs) will be compared to current water level conditions.
- Current water levels can be found specifically for Green Bay’s water level station (NOS Station #9087079) on NOAA’s Tides & Currents for the Great Lakes. For example, water levels at the Green Bay gage were approximately 578.00 ft. for an image that was taken on August 7, 2013.
- Record high levels on Lake Michigan may be found via the Great Lakes Water Level Dashboard. Turn off all lakes but Michigan-Huron, switch units to feet, and set the year sliders at bottom to show years between 1918 and 2013, which quickly shows the record average monthly lake level occurring in October of 1986 at 582.35 ft. / 177.5 m.
- The BFE values for the project area can be found by turning on the Flood Mapping (FEMA) layer (see “Layers” tab) in the Brown County Map Portal. For this area the BFE is 589 ft.
3. Determine object elevations and heights in photo.
Locate and correlate your photos with their appropriate parcel using the Brown County Map Portal. Use locally available LiDAR 2-foot contours and spot elevations along with a suitable high-resolution aerial image basemap to determine best ground elevation at the site of your reference object. This process requires GIS technical skills and software (i.e. ArcMap).
If you do not already have the measured height of the object, estimate it from the photo, or use the spot elevations to determine its top and then figure height. Knowing the amount of water level increase you need to show, you can now precisely locate this alternate waterline relative to your object's ground/top elevations.
4. Apply water level increases in CanVis.
To find the exact location of the water surface relative to an object in the photo, the Scale tool in CanVis will be used by sizing the ruler to the height of the reference object, then to measure precisely from the top or bottom of the reference object to your new waterline and note this mark. Refer to the Keeping It Real with CanVis article here. Next, the Texture tools are used to define and fill the area up to this waterline with a suitable water texture, and adjust tiling, perspective, color, transparency, and edge properties as appropriate.
Refer to the ‘Visualizing Sea Level Rise’ section of Using CanVis for Visualizations here, and use the method appropriate to your photo.
Communicating the Risk
Coastal managers of all kinds often face a common problem when speaking to stakeholders, other coastal programs, and the public: how does the organization communicate the true importance and impact of resource changes? In today’s visual world, charts, graphs, and statistics are not enough. Simulated images can be as or more effective than charts and graphs in conveying the on-the- ground impact of coastal change and development. Such visualizations can inform the decision-making process and spur stakeholders to develop strategies that mitigate the potential negative impacts of current land use decisions (NOAA CSC Using Photorealistic Visualizations).
Visualization results are shown below for two (2) sites located in the Township of Scott, Brown County. Note that the Base Flood Elevation (BFE) is not a still water elevation but rather includes wave run-up in the total height value; however, the CanVis simulation will show what inundation up to the BFE looks like in a way that visually resembles a still water level.
Site 1 (Parcel # SC-1603-39B) was chosen to help visualize lake level conditions where no structures (i.e. sea wall) exist. The original photo is shown along with the record high lake level and the currently adopted Base Flood Elevations. Due to tree shading it is difficult to see how high the BFE scenario lake levels potentially impact the house.
Current Lake Levels – August 7, 2013: 578.00’
Record High Lake Levels – October, 1986: 582.35’
Base Flood Elevation – 589’
Site 2 (Parcel # SC-1603-39B) was chosen to help visualize lake level conditions with a sea wall. The original photo is shown along with the record high lake level and the currently adopted Base Flood Elevations.
Current Lake Levels – August 7, 2013: 578.00’
Record High Lake Levels – October, 1986: 582.35’
Base Flood Elevation – 589’
Combining CanVis with inundation mapping or other map-based visualizations helps develop better context for viewing the various lake level scenarios. The Green Bay LakeViz Viewer is an interactive map detailing flooding incidence and other coastal hazards along Green Bay. This Viewer is a proof-of-concept (Elmer, 2012) for a broader interactive mapping project designed to assist public officials and private individuals in understanding the coastal hazards and flood management systems within Brown County. This prototype application employs a suite of spatiotemporal visualization solutions to explore the very local, micro-scale effects of lake level change as well as both historic and projected lake levels for Green Bay.