Spring 2023 Levee and Floodwall Update

Hi all!

It appears Indianapolis North Flood Damage Reduction Project progress continues!

The Federal Emergency Management Agency (“FEMA”) recently (January 20, 2023) responded to the United States Army Corps of Engineers (“USACE”) Levee System Evaluation Report (“LSER”) for the Indianapolis North Flood Damage Reduction Project.

As you may recall from the last update, when FEMA provides review comments, the applicant must adequately address all of the comments within 90 days.

I’ve pasted a version of the comments below (edited for brevity).

Some seem to require rather complicated technical analysis which I expect may take some time to address (hydraulic modelling).

Additionally, the Indianapolis Department of Public Works (“DPW”) indicates some comments may require clarification.

Once all review comments have been adequately addressed, FEMA will issue a Letter of Map Revision (“LOMR”) to the affected communities and provide copies to the requester.

Again, LOMRs which result in changes to regulatory flood hazard information then are subject to a statutory 90-day appeal period. FEMA publishes a notice of the appeal period in the local newspaper. This notice is published twice, shortly after the LOMR is issued. The 90-appeal period commences on the date of the second newspaper publication. LOMRs receiving no valid appeals will typically become effective approximately 4.5 months after issuance (120 days after the second newspaper publication).

Thanks, and, as always, please reach out with any questions, though I don’t expect I will be able to answer any technical questions that relate to hydraulic modelling (!!).

Jim Polito


FEMA’s Twenty-Two Comments

Duplicate Effective Model 

1. The duplicate effective hydraulic model is a copy of the hydraulic analysis used for the currently effective published FEMA flood hazard data, referred to as the current effective model. For situations where the effective hydraulic model is a model which runs on an older platform (HEC-2 vs. HEC-RAS), the duplicate effective model is created by directly converting the model and making minor adjustments which are necessary to get the model to run on the new platform. It is recommended that the duplicate effective model be truncated to the intended limits of the proposed revision to reduce the effort needed to create the duplicate effective model. Additionally,

a. Please revise the duplicate effective model to incorporate cross sections from the previously approved Letter of Map Revision (“LOMR”),  Case No. 17-05-3161P, so that it accurately represents the effective hydraulic model.

b. Please revise the duplicate effective model to ensure consistency between blocked obstructions in the effective model and the submitted duplicate effective model.

c. Please revise the duplicate effective model to ensure consistency between overbank and main channel lengths.

Corrected Effective Model

2. The corrected effective model is a model that corrects any modeling errors in the duplicate effective model, makes changes necessary to ensure the model meets current FEMA standards, and/or incorporates more detailed topographic information than that used in the effective model. A corrected effective model is required to ensure the final pre-project and post-project models meet FEMA standards. Please revise the submitted model to ensure channel distances between cross sections defined in the model used to make mapping revisions match the channel distances shown on the topographic work map.

Pre-Project and Post-Project Models

3. FEMA guidance specifies that both “with levee” and “natural valley” analyses should be performed for a hydraulic analysis in an area with a levee/floodwall. Please provide a natural valley (without levee) analysis as there is a difference in the placement of effective flow areas due to the as-built levee project compared to the effective model.

4. Comparing the georeferenced existing (post-project) conditions model geometry to the provided terrain data, several cross sections do not appear to accurately reflect the existing topography. Please ensure the model uses the most current topographic information so the model can provide the most realistic estimate of flooding based on current conditions.

5. The locations of the levee embankments and floodwalls are currently represented in the submitted existing (post project) conditions in a variety of ways. To ensure the model clearly presents the location of the levee/floodwall at all locations, the levee/floodwall should be documented/modeled in the post-project conditions model in a consistent manner.

6. Please ensure that all cross sections in the pre-project and post project conditions models contain the 500-year flood event. 

7. For LOMRs utilizing truncated models, known water surface boundary conditions are set to the values of the effective models (hydraulic analysis used for the currently effective published FEMA flood hazard data). For all submitted models that are truncated from the effective hydraulic model, please incorporate elevation values that correlate with the effective hydraulic model results in the known water surface downstream boundary condition option (huh??!!).

8. The submitted existing (post-project) conditions floodway analysis uses a combination of methods to calculate the floodway encroachments. Please ensure that the post-project floodway analysis relies upon the appropriate method to define the floodway encroachment stations at all cross sections.

9. The submitted existing (post-project) conditions floodway analysis shows a surcharge value of 0.15’ at cross section 241.9. Based on state requirements, surcharges must be below 0.15’. Please ensure all surcharges in the post-project floodway analysis are below 0.15’.

10. The top of road for the bridge at Reach Station 242.36 in the submitted duplicate effective, corrected effective, and existing (post-project) conditions hydraulic models indicates that the bridge deck is approximately 6 inches thick. Please confirm the top of road elevation information for this structure in all submitted hydraulic models.

Mapping Items

11. Please provide a topographic work map that shows all applicable locations and alignments, boundary delineations, logical tie-ins, topographic contours, and the flow line used in the hydraulic model.

12. Please provide an annotated Flood Insurance Rate Map (“FIRM”) that shows the revised boundary delineations of the base floodplain, 0.2-percent-annual-chance floodplain, regulatory floodway, and area protected by the levee system.

Levee System Components

13. The submitted documentation includes survey points that were collected while the project was incomplete. Please provide verification of the top-of-levee elevations in this area to confirm freeboard requirements are met.

14. The Levee System Evaluation Report (LSER) submitted references a document we have been unable to locate on the USACE website. Please clarify if this engineering circular methodology was incorporated into another document or if the methodology still represents current practices and conditions for this project.

15. The LSER specifies that the I-Wall completed in 2019 as part of Phase 3B may currently have settlement that is still occurring. Please confirm USACE still recommends a positive evaluation for accreditation without a settlement analysis.  

16. The LSER specifies that there is an automatic floodwall closure structure along Westfield Boulevard that was installed in 2019. Please provide verification of the invert elevations of this automatic closure structure. In addition, document traffic control to prevent damage to the closure and also include provisions for monitoring and manual backup for the activation of the automatic closure.  

Regulatory Items (Responsibility of Community)

17. The submitted application included an Operations, Maintenance, Repair, Replacement and Rehabilitation Manual (“O&M”).  Please provide evidence that the most recent operation and maintenance plans have been formally adopted by a Federal or State agency, an agency created by Federal or State law, or an agency of a community participating in the NFIP.

18. Please provide an addendum or appendix to the O&M to identify the City of Indianapolis personnel (name or title) who will be responsible for the actions and assignments of operations and maintenance of the levee system.

19. Before this Letter of Map Revision (“LOMR”) can be processed, please provide community acknowledgment in the form of a letter stating that the community has reviewed the revision request and understands the effects of the revision on flooding conditions in the community.

20. The State of Indiana requires approval before FEMA issues a LOMR affecting the Base Flood Elevations and/or the regulatory floodway. Before this LOMR can be processed, please submit documentation of Indiana Department of Natural Resources approval.

21. Before this LOMR can be processed, please submit a finalized copy of the public notice distributed by City of Indianapolis officials stating their intent to revise the regulatory floodway.

22. Before this LOMR can be processed, please submit documentation of the individual legal notices that were sent to property owners who are affected by any increases in width and/or shifting of the base floodplain and/or increase in Base Flood Elevations.


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