Discharge estimation in a backwater affected meandering river

Variable effects of backwaters complicate the development of rating curves at hydrometric measurement stations. In areas influenced by backwater, single-parameter rating curve techniques are often inapplicable. To overcome this, several authors have advocated the use of an additional downstream level gauge to estimate the longitudinal surface level gradient, but this is cumbersome in a lowland meandering river with considerable transverse surface level gradients. Recent developments allow river flow to be continuously monitored through velocity measurements with an acoustic Doppler current profiler (H-ADCP), deployed horizontally at a river bank. This approach was adopted to obtain continuous discharge estimates at a cross-section in the River Mahakam at a station located about 300 km upstream of the river mouth in the Mahakam delta. The discharge station represents an area influenced by variable backwater effects from lakes, tributaries and floodplain ponds, and by tides. We applied both the standard index velocity method and a recently developed methodology to obtain a continuous time-series of discharge from the H-ADCP data. Measurements with a boat-mounted ADCP were used for calibration and validation of the model to translate H-ADCP velocity to discharge. As a comparison with conventional discharge estimation techniques, a stage-discharge relation using Jones formula was developed. The discharge rate at the station exceeded 3300 m3 s-1. Discharge series from a traditional stage-discharge relation did not capture the overall discharge dynamics, as inferred from H-ADCP data. For a specific river stage, the discharge range could be as high as 2000 m3 s-1, which is far beyond what could be explained from kinematic wave dynamics. Backwater effects from lakes were shown to be significant, whereas the river-tide interaction may impact discharge variation in the fortnightly frequency band. Fortnightly tides cannot easily be isolated from river discharge variation, which features similar periodicitie

Climatology of daily rainfall semi-variance in The Netherlands

Rain gauges can offer high quality rainfall measurements at their locations. Networks of rain gauges can offer better insight into the space-time variability of rainfall, but they tend to be too widely spaced for accurate estimates between points. While remote sensing systems, such as radars and networks of microwave links, can offer good insight in the spatial variability of rainfall they tend to have more problems in identifying the correct rain amounts at the ground. A way to estimate the variability of rainfall between gauge points is to interpolate between them using fitted variograms. If a dense rain gauge network is lacking it is difficult to estimate variograms accurately. In this paper a 30-year dataset of daily rain accumulations gathered at 29 automatic weather stations operated by KNMI (Royal Netherlands Meteorological Institute) and a one-year dataset of 10 gauges in a network with a radius of 5 km around CESAR (Cabauw Experimental Site for Atmospheric Research) are employed to estimate variograms. Fitted variogram parameters are shown to vary according to season, following simple cosine functions. Semi-variances at short ranges during winter and spring tend to be underestimated, but semi-variances during summer and autumn are well predicted

Erosion of mud/sand mixtures

The sediments found in tidal rivers, estuaries and coastal zones are usually a mixture of sand and mud. The accumulation and the erosion of these sediments have a large impact on the accessibility of harbours and on the necessary maintenance dredging operations. The ability of the mud fraction to adsorb large amounts of contaminants makes it even more important to fully understand the mixture behaviour. The sediment bed in a combined sewer system can also be described as a mixture of cohesive and cohesionless sediments. The accumulation of sediments reduces the sewer capacity and the erosion of the sediment bed can cause environmental problems when part of the flow is discharged into surface waters. Again, it is important that the behaviour of the sediment mixture is properly understood.This thesis represents the results of over five years of laboratory experiments on the erosion of mud/sand mixtures in uniform flow. The aim was to examine the effect of the mixture composition on the behaviour of the sediment bed in uniform flow conditions. The transition from cohesionless to cohesive behaviour, with respect to erosion resistance and mode of erosion, has been studied by adding more and more cohesive sediment to sand. A critical mud content is found above which the mixture can be described as a cohesive sediment; below this limit the mixture acts like sand only. The existence of a critical mixture composition has been explained in terms of the different structures formed inside the homogeneous mixture. Furthermore, the formation of a layered bed from a mud/sand suspension waS followed. The influence of the mixture composition on the sedimentation and erosion processes has been studied. The sand fraction seemed to enhance consolidation and reduce the resulting bed thickness. The erosion of the stratified deposit was a sequence of suspended load and bed load transport phases. In order to extrapolate the laboratory results to field conditions, the influence of the shape and the scale of the flume cross section on bed shear streSS distributions has been studied in detail. Both the shape and the aspect ratio of the flume were found to have an important effect on secondary currents and hence on bed shear stresses. Finally, based on the results of the experimental study, some guidelines to model the erosion resistance and erosion rates of mud/sand mixtures have been formulated

Multi-level optical signal generation using a segmented-electrode InP IQ-MZM with integrated CMOS binary drivers

We present a segmented-electrode InP IQ-MZM, capable of multi-level optical signal generation (5-bit per I/Q arm) by employing direct digital drive from integrated, low-power (1W) CMOS binary drivers. Programmable, multi-level operation is demonstrated experimentally on one MZM of the device

