Types of survey:
There are mainly three types of surveys which are as follows:
- Reconnaissance survey
- Detailed survey
- Preliminary survey
In Reconnaissance survey, the following information is collected :
- The size of catchment area, vegetation in the catchment area, soil type, slopes, existing ponds and other irrigation project if any in that catchment area.
- The command area: It includes enquiry, inspection of soil type, thickness, crops growth and distance of source.
- Dam site: It includes approximate length of dam, height of dam, soil, its type, its suitability, population, site for spillway, and area of sub mergence etc.
- Rainfall and river gauge data if available at nearby station.
- Population: It includes number of people those co-operate or opposes the proposed scheme.
- History of any previous investigation.
The detailed survey consist of following points,
- Survey of command area.
- Type of suitable dam.
- Boring/trial pits at dam site.
- Detailed report of soil investigation, strata available with various depths.
- Detail of area under submergence.
- Details of people comes under influence.
- Existing sediment problem if any.
- Material available, quarry sites available nearby the project.
- Gauging of river.
- This investigation is carried out by team of engineers under experienced supervision with modern instruments however it may take few months to one or two years depending on size of project survey work is carried out in dry season with careful planning and proper coordination.
- Preliminary investigation is divided into three parts:
- Engineering survey
- Hydrological survey
- Geological survey
- These are conducted for the dam, reservoir and other work.
- In this survey, One carries out topographic survey and prepares contour plan.
- The following information is prepared and recorded in engineering survey:
- The size (area in Km²)
- Area under cultivation, under forest and under habitation.
- The type of soil.
- Existing ponds and size, their capacities.
- River sites in that area.
- Flood levels if available from past record if any.
- Slope of hills.
- One carries out Hydrological survey to collect data like rain fall temperature, direction of wind, velocity, evaporation, flood marks if any etc.
- It is necessary for:
- Firstly, to study runoff pattern and to estimate yield.
- Secondly, to determine maximum discharge at site.
- Lastly, determination of hydrograph of worst flood to determine spillway capacity and its design.
- Geological investigation is necessary for:
- Firstly, Suitability of foundation for the dam
- Secondly, Water tightness of the reservoir basin
- Lastly, Location of quarry sites for construction materials
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