7 Sep 2021

Sabine Pass to Galveston Bay, TX Pre-Construction, Engineering and Design (PED): Coastal Storm Surge and Wave Hazard Assessment: Report 1 – Background and Approach

Abstract: The US Army Corps of Engineers, Galveston District, is executing the Sabine Pass to Galveston Bay Coastal Storm Risk Management (CSRM) project for Brazoria, Jefferson, and Orange Counties regions. The project is currently in the Pre-construction, Engineering, and Design phase. This report documents coastal storm water level and wave hazards for the Port Arthur CSRM structures. Coastal storm water level (SWL) and wave loading and overtopping are quantified using high-fidelity hydrodynamic modeling and stochastic simulations. The CSTORM coupled water level and wave modeling system simulated 195 synthetic tropical storms on three relative sea level change scenarios for with- and without-project meshes. Annual exceedance probability (AEP) mean values were reported for the range of 0.2 to 0.001 for peak SWL and wave height (Hm0) along with associated confidence limits. Wave period and mean wave direction associated with Hm0 were also computed. A response-based stochastic simulation approach is applied to compute AEP runup and overtopping for levees and overtopping, nappe geometry, and combined hydrostatic and hydrodynamic fluid pressures for floodwalls. CSRM structure crest design elevations are defined based on overtopping rates corresponding to incipient damage. Survivability and resilience are evaluated. A system-wide hazard level assessment was conducted to establish final recommended system-wide CSRM structure elevations.

24 Aug 2021

Expert Elicitation Workshop for Planning Wetland and Reef Natural and Nature-Based Features (NNBF) Futures

Abstract: This special report discusses the outcomes of a September 2019 workshop intended to identify barriers to the consideration and implementation of natural and nature-based features (NNBF) in US Army Corps of Engineers (USACE) civil works projects. A total of 23 participants representing seven USACE districts, the US Army Engineer Research and Development Center (ERDC), and the University of California–Santa Cruz met at USACE’s South Atlantic Division Headquarters in Atlanta, Georgia, to discuss how to facilitate the implementation of NNBF into USACE project planning for wetlands and reefs using six categories: (1) site characterization, (2) engineering and design analysis, (3) life-cycle analysis, (4) economic analysis, (5) construction analysis, (6) and operation and maintenance (and monitoring). The workshop identified seven future directions in wetland and reef NNBF research and development: • Synthesize existing literature and analysis of existing projects to better define failure modes. • Determine trigger points that lead to loss of feature function. • Identify performance factors with respect to coastal storm risk management (CSRM) performance as well as ecological performance. • Focus additional research into cobenefits of NNBF. • Quantify the economic life-cycle costs of a project. • Improve technology transfer with regards to NNBF research and topics.

13 Aug 2021

Geotechnical Inspection and Technical Review of Santa Margarita River Marine Corps Air Station Levee, U.S. Marine Corps, Camp Pendleton, CA, 19-20 November 2019

Abstract: This report describes activities performed, results obtained, and conclusions made from an independent technical review of past levee inspections and the proposed remediation plan for the Santa Margarita Levee that surrounds the U.S. Marine Corps Air Station (MCAS) Camp Pendleton. In support of the technical review, ERDC personnel performed a supplemental levee inspection on 19 and 20 November 2019 with MCAS personnel. Previous levee inspections had rated the levee system as Unacceptable due to unwanted vegetation encroaching on the levee right-of-way, which prevents full inspection during flooding. Concerns were raised by the U.S. Fish and Wildlife (USFW) about environmental impacts of the proposed remediation measures and the necessity of such actions. USFW personnel requested an engineering review from an independent party, and ERDC was tasked with performing the independent technical review. The following special report describes the tasks performed and results obtained from the independent technical review.

12 Aug 2021

Rapid Tidal Reconstruction with UTide and the ADCIRC Tidal Database

Abstract: The quantification of storm surge is vital for flood hazard assessment in communities affected by coastal storms. The astronomical tide is an integral component of the total still water level needed for accurate storm surge estimates. Coastal hazard analysis methods, such as the Coastal Hazards System and the StormSim Coastal Hazards Rapid Prediction System, require thousands of hydrodynamic and wave simulations that are computationally expensive. In some regions, the inclusion of astronomical tides is neglected in the hydrodynamics and tides are instead incorporated within the probabilistic framework. There is a need for a rapid, reliable, and accurate tide prediction methodology to provide spatially dense reconstructed or predicted tidal time series for historical, synthetic, and forecasted hurricane scenarios. A methodology is proposed to combine the tidal harmonic information from the spatially dense Advanced Circulation hydrodynamic model tidal database with a rapid tidal reconstruction and prediction program. In this study, the Unified Tidal Analysis program was paired with results from the tidal database. This methodology will produce reconstructed (i.e., historical) and predicted tidal heights for coastal locations along the United States eastern seaboard and beyond and will contribute to the determination of accurate still water levels in coastal hazard analysis methods.