84 Gbit/s SiGe BiCMOS duobinary serial data link including Serialiser/Deserialiser (SERDES) and 5-tap FFE

The increasing demand for bandwidth fuels the development towards high data rate electrical serial links. These links generally suffer from considerable frequency-dependent loss, introducing the need for equalisation at 10 Gbit/s and higher. Modulation schemes with improved spectral efficiency, with respect to non-retrun to zero (NRZ), combined with feed-forward equalisation (FFE), allow increasing the chip-to-chip data rate with the drawback of a more complex, e.g. multi-level, receiver (Rx). The use of duobinary modulation (DB) is presented to realise a high-speed serial link. The increase in complexity of a DB Rx is limited, whereas the required channel bandwidth compared with NRZ is reduced. Furthermore, the need for equalisation when compared with PAM4 is reduced as the required roll-off that is needed to create a duobinary modulated signal from an NRZ stream can incorporate the frequency-dependent loss of the link

100 Gbit/s serial transmission using a silicon-organic hybrid (SOH) modulator and a duobinary driver IC

100 Gbit/s three-level (50 Gbit/s 00K) signals are generated using a silicon-organic hybrid modulator and a BiCMOS duobinary driver IC at a BER of 8.5x10(-5)(<10(-12)). We demonstrate dispersion-compensated transmission over 5 km

Anti-inflammatory phytotherapeutics: a valuable alternative to NSAID treatment in horses?

ABSTRACT In equine practice, phytotherapy is meeting the increasing demand of horse owners for &quot;natural&quot;, safe treatment methods. Long-term use of NSAIDs can cause severe adverse effects, hence the growing popularity of anti-inflammatory phytotherapeutics. At the current time, several different herbal mixes are being commercialized, which makes it difficult for horse owners and veterinarians alike to make a well-founded choice. Harpagophytum procumbens (devil&apos;s claw), Salix spp. (willow) and Ribes nigrum (blackcurrant), three plants that are often used in these mixes, have been evaluated both in vitro and in vivo. Based on published studies and the evaluation of these studies, for example by the Cochrane Collaboration, there seems to be some evidence for Harpagophytum procumbens and Salix spp. having a stronger analgesic and anti-inflammatory effect than placebos in humans. In horses, however, only one limited clinical study on Harpagophytum has been performed up until now, while no studies were found on the use of Salix in horses. More research is needed before any claims concerning efficacy or safety can be made regarding the use of these plants in treating horses. It has also been claimed that Ribes nigrum leaves have an anti-inflammatory effect, though this has not yet been clinically proven either in humans or in horses. Although veterinary phytotherapy is as old as animal husbandry itself, little scientific proof can be found regarding its uses. More research is needed before phytotherapy can be advertised as a valuable and safe alternative to the more conventional treatment protocols. SAMENVATTING In de paardengeneeskunde is fytotherapie een antwoord op de toenemende vraag van eigenaren naar &quot;natuurlijke&quot;, veilige behandelmethoden. Het langdurig gebruik van NSAID&apos;s kan ernstige bijwerkingen geven, vandaar de groeiende populariteit van ontstekingsremmende fytotherapeutica. Momenteel zijn er meerdere kruidenpreparaten commercieel beschikbaar maar het is moeilijk voor de paardeneigenaar en de dierenarts om hier een verantwoorde keuze uit te maken. Harpagophytum procumbens (duivelsklauw), Salix spp. (wilg) en Ribes nigrum (zwarte bes of cassisbes), drie planten die veel gebruikt worden in de commerciële preparaten, werden zowel in vitro als in vivo geëvalueerd. Op basis van gepubliceerde studies en de beoordeling van deze studies door onder andere de Cochrane Collaboration zijn er aanwijzingen dat Harpagophytum procumbens en Salix spp. bij de mens een groter analgetisch en ontstekingsremmend effect hebben dan een placebo. Bij paarden is er echter slechts één beperkte klinische studie met Harpagophytum uitgevoerd, en het effect van Salix werd nog nooit onderzocht. Om de werkzaamheid en veiligheid van deze planten bij het paard te kunnen beoordelen, dient er meer onderzoek verricht te worden. De bladeren van Ribes nigrum zouden ook een ontstekingsremmende werking hebben, maar dit is momenteel noch bij de mens, noch bij het paard klinisch aangetoond. Hoewel de veterinaire fytotherapie al even lang bestaat als de dierhouderij, is er weinig wetenschappelijk bewijs omtrent een efficiënte werking ervan. Vooraleer men de fytotherapie kan aanraden als een waardevol en veilig alternatief voor de conventionele behandelmethoden, is er duidelijk nog meer onderzoek nodig

100 Gbit/s serial transmission using a silicon-organic hybrid (SOH) modulator and a duobinary driver IC

100 Gbit/s three-level (50 Gbit/s 00K) signals are generated using a silicon-organic hybrid modulator and a BiCMOS duobinary driver IC at a BER of 8.5x10(-5)(<10(-12)). We demonstrate dispersion-compensated transmission over 5 km