Floodplain Management
Floodplain Mapping Modernization
Converting floodplain maps to a digital format is one more step towards FEMA’s goal to acquire better more accurate mapping. It does not address all the flaws in existing maps. However it will make the maps easier to change in the future and reduce the costs of printing new maps in the long term. Processing Maine’s floodplain maps to a digital format for distribution in electronic media and made available on the internet will increase availability to more people than ever before. The first counties to be remapped into a completely digital format are Oxford, Kennebec, Cumberland and York
Oxford County
Oxford will be the first county in Maine to have digitized maps available on line. The process which began in 2004 will result in floodplain maps overlaid on a new ortho photo base map which will be easier to read and associate with specific properties. Progressive communities with digitized parcel data will be able to overlay tax map information and determine which properties are within the floodplain.
New Base Flood Elevations (BFE) were established in four communities, Bethel, Hiram, Otisfield and Paris.
Preliminary maps were issued in November of 2007. Mapping Coordination meetings (Link to Meeting Minutes new tab and page) were held in February of 2008 at the Mexico Town Office and the Paris Fire Station. Notice of Proposed Flood Elevation Determinations were published in the Federal Register, on January 16, 2008 at Part 67, Volume 73, Pages 28621-2862. Notices were also published in The Bethel Citizen, The Weekly Shopping Guide, The Portland Press Hearld and The Advertiser Democrat with the date of the latest publication falling on April 24, 2008. The formal appeals process began on April 24, 2008 and will run for 90 days. Comments and appeals must be filed prior to July 23, 2008 for consideration in this revision process. Any comments received after that date will be reviewed by FEMA and taken into consideration for future mapping updates.
Kennebec County
Kennebec County will be receiving Preliminary Maps during the summer of 2008. Once they are available mapping coordination meetings will be held and community officials will be invited to review the maps, make comments and learn about the process. If the process proceeds without any adjustments communities could be ready to adopt new maps by the end of 2009
Floodplains along the Kennebec River are being re-delineated however than that the rest of the floodplains will be transferred to the new ortho photo base maps.
York County
Scoping to determine the extent of mapping needs was completed in March of 2005. Since then work has continued in developing new ortho photo base maps and acquiring LiDAR (Link to description of LiDAR) topographic data for the coastal sections of the county of all communities from South Berwick to Old Orchard Beach, York County LiDAR Map. With this new data new hydraulic and hydrological analysis will be done in the coastal sections of towns of Kittery, Ogunquit, Kennebunk, Kennebunkport, Biddeford and Old Orchard Beach during the spring and summer of 2008. New floodplain maps will be developed for these communities and it is expected that there may be significantly higher base flood elevations determined from the new models.
Preliminary maps are expected to be available near the end of 2008 or beginning of 2009 with a projected completion of the Map Adoption process in 2010.
The Maine Geological Survey has been doing coastal erosion studies in southern Maine that provide provocative and interesting analysis of potential flooding changes based on rising sea levels predicted to occur as a result of global warming.
Cumberland County
Scoping to determine the extent of mapping needs was completed in March of 2006. Since then work has continued in developing new ortho photo base maps and acquiring LiDAR (Link to description of LiDAR) topographic data for the coastal sections of the county of all communities from Scarborough to Harpswell and including some of Bath, Cumberland County LiDAR Map. With this new data new hydraulic and hydrological analysis will be done in the coastal sections of towns of Scarborough, Cape Elizabeth South Portland, Portland Cumberland and Harpswell during the spring and summer of 2008. New floodplain maps will be developed for these communities and it is expected that there may be significantly higher base flood elevations determined from the new models.
Preliminary maps are expected to be available near the end of 2008 or beginning of 2009 with a projected completion of the Map Adoption process in 2010.
The Maine Geological Survey has been doing coastal erosion studies in southern Maine that provide provocative and interesting analysis of potential flooding changes based on rising sea levels predicted to occur as a result of global warming.
Challenges to Good Floodplain Mapping
Good Elevation Data
Floodplains are called that because they tend to be wide and relatively flat. When the river floods it spreads out and inundates a large area. Depth of water is measured in feet and may be as much as 30 feet above the normal high water mark of the river or stream. So when mapping a flood plain it is important to be able to determine land elevations very accurately.
The problem here in Maine is that for most of the State elevation data has not been remapped since the 1920’s when the United States Geological Survey completed a nation wide survey to determine elevations. Most of the maps show topographic elevations in terms of 10 or 20 feet increments. Consequently it is impossible to delineate floodplain boundaries that generally fall within a range of a few feet accurately.
Cost
The process of creating completely new Floodplain maps is incredibly costly, time consuming and complex. Google Earth and other similar programs lure you into the impression that it is mere childs play to create simple easy to use maps.
Creating new digital floodplain maps is neither simple nor easy. Even the shortened process of upgrading existing floodplain maps to overlay new ortho-photo base maps is an expensive time consuming process that requires a significant amount of time and effort. Even with the increased funding FEMA has received for upgrading the nations floodplain maps it is insufficient to correct all the known shortcomings.
This process requires building new maps with several layers of information and integrating huge databases of supporting documentation. Each layer must be registered to the new base map and go through a rigorous quality analysis and control process to ensure that the databases have been accurately compiled, before it is stored on the FEMA mapping information platform. In addition because the various layers of information are mapped at different scales each layer must be electronically manipulated to fit as closely as possible to the base map.
Just this relatively simple process will cost over $2,000 per floodplain panel and in Maine with over 1800 map panels the total cost of just converting to digital be over 3.5 million dollars. This does not include any additional funding for new topography, hydraulic, hydrological analysis or re-delineation of floodplain boundaries. Early estimates of costs for new high resolution topographical data come in at approximately 5 million dollars and completing new hydrological and hydraulic data to cover areas that have been mapped with only approximate studies have not been estimated with any degree of accuracy but would undoubtedly run into the millions of dollars also.
Sadly until we can obtain high resolution topography more accurate floodplain maps will be hard to come by.
If you would like to learn more about estimating mapping values FEMA publishes a Blue Book that establishes values of products provided by out side agencies that can be used in developing floodplain maps.
