The impact of stormwater on a soil profile in an infiltration basin

The effects of urban stormwater on the soil of an infiltration/ holding basin were studied within the framework of research carried out by OTHU (Urban Hydrology Field Observatory of Lyon, France). The biophysicochemical impacts of stormwater from an industrial watershed on the local soil (to a depth of 4 m in the unsaturated zone) were measured. Several types of measurement (pH, organic matter, particle size, heavy metals content, and heterotrophic viable bacterial counts) for three vertical soil profiles were carried out. High concentrations of heavy metals and significant variations in pH and silt to a depth of 1.5 m were observed. The concentrations decreased as a function of distance from the stormwater discharge pipe. Changes in the bacterial population were also observed, varying in accordance with the depth and location of the profile.

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Resumen Se estudiaron los efectos de tormentas en zonas urbanas sobre el suelo de una cuenca retenedora/de infiltración dentro del marco de investigación llevado a cabo por OTHU (Laboratorio de Observación de Campo de Hidrología Urbana, Lyon, Francia). Se midieron los impactos biofisicoquímicos de la tormenta en una cuenca industrial sobre el suelo local (a una profundidad de 4m en la zona no saturada). Se llevaron a cabo varios tipos de mediciones (pH, materia org′nica, tama?o de partículas, contenido de metales pesados, y conteo de bacterias viables heterotróficas) en tres perfiles ed′ficos. Se observaron altas concentraciones de metales pesados y variaciones significativas en pH y limo a una profundidad de 1.5m. Las concentraciones disminuyeron en función de la distancia del tubo de descarga de las aguas de la tormenta. También se observaron cambios en las poblaciones de bacterias los cuales variaban en función de la profundidad y localización del perfil.

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Résumé Dans le cadre de la fédération de recherche OTHU (Observatoire de Terrain en Hydrologie Urbaine de Lyon) une étude sur l’impact des eaux pluviales sur le sol d’un bassin d’infiltration / rétention est présentée. Il s’agit d’évaluer l’impact biophysicochimique des eaux pluviales issues d’un bassin versant industriel sur une profondeur d’environ 4 m de zone non saturée. Pour cela plusieurs types de mesures ont été effectuées (pH, perte au feu, teneur en Cu, Pb, Cd, dénombrement bactérien) suivant trois profils verticaux. Les résultats montrent des concentrations importantes de métaux et des variations de pH jusqu’à 1.5 m de profondeur. De plus, les résultats montrent une variation suivant la position des points de prélèvements. Des modifications de la population bactérienne sont également observées suivant la profondeur et l’emplacement des profils.

     

降雨入渗条件下交河故城土质崖体渗流场计算及稳定性分析

交河故城土遗址是国家重点文物保护单位。其周边直立土质崖体的安全稳定性对整个土遗址的保护有着重要的意义。崖体的安全隐患主要在于其顶部存在众多的宽深裂缝,局部崖体顶部甚至出现了较大的临空块体。根据降雨非饱和入渗理论,建立饱和-非饱和降雨入渗模型,并发展了相应的数值模拟技术,详细分析了在一个较为完整降雨入渗过程中土质崖体内部渗流场的分布特征。在此基础上,根据非饱和土强度理论,考虑了降雨过程中土质崖体非饱和区的强度变化及饱和区渗透体积力的影响,选取了一典型剖面,应用强度折减法计算了崖体支护前后的稳定性,并对现有的加固支护措施作了评价。结果表明:所建立的饱和-非饱和降雨入渗模型较好地描述了降雨过程中崖体内部的渗流场分布;降雨过程中崖体的安全系数逐渐减小;在现有加固支护条件下,崖体的整体稳定性较好,但安全裕度略低,建议对崖体局部临空块体采取进一步的加固措施。     

A kinetic approach for simulating redox‐controlled fringe and core biodegradation processes in groundwater: model development and application to a landfill site in Piedmont,Italy

