Atlas 14 xte rna l Sta ke ho lde rs Me e ting RST July 17, 2018 - - PDF document

Atlas 14

UNDE RST ANDING AUST IN’S F L OOD RISK

E xte rna l Sta ke ho lde rs Me e ting July 17, 2018

Ove r vie w

Ra infa ll Da ta Cha ng e s Ne e d fo r Ac tio n So lutio n Optio ns Re c o mme nde d Co de Ame ndme nts I

mpa c ts to Re side nts a nd De ve lo pme nt

Disc ussio n/ Ne xt Ste ps

2

NOAA Atlas 14 - Bac kgr

• und

 Na tio nwide study

• f ra infa ll inte nsitie s

 Pa rtne rs:

 F

e de r al: Na tio na l

We a the r Se rvic e , U. S. Army Co rps o f E ng ine e rs, F e de ra l Hig hwa y Administra tio n

 State / L

• c al: T

xDOT , Ha rris Co unty F lo o d Co ntro l Distric t, City o f Austin, e t a l.

3

Histor y of Rainfall Inte nsity Studie s for Austin

4

10.1 12.5 10.2 13.2

8 9 10 11 12 13 14 1960 1970 1980 1990 2000 2010 2020

Ra infa ll De pth (inc he s) Ye a r Study Pub lishe d

Ra infa ll fro m 100-ye a r 24 hr sto rm

T P-40, 1961 Austin DCM, 1977 USGS, 1998 Atlas 14, 2018

Rainfall De pth Change s (Pr e liminar y)

5

R e c ur r e nc e Inte r val Cur r e nt R ainfall De pth in inc he s Atlas 14 R ainfall in inc he s 25-ye ar 7.6 Almost 10 100-ye ar 10.2 Up to 13+ 500-ye ar 13.5 Not ye t available

Ar e a Cur r e nt 100-Ye ar Cur r e nt 500-Ye ar Diffe r e nc e

City L imits 3,702 6,533 2,831

Ar e a Cur r e nt 100-Ye ar Cur r e nt 500-Ye ar % L ar ge r

City L imits 7% 9% 26%

6

City-wide Atlas 14 Impac ts

 Appro xima te numbe r

• f buildings in floodplain (e xc luding Co lo ra do

Rive r flo o dpla in)

 Appro xima te pe r

c e nt of ar e a in the floodplain (e xc luding Co lo ra do

Rive r flo o dpla in)

Ne e d for Ac tion

7

200 400 600 800 1,000 1,200 1,400 1940 1950 1960 1970 1980 1990 2000 2010

Numbe r

• f Str

uc tur e s

De c ade Built

Wate r she d Re gulations: F lood Mitigation

Count of structures in the current 100‐year floodplain by decade

1983: Regulations

introduced to prevent encroachment into the 100‐ year floodplain

2,000 4,000 6,000 8,000 10,000 12,000 14,000 1940 1950 1960 1970 1980 1990 2000 2010 2020

Cumulative No. Str uc tur e s in F loodplain

De c ade Built Count of structures in the current 100‐year floodplain by decade Hypothetical number of structures in floodplains without regulatory protections

12,000

Wate r she d Re gulations: F lood Mitigation

Re gulation Re vision Options

Do No thing Wa it to c ha ng e re g s until flo o dpla in

studie s a re fina l

Upda te re g s no w using c urre ntly

a va ila b le da ta

10

Re gulation Re vision Options

Do No thing

Disr

e gar d Atlas 14 and maintain c ur r e nt r e gs

Doe sn’t pr

• te c t r

e side nts fr

• m flood

hazar ds base d on ne w unde r standing of flood r isks

11

Re gulation Re vision Options

Wa it to c ha ng e re g s until flo o dpla in

studie s a re upda te d

Updating floodplain studie s will take a

minimum of two ye ar s

L

ife / safe ty implic ations ar e too signific ant to de lay

WPD will initiate floodplain study update s

imme diate ly

12

Re gulation Re vision Options

Upda te re g s using c urre ntly a va ila b le

da ta

Pr

• vide s imme diate pr
• te c tion and vital

infor mation to r e side nts

Use s r

e adily available , valid data

13

Pr

• pose d Code Ame ndme nt

Re vise flo o dpla in de finitio ns Re de ve lo pme nt e xc e ptio n Co lo ra do Rive r e xc e ptio n Cha ng e minimum fre e b o a rd to 2 fe e t

