Long-term improvements in water quality due to sewage abatement in the lower Hudson River

Long-trend trends in dissolved oxygen (DO) and total coliform bacteria concentrations are used to evaluate the impact of almost 60 yr of sewage abatement and treatment in the lower Hudson River near New York City. Although some water pollution control plants have been in operation in the region since the 1930s, the most significant abatement of untreated sewage in the lower Hudson River has occurred since the late 1970s, when most of the existing plants were upgraded to secondary treatment, and additional plants were constructed. From at least 1922 through the early 1960s, average summer DO percent saturation varied between 35% and 50% in surface waters and 25% and 40% in bottom waters. Beginning in the late 1970s, DO concentrations generally increased through the 1980s and especially into the 1990s, coinciding with the upgrading of the 7.4 m³ s^?1 (170 million gallons per day, mgd) North River plant to secondary treatment in the spring of 1991. Average summer percent saturation in the early 1990s exceeded 80% in surface waters and 60% in bottom waters. In addition, summer DO minima have increased from less than 1.5 mg 1^?1 in the early 1970s to greater than 3.0 mg 1^?1 in the 1990s, and the duration of hypoxia during summer months has been reduced. Total coliforms also display strong declining trends from the 1970s into the 1990s, with declines attributed to plant upgrades, construction of two New York City plants (North River and Red Hook) in the mid 1980s, and improved operation of the sewer system.     

Hydrological regimes in a tropical valley of New Caledonia (SW Pacific): Impacts of wildfires and invasive fauna

In New Caledonia wildfires and invasive mammals (deer and wild pigs) constitute the major agents of land surface degradation. Our study reveals the linkage between land cover and water balance on the northeast coast of New Caledonia (2400 mm annual rainfall) located on a micaschist basement. The hydrological regime of characteristic and representative land surfaces is assessed using a 1-year record from three 100 m² plots each, located in a forest area degraded by an invasive fauna, in a woody savannah which is regularly burned, and in a healthy forest area. The three plots present highly contrasting hydrological regimes, with annual and maximum runoff/rain ratios during a rain event of, respectively, 0.82, 0.16, 0.03, and 2.7, 0.7, 0.2, for the degraded forest, the savannah and the healthy forest. Such results suggest that subsurface flow originating from the contributing area above the degraded forest plot should exfiltrate inside the plot. A conceptual model for the degraded forest plot shows that water exfiltrating inside the plot represents 61% of the observed runoff. In savannahs, water should mainly be transferred downstream by subsurface flow within a thick organic soil layer limited by an impervious clay layer at a 20–30 cm depth. Savannahs are generally located above forests and generate the transfer of rainwater to downslope forests. Exfiltration into the forests can be the result of this transfer and depends on the thickness and permeability of the forest topsoils and on topographic gradients. Water exfiltration in forest areas highly degraded by pigs and deer enhances erosion and increases further degradation. It probably also limits percolation in the areas located downstream by increasing the amount of superficial runoff concentrated in gullies.     

Hedgerow impacts on soil-water transfer due to rainfall interception and root-water uptake

Hedgerow is one of the most important rural landscapes in the world, especially in Europe. Knowledge about the hydrological role of hedgerows is useful in many fields of study, such as hydrological modelling and rural landscape management. The aim of this study was to investigate the impact of a hedgerow on rainfall distribution, soil-water potential gradient, lateral water transfer and water balance. A hillslope with a hedgerow perpendicular to the slope was monitored. To evaluate hedgerow rainfall interception, rainfall was measured (hourly, daily, and by rainfall event) both next to and up to 16 m upslope and 12 m downslope perpendicularly away from the hedgerow. The strongest correlation between rainfall next to the hedgerow and rainfall at more distant points was obtained using data measured per rainfall event. The average percentage of rainfall intercepted equalled 28% for the leafed period and 12% for the leafless period. The impact of the hedgerow on spatial rainfall distribution was related to distance from the hedgerow and rainfall amount. Annual distribution of soil-water potential showed that the hedgerow influenced it up to 9 m upslope and 6 m downslope, the area in which most of the hedgerow's roots were observed. The soil was driest at the end of summer, which delayed soil rewetting during autumn in areas surrounding the hedgerow. Annual groundwater dynamics exhibited three distinct periods due to temporal rainfall distribution and, especially at the end of summer, root-water uptake. In addition, the total potential gradient showed that unsaturated flow was directed towards the hedgerow in summer and autumn. These results indicate that at the local scale hedgerows influences (1) spatial rainfall distribution, (2) soil rewetting, and (3) groundwater recharge, often at distances well beyond the hedgerow's drip line. Consequently, the processes involved in soil-water dynamics around hedgerows should be integrated into relevant hydrological models, especially for catchments with a dense hedgerow network. Copyright © 2008 John Wiley & Sons, Ltd.     

