Intertidal sand body migration along a megatidal coast, Kachemak Bay, Alaska

Adams, P. N.; Ruggiero, Peter; Schoch, G. Carl; Gelfenbaum, Guy

doi:10.1029/2006jf000487

Cited by 13 publications

(4 citation statements)

References 25 publications

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“… Rubin [2004] and Buscombe and Masselink [2009] have developed similar systems for examining sand bed grain size parameters at scales of a few centimeters. This technology has been extended for application on gravel‐sized particles [ Adams et al , 2007; Ruggiero et al , 2007].…”

Section: Introductionmentioning

confidence: 99%

Maximizing the accuracy of image‐based surface sediment sampling techniques

Graham

Rollet

Piégay

et al. 2010

Water Resources Research

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[1] Recent years have seen increased interest in automated methods, utilizing photographs collected with a handheld digital camera, for determining the grain size distribution of coarse river sediments. Such methods are as precise as traditional field methods and have considerable time and cost advantages. Nevertheless, several unresolved issues pertaining to their deployment remain to be addressed. Using data sets collected from seven gravel bed rivers, this paper examines four key issues: (1) the minimum area required to obtain a representative sample, (2) the effect of lower-end truncation on grain size percentiles, (3) the effect of river bed structure such as imbrication and hiding, and (4) the potential benefits of using individual particle measurements rather than the number (or mass) of particles per size class to calculate percentiles. It is demonstrated that sampling areas of between 50 and 200 times that of the largest grain are adequate to achieve percentile errors of <10% (in mm). The appropriateness of lower-end truncation depends on the study aims and sediment properties. It has a limited effect on higher percentiles, except where sand is a major constituent. Understanding the influence of bed structure on image-derived size information is complicated by the absence of error-free benchmarks against which accuracy may be evaluated, but it is likely that other errors are more important. The use of individual particle measurements to calculate percentiles in preference to classified data is shown to have a small, but appreciable, effect on precision. These results will assist practitioners in making appropriate operational decisions to maximize data quality using image-based grain size data capture.

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Section: Introductionmentioning

confidence: 99%

Maximizing the accuracy of image‐based surface sediment sampling techniques

Graham

Rollet

Piégay

et al. 2010

Water Resources Research

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“…The migration speeds of bars in the megatidal setting of Regnéville inlet accelerated before welding onto the high-tide beach, whereas the migration speeds of bars monitored by FitzGerald [1984,1988] in a microtidal to weakly mesotidal setting decelerated as bars approached the high-tide beach due to lesser exposure to waves. Working on intertidal sand bodies (not inlet vicinity swash bars) in a megatidal embayment in Alaska, Adams et al [2007] also identified pulses in migration speeds that they related to wave energy variations. The acceleration of bar migration speeds in Normandy is probably due to larger wave energy at high tide as the bar approaches the high-tide beach.…”

Section: Robin Et Al: Bar Migration and Shoreline Changesmentioning

confidence: 99%

Short‐term to decadal‐scale onshore bar migration and shoreline changes in the vicinity of a megatidal ebb delta

Robin¹,

Levoy²,

Monfort³

et al. 2009

J. Geophys. Res.

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[1] Swash bar development has been well documented from coasts with low to moderate tidal ranges, while studies of the effects of these forms on the morphology and dynamics of the adjacent shore in large tide range environments are rare. The analysis of sequential vertical aerial photographs was combined with field work in order to highlight the effects of swash bar development on the adjacent shoreline in the vicinity of a megatidal inlet (mean spring tidal range of 11 m). Swash bars are observed to form on the ebb tidal delta and to migrate landward before welding onto the coast. A close relationship was noticed between the position of the swash bar and shoreline dynamics. The bar protects the shore against wave attack in a sedimentary system controlled by longshore transport. This protective role is, however, modulated by the large tidal range. As the bar migrates upward toward the high-tide level and the subaerial beach, it develops morphologically into a transverse form that acts as a cross-shore obstacle to longshore sediment transport, thus resulting in shoreline accretion updrift and in strong erosion downdrift. This disturbance may persist for years because of the relatively slow speed of movement of the bar at this stage, an aspect characteristic of large tide range environments. This pattern of behavior differs fundamentally from that documented in the literature where the perturbation of the longshore sediment transport occurs over shorter periods. An original conceptual model of swash bar morphodynamics and repercussions on the adjacent shoreline for this megatidal environment is proposed.Citation: Robin, N., F. Levoy, O. Monfort, and E. Anthony (2009), Short-term to decadal-scale onshore bar migration and shoreline changes in the vicinity of a megatidal ebb delta,

