Definition: The general examination of fairly broad stretch of land along the proposed alternative routes marked on the map is called reconnaissance survey.
About Reconnaissance Survey
It is a rapid and rough survey of the area lying between the terminal stations of the proposed alignment. Only very simple instruments like Abney level, tangent clinometer, etc. are used by the survey parts to collect additional details rapidly.
All relevant details not available in the map are collected and noted down. After the study of the details collected during the reconnaissance, a few alternate alignments may be chosen for further study.
The Details to be Collected During Reconnaissance Survey
Some of the details to be collected during reconnaissance are given below:
i) Valleys, ponds, lakes, marshy land, ridge, hills permanent structures and other obstructions along the route which are not available in the map.
ii) Number and kind of cross drainage structures, most extreme flood level and normal groundwater level along the probable routes.
iii) Approximate values of the gradient, length of gradients and radius of curves of alternate alignments.
iv) Soil type along the routes.
v) Sources of construction materials. From the details collected during the reconnaissance, the alignment proposed after study may be altered or even changed completely.