Floodplain Mapping Program
The Department of Environmental Conservation has a burgeoning Floodplain Mapping Program. Under a Cooperative Technical Partnership with the Federal Emergency Management Agency (FEMA), the Department has begun conducting new Flood Insurance Studies (FIS) for the State of New York. The program employs cutting edge geographic information technology to produce some of the most accurate, advanced floodplain maps in the nation.
A pilot FIS in Schoharie County defined business processes and set data standards in what is a dynamic work environment. Customized geospatial applications were developed to aid in project management, engineering integration, and data processing. The final studies consist of a rich set of geospatial data for floodplain management, flood mitigation, and emergency management. The published FIS makes it possible to use the same data for other water quality and quantity programs.
New York's high resolution National Hydrography Dataset (NHD) provides the underlying geospatial reference for project development and management within the floodplain mapping program. An iterative process of study scoping and revision takes advantage of the dynamic segmentation afforded by NHD. Upon completion of a flood study, newly digitized, high resolution stream lines are used to update the existing NHD.
- A Spatial Link Manager Tool set (SLM) was developed to create and edit linear events in ArcView 3.x. The SLM uses templates, which enables the user to specify and modify event attributes.
- Initially, FIS event data is developed to represent the existing FEMA studies. Stream study type, as well as various tracking information, is entered into the event tables (*.dbf).
- Community, engineering, and management input, as well as budgetary constraints, determine the final project FIS.
- Output products of the project development phase include project management databases, survey planning maps, and data CD-ROMs.
Light Detection and Ranging (LiDAR) data plays a critical role in achieving the high level of accuracy found in the new flood insurance studies. Vertical accuracy of the LiDAR captured is approximately +/- 24 centimeters (or 9.5 inches). The proper application of LiDAR data to flood hazard mapping involves capture during leaf-off season, followed by:
- An active Quality Control and Quality Assurance program at both the LiDAR vendor's site and the LiDAR consumer's site.
- Reliable vegetation, building, and "pot-hole" removal mechanisms to achieve a bare-Earth elevation model.
- Procedures for the incorporation of field survey with LiDAR to augment the definition of hydraulic obstructions and controls.
- Specialized interpolation methods to produce the hydrological representation of the stream beds.
Upon completion of the pilot in Schoharie County, 73 separate engineering studies had been conducted for approximately 200 stream miles. For each one of those studies, 30 final data sets were produced, with many more temporary data sets created during the process. Of the 30 final data sets, 13 receive special processing to meet FEMA's paper map production requirements, as defined in their Enhanced and Standard Digital Flood Insurance Rate Map standards. For its part, the Department has:
- Created data development standards for processing and formatting the engineering data to meet both Department and FEMA requirements.
- Employed quality assurance & quality control by utilizing over 20 specialized tools that help automate data processing, in turn reducing human error.
- Developed FGDC-compliant metadata as well as standardized issue tracking and reporting.
FEMA's new hardcopy Flood Insurance Rate Maps (FIRMs) are a vast improvement over their predecessors. One of the most obvious improvements is the inclusion of base map imagery. FEMA and the Department have taken advantage of New York's statewide orthoimagery program and data sharing cooperative, and use the most recently flown imagery.
A New York State Floodplain Management Map (NYSFMM) series has been developed to provide floodplain managers, municipal planners, and other professionals with a tool for mitigation and planning. In addition to the information found on a FIRM, the NYSFMMs also contain department-set survey reference marks and flood depth contours. The maps are produced at a scale of 1:4800, follow a paneling scheme based on a subset of the 7.5 minute quadrangle, and utilize the most recent base map imagery.