20 Aug 2020

PUBLICATION NOTICE: Utilizing Stream Flows to Forecast Dredging Requirements

Abstract: In recent years, the United States Army Corps of Engineers (USACE) has spent an average of approximately a billion dollars annually for navigation channel maintenance dredging. To execute these funds effectively, USACE districts must determine which navigation channels are most in need of maintenance dredging each year. Traditionally, dredging volume estimates for Operations and Maintenance budget development are based on experiential knowledge and historic averages, with the effects of upstream, precipitation-driven streamflows considered via general-rule approximations. This study uses the Streamflow Prediction Tool, a hydrologic routing model driven by global weather forecast ensembles, and dredging records from the USACE Galveston District to explore relationships between precipitation-driven inland channel flow and subsequent dredged volumes in the downstream coastal channel reaches. Spatially based regression relationships are established between cumulative inland flows and dredged volumes. Results in the test cases of the Houston Ship Channel and the Sabine-Neches Waterway in Texas indicate useful correlations between the computed streamflow volumes and recorded dredged volumes. These relationships are stronger for channel reaches farther inland, upstream of the coastal processes that are not included in the precipitation-driven hydrologic model.

11 Aug 2020

PUBLICATION NOTICE: Post-Project Monitoring of a Navigation Solution in a Dynamic Coastal Environment, Smith Island, Maryland: Year One of Post-Project Monitoring

Abstract: In 2018, jetties and a sill were constructed by the US Army Corps of Engineers (USACE) adjacent to the Sheep Pen Gut Federal Channel at Rhodes Point, Smith Island, Maryland. These navigation improvements were constructed under Section 107 of the Continuing Authorities Program. Material dredged for construction of the navigation structures and realignment of the channel were used to restore degraded marsh. Following construction and dredging, 1 year of post-project monitoring was performed to evaluate the performance of navigation improvements with respect to the prevention of shoaling within the Sheep Pen Gut channel, shoreline changes, and impacts to submerged aquatic vegetation (SAV). Given the short period of record after the completion of the navigation improvements, it was difficult to draw conclusions regarding stability of the channel, structures, and shoreline. Therefore, this report documents methodology and baseline conditions for monitoring, except for SAV, which was found to be potentially impacted by construction. A second year of monitoring was funded by the USACE Regional Sediment Management Program for fiscal year 2020. Findings can be used to inform plan formulation and design for USACE navigation projects by illuminating considerations for placement of structures to prevent shoaling and by informing SAV management decisions.

30 Jul 2020

PUBLICATION NOTICE: Erosion Thresholds and Rates for Sand-Mud Mixtures

Abstract: Differences in erosion behavior of non-cohesive and cohesive sediments are widely recognized. In many natural environments, sand and mud are not completely separated and occur as mixtures. Significantly less research has been conducted on the erosion behavior of sand-mud mixtures compared to the separate treatment of sand and mud erosion. Sedflume erosion experiments were conducted on sand-mud mixtures with varying mud content to define the relationships between mud content, critical stress for erosion (τc), and erosion rate. Sand-mud mixtures were prepared with three mud sources: (1) non-swelling clay (kaolinite), (2) swelling clay (kaolinite/bentonite), and (3) a swelling, natural mud from the Mississippi River. Test results showed that critical shear stresses of the mixed sediments departed from that of pure sand with mud fractions on the order of 2% to 10%. Peak τc was observed between 30% to 40% mud content, with swelling muds achieving a ten-fold increase in τc while a five-fold increase in τc was measured for kaolinite. Additionally, this study demonstrated that the introduction of small amounts (≤5%) of mud to sand reduced erosion rates by a factor of 10 to 100. This observed abatement of erosion rate has implications for the use of dredged materials in civil and environmental engineering projects.

10 Jun 2020

PUBLICATION NOTICE: Nearshore Placement Workshop 2019: Sediment Nourishment of the Nearshore Environment

Abstract: The Coastal Inlets Research Program and the Regional Sediment Management Program co-sponsored the 2019 Nearshore Placement Workshop. Thirty-four participants from the US Army Engineer Research and Development Center (ERDC) and numerous districts met in Vicksburg on January 29–30, 2019, as a part of the workshop. This workshop was convened to facilitate discussions on concerns districts face regarding nearshore placements from resource agencies and stakeholders, challenges to placing sediment in the nearshore, and future research needs. The workshop included ERDC presentations on the state of the science regarding nearshore placements; specific implementations of nearshore placements within various US Army Corps of Engineers districts; break-out-style discussions on nearshore placement challenges and potential paths forward; and group discussions on metrics for success, quantification of benefits, Statements of Need (SON), and research priorities. A few of the major recurring themes throughout the workshop were the importance of monitoring, concerns over the fate of fine-grained sediment, and difficulties conveying the benefits of nearshore placements to a wide range of audiences. The workshop culminated in a discussion of possible SON to be put forth to the ERDC research and development community. This special report describes the discussions and outcomes of the 2019 Nearshore Placement Workshop.