Item 15 - Pomerado Creek FEMA Study Review
- -
AGEND, ,EPORT SUMMARY
TO: Honorable Mayor and Members of the City Council
- James L. Bowersox, City Man~ ..'
FROM:
INITIATED BY: John D. Fitch, Assistant City ManagerLJ,li
~ark S. Weston, Director of Engineeri~ Services~
Javid Siminou, Senior Civil Engineer .j
Roger A. Free, Associate Civil Engineer..)Z.[I. .
DATE: August 15, 1995
SUBJECI': Pomerado Creek FEMA Study Review
ABSTRACT 2-~
On the updated National Flood Insurance Program (NFIP) maps studied and ~epared by the
Federal Emergency Management Agency (FEMA), Pomerado Creek is depicted as being in the
floodway and special flood hazard area. Previous maps did not show this area in a
special flood hazard area. Flood insurance is required of the property owners having
property in these zones as a requirement of the City of Poway's participation in the
National Flood Insurance Program (NFIP) administered by the Federal Emergency
Management Agency (FEMA). This report presents a synopsis of what has transpired
concerning this change.
-, ENVIRONMENTAL REVIEW
No C.E,Q.A, review is required for this report.
FISCAL IMPACI'
None.
ADDITIONAL PUBLIC NOTIFICATION AND CORRESPONDENCE
None.
RECOMMENDATION
It is recommended that the City Council receive and file this report.
ACTION
-
1 nF q I'IUU .L ~- 'lIEIf' .LJ
AGENDA REPOR1'
CITY OF POW A Y
This report is included on the Consent Calendar. There will be no separate discussion of the report prior to approval by the
City Council unless members of the Council, staff or public request it to be removed from t~e Consent Calendar and
discussed separately. If you wish to have this report pulled for discussion, please fill out a shp indIcating the report number
and give it to the City Clerk prior to the beginning of the City Council meeting
TO: Honorable Mayor and Membe~e City Council
FROM: James L, Bowersox, City M ,
INITIATED BY: John D. Fitch, Assistant City ManagerCf:,\ ~
~Mark S, Weston, Director of Engineer~g Services
Javid Siminou, Senior Civil Engineer
Roger A. Free, Associate Civil Engineerj.o3.
DATE: August 15, 1995
SUBJECT: Pomerado Creek FEMA Studv Review
BACKGROUND:
On the updated National Flood Insurance Program (NFIP) maps studied and
prepared by the Federal Emergency Management Agency (FEMA). Pomerado Creek is
depicted as being in the floodway and special flood hazard area (Attachments 1
and 2). Previous maps did not show this area in a special flood hazard area
(Attachment 3). Flood insurance is required of the property owners having
property in these zones as a requirement of the City of Poway's participation
in the National Flood Insurance Program (NFIP) administered by the Federal
Emergency Management Agency (FEMA).
We recently received notification from FEMA that they will officially notify
the public of proposed Base Flood Evaluations (BFE's) for properties located
along Pomerado Creek from its confluence with Poway Creek to approximately 50'
down stream of Glen Oak Road.
The proposed Base Flood Elevations will become the basis for flood plain
measures that we must adopt in order to qualify for participation in the
National Flood Insurance Program (NFIP). The City has 90 days to review and
appeal the proposed BFE's based on scientific and technical data to prove that
the proposed BFE's by FEMA are incorrect, The Engineering Services Department
hired a consultant to review the assumptions, criteria, and methodology used
in the FEMA study to determine whether to appeal the change, Along with
available data, surveys of several pad elevations were taken. Results of this
investigation reveal that all assumptions, criteria, and methodology in the
study were reasonable.
Previous studies were done to study the flooding problems in this area. In
early 1967, community meetings were held to present findings and possible
ACTION:
AUG 1 5 1995 ITEM 15 I'll
2 OF 9
- -
Pomerado Creek FEMA Stu~j Review
August 15, 1995
Page 2
solutions and to obtain input. This input included a specially designed
questionnaire for the Poway area,
As a result, a March, 1967 study prepared by Boyle Engineering entitled Powav
Valley Flood Control StudY, proposed various concrete channel improvements to
alleviate the flooding along Pomerado Creek. These improvements were opposed
by the citizens.
In September, 1972, the San Diego County Department of Sanitation and Flood
Control developed The Revised Plan for Flood Control Imorovements in Poway
Vallev in response to the citizen's concerns with the 1967 study. It proposed
more natural alternatives but did not solve problems in areas already
developed such as along Pomerado Creek.