14

Pr

• pose d Code Ame ndme nt

15

Re c ur r e nc e Inte r val Cur r e nt R ainfall De pth in inc he s Atlas 14 25-ye ar 7.6 Almost 10 inc he s 100-ye ar 10.2 Up to 13+ inc he s 500-ye ar 13.5 Not ye t available

Re vise floodplain de finitions

100-ye ar

=

Atlas 14 100-ye ar

• r

F E MA 500-ye ar

25-ye ar

=

Atlas 14 25-ye ar

• r

fully de ve lope d 100-ye ar

16

Re vise floodplain de finitions

17

E

nc ro a c hme nt

Must satisfy

floodplain r ule s

Sa fe a c c e ss

Ac c e ss path

• min. 1-ft above

F

re e b o a rd

Min. 2-ft above

Color ado Rive r F loodplain

 Maintain c urre nt

100-ye a r flo o dpla in a lo ng Co lo ra do Rive r

18

Re vise floodplain de finitions – Why?

19

I

nfo rm pub lic o f c urre nt unde rsta nding o f flo o d risk

Curre nt, va lid 500-ye a r is a ppro xima te

ne w 100-ye a r

Atla s 14 c ha ng e s no t

e xpe c te d to sig nific a ntly a ffe c t Co lo ra do Rive r wa te rshe d upstre a m o f Austin

20

Color ado R ive r wate r she d

Re vise floodplain de finitions – Why?

Re de ve lopme nt e xc e ption

A re side ntia l b uilding in the 25- o r 100-ye a r

flo o dpla in c a n b e re de ve lo pe d a s lo ng a s:

Above 100-ye ar

floodplain by 2 fe e t

A maximum gr

• ss floor

ar e a that is the lar ge r

• f e xisting or

2,200 squar e fe e t

Doe s not inc r

e ase numbe r

• f dwe lling units

Re pla c e s the pre -1983 e xc e ptio n

21

Unde r c ur r e nt r ule s:

Pro pe rtie s in g re e n like ly to re de ve lo p unde r the pre -1983 e xc e ptio n Pro pe rtie s in ye llo w like ly to re de ve lo p with a n a dministra tive va ria nc e Pro pe rtie s in re d re q uire a Co unc il va ria nc e to re de ve lo p

Re de ve lopme nt e xc e ption

22

100-ye ar floodplain 25-ye ar floodplain

Re de ve lopme nt e xc e ption

23

Unde r ne w r ule s:

All pro pe rtie s ha ve sa me

• ppo rtunity to re de ve lo p

with a size limita tio n a nd e le va te d finishe d flo o r unde r a n e xc e ptio n

F lood r isk will be r e duc e d in all c ase s

100-ye ar floodplain 25-ye ar floodplain

Re de ve lopme nt e xc e ption

Ho w do e s this a pply to a dditio ns?

If the home me e ts fr

e e boar d and the pr

• pose d total squar

e footage doe sn’t e xc e e d the size limitation, the n it may be appr

• ve d unde r

this e xc e ption

24

Re de ve lopme nt e xc e ption

Ho w do e s this a pply to re no va tio ns?

If the r

e novation is not a substantial impr

• ve me nt, the n it may be appr
• ve d

unde r the e xisting c ode

If the r

e novation is a substantial impr

• ve me nt and the home me e ts

fr e e boar d, the n it may be appr

• ve d

unde r this e xc e ption

25

R e de ve lopme nt e xc e ption – Why?

I

nc e ntivize s re de ve lo pme nt while re duc ing flo o d risk

Ove r time re duc e s the numb e r o f

b uilding s a t risk o f flo o ding

Simplify c o de 2,200 sq . ft. is me dia n sing le -fa mily

ho me size in Austin

26

Color ado Rive r e xc e ption

 E

xpand 100-ye a r

e nc ro a c hme nt e xc e ptio n to inc lude L a ke Austin a nd L a ke T ra vis

27

Color ado R ive r e xc e ption – Why?

