318 / 2024-02-29 15:05:30

Evaluation of Inundation Mitigation Effects of Storage Facilities by Tracer Model

inundation flow analysis,storage facilities,flood mitigation,tracer model

To address the frequent water-related disasters in Japan, the Japanese government has established a new policy called “River Basin Disaster Resilience and Sustainability by All,” in which all stakeholders in the river basin spaces, including the watershed and floodplain areas, work together to reduce flood damage. Flood prevention measures in the policy require the novel utilization of existing facilities, such as paddies and reservoirs in the watershed, to control rainwater runoff in the catchment area. It is necessary to develop a methodology to quantitatively evaluate and visualize the flood mitigation effects yielded by control measures of floodwater runoff to support the policy.

Current policies focus on having more storage capacity, such as by requiring more storage tanks to be installed. They do not show how the storage facilities work and affect the basin in detail. This study uses a tracer model to clarify the impact of storage facilities on inundated areas.

We used a combined 1D and 2D inundation simulation model and incorporated models for four types of storage facilities: Paddy Field Dams, Ponds, School Ground/Park Storage, and Residential Storage. The target area is an urban and adjacent catchment area in Shimane Prefecture, Japan. The rainfall given was from an actual heavy rainfall event.

We evaluated the mitigation effect of the storage facilities on pluvial inundation in the urban area by comparing the results with and without storage measures. The tracer was given to water in meshes categorized as paddy fields, ponds, and school grounds/parks, and we tracked how the water flowed. The results confirmed that storage facilities connected to channels, such as paddy fields and ponds, were able to reduce runoff into the channels due to the storage measures. On the other hand, tracer in school grounds and parks was reduced in areas that were not connected to channels by the storage measures. It was found that school ground/park storage can directly reduce the inundation of the surrounding inundated areas. 

The tracer model could be used to identify the effects of storage facilities on the inundation area. Not only the effectiveness of storage facility measures but also the impact of sluice gate operations could be discussed using the tracer model.