The lowland region was prone to flooding during the rainy season.
1 more example
However, between Monrovia (6°20'N/10°46'W) and Buchanan (5°57'N/10°02'W) highlands approach to within 25 km of the coast. East of Buchanan the lowlands reach nearly 100 km inland, in the Cestos Valley, but narrow again to 30 km towards the eastern border.(Can we date this quote?), “Liberia”, in Wetlands.org, archived from the original on 28 Jul 2011, page 1:
Brora coal, costing 10s. a ton, was hauled along the tramway to the station and there mixed with Lowland Scottish coal, brought north by rail and costing twice the local variety. Some of this mixed coal was sent to various destinations along the railway, but most was hauled along the tramway to the harbour for shipment to the Moray towns, where it was sold for slightly less than pure Lowland coal.1960 January 23, Iain D. O. Frew, “The Brora Colliery Railway”, in Railway Magazine, page 56: