Comparing quantitative precipitation forecast methods for prediction of sewer flows in a small urban area

Abstract

Due to the relatively small spatial scale, as well as rapid response, of urban drainage systems, the use of quantitative rainfall forecasts for providing quantitative flow and depth predictions is a challenging task. Such predictions are important when consideration is given to urban pluvial flooding and receiving water quality, and it is worthwhile to investigate the potential for improved forecasting. In this study, three quantitative precipitation forecast methods of increasing complexity were compared and used to create quantitative forecasts of sewer flows 0–3 h ahead in the centre of a small town in the north of England. The HyRaTrac radar nowcast model was employed, as well as two different versions of the more complex STEPS model. The STEPS model was used as a deterministic nowcasting system, and was also blended with the Numerical Weather Prediction (NWP) model MM5 to investigate the potential of increasing forecast lead-times (LTs) using high-resolution NWP. Predictive LTs between 15 and 90 min gave acceptable results, but were a function of the event type. It was concluded that higher resolution rainfall estimation as well as nowcasts are needed for prediction of both local pluvial flooding and combined sewer overflow spill events.

Editor D. Koutsoyiannis; Guest editor R.J. Moore     

Spatial modeling of drought events using max-stable processes

With their severe environmental and socioeconomic impact, drought events belong to the most far-reaching natural disasters. Effects are tremendous in rain-fed agricultural areas as in Africa. We analyzed and modeled the spatio-temporal statistical behavior of the Normalized Difference Vegetation Index as a risk indicator for drought, reflecting its stochastic effects on vegetation. The study used a data set for Rwanda obtained from multitemporal satellite remote sensor measurements during a 14-year period and divided into season-specific spatial random fields. Maximal deviations from average conditions were modeled with max-stable Brown–Resnick processes taking methodological and computational challenges into account. Those challenges are caused by the large spatial extent and the relatively short time span covered by the data. Extensive simulations enabled us to go beyond the observations and, thus, to estimate several important characteristics of extreme drought events, such as their expected return period.     

Sound velocity measurements in dhcp-FeH up to 70 GPa with inelastic X-ray scattering: Implications for the composition of the Earth's core

We have determined the density evolution of the sound velocity of dhcp-FeH_x (x ≈ 1) up to 70 GPa at room temperature, by inelastic X-ray scattering and by X-ray diffraction. We find that the variation of V_P with density is different for the ferromagnetic and nonmagnetic dhcp-FeH_x, and that only nonmagnetic dhcp-FeH_x follows Birch's law. Combining our results with Birch's law for iron and assuming an ideal two-component mixing model, we obtain an upper bound of the hydrogen content in the Earth's inner core, 0.23(6) wt.% H, corresponding to FeH_0.13(3). The iron alloy with 0.23(6) wt.% H can satisfy the density, and compressional and shear sound velocities of the PREM inner core, assuming that there are no other light elements in the inner core.     

Modelling biofilm growth in the presence of carbon dioxide and water flow in the subsurface

The concentration of greenhouse gases – particularly carbon dioxide (CO₂) – in the atmosphere has been on the rise in the past decades. One of the methods which have been proposed to help reduce anthropogenic CO₂ emissions is the capture of CO₂from large, stationary point sources and storage in deep geological formations. The caprock is an impermeable geological layer which prevents the leakage of stored CO₂, and its integrity is of utmost importance for storage security. Due to the high pressure build-up during injection, the caprock in the vicinity of the well is particularly at risk of fracturing. Biofilms could be used as biobarriers which help prevent the leakage of CO₂ through the caprock in injection well vicinity by blocking leakage pathways. The biofilm could also protect well cement from corrosion by CO₂-rich brine.     

Backazimuthal Variations of Splitting Parameters of Teleseismic SKS Phases Observed at the Broadband Stations in Germany

—SKS phases observed at broadband stations in Germany show significant shear-wave splitting. We have analyzed SKS and SKKS phases for shear-wave splitting from 13 stations of the German Regional Seismic Network (GRSN), from 3 three-component stations of the Gräfenberg array (GRF) and from one Austrian station (SQTA). The data reveal strong differences in the splitting parameters (fast direction φ and delay time δt from a single event at various stations as well as variations at the individual stations for events with different backazimuths. The backazimuthal variations of the splitting parameters at some stations can be explained by two-layer anisotropy models with horizontal symmetry axes. The best resolved two-layer model is the GRA1 model (upper layer φ = 40°, δt = 1.15s; lower layer φ = 115°, δt = 1.95s). The upper layer can be attributed to the lithosphere. Because of the magnitude of the delay time of the upper layer, the lower layer must lie within the asthenosphere. At other stations splitting parameters are consistent with an anisotropic one-layer model for the upper mantle. Stations near the Bohemian Massif show fast directions near EW. Throughout NE Germany the directions are oriented NW/SE. The reason for this direction is probably the nearby Tornquist-Teisseyre line. The observed fast axes are subparallel to this prominent Transeuropean suture zone. At stations in southern Germany near the Alps we observed ENE/WSW directions. Below some stations we also found indications of inclined anisotropic layers.     

