The Vegetation Challenge Sacramento, California August 28-29, 29, 2007

Transcription

1 The Vegetation Challenge Sacramento, California August 28-29, 29, 2007 David A. Pezza, P. E. U. S. Army Corps, Headquarters Engineering and Construction Chief, Civil Works Branch

2 ASCE Civil Engineering Magazine, Nov 2005 UNCLASSIFIED

3 Congressional Legislation UNCLASSIFIED Corps received $30M in the 3 rd Supplemental Act in FY06 Currently there is $10 million in the budget for FY07 to continue work The proposed WRDA also has a provision to create a National Levee Safety Program similar to the National Dam Safety Program

4 Federal Program PL and USACE Rehabilitation and Inspection Program National Flood Insurance Program Certification per 44 CFR Sponsor O&M responsibilities per 33 CFR Project Cooperation Agreements

5 Same Levee Two Levels of Care UNCLASSIFIED

6 Existing Policy and Guidance

7 Regional Variance, ER , 1, Section 22 UNCLASSIFIED 1. The safety, structural integrity, and functionality of the levee are retained, and; 2. Accessibility for inspection and flood fighting purposes are retained, and 3. The level of protection does not fall below the level necessary for levee certification under the National Flood Insurance Program if the levee is currently so certified, and; 4. The level of protection does not fall below the minimum permissible for PL acceptability

8 Overbuilt Levee Section

9 Engineering Manual , December 1972 UNCLASSIFIED

10 White Paper DRAFT FINAL WHITE PAPER Treatment of Vegetation within Local Flood-Damage-Reduction Systems 20 April 2007

11 SLIDE: 33 CFR 203, Subpart D Rehabilitation Assistance for Flood Control Works Damaged by Flood or Coastal Storm: The Corps Rehabilitation and Inspection Program UNCLASSIFIED In accordance with Section , in order for a flood control work to be eligible for Rehabilitation Assistance, it must be in an Active status at the time of damage from a flood or coastal storm event. To gain an Active status, on non-federal flood control work must meet certain engineering, maintenance, and qualification criteria, as determined by the Corps during an Initial Eligibility Inspection. To gain an Active status, Federal and non-federal control works must continue to meet inspection criteria set by the Corps, as determined by the Corps during a Continuing Eligibility Inspection. All flood control works not in an Active status are considered to be Inactive, regardless of whether or not they have previously received a Corps inspection, or Corps assistance

12 System Components Structural Components Levees Flood Walls Interior Drainage Systems Pump Stations Channels Non-Structural Components Operations and Maintenance Emergency supplies and equipment Flood Preparedness and Training Risk Reduction Measures

13 Inspection and Assessments Routine Inspection - verifies proper maintenance, owner preparedness, and component operation Periodic Inspection - verifies and evaluates operational adequacy, structural stability, and safety of the system Periodic Assessment - Combination of PI and potential failure mode and consequence analysis to prioritize risk assessments Risk Assessment - Determine residual risk of the levee system

14 Inspection Ratings for Components UNCLASSIFIED Acceptable - in satisfactory condition with no deficiencies, functions as intended during next flood event Minimally Acceptable - has one or more deficiencies, do not seriously impair the function during the next flood event Unacceptable - has one or more deficiencies, will seriously impair function during the next flood event

15 Ratings for Overall System Acceptable - all components rated acceptable, overall system condition rated as acceptable Minimally Acceptable- one or more components rated as Minimally Acceptable or Unacceptable, and engineering determination concludes unacceptable items would not prevent system from performing Unacceptable - One or more components rated as Unacceptable, would prevent system from performing as intended, or deficiencies not corrected within time frame not to exceed two years

16 Risk Reduction Measures Public Awareness and Risk Communication Improved Evacuation Increased Frequency/Focus on Inspections Warning System Stockpiling of Materials Require Flood Insurance

17 Risk Equation Pe x Pf x C = Risk Pe - Probability of Event Pf - Probability of Failure C Consequences (Life, Property, Habit) Risk The annual probability for such consequences

18 Minimum Safety Requirements UNCLASSIFIED The system must be safe, structurally stable and function under applied event loads; The system must remain accessible for inspection, maintenance, and flood fighting purposes; The system must meet minimum maintenance and operations standards; and The system must be periodically and continually reevaluated to address changes in hazard (flooding, seismic, and security) and changes in the state of the art in engineering and science.