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“…In recent geologic history, the 1964 Valdez earthquake redirected the mouth of the river nearly 2.5 km south of its previous position, coinciding with 1–2 m of subsidence in the area (Coulter & Migliaccio, 1966). In Homer, directly across Kachemak Bay from the WRD (~5 km), the mean maximum semidiurnal tidal range is 5.6 m, with extreme tides exceeding 9 m. Mean wave heights are 0.5 and 0.8 m for summer and winter, respectively, although they have been observed in excess of 2.5 m (Adams et al, 2007). These oceanographic conditions enable a powerful means to recirculate seawater back through the porous media of the WRD and effectively pump nutrients and solutes via SGD pathways.…”

Section: Study Areamentioning

confidence: 99%

Physical and chemical characterization of remote coastal aquifers and submarine groundwater discharge from a glacierized watershed

Russo,

Jenckes,

Boutt

et al. 2024

Hydrological Processes

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Coastal aquifers play an important role in marine ecosystems by providing high fluxes of nutrients and solutes via submarine groundwater discharge pathways. The physical and chemical characterization of these dynamic systems is foundational to understanding the extent and magnitude of hydrogeologic processes and their subsequent contributions to the marine environment. We describe a km‐scale experimental field site located in a glaciofluvial delta entering Kachemak Bay, Alaska. Our characterization applies geophysical (ERT and HVSR), hydrogeologic (grain size analyses, slug tests and tidal response analyses) and geochemical (major ions and stable water isotopes) methods to describe the complexity of coastal aquifers in proglacial environments currently experiencing rapid transformations. The hydrogeologic and geophysical techniques revealed thick (20–84 m) sediments dominated by sands and gravels and delineated zones of freshwater, brackish water and saltwater at both high and low tides within the subterranean estuary. Estimates of hydraulic conductivities via multiple approaches ranged from 2 to 250 m d−1, with means across the four methods within the same order of magnitude. Tidal response analyses highlighted a coastal aquifer in strong connection with the sea as evidenced by clear spring‐ and neap‐tidal signals within a proximal piezometric hydrograph. Geochemical sampling revealed coastal groundwaters as substantially enriched in solutes compared to proximal river samples with limited variability across seasons. A clear connection between the Wosnesenski River and the adjacent aquifer was also observed, with concentrated recharge from the river corridor during the meltwater season. This combination of approaches provides the basis for a conceptual model for coastal aquifer systems within the Gulf of Alaska and an upscaled mean daily yield of freshwater and solutes from the delta subsurface. Our findings are critical for subsequent numerical simulations of groundwater flow, tidal pumping and chemical reactions and transport in these understudied environments. This approach may be applied for low‐cost, large‐scale hydrogeologic investigations in coastal areas and may be particularly useful for remote sites where access and mobility are challenging.

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Intertidal sand body migration along a megatidal coast, Kachemak Bay, Alaska

Cited by 13 publications

References 25 publications

Maximizing the accuracy of image‐based surface sediment sampling techniques

Maximizing the accuracy of image‐based surface sediment sampling techniques

Short‐term to decadal‐scale onshore bar migration and shoreline changes in the vicinity of a megatidal ebb delta

Physical and chemical characterization of remote coastal aquifers and submarine groundwater discharge from a glacierized watershed

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