M.6 Hydrology Submittal Standards
Summary of questions/comments received for the Hydrology section on DHS Interactive and responses provided through October 10, 2008.
| Topic | Comment | Response |
|---|---|---|
| Limited Detailed Study | Limited detailed studies are NOT defined in Appendix C, or anywhere in the Guidelines and Specifications - a much needed addition. | FEMA provided a definition for Limited Detailed Study in Appendix C, which is currently being updated and will be available for review soon. |
| List of Hydrology Comments | Here is a list of hydrology errors/issues we have run into so far: The NODE_ID field in S_Nodes is a long, in S_Profil_Basln it is a text field. It would helpful if it was the same type in both so they could be linked in GIS. For Node_Typ in S_Nodes, it is listed as short. However, there are no short number values to use in the referenced domain table, D_Nodes. In S_Nodes, the following field names are too long to be used in a shapefile: DISCH_10PCT, DISCH_ PT2PCT, WSEL_PT2PCT In D_Nodes, another useful type would be Pour Point, since the nodes are used for hydrology as well as link/node hydraulics models. Under D_Hydro, ICPR should be added. It is used for both hydrology and hydraulics. |
We agreed with the comments about field length and variable type and these changes were incorporated into the updated document, which was posted in September 2008. The value "OUTLET" has been added as a domain value in D_Nodes. This value should be used to represent the pour point. Currently ICPR is one of the values in D_Hydra. It cannot be added to the D_Hydro domain table at this time because it is not considered to be one of FEMA's approved hydrologic models. For reference, FEMA's accepted models are listed on the following page: Hydrologic Models Meeting the Minimum Requirement of NFIP. |
| Data Files | Descriptions reference file named S_Basin but section M.11 names this file S_Subbasins. | There was an inconsistency in the naming convention in the January 2008 version of Appendix M. This was corrected in section M.6 to be consistent with section M.11 and the correct notation is S_Subbasins. |
| Directory Structure | Problem: Supplemental and other data formats. Proposed Resolution: Provide a folder for this type of data. |
The supplemental data analyses and backup files are to be placed in the Hydrology Data folder which will be re-named as \ Hydrology Models\ "Stream Name"\Hydrology Supplemental Data. The acceptable data formats are described in Section M.6.2.4, which were revised in the revised document posted in late September 2008. |
| Approximate Studies | Submittal requirements for approximate studies should be limited to a project description and narrative. Publishing discharges based on approximate methods opens up the door for appeals since most accepted approximate hydrology methods have known errors. | There is no requirement to publish the discharges for approximate studies. The concern may be about the statement in Section M.6.2.1 that indicates the Mapping Partner must submit "A draft text file that provides the required information for inclusion in Section 3.1 Hydrologic Analyses in the FIS report." This file should describe how the discharges were estimated but does not mean that the discharges have to be published in the Summary of Discharges Table. It would improve the documentation for the study if the discharges were published. The S_Nodes and S_Subbasins spatial files are no longer required for approximate studies in the revised version of Appendix M posted in September 2008, but if they are available, they should be provided. |
| Approximate Studies | Under FEMA rules, an Appeal is not possible for an approximate area. Also, why wouldn't it be helpful to store the Hydrology done for approximate studies for use in LOMA determinations? Why pay the FEMA contractor (or the property owner's engineer) to re-do the hydrology for a future LOMA at the same location? If someone submits more extensive Hydrology for a LOMA than what was done for the approximate mapping, then the LOMA reviewer can accept that new Hydrology in place of what was done for the mapping. |
We agree with these statements. The concept is to store or archive the hydrologic analyses used for the approximate study. This provides the needed documentation for the flood boundaries. Only the base flood elevations can be appealed so it is correct that an appeal is not applicable to approximate studies. However, there can be a protest for the flood boundaries. |
Last Modified: Wednesday, 29-Oct-2008 10:02:14 EDT