The Zone 1 Comprehensive Plan, July, 1976, identified Pomerado Creek as a
problem area for 100 year flooding. This area was already developed in 1976
having 6B acres and 163 homes identified as subject to flooding. The plan
recommended a detention basin north of Glen Oaks. At the time of the report,
design was underway for creek improvements (concrete channel, new road
crossings) ,
Since 1976, two more studies were done which are City of Poway Master Plan of
Drainaae. June 1983 and FEMA Studv. 1993, The studies contain the term "cfs"
which is a cubic foot per second and is the basic measure of the flow of water
volumes past a stationary point,
FINDINGS:
The 1976 Zone 1 Report assumed that the proposed detention basin at SR56 was
in place. The Zone 1 Report flows, therefore, are much lower at Holland Road
(900 cfs) than either the 1983 Study (1,800 cfs) or the 1993 Study (2,300
cfs) . The Zone 1 Report listed the capacity at the concrete channel
downstream of Holland Road as 1000 cfs. It appears that the improvements to
the concrete channel further south were based on the Zone 1 Report's flow of
900 to 1,430 cfs with the detention basin in place. Those designs were
underway in 1976 while the Zone 1 Report was being prepared. Adding the
proposed detained flow to the Zone 1 Report's 900 cfs would give approximately
1,600 cfs. which is 90% of the 1983 Master Plan flow and 70% of the 1993 FEMA
flow.
100 Year Flows (cfs)
I LOCATION I FEMA (1993) I MASTER PLAN ( 1983) I ZONE 1 (1976)* I
Ho 11 and Road 2300 1775 900
Vauqhn Road 2590 1810 900
Tassel Road 2840 1995 1430
- Poway Creek 2900 2235 1430
*Assumes detention basin at SRS6; 2,080 cfs in, 800 cfs out
AUG 1 5 1995 ITEM 15 OIl
3 OF 9
Pomerado Creek FEMA .udy Review
August IS, 1995
Page 3
There is a combination of reasons causing the 100 year flows (cfs) to be
greater in the FEMA (1993) study than the Zone 1 (1976) study. These are
change'; in the way elements of the equations are calculated, changes in the
ultimate land use based on the City of Poway General Plan and more accurate
rainfal I measurements, etc.
As a result, flood insurance will now be a requirement of the property owners
in th is area unt i 1 and if the channel is improved to the poi nt where it is
capable of carrying the quantity of water to remove these properties from the
floodway and flood hazard areas,
ENVIRONMENTAL IMPACT:
No C.E.Q.A. review is required for this report.
FISCAL IMPACT:
None.
ADDITIONAL PUBLIC NOTIFICATION l CORRESPONDENCE:
None.
RECOMMENDATION:
It is recommended that the City Council receive and file this report
JLB:MSW:JS:RAF:bw
ATTACHMENTS:
1. Vicinity Map
2. 1995 FEMA Map and Legend
3, 1985 FEMA Map and Legend
AUG 1 5 1995 ITEM 15 .,
4 OF 9
- -
-
!
_ITT
"
, "
,
, "I
ISC["t781 ~I -
I c..M:ll.1'l:II~
lorr_IXSQ "
" -...ulloa:.
1~ll(WII;IIW....
, "
POMER"O<!, CREEK ~ 9Tll ST ~
j i u." ! PO.~ H
LlOHAf l.H -
l:MOO: u
EF.
~~
I'~
-'~
!
'"
"",,,
~ 1'1.lSrIN S"l' ,
;: E1'''-Tf
"
'-
--
C -I
23 i
IT..
3'
;'4~ .ft>' .'
I ,
Pomerado Creek FEMA
CITY OF POWAY ITEM : 5tudv Review
@ TITLE : VICINITTY MAP
~ SCALE : N.T.S. A TT ACu'r~ ~~,
.On
5 OF 9
I
.'"",,"
11
\
I>
POMERADO CREEK 14
t...........
'"'
IOv,....o
RM199 -"
I
'lll<tfH'EC"
!
r
I
.&- I !
~oc.< '""'-"'>f ,,".VI"
ZOHI X i
ZONE X
""
"'''''i''I....,
"'"
~' -
Pomerado Creek FEMA
CITY OF POWAY ITEM: Study Review
~ TITLE: 1995 FEMA MAP
SCALE: N.T.S. ATTACHMENT: 2
6 OF 9
-
KEY TO MAP
SOD-Year Flood Boundary
lOO.Year Flood Boundary
Zone Designations
lOO-Year Flood Boundary
SOD-Year Flood Boundary
Base Flood Elevation Line 513
With Elel'.j[ion In Feet....
Base Flood Elevation In Feel (EL 987)
Whell' Uniform With in Zone'""
ElelJ!ion Refc!t'ncc Mal~ RM7x
lone 0 Boundar} -
Rive'Mile _M1.5
.*Rl'!e:cll.:ed to the NJtional Geodetic Vertical Datum of 1929
EXPLANATION OF ZONE DESIGNATIONS
ZONE EXPLANATION
A Areas of lOO-year flood; base flood elevalions Jnd
flood hazard factors not determined.
AO Areas of 1 DO-year shJ.lIow flooding where depths
are between one ll) and three (3) feet; average depths
of inundation are shown, but no flood hazard factors
are determined.
