Wave forces on vertical cylinders upon shoals

An experimental study has been carried out on the forces from plunging breaking regular and irregular waves on a vertical cylinder on a shoal. Total as well as local wave forces have been measured. Engineering formulae for the calculation of the horizontal forces and overturning moments have been derived. The duration of the impact forces have been measured and compares fairly well with theoretical values.     

Road Traffic and Avalanches – Methods for Risk Evaluation and Risk Management

This paper considers the methods for risk analysis and management in connection with avalanches and road traffic. Examples with calculations of encounter probability and quantification of uncertainty are given, along with suggestions for risk management in Norway.     

Soil frost effects on soil water and runoff dynamics along a boreal forest transect: 1. Field investigations

To determine how soil frost changes flowpaths of runoff water along a hillslope, a transect consisting of four soil profiles directed towards a small stream in a mature forest stand was investigated at Svartberget, near Vindeln in northern Sweden. Soil temperature, unfrozen water content, groundwater level and snow depth were investigated along the transect, which started at the riparian peat, and extended 30 m upslope into mineral soils. The two, more organic‐rich profiles closest to the stream had higher water retention and wetter autumn conditions than the sandy mineral soils further upslope. The organic content of the soil influenced the variation in frost along the transect. The first winter (1995–96) had abnormally low snow precipitation, which gave a deep frost down to 40–80 cm, whereas the two following winters had frost depths of 5–20 cm. During winter 1995–96, the two organic profiles close to the stream had a shallower frost depth than the mineral soil profile higher upslope, but a considerably larger amount of frozen water. The fraction of water that did not freeze despite several minus degrees in the soil was 5–7 vol.% in the mineral soil and 10–15 vol.% in the organic soil. From the measurements there were no signs of perched water tables during any of the three snowmelt periods, which would have been strong evidence for changed water flowpaths due to soil frost. When shallow soil layers became saturated during snowmelt, especially in 1997 and 1998, it was because of rising groundwater levels. Several rain on frozen ground events during spring 1996 resulted in little runoff, since most of the rain either froze in the soil or filled up the soil water storage. Copyright © 2001 John Wiley & Sons, Ltd.     

Some investigations in hydrological forecasting

Summary In the northern parts of Sweden precipitation falls during the winter as snow which melts only in spring, i. e. in April and May, or in the northern mountainous regions in June or even in July. Under natural conditions the water level and the flow are high during late spring and summer and low in winter. In order to reach a better utilization of the water power storage magazines have been created and thus the flow can be regulated in order to obtain more power during the winter time. To be able to do this in the most profitable way it is necessary to find the relations between the net influx and the relevant meteorological factors and then to make forecasts concerning the water supply for rather long periods. Some results from such already established forecast relations are discussed. There forecasts are concerned with the total flow of water during the spring time and are based only upon the amount of precipitation during the winter. Some preliminary results are also given from trials, just being started and aiming at forecasts of the variation with time of the flow during the spring.

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Zusammenfassung Der Niederschlag in den n?rdlichen Teilen von Schweden f?llt w?hrend des Winterhalbjahres in Form von Schnee, der erst im Frühling, d. h. im April und Mai oder in den n?rdlichen Gebirgslagen sogar erst im Juni oder Juli, schmilzt. In den natürlichen Wasserl?ufen sind Wasserstand und Abflu? hoch w?hrend des Sp?tfrühlings und des Sommers, niedrig w?hrend des Winters. Um die Wasserkraft besser ausnutzen zu k?nnen, wurden Wasserreservoire geschaffen, wodurch die Wassermenge reguliert und die Energie auch im Winter ausgenützt werden kann. Um diese Wasserkraft in der günstigsten Weise ausnützen zu k?nnen, ist es notwendig, die Beziehungen zwischen dem Zuflu? und den wirksamen meteorologischen Faktoren festzulegen und nach M?glichkeit Prognosen über die Wasserausbeute auf l?ngere Sicht zu machen. Im vorliegenden Aufsatz werden die Ergebnisse von einigen solchen Prognoseversuchen er?rtert, die nur auf dem Winterniederschlag basieren und den totalen Abflu? ergeben. Weiterhin werden einige vorl?ufige Ergebnisse von neuerdings angefangenen Versuchen berichtet, die zeitlichen Schwankungen des Frühjahrshochwassers vorauszusagen. Résumé Dans les parties septentrionales de la Suède, les précipitations tombent, pendant la saison hivernale sous la forme de neige, qui ne se fond qu'au printemps, c'est-à-dire en avril et mai ou, dans les parties montagneuses du nord, même en juin ou juillet. Dans les courants d'eau naturels la hauteur d'eau et le débit sont élevés vers la fin du printemps et en été, bas pendant l'hiver. Pour mieux exploiter les forces hydrauliques, des réservoirs d'eau ont été construits, par lesquelles le débit peut être réglé et la force hydraulique peut être exploitée aussi pendant la saison d'hiver. Pour arriver à des résultats plus favorables il est nécessaire d'étudier les relations entre l'afflux et les facteurs météorologiques et de faire dans la mesure du possible des prévisions de l'évolution du débit d'eau à plus longue échéance. Quelques résultats de tels essais de prognostics établis, basés uniquement sur la précipitation d'hiver et donnant le volume total d'eau, sont discutés. En outre, on donne des résultats provisoires des essais qui ont été commencés récemment et qui concernent les possibilités de la prévision des variations temporaires des grandes crues de printemps.

