Bob Jacobsen PE. Consulting Hydrologist

Transcription

1 Bob Jacobsen PE Consulting Hydrologist Amite River Basin Commission Baton Rouge LA for: American Society of Civil Engineers Louisiana Engineering Society Louisiana Urban Stormwater Coalition Center for Planning Excellence Together Baton Rouge Louisiana Floodplain Management Association Sierra Club of Baton Rouge Tulane Engineering Forum

2 Bob Jacobsen PE MSCE LSU; PhD Coursework Environmental/Coastal/Flood Hydrology Flood Hydrology (since 1982): Central LA Rivers (1982) Mississippi River-near Darrow LA (1984) Amite River Basin (2002-Present) Coastal Storm Surge Modeling/ Hazard/Risk Analysis & Reduction (2004-P) High Resolution/ Supercomputing (2004-P) Clients: Amite River Basin Commission (ARBC) Louisiana Coastal Protection & Restoration Authority SE LA Flood Protection Authority East US Army Corps of Engineers Federal Emergency Management Agency President of ASCE Louisiana Section Authored by Bob Jacobsen 1982

3 2,000-yr Old Saying About Wise and Foolish Builders A wise man built his house on the rock the rain came down, the streams rose, and the winds blew and beat against that house; yet it did not fall, because it had its foundation on the rock. A foolish man built his house on sand the rain came down, the streams rose, and the winds blew and beat against that house; and it fell with a great crash. from The Sermon on the Mount Matthew: Chapter 7

4 Overview I. The Amite River Basin. II. The August 2016 Flood. III. History of ARB Flood Risk Management. IV. The Challenges of Regional Flood Risk Management.

5 The Amite River Basin 2,200 sqmi Amite River 170 miles 6 LA parishes 1/4 th of ARB in MS Amite River Diversion Canal 1960s shortcut to Blind River & Lake Maurepas. Lower ARB includes Blind River Sub- Basin. Lower ARB is coastal and subject to storm surge.

6 The Amite River Basin 1. Upper Amite River 2. Middle Amite River 3. Comite River 4. Lower Amite River 5. Honey Cut Bayou/Jones Creek/ Clay Cut Bayou 6. Bayou Manchac 7. Grays Creek/Colyell Creek 8. Blind River Sub-Basins 70 Major Streams

7 Population Density Baton Rouge Metropolitan Area eastbank population is concentrated in the southern half of the ARB.

8 ARB Topography

9 Flash Flooding Localized, intense rainfall inundates topographic bowls. Rainfall not conveyed away fast enough by runoff & urban drainage networks. Neighborhood/ Local drainage issue.

10 River Headwater Flooding Flood wave moves down river Peak/timing/duration dictated by 1. Rainfall location/duration/intensity. 2. Drastic change in floodplain width/slope from upper to middle to lower ARB. 3. Wave slows with widening/flattening of floodplains to south. Local/Regional flood management issue.

11 River Backwater Flooding Significant impact to local stream level from major flood in receiving water body. Exacerbated by terrain change from upper to lower basin. Actual flow can but does not have to reverse. Regional flood management issue. 17% of ARB 42% of ARB

12 Coastal Flooding Lake Maurepas is tidal lake. Added impact of strong, longduration southerly wind. Prolonged coastal 30 mph SE wind can raise Lake Maurepas by several feet. Long recognized in southern ARB. Hurricane surge is cause of most extreme flood levels in southern ARB. Regional flood management issue.

13 River Morphodynamics 1. Dredging, widening, straightening in Lower/Middle ARB 2. Extensive sand & gravel mining. Produce: A. Erosion/head-cutting toward Upper ARB B. Sedimentation/filling in Lower ARB Since early 20 th Century

14 River Morphodynamics Significantly changes Stage-Discharge Relationships in Amite & Comite Rivers Upper River: Flood levels drop Lower River: Flood levels rise See George Hudson PE work on Amite & Comite Rivers

