What to Expect When You re Expecting A LOMR. Mark Seidelmann, PE, GISP ASFPM 2015, Atlanta Georgia

Transcription

1 What to Expect When You re Expecting A LOMR Mark Seidelmann, PE, GISP ASFPM 2015, Atlanta Georgia Thursday, June 4 th, 2015

2 Agenda 1 Why File a Letter Of Map Revision (LOMR)? 2 Basic Requirements and Common Pitfalls 3 Case Study Lindsey Creek 4 Lessons Learned

3 1 Why File a Letter Of Map Revision (LOMR)?

4 Why File a Letter Of Map Revision (LOMR)? Reasons Replace dated or erroneous mapping New Construction Community ownership of map updates

5 2 Basic Requirements and Common Pitfalls

6 Basic Requirements and Common Pitfalls Basic Requirements Completed MT-2 Forms Certified Topographic Workmaps Supporting technical data. Public Notification $ Money

7 Basic Requirements and Common Pitfalls Common Pitfalls Unique technical issues Mapping Public Notification / Outreach Incomplete supporting technical data.

8 3 Case Study Lindsey Creek (Columbus, Georgia)

9 Lindsey Creek Background Location and Scope Located in Central Columbus Primary Study Reach Length: 2.5 miles. Area of high re-development interest Experienced 2-percent-annual-chance (50-year) flood equivalent LOMR Purpose Utilize new topographic data sources and engineering methods to develop accurate floodplains in a high growth and development area.

10 Lindsey Creek Background Effective Data Dated effective study Technical data from 80 s Location of technical support data unknown Delineated with 10 foot topography

11 Concrete Channel 30 feet wide x 12 feet deep to 30 feet wide x 8 feet deep

12 Drop Structures

13 Drop Structures

14 Dams Watershed Data 9.5 Sq. Miles 6.4 Sq. miles impounded 3 large SCS dams 4 other misc. storage locations Drainage Area Impounded By Dams Lindsey Creek Watershed

15 Dams Heath Lake Dam Airport Dam

16 Dams Weems Road Dam Airport Culvert Storage (Typical of misc. storage areas)

17 Lindsey Creek Approach Previous Attempt No revisions to hydrology Mapping did not match flood conditions observed by community The LOMR eventually timed out due to difficulties in modeling the drop structures New Approach New hydrology (rainfall runoff model) Drop structures independently simulated Model spilt into 6 separate reaches Boundary conditions included the headloss of the drop structure

18 Lindsey Creek Approach FEMA Review Issues LOMR application costs Drop Structures Hydrology Additional survey sources and certifications.

19 Lindsey Creek Approach LOMR Application Costs It was assumed the LOMR application would have no cost goal to improve existing conditions modeling based on new data sources: LOMR Based Solely on Submission of More Detailed Data. FEMA review staff, in reviewing the bridge structures noted that modifications had been made since the 1980 s (surprise!) Constituted manmade modifications requiring review fees of $6,500 (now days would be $8,250)

20 Lindsey Creek Approach LOMR Application Costs

21 Lindsey Creek Approach Drop Structures Lindsey Creek Plan: Drop 1-2_Revised 5/31/2015 Lindsey - 1 REACH 2 Legend WS 500 WS 100 WS FW WS 50 WS 10 Ground Elevation (ft) Main Channel Distance (ft)

22 Lindsey Creek Approach Drop Structures FEMA review team did not want a 2.5 mile length of stream modeled as 6 separate reaches, but had no other objections to the drop structure approach. Solution: Main HEC-RAS model unified into one reach with headlosses applied internally using little know HEC-RAS feature.

23 Lindsey Creek Approach Hydrology Upstream discharges could not be higher than downstream without reason Hydrology methods for watershed LAG times were in contention, specifically the use of Georgia regression methods for computing LAG times in urban watersheds.

24 Lindsey Creek Approach Hydrology Solutions Hydraulic model limits were extended an additional 2 miles upstream so flows would tie in at the cost of additional survey, engineering and schedule. Hydrology lag times were initially revised to use TR-55 methodology, with the backing of a 3rd party, hydrology was reverted to use Georgia regression equations.

25 Lindsey Creek Approach Additional Survey Sources New topographic sources were introduced by two local stakeholders during FEMA review periods. Each new survey source requires its own certification by a registered professional surveyor. Stakeholders also requested 3rd party review of revised study submissions

26 Lindsey Creek Summary Project Timeline Start of new LOMR: Completion of Initial Engineering: Initial submittal to FEMA: 2/22/2012 First FEMA Response: 4/25/2012 Completion of model extension: 6/21/2012 Additional LOMR submittals: 9/19/2012 1/8/2013 7/30/2013 Core Issues: hydrology, drop structure losses and mapping 8/8/2013 Public notice request Final Letter of Final Determination: 6/2/2014

27 Lindsey Creek Summary Costs Initial Engineering Application fees Model extension and survey

28 Lindsey Creek Summary Benefit Modern mapping with updated methodology, data and resident buy in Dozens of residencies no longer in dated regulatory floodplain. Savings on premiums for structures no longer identified in the SFHA More confidence in future development in the area

29 4 Lessons Learned

30 Lessons Learned Tips for LOMR Success Plan for a long FEMA review schedule Anticipate review fees Check hydrology tie ins as well as BFE tie ins Get as many local interests in the project as possible. Stay Positive Dot the i s Call em they won t call you.

31 Questions? Mark Seidelmann, PE, GISP Project Manager Stantec 1500 Lake Shore Drive Suite 100 Columbus OH Phone: (614) Fax: (614)