Presentation on theme: "HSDRRS Wave Overtopping Risk Reduction for Return Events Greater than 100 yr. By: John Monzon, P.E. Flood Protection Division Chief and Rickey Brouillette,"— Presentation transcript:
HSDRRS Wave Overtopping Risk Reduction for Return Events Greater than 100 yr. By: John Monzon, P.E. Flood Protection Division Chief and Rickey Brouillette, P.E. Flood Protection
Current HSDRRS designed to withstand 100 year events Minimal O vertopping (mostly waves) 100 yr. El.
Storms greater than a 100 year return will produce overtopping flow rates that may scour levees Overtopping from Storm Surge Overtopping from Large Waves 100 yr. El.
Methods for Risk Reduction Strengthening existing structures by armoring to reduce the risk of scour. Raise structures to reduce the overtopping rates and reduce the risk of scour. A combination of strengthening and Raising.
To reduce the risk of erosion by overtopping, the USACE focused their efforts on strengthening the earthen levees by Armoring.
Proposed Armoring Materials and Overtopping Performance Range PRELIMINARY PERFORMANCE RANGES MATERIALPERFORMANCE RANGE (CFS) EQUIVALENT WATER HEIGHT OVERTOPPING LEVEE (weir flow) (FT) BERMUDA GRASS0-10.5 ENHANCED GRASS0-1*0.5 HPTRM (Reinforced Mats) High Performance Turf Reinforcing Mat 1-40.5 - 1.1 ACB Articulated Concrete Block >4>1.1 *Estimated Value
Concerns with Armoring 1.While Reinforcing mats improve resiliency by hardening the levee, It does nothing to reduce the damages produced by overtopping. 2.Reinforcing mats materials have to be properly installed to avoid costly maintenance. 3.Reinforcing mats will have to be replaced every time a new lift is placed
Issue No. 1 1.While Reinforcing mats improve resiliency by hardening the levee, It does nothing to reduce the damages produced by overtopping. 0.002 0.0013 Kenner and Metairie West of Cleary
Reach J3- Water Elevation and Damages Water Surface Elevation and Resulting Damages from overtopping (No Fail, 50% Pumping Capacity) Excedence %Storm Event Water Surface Elevation (Ft) Water Depth (Vintage @ Williams) El. Appx -6.0 Damages, Average (2010 USD) 0.01000100-51 $ 96,000,000.00 0.00200500-24 $ 9,794,000,000.00 0.0013375006 $ 13,449,000,000.00
Water Surface Elevation and Resulting Damages from overtopping (SC2- No Fail, 50% Pumping Capacity) Excedence %Storm EventWater Surface Elevation (Ft) Water Depth (Armond S. of Airline) El. Appx 0.0 Damages, Average ( 2010 USD) 0.0100010044 $ 470,000,000.00 0.0020050055 $ 657,000,000.00 0.0013375066 $ 581,000,000.00 Reach SC2- Water Elevation and Damages
Water Surface Elevation and Resulting Damages from overtopping (JW4- No Fail, 50% Pumping Capacity) Excedence %Storm EventWater Surface Elevation (Ft) Water Depth (Harvey Blv.@ Engineers Rd.) Appx -5.0 Damages, Average ( 2010 USD) 0.01000100-6 $ 1,000,000.00 0.00200500-41 $ 364,000,000.00 0.00133750-32 $ 1,545,000,000.00 Reach JW4- Water Elevation and Damages
HPTRM can be difficult to install and maintain Issue No. 2 INSTALLATION OF TRM IN LAFITTE PEN LEVEE, JULY 2008 TRM “POP UP” PEN LEVEE, JULY 2011
Issue No. 3 HPTRM will have to be replaced every time a new lift is placed. This is a costly and wasteful proposition given the short rate of return. 20152027 2045 V Line levee East of Vertex Lift Schedule Note: Design Grade elevation increases with time to compensate for relative sea level rise which includes subsidence.
Based on the lift schedule there are levees where grass and reinforcement mats will provide adequate resiliency due to low overtopping rates. Where a lift schedule places the next lift in less than 10 years we believe the USACE should either: 1.Place an additional lift now with reinforcing mats to move the next lift beyond 10 years. 2.Harden the levee crown with asphalt and place a concrete gravity wall or I-Wall to reduce the overtopping rates to less than 1 cfs. Preliminary estimates by OCPR show that an additional 3 ft. above design grade can reduce overtopping rates to less than 1 cfs even for a 750 yr. event. Well within the tolerance of grass. Possible Alternatives to Improving Resiliency
Place Additional Lift Design Elevation Construction Elevation Additional Elevation TRM Additional lift moves next lift beyond 10 years. TRM and additional height provides resiliency.
Hardened Crown with Gravity Wall “Green Alternative” Concrete wall provides additional height required to reduce overtopping rates to less than 1cfs. Asphalt crown provides Erosion protection. When additional lift is needed concrete wall is removed and asphalt milled and recycled. After lift is placed new asphalt is placed and concrete wall replaced. Asphalt
Earthen Levee with added height, concrete pad and Pyramat® reinforcing mat
Risk can be managed by making the system more reliable or by reducing the consequences of failure. …Reliability can be influenced by strengthening existing structures (Armoring) or by adding additional protection (raising levees)… USACE Risk Analyss of Armoring Alternatives, Draft Report, 16 June 2011 RISK = HAZARD PROBABILITY x VULNERABILITY x CONSEQUENCES It is important to evaluate both scenarios in order to create the best level of Risk Reduction
Authorization & Appropriation 4 th and 6 th supplemental regarding inclusion of hurricane and storm damage reduction and flood damage reduction in the Greater New Orleans and surrounding areas. Both supplementals incorporate 33 USC § 701n by reference. The Fourth and Sixth Supplemental Appropriations include $170,000,000 and $459,000,000, respectively, for armoring levees in the greater New Orleans area.
Authorization & Appropriation Neither supplemental defines “armoring.” However, both clearly define the purpose of the overall appropriations (of which the armoring appropriations are an element) as being to reduce hurricane and storm damage. Both supplementals incorporate 33 USC § 701n by reference. This statute provides (in pertinent part) as follows: – (a)(1) There is hereby authorized an emergency fund to be expended in preparation for emergency response to any natural disaster, in flood fighting and rescue operations, or in the repair or restoration of any flood control work threatened or destroyed by flood, including the strengthening, raising, extending, or other modification thereof as may be necessary in the discretion of the Chief of Engineers for the adequate functioning of the work for flood control, or...