15 Part II. The August 2016 Flood References: NOAA/NWS Dr. Barry Keim USGS EBR

16 The Rainfall Pseudo tropical storm. Un-named not taken seriously enough? Barry Keim (LA State Climatologist): Tropical Wave Boudreaux Very slow-moving. Unprecedented precipitable water in atmosphere. Not unlike TS Allison (2001). Extreme 3-day ARB regional rainfall (and to the west). Many station 2-day totals > NOAA 1,000-yr event

17 NWS KLIX Radar Loop Thu, Aug 11 thru Sat, Aug 13, 2016 Building a Weather-Ready Nation

18 Near Record Atmospheric Moisture Climatology of the moisture content in the atmosphere from all of our office weather balloon releases since rd highest value on record was recorded during this event. 2.8 inches was observed twice and we were 2.4 inches or higher Aug 9-12 Building a Weather-Ready Nation

19 Lower Mississippi River Forecast Center Rainfall

20 2-Day Rainfall ARB Rainfall Stations Location 2-day 100-yr 1000-yr BR-Concord BTR BR-SHER Livingston Norwood Gonzales Watson Brownfields Denham Springs Monticello Central Wakefield Jackson Gonzales Baton Rouge The 2-day PMP estimate for this region is 51.8 inches. From Dr. Barry Keim

21 2-Day Rainfall ARB Rainfall Stations Location 2-day 100-yr 1000-yr BR-Concord BTR BR-SHER Livingston Norwood Gonzales Watson Brownfields Denham Springs Monticello Central Wakefield Jackson Gonzales Baton Rouge The 2-day PMP estimate for this region is 51.8 inches. From Dr. Barry Keim

22

23 Full-Spectrum Rainfall Hazard for BR:

24 Full-Spectrum Rainfall Hazard for BR: Uncertainties of +22 & +27% SCIENTIFIC GUESSTIMATES

25 Comite River Flood Waves

26 Amite River Flood Waves

27 River Crests GAGE Date Crest* Previous Record Crest* Previous Record Date Amite River-Darlington 08/12/ /25/1990 Amite River-Grangeville 8/12/ /14/1955 Amite River-Magnolia 08/13/ /23/1977 Amite River-Denham Springs 08/14/ /08/1983 Amite River-Bayou Manchac Point 08/14/ /08/1983 Amite River-Port Vincent 08/15/ /09/1983 Amite River-French Settlement 08/16/ /25/1977 Comite River-Olive Branch 08/13/ /18/1961 Comite River-Joor Road 08/14/ /09/2001 *Gauge Datum.

28 10 Consequences (Additional impacts to west & in other parts of state; & from March Flood) 1. 9 deaths;. 2. 1,000s rescued. 3. ~$5 billion in estimated damages. 4. ~93,000 EBR, Ascension, Livingston homes, businesses, other bldgs damaged th biggest flood event in NFIP history. (29,000 NFIP claims incl. areas to west) 6. But >50% of damaged property not covered by flood insurance. 7. Billions of dollars in lost insurance compensation! 8. Hundreds of millions of dollars in damage to public facilities and infrastructure. 9. Property devaluations (35%). 10. Reduced tax revenue for state/local government.

29 Response/Recovery Highlights 1. Cajun Navy & Evacuation/Sheltering/ Red Cross. 2. Early phase emergency Aid/D-SNAP/ Sheltering Hotels. 3. Debris removal and disposal. 4. Special Federal Disaster Aid $1.7 billion primarily to give lowmoderate income victims some help; homeowners outside 100-yr flood zone. 5. Rebuilding $ for home-owners without flood insurance far exceeds aid. 6. Communities relaxed rebuilding codes: substantial damage threshold and elevation requirements. 7. Lack of flood hazard/risk info hampers rebuilding decisions. 8. Renewed focus on hope for major flood fixes:" Comite River Diversion Canal (CRDC) Interstate 12 median barrier Bayou Manchac improvements

30 Flood Data USGS Gauges FEMA/USGS High Water Mark Survey ARBC self-funded HWM Survey along ARB major streams Bob Jacobsen PE + SJB, Stantec, T. Baker Smith, BR Land Surveying 44 USGS Gauges 199 USGS HWMs 252 ARBC HWMs

