Higashihiroshima City, in Hiroshima Prefecture, Japan, recently implemented a flood hazard and disaster prevention web GIS application developed using 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. The entirety of Japan contains 31,600 priority-level agricultural reservoirs, many constructed hundreds of years ago, prior to the Edo period (1603-1868). Simultaneous monitoring of so many locations during and following periods of heavy Typhoon rainfall or a seismic event is challenging, particularly considering that priority is given to monitoring and mitigating risks associated with river flooding and landslides. According to the Higashihiroshima Agriculture and Forestry Division, 48 agricultural reservoirs in Hiroshima Prefecture (some in the territory of Fukuyama City) collapsed in 2018, sometimes resulting in deaths. This application helps citizens to become more aware in advance of the risk posed by nearby reservoirs and be better prepared.
 

Flood scenario triggered by potential collapse of the Senzoku Reservoir.

 

A simulated flood presentation is available for each reservoir using unfavorable assumptions that the reservoir is full and the collapse is instantaneous. When a flood scenario is called by an online user, depth gradients of the inundation are rendered on the map using vector polygons. For example (see image above), 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.

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 and for citizens to print out to study and have handy at the time of a disaster.
 

Flood scenario with north arrow, scale, and other map information set up
by an online user for download as a PDF image file.

 

TatukGIS support for the WMTS (Web Map Tile Service) protocol and a built-in Leaflet library are used to incorporate into the project map layers streamed from remote servers: an aerial image layer from the Japan Geographic Survey Institute WTMS and an OpenStreetMap layer from the Geospatial Information Authority of Japan. Locally stored vector map layers are in the SHP file format and/or TatukGIS SQL native structure format running on SQLite database. DK functionality efficiently converts layers on-the-fly to the map presentation coordinate system. Other DK functionality used in the application include the print-to-PDF feature, north arrow and scale controls, and support for Japanese language characters (the DK supports language characters for all languages).
 

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

The Higashihiroshima City reservoir flood 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 framework. The application runs on Windows IIS 11. Though the DK for ASP.NET also supports Microsoft ASP.NET Core framework, the older Web Forms framework was used for this project because the flood hazard application needed to be completed and available to the public quickly. Tsukasa later ported the application to ASP.NET Core for improved online user experience and ability to host the application on Linux and macOS servers (as well as Windows servers).

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