Increasingly shifting ecology of the coastal terrains is a challenge to local communities in developing practical ways of adapting to the constant changes in their environment. Rechannelling upstream of a shallow river allows sea water to to flow further inland. Tidal flooding causes major erosion around houses and salinates much agricultural land, leaving it useless for many crops. The problem of drainage becomes progressively more acute. Shallow wells have a higher salt content, and fresh water may be found in only a few wells further inland. Road construction is impracticable, as it would require many major bridge spans; and tides determine water transport by anything larger than small fishing boats, implying adjustments to schedules and making transportation less adaptable to the community's needs. People are forced to locate farmland away from their villages and thus must travel back and forth. Finally, people begin to leave their villages altogether and relocate near their newly acquired land.