31 Post-Flood Analysis USGS Partial inundation map based on USGS HWMs. Does not include southwest portions of ARB. USGS: Amite River at Denham Springs flow 205K cfs > 500-yr But was it really? Need State of the Art H&H model & hindcast. Flood hazard analysis. Characterization of Peak Streamflows and Flood Inundation of Selected Areas in Louisiana from the August 2016 Flood

32 Post-Flood Analysis

33 Post-Flood Analysis ARBC Quality checks on USGS and ARBC HWMs. Preliminary peak flood profiles along 70 major streams based on all HWMs. Need hindcast model of flood to finish high quality inundation map.

34 Post-Flood Analysis ARBC

35 Post-Flood Analysis ARBC

36 Post-Flood Analysis ARBC

37 Post-Flood Analysis Others DOTD-Public Works & Water Resources with support from Louisiana DOA, Office of Community Development: Developing updated ARB NFIP-style 1D/2D model based on new LIDAR; expect May include hindcast of 2016 Flood for model validation. Touted as potential future floodplain management tool evaluate regional flood risk; mitigation proposals & proposals with potential adverse impact To be distributed through LSU Center for River Studies. Affect of I-12 barrier lawsuit on future design of floodplain crossings? FEMA/GOHSEP/OCD Watershed Resiliency Study support for GIS Web Portal? Mitigation $200 Million to Parishes/Communities CDBG grants $Billion TBD East Baton Rouge Parish developing their own new NFIP-style 1D/2D model & a Stormwater Management Plan to evaluate parish drainage projects. Ascension Parish own new NFIP-style 2D model; Laurel Ridge Levee Extension; dredging of Bayou Manchac. Iberville Parish proposing raising Manchac Road. City of Central working with USGS on flood forecasting tool; drainage improvements. Livingston Parish drainage improvements; dredging of Lower Amite River.

38 Post-Flood Analysis GIS Web Portal Cloud layers with clickable features & pop-up info: Imagery Various jurisdictional boundaries New LIDAR DEMs New Hydrography NHD Need to update New watershed boundaries for all named streams Topo/bathy breaklines (embankments, ridges, channel banks, etc.) Stream/floodplain surveyed cross sections Hydraulic structures bridges, culverts, weirs, gates, etc. Urban/suburban gravity & forced drainage networks Land cover Infrastructure roads, railroads, pipelines, utilities, etc. Key facilities schools, hospitals, govt buildings, etc. Population Buildings Stream gauges NFIP FIS FIRM zones & LOMRs Previous major ARB Studies/Information 2016 Flood HWMs, Flood Inundation Area, Elevation & Depth Map Use to solicit Public Comments & Additional Info!

39 Part III. History of ARB Flood Risk Management References: ARBC Draft Floodplain Management Plan FEMA LSU AgCenter

40 Pre-1983 Flood 1928 USACE completed channel improvements in the Amite River from Denham Springs to Lake Maurepas LA DPW and East Baton Rouge made improvements to Ward Creek, Clay Cut Bayou, Jack s Bayou, Bayou Duplantier, and White Bayou 1955 USACE published a flood control study of the ARB and its tributaries 1964 USACE completed channel improvements to upstream portions of Amite River, and to lower portions of Comite River, Blind River, and Bayou Manchac; including construction of the Amite River Diversion Canal 1972 USACE completed a flood control study for the Amite River and Tributaries; evaluated four reservoir plans; two diversion plans; and four channel modifications 1978 FEMA (predecessor) undertook flood insurance studies for participating communities within the Amite River Basin 1981 Amite River Basin Drainage and Water Conservation District formed

