Virginia Law

A. Dam break inundation zone maps or an acceptable electronic format of the limits of the dam break inundation zone and analyses shall be provided to the department, except as provided for in 4VAC50-20-501, to meet the requirements set out in 4VAC50-20-40 and 4VAC50-20-175, as applicable. In accordance with subsection G of this section, a simplified dam break inundation zone analysis may be completed by the department and shall be provided to the impounding structure's owner to assist such owner in complying with the requirements of this chapter. All analyses shall be completed in accordance with 4VAC50-20-20 D.

B. The location of the end of the inundation zone should be where the water surface elevation of the dam break inundation zone and the water surface elevation of the spillway design flood during an impounding structure nonfailure event converge to within one foot of each other. Any inundation maps provided shall be supplemented with water surface profiles showing the peak water surface elevation prior to failure and the peak water surface elevation after failure.

C. All inundation zone maps shall be signed and sealed by a licensed professional engineer. A cover letter, signed and sealed by a professional engineer, must be submitted with the electronic format of the limits of the dam break inundation zone.

D. Present and planned land use for which a development plan has been officially approved by the locality in the dam break inundation zones downstream from the impounding structure shall be considered in determining the classification.

E. For determining the hazard potential classification, an analysis including those hazards created by flood and nonflood dam failures shall be considered. At a minimum, the following shall be provided to the department:

1. A sunny day dam break analysis utilizing the volume retained at the normal or typical water surface elevation of the impounding structure;

2. A dam break analysis utilizing the spillway design flood with a dam failure;

3. An analysis utilizing the spillway design flood without a dam failure; and

4. A dam break analysis utilizing the probable maximum flood with a dam failure.

F. To meet the Emergency Action Plan requirements set out in 4VAC50-20-175, all owners of high hazard potential or significant hazard potential impounding structures shall provide dam break inundation zone maps or an acceptable electronic format of the limits of the dam break inundation zone representing the impacts that would occur with both a sunny day dam failure and a probable maximum flood with a dam failure.

1. The maps or the limits of the dam break inundation zone shall be developed at a scale sufficient to graphically display downstream inhabited areas and structures, roads, public utilities that may be affected, and other pertinent structures within the identified inundation area. In coordination with the local emergency management coordinator, a list of downstream inundation zone property owners and occupants, including telephone numbers, may be plotted on the map or may be provided with the map for reference during an emergency.

2. Each map or the limits of the dam break inundation zone shall include the following statement: "The information contained in this map is prepared for use in notification of downstream property owners by emergency management personnel."

G. Upon receipt of a written request in accordance with 4VAC50-20-40 C and receipt of a payment in accordance with 4VAC50-20-395, the department shall conduct a simplified dam break inundation zone analysis. In conducting the analysis, a model acceptable to the department shall be utilized. The analysis shall result in Geographic Information System shape files for viewing and analyzing and shall meet the other analysis criteria of this section.

Upon completion of the analysis, the department shall issue a letter to the owner communicating the results of the analysis, including the shape files, stipulating the department's finding regarding hazard potential classification based on the information available to the department, and explaining what the owner needs to do procedurally with this information to be compliant with the requirements of the Dam Safety Act and this chapter.