Co lo ra do Rive r

flo o ding is no t e xpe c te d to ha ppe n in a “fla sh”

Still re q uire s no

a dve rse impa c t a nd fre e b o a rd – wa ive s sa fe a c c e ss

28

Minimum fr e e boar d to 2 fe e t

Minimum he ig ht

b e twe e n b uilding ’ s lo we st flo o r a nd 100- ye a r flo o dpla in

Mo re tha n 140 T

e xa s c o mmunitie s ha ve fre e b o a rd o f 2 fe e t o r hig he r

29

2-ft

Minimum fr e e boar d to 2 fe e t – Why?

F

re e b o a rd is the sing le -mo st e ffe c tive me a ns fo r re duc ing flo o d risk to a b uilding in the flo o dpla in

Simplify c o de – c urre nt fre e b o a rd re q uire me nt fo r

a dministra tive flo o dpla in va ria nc e s a nd Ce ntra l Busine ss Are a e xc e ptio n is 2 fe e t, e lse whe re it’ s 1 fo o t

Re duc e d flo o d insura nc e c o sts c a n o ffse t inc re a se d

c o nstruc tio n c o st

30

Atlas 14 Impac t to home owne r s

Ne w unde rsta nding o f flo o d risk F

lo o d insura nc e c ha ng e s a t le a st 3 ye a rs a wa y

Rate s may go up Insur

anc e r e quir e me nts may c hange

T

alk to an insur anc e age nt now

Se e impa c ts a t AT

Xflo o dpro .c o m

31

Atlas 14 Impac t to De ve lopme nt

Whe n mig ht the se c ha ng e s sta rt b e ing

e nfo rc e d?

Will the se c ha ng e s a ffe c t

de ve lo pme nt a lre a dy sub mitte d?

Will the se c ha ng e s a ffe c t b uilding

pe rmits fo r pla tte d sub divisio ns?

DSD me mo about r

e c omme ndations

32

33

Atlas 14 Impac t to De ve lopme nt

Atlas 14 Impac t to De ve lopme nt

Sto rm dra in de sig n De te ntio n po nd de sig n Pha se d de ve lo pme nt

34

Rainfall De pth Change s (Pr e liminar y)

Onio n Cre e k a t Buda ra in g a ug e

Re c ur r e nc e Inte r val (ye ar s) R ainfall T

• tals

(inc he s) Inc r e ase in R ainfall T

• tals (inc he s)

1-hr 24-hr 1-hr 24-hr 25 9.8 2.2 100 13.2 3.0

35

Rainfall De pth Change s (Pr e liminar y)

Onio n Cre e k a t Buda ra in g a ug e

Re c ur r e nc e Inte r val (ye ar s) R ainfall T

• tals

(inc he s) Inc r e ase in R ainfall T

• tals (inc he s)

1-hr 24-hr 1-hr 24-hr 25 3.7 9.8 0.4 2.2 100 4.7 13.2 0.3 3.0

36

Var iation of Rainfall Ac r

• ss Re gion

 Pre vio us ra infa ll studie s

yie lde d re la tive ly c o nsiste nt va lue s a c ro ss the Austin Me tro a re a

 Atla s 14 sho ws sig nific a nt

va ria tio n

 Optio ns fo r Crite ria

 Sing le va lue a ssuming the ma ximum  Sing le va lue a ssuming a n a ve ra g e  Multiple va lue s b a se d o n wa te rshe ds  Multiple va lue s b a se d o n c o unty

b o unda rie s

37

Code Ame ndme nt Pr

• c e ss and

T ime line

38

Pla nning Co mmissio n Pla nning Co mmissio n Pub lic He a ring Ordina nc e Ado ptio n C&O Co mmitte e (PC & ZAP) E nviro nme nta l Co mmissio n Pub lic He a ring City Co unc il Pub lic He a ring I nte rna l a nd E xte rna l Sta ke ho lde r Me e ting s