41 Post-1983 Flood 1984 USACE completed a reconnaissance level study of a number of flood control alternatives and initiated feasibility studies on Comite Diversion, Darlington Reservoir, East Baton Rouge Parish Watershed, and in Livingston Parish 1984 LDOTD contracted engineering studies for development of the Darlington Reservoir 1990 Governor s Interagency Task Force produced recommendations for the Amite River Basin 1990 East Baton Rouge Parish completed a Comprehensive Land Use and Development Plan (known as the Horizon Plan); study addressed current and future drainage and flood control needs 1991 USACE completed feasibility study for Comite River Diversion Canal 1992 USACE completed feasibility study for Darlington Reservoir; found insufficient project benefits 1995 USACE completed feasibility study for channel improvement flood control measures in East Baton Rouge Parish 1995 City of Baton Rouge Department of Public Works completed a study of additional flood storage measures 1997 USACE completed feasibility study for channel improvement flood control measures in Livingston Parish

42 Post-1983 Flood 1997 ARBC and LDOTD completed additional studies to evaluate Darlington Reservoir recreational benefits 1997 USACE completed a re-evaluation of Darlington Reservoir benefits and costs; found sufficient benefits; further work on the project halted due to a lack of state and local sponsorship funds 1998 ARBC in conjunction with USGS and the LDOTD, LOEP, and the USACE established a Flood Warning System for the Amite River Basin 1999 Dr. Jim Cruise initiated development of real-time rainfall runoff and flood inundation forecasting model for ARBC ARBC/communities completed Amite River Basin Flood Hazard Mitigation Plan subsequent ARBC updates in 2002, 2005, and USACE completed post-feasibility design studies for the CRDC 2000 USACE completed Reconnaissance Study for Amite River Basin Ecosystem Restoration major river morphodynamic changes due to decades of lower Amite/Comite River channel improvements and up-river sand & gravel mining ARBC succeeded in getting property tax passed to provide local funding for CRDC 2001 CRDC Project Cooperative Agreement signed

43 Post-2001 TS Allison Flood 2001 USACE completed a Reconnaissance Study for Bayou Manchac Clearing and Snagging Project 2002 ARBC drafted Watershed Management Program 2002 ARBC evaluated potential issues with flood mapping resolution and use of Light Detection and Ranging (LIDAR) technology in conjunction with LSU 2002 USACE completed a Reconnaissance Study for Bayou Manchac Watershed Flood Damage Reduction and Ecosystem Restoration 2003 USACE began construction on Lilly Bayou Drop Structure for CRDC 2003 FEMA sponsored report reviewing earlier Amite River Basin Flood Hazard Mitigation Plan completed 2005 ARBC prepared Draft Floodplain Management Plan in support of the CRDC 2008 ARBC sponsored Comite River Basin H&H Study (HEC-RAS unsteady analysis of CRDC); considered impact of Comite River morphodynamics on CRDC 2009 Pontchartrain Levee District completed feasibility study (with H&H study) for flood mitigation alternatives for Upper Bayou Manchac (Above Ward s Creek junction)

44 Since Pontchartrain Levee District completed Amite River Basin Ecosystem Restoration Feasibility Study (with detailed H&H study of Amite and Comite River morphodynamics) 2010 Louisiana Coastal Protection and Restoration Authority completed H&H study for Restoring Lower Amite River (ARDC) Swamp 2011 USACE undertook additional H&H Study of the CRDC 2015 ARBC updated the Draft Floodplain Management Plan in support of the CRDC ARBC completed H&H study for Rehabilitating the ARDC Weir

45 Flood Insurance Rate Maps 100-yr flood zones East Baton Rouge Livingston Iberville Ascension

46 Flood Insurance Rate Maps 1. Currently the only source of ARB flood hazard information. 2. FEMA sponsors/funds through the National Flood Insurance Program (NFIP). 3. Developed in Flood Insurance Studies nearly 80 separate ARB FISs. 4. But NOT Full-Spectrum: emphasize single hazard level 100-yr 5. Even new FIRMs reflect critical NFIP limitations They do NOT show uncertainty Bias many updates are one-sided! Reduce flood zones 6. Most ARB FIS H&H studies are antiquated. FEMA re-mapped flood zones w/lidar DEMs, but didn t redo H&H. 7. No date set to redo ARB H&H/FIRMs.

