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Flood Hazard Web GIS Application in Japan

August 29, 2023

Higashihiroshima City, in Hiroshima Prefecture, Japan, recently hosts a flood hazard and disaster prevention related web GIS application developed with the TatukGIS Developer Kernel (DK) for ASP.NET edition that focuses on flood risks posed by hundreds of agricultural irrigation reservoirs. The web mapping application enables anyone in the vicinity of a reservoir to understand in advance the flooding impact if the reservoir fails - such as due to an earthquake or heavy rainfall during a typhoon. Citizens can easily understand if their home or business is at risk, how much time following a reservoir collapse before flood water reaches their location (i.e., time available to evacuate), projected depth of the inundation (represented using color gradients), and optimal evacuation path to higher ground and emergency shelter.

The territory of Higashihiroshima City contains 1,821 priority-level agricultural reservoirs, more than any other city in the Hiroshima Prefecture, and approximately 2,200 smaller irrigation ponds. According to the Higashihiroshima Agriculture and Forestry Division, 48 agricultural reservoirs in Hiroshima Prefecture collapsed in 2018, sometimes resulting in deaths. It is hoped this application will help citizens become more aware in advance of the risk posed by nearby reservoirs and be better prepared.

A simulated flood presentation is available for each reservoir using unfavorable assumptions that the reservoir is full and the collapse is instantaneous. For example (refer to the following image), a sudden collapse of the Senzoku Reservoir located in Saijo Town ward would result in flood water reaching National Highway 375, approximately 2 kilometers to the west, in approximately 15 minutes. Sections along the highway would become flooded to a depth of 2 to 3 meters.

Flood scenario triggered by collapse of the Senzoku Reservoir.


Any flood presentation on a map area defined by the online user can be downloaded as a full resolution PDF image file, such as for use in reports or for citizens to print out to study and have handy at the time of a disaster.

Scenario exported to PDF image file with TatukGIS hosted OSM layer
providing elevation contour lines and other detail.


The Higashihiroshima City reservoir hazard web mapping application is developed by Tsukasa Consulting Co. in Japan using the DK for ASP.NET edition with Microsoft Visual Studio and ASP.NET Web Forms. A Leaflet library built into the DK enables efficient inclusion of the TatukGIS hosted OpenStreetMap tile server, with elevation contour lines and Japanese language labels, as a background layer. DK support for the WMTS (Web Map Tile Service) protocol is used to incorporate an aerial image layer sourced via the internet from a Japan Geographic Survey Institute WMTS server. Locally stored vector map layers are in the SHP file format and/or TatukGIS SQL native structure format running on SQLite database. As required, the DK reprojects layers on-the-fly to the map presentation coordinate system. The DK also provides the print to PDF functionality. The application runs on IIS Windows 11.

The Reservoir Hazard Map and Disaster Prevention resource is described on the Higashihiroshima City web site at: https://www.city.higashihiroshima.lg.jp/bosai/10/36731.html

Flood presentation on an aerial image layer streamed from Japan Geographic
Survey Institute WMTS server.