Surface Erosion Prevention Method Utilizing Soil Algae (BSC (*1) method)

Nippon Koei Co., Ltd.

Updated	December 25, 2023 (Posted on December 27, 2023)
Publication date	May 31, 2023
Sector	Natural Disasters and Coastal Areas / Natural Ecosystems

Company Overview

Climate Change Impacts

In the southwestern islands, heavy rainfall causes soil runoff from development sites and agricultural land, which destroys the coral reef ecosystem in coastal waters and adversely affects the fishing and tourism industries. This is called the "red soil problem”. As a result of climate change, it is expected that similar problems will spread as the risk of slope collapse or muddy water generation due to soil erosion increases in various regions due to various factors including increased rainfall intensity.

Adaptation Initiatives

In collaboration with the National Research and Development Agency Public Works Research Institute, we developed the "BSC Method," a technology utilizing soil algae (*2). The purpose and method of this technology are as follows.

• Objective: Preventing the erosion of collapsed slopes and built-up slopes (nori-men) (*3) and formation of natural vegetation
• Method: Materialize soil algae and spread them on the ground surface of the collapsed areas and slopes (Figs. 1 and 2)
• Technical background: Research on red soil control conducted in Okinawa has demonstrated that the amount of sediment runoff is low in areas where soil algae have developed and that the amount of runoff is reduced by 1/10 to 1/20 in fields where BSCs have been formed.
• Advantages: Lower cost than conventional natural greening methods, applicability to regulated areas of environment preservation, and construction without slope shaping.

The "BSC method" uses soil algae that exist throughout the world, so it has the advantage of having little environmental impact on native species. Since soil algae are clonally propagated, there is no risk of genetic disruption, making the BSC method applicable in various domestic and international regions. This method is being promoted in countries outside of Japan including Nepal and Malaysia.

Effects / Expected Benefits

Vegetation generally transitions from bare soil to the state where the soil surface is covered with algae and moss (BSC), but this transition takes time under natural conditions. In this method, where soil algae are applied, BSCs are formed in a short period of time, from two weeks to one month (Fig. 3). BSCs have the effect of preventing surface erosion, and early formation will lead to erosion control, turbidity control, and vegetation restoration/introduction by taking advantage of natural phenomena.