Assessing “Urban Karst” Effects from Groundwater–Storm Sewer System Interaction in a Till Aquitard     

Martin G. Shepley  Nick Schmidt  Matt J. Senior  Stephen R. H. Worthington  Ron B. Scheckenberger 《Ground water》2020,58(2):269-277

Storm sewer systems and their associated utility trenches may strongly influence the effects of urbanization on a groundwater system. This study was undertaken to identify the causes of district-wide basement infiltration in an aquitard system. It comprised widespread continuous monitoring of utility trench wells and dye tracing from storm sewer system exfiltration tests. The results indicate that a major effect of urbanization on shallow groundwater is related to storm sewer system exfiltration, which is marked by a characteristic pattern of head variations in the aquitard unrelated to distributed surface infiltration. The aquitard constrains flow from storm sewer system exfiltration to the utility trench, creating an urban flow path for groundwater discharge. Temporary buildup of water levels in the utility trench drives relatively high-velocity flow through the permeable sewer bedding material of the utility trench to a separate foundation drainage collector system, ultimately causing a severe “urban karst” effect that produces system surcharging and widespread basement water infiltration. The main conditions causing the “urban karst” are the large hydraulic conductivity ratio between the utility trench material and the aquitard, and the shallow depth and low gradient of the storm sewer system imposed by a very flat drainage basin.  相似文献   

The dynamics of mountain erosion: Cirque growth slows as landscapes age     

Iestyn D. Barr  Jeremy C. Ely  Matteo Spagnolo  Ian S. Evans  Matt D. Tomkins 《地球表面变化过程与地形》2019,44(13):2628-2637

Glacial cirques are widely used palaeoenvironmental indicators, and are key to understanding the role of glaciers in shaping mountain topography. However, notable uncertainty persists regarding the rate and timing of cirque erosion. In order to address this uncertainty, we analyse the dimensions of 2208 cirques in Britain and Ireland and model ice accumulation to investigate the degree of coupling between glacier occupation times and cirque growth. Results indicate that during the last ~120 ka, cirques were glacier-free for an average of 52.0 ± 21.2 ka (43 ± 18%); occupied by small (largely cirque-confined) glaciers for 16.2 ± 9.9 ka (14 ± 8%); and occupied by large glaciers, including ice sheets, for 51.8 ± 18.6 ka (43 ± 16%). Over the entire Quaternary (i.e. 2.6 Ma), we estimate that cirques were glacier-free for 1.1 ± 0.5 Ma; occupied by small glaciers for 0.3 ± 0.2 Ma; and occupied by large glaciers for 1.1 ± 0.4 Ma. Comparing occupation times to cirque depths, and calculating required erosion rates, reveals that continuous cirque growth during glacier occupation is unlikely. Instead, we propose that cirques attained much of their size during the first occupation of a non-glacially sculpted landscape (perhaps during the timeframe of a single glacial cycle). During subsequent glacier occupations, cirque growth may have slowed considerably, with the highest rates of subglacial erosion focused during periods of marginal (small glacier) glaciation. We propose comparatively slow rates of growth following initial cirque development because a ‘least resistance’ shape is formed, and as cirques deepen, sediment becomes trapped subglacially, partly protecting the bedrock from subsequent erosion. In support of the idea of rapid cirque growth, we present evidence from northern British Columbia, where cirques of comparable size to those in Britain and Ireland developed in less than 140 ka. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.  相似文献   

Wave-tide interaction modulates nearshore wave height     

Lewis  Matt J.  Palmer  Tamsin  Hashemi  Resa  Robins  Peter  Saulter  Andrew  Brown  Jenny  Lewis  Huw  Neill  Simon 《Ocean Dynamics》2019,69(3):367-384

Ocean Dynamics - The combined hazard of large waves occurring at an extreme high water could increase the risk of coastal flooding. Wave-tide interaction processes are known to modulate the wave...  相似文献   

The release of dissolved actinium to the ocean: A global comparison of different end-members   总被引：1，自引：1，他引：0  

Walter Geibert  Matt Charette  Guebuem Kim  Willard S. Moore  Joseph Street  Megan Young  Adina Paytan   《Marine Chemistry》2008,109(3-4):409

