- It is a temporary arrangement which is adopted to store extra water during low flows in the river.
- At large floods they are either removed or allowed to drop on D/S side if hinged at the crest.
- Flash Boards are made by joining wooden planks which are fixed against the pins.
- The pins are installed over the crest at suitable
- intervals. Flash Boards when in position may be vertical or inclined. See Fig. 14.19.
STOP LOG OR NEEDLE GATES
- In this case, piers are located at suitable intervals on the crest and stop logs
- Which are nothing but timber planks fixed horizontally in the grooves of the piers, one above the other.
- While opening, the stop logs are removed one by one. See Fig. 14.20 (b).
- In the case of needle gates, wooden planks are not used horizontally but vertically.
- A groove is developed at the crest of the spillway.
- The bridging girder is also put parallel to the crest of the spillway.
- The wooden needles are fixed with their bottom in a groove in the crest and top against the bridging girder. See Fig. 14.20 (a).