Safeguarding the Public Downstream of Dams With GIS

Chris Wang PE, CMS

Geographic Information Systems (GIS) play a big role in helping the Federal Energy Regulatory Commission (FERC) administer its hydropower program to better safeguard the public living downstream of water retaining structures such as dams. Dam safety is a critical part of the Commission’s hydropower program, and to the Division of Dam Safety and Inspections (D2SI), which is composed of five regional offices and the FERC headquarters office in Washington D.C. D2SI oversees approximately 2,500 dams across the continental US, Alaska, and Puerto Rico. Part of D2SI’s program mission is to administer the Emergency Action Plan (EAP) Program. The EAP Program uses spatial information that is created, gathered, stored, and utilized in databases, shapefiles, or geodatabases.

Figure 1. Typical inundation map used by emergency responders

The primary responsibility of the D2SI is to oversee the safe construction and operation of new and existing dams, powerhouses, and other features that impound or divert water from rivers and streams for power generation. These dams can enhance recreational opportunities, create habitat for wildlife, and create power for homes and businesses. However, the reservoirs stored behind these dams can pose large potential consequences to downstream life, health, and property if they were to be catastrophically released. The D2SI utilizes the geospatial information it gathers from the projects and other publicly available sources to perform analyses for dam safety purposes.

Figure 2. Inundation map showing depth of flow by color and cross sections with flood wave information. 

Every FERC regulated water retaining structure (e.g. dam) is assigned a hazard potential classification (High, Significant, or Low), which is based on the potential downstream impacts as evaluated from a hypothetical “dam break” study. As a matter of regulation, all dam owners are required to develop an Emergency Action Plan (EAP), which is based on the findings from downstream flood inundation maps[1]. These maps show the estimated limits of the dam break induced flood, flood wave characteristics, and other pertinent information that would help emergency management agencies evacuate and warn the public. Several pre-determined locations, known as cross sections, are selected at key points (homes, bridges, etc.) below the dam to guide Emergency Management Agencies (EMAs) for planning and assisting emergency responders in the field. The flood characteristics are important during an emergency and provide time sensitive information about the flood wave to the emergency responders downstream of the dam. The dam owners are strongly encouraged to submit to the FERC the GIS shapefiles in accordance with the technical specifications (further described below) as well as to any Emergency Management Agencies that have GIS capability. These files include the inundation limit polygon, cross section, and a point file. Flood and time dependent information, as well as other pertinent GIS information identified (e.g. roads, bridges, campsites, etc.) are included in the inundation map product and are inserted in the appendix of the EAP document. See figures 1 and 2 for examples.

The Old Inundation Maps

Inundation maps were first introduced as part of the Commission’s regulations on January 21, 1981, but were not required until the Emergency Action Plan Guidelines were revised on April 5, 1985. The inundation maps were developed in hard copy form and were based on best available basemaps and pertinent information at the time of development. The inundation maps were rarely proactively updated with information reflective of the changing environment, such as new residential developments, re-routed roads, and other time dependent information. As a result, these maps could become outdated within a few years of their development, which means that actions taken by emergency responders to determine evacuation routes and make life safety decisions would be impacted. Unfortunately, map updates were often inconsistent and cumbersome, and technology limitations often made the work expensive. The inundation maps developed across the FERC’s portfolio varied in image quality, resolution, scale, and quality. However, the main pain point was that geospatial information could not be transposed easily to other electronic systems used by Emergency Management Agencies. This was recognized early on and was a frequent discussion topic between the EMAs and dam owners. EMAs complained that hardcopy maps were not as useful because the flood limits and scales could not be changed or transposed to their own mapping and database systems, which were vital to their operations. Thus, it was determined that relying on two systems could delay response times to impacted downstream entities and affect warning and evacuation procedures.