The measurement of short-lived ²²³Ra often involves a second measurement for supported activities, which represents ²²⁷Ac in the sample. Here we exploit this fact, presenting a set of 284 values on the oceanic distribution of ²²⁷Ac, which was collected when analyzing water samples for short-lived radium isotopes by the radium delayed coincidence counting system. The present work compiles ²²⁷Ac data from coastal regions all over the northern hemisphere, including values from ground water, from estuaries and lagoons, and from marine end-members. Deep-sea samples from a continental slope off Puerto Rico and from an active vent site near Hawaii complete the overview of ²²⁷Ac near its potential sources.The average ²²⁷Ac activities of nearshore marine end-members range from 0.4 dpm m^− 3 at the Gulf of Mexico to 3.0 dpm m^− 3 in the coastal waters of the Korean Strait. In analogy to ²²⁸Ra, we find the extension of adjacent shelf regions to play a substantial role for ²²⁷Ac activities, although less pronounced than for radium, due to its weaker shelf source. Based on previously published values, we calculate an open ocean ²²⁷Ac inventory of 1.35 * 10¹⁸ dpm ²²⁷Ac_ex in the ocean, which corresponds to 37 moles, or 8.4 kg. This implies a flux of 127 dpm m⁻² y^− 1 from the deep-sea floor. For the shelf regions, we obtain a global inventory of ²²⁷Ac of 4.5 * 10¹⁵ dpm, which cannot be converted directly into a flux value, as the regional loss term of ²²⁷Ac to the open ocean would have to be included.Ac has so far been considered to behave similarly to Ra in the marine environment, with the exception of a strong Ac source in the deep-sea due to ²³¹Pa_ex. Here, we present evidence of geochemical differences between Ac, which is retained in a warm vent system, and Ra, which is readily released [Moore, W.S., Ussler, W. and Paull, C.K., 2008-this issue. Short-lived radium isotopes in the Hawaiian margin: Evidence for large fluid fluxes through the Puna Ridge. Marine Chemistry]. Another potential mechanism of producing deviations in ²²⁷Ac/²²⁸Ra and daughter isotope ratios from the expected production value of lithogenic material is observed at reducing environments, where enrichment in uranium may occur. The presented data here may serve as a reference for including ²²⁷Ac in circulation models, and the overview provides values for some end-members that contribute to the global Ac distribution.  相似文献   

Basic hydrology,limnology, and meteorology of modern Lake El’gygytgyn,Siberia     

Matt Nolan  Julie Brigham-Grette 《Journal of Paleolimnology》2007,37(1):17-35

A survey of the modern physical setting of Lake El’gygytgyn, northeastern Siberia, is presented here to facilitate interpretation of a 250,000-year climate record derived from sediment cores from the lake bottom. The lake lies inside a meteorite impact crater that is approximately 18 km in diameter, with a total watershed area of 293 km², 110 km² of which is lake surface. The only surface water entering the lake comes from the approximately 50 streams draining from within the crater rim; a numbering system for these inlet streams is adopted to facilitate scientific discussion. We created a digital elevation model for the watershed and used it to create hypsometries, channel networks, and drainage area statistics for each of the inlet streams. Many of the streams enter shallow lagoons dammed by gravel berms at the lakeshore; these lagoons may play a significant role in the thermal and biological dynamics of the lake due to their higher water temperatures (>6°C). The lake itself is approximately 12 km wide and 175 m deep, with a volume of 14.1 km³. Water temperature within a column of water near the center of this oligotrophic, monomictic lake never exceeded 4°C over a 2.5 year record, though the shallow shelves (<10 m) surrounding the lake can reach 5°C in summer. Though thermally stratified in winter, the water appears completely mixed shortly after lake ice breakup in July. Mean annual air temperature measured about 200 m from the lake was −10.3°C in 2002, and an unshielded rain gage there recorded 70 mm of rain in summer of 2002. End of winter snow water equivalent on the lake was approximately 110 mm in May 2002. Analysis of NCEP reanalysis air temperatures (1948–2002) reveals that the 8 warmest years and 10 warmest winters have occurred since 1989, with the number of days below −30°C dropping from a pre-1989 mean of 35 to near 0 in recent years. The crater region is windy as well as cold, with hourly wind speeds exceeding 13.4 m s⁻¹ (30 mph) typically at least once each month and 17.8 m s⁻¹ (40 mph) in winter months, with only a few calm days per month; wind may also play an important role in controlling the modern shape of the lake. Numerous lines of evidence suggest that the physical hydrology and limnology of the lake has changed substantially over the past 3.6 million years, and some of the implications of these changes on paleoclimate reconstructions are discussed. This is the second in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue.  相似文献   

Attenuation effect on seasonal basin-scale water storage changes from GRACE time-variable gravity   总被引：3，自引：0，他引：3  

J. L. Chen  C. R. Wilson  J. S. Famiglietti  Matt Rodell 《Journal of Geodesy》2007,81(4):237-245

In order to effectively recover surface mass or geoid height changes from the gravity recovery and climate experiment (GRACE) time-variable gravity models, spatial smoothing is required to minimize errors from noise. Spatial smoothing, such as Gaussian smoothing, not only reduces the noise but also attenuates the real signals. Here we investigate possible amplitude attenuations and phase changes of seasonal water storage variations in four drainage basins (Amazon, Mississippi, Ganges and Zambezi) using an advanced global land data assimilation system. It appears that Gaussian smoothing significantly affects GRACE-estimated basin-scale seasonal water storage changes, e.g., in the case of 800 km smoothing, annual amplitudes are reduced by about 25–40%, while annual phases are shifted by up to 10°. With these effects restored, GRACE-estimated water storage changes are consistently larger than model estimates, indicating that the land surface model appears to underestimate terrestrial water storage change. Our analysis based on simulation suggests that normalized attenuation effects (from Gaussian smoothing) on seasonal water storage change are relatively insensitive to the magnitude of the true signal. This study provides a numerical approach that can be used to restore seasonal water storage change in the basins from spatially smoothed GRACE data.  相似文献   

