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Half Tide Dock
A half tide dock is a partially tidal dock. Typically the dock is entered at high tide. As the tide ebbs a sill or weir prevents the level dropping below a certain point, meaning that the ships in the dock remain afloat, although they still rise and fall with the tides above this. Half tide docks are particularly useful in areas with a large tidal range. The sill of a half tide dock must be set sufficiently far below the daily high tide mark to allow ships to pass over it. Obviously this was easier to achieve with small ships of shallow draught, or in areas with a large tidal range. Inside the dock, the depth of water beneath the sill's level depends only on the depth to which the dock was excavated, although this obviously increases construction costs. The importance of the sill, and the tide's height above it, is reflected by these dock sills becoming an important local datum level and for tide tables being calculated for heights above it (i.e. clear draught in and out of the do ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dock (maritime)
A dock (from Dutch ''dok'') is the area of water between or next to one or a group of human-made structures that are involved in the handling of boats or ships (usually on or near a shore) or such structures themselves. The exact meaning varies among different variants of the English language. "Dock" may also refer to a dockyard (also known as a shipyard) where the loading, unloading, building, or repairing of ships occurs. History The earliest known docks were those discovered in Wadi al-Jarf, an ancient Egyptian harbor, of Pharaoh Khufu, dating from c.2500 BC located on the Red Sea coast. Archaeologists also discovered anchors and storage jars near the site. A dock from Lothal in India dates from 2400 BC and was located away from the main current to avoid deposition of silt. Modern oceanographers have observed that the ancient Harappans must have possessed great knowledge relating to tides in order to build such a dock on the ever-shifting course of the Saba ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weir
A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. Weirs are also used to control the flow of water for outlets of lakes, ponds, and reservoirs. There are many weir designs, but commonly water flows freely over the top of the weir crest before cascading down to a lower level. Etymology There is no single definition as to what constitutes a weir and one English dictionary simply defines a weir as a small dam, likely originating from Middle English ''were'', Old English ''wer'', derivative of root of ''werian,'' meaning "to defend, dam". Function Commonly, weirs are used to prevent flooding, measure water discharge, and help render rivers more navigable by boat. In some locations, the terms dam and weir are synonymous, but normally there is a clear distinction made between the structures. Usually, a dam is designed specifically to impound water beh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tide Table
Tide tables, sometimes called tide charts, are used for tidal prediction and show the daily times and levels of high and low tides, usually for a particular location. Tide heights at intermediate times (between high and low water) can be approximated by using the rule of twelfths or more accurately calculated by using a published tidal curve for the location. Tide levels are typically given relative to a low-water vertical datum, e.g. the mean lower low water (MLLW) datum in the US. NOAA Special Publication NOS CO-OPS 1, Silver Spring MD, June 2000. Publication and scope Tide tables are published in various forms, such as paper-based tables and tables available on the Internet. Most tide tables are calculated and published only f ...[...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sharpness
Sharpness ( ) is an English port in Gloucestershire, one of the most inland in Britain, and eighth largest in the South West. It is on the River Severn at , at a point where the tidal range, though less than at Avonmouth downstream ( typical spring tide), is still large ( typical spring). There is a small community of approximately 100 residents directly adjacent to the port, in addition to the subvillage of Newtown approximately 0.5 miles to the south-east. Four miles to the south lies the small town of Berkeley. Docks Sharpness docks began as a basin giving access to the Gloucester and Sharpness Canal. There were no port facilities at Sharpness itself and all traffic proceeded up the canal to Gloucester. The original Old Dock opened, with the canal, in 1827. The dock was separated from the Severn by a lock gate. The level of the basin varied for the hour or two for which the gate was open and so it was isolated from the canal by a lock with two gates. This lock was imp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Severn Estuary
The Severn Estuary ( cy, Aber Hafren) is the estuary of the River Severn, flowing into the Bristol Channel between South West England and South Wales. Its high tidal range, approximately , means that it has been at the centre of discussions in the UK regarding renewable energy. Geography Definitions of the limits of the Severn Estuary vary. At the upstream boundary, the tidal limit of the river is at Gloucester. Downstream, the International Hydrographic Organization places the boundary between the estuary and the open sea of the Bristol Channel at a line between Sand Point, Somerset (immediately north of Weston-super-Mare) and Lavernock Point (immediately south of Penarth in south Wales). This definition is used by the Severn Estuary Partnership and Visit England. A narrower definition adopted for navigation purposes by some maps includes only the area downstream of the Second Severn Crossing near Severn Beach, South Gloucestershire. The definition used on Admiralty Chart SC1 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Old Dock
The Old Dock, originally known as Thomas Steers' dock, was the world's first commercial wet dock. The dock was built on the River Mersey in Liverpool, England, starting in 1710 and completed in 1716. A natural tidal pool off the River Mersey, which probably gave its name to Liverpool centuries earlier, was partially filled and locked in from the river with quay walls erected. History The Old Dock was built at a cost of £11,000 and opened on 31 August 1715. Thomas Steers was the engineer responsible; and additional advice was obtained from George Sorocold. Originally a tidal basin was accessed directly from the river, and from 1737 access was via Canning Dock. The dock was built with one graving dock; a second and third graving dock were added in 1746 and the 1750s. The dock walls were constructed from brick laid directly on to sandstone bedrock. The dock gates would have allowed as much as 10% of the water out between high tides, resulting in a water level drop of severa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Floating Dock (impounded)
A floating dock, floating harbour or wet dock is a dock alongside a tidal waterway which maintains a 'constant' level, despite the changing tides. Operation At the most basic level, a floating dock is isolated from tidal water by a lock gate, at least, although in many dock systems the entrance is more complex than this. Development and early docks London The first wet dock was Howland Great Wet Dock or Greenland Dock, built in London at the end of the 17th century. This was not a commercial dock and had no warehouses, but was intended solely for ship replenishment and refitting. Liverpool (Old Dock) In 1715 the first commercial wet dock, Liverpool's Old Dock, opened. Early docks were of simple construction: a single lock gate isolating them from the tidal water. The gates were opened during the last hour r twoof the rising tide, giving a short window of opportunity to let ships in on the rise and releasing outgoing ships while the tide was on the turn. The gates ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coastal Construction
The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in natural ecosystems, often home to a wide range of biodiversity. On land, they harbor important ecosystems such as freshwater or estuarine wetlands, which are important for bird populations and other terrestrial animals. In wave-protected areas they harbor saltmarshes, mangroves or seagrasses, all of which can provide nursery habitat for finfish, shellfish, and other aquatic species. Rocky shores are usually found along exposed coasts and provide habitat for a wide range of sessile animals (e.g. mussels, starfish, barnacles) and various kinds of seaweeds. Along tropical coasts with clear, nutrient-poor water, coral reefs can often be found between depths of . According to a United Nations atlas, 44% of all people live within 5 km (3.3mi) of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
