Assessment of Climatic and Anthropogenic Controls on Bridge Deck Drainage and Sediment Removal

Bridge deck drainage is essential to prevent hydroplaning and maintain safety along major roadways. With projected changes in climate, current designs may not be sufficient and a better understanding of the primary controls (climate, bridge deck, and inlet design) on the hydraulic efficiency and sediment removal of drainage systems is needed to maintain public safety. To evaluate the controls on hydraulic drainage efficiency, 576 controlled laboratory experiments were conducted testing grate type (rectangular bar vs. curved vane) and downspout configuration (square vs. circular and 20 cm vs. 25 cm) across a range of flow rates, cross slopes, and longitudinal slopes. An additional 144 sediment erosion experiments were performed to identify controls on the removal of sediment. Hydraulic testing indicated that inflow driven by climate is a primary control on drainage efficiency and spread of water on a roadway. For anthropogenic controls, downspout opening size was found to be the primary control followed by longitudinal slope. Sediment removal results indicated that inflow regime and grate type were the primary controls on the sediment removal rate. Given that inflow, driven by climate, is a control on both hydraulic and sediment removal performance, hydraulic engineers should consider forecasted changes in rainfall intensity in their present-day drainage designs. We provide design guidance and discussion for developing a proactive approach to hydraulic infrastructure in the face of future climate uncertainty.

Analysis and calculation of sediment scouring rate at different locations of storm sewer

To explore the migration differences of sediments at the front, middle, and end sections of a storm sewer when scoured by water, and further evaluate the pollution load, the scouring process of sediments at different locations of a storm sewer was simulated and mathematical models were built to calculate the scouring rate. Results show that scouring rate is affected by sediment particle size, pipeline slope, sediment thickness, and water flow velocity. As the slope increased, scouring rate at the end section increased more obviously. The scouring rate at the front section slightly decreased with increasing sediment thickness, but opposite trends were observed at the middle and end sections. When the particle size (0.33 mm–0.83 mm) and flow velocity (0.15 m/s–0.65 m/s) increased within their ranges, scouring rate increased across all three locations. Models for calculating scouring rate were established via two data fitting. The calculated values were compared with measured values at a scouring time of 1 min. Under different particle sizes, the difference between the calculated and measured values at front, middle, and end sections were in the ranges of −0.63% to 0.63%, −0.01% to 0.02%, and −0.13% to 0.16%, respectively, all of which showed good consistency.

Two new species of nematodes from shallow and deep-water sediments in the South China Sea

Two new species of free-living marine nematodes from the South China Sea are described: Gomphionema setiforme sp. nov. from intertidal sediment and Paracomesoma longissimum sp. nov. from upper continental slope sediment. Gomphionema setiforme sp. nov. is characterized by the punctated cuticle without lateral differentiation and cuticular pores; short cephalic setiform sensilla; spiral amphideal fovea with 4 turns close to the anterior body extremity; large cuticularized buccal cavity with a massive dorsal tooth; pharynx with a large posterior bulb; short, curved spicules; knife-like gubernaculum without apophyses and 11 cup-shaped precloacal supplements. Paracomesoma longissimum sp. nov. is characterized by cuticle with transverse rows of fine punctuations without lateral differentiation; buccal cavity with three teeth; lateral outer labial setiform sensilla 1.5 times as long as the other four outer labial setiform sensilla; spiral amphideal fovea with 2.5 turns; spicules 350–360 μm long or 15.7–16 times cloacal body diameter; plate-like gubernaculum without apophyses and 25–28 papilliform precloacal supplements.

Stratigraphy and palaeoenvironmental interpretation of late Quaternary colluvial slope deposits in southern Africa

Slope and lowland sediment systems throughout southern Africa are dominated by the presence of colluvium with interbedded palaeosols and hardground duricrusts. These sediments correspond to phases of land surface instability and stability, respectively, during the late Quaternary. This study examines the stratigraphy and environmental interpretation of slope sediment records from specific sites in southern Africa for the period of marine isotope stages (MIS) 6 to 1 (~191 ka to present), informed by theoretical ideas of the dynamics of slope systems including sediment supply and accommodation space. Based on this analysis, phases of land surface instability and stability for the period MIS 6 to 1 are identified. The spatial and temporal patterns of land surface conditions are not a simple reflection of climate forcing, but rather reflect the workings of slope systems in response to climate in addition to the role of geologic, edaphic and ecological factors that operate within catchment-scale sediment systems. Considering these systems dynamics can yield a better understanding of the usefulness and limitations of slope sediment stratigraphies.