A three‐dimensional model for predicting redox controlled, multi‐species reactive transport processes in groundwater systems is presented. The model equations were fully integrated within a MODFLOW‐family reactive transport code, RT3D. The model can simulate organic compound biodegradation coupled to different terminal electron acceptor processes. A computational approach, which uses the spatial and temporal distribution of the rates of different redox reactions, is proposed to map redox zones. The method allows one to quantify and visualize the biological degradation reactions occurring in three distinct patterns involving fringe, pseudo‐core and core processes. The capabilities of the numerical model are demonstrated using two hypothetical examples: a batch problem and a simplified two‐dimensional reactive transport problem. The model is then applied to an unconfined aquifer underlying a leaking landfill located near the city of Turin, in Piedmont (Italy). At this site, high organic load from the landfill leachate activates different biogeochemical processes, including aerobic degradation, denitrification, manganese reduction, iron reduction, sulfate reduction and methanogenesis. The model was able to describe and quantify these complex biogeochemical processes. The proposed model offers a rational framework for simulating coupled reactive transport processes occurring beneath a landfill site. Copyright © 2008 John Wiley & Sons, Ltd.     

Runoff generation mechanisms in pastures of the Sand Mountain region of Alabama—a field investigation

Excessive application of poultry litter to pastures in the Sand Mountain region of north Alabama has resulted in phosphorus (P) contamination of surface water bodies and buildup of P in soils of this region. Since surface runoff is recognized as the primary mechanism of P transport, understanding surface runoff generation mechanisms are crucial for alleviating water quality problems in this region. Identification of surface runoff generation mechanisms is also important for delineation of hydrologically active areas (HAAs). Therefore, the specific objective of this study was to identify surface runoff generation mechanisms (infiltration excess versus saturation excess) using distributed surface and subsurface sensors and rain gauge. Results from three rainfall events (2·13–3·43 cm) of differing characteristics, and sensor data at four locations with differing soil hydraulic properties along the hillslope showed that the main surface runoff generation mechanism in this region is infiltration excess. Because of this, rainfall intensity and soil hydraulic conductivity were found to play dominant roles in surface runoff generation in this region. Further, only short periods of a few rainfall events during which the rainfall intensity is high produce surface runoff. This study indicates that perhaps subsurface flows and transport of P in subsurface flows need to be quantified to reduce P contamination of surface water bodies in this region. Current studies at this location are identifying spatial and temporal distribution of HAAs, quantifying rainfall characteristics that generate runoff, and estimating runoff volume that results from connected HAAs. Copyright © 2008 John Wiley & Sons, Ltd.     

Fire effects on rangeland hydrology and erosion in a steep sagebrush‐dominated landscape

Post‐fire runoff and erosion from wildlands has been well researched, but few studies have researched the degree of control exerted by fire on rangeland hydrology and erosion processes. Furthermore, the spatial continuity and temporal persistence of wildfire impacts on rangeland hydrology and erosion are not well understood. Small‐plot rainfall and concentrated flow simulations were applied to unburned and severely burned hillslopes to determine the spatial continuity and persistence of fire‐induced impacts on runoff and erosion by interrill and rill processes on steep sagebrush‐dominated sites. Runoff and erosion were measured immediately following and each of 3 years post‐wildfire. Spatial and temporal variability in post‐fire hydrologic and erosional responses were compared with runoff and erosion measured under unburned conditions. Results from interrill simulations indicate fire‐induced impacts were predominantly on coppice microsites and that fire influenced interrill sediment yield more than runoff. Interrill runoff was nearly unchanged by burning, but 3‐year cumulative interrill sediment yield on burned hillslopes (50 g m^?2) was twice that of unburned hillslopes (25 g m^?2). The greatest impact of fire was on the dynamics of runoff once overland flow began. Reduced ground cover on burned hillslopes allowed overland flow to concentrate into rills. The 3‐year cumulative runoff from concentrated flow simulations on burned hillslopes (298 l) was nearly 20 times that measured on unburned hillslopes (16 l). The 3‐year cumulative sediment yield from concentrated flow on burned and unburned hillslopes was 20 400 g m^?2 and 6 g m^?2 respectively. Fire effects on runoff generation and sediment were greatly reduced, but remained, 3 years post‐fire. The results indicate that the impacts of fire on runoff and erosion from severely burned steep sagebrush landscapes vary significantly by microsite and process, exhibiting seasonal fluctuation in degree, and that fire‐induced increases in runoff and erosion may require more than 3 years to return to background levels. Published in 2008 by John Wiley & Sons, Ltd.     