A model for conductive faults with non-matching grids

In this paper, we are interested in modeling single-phase flow in a porous medium with known faults seen as interfaces. We mainly focus on how to handle non-matching grids problems arising from rock displacement along the fault. We describe a model that can be extended to multi-phase flow where faults are treated as interfaces. The model is validated in an academic framework and is then extended to 3D non K-orthogonal grids, and a realistic case is presented.     

The spatio-temporal development of Copenhagen’s bicycle infrastructure 1912–2013

Cycling plays an important role in low-carbon transitions. Around the globe, cities are constructing bicycle infrastructure. The city of Copenhagen has a bicycle-friendly infrastructure celebrated for its fine-meshed network. This study documents the spatio-temporal development of Copenhagen’s bicycle infrastructure and explores how the development corresponds to other processes of urban transformation. The study builds on historical maps of bicycle infrastructure that are digitised into geographical information, which allows for a comprehensive analysis of the formation of the network. In search for identifying drivers, the study analyses the city’s spatial growth pattern, migration pattern, development of road network and changes in the transport culture. Analyses reveal that the bicycle infrastructure expanded at a relatively constant pace during distinct periods of urban transformation, including periods when the city suffered from spatial, economic and demographic decline, and dominance of car traffic. By discussing reasons and demands for constructing bicycle infrastructure, the study identifies four distinct periods in which bicycle infrastructure was constructed to enhance comfort and safety (first cycling city); the flow for cars (car city); urban liveability for soft transport (liveable city); and, finally, to improve the flow for cyclists as part a strategic re-design of urban space (liveable cycling city).     

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Vertical accuracy evaluation of freely available latest high-resolution (30 m) global digital elevation models over Cameroon (Central Africa) with GPS/leveling ground control points.

Digital Elevation Models (DEMs) contain topographic relief data that are vital for many geoscience applications. This study relies on the vertical accuracy of publicly available latest high-resolution (30?m) global DEMs over Cameroon. These models are (1) the ALOS World 3D-30?m (AW3D30), (2) the Shuttle Radar Topography Mission 1 Arc-Second C-Band Global DEM (SRTM 1) and (3) the Advanced Spaceborne Thermal Emission and Reflection Global DEM Version 2 (ASTER GDEM 2). After matching their coordinate systems and datums, the horizontal positional accuracy evaluation was carried out and it shows that geolocation errors significantly influence the vertical accuracy of global DEMs. After this, the three models are compared among them, in order to access random and systematic effects in the elevation data each of them contains. Further, heights from 555 GPS/leveling points distributed all over Cameroon are compared to each DEM, for their vertical accuracy determination. Traditional and robust statistical measures, normality test, outlier detection and removal were used to describe the vertical quality of the DEMs. The test of the normality rejected the hypothesis of normal distribution for all tested global DEMs. Overall vertical accuracies obtained for the three models after georeferencing and gross error removal in terms of Root Mean Square (RMS) and Normalized Median Absolute Deviation (NMAD) are: AW3D30 (13.06?m and 7.75?m), SRTM 1 (13.25?m and 7.41?m) and ASTER GDEM 2 (18.87?m and 13.30?m). Other accuracy measures (MED, 68.3% quantile, 95% quantile) supply some evidence of the good quality of AW3D30 over Cameroon. Further, the effect of land cover and slope on DEM vertical accuracy was also analyzed. All models have proved to be worse in the areas dominated by forests and shrubs areas. SRTM 1 and AW3D30 are more resilient to the effects of the scattering objects respectively in forests and cultivated areas. The dependency of DEMs accuracy on the terrain roughness is evident. In all slope intervals, AW3D30 is performing better than SRTM 1 and ASTER GDEM 2 over Cameroon. AW3D30 is more representative of the external topography over Cameroon in comparison with two others datasets and SRTM 1 can be a serious alternative to AW3D30 for a range of DEM applications in Cameroon.