Avaliação da aplicação de modelos de desprendimento em bacia experimental do semiárido brasileiro

Granulometria é um dos principais fatores que afetam a dinâmica de sedimentos em bacias hidrográficas, desde seu desprendimento do solo matriz até o transporte ou deposição pela rede e reservatório. Objetivou-se com esse trabalho analisar o comportamento granulométrico dos sedimentos em uma bacia do semiárido brasileiro, no bioma Caatinga e analisar a eficiência da aplicação de modelos de estimativa do padrão granulométrico do sedimentos desprendido das encostas. O estudo foi realizado na bacia hidrográfica do Pentecoste, situada no semiárido do Ceará. A parte experimental da pesquisa foi realizada na Bacia Experimental do Vale do Curú (BEVC) com coleta de dados pluviométricos e hidrossedimentológicos, amostras de solo da bacia de captação, precipitação diária e de escoamentos superficiais, durante a quadra chuvosa entre os anos de 2015 e 2017. Modelos de desprendimento de sedimentos divulgados na literatura foram testados e aplicados para a área de estudo. Os resultados mostraram que o modelo de desprendimento de sedimento da encosta proposto por Foster et al. (1981) apresentou os melhores resultados quando comparado aos demais, com coeficiente de Nash e Sutcliff (NS) de 0,99, em ambiente de cobertura vegetal mista. Evaluation of the application of detachment models in the experimental basin of the Brazilian semi-arid region A B S T R A C TSize grain is one of the main factors that affect sediment dynamics in watersheds, from its detachment from the soil to the transport or deposition through the drainage network and reservoir. The objective of this research was to analyze the granulometric behavior of the sediments in a Brazilian semi-arid basin in the Caatinga biome and to analyze the efficiency of the application of models for the estimation of the granulometric pattern of sediments detached on slopes. The study was carried out in the Pentecost basin, located in the semi-arid region of Ceará. The experimental part of the research was conducted in the Curú Valley Experimental Basin (BEVC) with rainfall and hydrosedimentological data collection, soil samples from the catchment basin, daily precipitation and surface runoff during the rainy season between 2015 and 2017. Models of sediment release disclosed in the literature were tested and applied to the study area. The results showed that the slope sediment detachment model proposed by Foster et al. (1981) presented the best results when compared to the others, with Nash and Sutcliff coefficient (NS) of 0.99, under mixed vegetation cover.Keywords: size grain, Foster model, Experimental Basin of the Curú Valley, Caatinga biome.

Lake Chala turbidites produced by surficial slope sediment remobilization: A mechanism to bring near-shore macrofossils to the deep basin with only limited time offset

<p>In paleoclimate and paleoenvironmental studies, turbidites are usually considered as interruptions of the sedimentary sequence and therefore ignored. However, turbidites are composed of sediments from the (shallow) slopes along the lake’s periphery where fossil assemblages are often different to those in the deep basin. Turbidites may thus be valuable as carriers of this near-shore proxy information to a profundal core site. However, as turbidites are composed of reworked (older) sediments, their fossil content can only be exploited if their “mean time offset” can be readily estimated or ascertained to be minimal.</p><p>Several recent studies have shown that turbidites can indeed form as a result of surficial slope sediment remobilization, a process – independent of slope failure – in which only a thin veneer (20 cm) of surficial sediment is being remobilized, for example by earthquake shaking, and subsequently transported by a turbidity current. However, demonstrating that this process is active in a basin and determining the remobilization depth, is challenging, especially in the absence of slope cores. Here we study the turbidite record of the 215 m (~260 kyr) long composite core of Lake Chala in the framework of the ICDP project DeepCHALLA. We analyzed its sediment color at a 0.5-cm interval using a spectrophotometer and determined the average color for each of the 391 thickest turbidites (> 3 datapoints) in the L*a*b* color space. For the entire dataset, we performed a linear regression of the turbidite color against the average color of different intervals (2-55 cm) of laminated sediment below. For each combination of paired values, the highest R² values are found for the upper 7-15 cm of matrix sediment below the turbidites, which can thereby be interpreted as the average remobilization depth. These results are mainly based on the a* value, which shows (i) relatively poor correlations between adjacent intervals of laminated sediment (thereby not smearing the signal), and (ii) the most constant values in sediments from across the basin as determined by short-core transects. Depth-dependent variations of sediment color as determined from these transects further allows to estimate the water depth from which the turbidites were sourced.</p><p>Our results show that the sediments of most Lake Chala turbidites are 100-200 yrs older than the laminated sediments upon which they are deposited. We conclude that the turbidites can be used as ‘sampling windows’ to study temporal trends in macrofossils such as ostracods, chironomids and fish teeth, which are much more common along the basin periphery than in the deep basin.</p>

BPOP-v1 model: exploring the impact of changes in the biological pump on the shelf sea and ocean nutrient and redox state

