Estimation of Erodibility Coefficients Based on Geophysical Forest Properties in Ogouchi Dam Watershed

Decadal Changes in Soil Water Storage Characteristics Linked to Forest Management in a Steep Watershed

“…At present, the Bureau of Waterworks of the Tokyo Metropolitan Government has been purchasing poorly managed private forests to achieve unified management of the water resource facilities in the catchment, including the 23,719 ha of forest which they also termed green dams. The continuous efforts to expand the area of well-managed forests in the upstream catchment can be considered the most significant cause of why the Ogouchi Reservoir has maintained its low sedimentation rate at 350 m 3 km −2 per year in the past two decades [39].…”

“…Thus, the decadal trends from this current approach agreed with the previous findings from the rainfall-runoff correlation analysis [44] that long-term and continuous environmental rehabilitation practices are likely to bring a positive effect on the soil water storage characteristics of the forested watershed in the long run. Aside from their remarkable effects on soil water storage and availability, the healthy and well-protected forest floor in the watershed also increases erosion resistance and, overall, can contribute to the sediment stabilization in the Ogouchi Reservoir [39].…”

“…remarkable effects on soil water storage and availability, the healthy and well-protected forest floor in the watershed also increases erosion resistance and, overall, can contribute to the sediment stabilization in the Ogouchi Reservoir [39].…”

“…With the recent increase in the sika deer (Cervus nippon) population that causes Japanese forests to suffer from their heavy grazing [36], the installation of deer-prevention fences becomes a widely adopted countermeasure. Previous studies reported that the security and enclosure provided by the fences were effective for recovering from excessive deer grazing [37,38] and enriching the grasslands and understory layers of the forest [39], which, in effect, influence the soil water characteristics [40,41]. Lastly, earth-retaining fences in forests, in the form of lined felled trees, serve as a slope stabilizer and runoff buffer, specifically reducing the peak flow and delaying the runoff time [42,43].…”