A Marine Isotope Stage 4 age for Pleistocene raised beach deposits near Fethard,southern Ireland          下载免费PDF全文

Colman Gallagher  Matt W. Telfer  Colm Cofaigh 《第四纪科学杂志》2015,30(8):754-763

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Multiple re‐advances of a Lake Vättern outlet glacier during Fennoscandian Ice Sheet retreat,south‐central Sweden          下载免费PDF全文

Sarah L. Greenwood  Matt O'Regan  Henrik Swärd  Tom Flodén  Roman Ananyev  Denis Chernykh  Martin Jakobsson 《Boreas: An International Journal of Quaternary Research》2015,44(4):619-637

Lake Vättern represents a critical region geographically and dynamically in the deglaciation of the Fennoscandian Ice Sheet. The outlet glacier that occupied the basin and its behaviour during ice‐sheet retreat were key to the development and drainage of the Baltic Ice Lake, dammed just west of the basin, yet its geometry, extent, thickness, margin dynamics, timing and sensitivity to regional retreat forcing are rather poorly known. The submerged sediment archives of Lake Vättern represent a missing component of the regional Swedish deglaciation history. Newly collected geophysical data, including high‐resolution multibeam bathymetry of the lake floor and seismic reflection profiles of southern Lake Vättern, are used here together with a unique 74‐m sediment record recently acquired by drill coring, and with onshore LiDAR‐based geomorphological analysis, to investigate the deglacial environments and dynamics in the basin and its terrestrial environs. Five stratigraphical units comprise a thick subglacial package attributed to the last glacial period (and probably earlier), and an overlying >120‐m deglacial sequence. Three distinct retreat–re‐advance episodes occurred in southern Lake Vättern between the initial deglaciation and the Younger Dryas. In the most recent of these, ice overrode proglacial lake sediments and re‐advanced from north of Visingsö to the southern reaches of the lake, where ice up to 400 m thick encroached on land in a lobate fashion, moulding crag‐and‐tail lineations and depositing till above earlier glacifluvial sediments. This event precedes the Younger Dryas, which our data reveal was probably restricted to north‐central sectors of the basin. These dynamics, and their position within the regional retreat chronology, indicate a highly active ice margin during deglaciation, with retreat rates on average 175 m a^?1. The pronounced topography of the Vättern basin and its deep proglacial‐dammed lake are likely to have encouraged the dynamic behaviour of this major Fennoscandian outlet glacier.  相似文献   

The relationship between temperature and assault in New Zealand     

Matt N. Williams  Stephen R. Hill  John Spicer 《Climatic change》2015,131(4):559-573

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Origin of Carboniferous sandstones fringing the northern margin of the Wales‐Brabant Massif: insights from detrital zircon ages     

Andrew Morton  Colin Waters  Mark Fanning  Ian Chisholm  Matt Brettle 《Geological Journal》2015,50(5):553-574

A study of detrital zircon age populations in Namurian–Westphalian (Carboniferous) sandstones in the southern Central Pennine Basin of the UK has revealed considerable complexity in their provenance history. The Pendleian–Marsdenian Morridge Formation, which is known to have been derived from the Wales‐Brabant Massif to the south on the basis of palaeocurrent and petrographic information, is dominated by zircons ultimately derived from the Caledonian belt to the north. These zircons were recycled from sandstones of northern origin that had been previously deposited over the massif during Middle to Late Devonian times. The Morridge Formation also includes Late Neoproterozoic zircons of local Wales‐Brabant Massif origin. The south lobe of the Yeadonian Rough Rock has been previously interpreted as having a complex provenance including sediment of northern origin interbedded with sediment ascribed to a Wales‐Brabant Massif source. However, the zircon spectrum lacks a Late Neoproterozoic component that would have been diagnostic of input from the Wales‐Brabant Massif, and the provenance history of the Rough Rock south lobe therefore remains enigmatic. The Langsettian Ludgbridge Conglomerate is dominated by Late Neoproterozoic zircons of Wales‐Brabant Massif origin, but even in this evidently proximal deposit, the provenance is complex since the main zircon group (ca. 640 Ma) cannot be matched with known local Neoproterozoic basement sources. The data either indicate the presence of hitherto‐unknown magmatic rocks of this age adjacent to the South Staffordshire coalfield or indicate that the zircons were recycled from sediment with a more distal origin. Finally, the Duckmantian Top Hard Rock contains zircons that can be reconciled with a source in the Irish Caledonides, consistent with the palaeocurrent evidence, supplemented by zircons derived from the Wales‐Brabant Massif, possibly including the Monian Composite Terrane of Anglesey. The study reinforces the important message that failure to recognize the presence of recycled zircon could lead to erroneous reconstructions of sediment provenance and transport history. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献