1 Jul 2021

Coastal Texas Protection and Restoration Feasibility Study: Coastal Texas Flood Risk Assessment: Hydrodynamic Response and Beach Morphology

Abstract: The US Army Corps of Engineers, Galveston District, is executing the Coastal Texas Protection and Restoration Feasibility Study coastal storm risk management (CSRM) project for the region. The project is currently in the feasibility phase. The primary goal is to develop CSRM measures that maximize national net economic development benefits. This report documents the coastal storm water level and wave hazard, including sea level rise, for a variety of flood risk management alternatives. Four beach restoration alternatives for Galveston Island and Bolivar peninsula were evaluated. Suites of synthetic tropical and historical non-tropical storms were developed and modeled. The CSTORM coupled surge-and-wave modeling system was used to accurately characterize storm circulation, water level, and wave hazards using new model meshes developed from high-resolution land and sub-aqueous surveys for with- and without-project scenarios. Beach morphology stochastic response was modeled with a Monte Carlo life-cycle simulation approach using the CSHORE morphological evolution numerical model embedded in the StormSim stochastic modeling system. Morphological and hydrodynamic response were primarily characterized with probability distributions of the number of rehabilitations and overflow.

15 Jun 2021

Red River Structure Physical Model Study: Bulkhead Testing

Abstract: The US Army Corps of Engineers, St. Paul District, and its non-federal sponsors are designing and constructing a flood risk management project that will reduce the risk of flooding in the Fargo-Moorhead metropolitan area. There is a 30-mile long diversion channel around the west side of the city of Fargo, as well as a staging area that will be formed upstream of a 20-mile long dam (referred to as the Southern Embankment) that collectively includes an earthen embankment with three gated structures: the Diversion Inlet Structure, the Wild Rice River Structure, and the Red River Structure (RRS). A physical model has been constructed and analyzed to assess the hydraulic conditions near and at the RRS for verification of the structure’s flow capacity as well as optimization of design features for the structure. This report describes the modeling techniques and instrumentation used in the investigation and details the evaluation of the forces exerted on the proposed bulkheads during emergency operations for the RRS.

14 May 2021

Remotely Sensed Habitat Assessment of Bottomland Hardwood and Swamp Habitat: West Shore Lake Pontchartrain Hurricane Storm Damage Risk Reduction System Potential Impact Area

Purpose: This study used remote sensing techniques to identify and assess the current condition of bottomland hardwood (BLH) and swamp habitats within the West Shore Lake Pontchartrain (WSLP) hurricane storm-damage risk reduction system (HSDRRS) project area. This effort provides baseline knowledge of the location and quality of these habitats prior to the construction of the WSLP HSDRRS project. The resultant products will assist the USACE—New Orleans District (MVN) by informing ecosystem decision-making related to environmental assessments.

12 May 2021

Wintertime Snow and Precipitation Conditions in the Willow Creek Watershed above Ririe Dam, Idaho

ABSTRACT:  The Ririe Dam and Reservoir project is located on Willow Creek near Idaho Falls, Idaho, and is important for flood risk reduction and water supply. The current operating criteria is based on fully storing a large winter runoff event. These winter runoff events are generally from large storm events, termed atmospheric rivers, which produce substantial precipitation. In addition to the precipitation, enhanced runoff is produced due to frozen soil and snowmelt. However, the need for additional water supply by local stakeholders has prompted the U.S. Army Corps of Engineers to seek to better understand the current level of flood risk reduction provided by Ririe Dam and Reservoir.  Flood risk analysis using hydrologic modeling software requires quantification of the probability for all of the hydrometeorologic inputs. Our study develops the precipitation, SWE, and frozen ground probabilities that are required for the hydrologic modeling necessary to quantify the current winter flood risk.

12 May 2021

Automated Characterization of Ridge-Swale Patterns Along the Mississippi River

Abstract: The orientation of constructed levee embankments relative to alluvial swales is a useful measure for identifying regions susceptible to backward erosion piping (BEP). This research was conducted to create an automated, efficient process to classify patterns and orientations of swales within the Lower Mississippi Valley (LMV) to support levee risk assessments. Two machine learning algorithms are used to train the classification models: a convolutional neural network and a U-net. The resulting workflow can identify linear topographic features but is unable to reliably differentiate swales from other features, such as the levee structure and riverbanks. Further tuning of training data or manual identification of regions of interest could yield significantly better results. The workflow also provides an orientation to each linear feature to support subsequent analyses of position relative to levee alignments. While the individual models fall short of immediate applicability, the procedure provides a feasible, automated scheme to assist in swale classification and characterization within mature alluvial valley systems similar to LMV.

14 Oct 2020

Red River Structure Physical Model Study

Abstract: A proposed Red River Structure (RRS), intended to function as one of three gated structures comprising the Fargo-Moorhead Metropolitan Area Flood Risk Management Project, was tested in a general physical model. A 1:40 Froude-scale was applied to model the structure, engineered channels, existing bathymetry/topography in the Red River and overbank areas, and the proposed Southern Embankment. The physical model was used to ensure that the RRS could pass at least 104,300 cfs during the Probable Maximum Flood while maintaining a maximum pool water surface elevation of 923.5 ft. The physical model was also utilized to optimize the approach structure, stilling basin, retaining walls, and erosion protection designs. The physical modeling effort resulted in an optimized stilling basin wall, retaining wall, and end sill geometry/configuration where erosive conditions were not observed outside and adjacent to the stilling basin. Properly designed riprap (St. Paul District’s R470 gradation) proved to be successful in protecting the proposed RRS from potential scour downstream. The modified approach wall design proved to be successful in creating safe approach flow conditions as well as acceptable flow separation patterns. It is recommended that Alternative 3 be the design used going forward.