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

OOD RISK L IN’S F ANDING AUST Atlas 14 xte rna l Sta ke ho lde rs Me e ting RST July 17, 2018 UNDE E

Ove r vie w 2  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

NOAA Atlas 14 - Bac kgr ound 3  Na tio nwide study o f ra infa ll inte nsitie s  Pa rtne rs:  F al: Na tio na l e de r 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 oc al: T xDOT , Ha rris Co unty F lo o d Co ntro l Distric t, City o f Austin, e t a l.

Histor y of Rainfall Inte nsity Studie s for 4 Austin Ra infa ll fro m 100-ye a r 24 hr sto rm 14 Austin DCM, 1977 Atlas 14, 2018 13 13.2 Ra infa ll De pth (inc he s) 12 12.5 11 10.1 10.2 10 T P-40, 1961 9 USGS, 1998 8 1960 1970 1980 1990 2000 2010 2020 Ye a r Study Pub lishe d

Rainfall De pth Change s (Pr e liminar y) 5 R e c ur r e nc e Cur r e nt R ainfall Atlas 14 R ainfall in Inte r val De pth in inc he s 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

City-wide Atlas 14 Impac ts 6  Appro xima te numbe r of buildings in floodplain (e xc luding Co lo ra do Rive r flo o dpla in) Cur r e nt Cur r e nt Ar e a Diffe r e nc e 100-Ye ar 500-Ye ar City 3,702 6,533 2,831 L imits  Appro xima te pe r e a in the floodplain (e xc luding Co lo ra do c e nt of ar Rive r flo o dpla in) Cur r e nt Cur r e nt Ar e a % L ar ge r 100-Ye ar 500-Ye ar City 7% 9% 26% L imits

Ne e d for Ac tion 7

Wate r she d Re gulations: F lood Mitigation 1,400 1983: Regulations introduced to prevent e s 1,200 encroachment into the 100‐ uc tur year floodplain 1,000 of Str 800 600 Numbe r 400 200 0 1940 1950 1960 1970 1980 1990 2000 2010 De c ade Built Count of structures in the current 100‐year floodplain by decade

Wate r she d Re gulations: F lood Mitigation 14,000 Hypothetical number of structures in floodplains without 12,000 e s in 12,000 regulatory protections uc tur 10,000 loodplain Cumulative No. Str 8,000 6,000 F 4,000 2,000 0 1940 1950 1960 1970 1980 1990 2000 2010 2020 De c ade Built Count of structures in the current 100‐year floodplain by decade

Re gulation Re vision Options 10  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

Re gulation Re vision Options 11  Do No thing  Disr e gar d Atlas 14 and maintain c ur r e nt r e gs  Doe sn’t pr ote c t r e side nts fr om flood hazar ds base d on ne w unde r standing of flood r isks

Re gulation Re vision Options 12  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

Re gulation Re vision Options 13  Upda te re g s using c urre ntly a va ila b le da ta  Pr ovide s imme diate pr ote c tion and vital infor mation to r e side nts  Use s r e adily available , valid data

Pr opose d Code Ame ndme nt 14  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

Pr opose d Code Ame ndme nt 15 Re c ur r e nc e Cur r e nt R ainfall Atlas 14 Inte r val De pth in inc he s 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 16  100-ye ar = Atlas 14 100-ye ar or F E MA 500-ye ar  25-ye ar = Atlas 14 25-ye ar or fully de ve lope d 100-ye ar

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 18  Maintain c urre nt 100-ye a r flo o dpla in a lo ng Co lo ra do Rive r

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

Re vise floodplain de finitions – Why? 20 Color ado R ive r wate r she d  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

Re de ve lopme nt e xc e ption 21  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 oss floor ar e a that is the lar ge r of e xisting or 2,200 squar e fe e t  Doe s not inc r e ase numbe r of dwe lling units  Re pla c e s the pre -1983 e xc e ptio n

Re de ve lopme nt e xc e ption 22 Unde r c ur r e nt r ule s: 100-ye ar floodplain 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 25-ye ar floodplain

Re de ve lopme nt e xc e ption 23 100-ye ar Unde r ne w r ule s: floodplain All pro pe rtie s ha ve sa me o 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 25-ye ar floodplain

Re de ve lopme nt e xc e ption 24  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 opose d total squar e footage doe sn’t e xc e e d the size limitation, the n it may be appr ove d unde r this e xc e ption

Re de ve lopme nt e xc e ption 25  Ho w do e s this a pply to re no va tio ns?  If the r e novation is not a substantial impr ove me nt, the n it may be appr ove d unde r the e xisting c ode  If the r e novation is a substantial impr ove me nt and the home me e ts fr e e boar d, the n it may be appr ove d unde r this e xc e ption

R e de ve lopme nt e xc e ption – Why? 26  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

Color ado Rive r e xc e ption 27  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

Color ado R ive r e xc e ption – Why? 28  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

Minimum fr e e boar d to 2 fe e t 29  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 2-ft c o mmunitie s ha ve fre e b o a rd o f 2 fe e t o r hig he r

Minimum fr e e boar d to 2 fe e t – Why? 30  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

Atlas 14 Impac t to home owne r s 31  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

Atlas 14 Impac t to De ve lopme nt 32  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

Atlas 14 Impac t to De ve lopme nt 33

Atlas 14 Impac t to De ve lopme nt 34  Sto rm dra in de sig n  De te ntio n po nd de sig n  Pha se d de ve lo pme nt

Rainfall De pth Change s (Pr e liminar y) 35  Onio n Cre e k a t Buda ra in g a ug e R ainfall T otals Inc r e ase in R ainfall Re c ur r e nc e (inc he s) T otals (inc he s) Inte r val (ye ar s) 1-hr 24-hr 1-hr 24-hr 25 9.8 2.2 100 13.2 3.0

Rainfall De pth Change s (Pr e liminar y) 36  Onio n Cre e k a t Buda ra in g a ug e R ainfall T otals Inc r e ase in R ainfall Re c ur r e nc e (inc he s) T otals (inc he s) Inte r val (ye ar 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