Remote Sensing and GIS - 2

This is the second part of the article on remote sensing and GIS dealing with the applications of remote sensing and GIS in civil engineering. The previous article was aimed at letting you know 'what remote sensing and GIS means'. Because only after knowing that, we can learn about their applications in civil engineering.

Regional Planning and Site Investigations

Site investigations in general require topographic and geologic considerations. Remote sensing data permits such an assessment. In case of dam site investigation, information on topography is essential. Geological consideration involves the different soil and rock types and physical properties.

In selecting river-crossing sites for bridges and pipelines, an important consideration is the stability of slopes leading down to and up from the water crossing. Such slopes include riverbanks, terrace faces and valley wall. History of river erosion and sedimentation would give clues needed for locating the sites where scour is likely to occur. High spatial resolution satellite data with stereo vision capability can facilitate depth perception in the above said investigations and also for regional planning of large commercial airports, harbors, industrial towns and recreational sites. The hydro geological and geomorphologic information along with geological structures derived from satellite data are very useful in sitting the ground – water bore holes.

Terrain Mapping and Analysis

Assessment of the performance of the terrain for specific developmental activities can be made through terrain evaluation. For this, terrain information can be acquired from RS data and by generating the Digital Terrain Model (DTM). A DTM is an ordered array of numbers representing the spatial distribution of terrain characteristics stored in a computer so as to enable the determination of any quantitative data pertaining to terrain. DTMs facilities investigation of a number of alternative horizontal and vertical alignments of canals, roads, pipelines or corridors for any such applications. In engineering construction like dam, the knowledge of material comprising the terrain is essential for proper planning, location, construction and maintenance of engineering facilities. For computation of hydro graph parameters like peak runoff rate, time of concentration and time to peak, the height and slope information derived from Digital Elevation Model (DEM) are useful.

The information on regional engineering soils is essential for general planning and site evaluation purposes. High spatial resolution satellite data can be analyzed to delineate various landforms, mapping of soil classes of significance to engineering construction, delineation of landforms – engineering, soil relationships and grouping of landforms with various physio graphic setting or terrain associations.

Remote sensing based inventory of construction material such as boulders, quarry rock, sand – clay mixtures etc., would help to locate suitable sites of construction materials for building up of water resources engineering projects like dams, bridges, etc., across the rivers.

Water Resources Engineering

By analyzing multidate RS data, it would be possible to monitor the effects of dam construction. Remotely sensed data of pre and post dam construction can reveal the forest and other land at different water levels. This would also help in preliminary investigation of finding suitable areas for human resettlement.

To study the feasibility of inter basin transfer of surplus flood flows, RS data can be cost effective. In large area reconnaissance studies, various technically feasible and economically viable alternatives in locating surplus flow diversion routes to water deficient basins can be arrived at. Also, reservoir sites to store the surplus flows in these basins could be identified. Such projects of large dimensions require considerations of land use / land cover, soil and geological mapping, terrain evaluation, construction material inventory etc. the latter are derived from satellite remote sensing data of particular resolution depending upon the scale on which such information is required.

The water storage built in through reservoirs, tanks, etc., are often reduced due to sedimentation. Remotely sensed data can be used to monitor the water bodies over time and assess the silting condition. In case of gauged reservoirs of medium to large sizes, RS data can provide an assessment of sediment volume and reduction in the capacity of sediment volume and reduction in the capacity of the reservoir. In case of small water bodies such as tanks, it is possible to come out with a list of problematic tanks with symptoms of heavy siltation and loss of water holding capacity. The condition of tank bunds, fore shore encroachment, etc., also can be analysed with the help of high spatial resolution RS data.

Characterization of water bodies in terms of geological, geomorphological, hydro geological, soil and land use / land cover parameters carried out using RS data enables conservation of land and water resources. The RS based input integrated with ground based information through GIS is useful for broad reconnaissance level interpretation of land capability, irrigation suitability, potential land use, water harvesting areas, monitoring the effects of soil and water conservation measures, estimation of run off and sediment yields and monitoring land use change including land degradation.

The commercial areas of irrigation projects are fed by different sources of irrigation like reservoir, tanks, ponds and wells. Assessment of command areas and crops would be highly useful in water release policy or conjunctive use of water in the overall project command area. Satellite data has been advantageously used to obtain such information on surface irrigation projects.

In case of floods, appropriate flood management work has to be executed to reduce the damages and utilize the floodwaters. For this purpose satellite RS provides comprehensive, reliable and timely information (multidate) on flood inundated and drainage congested areas, extent of damage to crops, structure etc., river configuration, silt deposits and vulnerable areas of bank erosion. Flood mapping and damage assessment, using satellite data, is being done in India for more than two decades.

Satellite derived snow cover assessment is being extensively used as an important input in snow melt runoff prediction models to assist in multi purpose reservoir operations. Seasonal snow melt inflow forecasts for Bhakra reservoir in Sutlej basin are being operationally issued every year with the accuracy better than 90% to Bhakra Beas Management Board.

Town Planning And Urban Development

The unprecedented growth of urbanization in India has given rise to problems of housing, sanitation, power, water supply, disposal of effluents and environmental pollution. Systematic mapping and periodic monitoring of urban land use is therefore necessary for proper planning, management and policy making (with the help of RS and GIS optimal master plan for development and management of urban settlements can be prepared).

For sustainable development of urban agglomeration, optimal urban land use plans and resources development models need to be generated by integrating the information on natural resources, demographic and socio – economic data in a GIS domain with the currently available satellite data.

Transportation Network Analysis

With the help of high spatial resolution data, mapping of road and rail network can be accomplished. This facilitates in deciding optimal routing for transport of construction materials. Even, identification of village roads is possible in certain cases.

Landslide Studies

Landslides are the most common and recurring hazards in mountainous areas causing enormous loss of life and property every year. The parameters that contribute directly or indirectly include litho logy and structure, landform, slope, aspect, relief, vegetation cover, climatic and human activities. Information on these aspects can be collected and integrated for preparing a landslide hazard zone map that can be done through RS and GIS.