47 FIRM Uncertainty Example of 100-yr Flood Zone Uncertainty Amite River at US ft NAVD88 08/14/ ft NAVD88 04/08/ ft NAVD88 FIRM 100-yr

48 FIRM Uncertainty Example of 100-yr Flood Zone Uncertainty Amite River at US ft NAVD88 08/14/ ft NAVD88 04/08/ ft NAVD88 FIRM 100-yr BUT >>1 ft of uncertainty for 100-yr flood at this location! Aug 16 at DS possibly 100-yr Flood! Remember Scientific Guesstimate

49 Comite River Diversion Canal USACE/DOTD/ARBC/EBR partners in planning/funding/construction. USACE design ~Qtr Century Old! Low B:C & has limited federal funding & delayed construction. Delay has been blamed for some of August 2016 flooding. New H&H analysis of CRDC been urged since 2008! Modernize modeling techniques Evaluate more rainfall scenarios Account for long-term river changes: erosion & sedimentation Look at distribution of growth in ARB and refine who benefits/how much. Needed to really understand potential impact of CRDC on August 2016 Flood.

50 Comite River Diversion Canal USACE 1994 Estimates of Downstream Flood Reductions

51 Comite River Diversion Canal USACE 1994 Estimates of Downstream Flood Reductions 1994 Modeling: VERY old technology (1D steady-state) Limited rainfall/flood scenarios similar to 83 Flood Rainfall in Mid-ARB is different scenario Declining benefit downstream Declining benefit with higher flood levels Nearly 25 years of changes to Comite/ Amite Rivers

52 Local Communities Some sponsor LOMRs but only to reduce 100-yr flood elevation! Developed Flood Hazard Mitigation Plans in late 1990s. Voluntary participation in NFIP Community Rating System (CRS). Incentivizes communities to adopt more stringent development/building regulations get lower NFIP premiums. Fill and construction can t impact surrounding 100-yr flood elevation. New construction elevations: Post-flood rebuilding requirements: 1. Threshold for substantial damage: < 50% >> 100-yr flood elevation 2. Flood zone applicability: not just 100-yr flood zone 3. Rebuild elevation: >>100-yr flood elevation BUT: Post-August Flood, local communities have rolled back their CRS rebuilding requirements!

53 Part IV. The Challenges of Regional Flood Risk Mitigation

54 Three Challenges: Educational Technical Political

55 Educational Challenges Citizens/Leaders are under informed re concepts of hazard/risk: There s never been that much water before. NFIP/FIRM False Binary Over emphasis of single hazard level Below/Above 100-yr zone Risk/No Risk Reinforced by lenders flood insurance requirements based on exposure to 100-yr flood Not Full-Spectrum Ignores uncertainty Grossly obsolete Need to understand $ risk over a 30-yr mortgage/lifetime!

56 Examples Probabilities for a 30-yr Duration: 50-yr flood (45.5%): flip a coin (50%); 100-yr flood (26.0%): draw a heart from a deck of cards (25%); 250-yr flood (11.3%): roll a 5 with a pair of dice (11.1%); 500-yr flood (5.8%): roll an 11 with a pair of dice (5.6%) 1,000-yr flood (3.0%): roll snake eyes with a pair of dice (2.8%) Greater than the chance of a house fire! Close to an 8% life-time chance! For multiple independent locations: 30% over a 50-yr period!

57 Real Flood Risk Full-Spectrum : 50 to 10,000-yr floods Total Flood Cost: structure, contents, cars, temporary housing, income, medical, pets, etc.

58 Real Flood Risk Basis for Flood Insurance Actuarial Cost In this Example: Average Annual Cost ~$2,000 Present Value ~$40,000

59 Real Flood Risk Basis for Flood Insurance Actuarial Cost In this Example: Average Annual Cost ~$2,000 Present Value ~$40,000

60 Educational Challenges Real Flood Risk is best way to inform ALL decisions: For individuals & businesses: Property investment decisions and risk management. For flood insurance companies: Coverage and premiums. For local governments: Floodplain regulations, building codes, development control, local neighborhood drainage improvements For regional flood authorities: River flood mitigation projects. Real Risk for wind, precipitation & other hazards has been around for decades!

