(a) Describe any three of the following survey instruments: (i) ranging poles; (ii) chain; (iii) cross staff; (iv) arrows. (b) Outline the processes involved in carrying out a Chain Survey.
Explanation
i. Description of Ranging Poles (1) Made of light poles of circular section — 25 to 30 mm in diameter (2) A pole has iron shoe at one end to allow it to be fixed into the ground (3) The poles are made of light metals or seasoned wood. (4) Painted in alternate bright colours as white, red and black to make it visible from afar (5) A ranging pole is between 1.8m — 3m in length ii. Description of chain (a) Formed by 100 pieces of wire (b) Connected by small links (c) Brass handles for holding at the end of the chain (d) The handles form part of the distance (e) The chain has 100 links (f) The chain can be 66 ft or 100 ft, 20 m or 30 m long (g) At every metre of the chain, there is a brass tag or tally to aid reading (h) Every 5 m and 10 m of the chain also carries a different tag for identification iii. Description of Cross Staff (1) Made of metals (2) The head is mounted on a shortened version of a ranging pole (3) Consists of cross with vertical end members (3) Each has slits (4) The line of sight is between cross at right angles (5) The arms are turned upwards at their ends. iv. Description of arrows (a) Thin pointed steel wires (b) Pointed metal markers (c) About 381 mm or 15 inches long (d) Bent at the top into a ring (e) To which red pieces of cloth can be tied to make them easier to see (f) Painted in bright colours to be easily seen Question Procedure for carrying out chain survey (a) Reconnaissance survey of the area (b) Sketch map (c) Chain surveying requires a surveyor and two assistants (d) Surveyor stays at the starting point and a station is fixed (e) A lead chainman is in front while the other holds the chain at the zero end. (f) Leader carries arrows and ranging poles (g) With the poles, he aligns the points and moves the chain to line (h) When the chain is steady at the zero point on station A, the lead chainman fixes an arrow at the end of the chain length (i) The leader then drags on the chain towards the station set following the same procedure (j) The distances measured are entered in the field notebook (k) Offsets are indicated (I) The measured distances and offsets are plotted
