Appendix D - beaverlooproad.com D Floodplain Memo.pdf · pedestrian and bicycle pathway. The BLR...
Transcript of Appendix D - beaverlooproad.com D Floodplain Memo.pdf · pedestrian and bicycle pathway. The BLR...
AWR Engineering, LLC Alaska Water Resources
Memorandum
To: John Pekar, PE and Art Johnson, PE
From: Janie Dusel, PE
Date: March 3, 2015
RE: Floodplain Mapping for the Beaver Loop Road Improvements Project
The purpose of this memorandum is to present a discrepancy in the Federal Emergency Management Agency (FEMA) mapping of the Beaver Loop Road (BLR) area and to document that BLR is not believed to be located in a floodplain.
Beaver Loop Road is located on the east side of Kenai, Alaska inside the limits of the City of Kenai and within the Kenai Peninsula Borough (KPB). The Alaska Department of Transportation and Public Facilities (ADOT&PF) is planning improvements to the existing road, including widening the roadway shoulders and adding a pedestrian and bicycle pathway.
The BLR area is shown on FEMA Flood Insurance Rate Map (FIRM) panels 0200122035A and 0200122030A which are both dated 1981. FEMA mapping of much of the KPB has been updated in recent years, but the City of Kenai does not participate in the National Flood Insurance Program and mapping of the area inside the city limits was not included in the update.
FEMA FIRM panel 0200122035A shows that a small portion of BLR, just west of the intersection of the BLR and the Kenai Spur Highway, is located in a Zone A floodplain that surrounds Beaver Creek, upstream of the confluence of Beaver Creek and the Kenai River. For reference, the FEMA FIRM is attached to this memo. Zone A floodplains are defined by FEMA as, “Areas of the 100‐year flood; base flood elevations and flood hazard factors not determined.” As required by Executive Order 11988, ADOT&PF asked AWR Engineering, LLC (AWR) to examine the potential impacts that the BLR project may have on the floodplain area. The initial scope of work to (1) determine if the project would cause a significant encroachment as defined by 23 CFR 650.105(q) and (2) determine if the proposed action would increase the base flood elevation one‐foot or greater.
Because the floodplain is a Zone A and does not have an associated flood elevation, AWR wanted to examine the location of the proposed improvements relative to the floodplain width and to compare the floodplain volume to the volume of the proposed improvements. To do this, the FEMA mapping was brought into ArcGIS Desktop as an image, and AWR attempted to fit the map to the local area as much as possible using geo‐referencing tools. Local area information was based on GIS data provided by the KPB. This included roadway locations, water bodies, ortho‐rectified aerial imagery, and 4‐foot contours from LIDAR data. Based on previous experiences, when the FEMA mapping is fairly old, a perfect fit to current conditions is not expected, but the mapping can typically be reconciled sufficiently to perform required floodplain analyses.
Appendix D1
RE: Floodplain Mapping for the Beaver Loop Road Improvements Project
Page 2 of 2
In this case, AWR aligned the FEMA stream location with the actual stream location shown on the aerial imagery and on the GIS water bodies data. The roadway locations shown on the FEMA map were lined up with actual roadway locations as best as possible. A “FIRMette” created from FEMA’s online mapping tool was used for this exercise to reduce the size of the image and eliminate white space. (The FIRMette is also attached.) The scale of the FEMA mapping was checked to ensure that it was not distorted in the reference process. Attached Figure 1 shows an overlay of the FEMA mapping, KPB aerial imagery, and GIS data of the existing roadways. Figure 2 shows the same overlay with the 4‐foot contours added.
Generally, the FEMA‐mapped floodplain area follows the 4‐foot contours fairly well. The map shows that the floodplain is bounded by a rise in topography on both sides of Beaver Creek, and the locations of the water features are generally correct. However, the FEMA map shows that BLR is much closer to Beaver Creek than it actually is. As a reference point, AWR lined up the location where Beaver Creek crosses the Kenai Spur Highway on both maps. This point provided a good reference because it has not changed since the FEMA map was developed. The FEMA maps shows that the intersection of BLR and the Kenai Spur Highway is approximately 250 feet from that point, but it is actually approximately 780 feet from that point. The FEMA mapping also shows that BLR is located in the floodplain, shown as a topographic low area around Beaver Creek. At the closest point, BLR is actually located approximately 330 feet east of the mapped floodplain and 230 feet east of the topographic bluff that follows the mapped floodplain. In this same area, the KPB contours show that the edge of the floodplain is generally defined by the 32‐foot contour and BLR is at the 52‐foot contour.