One‐ and two‐dimensional modelling of overland flow in semiarid shrubland,Jornada basin,New Mexico

Two distributed parameter models, a one‐dimensional (1D) model and a two‐dimensional (2D) model, are developed to simulate overland flow in two small semiarid shrubland watersheds in the Jornada basin, southern New Mexico. The models are event‐based and represent each watershed by an array of 1‐m² cells, in which the cell size is approximately equal to the average area of the shrubs. Each model uses only six parameters, for which values are obtained from field surveys and rainfall simulation experiments. In the 1D model, flow volumes through a fixed network are computed by a simple finite‐difference solution to the 1D kinematic wave equation. In the 2D model, flow directions and volumes are computed by a second‐order predictor–corrector finite‐difference solution to the 2D kinematic wave equation, in which flow routing is implicit and may vary in response to flow conditions. The models are compared in terms of the runoff hydrograph and the spatial distribution of runoff. The simulation results suggest that both the 1D and the 2D models have much to offer as tools for the large‐scale study of overland flow. Because it is based on a fixed flow network, the 1D model is better suited to the study of runoff due to individual rainfall events, whereas the 2D model may, with further development, be used to study both runoff and erosion during multiple rainfall events in which the dynamic nature of the terrain becomes an important consideration. Copyright © 2006 John Wiley & Sons, Ltd.     

An investigation of the geometric controls on the morphological evolution of small-scale salt terrains,Cardona, Spain

Small-scale terrains on salt materials were surveyed with a Total Station and a series of digital elevation models (DEMs) constructed. Two sets of observations were made, eight months apart, during which the terrains underwent significant erosion. The difference in elevation shown by the DEMs, calculated by subtraction, is a measure of surface erosion of the salt terrains. The erosion rate was analysed with respect to four terrain parameters calculated in the software. High erosion rates, and their strong control by terrain slope, are demonstrated, supporting an earlier study using erosion pins. Slope profile curvature is also indicated as having some influence. The combination of scanning Total Station and DEM software is shown to be an effective tool for investigating rapid geomorphic change at this scale of study.     

Late Quaternary basin evolution of the Gulf of Corinth: Sequence stratigraphy, sedimentation, fault–slip and subsidence rates

The Gulf of Corinth is a graben, which has undergone extension during the Late Quaternary. The subsidence rate is rapid in the currently marine part whereas uplift now affects a large part of the initially subsiding area in the North Peloponnese. In this paper, we document the rates of subsidence/uplift and extension based on new subsurface data, including seismic data and long piston coring in the deepest part of the Gulf. Continuous seismic profiling data (air gun) have shown that four (at least) major oblique prograding sequences can be traced below the northern margin of the central Gulf of Corinth. These sequences have been developed successively during low sea level stands, suggesting continuous and gradual subsidence of the northern margin by 300 m during the Late Quaternary (last 250 ka). Subsidence rates of 0.7–1.0 m kyr^− 1 were calculated from the relative depth of successive topset to foreset transitions. The differential total vertical displacement between the northern and the southern margins of the Corinth graben is estimated at about 2.0–2.3 m kyr^− 1.

