Description: http://www.isde.ie/#/4fc6c154-dddf-4587-b741-5929d502ce89 science, geography, hydrography
OSi Discovery Series Low Water Mark (LWM) polyline boundary. A Low Water Mark represents the lowest point of tidal water or the level reached by seawater at low tide or by other stretches of water at their lowest level. The zone between the Low Water Mark and High Water Mark is known as the intertidal zone.
Definition Expression: N/A
Copyright Text: Ordnance Survey Ireland Discovery Series
Description: http://www.isde.ie/#/61031f0c-8f5d-42fc-b750-02b8e616a252 science, geography, hydrography
Discovery Series High Water Mark HWM vector polyline. A High Water Mark is a point that represents the maximum rise of a body of water over land. Such a mark is often the result of a flood, although high water marks may reflect an all-time high, an annual high (i.e., highest level to which water rose that year), or the high point for some other division of time. Knowledge of the high water mark for an area is useful in managing the development of that area, particularly in making preparations for flood surges. High Water Mark from floods have been measured for planning purposes since at least as far back as the civilisations of ancient Egypt. It is a common practice to create a physical marker indicating one or more of the highest water marks for an area, usually with a line at the level to which the water rose, and a notation of the date on which this high water mark was set. This may be a free-standing flood level sign or other marker, or it may be affixed to a building or other structure that was standing at the time of the flood that set the mark. A High Water Mark is not necessarily an actual physical mark, although it is possible for water rising to a high point to leave a lasting physical impression, such as floodwater staining. A landscape marking left by the high water mark of ordinary tidal action may be called a strand line, and is typically composed of debris left by high tide. The area at the top of a beach where debrisis deposited is an example of this phenomenon. Where there are tides, this line is formed by the highest position of the tide, and moves up and down the beach on a fortnightly cycle. The debris is chiefly composed of rotting seaweed, but can also include a large amount of litter, either from ships at sea or from sewage outflows.
Definition Expression: N/A
Copyright Text: Ordnance Survey Ireland Discovery Series