I recommend that wherever possible specific technical criteria be removed from the regulations and placed in guidance documents.  One reason for this is that once specific technical criteria becomes part of a regulation, the ability to amend or possibly even “correct” the criteria, based on newer or more technically accurate information, becomes difficult to accomplish in a timely fashion.  For example, it is recommended that the threshold criteria related to incremental damage analysis (IDA) be placed in a guidance document providing detailed technical IDA procedures rather than appearing in the regulations.  One good example of this approach is the guidance document for performing incremental damage analysis found in the “Ohio Critical Flood Guidelines” at http://www.dnr.state.oh.us/water/dsafety/critfld/tabid/3325/Default.aspx.  The threshold criteria and technical guidance provided in this document are clearly presented and in keeping with industry standards and I recommend that something similar be considered for Virginia.

Whether or not the IDA threshold criteria presented in section 4VAC50-20-52C is removed from the proposed regulations, the thresholds should relate to the incremental increase in water surface elevation and velocity associated with the non-failure and failure scenarios for a particular design storm, which is in keeping with the IDA guidelines presented in both the “Federal Guidelines for Dam Safety: Selecting and Accommodating Inflow Design Floods for Dams, FEMA 94” and the “Ohio Critical Flood Guidelines”.  The current wording in the proposed regulations does not clearly refer to the incremental increase in flood depth or velocity.

Similarly it is recommended that specific technical criteria related to development of spillway design floods (SDF), such as the required storm durations proposed in section 4VAC50-20-50D, be removed from the regulations and placed in a guidance document concerning SDF development.