3 pub lic he a ring s

At le a st 4 sta ke ho lde r me e ting s

C&O Co mmitte e (PC & ZAP) July I nte rna l a nd E xte rna l Sta ke ho lde r Me e ting s July DI F M Co mmitte e (E nviro nme nta l Co mmissio n) July June July Aug ust Aug ust Aug ust Oc to b e r Pub lic E duc a tio n & Outre a c h

Ne xt Ste ps

Pub lic He a ring s & Sta ke ho lde r Me e ting s

Che c k AustinT

e xas.gov/ atlas14 for de tails

Pub lic E

duc a tio n & Outre a c h

Post c ar

ds to pr

• pe r

tie s in 100/ 500-ye ar floodplains

Ge ogr

aphic ally base d public me e tings

WPD sta ff to de te rmine a pplic a tio n o f ra infa ll va lue s

fo r Austin a re a (Oc t-De c 2018)

Rule s c ha ng e pro c e ss – DCM (Q2 o r Q3 o f F

Y 2019)

Re -ma pping o f Austin flo o dpla ins (2019 – 2021)

39

Disc ussion/ Que stions?

Rainfall De pth Change s (Pr e liminar y)

 Onio n Cre e k a t Buda ra in g a ug e

Re c ur r e nc e Inte r val (ye ar s) Annual Chanc e (% ) Rainfall T

• tals (inc he s) for

Var ious Dur ations Inc r e ase in Rainfall T

• tals (inc he s) for

Var ious Dur ations 1-hr 2-hr 3-hr 6-hr 12-hr 24-hr 1-hr 2-hr 3-hr 6-hr 12-hr 24-hr

2 50 2 2.6 2.8 3.2 3.7 4.2 0.3 0.4 0.5 0.5 0.6 0.8 5 20 2.3 3.4 3.9 4.7 5.4 6.1 0.0 0.5 0.8 1.1 1.3 1.1 10 11 3.1 4.2 4.9 5.9 6.8 7.7 0.4 0.8 1.2 1.7 2.0 1.6

25

4

3.7

5.3 6.3 7.6 8.7

9.8 0.4

1.1 1.7 2.5 2.8

2.2

50 2 4.2 6.1 7.2 8.9 10.2 11.5 0.4 1.2 1.9 3.0 3.3 2.6

100

1

4.7

7 8.3 10.1 11.7

13.2 0.3

1.3 2.2 3.3 3.7

3.0

41

Rainfall De pth Change s (Pr e liminar y)

 Ca mp Ma b ry ra in g a ug e

Re c ur r e nc e Inte r val (ye ar s) Annual Chanc e (% ) Rainfall T

• tals (inc he s) for

Var ious Dur ations Inc r e ase in Rainfall T

• tals (inc he s) for

Var ious Dur ations 1-hr 2-hr 3-hr 6-hr 12-hr 24-hr 1-hr 2-hr 3-hr 6-hr 12-hr 24-hr

2 50 2 2.4 2.6 3.2 3.7 4.1 0.3 0.2 0.3 0.5 0.6 0.7 5 20 2.5 3.3 3.9 4.7 5.4 6 0.2 0.4 0.8 1.1 1.3 1.0 10 11 3.1 4.3 4.9 5.8 6.7 7.5 0.4 0.9 1.2 1.6 1.9 1.4

25

4

3.8

5.3 6.3 7.4 8.7

9.6 0.5

1.1 1.7 2.3 2.8

2.0

50 2 4.3 6.3 7.3 8.9 10.2 11.3 0.5 1.4 2.0 3.0 3.3 2.4

100

1

4.8

7.2 8.5 10.2 11.6

12.9 0.4

1.5 2.4 3.4 3.6

2.7

42

43

Rule s c hange pr

• c e ss – DCM

Se c tio n 2.4.3

Rainfall Inte nsity value update s Stor

m dr ain de sign

Se c tio n 2.5.1

Austin 24-Hour

Stor m Rainfall Distr ibution

T

ime line

Q2 or

Q3 of F Y 2019