Ground penetrating radar (GPR) records of groundwater surface (GWS) reflections have been analyzed from 40 across-barrier profiles, totaling 50 km in combined length, taken from barrier spits and beach plains of the Columbia River littoral system. The barriers and beach plains host shallow fresh-water aquifers in the prograded beach deposits and abandoned foredune ridges, totaling 10–30 m in thickness. Study results demonstrate that GWS reflections could be traced continuously at subsurface depths of 1–15 m with the GPR 100 MHz and 50 MHz antennae using 400 V and 1000 V transmitters. Boreholes (62 in number) and lake water levels (24 in number) provide ground-truthing of the across-barrier GWS trends interpreted from the GPR profiles. The GWS rises in elevation (4–8 m above base level) under high, broad foredune-ridges and drops under interdune ridge valleys (1–3 m above base level). Continuous profiles of GWS demonstrate that lakes, ponds, and bogs of the barriers and beach plains are “windows” into the shallow coastal aquifer. The GPR records demonstrate that the GWS slopes either to seaward (0.003–0.04 gradient) or to landward (0.001–0.05 gradient) from divides under the largest, shore-parallel dune ridges in the barriers. The GWS gradients indicate that subsurface contaminant transport from the developed dune ridges will be intercepted by intervening lakes and ponds in the interdune-ridge valleys. The GPR records also establish the effect of drainage ditches in lowering GWS elevations (1–2 m) in sensitive wetlands located 100s of meters in distance from the constructed ditches.

ABSTRACT From its inception, New Orleans was an “island city” surrounded by water. When it was surveyed in 1720, each block was circled with drainage ditches. These small channels established New Orleans' dependence on a levee/drainage network. Levee construction began as early as 1718. By 1727, a hand-made embankment protected the earliest city–the “Vieux Carre.” With time the initial levee extended along the Mississippi River for a total of 67.6 km. The first artificial levee built to protect New Orleans was in place, but it was neither high enough nor wide enough. By the 1850s, intermittent dikes flanked most of the lower Mississippi River. After the devastating flood of 1927, the Mississippi River was locked into a conduit framed by artificial levees. The river can no longer inundate its historic flood plain. Sediments are channeled away from the wetlands. Loss of these sediments deprives the coast of the material necessary to build new land at a rate slightly greater than subsidence. There is nothing available that can offset the rapid rate of wetland loss. Consequently, to exist in this dynamic and sometimes inhospitable physiographic province, the population had to develop and utilize innovative engineering techniques, unconventional wisdom, and unique cultural occupancy patterns.

The early Pleistocene (Blancan) Rita Blanca lake deposits in the north-western part of the Panhandle of Texas occupy a deflation basin cut through the caprock of the Pliocene Ogallala Group. During its maximum development, Rita Blanca lake had an elliptical shape with a north-south length of about 6 miles and a breadth of about 3.5 miles. The lower exposures of the Rita Blanca deposits contain an areally restricted clay bed with a maximum observed thickness of 65 inches that contains abundant fossils representing the lacustrine and riparian environments, and a plains community of mixed sagebrush and grass. The clay bed also contains two types of cyclic lithology: (1) an alternation of light- and dark-colored clay zones on the scale of centimeters and decimeters, and (2) couplets of light- and dark-colored laminae with an average thickness of 0.9 mm. The light-colored laminae are rich in calcium carbonate, quartz silt grains, and ostracodes; the dark-colored laminae are composed principally of illite and organic matter. The laminae can be correlated with little change over 300 yards, and changes in the proportion of the constituents are responsible for the larger scale cyclic bedding. The microstratigraphic position and associations of the ostracodes Lim - nocythere, Cyprideis, and Candona, deciduous leaves of oak ( Quercus ) and willow ( Salix ), Artemisia pollen, pupae and adults of Chironomidae (midges), and carbon and oxygen isotope ratios demonstrate that the light-colored high-carbonate laminae were deposited in the summer and the dark-colored low-carbonate laminae were deposited in the winter and spring. A saline temporary hard-water lake is suggested by sediment composition and by four kinds of fossils that customarily reflect a saline or alkaline environment but are not necessarily restricted to it ( Ruppia maritima , ditch grass; Fundulus , killifish; Limnocythere and Cyprideis , ostracodes; a species of Chironomus , midge). The entire fossil assemblage, with the exception of fungal spores, was transported to site of deposition in the profundal zone of the lake. The absence of a benthonic fauna, the distinct laminations and the saline character of the water suggests meromixis. The continuous 1,400-year varve series was sampled on a time-series basis and the long-term associations subjected to regression, Fourier, and bi-spectral analysis. Clay is negatively associated with calcium carbonate for intervals longer than 60-70 years, whereas the association is positive for short-term changes — which is interpreted to mean that some calcium carbonate was washed in with the clay but the long-term changes in carbonate were the result of carbonate precipitation in the lake. Harmonic analysis of couplet thickness revealed a moderately well-defined 22-year period that was also present in the carbonate fraction but not in the clay fraction. Seasonal and long-term associations of clay, silt, carbonate, organic matter, fungal spores, and ostracodes parallel each other, and the negative long-term association of clay and carbonate is interpreted as intervals of cool-moist climate alternating with intervals of warm-dry climate. The fossils and lithologic changes suggest a climatic regime with cooler temperatures and with the same or less moisture than the present area receives today, but with most of the moisture arriving in the cool season rather than in the warm season.