[env-trinity] Public Notice on Bucktail Project

Tom Stokely tstokely at att.net
Wed Jun 15 12:08:37 PDT 2016


>From the Trinity Journal:
PUBLIC NOTICE

TRINITY COUNTY PLANNINGDEPARTMENT PERMITTING REVISIONS OF FLOOD HAZARD AREAS IN BUCKTAIL AREA OFTRINITY RIVER

The Trinity County Planning Department, in accordance withNational Flood Insurance Program regulation 65.7(b)(1), hereby gives notice of theCounty's intent to permit revision of the floodway, generally located betweenBucktail Bridge and Gold Bar on the Trinity River.  Specifically, the floodway would be revisedfrom a point approximately 500 feet upstream from Bucktail Bridge to a pointapproximately 4,100 feet upstream from Bucktail Bridge (just below Gold Bar).As a result of the floodway revision, the floodway would be widened with amaximum widening of 120.62 feet at a point approximately 1,200 feet upstreamfrom Bucktail Bridge. 

In addition, the 1% annual chance water-surface elevations (“BaseFlood Elevations - BFEs”) and/or the 1% annual chance floodplain (“100-yearfloodplain”) would be revised from a point approximately 70 feet upstream ofBucktail Bridge to a point approximately 4,100 feet upstream from BucktailBridge. As a result of the revision, the 1% annual chance water-surfaceelevations would both increase and decrease within this area, and the 1% annualchance floodplain would be widened within a portion of the area of revision. Noincreases in the BFE are expected around insurable structures. 

Maps and detailed analysis of the revision can be reviewed at theTrinity River Restoration Program at 1313 South Main Street (next to TopsMarket) or online at http://www.trrp.net/restore/rehab/current/bucktail/.  Individual notices will be mailed tolandowners in the Bucktail area with specific information regarding individualparcels.

Interested persons may call the County at 530-623-1365, ext 3400,for additional information.

 

 


Understanding New FEMA Flood Insurance Rate Maps and theTRRP’s Expected Revisions


The Federal Emergency Management Agency (FEMA) is adoptingnew Trinity River Flood Insurance Rate Maps (FIRMs) on July 20, 2016. Becausethe County administers the National Flood Insurance Program (NFIP), they areworking with FEMA to disseminate the new FIRMs and are fulfilling new FEMAfloodplain permit requirements for proposed projects in flood hazardareas.  The new Trinity River FIRMs depictthe floodway, 100-year floodplain, and the 500-year floodplain and areavailable at:

http://trinitycounty.maps.arcgis.com/apps/Viewer/index.html?appid=320cf1c1558c43c8b1f2f70c23d35026

The Trinity River Restoration Program’s (TRRP) proposedBucktail channel rehabilitation project is now required to meet new FEMAfloodplain permitting requirements for proposed 2016 work upstream of theBucktail bridge. New floodplain permit conditions (required by the County tomeet FEMA needs) include detailed forecasting (modeling of design conditionsusing the HEC-RAS model to predict future water surface elevations) of expectedchanges to flood elevations that will result from implementation of proposed channelrehabilitation projects. As part of the permit process, the TRRP will also berequired to report actual changes (based on modeling of as-built projectconditions using the HEC-RAS model to predict flood water surface elevations) tothe channel and floodplain after the rehabilitation project is completed.

With the Bucktail channel rehabilitation project planned forthis summer, our forecasting of changes in flood hazard areas is concurrentwith FEMA’s adoption of the new Trinity River FIRMs, which may cause someconfusion.  The new FEMA FIRMs will be adoptedin July 2016 regardless of TRRP restorationactivities.

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 staffto complete the application process and meet FEMA requirements.  Steps include:

1.    Modeling of Bucktail Project design conditionsusing the HEC-RAS model to predict future water surface elevations. The HEC-RASmodel is the FEMA flood analysis tool used throughout the USA for mapping floodelevations. 

2.    Requesting conditional approval of proposed designconditions.  Trinity County is requestinga “Conditional Letter of Map Revision,” or CLOMR from FEMA. The CLOMR applicationprocess includes public notification of forecast water surface elevationchanges that would result from Project implementation.

3.    Surveying post-construction floodplain andin-channel conditions (expected fall 2016 at the Bucktail Project). Collectedtopography is input into the HEC-RAS model for flood forecasting. 

4.    Requesting a final revision of FIRMs in the Bucktailarea based on actual conditions after the Project is complete.  Trinity County is required to submit a requestfor a “Letter of Map Revision,” or LOMR, from FEMA based on HEC-RAS modeling ofwater surface elevations over surveyed (actual) post construction topography.

After technical review of all post-projectinformation, FEMA will issue a LOMR, thus updating revised sections of FIRMs inthe Bucktail area. 

Modeling of the Bucktail designcondition estimates that there will be no rise in flood elevations aroundinsurable, permitted structures (e.g., houses). Therefore, the Bucktail Projectis not expected to add structures into flood hazard areas requiring floodinsurance 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 floodplainis expected to stay the same as they appear on the new FIRMs becoming effectivein July, 2016. Overall, the model forecasts some minor decreases in floodelevations for the Bucktail subdivision from Project implementation. Some smallincreases (less than one foot) in flood elevations are forecast at, andupstream of, the Bucktail boat ramp.

Four maps illustrate the process:

Exhibit A.   Depictsthe Bucktail channel rehabilitation project planned for 2016 construction.Approximate and surveyed property boundary lines are included so thatlandowners may locate their properties. 

Exhibit B.    Depictsthe FEMA Flood Insurance Rate Map (FIRMs) with flood hazard areas that are plannedfor adoption by FEMA in July 2016, regardlessof TRRP actions.  

Exhibit C.    Depictspost-Bucktail Project conditions on the “Pending” FEMA floodway.  Modeled changes to 100-year flood elevationsare included. Green lines (in the Bucktail subdivision area) indicate a forecastlowering of flood elevations. Thismap also indicates forecast changes to the 100-year floodplain and floodway.Reductions are indicated in white and increases in black.

Exhibit D.   DepictsBucktail Project conditions from Exhibit C with a focus on the Bucktail subdivision.


 
Please study the provided information and contact LeslieHubbard (Trinity County point of contact for the adoption of the FEMA FIRMs)with questions at (530) 623-1365 Ext. 3400 or lhubbard at trinitycounty.org . Thank you.


 

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