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With 2 Figures

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Dedicated to Dr.Anders K. ?ngstr?m on the occasion of his 70th birthday.     

Pasture enclosures increase soil carbon dioxide flux rate in Semiarid Rangeland,Kenya

Background

Pasture enclosures play an important role in rehabilitating the degraded soils and vegetation, and may also influence the emission of key greenhouse gasses (GHGs) from the soil. However, no study in East Africa and in Kenya has conducted direct measurements of GHG fluxes following the restoration of degraded communal grazing lands through the establishment of pasture enclosures. A field experiment was conducted in northwestern Kenya to measure the emission of CO₂, CH₄ and N₂O from soil under two pasture restoration systems; grazing dominated enclosure (GDE) and contractual grazing enclosure (CGE), and in the adjacent open grazing rangeland (OGR) as control. Herbaceous vegetation cover, biomass production, and surface (0–10 cm) soil organic carbon (SOC) were also assessed to determine their relationship with the GHG flux rate.

Results

Vegetation cover was higher enclosure systems and ranged from 20.7% in OGR to 40.2% in GDE while aboveground biomass increased from 72.0 kg DM ha^?1 in OGR to 483.1 and 560.4 kg DM ha^?1 in CGE and GDE respectively. The SOC concentration in GDE and CGE increased by an average of 27% relative to OGR and ranged between 4.4 g kg^?1 and 6.6 g kg^?1. The mean emission rates across the grazing systems were 18.6 μg N m^?2 h^?1, 50.1 μg C m^?2 h^?1 and 199.7 mg C m^?2 h^?1 for N₂O, CH₄, and CO₂, respectively. Soil CO₂ emission was considerably higher in GDE and CGE systems than in OGR (P?<?0.001). However, non-significantly higher CH₄ and N₂O emissions were observed in GDE and CGE compared to OGR (P?=?0.33 and 0.53 for CH₄ and N₂O, respectively). Soil moisture exhibited a significant positive relationship with CO₂, CH₄, and N₂O, implying that it is the key factor influencing the flux rate of GHGs in the area.

Conclusions

The results demonstrated that the establishment of enclosures in tropical rangelands is a valuable intervention for improving pasture production and restoration of surface soil properties. However, a long-term study is required to evaluate the patterns in annual CO₂, N₂O, CH₄ fluxes from soils and determine the ecosystem carbon balance across the pastoral landscape.

     

Temporal trends in dioxins (polychlorinated dibenzo-p-dioxin and dibenzofurans) and dioxin-like polychlorinated biphenyls in Baltic herring (Clupea harengus)

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyl (dl-PCBs) concentrations in Baltic herring (Clupea harengus) have been relatively stable since the mid to late 1990s. It is unclear why concentrations in Baltic herring are not following the observed decreases in other environmental matrices. Here, changes in long-term temporal trends in Baltic herring were examined. A number of biological variables were examined alongside the temporal trends to investigate whether fish biology e.g., growth (length, weight, age), lipid content, reproductive phase or fishing date may provide an explanation for the temporal trends observed.     

Metal speciation in rivers affected by enhanced soil erosion and acidity

Dissolved (<1 kDa), colloidal (1 kDa–0.45 μm) and particulate (>0.45 μm) size fractions of 30 elements were determined for four rivers (Sirppujoki, Laajoki, Mynäjoki and Paimionjoki), including 12 low-order inflow streams, largely affected by soil erosion and acidity in SW Finland. In addition, geochemical modelling was used to predict the formation of free ions and complexes in these rivers. Total metal concentrations were relatively high but most of the elements occurred mainly in a colloidal or particulate form and even elements expected to be very soluble occurred to a large extent in colloidal form. According to geochemical modelling these patterns could be explained by in-stream metal complexation/adsorption only to a limited extent. Instead there were strong indications that the high metal concentrations and dominant solid fractions were largely caused by erosion of metal bearing phyllosilicates. A strong influence of acid sulphate (AS) soils, known to exist in the catchment, could be clearly distinguished in Sirppujoki river as it had very high concentrations of dissolved metals, while in the two nearby rivers (Laajoki and Mynäjoki) the influence of AS soils was largely masked by eroded phyllosilicates. In Paimionjoki river the colloidal and particulate fractions dominated very strongly, indicating that total metal concentrations are almost solely controlled by erosion of phyllosilicates. Consequently, rivers draining clay plains sensitive to erosion, like those in SW Finland, have generally high “background” metal concentrations due to erosion of relatively non-toxic colloidal/particulate phyllosilicates. Thus, relying on only semi-dissolved (<0.45 μm) concentrations obtained in routine monitoring and/or speciation modelling can lead to a great overestimation of the water toxicity in this environment.