What a harbour needs

A harbour is a sheltered water area where ships can lie safely and load or unload. A port adds the land-side facilities, berths, yards, warehouses, road and rail links, that move cargo and passengers.

Shelter comes from natural features such as bays and estuaries, or from breakwaters. Rubble-mound breakwaters, built of quarry stone with heavy armour units on the outside, absorb waves on a sloping face. Vertical caisson breakwaters reflect them and suit deeper water.

Ships need depth. The approach channel and berth pockets must be deep enough for the largest design vessel at low tide, with allowances for squat, wave motion and a safety margin, which is why ports dredge, and keep dredging as sediment returns.

Berths come in several forms: solid quay walls, open piled jetties, and offshore moorings for tankers. Cranes, fenders and bollards, and bearing capacity for heavy stacking of containers, complete the picture.

Planning starts with the ships the port expects, since their length, beam and draught set channel width, turning circle, berth length and depth. Wave studies, often with physical or numerical models, decide the breakwater layout so that waves inside stay calm enough for safe loading. Sediment studies predict how fast channels will silt up, and the land side is sized for the cargo volumes forecast over the port's life.