Geography of the European Netherlands European part of the country can be split into two areas: the low and flat lands in the west and north, and the higher lands with minor hills in the east and south. The former, including the reclaimed polders and river deltas, make up about half of its surface area and are less than above sea level, much of it actually below sea level. An extensive range of seawalls and coastal dunes protect the Netherlands from the sea, and levees and dikes along the rivers protect against river flooding. The rest of the country is mostly flat; only in the
Indus River Delta-Arabian Sea mangroves time it reaches the delta, the flow of freshwater is down by more than 90% compared to historic levels. Active flow only lasts for about two months, and the sediment load is similarly diminished. Saline water intrudes upstream for about and this affects both the mangroves growing in the area and the agricultural land. Loss of sediment causes increased coastal erosion, and this is exacerbated by land subsidence and rising sea levels. Other factors affecting the mangrove areas are pollution from sewage and industrial effluent, and parts of the mangrove area have been lost to agriculture and urban development. The