Sediment Deposition within Fish Pool Structures Over a 3-year Period after Installation in an Agricultural Drainage Channel

Abstract

We investigated sediment deposition in fish pool structures and particle size distributions of the deposited sediments as well as those from paddy fields and levees over a 3-year period after installation of the structures in an agricultural drainage channel in Matsusaka City, Mie Prefecture, Japan. Sediment deposited in the upstream fish pool structure amounted to 18%–39% of the pool volume per year, whereas that deposited in the downstream structure amounted to 11%–17% of the pool volume per year. The water depth in fish pool structures used as wintering habitat could potentially be maintained in the downstream structures by constructing those adjacent to the upstream structures or sedimentation pools. This in turn might result in a reduction in the required frequency of dredging by farmers. Pool volumes were already filled 23%–29% by sediment just after installation. Particle size distributions of the sediments in the upper fish pool structure and channel side levees were coarser than those of paddy field side levees and paddy fields. This may indicate that sediments in the fish pool were supplied from channel side levees during rain events. Therefore, promoting the growth of native vegetation cover along the levees at the end of land consolidation projects might be an effective method for reducing soil erosion and sediment deposition in the fish pool structures.