61 Educational Challenges Cell phone App coming soon to provide Real Flood Risk for any home? See: The Flood Risk Game Real Flood Risk

62 Technical Challenges Basic Science of Real Flood Risk analysis long understood: H&H 2D hydrodynamics Statistics/joint probability analysis Risk assessment/actuarial $ Goal has been: Rigorous inundation analysis: Regional Scale + High Resolution Capture detailed floodplain H&H 1,000s of simulations to evaluate Full-Spectrum of hazards > 2000: dramatic evolution in Tools to provide Real Flood Risk Pushed by research for better analysis of coastal surge risk.

63 Technical Challenges State-of-the-Art: Big Data/Cloud: GIS layers DEMs, land cover, property structures/ values Computational tools for spatial analysis with GBs of data terrain feature evaluations Supercomputers: LSU Queen Bee Supercomputer 100s of CPUs Parallelized H&H model codes Data Management/Analysis: QA/QC & evaluate results from 1,000s of scenarios Joint Probability Analysis account for multiple factors influencing frequency of extreme floods Structure-by-Structure depth-damage assessment across an entire region

64 Technical Challenges State-of-the-Art will finally enable Real Flood Risk: 1. Full Spectrum of flood hazard & actuarial cost: For any individual property! For all properties in a region! 2. Better B:C assessments & prioritization of flood risk mitigation projects/programs. 3. Addressing degree of uncertainty in flood hazard/risk. 4. Assessing change assumptions: Climate trends/cycles Sea level rise Regional landscape conditions CPRA Coastal Louisiana Risk Assessment incorporates many SOA approaches Residential & infrastructure development

65 Technical Challenges SOA Push from Grassroots Private Sector Businesses trying to optimize decisions. Private Flood Insurance companies refining policies. Specialty flood hazard consultants.

66 Technical Challenges The Grassroots revolution in Real Flood Risk means Question is NOT IF BUT WHEN the revolution impacts everyone! Impact on residential property valuations likely to come from private sector in << decade: The App is Coming! Bond market will be looking at local flood risk and extent of insurance coverage for community bond ratings!

67 Political Challenges NFIP Obsolete/inadequate 50-year old NFIP flood risk policy framework. Decades of bad urban floodplain development policies driven by NFIP. Gross distortion of flood risk for floodplain property and thus property values! NFIP debt and suboptimal flood mitigation investments. Some communities want to leave NFIP! NFIP Limitations + SOA + Grassroots Revolution = Rise of Real Flood Risk + Private Flood Insurance Big changes coming for flood risk policy framework regardless of NFIP Reauthorization!

68 But Jurisdictional Mess Overlapping/conflicting/ossified/ underfunded roles/programs. Federal FEMA, Corps, USGS, NOAA/NWS, HUD. LA Department of Insurance/ DOTD/OCD/GOHSEP Local Parishes and Cities Absence of empowered regional, basin-focused flood agencies. Hampers: Making Real Flood Risk info widely available. Good decisions based on Real Flood Risk by all decision makers (homeowners, businesses, agencies) and hence community resiliency. Planning and implementing optimal mitigation measures. Enhancing No Adverse Impact for future floodplain development. Why haven t the ARBC and other basin-oriented authorities been effectively stood up to lead on Real Flood Risk issues?

69 Political Challenges Top priorities to adjust to Real Flood Risk: Cities/Parishes 1. Fix neighborhood/community drainage problems that impact local 100-yr hazard but have limited regional impact. Basin-Scale Agencies 1. Address home/business owners/lenders demand for accurate Real Flood Risk info conduct SOA flood hazard analyses. 2. Pursue cost-effective regional mitigation of Real Flood Risk paid for by reductions in basin Real Flood Risk i.e., lower flood insurance costs. Treat More Like Fire Risk! State: 1. Facilitate broad participation in flood insurance as key step in community resiliency, esp. with climate change. State/Federal: 1. Subsidize flood insurance affordability/equity from general revenue NOT by increasing cost of low/mod hazard policies! 2. Improve forecasting/evacuation for protecting lives.

70 Thank You! Questions? Discussion...