The Trinity River Restoration Program’s Bucktail Project forecasts
no rise in flood elevations around insurable, permitted structures (e.g., homes).
Explanation of New FEMA Flood Insurance Rate Maps and the TRRP’s Expected Revisions
The Federal Emergency Management Agency (FEMA) is adopting new Trinity River Flood Insurance Rate
Maps (FIRMs) on July 20, 2016. Because the County administers the National Flood Insurance Program
(NFIP), they are working with FEMA to disseminate the new FIRMs and are fulfilling new FEMA
floodplain permit requirements for proposed projects in flood hazard areas. The new Trinity River
FIRMs depict the floodway, 100-year floodplain, and the 500-year floodplain and are available at:
http://trinitycounty.maps.arcgis.com/apps/Viewer/index.html?appid=320cf1c1558c43c8b1f2f70c23d35026
The Trinity River Restoration Program’s (TRRP) proposed Bucktail channel rehabilitation project is now
required to meet new FEMA floodplain permitting requirements for proposed 2016 work upstream of
the Bucktail bridge. New floodplain permit conditions (required by the County to meet FEMA needs)
include detailed forecasting (modeling of design conditions using the HEC-RAS model to predict future
water surface elevations) of expected changes to flood elevations that will result from implementation
of proposed channel rehabilitation projects. As part of the permit process, the TRRP will also be required
to report actual changes (based on modeling of as-built project conditions using the HEC-RAS model to
predict flood water surface elevations) to the channel and floodplain after the rehabilitation project is
completed.
With the Bucktail channel rehabilitation project planned for this summer, our forecasting of changes in
flood hazard areas is concurrent with FEMA’s adoption of the new Trinity River FIRMs, which may cause
some confusion. The new FEMA FIRMs will be adopted in July 2016 regardless of TRRP restoration
activities.
Before implementing the Bucktail channel rehabilitation project, the TRRP must obtain a floodplain
development permit from Trinity County. The TRRP is working with Trinity County staff to complete the
application process and meet FEMA requirements. Steps include:
1. Modeling of Bucktail Project design conditions using the HEC-RAS model to predict future water
surface elevations. The HEC-RAS model is the FEMA flood analysis tool used throughout the USA
for mapping flood elevations.
2. Requesting conditional approval of proposed design conditions. Trinity County is requesting a
“Conditional Letter of Map Revision,” or CLOMR from FEMA. The CLOMR application process
includes public notification of forecast water surface elevation changes that would result from
Project implementation.
3. Surveying post-construction floodplain and in-channel conditions (expected fall 2016 at the
Bucktail Project). Collected topography is input into the HEC-RAS model for flood forecasting.
4. Requesting a final revision of FIRMs in the Bucktail area based on actual conditions after the
Project is complete. Trinity County is required to submit a request for a “Letter of Map
Revision,” or LOMR, from FEMA based on HEC-RAS modeling of water surface elevations over
surveyed (actual) post construction topography.
After technical review of all post-project information, FEMA will issue a LOMR, thus updating revised
sections of FIRMs in the Bucktail area.
Modeling of the Bucktail design condition estimates that there will be no rise in flood elevations
around insurable, permitted structures (e.g., houses). Therefore, the Bucktail Project is not expected
to add structures into flood hazard areas requiring flood insurance that are not already included in
the 2016 FIRMs. After the Bucktail Project is constructed, the presence of insurable, permitted
structures in relation to the floodplain is expected to stay the same as they appear on the new
FIRMs becoming effective in July, 2016. Overall, the model forecasts some minor decreases in flood
elevations for the Bucktail subdivision from Project implementation. Some small increases (less than
one foot) in flood elevations are forecast at, and upstream of, the Bucktail boat ramp.
Four maps illustrate the process:
Exhibit A. Depicts the Bucktail channel rehabilitation project planned for 2016 construction.
Approximate and surveyed property boundary lines are included so that landowners may
locate their properties.
Exhibit B. Depicts the FEMA Flood Insurance Rate Map (FIRMs) with flood hazard areas that are
effective July 20, 2016, regardless of TRRP actions.
Exhibit C. Depicts forecast post-Bucktail Project conditions on the July 20, 2016 FEMA floodway.
Forecast changes to 100-year flood elevations are included. Green lines (in the Bucktail
subdivision area) indicate a forecast lowering of flood elevations. This map also indicates
forecast changes to the 100-year floodplain and floodway. Reductions are indicated in white
and pale beige, while increases are in black.
Exhibit D. Depicts Bucktail Project conditions from Exhibit C with a focus on the Bucktail subdivision.
Please study the provided information and contact Leslie Hubbard (Trinity County point of contact for
the adoption of the FEMA FIRMs) with questions at (530) 623-1365 Ext. 3400 or
[email protected] . Thank you.