Start with a baseline survey of the bulkhead cap, walers and tie rods, plus survey points on the retained ground behind it, before any dredging begins. Compare every later reading against that baseline, not against the previous reading.
Monitor the bulkhead top for horizontal and vertical movement, and check tie rod tension or tilt where accessible. Add inclinometers or settlement points in the backfill if the dredge cut is deep or close to the wall. Take readings more often during the active cut and at each dredge-depth stage, then less often once movement settles. Set trigger levels with the engineer before work starts, and stop dredging if they are exceeded. The engineer should decide the actual limits and frequency based on the wall's condition and design, which I cannot assess from here. What is the wall type (anchored sheet pile, gravity, or relieving platform) and how far is the dredge line from its face?
Pile Buck's Sheet Pile Design notes that initial readings on all instruments should be taken immediately after installation, since later data is judged against them (Sheet Pile Design by Pile Buck, page 437). The Pile Buck Guide to Soil Mechanics and Testing also stresses plotting settlement against time to judge when movement has slowed (The Pile Buck Guide to Soil Mechanics and Testing, page 262). The full book is in the Pile Buck Store.
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