Soil erosion is a big problem in agriculture. Rich topsoil are blown off by strong wind, or brought down the streams, rivers and into the ocean by strong rains and flash floods. That's the usual scene in many agricultural lands, especially on sloping or hilly farms and the land is regularly plowed or tilled. An otherwise slightly compacted top soil are being loosened and "disturbed", so when strong rains and flash flood come, the loosened soil are easily eroded.
In the cities and coastal areas, especially on mouths of rivers, the eroded soil make their exit. The soil is visible in the air – usually brownish and muddy. If the city or coastal area is very entrepreneurial, then they should be able to “create” new land area and extend the beaches by several meters outwards into the sea, depending on the volume of the eroded soil and the technology used in land reclamation.
In my trip to Seoul from Manila more than 2 years ago, I saw in the southern part of Korea (Jeju islands and surrounding small islands) while the plane was slowly descending, some coves or small bays being “enclosed” by a straight line of short dam of stones and rocks with a cemented road on top of them. A bridge continues the road system so the “enclosed” water below can go out to the open sea in the narrow water outlet. Said short dam is just waiting for the eroded soil from rice fields and other agricultural lands upstream, perhaps 20 years, or 50 years or more, before the enclosed area can be filled with soil, slowly compacting, and from which future land for commercial, industrial and residential uses will be created.
Some of those straight dams of big rocks and stones on other smaller bays already have thick deposit of brownish soil. Perhaps these are old dams built many years ago, and they have accumulated a big deposit of eroded soil already. All that the developers of those lands will do is wait for the still muddy-looking soil to be hardened and compacted, before structures can be built on them.
On my recent trip from the US back to Manila (I attended a conference in Atlanta last April), my plane made a stop-over at Narita airport, Japan. While the plane was slowly descending, I saw land reclamation projects in some less dense coastal areas. One such reclaimed land project was obviously a rice field of several hectares! I was amazed because I have thought that since land reclamation is an expensive project, the enterprises which develop such projects, whether public or private, will only use the land for commercial/residential and industrial use, where land valuation per square meter or per hectare is usually higher compared to agricultural land.
So, while soil erosion downstream is a bad thing for agriculture, it can be a good thing for urban and coastal land development and expansion. One can look at it as an alternative to upland movement of expanding population (by natural birth or migration) seeking new frontiers for residential, agricultural, commercial and industrial lands. Instead of people converting more forest land in the mountains to non-forest uses, people can go to a portion of the “sea” which has become habitable.
This is not to justify, if not encourage, soil erosion in order to hasten land reclamation. The rich topsoil in agricultural land should remain where they are. The topsoil should in fact become thicker through the addition of a new layer of newly decomposed biodegradable materials, so that agricultural productivity at low farming costs will be sustained. But since not all farmers are practitioners of erosion-control technologies like no-tillage farming, and there are simply plenty of strong typhoons and monsoon rains that can wash away topsoil, soil erosion is an inevitable and natural phenomenon.
The entrepreneurial capacity of those working in river mouths should only be encouraged in order to optimize the use of the eroded soil for various human activities.