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This article throws light upon the top ten uses of aerial photographs in civil engineering projects. The uses are: 1. Preliminary Surveys 2. Acquisition of Land 3. Water Supply and Power Schemes 4. Transmission Lines 5. Road and Railway Engineering 6. Town and Country Planning 7. Land Drainage and Flood Prevention 8. Navigation Channels, Harbours and Coast Defense and Others.
Use # 1. Preliminary Surveys:
Prior to planning large scale engineering projects, it is sufficient of 6″ to a mile (1:1000) scale maps are available. These maps can very rapidly and easily be obtained by conducting preliminary surveys from air, to a scale sufficient for locating, aligning prior to construction.
Use # 2. Acquisition of Land:
In any engineering project it becomes necessary to acquire portion of private land, such a right of way over a private land, such as in case of laying a transmission line, this method offers the advantages that the entire plan can be made before matter is known to the owner.
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The presence of a surveyor in an area proposed to be developed has the remarkable effects in increasing land value of adjoining lands. Moreover right of entry to private land is always restricted. Surveying from air does not bother about that.
Use # 3. Water Supply and Power Schemes:
Careful interpretation of air photographs for understanding the mature of the terrain and soil is a fundamental pre-requisite to construction of water supply, power and other schemes.
Selection and supply of reservoir sites, catchment areas and ram sites have been carried out satisfactorily from air photographs, while approximate capacity of reservoir can be found by stereoscope examination of air maps.
In Canada maps produced from air photographs for a length of 160 km with ground level were found accurate enough to design power schemes. Air survey is also being used for locating aqueducts and water power lines for estimating approximate falls and the head of water available.
Use # 4. Transmission Lines:
The selection of actual position of transmission towers, their spacing foundation of clearance of wires can be done easily on the air photographs with the aid of stereoscope observation, with the aid of parallax measurement approximate height can also be determined.
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Use # 5. Road and Railway Engineering:
Maps produced from air photographs aided by ground measurement for height control enable a road or a railway engineer to align roads and railways routes. Examination of photographs under stereoscope observation, showing main traffic lines enable delicious layout of road crossing and junctions. The density of vehicular traffic can also be determined.
Use # 6. Town and Country Planning:
For a town planner the problem is to have a general picture of the existing condition, as well as future developments that shall takes place after lapse of several years. Hence, knowing the trend of further development he can align proposed boundary extensions, making improvement in layouts of parks and other building with the help of air photographs.
In case of Bihar earthquake of 1934, the reconstruction of the city was carried from maps produced from air photographs drawn to scale of 1:200.
Use # 7. Land Drainage and Flood Prevention:
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Large swampy and marshy places which are inaccessible to a ground surveyor for surveying in connection with drainage problems can be easily surveyed from air and plans produced for preparation of schemes in case of high floods.
Maps produced from air photographs could help to indicate the limits of damage done by floods. The position of existing drains and, therefore, lines of existing drainage from air photographs identified from difference of tone will help to prepare drainage schemes.
Use # 8. Navigation Channels, Harbours and Coastal Defenses:
Air photographs by tone variation will indicate the nature of banks, soil, presence of sand and mapping from them indicates the cast where erosion is taking place and the coastline.
Use # 9. Study of Geology:
The wealth of a country is buried underground and the economic development of a country depends on the success to which extent geologist has been able to explore the same. The knowledge of general characteristics and the behaviour of rocks enable geologist to interpret rocks and explore wealth, which are hidden in place inaccessible to man.
A pair of photographs when viewed from a stereoscope presents a three-dimensional model and helps to identify rocks and mines.
Use # 10. Mining Projects:
As for the rocks so also in case of mine exploration, photograph has been an asset to the mines.