地理と自然災害のジャーナル
オープンアクセス
ISSN: 2167-0587
ISSN: 2167-0587
Colyer Phillip
Various investigations have recognized the issue of street surface spillover as a wellspring of pollution into streams, however the effect of vehicular wash-off is less surely known. Portage intersections give pathways to vehicle-got toxins exuding from both street surface spillover and vehicular wash-off into a stream framework. Twyford Lane (Ford 1) and Birchgrove Lane (Ford 2), found ca. 600m separated on a feeder of the River Ouse in Sussex (UK), were the focal point of this investigation. Biomonitoring and chemical assessments of water and sediments have been undertaken to determine any detrimental impacts, such as a lack in biodiversity, resulting from the ford crossings. Sediment concentrations of chromium (Cr3+), lead (Pb) and zinc (Zn) were generally elevated at Ford 1, attenuating at sampling points between the fords to then peak at Ford 2. Soil organic matter (SOM) and sediment particle size were seen to have an influence on elemental concentrations. In general, an increase in elemental concentrations was associated with a higher percentage of fine-grained sediments (≤63 μm). Elevated concentrations of Zn and magnesium (Mg) were identified within water samples taken during a precipitation event following a prolonged dry period. The biomonitoring results found reduced BMWP scores at positions close to the ford crossings, and in proximity to the roadside. Sensitive Ephemeroptera were largely absent at sampling points closest to the fords, which is likely to be associated with elevated Zn (Fig. 1). The results suggest that careful consideration should be applied when selecting crossing points over sensitive waters.
A portage is a lot less expensive type of waterway crossing than a scaffold, yet it might get closed after substantial downpour or during flood conditions. A passage is consequently typically just appropriate for extremely minor streets (and for ways expected for walkers and pony riders and so forth) Most current passages are typically shallow enough to be crossed via vehicles and other wheeled or followed vehicles (a cycle known as "fording").
In New Zealand, nonetheless, portages are a typical piece of significant streets, including, until 2010, along State Highway 1 on the South Island's east coast.[2] As most between city homegrown travelers travel via air and as much freight passes via ocean, significant distance street traffic is low and passages are hence a reasonable necessity[clarification needed] for intersection occasional waterways. In dry climate, drivers become mindful of a portage by crunching across outwash debris on the street. A bailey scaffold might be worked off the principle line of the street to convey crisis traffic during high water.
At places where the water is adequately shallow, yet the material on the riverbed won't maintain heavy vehicles, portages are occasionally improved by building a brought down strong floor. In such cases a control (kerb) is consistently situated on the downstream side to thwart vehicles sneaking off, as improvement of green development will as often as possible make the piece very risky. Portages may be furthermore equipped with a post exhibiting the water significance, so customers may know whether the water is too significant to even consider evening consider endeavoring to cross. Some have a neighboring footbridge so walkers may cross dryshod.