Wet dock systems in harbour engineering: identify the correct features — maintenance of minimum water depth, provision of entrance locks with massive gates, powered operation of dock gates/bridges, and relatively high construction cost.

Introduction / Context:
Wet docks are enclosed basins that keep vessels afloat at a near-constant level, independent of external tides. Their design uses locks and robust gates, along with mechanical systems for operation and access, and therefore tends to be costlier than simple quay arrangements.

Given Data / Assumptions:

• Controlled basin water level to ensure safe, continuous berthing depth.
• Entrance locks with large, heavy gates (e.g., miter or caisson).
• Mechanical/hydraulic systems operate gates and associated movable bridges (including bascule road bridges over entrances).
• Substantial civil, hydraulic, and mechanical works imply higher cost.

Concept / Approach:
Maintaining minimum depth requires isolated basin control via locks. Large gates and machinery provide the necessary sealing and movements. Integration with traffic (bascule bridges) is common at dock entrances. The extensive infrastructure drives up capital cost versus open roadsteads.

Step-by-Step Solution:
Check depth control: accurate—core function of a wet dock.Check lock/gate provision: standard for isolating the basin from tidal waters.Check mechanical operation: heavy-duty systems (hydraulic/gear) and bascule bridges are typical at entrances.Check cost: high due to complex structures and equipment.Therefore, 'all the above' accurately summarizes wet dock features.

Verification / Alternative check:
Harbour engineering references describe wet docks with lock-gated basins and associated movable bridges and machinery.

Why Other Options Are Wrong:

• Choosing fewer features ignores integral components of wet docks.

Common Pitfalls:

• Confusing bascule bridges (road access) with the lock gates themselves; both can coexist in a wet dock layout.

Final Answer:
all the above.