Long-term morphological change in the Ribble Estuary, northwest England

We investigated the role submarine groundwater discharge (SGD) plays in the delivery of nutrients and copper to the Elizabeth River (Virginia) estuary, a major subestuary of lower Chesapeake Bay. Using an approach based on radium isotopes, we concluded that two distinct sources of groundwater were equally impacting the estuary: a surface (marsh) aquifer and deep aquifer source each with a unique 228 Ra/ 226 Ra activity ratio. Considering each of these sources, we calculated an SGD flux of I × 10 6 m 3 d -1 (± 10%), which represented ∼6% of the SGD flux for the entire Chesapeake Bay and ∼5% of the James River, a major source of freshwater to lower Chesapeake Bay. SGD-derived dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) fluxes averaged 4.5 (±4.6) and 0.16 (±0.17) mmol m -2 d -1 , respectively, and compared well with area-normalized fluxes to Chesapeake Bay. In contrast, SGD-derived Cu input of 730 (±390) kg yr -1 was a relatively small source of Cu (∼3%) to the Elizabeth estuary given that surface water inputs, such as antifouling paints associated with naval operations, are a major component of the Cu budget for this system These findings were in general agreement with prior studies of SGD for this region.

https://aslopubs.onlinelibrary.wiley.com/doi/epdf/10.4319/lo.2004.49.2.0376

Submarine groundwater discharge of nutrients and copper to an urban subestuary of Chesapeake Bay (Elizabeth River)

Knowledge of aggregate size in estuaries is important to determining the fate and transport of suspended sediment and particle adherent contaminants. We have used a suite of in situ instruments to determine the controls of aggregate size distributions in three muddy, partially mixed estuaries in the mid-Atlantic USA. A novel method is presented to estimate turbulent kinetic energy (TKE) production and the resulting Kolmogorov microscale (λK) using a profiling acoustic Doppler velocimeter that has been contaminated by boat motion. The physical processes that control particle size distribution differ in the three estuaries due to the different hydrodynamics and benthic characteristics. Controls within each estuary also vary with different depth regimes. Surface particle size dynamics in all the studied estuaries are affected by irregular advection events. In the hydrodynamically energetic York River, mid-depth regions are controlled tidally by the combined processes of small λK decreasing particle size at high TKE and differential settling increasing particle size during lower TKE, more stratified conditions. Mid-depth regions in the lower energy Elizabeth River are controlled by irregular resuspension and trapping at the pycnocline of large low density particles. Bottom regions in all estuaries are most strongly influenced by resuspension, tidally in the energetic estuaries and irregularly in the low energy estuary. Near-bed particle size distributions are controlled by both λK and the distribution of particles in the bed in the higher energy estuaries. Just above the bed, large porous particles survive resuspension in the lower energy Elizabeth River, particles become smaller with decreased λK in the more energetic York River, and biological aggregation causes large dense particles to resist turbulent breakup in the Chesapeake Bay, which has a more active benthic community. The net result just above the bed is that particle size and settling velocity are positively correlated to TKE production and sediment concentration in the estuary with higher currents and a biologically active bed, negatively correlated in the estuary with higher currents and a bed reworked by rapid erosion and deposition, and poorly correlated in the estuary with lower currents and a disturbed and contaminated bed.

Controls on suspended aggregate size in partially mixed estuaries

Modeling the tidal channel morphodynamics in a macro-tidal embayment, Hangzhou Bay, China.

Subtropical Convergence Environments

The history of dredging and disposal has been compiled from historical charts and records to determine the course of harbor evolution at Norfolk, Virginia. Dredging activities between 1872 and 1982 have produced large geometric changes with important hydrographic and sedimentological consequences. The harbor once had a shallow irregular channel floor bordered by broad shoals, marshland and tributary creeks. Today after 100 years, dredging has deepened the channel 1.8 fold, smoothed the natural profile and increased sedimentation rates more than 90 times expected rates. Disposal as land fill has buried many creeks and marshes, moved the shore channelward and reduced the estuary area 26%. As a consequence these changes have reduced the tidal prism and entrance exchange. The dredge-fill-sedimentation cycle follows three stages of harbor evolution: (1) dredging entrance bars and the estuary head, (2) channel enlargement seaward with bordering landfill and open water disposal, and (3) contained disposal seaward of the early port, or ocean disposal. This case study shows that a series of small dredge and disposal projects in a small estuarine harbor can produce large cumulative effects that are the same order as natural geologic processes. Several other harbors follow similar stages of harbor evolution.

/pdf/evolution-of-an-urban-estuarine-harbor-norfolk-virginia-2zr9iquxun.pdf

Mary M. Howard-Strobel

Papers

Evolution of an Urban Estuarine Harbor: Norfolk, Virginia