How can dikes and drainage reclaim shallow coastal waters and tidal marshes?

Land reclamation in shallow coastal waters and tidal marshes is primarily achieved through the construction of dikes built roughly parallel to the shoreline, which enclose the target area. Once enclosed, the water between the dikes and the natural coastline is removed through drainage.12

The specific drainage method depends on the elevation of the land relative to the tide:
* Above low-tide level: Water can be discharged into the sea using tide gates, which open at low tide and automatically close to prevent seawater from re-entering at high tide.12
* Below low-tide level: Mechanical pumps are required to lift water over the dikes.12

In some cases, sediment-laden streams are diverted into the enclosed area to build up the land level, which facilitates the drainage process. Once drained, the land—often called a polder—requires additional treatment to remove salt and, in the case of sulfide-rich "cat clays," neutralization with lime to prevent excessive acidity before it can support agriculture.12