H&H Archives

Simulating Compound Flooding During Hurricane Harvey with AdH

Simulating Compound Flooding During Hurricane Harvey with AdH Harris County, Texas DCCM was tasked by the USACE ERDC Coastal Hydraulics Laboratory to utilize and test an in-development version of the Adaptive Hydraulics Model (AdH) software to complete a monolithic simulation of Hurricane Harvey compound flooding that occurred in August 2017. Many efforts investigating the effects of compound flooding have relied on discrete models that simulate each flooding process separately. Consequently, they fail to mechanistically account for the complex interaction of multiple flood processes and the resulting impact on hazard estimates. Novel capabilities of AdH enable economical simulations of very large model domains while providing a high-resolution description of flood hazards in two dimensions. AdH provides the capability to simultaneously implement spherical coordinates and solve the shallow water equations and diffusive wave equations within a simulation. The combination of these capabilities makes AdH an effective model to simulate rainfall, overland flow, and storm surge to produce estimates that account for the interacting effects of pluvial, fluvial, and coastal flooding. Model terrain derived from LiDAR provided a high-resolution description of topography and large river channel bathymetry was resolved. Spatially and temporally variable rain rates and wind fields within the model resolved heterogenic storm characteristics. Model results were compared to stage and discharge time series observations at over 30 locations throughout Harris County and Galveston Bay. Modeled peak stages are within 1 m of observed peaks at more than 80% percent of the stations. The methods presented here can serve as a template for estimating flood hazards that result from compound flood events, and the results have documented the ability to mechanistically account for the interacting effects of multiple flood processes with a 2-D hydrodynamic model. At a Glance $168,500 Project Cost Markets Water Government Services Water & Wastewater

Artesian Slough Hydraulic Model and Closure Structure Conceptual Design

Artesian Slough Hydraulic Model and Closure Structure Conceptual Design Santa Clara County, California DCCM was contracted by the USACE San Francisco District to complete a hydraulic analysis and conceptual design for a water control structure on Artesian Slough. The San Jose – Santa Clara Regional Wastewater Facility (SJRWF) discharges effluent to the upper end of Artesian Slough, which terminates in South San Francisco Bay. An engineered levee is proposed to cross Artesian Slough and a gated outfall structure is required at the levee crossing to allow SJRWF effluent discharges to pass while protecting areas behind (south) the levee during extreme high tide events. A 2D HEC-RAS model was constructed representing the existing site conditions and calibrated to observed water level data above and below the SJRWF weir. A 1D model was also developed and calibrated for rapid simulations of various closure culvert designs. With-project conditions (WPC) 2D and 1D models were developed. The 1D WPC model was utilized to perform the closure design analysis. Sea-level rise (SLR) estimates were computed for the area based on the Coyote Creek tide gage and the USACE high SLR curve. The models were run for current and year-50 tidal signals, adjusted by the SLR curve. A total opening area of 210 square feet was selected to minimize the increase in water surface elevations upstream of the structure while considering cost-efficiency. The conceptual design was informed by the hydraulic analysis and looking ahead to maximize cost efficiency, be readily constructable, and minimize maintenance procedures and costs. It consists of six 72-inch by 70-inch culverts for a total opening of 210 square feet. The conceptual design has two sets of 3 culverts spaced closely together near each wing of the closure, with staggered outlets turned 90-degrees inward, which improves construction and maintenance efficiency. The conceptual design was translated to the 2D HEC-RAS model and run for six cases of varied tidal conditions, SJRWF outflow, and sea level. The water level results from the 2D HEC-RAS model were modified for areas above closure structure to account for the 90-degree bends recommended in the conceptual design. The water level, velocity, and shear stress results from the cases tested in the 2D model of the conceptual design were used to make conclusions regarding closure operations and erosion potential. At a Glance $170,000 Project Cost Markets Water Government Services Water & Wastewater

Upper Mississippi River Dogtooth Island Peninsula Sediment Transport Study

Upper Mississippi River Dogtooth Island Peninsula Sediment Transport Study Thebes, Illinois, to Birds Point, Missouri DCCM completed a hydrodynamic and sediment-transport study to assess the risk of the Mississippi River forming a cutoff across the Dogtooth Island Peninsula following the Len Small Levee breach. The team developed a high-resolution, two-dimensional Adaptive Hydraulics model covering the Upper Mississippi River from Thebes, Illinois, to Birds Point, Missouri. The model evaluated three terrain conditions representing the levee before the 2016 breach, immediately following the breach, and after the 2017 flood. It was calibrated using data from the 2011, 2015–2016, and 2017 floods, with a focus on flows exceeding 400,000 cubic feet per second. Nine conditions were analyzed to evaluate floodplain shear stress, flow patterns, and sediment movement. The model also assessed structural and nonstructural alternatives, including an overflow weir, revetment closure, kicker dike, and grade-control improvements, to help USACE manage flow and sediment across the peninsula. At a Glance 400,000+ CFS High-Flow Model Calibration Markets Water Government Environmental Services Water & Wastewater

