The states of surface and sub-surface water at a building site are important. The surface water may take various forms, such as streams, rivers, ponds and lakes. Drainage basins (watersheds) will have to be identified for they may drain into a particular building site during heavy rains. If the building is to be located in a flood plain, special precautions will have to be undertaken. Equally important is the position of underground water table and its variations. The capability of the hydrological systems at subsurface level (wells and acquifers) becomes important if water is to be tapped and utilised for household or industrial use.
Flood Plains and Flood Protection
Many structures and potential building sites are located in flood plains and thus, are susceptible to flooding.
Studies about the use of flood plain by the building industry show that some encroachment is undertaken in ignorance of the consequent hazard; most of the encroachment takes place because it is profitable for private owners to undertake such development and shift the cost of eventual hazard to the society.' To escape this dismal cycle of losses, partial protection, further induced development and further, unnecessary losses, careful building regulations and development policies will have to be laid down.
Gathering and dissemination of data on past floods, making estimates of future floods and investigating alternate methods of dealing with flood losses in areas where intensive development is envisaged, should be all be done before major actions are taken.
Flood protection requires adjustments both in structures and in building utilization practice, and itinvolves keeping water out as well as reducing the effects of water entry into a building. It is better to avoid the construction of important buildings in flood plains (Joseph De Chiara, 1978).
Ground Water and Drainage
Essential factors (in site selection) include a water table low enough to protect buildings against basement flooding and interference with sewerage, the absence of swamps and marshes, and sufficient scope to permit surface drainage of normal rainfall and a free flow of sanitary sewers. Periodic flooding due to high ground water table should disqualify a site,
For drainage of a relatively flat site, it must be remembered that the minimum slope for paved gutters is 1 in 200.
Surface and subsurface drainage systems are to be provided by the engineers for the collection and disposal of storm drainage and subsurface water. The selection of a site should thus be based on drainage requirements also.
Water Supply Requirements
One of the first steps in the selection of a suitable water supply :source is determining the water demand based the average daily water consumption and the peak rate of demand. Protected water supply, under pressure, from municipal sources is not to be taken for granted, supply from shallow or deep wells has to be planned for. The importance of a sanitary survey of water sources cannot be over emphasized. Persons trained and competent in public health engineering acid in the epidemiology of water borne diseases should conduct this sanitary survey.
If ground water is proposed to be utilised, the character of local geology, nature of soil and underlying porous strata, scope of water table, extent of drainage area likely to contribute water to the supply, and the type and cost of the wells required are all to be sstudied at the planning and site selection stage itself.
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