The biological pump of the ocean has changed over Earth's history, from one dominated by prokaryotes to one involving a mixture of prokaryotes and eukaryotes with trophic structure. Changes in the biological pump are in turn hypothesized to have caused important changes in the nutrient and redox properties of the ocean. To explore these hypotheses, we present here a new box model including oxygen (O), phosphorus (P) and a dynamical biological pump. Our Biological Pump, Oxygen and Phosphorus (BPOP) model accounts for two – small and large – organic matter species generated by production and coagulation, respectively. Export and burial of these particles are regulated by a remineralization length (zrem) scheme. We independently vary zrem of small and large particles in order to study how changes in sinking speeds and remineralization rates affect the major biogeochemical fluxes and O and P ocean concentrations. Modeled O and P budgets and fluxes lie reasonably close to present estimates for zrem in the range of currently measured values. Our results highlight that relatively small changes in zrem of the large particles can have important impacts on the O and P ocean availability and support the idea that an early ocean dominated by small particles was nutrient rich due to the inefficient removal of P to sediments. The results also suggest that extremely low oxygen concentrations in the shelf can coexist with an oxygenated deep open ocean for realistic values of zrem, especially for large values of the small-particle zrem. This could challenge conventional interpretations that the Proterozoic deep ocean was anoxic, which are derived from shelf and slope sediment redox data. This simple and computationally inexpensive model is a promising tool to investigate the impact of changes in the organic matter sinking and remineralization rates as well as changes in physical processes coupled with the biological pump in a variety of case studies.

Modeling the impacts of cave ventilation and CO2 dynamics on speleogenesis

<div>Approximately 10 years worth of field observations of dissolved and gaseous CO<sub>2</sub> within caves and karst springs across a variety of settings suggest that CO<sub>2</sub> dynamics provide a first-order control on both the spatial and temporal variability in dissolution rates within karst systems. Three primary effects emerge from the field studies: 1) Changes in stream slope, sediment characteristics, and resulting CO<sub>2</sub> production and exchange can drive longitudinal variability in dissolution rates along cave streams; 2) Cave airflow patterns, and resulting cave gaseous CO<sub>2</sub> concentrations, can be the primary control on the variability of in-stream dissolution rates over storm to seasonal timescales; 3) The maturation of karst systems and resulting increases of permeability within the vadose zone can increase ventilation of the subsurface, reduce the PCO<sub>2</sub> of water flowing through cave passages, and ultimately reduce dissolution rates within these passages. While these effects are evident from the field data, it is difficult to quantify the long-term impacts of these effects on the evolution of karst systems using field data alone. The processes of CO<sub>2</sub> production, cave ventilation, and CO<sub>2</sub> exchange between gas and liquid phases have not been included in previous numerical models of speleogenesis. Here we extend existing models of speleogenesis to incorporate a suite of processes that are relevant for simulating physically realistic CO<sub>2</sub> dynamics. We use this new model to explore the impacts of ventilation and CO<sub>2</sub> exchange over timescales relevant for the evolution of karst aquifers. </div><div> </div>

BPOP-v1 model: exploring the impact of changes in the biological pump on the shelf sea and ocean nutrient and redox state

The ocean’s biological pump has changed over Earth history from one dominated by prokaryotes, to one involving a mixture of prokaryotes and eukaryotes with trophic structure. Changes in the biological pump are in turn hypothesised to have caused important changes in the ocean’s nutrient and redox properties. To explore these hypotheses, we present here a new box model including oxygen (O), phosphorus (P) and a dynamical biological pump. Our Biological Pump, Oxygen and Phosphorus (BPOP) model accounts for two – small and large – organic matter species generated by production and coagulation, respectively. Export and burial of these particles are regulated by a remineralization length (zrem) scheme. We independently vary zrem of small and large particles in order to study how changes in sinking speeds and remineralization rates affect the major biogeochemical fluxes, and O and P ocean concentrations. Modelled O and P budgets and fluxes lay close to present estimates for zrem in the range of currently measured values. Our results highlight that relatively small changes in zrem of the large particles can have important impacts on the O and P ocean availability and support the idea that an early ocean dominated by small particles was nutrient rich due to inefficient removal to sediments. The results also highlight that shelf ocean anoxia can coexist with an oxygenated deep open ocean for realistic values of zrem, especially for large values of the small particle zrem. This could challenge conventional interpretations that the Proterozoic deep ocean was anoxic, which are derived from shelf and slope sediment redox data. This simple and computationally inexpensive model is a promising tool to investigate the impact of changes in the organic matter sinking and remineralization rates as well as changes in physical processes coupled to the biological pump in a variety of case studies.