19 Forces vs. Failure Modes Forces Failure Modes Static forces due to gravity Internal hydraulic forces due to hydraulic gradients Eternal hydraulic forces due to turbulent flow, wave action, or runoff Dynamic forces due to ground motions Slope instability in the form of deep-seated or shallow surface slides Through seepage Under seepage Overtopping Current and wave attack Surface erosion Liquefaction

20 Typical Failure Modes UNCLASSIFIED FLOODSIDE LANDSIDE FLOODSIDE LANDSIDE Flood water Levee BOIL Flood water Levee SLOUGH SEEPAGE Impervious Top Stratum Pervious Substratum Impervious Top Stratum Pervious Substratum UNDERSEEPAGE / BOIL SLOUGHING / SLIDE FLOODSIDE LANDSIDE FLOODSIDE Flood water EROSION Levee LANDSIDE Flood water Levee SEEPAGE Impervious Top Stratum Impervious Top Stratum Pervious Substratum EROSION OF LEVEE SLOPE Pervious Substratum THROUGH SEEPAGE PIPING

21 USACE Technical Guidance EM , Design and Construction of Levees, sections 4-4 and EM , Retaining Walls and Floodwalls, section EM , Environmental Engineering and Local Flood Control Channels, sections 4-8.d (4) and 5-1. EM , Guidelines for Landscape Planting and Vegetative Management at Floodwalls, Levees and Embankment Dams ER , Emergency Employment of Army Resources, Civil Emergency Management Program Flood Damage Reduction Inspection Report

22 Fragility Curve Food Elevation Traditional Fragility Curve Instant Failure True Fragility Curve Stress Deterioration Overtopping 0 Probability of Failure 1

23 Example of Unknowns in a Foundation UNCLASSIFIED Mechanism 3 & 4 through the foundation into foundation or dam

24 A Boil

25 Major Threats to Levees and Public Safety by Relative Risk UNCLASSIFIED Levee underseepage Bank erosion and toe scour Levee overtopping Levee seepage Levee encroachments and barriers Structural capacity/stability Burrowing animals Inappropriate vegetation on levees

26 Augusta Levee Georgia UNCLASSIFIED

27 Repair Evaluation Maintenance and Rehabilitation Research Program (REMR) UNCLASSIFIED

28 Bay Island

29 Vegetation Free Zone

30 Engineering and Science Observation Decades of documented and directly attributed deficiencies to woody vegetation (ex: 2005, Albuquerque Levees, Sacramento Levees) Correlation to failures in like structures: Air Force Academy Waste Lagoon Pond (1999) Kelly Barnes Dam Failure (1977) Experiment Impacts of Plants on Earthen Dams (FEMA 534, Sep 05) REMR documents EI-M-1.3 & 1.4 standards are justified by absence of data Forestry Strategies to Protect Floodplain Systems (USDA, 1991) concerns (engineering) must be addressed first

31 Flooding Fighting

32 Sandbag Usage For Flood Fighting UNCLASSIFIED Sandbags to raise levee Sandbags around the boil Boil Impervious Levee Semipervious - Impervious Topstratum Seepage Pervious Substratum Seepage

33 Vegetation, Science, and System Reliability Feature The Scorecard Seepage & Piping Windthrow Global Stability Inspection Flood Fighting Burrows Scour Protection Hydraulic Capacity Component Interface UNCLASSIFIED

34 Risk vs. Minimum Safety Requirements UNCLASSIFIED We do not trade off or marginalize minimum safety requirements through the use of risk informed approaches. Minimum safety requirements represent "go/no-go" decisions or thresholds after which satisfied, support use of risk informed tradeoffs. Risk does not replace but complements traditional and deterministic engineering standards, this is the essence of risk informed vice risk based approaches. There are no simple, numerical solutions from the use of risk because the use of experience and practice is essential to our profession and good decision making. Eric Halpin, Special Assistant for Dam and Levee Safety, U. S. Army Corps of Engineers, Headquarters

35 Challenges under PL Integrity of your system Constraints that prohibit effective maintenance and impinge on emergency operations during flood fights

36 Next Steps 1. Evaluate our existing public safety standards using engineering and science 2. Develop and implement a plan to transition from existing conditions to approve public standards

37 Areas that Need More Engineering and Science UNCLASSIFIED 15 ft Slurry Wall 15 ft 15 ft

38 Trees by SGT Joyce Kilmer AEF, 165th Infantry, U. S. Army, Killed in Action 1918 UNCLASSIFIED I think that I shall never see, a poem lovely as a tree, A tree whose hungry mouth is pressed, against the earth s sweet flowing breast, A tree that looks at God all day, and lifts her leafy arms to pray, A tree that may in Summer wear, a nest of robins in her hair, Upon whose bosom snow has lain, who intimately lives with rain, Poems are made by fools like me, but only God can make a tree.

39 Sustainable Design Levees are made by fools like me where even God lacks space to plant a tree