Sussex County, DE Preliminary Study Overview

Transcription

1 Sussex County, DE Preliminary Study Overview Coastal study scope: 102 miles of entire County shoreline Revised 102 panels for coastal study Riverine study scope: 14 streams, 67.1 miles, within the Nanticoke River Watershed Revised 43 panels for riverine study prelim 12/30/2010 Revised FIS 1

2 What s New: Topographic Data 2007 LiDAR data: averaged 1.4 meters point spacing. Vertical accuracy (cm): 18.5 RMSEz* Horizontal accuracy (cm): 100 *RMSEz: root mean square error

3 Sussex County, DE Preliminary Riverine Study 67.1 miles of limited detail study 30 road structure crossings 4 frequencies were modeled: 10-,2-,1- and 0.2-percentannual-chance event 1- and 0.2-percentannual-chance event floodplain boundaries and BFEs were placed on the maps

4 What is a limited detail study? CW10 Road crossings were surveyed with limited methods and modeled LiDAR used for channel geometry Manning s n values were determined using survey pictures and imagery Cross-sections are placed approximately 500 ft apart No calibration to historical data was conducted No floodway was developed BFEs are shown on the maps Profiles for 4 frequencies in FIS

5 Slide 4 CW10 Add survey photo Christine Worley, 10/17/2012

6 What s New: Hydrology and Hydraulics Hydrology New hydrology computed using USGS regression equations with the proper environmental parameters Hydraulics Hydraulics analysis was conducted using HEC-RAS ft DEM from 2007 LiDAR was used to delineate watershed boundaries and sub watersheds Data from DE DataMIL was used: 2009 soil data and 2007 landuse

7 Effective Zone A vs. Preliminary Zone AE 6

8 Effective vs. New Coastal Study Coastal Study Component Effective Study (2005) New Study (2012) Topographic Data 1984 U.S. Department of interior topo maps meter LiDAR SWELs 1991 and 1984 USACE studies 2012 USACE study Modeled Transects Erosion Analysis Yes Yes Wave Setup No Yes Wave Runup Yes Yes LiMWA No Yes

9 Sussex County, DE Preliminary Coastal Study 96 published transects and 226 additional mapping transects New 1% annual chance storm surge analysis results: ft along the shore compared to the effective surge values of ft along the shore 2007 LiDAR topographic data

10 Coastal Mapping Base Flood Elevation (BFE): The height in feet above a certain datum, in this case North American Vertical Datum of 1988 (NAVD 88), that flood waters have a 1 percent annual chance of reaching or exceeding in any given year Primary Frontal Dune (PFD): A continuous or nearly continuous mound or ridge of sand with relatively steep seaward and landward slopes immediately landward and adjacent to the beach and subject to erosion and overtopping from high tides and waves during major coastal storms Zone VE: Defined by wave heights of 3 ft. or greater, or by the PFD Zone AE: Defined by wave heights ranging from 0-3 ft. Limit of Moderate Wave Action (LiMWA): Defined by the area subject to wave action with waves greater than 1.5 ft. in height

11 Coastal Mapping

12 LiMWA on the Map

13 Wave Runup Wave runup analysis performed on shoreline plateau features with mild slopes Runup 2.0 method applied based on slopes 12

14 Wave Runup How runup is mapped Terrain shows different slope at the shore

15 0.2% Floodplain for Inland Bays 14

16 Flood Map Resources Preliminary FIRM & FIS available at: Effective and superseded FIRM & FIS available at: For other information call the FEMA Map Information exchange (FMIX) at FEMA MAP Flood Information Portal:

17 Questions?