3 Jun 2021

Elevation of underlying basement rock, Ogdensburg Harbor, NY

Abstract: Over six linear miles of shallow acoustic reflection geophysical data were collected in an 800 ft by 300 ft survey region at Ogdensburg Harbor, Ogdensburg, NY. To better accommodate modern commercial vessels and expand the harbor’s capacity, the current navigable depth of -19 ft Low Water Depth (LWD) needs to be increased to -28 ft LWD, and an accurate map of the nature of the riverbed material (e.g., unconsolidated sediment, partially indurated glacial till, or bedrock) is required to effectively plan for removal. A total of 28 boreholes were previously collected to map the stratigraphy, and the effort revealed significant spatial variability in unit thickness and elevation between adjacent boreholes. To accurately map this variable stratigraphy, chirp sub-bottom profiles were collected throughout the region, with an average line spacing of 13 ft. These sub-bottom data, validated and augmented by the borehole data, resulted in high-resolution spatial maps of stratigraphic elevation and thickness for the study area. The data will allow for more accurate assessment of the type and extent of different dredging efforts required to achieve a future uniform depth of -28 ft LWD for the navigable region.

24 Sep 2020

Study of Sand Boil Development at Kaskaskia Island, IL, Middle Mississippi River Valley

Abstract: Mississippi River flooding in 2013 and 2016 caused severe underseepage and development of several medium to large high-energy sand boils behind the landside levee toe at Kaskaskia Island, IL. This levee system is located between St. Louis and Cape Girardeau, MO, and is part of the Kaskaskia Island Drainage and Levee District on the Middle Mississippi River. Flooding on the Mississippi River in 2013 and 2016 was below the design flowline for this levee. This report documents a case history study into the causes of seepage, piping, and sand boil development at a levee reach at Kaskaskia. Site-specific geotechnical data were collected and evaluated to determine the causes for poor performance at the studied levee reach locations. Data collected involved design documents, geologic and geotechnical borings, closely spaced cone-penetrometer tests (CPTs), electrical resistivity surveys, laboratory soil testing of sand boil ejecta, CPT samples from targeted stratigraphic horizons in the subsurface, and both piezometer and river-stage data. These data indicate sand boils present within this levee reach involved a chronic seepage condition that became progressively worse through time. This condition was directly related to the underlying site geology, namely the top stratum thickness and the depositional environment in this levee reach.