HYDROLOGICAL ASPECTS
Any paved surfaces scraped and sloped n order to allow the run off of rain water, snow, hail etc. It should be remembered that the behavior of the water varies depending on the area of the project. its position and, more generally, the geological, soil and morphological characteristics, the vegetation cover and the whole condition of the hydrological basin. A basin is an area where the surface waters converge on a precise geographical place. Its characteristics vary due to the type of surface, terrain, vegetation, slope, size, orientation and exposure. Any project on the land leads to the alteration of the behavior of the Iocalized and distant Vows of the surface and underground waters. The under-evaluation of this principle has contributed to the hydrological problems in our area including the alteration of the water table and an increase in subsidence. The need to conserve and plan water reserves and water quality is now the focus of attention Iron' the public and also from the local authorities, Because of this much more attention is paid to the study of draining and run off of water with new architectural projects.
The complex equilibrium of a basin should be maintained and excessive run off, erosion and subsidence due to excess water on the surface should be avoided Mere we will mention briefly the problems related to surface draining i.e. water collection systems, management and control of surface waters.
The objective i.e. draining of the surface, involves the collection of the rain water etc. and sending it into channels or covered drains, water courses or surface bodies of water, or letting it percolate into the ground. The first action may occur with surface run off and channels on the surface or underground. The second involves the formation of wells or draining channels or reservoirs and the dispersion of the water. Run off occurs due to the effect of gravity on the whole of an impermeable paved area which must have suitable slope to avoid the formation of puddles and to make the water flow towards suitable drains. The minimum slope necessary for this in the case of porphyry is at least 1.5%.
The collection and directing of the surface water are carried out by means of channels, ditches and gutters of various sizes.
These pieces can be produced and/or faced with cubes, 'binderi' blocks or tiles of porphyry in the appropriate size, especially if, due to steep slope, the water reaches a high speed. Remember that porphyry is one of the rock materials which is most resistant to sliding friction.
In urban areas the rain water etc. is usually collected through drain holes situated at convergent points of the paving and they lead to, with inspection wells with siphons, an underground network of pipes, which carry the water by gravity towards certain outlets. The outlets are gills, manholes, drain holes, etc. in walls and kerbs. Grills allow a continuity of surface, instant run off o a large volume of water and the possibility to collect and interrupt completely the linear flow from ramps, steps or steep slopes. They are usually made of metal but can be obtained to order in porphyry in different shapes, thicknesses arid outlets (slots, holes etc.).
Drain hoes have the advantage of getting in the way the least and being least noticeable in the architectural setting but they are difficult to maintain and clean.
Manhole covers are one of the most common features. Their shape may vary square, rectangular, round etc. as may the grill. In urban centers, gardens or other such places, it is better to use shapes and materials (stone cast iron) which conform to the traditions of the place. Manhole covers are produced in porphyry according to the required design and thickness which must take into account the volume of water to drain and also the load it will have to bear. The most common types are square with three more rectangular cuts, o in the central part they are lower in the shape o' a spherical vault, or holes of suitable diameter where the water falls.
All these collecting structures must be positioned. for obvious reasons of function, but also of appearance, perpendicular to the slope and flow of rain water.
