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Survey practice
Interactive practice needs JavaScript. Read the central hair; enter Back, Inter or Fore. Keep the change-point contact fixed when you move the instrument.
Rise and fall: next RL = previous RL + rise - fall. Height of instrument: HI = known RL + Back; point RL = HI - reading. AHD = gauge datum level + 42.000. In RISE/FALL, positive means rise and negative means fall.
The complete synthetic survey record is provided below. Cross-section distance = (upper hair - lower hair) × 100, with horizontal sight, vertical staff and zero additive constant. Instrument and staff stay on one straight section line. The first backsight anchors chainage zero. Each change-point backsight re-establishes the instrument chainage from the saved contact. Add distance towards the right bank or subtract it towards the left bank.
| BACK | INTER | FORE | RISE/FALL | GAUGE DATUM | AHD | POINT | REMARKS |
|---|---|---|---|---|---|---|---|
| 1.237 | 0.000 | 3.650 | 45.650 | BMGS | Top of channel at gauge range | ||
| 1.887 | -0.650 | 3.000 | 45.000 | SG3 | 3.000 m graduation, top of 2 to 3 m plate | ||
| 0.924 | 1.737 | 0.150 | 3.150 | 45.150 | CP1 | Top of 2 to 3 m SG post | |
| 1.074 | -0.150 | 3.000 | 45.000 | SG3 | 3.000 m graduation, repeat after move | ||
| 2.074 | -1.000 | 2.000 | 44.000 | SG2 | 2.000 m graduation, top of 1 to 2 m plate | ||
| 3.074 | -1.000 | 1.000 | 43.000 | SG1 | 1.000 m graduation, top of 0 to 1 m plate | ||
| 2.657 | 2.954 | 0.120 | 1.120 | 43.120 | CP2 | Top of 0 to 1 m SG post | |
| 2.777 | -0.120 | 1.000 | 43.000 | SG1 | 1.000 m graduation, repeat after move | ||
| 3.034 | -0.257 | 0.743 | 42.743 | WL | Water level at 10:15 | ||
| 3.532 | -0.498 | 0.245 | 42.245 | CTR | Top of brass termination fitting | ||
| 1.777 | 1.755 | 2.000 | 44.000 | SG2 | 2.000 m graduation, repeat on return | ||
| 0.130 | 1.647 | 3.647 | 45.647 | BMGS | Top of channel at gauge range, close |
Weir profile worked book
| SETUP | SIGHT | CENTRAL | UPPER | LOWER | DISTANCE | DIRECTION | CHAINAGE | GAUGE DATUM | POINT |
|---|---|---|---|---|---|---|---|---|---|
| 1 | BS | 1.123 | 1.173 | 1.073 | 10.0 | Right | 0.0 | 5.000 | BMXS |
| 1 | IS | 1.123 | 1.183 | 1.063 | 12.0 | Right | 2.0 | 5.000 | LB |
| 1 | FS | 3.123 | 3.187 | 3.059 | 12.8 | Right | 2.8 | 3.000 | CPWL |
| 2 | BS | 3.427 | 3.488 | 3.366 | 12.2 | Left | 2.8 | 3.000 | CPWL |
| 2 | IS | 3.427 | 3.475 | 3.380 | 9.5 | Left | 5.5 | 3.000 | WTL |
| 2 | IS | 4.427 | 4.475 | 4.380 | 9.5 | Left | 5.5 | 2.000 | WBL |
| 2 | IS | 4.427 | 4.460 | 4.395 | 6.5 | Left | 8.5 | 2.000 | WBR |
| 2 | IS | 3.427 | 3.460 | 3.395 | 6.5 | Left | 8.5 | 3.000 | WTR |
| 2 | FS | 3.427 | 3.446 | 3.408 | 3.8 | Left | 11.2 | 3.000 | CPWR |
| 3 | BS | 3.123 | 3.267 | 2.979 | 28.8 | Left | 11.2 | 3.000 | CPWR |
| 3 | IS | 1.123 | 1.263 | 0.983 | 28.0 | Left | 12.0 | 5.000 | RB |
| 3 | IS | 1.123 | 1.253 | 0.993 | 26.0 | Left | 14.0 | 5.000 | RF |
| 3 | FS | 1.123 | 1.323 | 0.923 | 40.0 | Left | 0.0 | 5.000 | BMXS |
Two change points, three setups. Exercise closure limit: (1 + √2) mm. Compare the magnitude of the closing error with the limit.