August 11, 2003
More about guttering and things
Had a walk along the river today, hot but nice in the park under the trees. The most impressive thing we saw as we walked along the far bank was the flood damage from last year. We watched them putting up an exhibition of photographs of the damage that had been caused. When you started to look around you could see the plaster had been knocked off all the buildings up to a height of about two metres. In most cases the repairs had been done. It looked fantastic considering. I went for my early run this morning the city is very difeerent on a Monday morning at 7:00am compared to the same time on a Sunday. Busy working people compared to tired clubbers on their way home. The Public transport system is impressive. There was not really a rush hour. Red CZ sorted the problem could red Ken Linvingstone.
I was thinking a little more about guttering and shapes of roofs. The larger the area of the roof that is collecting water for one drain pipe the larger the hole needs to be to remove the water. Another factor is the amount of water falling per metre square. What you would need to calculate is the maximum amount of water falling from the sky – major thunderstorms - on to the area of your roof that is reliant on a particular drain. Assuming you have not got "leaves on the track". Now what I was pondering was does the slope of the roof make a difference, at first I thought it did, the velocity of the water will be greater but the volume will be the same. Therefore, hole can be same size but collection vessel needs to be larger to prevent sloshing. Any way, the key factor for drainage is the number of drains and the size of the holes. Prague guttering is interesting. If I had access to the net I good try some searches. I am sure there is plenty of information but whether I will understand it is another matter. Here are couple of pictures,
notice the extra anchors to hold them in place.
The other matter that interested me was what has been happening to the man who works downstairs with stoking the fires and making life uncomfortable for those who do not follow the chosen faith. I think he had a bad time in Prague. On the other hand there is plenty of evidence that those with pointy hats as well as those who have points on their heads get a prickly time.
Fascinating reflections on volume and area Mike - a natural mathematician of everyday life.They had a frightening time in Prague with the floods. I suppose some signs of the damage will remain. Here is some further information on drainage:
The amount of storm-water drainage to be carried away depends on the amount of rainfall as well as on the runoff or yield of the watershed
Drainage, removal of surface or subsurface water from a given area by natural or artificial means. The term is commonly applied to the removal of excess water by canals, drains, ditches, culverts, and other structures designed to collect and transport water either by gravity or by pumping. A drainage project may involve large-scale reclamation and protection of marshes, underwater lands, or lands subject to frequent flooding. Such a project usually involves a system of drainage ditches and dikes; often pumps are required to raise the water into the drainage network (see Canal; Pump).
In cases of large-scale drainage it is essential to improve the discharge capacity of natural channels to protect adjacent properties, and to upgrade the ditches and channels that convey the runoff from farm drainage systems to the improved channels. Such connecting drains commonly follow the natural surface drainage pattern of the area, intercepting the normal surface runoff that takes place during periods of excessive rainfall.
Small-scale drainage is often practiced by farmers and other landowners who wish to remove surface water from arable fields or to improve water-laden soil. Properly constructed drainage systems can also prevent erosion and gullying of land on slopes by catching the surface water before it reaches the slope. Another important purpose of drainage is to prevent an excessive accumulation in the soil of soluble salts that might be detrimental to plant growth.
The essential principle of any type of land drainage is to provide an open, adequate, and readily accessible channel through which the surface or subsoil water can flow. For this purpose open ditches are sometimes used, but these are not always satisfactory because they may become choked with sediment and vegetation. Underground drains are usually employed, particularly on land that is to be plowed. Of the different types of closed drains, the most efficient is the so-called tile drain, which is composed of pipes made of sections of hollow earthenware or concrete tiles that are buried at a depth of about 1 to 2 m (about 3 to 6 ft). Excess water in the soil seeps into the pipes through apertures in the tiles.
In draining comparatively flat land, common practice is to lay along one side of the plot a main drain to which a number of transverse laterals are connected. The laterals are often set parallel to the main drain, coming together to join it at the lower end of the field. Local conditions of soil and terrain govern the spacing of laterals and the depth at which they are placed. Laterals may be from 5 to 91 m (15 to 300 ft) apart and from less than a meter to just a meter (2 to 4 ft) below the surface.
To prevent water from higher ground from reaching lower areas, catchment or interception drains are frequently built. They consist of ditches or underground drains, placed across the slope, that catch water and carry it away before it reaches the low ground.
The drains just discussed operate by gravity, but in the drainage of low-lying areas it is not always possible to set the outlet of the drain low enough to obtain a natural flow of water. This situation occurs in many areas of the Netherlands and Belgium, in the Fens country of England, in large portions of the southern United States, and in many small areas throughout the world, such as at some airports in river-bottom areas near large U.S. cities. Where gravity flow is impossible, the water from the drainage system is pumped away into streams or canals, the level of which is often higher than that of the drained land. Drained land frequently settles as its moisture content is lowered, and this increases the difficulty of drainage in low areas. In the English fens this sinking has amounted to an average of 46 cm (18 in). If the soil rests on a water-bearing foundation such as gravel, subsurface drainage may be provided by pumping water from wells, thus lowering the water level in the soil.
Posted by: Chris at August 11, 2003 07:15 PM