GIS Enters the Picture

The FERC recognized the positive aspects of technological advancements for emergency response, and in 2007 the FERC issued a letter to all hydropower project owners with High hazard dams to develop flood inundation maps in GIS format, or equivalent, and disseminate the files to Emergency Management Agencies to aid in performing their duties. Because every EMA had varying degrees of technological skills, capabilities, and resources, the GIS initiative was not required if the participating EMAs did not have GIS capabilities, but required them to verify their technological capabilities annually.

The GIS specifications were basic in nature and consisted of the following data files:

1.     Point File – consists of project structures and reference points (3) for georeferencing the raster maps.

2.     Rasters – Digital copy of the paper inundation map(s) used to delineate the flood limits and habitable structure on a basemap.

Figure 3. Field names and other specifications required in the shapefile submittal for cross sections.

3.     Failure Inundation Polygon – Shapefile feature showing the various flood limits under normal and extreme flood area from a dam break.

4.     Cross Section File - Shown at key downstream flood areas and shows the timing and depth at a given location. See figure 3 for specifications.

5.     Metadata Text File – Describes important details of the files such as author, year produced, units, datum, and coordinate systems for each electronic file.

Figure 4.  FERC GIS help page

The GIS guidelines were again updated in 2015 to include an expanded set of GIS specifications, from advances in flood modeling technology to inclusion of free and open GIS software (QGIS). The FERC also created a webpage that assisted owners in developing and submitting GIS inundation maps. The webpage contained a General Specifications of GIS document, Frequently Asked Question (FAQ) document, and sample map files. The web URL is listed below and shown in figure 4:

The FERC’s GIS initiative streamlined information between dam owners, EMAs, and regulatory agencies. Dam break information and flooding now can be utilized in various platforms such as AutoCAD and Google Earth. It has been used to help identify weaknesses in the emergency action planning processes and has led to other FERC public safety initiatives. In addition, adding other pertinent information such as watershed boundaries has provided cost savings opportunities by allowing dam owners within a watershed or have common emergency responders to perform a combined exercise. 

The Next Step to Improve Emergency Response

The GIS Initiative was only the first part to improve the Emergency Action Plan process.  Other initiatives soon followed: the Time Sensitive EAP initiative in 2009 and the High Flow Operations Plan in 2013. These improvements, along with other dam safety programs, have helped shape the FERC hydropower program.

The Time Sensitive EAP initiative requires dam owners to assess the tim­­ing involved in their EAPs from detection and response times with regard to flood wave arrival times to downstream population. The goal of this initiative is to ensure the effectiveness of the EAPs and minimize response time during a potential dam failure. The owner is required to conduct a Sudden Failure Assessment (SFA), which requires the use of the inundation flood information in order to calculate the difference between detection time and response time. Flood wave information from the inundation maps are used to perform the SFA. Where negative response times from detection to dam failure impact are identified, the dam owners need to develop enhancements, such as installing a siren for warning, or public education as mitigation.

The High Flow Operations Plan conveys to outside entities that downstream areas may be affected by the dam’s release of water (e.g. following a large precipitation event). Although the amount of flooding may be beyond the control of the dam owner, information on the timing and amount of release from the dam may be helpful to make decisions regarding warning and evacuation. GIS data and aerial imagery can identify what population centers or structures are affected during reservoir releases.


Technological advances in geospatial data and remote sensing have bridged the gap in communicating the flood hazards to the emergency responders so that valuable time is not wasted during an emergency and rescue operation. GIS professionals are critical in helping communicating important information that is used by emergency management agencies and regulators in their decision making process. The FERC continues to set guidelines to help reduce the risk to the public living downstream of dams. As demonstrated by the FERC Emergency Action Plan program, response time is critical and GIS professionals continue to remain an important part of the process in safeguarding the public.


[1] The EAP is developed based on possible incremental consequences from the dam storage only and is independent from the stability or general health of the dam.


The opinions and views offered here are those of the author, and are not necessarily those of the Federal Energy Regulatory Commission, individual Commissioners, or other members of the Commission’s staff.

Fall 2016 Volume 9 Issue 2

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