30 Aug 2022

Legacy Datums and Changes in Benchmark Elevation through Time at the Old River Control Structure, Louisiana

Abstract: Vertical datums used in the study area at the Old River Control Structure in southern Louisiana have involved Memphis Datum, Mean Gulf Level, Mean Sea Level, Mean Sea Level Datum of 1929, National Geodetic Vertical Datum of 1929, and the North American Vertical Datum of 1988. The focus of this study was to examine historic benchmarks in the study area to determine the magnitude of elevation changes associated with the different legacy datums that have been used by the US Army Corps of Engineers. Comparison of elevation values across these legacy datums has involved examining historic hydrographic surveys, compiling a list of known benchmarks from these surveys, and comparing their elevation values against publications involving spirit-leveling surveys from the Lower Mississippi Valley and the National Geodetic Survey database for benchmarks. This study describes the history of legacy datums, floodplain geology at the Old River Control Structure, potential subsidence impacts affecting the benchmarks, methods for identification and tracking benchmarks, and the results obtained from this study.

9 Feb 2022

Implementation of Flexible Vegetation into CSHORE for Modeling Wave Attenuation

Abstract: This technical report presents the new numerical modeling capabilities for simulating wave attenuation and mean water level changes through flexible vegetation such as smooth cordgrass in coastal and marine wetlands. These capabilities were implemented into the Cross-SHORE (CSHORE) numerical model. The biomechanical properties of vegetation such as dimensions, flexibility, and bending strength are parameterized in terms of the scaling law. Correspondingly, a new formulation of the vegetation drag coefficient, CD, is developed using field data from a salt marsh in Terrebonne Bay, LA, by considering spatially varying effective stem and blade heights of species. This report also presents a general procedure for using the model to simulate hydrodynamic variables (i.e., waves, currents, mean water levels) at vegetated coasts, which are used to quantify the effects of wave attenuation and reduction of surge and runup due to vegetation. Preliminary model validation was conducted by simulating a set of laboratory experiments on synthetic vegetation, which mimicked the flexibility of Spartina alterniflora. The validation results indicate that the newly developed vegetation capabilities enable CSHORE to predict changes of wave heights and water levels through marshes by considering species-specific biomechanical features. The model is also applicable to assess vegetation effectiveness against waves and surges.

25 Aug 2021

Hydrologic Analysis of Field Delineated Ordinary High Water Marks for Rivers and Streams

Abstract: Streamflow influences the distribution and organization of high water marks along rivers and streams in a landscape. The federal definition of ordinary high water mark (OHWM) is defined by physical and vegetative field indicators that are used to identify inundation extents of ordinary high water levels without any reference to the relationship between streamflow and regulatory definition. Streamflow is the amount, or volume, of water that moves through a stream per unit time. This study explores regional characteristics and relationships between field-delineated OHWMs and frequency-magnitude streamflow metrics derived from a flood frequency analysis. The elevation of OHWM is related to representative constant-level discharge return periods with national average return periods of 6.9 years using partial duration series and 2.8 years using annual maximum flood frequency approaches. The range in OHWM return periods is 0.5 to 9.08, and 1.05 to 11.01 years for peaks-over-threshold and annual maximum flood frequency methods, respectively. The range of OHWM return periods is consistent with the range found in national studies of return periods related to bankfull streamflow. Hydraulic models produced a statistically significant relationship between OHWM and bank-full, which reinforces the close relationship between the scientific concept and OHWM in most stream systems.

30 Jul 2020

PUBLICATION NOTICE: Investigation of Shoaling in the Federal Navigation Channel, Waukegan Harbor, Illinois

Abstract: Persistent and excessive shoaling occurs in the Outer Harbor and Approach Channel of the Waukegan Harbor, Illinois. This report describes a numerical modeling study performed for the US Army Corps of Engineers, Chicago District, to evaluate the existing harbor and 11 structural alternatives for three crest elevations. This report provides details of numerical modeling study, analysis of field data, and estimates of shoaling. The focus of the study is the investigation of a variety of structural solutions intercepting and/or diverting sediments to reduce shoaling in the navigation channel. These include breakwaters, groins, spurs, and structural extensions with varying length and crest elevation connecting to the north beach and existing north breakwater. Estimates of both shoaling volume and height are developed with and without project using an integrated wave-flow-sediment transport numerical modeling approach. Quantitative reduction estimates are provided for each structural alternative investigated.

28 Apr 2020

PUBLICATION NOTICE: Lower Columbia River Adaptive Hydraulics (AdH) Model: Development, Water Surface Elevation Validation, and Sea Level Rise Analysis

Abstract: A numerical model of the Lower Columbia River, validated to water surface elevations, has been generated using the Adaptive Hydraulics (AdH) code. The model boundary conditions include an ocean tidal boundary and five inflows: the Lewis, Cowlitz, Willamette, and Sandy Rivers, and the Columbia River at Bonneville Lock and Dam. The model, which spans approximately 146 river miles, accurately reproduces water surface elevations measured in the field at several locations along the model domain. An examination of the AdH model’s Friction Library was also conducted. The Friction Library was used in this application to estimate the effects of pile dikes. Rather than model individual piles in the model mesh, the piles were modeled using the Friction Library’s submerged vegetation material type. Through testing of this application, it was determined that the Friction Library approach, which enhances model run time and efficiency, can accurately reproduce the global effects of pile dike fields. Additionally, the validated model was used to analyze three sea level rise (SLR) scenarios, which correspond to predicted SLR at Astoria, OR, at 50, 75, and 100 years from the present (0.5 meter [m], 1.0 m, and 1.5 m, respectively).