Design Services for Turpentine Run

Design Services for Turpentine Run U.S. Virgin Islands Turpentine Run, the only perennial stream on St. Thomas, experiences significant flooding due to intense rainfall, steep topography, and shallow soils. The Nadir neighborhood and surrounding area have endured flooding from Hurricane Maria, tropical storms, and other major rainfall events over the past 50 years. DCCM provided hydraulic modeling, analysis, and design support for improvements intended to protect the community from a 25-year storm event. The team conducted field investigations and gathered local flood-history information, including observed high-water marks. HEC-HMS was used to model watershed runoff for 25- and 100-year storm events, while a two-dimensional HEC-RAS model evaluated existing and proposed hydraulic conditions. The design focused on safely routing approximately 8,000 cubic feet per second through a constrained corridor between a roadway and the neighborhood, beneath a bridge, through dense vegetation, and ultimately to the sea. The analysis also informed streambed and bank protection, riprap sizing, and the evaluation of sea-level rise impacts. DCCM performed flood-frequency and hydrologic-hazard analyses to evaluate water-surface elevations, uncertainty, and residual risk under existing and proposed conditions. Multiple design alternatives were modeled and compared with computational fluid dynamics results to optimize performance. The findings supported USACE’s risk analysis and development of a Risk-Informed Design for the project. At a Glance 8,000 CFS Design Flow $93 million Estimated Construction Cost Markets Water Government Environmental Services Water & Wastewater

EFDC+ Salinity Modeling for Jacksonville Harbor

EFDC+ Salinity Modeling for Jacksonville Harbor Jacksonville, Florida With the expansion of the Panama Canal, ocean-going cargo vessels have increased in size to improve efficiency and carrying capacity. In order to accommodate the increasing drafts of these ships. Channel deepening projects can cause salinity intrusion into freshwater portions of the river system resulting in significant water quality impacts to the ecosystem. A coarse-grid model of a portion of the St. Johns River was originally developed for the Jacksonville Harbor Deepening Project Feasibility Study. DCCM was contracted by the Jacksonville District USACE to develop, calibrate and validate a more comprehensive and representative hydrodynamic and salinity water quality model of the Jacksonville Harbor. The model incudes 121 miles of the St. Johns River, adjacent wetlands and freshwater tributaries. The newly calibrated and expanded 3-D hydrodynamic model was developed using a newly developed version of the Environmental Fluid Dynamics Code (EFDC) and was used to evaluate the impacts of the channel deepening on salinity intrusion and stratification in the St. Johns River. The new multiprocessor version of EFDC was used to improve runtimes and the SIGMA-ZED vertical layering option within the gridding package was used to improve computational efficiency and the simulation of vertical stratification. In order to assess navigation channel modification impacts to circulation processes and salinity in the St Johns River, DCCM performed two simulations covering a 5 year-long period (2017-2022). The first simulation represented the existing channel bathymetry without deepening and the second simulation included the with-project (channel deepened) condition. Simulated water levels, flows, velocity, water age as a measure of residence time, and salinity were compared for each simulation. Numerous diagnostic simulations were conducted to evaluate contributions to increased salinity, difference between project induced salinity increases and salinity increases related to other processes such as freshwater flow variations, subtidal variations, offshore salinity variations, sea level rise, variations of wind velocities and directions. To improve the simulation of freshwater contributions from the adjacent watershed, DCCM evaluated and recalibrated existing HSPF watershed model. DSLLC processed USGS flow and groundwater data for the HSPF model, recalibrated the HSPF model and extended the simulation period. DSLLC then linked the recalibrated hydrologic model results as input to the Jacksonville Harbor 3D EFDC hydrodynamic model to simulate a more natural stormwater response from freshwater tributaries. The model results with the new EFDC Pre-Project model showed improved calibration and much shorter runtimes. At a Glance 121 miles 3D Hydrodynamic Model Domain 165 tributaries HSPF Hydrologic Model Area Markets Water Government Environmental Services Water & Wastewater