Over the past five years, Distributed Temperature Sensing (DTS) along fiber optic cables using Raman backscattering has become an important tool in the environmental sciences. Many environmental applications of DTS demand very accurate temperature measurements, with typical RMSE < 0.1 K. The aim of this paper is to describe and clarify the advantages and disadvantages of double-ended calibration to achieve such accuracy under field conditions. By measuring backscatter from both ends of the fiber optic cable, one can redress the effects of differential attenuation, as caused by bends, splices, and connectors. The methodological principles behind the double-ended calibration are presented, together with a set of practical considerations for field deployment. The results from a field experiment are presented, which show that with double-ended calibration good accuracies can be attained in the field.

Population growth, increasing energy demand and the depletion of fossil fuel reserves necessitate a search for sustainable alternatives for electricity generation. Hydropower could replace a large part of the contribution of gas and oil to the present energy mix. However, previous high-resolution estimates of hydropower potential have been local, and have yet to be applied on a global scale. This study is the first to formally present a detailed evaluation of the hydropower potential of each location, based on slope and discharge of each river in the world. The gross theoretical hydropower potential is approximately 52 PWh/year divided over 11.8 million locations. This 52 PWh/year is equal to 33% of the annually required energy, while the present energy production by hydropower plants is just 3% of the annually required energy. The results of this study: all potentially interesting locations for hydroelectric power plants, are available online.

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Plastic debris in water systems is a major challenge for our ecosystem, because it is extremely persistent in the environment. Apart from the importance of reducing the amount of plastic entering the ocean, clearing the rivers from debris is important for societal concerns, such as flood risks. Plastic waste accumulation at trash racks leads to a rise in upstream water level and may increase urban flood risk. Until now, most studies of riverine debris accumulation predominantly focused on organic accumulations at trash racks and bridge piers. In this study, flume experiments were used to study the behavior of plastic and mixed debris accumulations. One of the key findings from this study is that plastic debris causes a faster blockage than organic matter, as the plastic blockage contains fewer voids and therefore has a higher blockage density. In addition to the flume experiments, field measurements were performed in the Cikapundung River (Indonesia). This river is one of the tributaries of the Citarum River, which is considered one of the world's most heavily polluted rivers. Combining the results of the flume experiments and field measurements demonstrated that a backwater rise of 1 m/h is plausible for a blocked trash rack in the Cikapundung River, illustrating the additional flood risk caused by plastic pollution. Our results emphasize the need for further quantifying riverine (plastic) debris and investigating its relation to changes in the water system behavior, including its influence on urban flood risk.

An appropriate distribution of flood losses over time span may dampen the degree of disruption. Flood insurance is one of the effective ways in order to cope with the aftermaths of flood events. In the absence of an acceptable risk-based assessment framework, flood insurance and its extensive benefits are not fully achieved yet. Consequently, flood insurance is trivially practiced worldwide. To ensure the integration of flood insurance into regular flood management practices, its acceptability by floodplain inhabitants is a prerequisite. Therefore, an admissible insurance rate is a vital factor for the acceptability of insurance policy. This article introduces a risk-based methodology to calculate insurance rate. Normally, insurance rates are based on historic flood events or on a specific design flood. Expected annual damages distribution map (EADDM) is developed to assess spatial distribution of risk. Distribution of flood losses against a specific flood is compared with EADDM. The impacts of both approaches on insurance provider and insured are studied. Single flood approach ignores the impacts because of other floods. Therefore, insurance rates based on single flood are not justifiable. The proposed framework not only facilitates risk-based insurance rate calculation but also endorse flood insurance acceptability. Collins and Simpson, 2007). The implementation of flood insurance is mostly supported by legal provisions, public incentives, and enforcement practices. For example, in the United States, no mortgage lenders that are federally bs_bs_banner J Flood Risk Management 7 (2014) 291-307

The government of the Netherlands has formulated an action programme to prepare the Dutch water systems for future changes like climate change, subsidence, and spatial developments, as these are expected to increase both frequency and damage of flood events. One of the commitments made was that all water agencies are obliged to test their regional surface water systems to new flood standards based on an acceptable probability of flooding. The question addressed in this paper is whether this type of flood standards is appropriate to ensure that cost-efficient measures are taken. A case study is used to illustrate that applying the proposed standards can lead to inefficient measures, and that a better objective is to minimize flood risk, within acceptable cost. Copyright # 2006 John Wiley & Sons, Ltd.key words: flood risk; flood standards; climate change RÉ SUMÉ Le gouvernement des Pays Bas a formulé un programme d'action pour préparer les systèmes hydrauliques hollandais à de futurs changements tels que le changement climatique, l'affaissement des sols, ou le développement de nouveaux espaces, car ces changements sont de nature à augmenter la fréquence et les dommages des inondations. Un des engagements pris consiste pour toutes les agences de l'eau à faire pour leurs systèmes régionaux d'eaux de surface le test de nouvelles normes d'inondation basées sur une probabilité acceptable d'inondation. La question posée dans cet article est de savoir si ce type de normes d'inondation permet de garantir l'efficience des mesures prises. Une étude de cas montre que l'application des normes proposées peut conduire à des mesures inefficientes, et qu'il est préférable d'avoir comme objectif la minimisation des risques d'inondation, tout en restant dans une fourchette de coûts acceptable.

Several recent studies have highlighted the potential of Actively Heated Fiber Optics (AHFO) for high resolution soil moisture mapping. In AHFO, the soil moisture can be calculated from the cumulative temperature (normalTcum), the maximum temperature (normalTmax), or the soil thermal conductivity determined from the cooling phase after heating (λ). This study investigates the performance of the normalTcum, normalTmax and λ methods for different heating strategies, i.e., differences in the duration and input power of the applied heat pulse. The aim is to compare the three approaches and to determine which is best suited to field applications where the power supply is limited. Results show that increasing the input power of the heat pulses makes it easier to differentiate between dry and wet soil conditions, which leads to an improved accuracy. Results suggest that if the power supply is limited, the heating strength is insufficient for the λ method to yield accurate estimates. Generally, the normalTcum and normalTmax methods have similar accuracy. If the input power is limited, increasing the heat pulse duration can improve the accuracy of the AHFO method for both of these techniques. In particular, extending the heating duration can significantly increase the sensitivity of normalTcum to soil moisture. Hence, the normalTcum method is recommended when the input power is limited. Finally, results also show that up to 50% of the cable temperature change during the heat pulse can be attributed to soil background temperature, i.e., soil temperature changed by the net solar radiation. A method is proposed to correct this background temperature change. Without correction, soil moisture information can be completely masked by the background temperature error.

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