Regarding the use and preparation of a lead line (sounding line) for depth measurement in hydrography, which of the following statements are accepted good practice?

Introduction / Context:
Lead lines offer a simple, robust method for measuring water depths in small-scale hydrographic work or in shallow areas where sophisticated echo sounders may be unavailable or impractical. Proper preparation and usage of the line are essential to minimize errors.

Given Data / Assumptions:

• A hemp or synthetic line with lead weight is used.
• Graduations (marks at known intervals) must remain reliable while wet.
• Very shallow depths may be measured by a sounding rod or pole; deeper by a lead line.

Concept / Approach:
Wet lines elongate; soaking and pre-stretching mitigates change in length after immersion. Periodic checks ensure graduation accuracy despite wear. Lead lines are preferred over poles beyond a few metres depth; a rule-of-thumb threshold beyond 6 m is commonly cited in instructional texts, though actual maximum usable depth can be far greater depending on conditions.

Step-by-Step Solution:
Pre-soak and stretch the line to stabilize length before marking.Verify and adjust graduations regularly to maintain accuracy.Use a lead line instead of a sounding rod for depths greater than roughly 6 m.Therefore, the inclusive answer “All the above” is correct.

Verification / Alternative check:
Training manuals recommend wet calibration of rope-based measuring lines; operational guidelines distinguish between poles for very shallow waters and lead lines for deeper waters.

Why Other Options Are Wrong:

• Choosing only one or two practices omits other equally essential preparations, leading to systematic errors.

Common Pitfalls:
Using a dry-calibrated line that elongates during use; letting knots slip; ignoring current and boat drift that bias the vertical measurement.

Final Answer:
All the above.