Hydrodynamics in a gravel beach and its impact on the Exxon Valdez oil

Abstract

[1] This paper investigated the interaction of groundwater and seawater in a tidally influenced gravel beach. Field observations of water table, pore water salinity were performed. The two-dimensional finite element model MARUN was used to simulate observed water table and salinity. Based on field observations and model calibrations, a two-layered beach structure was identified which is characterized by a high-permeability surface layer underlain by a low-permeability lower layer. The salt wedge seaward of the low tide line was almost invariant in comparison with the strong fluctuations of the salinity plume in the surface layer of the intertidal zone. The presence of the two layers prevented the presence of a freshwater discharge "tube" between the upper saline plume and salt wedge. This is in contrast with the previous works where freshwater discharge tube was observed. The tide-induced submarine groundwater discharge (SGD) was estimated at 9 m 3 d, a large value that is probably due to the large tidal range of ∼4.8 m and the very permeable surface layer. The freshwater-seawater dynamics revealed here may provide new insights into the complexity, intensity, and time scales of mixing between fresh groundwater and seawater in tidal beaches. The simulated water table of the beach was higher than the interface between the surface layer and the lower layer, which prevented Exxon Valdez oil from penetrating into the lower layer in 1989.

Groundwater dynamics in subterranean estuaries of coastal unconfined aquifers: Controls on submarine groundwater discharge and chemical inputs to the ocean

“…Fluctuations in SGD in response to the spring-neap tidal cycle has been widely reported [Kim and Hwang, 2002;Taniguchi, 2002;Robinson et al, 2007a;de Sieyes et al, 2008;Wilson et al, 2015]. While the salt distribution in a STE (including the configuration of an USP) typically does not oscillate considerably in response to semi-diurnal or diurnal tides (except for high permeability gravel beaches [Guo et al, 2010;Geng and Boufadel, 2017]), it does vary in response to the spring-neap signal. The expansion and contraction of the USP as the spring and neap tides approach, respectively, were observed experimentally for microtidal and macrotidal beaches [Robinson et al, 2007a;Abarca et al, 2013;Buquet et al, 2016].…”

Subsurface Flow and Moisture Dynamics in Response to Swash Motions: Effects of Beach Hydraulic Conductivity and Capillarity

“…The MARUN model has been validated and used extensively in our previous studies on beach hydrodynamics (Geng & Boufadel, 2015a;Geng et al, 2016b;Guo et al, 2010;. The model represented a 2-D cross-section of a beach aquifer, which was 250 cm long and 600 cm deep, and had a 17% slope (Figure 1c), spanning from the most landward instrument array to the seaward one.…”

Seawater-groundwater Exchange in a Silty Tidal Flat in the South Coast of Laizhou Bay, China

“…A series of experiments conducted in gravel beaches of Prince William Sound, Alaska, indicated that the twolayered structure of a high-permeability surface layer underlain by a low-permeability layer had significant impacts on the persistence of spilled oil ( Guo et al, 2010;Li and Boufadel, 2010; . Xia and Li ( 2012 ) made a comparative study between a bald beach and a mangrove beach with similar topography and tidal actions in the intertidal zones of Dongzhaigang in Haikou City of Hainan Province, indicating that the inland freshwater recharge and the mud-sand two-layered structure played key roles in the development of mangrove and their spatial distribution.…”

“…Seepage meters were also used to estimated SGD at local area, such as manual seepage instrument developed by Cable et al ( 1997 ) , heat pulse seepage meter developed by Taniguchi and Fukuo (1993) and ultrasonic flow meter developed by Paulsen et al (2001) . Numerical simulations usually focused on limited coastal transect, such as Guo et al (2010) , , Xia and Li (2012) , Xia et al (2010) .…”