AWR obtained historic aerial imagery of this area to confirm that the locations of BLR or Beaver Creek have not changed since the FEMA mapping was developed. The historic imagery was obtained from the KPB GIS mapping website. Figure 3 shows mapping from 1975 and Figure 4 shows mapping from 1981. Comparison of the historic images to current aerial imagery shows that the general shape and location of Beaver Creek and the location of BLR have not changed since 1975.
Based on review of the information discussed in the memorandum, the location of BLR is believed to be shown incorrectly on FEMA FIRM 0200122035A. BLR does not appear to be located in a floodplain at any location along the corridor that will be addressed by this project.
AWR contacted the KPB regarding the mapping discrepancy. The Floodplain Manager, Harmony Curtis, has provided a letter explaining her agreement that the FEMA mapping appears to be incorrect and that BLR does not appear to be located in a Special Flood Hazard Area. This letter is included as Attachment 7.
Attachments: 1. FEMA FIRM Panel 0200122035A (1 page) 2. FEMA FIRMette (1 page) 3. Figure 1: FEMA Map Overlay with Aerial Imagery and GIS Data (1 page) 4. Figure 2: Overlay with Contours (1 page) 5. Figure 3: 1975 Imagery of Beaver Creek (1 page) 6. Figure 4: 1981 Imagery of Beaver Creek (1 page) 7. Letter from KPB Floodplain Manager (4 pages including attachments)
Appendix D2
KENAI SPUR HWY
BEAVER LOOP R
D
TID
AL
ST
TOGIAK ST
AM
ES
RD
PH
ILLIPS
DR
FE
RN
ST
MUDHEN DR
DOLCHOK L
N
EA
GLE
ST
N DOGWOOD RD
IOW
A S
T
STA
ND
AR
D D
R
MINCHUMINA AVE
RIC
HF
IEL
D D
R
FIRE
WE
ED
LN
LUPINE DR
N LUPINE DR
PTARM
IGAN S
T
NE
VA
DA
ST
PAR
KS
IDE
DR
SHELL DR
ALE
EN
E W
AY
WO
RT
HA
M A
VEROBIN DR
SH
OTG
UN
DR
JULIU
SSEN ST
KIM N
ANG C
T
EIS
EN
HO
WE
R L
N
BOUNDBROOK DR
WILDROSE AVE
RA
VE
N S
T
DOGWOOD RD
N F
ER
N S
T
BASIN VIEW WAY
LENTFER AVE
VA
LHA
LL
A L
N
TOGIAK ST
SHELL DR
FEMA Map Intersection of Beaver Loop Road and Kenai Spur Hwy
Acutal Location of Intersection of Beaver Loop Road and Kenai Spur Hwy
0 1,000500 Feet
±
LegendStreets
SurfaceHydrology
Figure 1: FEMA Map Overlay with Aerial Imagery and GIS Data
Appendix D5
KENAI SPUR HWY
BEAVER LOOP R
D
TID
AL
ST
TOGIAK ST
AM
ES
RD
PH
ILLIPS
DR
FE
RN
ST
MUDHEN DR
DOLCHOK L
N
EA
GLE
ST
N DOGWOOD RD
IOW
A S
T
STA
ND
AR
D D
R
MINCHUMINA AVE
RIC
HF
IEL
D D
R
FIRE
WE
ED
LN
LUPINE DR
N LUPINE DR
PTARM
IGAN S
T
NE
VA
DA
ST
PAR
KS
IDE
DR
SHELL DR
ALE
EN
E W
AY
WO
RT
HA
M A
VEROBIN DR
SH
OTG
UN
DR
JULIU
SSEN ST
KIM N
ANG C
T
EIS
EN
HO
WE
R L
N
BOUNDBROOK DR
WILDROSE AVE
RA
VE
N S
T
DOGWOOD RD
N F
ER
N S
T
BASIN VIEW WAY
LENTFER AVE
VA
LHA
LL
A L
N
TOGIAK ST
SHELL DR
FEMA Map Intersection of Beaver Loop Road and Kenai Spur Hwy
Acutal Location of Intersection of Beaver Loop Road and Kenai Spur Hwy
0 1,000500 Feet
±
LegendStreets
SurfaceHydrology
KPB 4-ft Contours
Figure 2: Overlay with Contours
Appendix D6
Figure 3: 1975 Imagery of Beaver Creek
Beaver Loop Road
Kenai Spur Highway
Beaver Creek
Beaver Creek
Appendix D7
Figure 4: 1981 Imagery of Beaver Creek
Kenai Spur Highway
Beaver Loop Road
Beaver Creek
Beaver Creek
Appendix D8