Groynes == |+|
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|−|[[Image:File1.jpg|350px|thumbnail|right|Figure 1: Scheme of interaction of groynes, waves, currents and shore]] | |
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|−|A [[ groyne]] is an active structure extending from shore into sea, most often perpendicularly or slightly obliquely to the shoreline. Adequate supply of sediment and existence of satisfactorily intensive longshore sediment transport are the sine qua non conditions of groynes efficiency. |+|
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|−|Catching and trapping of a part of sediment moving in a surf zone (mainly in a longshore direction), as well as reduction of the sediment amount transported seawards, are the principle functions of the [[ groyne]]. |+|
of a of a a amount of the [] .
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|−|As revealed by experiments, during weak and moderate wave conditions, the groynes partly dissipate energy of water motion and lead to sand accumulation in the vicinity of a shore, thus causing its accretion. Under storm waves, mainly approaching the shore perpendicularly, the role of the groynes decreases and a beach is partly washed out. |+|
, , of the , ., , the of .
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|−|Groynes are frequently used. However, applied as a self-contained shore protection measure it is a very dubious solution. This is because of unfavourable side effects which they can cause locally. Satisfactory supply of sand and existence of longshore sediment transport are fundamental conditions for efficiency of groynes. The groins role distinctly increases if they are applied together with other (soft) shore protection measures, like artificial [[beach nourishment]] or [[shore nourishment]]. | |
Revision as of 11:57, 14 April 2008
Carrying capacity analysis
Figure 1: Beach tourism that may exceed local ecological limits
The concept of carrying capacity is rooted in a notion of “limits to growth”. The notion of carrying capacity or sustainability yield has become a basic criterion of sustainability. Ecosystems and populations have a limited capacity to cope with environmental stress; above a certain amount of stress there may be detrimental effects for the ecosystems. Carrying capacity is defined as “the growth limits an area can accommodate without violating environmental capacity goals” (Ortolano, 1984). Policies to regulate human activities and for anticipating environmental impacts can assist in attaining carrying capacity limits. For this it is necessary to translate an ecosystem’s limits into anthropogenic limitations and controls.
The notion of “limits” has several conceptual problems (ecosystem complexity, lack of data, gaps in science or bias of the scientists, etc.). Limits are, above all, conceptual constructs. It is therefore questionable whether it is possible to identify the geographical boundaries or area limits of natural ecosystems, much less to assess an ecosystem’s growth limits.
Things become more complicated when moving from limits to certain parameters or resources to carrying capacity limits for a whole area, as in the case of tourism carrying capacity. Limitations for critical ecological resources like water need to be defined while stress due to tourism, agriculture, industry, etc. need to be considered. To achieve the above task of carrying capacity analysis a significant mobilization of resources (scientific, technological, financial, etc.) is required.
- ↑ Ortolano, L. (1984), Environmental Planning and Decision Making, John Wiley and Sons, New York