Technical Note: Water flow routing on irregular meshes

International audienceFor spatially explicit hydrological modelling an algorithm was required that works as a cellular automata on irregular meshes. From literature it was found that the usual algorithms applied for this purpose do not route the water flow correctly between adjacent cells. In this study the hydraulic linking between mesh cells is done by calculating the flow cross section between the mesh cells. The flow cross sections are positioned in the centre of the mesh edges and are perpendicular to the local gradient of the digital elevation model. The presented algorithm is simple in its implementation and efficient in computation. It is shown that the proposed algorithm works correctly for different synthesised hill slope shapes

Measurement of spatial and temporal fine sediment dynamics in a small river

Empirical measurements on fine sediment dynamics and fine sediment infiltration and accumulation have been conducted worldwide, but it is difficult to compare the results because the applied methods differ widely. We compared common methods to capture temporal and spatial dynamics of suspended sediment (SS), fine sediment infiltration and accumulation and tested them for their suitability in a small, canalized river of the Swiss Plateau. Measurement suitability was assessed by data comparison, relation to hydrological data and in the context of previously published data. SS concentration and load were assessed by optical backscatter (OBS) sensors and SS samplers. The former exhibit a better temporal resolution, but were associated with calibration problems. Due to the relatively low cost and easy mounting of SS samplers, they can provide a higher spatial distribution in the river’s cross section. The latter resulted in a better correlation between sediment infiltration and SS load assessed by SS samplers than SS concentrations measured with OBS sensors. Sediment infiltration baskets and bed loadtraps capture the temporal and spatial distribution of fine sediment infiltration. Data obtained by both methods were positively correlated with water level and SS. In contrast, accumulation baskets do not assess the temporal behaviour offine sediment, but the net accumulation over a certain time period. Less fine sediment accumulated in upwelling zonesand within areas of higher mean water level due to scouring of fine sediments. Even though SS and sediment infiltration assessed with the bedload traps increased from up- to downstream, less fine sediment accumulated downstream. This is probably also attributable to more scouring downstream

www.hydrol-earth-syst-sci.net/11/1243/2007/ © Author(s) 2007. This work is licensed under a Creative Commons License. Technical Note: Water flow routing on irregular meshes

Abstract. For spatially explicit hydrological modelling an algorithm was required that works as a cellular automata on irregular meshes. From literature it was found that the usual algorithms applied for this purpose do not route the water flow correctly between adjacent cells. In this study the hydraulic linking between mesh cells is done by calculating the flow cross section between the mesh cells. The flow cross sections are positioned in the centre of the mesh edges and are perpendicular to the local gradient of the digital elevation model. The presented algorithm is simple in its implementation and efficient in computation. It is shown that the proposed algorithm works correctly for different synthesised hill slope shapes.

Modelling the effect of particle size, shape and orientation of light transfer through porous media

In this study, we present a radiative-transfer model to simulate reflectance and transmittance of light by soil slabs. The radiative-transfer model implemented, referred to as the beam-tracing model, uses cross-sectional images of scattering media to describe the geometry of the soil, i.e. soil texture and structure. This model traces the optical path of incident beams through such cross-sectional images. Tracing many light beams simulates the reflected and transmitted light intensities for the media. The accuracy of the beam-tracing model was tested by comparing its predictions with those of analytical solutions and with experimentally measured reflectance and transmittance data of soil samples. We implemented this model to explain the systematic deviation between measured data and those calculated with the four-flux model applied in Banninger (2004). With the beam-tracing model, we show that the small systematic inaccuracies of the four-flux model are caused by the simplified description of the geometry of the scattering medium. The beam-tracing model can be used to describe various optical properties of particulate media. As an application, we calculated the decrease of light intensity with depth

Effect of deworming on school-aged children's physical fitness, cognition and clinical parameters in a malaria-helminth co-endemic area of Côte d'Ivoire

Malaria and helminth infections are thought to negatively affect children's nutritional status and to impair their physical and cognitive development. Yet, the current evidence-base is weak. The purpose of this study was to determine the effect of deworming against soil-transmitted helminthiasis and schistosomiasis on children's physical fitness, cognition and clinical parameters in a malaria-helminth co-endemic setting of Côte d'Ivoire.; We designed an intervention study with a 5-month follow-up among schoolchildren aged 5-14 years from Niablé, eastern Côte d'Ivoire. In late 2012, a baseline cross-sectional survey was conducted. Finger-prick blood, stool and urine samples were subjected to standardised, quality-controlled techniques for the diagnosis of Plasmodium spp., Schistosoma spp., soil-transmitted helminths and intestinal protozoa infections. Haemoglobin level was determined and anthropometric measurements were taken for appraisal of anaemia and nutritional status. Children underwent memory (digit span) and attention (code transmission) cognitive testing, and their physical fitness and strength were determined (20 m shuttle run, standing broad jump and grip strength test). All children were treated with albendazole (against soil-transmitted helminthiasis) and praziquantel (against schistosomiasis) after the baseline cross-sectional survey and again 2 months later. Five months after the initial deworming, the same battery of clinical, cognitive and physical fitness tests was performed on the same children.; Lower scores in strength tests were significantly associated with children with harbouring nutritional deficiencies. Surprisingly, boys infected with Schistosoma mansoni achieved longer jumping distances than their non-infected counterparts. Light-intensity infection with S. mansoni was associated with slightly better aerobic capacity. Deworming showed no effect on haemoglobin levels and anaemia, but children with moderate- to heavy-intensity Schistosoma infection at baseline gained weight more pronouncedly than non-infected children. Interestingly, children with soil-transmitted helminth or Schistosoma infection at baseline performed significantly better in the sustained attention test than their non-infected counterparts at the 5-month follow-up.; This study revealed conflicting results regarding clinical parameters and cognitive behaviour of children after two rounds of deworming. We speculate that potential beneficial effects of deworming are likely to be undermined in areas where malaria is co-endemic and nutritional deficiencies are widespread

Modelling the effect of soil water content and sorption on dye-tracer fluorescence

Fluorescent dye tracers are used to show concentration maps of tracer fronts, plumes and pathways on soil profiles and in monolith cross sections. The physical process of fluorescence from the exposed soil surfaces must be understood in order to retrieve accurately the concentration of such compounds. We found in a laboratory experiment that the fluorescence of quartz sand stained with Acid Yellow depends both on the tracer concentration and the soil water content. In this study, we investigate the dependence of fluorescence on the water content by using a radiative transfer model. The hypothesis of our modelling approach is that fluorescence depends on water content (1) because of the adsorption properties of the tracer and (2) because the microscopic distribution of the water phase changes the positioning and emission of the excited fluorescence molecules in the sample. Our model results show that both factors influence fluorescence to a similar extent, as observed in the Acid Yellow experiment. Because these results explain only part of the overall variation in the experiment, further factors, in addition to the postulated causes, have to be considered for determining concentration maps of fluorescent tracers from real soil profiles