Remote sensing in landscape diagnosis

In landscape diagnosis landscapes are evaluated on the basis of their natural and technological characteristics with regard to the possibilities and risks of intensive utilization. Land use is an essential criterion for the evaluation of the condition of landscapes. Remote sensing will allow for an analysis of large areas with regard to land use. Landscape diagnosis through satellite photographs will be illustrated in two examples. In the first one multitemporal evaluation of satellite photographs is discussed with particular reference to attempts made to characterize the utilization of landscape potentials. In the second example attempts have been made to classify medium-sized landscape units by satellite photographs, with additional characterization through thematic maps based on the Atlas GDR.     

Chemical composition and stable carbon isotopic ratios of crude oils from Southern Germany

Thirty crude oils were sampled in the South German Molasse Basin. The crude oils were chemically separated into five component groups and their stable carbon isotopic ratios were determined by mass spectrometry. A distinct differentiation of four regionally connected groups can be inferred from the results of the δ¹³C values and chemical analyses. This grouping is in accordance with the present geologic information on the origin of crude oils in the Molasse Basin.The chemistry of crude oils seems to have been influenced by secondary processes in the eastern part of the Molasse Basin.     

Gases and water isotopes in a geochemical section across the Larderello,Italy, geothermal field

Steam samples from six wells (Colombaia, Pineta, Larderello 57, Larderello 155, Gabbro 6, and Gabbro 1) in a south to north section across the Larderello geothermal field have been analyzed for inorganic and hydrocarbon gases and for oxygen-18 and deuterium of steam. The wells generally decrease in depth and increase in age toward the south. The steam samples are generally characterized by

1. Total gas contents increasing south to north from 0.003 to 0.05 mole fraction;
2. Constant CO₂ (95±2 percent); near constant H₂S (1.6±0.8), N₂ (1.2±0.8), H₂ (2±1), CH₄ (1.2±1), and no O₂ in the dry gas;
3. Presence of numerous, straight chain and branched C₂ to C₆ hydrocarbons plus benzene in amounts independent of CH₄ contents with highest concentrations in the deeper wells;
4. Oxygen-18 contents of steam increasing south to north from ?5.0‰ to ?0.4‰ with little change in deuterium (?42±2‰).

These observations are interpreted as showing:

1. Decreasing gas contents with amount of production because the proportion of steam boiled from liquid water increases with production;
2. Synthesis of CH₄ from H₂ and CO₂ with CO₂ and H₂ produced by thermal metamorphism and rock-water reactions;
3. Extraction of C₂ to C₆ hydrocarbons from rock organic matter;
4. Either oxygen isotope exchange followed by distillation of steam from the north toward the south (2 plates at ～220°C) or mixture of deeper more-exchange waters from the north with shallow, less-exchanged recharging waters from the south.

     

Numerical analysis of seismoelectric wave propagation in spatially confined geological units

Using numerical modelling, we investigate the evolution of seismoelectric effects induced by seismic excitation in spatially confined lithological units. Typical geometries represent clay lenses embedded in an aquifer or petroleum deposits in a host rock. In fluid‐saturated rocks, seismic waves can generate electromagnetic fields due to electrokinetic coupling mechanisms associated with such processes in the vicinity of the fluid‐mineral interface. Two seismoelectric phenomena are investigated: (1) the co‐seismic field associated with the seismic displacement at each point in a subsurface and (2) the interface response generated at layer boundaries. Our modelling uses a simplified time‐domain formulation of the coupled problem and an efficient 2D finite‐element implementation. To gain insight into the morphogenetic field behaviour of the seismoelectric effects, several numerical simulations for various target geometries were treated. Accordingly, we varied both the thickness of the confined units and the value of the electrical bulk conductivity in porous media. Analysis of these effects shows differences between interface responses for electrically conductive versus resistive units. So the pertinent contrast in electrical bulk conductivity controls the shape and structure of these seismoelectric conversion patterns. Moreover, the seismoelectric interface response captures both the petrophysical and geometrical characteristics of the geological unit. These models demonstrate the value of using seismoelectric interface response for reservoir characterization in either hydrogeological or hydrocarbon exploration studies.