Sequence stratigraphic interpretation of seismic profiles from the basin suggests that the upper sediments (0.6 s twtt thick) in the depocenter were accumulated during the last 250 ka at a mean rate of 2.2–2.4 m kyr^− 1. Long piston coring in the central Gulf of Corinth basin enabled the recovery of lacustrine sediments, buried beneath 12–13.5 m of Holocene marine sediments. The lacustrine sequence consists of varve-like muddy layers interbedded with silty and fine sand turbidites. AMS dating determined the age of the marine–lacustrine interface (reflector Z) at about 13 ka BP. Maximum sedimentation rates of 2.4–2.9 m kyr^− 1 were calculated for the Holocene marine and the last glacial, lacustrine sequences, thus verifying the respective rates obtained by the sequence stratigraphic interpretation. Recent accumulation rates obtained by the ²¹⁰Pb-radiometric method on short sediment box cores coincide with the above sedimentation rates. Vertical fault slip rates were measured by using fault offsets of correlated reflector Z. The maximum subsidence rate of the depocenter (3.6 m kyr^− 1) exceeds the maximum sedimentation rate by 1.8 m kyr^− 1, which, consequently, corresponds to the rate of deepening of the basin's floor. The above rates indicate that the 2.2 km maximum sediment thickness as well as the 870 m maximum depth of the basin may have formed during the last 1 Ma, assuming uniform mean sedimentation rate throughout the evolution of the basin.     

The accountability imperative for quantifying the uncertainty of emission forecasts: evidence from Mexico

Governmental climate change mitigation targets are typically developed with the aid of forecasts of greenhouse-gas (GHG) emissions. The robustness and credibility of such forecasts depends, among other issues, on the extent to which forecasting approaches can reflect prevailing uncertainties. We apply a transparent and replicable method to quantify the uncertainty associated with projections of gross domestic product growth rates for Mexico, a key driver of GHG emissions in the country. We use those projections to produce probabilistic forecasts of GHG emissions for Mexico. We contrast our probabilistic forecasts with Mexico’s governmental deterministic forecasts. We show that, because they fail to reflect such key uncertainty, deterministic forecasts are ill-suited for use in target-setting processes. We argue that (i) guidelines should be agreed upon, to ensure that governmental forecasts meet certain minimum transparency and quality standards, and (ii) governments should be held accountable for the appropriateness of the forecasting approach applied to prepare governmental forecasts, especially when those forecasts are used to derive climate change mitigation targets.

POLICY INSIGHTS

• No minimum transparency and quality standards exist to guide the development of GHG emission scenario forecasts, not even when these forecasts are used to set national climate change mitigation targets.

• No accountability mechanisms appear to be in place at the national level to ensure that national governments rely on scientifically sound processes to develop GHG emission scenarios.

• Using probabilistic forecasts to underpin emission reduction targets represents a scientifically sound option for reflecting in the target the uncertainty to which those forecasts are subject, thus increasing the validity of the target.

• Setting up minimum transparency and quality standards, and holding governments accountable for their choice of forecasting methods could lead to more robust emission reduction targets nationally and, by extension, internationally.

     

并置VLBI站相对形变率及其与VTRF2005结果的比较

对杨志根等人在2005年估计的全球6个并置VLBI站的相对形变率(特别是相对垂直形变率)结果与最近的VLBI全球解VTRF2005的相应结果作了比较。结果表明,北美Greenbank的NRAO20和NRAO85_3两个VLBI站之间每年3—4mm的相对垂直形变率和Westford的WEST- FORD和HAYSTACK两个VLBI站间每年1-2mm的相应结果可以进一步得到肯定;太平洋夏威夷岛的KOKEE和KAUAI两个VLBI站每年2～5mm的相对水平形变率和日本鹿岛的KASHIMA和KASHIM34两个VLBI站间每年1-2mm的相应结果也可以得到确认。然而,每年2—4mm的KASHIMA和KASHIM34站间的相对垂直形变率结果,在过去所有观测研究的结果中都被基本肯定,在VTRF2005中的结果中却几乎消失了,对其中可能的原因作了讨论。此外,对北美的FD-VL- BA和HRASO85两个VLBI站间的相对垂直形变率仍不能肯定,在不同的全球解中,FD-VLBA站的形变率解结果是基本稳定的,而HRASO85站在VTRF2005中的垂直形变率结果为(2．61±3．91) mm／a,与估计的结果符号相反,并且比在VTRF2003中的相应结果大了2．2mm／a,估计误差也大了近7倍。有关的结果还有待采用更新的资料进行讨论。