AH Areas of IOO-year shallow flooding where depths
.- are between one (1) and three (3) feet; base flood
elevations are shown, but no flood hazard factors
are determined.
A l-A30 Areas of lOa-year flood; base flood elevations and
tlood hazard factors determined.
A99 Areas of lOa-year flood to be protected by flood
protection svstem under construction; base flood
elevations and flood hazard factors not determined.
B Areas between limits of the 100-year flood and 500-
year flood; or certain areas subject to 100-year flood-
ing with average depths less than one (1) foot or where
the contributing drainage area is less than one 5Quare
mile; or areas protected by levees from the base flood.
(Medium shading)
C Areas of minimal flooding. (No shading)
o Areas of undetermined, but possible, flood hazards.
V Areas of lOo-year coas.tal flood with velocity (wave
action); base flood elevations and flood hazard factors
not determined.
Vl-V30 Areas of lOO-year coastal flood with velocity (wave
action); base flood elevations and flood hazard foiI.ctors
determined.
NOTES TO USER
Certain areas not in the special flood hazard areas (zones A and V)
may be protected by flood control structures.
This map is for flood insurance purposes only; it does not neces-
saril.,. show all areas sublect to flooding in the community or
all planimetric features outside special flood hazard areas.
- ATTACHMENT 2
PAGE 2 OF 2
ITEM 15 I
7 OF 9 AUG 15 1995
----
:i \'
~I \J ~===~t
~ II
I VAUGHN RD "'",)1
I . 71
I II
J II
Q QU04$ II
oM' ~
, " 20'
~
~
Q
ST
POMERADO CREEK
0
0
..
'"
w
'"
Q
..
TASSEL RD 5
~
~
.. I
iD
NINTH ST w 0 i!
'" ~ Z
,,, 0
.", '" QROHAVEN
... w YANKTON ~ {
POWERS RD ... CN
OFt j
POWAY
IL.ENE
0
0 SLACK ST
.
ROCA GRANDE .
0" ~
POWAT LA VISTA WT
ZONEC
Pomerado Creek FEMA
CITY OF POWAY ITEM : Study Review
@ TITLE . 1985 FEMA MAP
.
AUG 1 5 1995 , 15
SCALE : N.T.S. ATTACHMENT:
PAGE 1 OF 2
8 OF 9
- -
LEGEND
- - SPEcv.L FLOOD HAZAAO ~ INUNDATED
BY l00-~ FlOOD
ZONE A No b.- .... ~ M....~....4.
ZONl! M a.e I100d .... M......d.
ZONI /oil flood dBph d 1 .tI) 3 .. ~ _
.. -; ... .... --
~..4....d.
ZONI 10.0 flood ... d , .. , .... (.-.Iy _
.... on ...... _; _ .....
~.,.i.llod. Fol' _ d...... fan ~
~ ., M...,~...d..
ZONI ..... To be ,.- '""" ___ Iood lll'
...... flood ~ _ ....-
~; no t.e .......... ......~...d.
ZONe v eo-Jflood_"""""'__
acdonl; fM) baR Aood ~ <M... "dned.
ZONE VI Cooaflood_"""""'__
&fill aakln); b.e Aood ~ ~...I..t.
FLooDW^Y ~ IN ZONE M.
I -I OTHER FLOOD ~
ZONl X """'ol~Iood;...of~
flood__..............
1 foot Of wtIh ... ... ... 1tw\
, tquare rnAe; and ..., pn:ItIeCIIld by
w- '""" ,_ .....
I I OTHER ^RfAS
ZONE x ^'- ~..';'Ied to be wIIide soo-.,-r
floodploln.
ZONE D "'- .. """" flood ......... Oft
under2omWned.
UNDEVELOPED CQ;,ST^!. BAARIERS
~ '\'\1 ~~,",'1 ~~0J
.......... .......... """""""
,.,., ,""" --
Coastal berner ...... ... nonNIy ~ wi1hin or edjecent ICI Speci.Il
Rood Huwt:I ~.
Rood eo.--,
--- Aoodwey Boundlry
- , Zone 0 lloundo<y
/ If 1,(_ ~ 8"""'" DMdI.. _ Rood
. . " - z.o., ond lloundo<y
~
. , DMdlng ..... <If 0Ilf0<0nt
eo... - Rood -
WIthin - Rood -
Zona
- Rood -.... Uno;
513 -.. ~ See Met) I~
for a..wbon o.cum..
@-------@ ero. Section line
- Rood -. .. -
(EL 91171 ....... l-.n - Zone.
RM7X Soo .... _... _ 00Iun\.
--......
. M2 - ....
- ~ eo............. .... on North
97007'30".32"22'30" _ Dooum of 'C7 (HAD 27)
"'--
ATTACHMENT 3
PAGE 2 OF 2
AUG 1 5 1995 ITEM 15
9 OF a