Levee and Super Levee

A levee is defined as a “man-made structure, usually an earthen embankment, designed and constructed in accordance with sound engineering practices to contain, control, or divert the flow of water so as to reduce risk from temporary flooding”.

Maruyama river Japan

Levees are designed to manage a certain amount of floodwater and can be overtopped or fail during flood events exceeding the level for which they were designed. Levee failures can also be caused by structural failures resulting from improper maintenance, inadequate foundations, seismic activity, erosion, seepage, or burrowing animals. 
Levees and floodwalls are typically built parallel to a waterway, most often a river, to reduce the risk of flooding on the landward side. Flood walls, which are typically made of concrete or steel, are often constructed on a levee crown to increase the height of the levee, without increasing the base of the embankment. Figure shows the components of a typical levee.
levee protection

Super Levee
When a levee fails, the result can be more catastrophic than if the levee had never been constructed. For that reason, some urban areas in Japan (especially in Tokyo and Osaka) developed a new flood protection known as Super levee. Super levees are thicker levees that will not fail even in the most extreme events. Super levees are failure proof embankments that ensure safety even during a flood larger than the design one. The three main examples describing the safety advantages of Super Levees are:
  • Overtopping. During unexpectedly extreme events, water may overtop and break ordinary levees. On the other hand, super levee will not break and water will flow slowly on the levee.
  • Seepage. Water seeps may break the levee. On the other hand, super levee will not break because it is wide.
  • Earthquake. During earthquakes ordinary levees may experience liquefaction and fail. On the other hand, super levees will are strong against liquefaction because the ground is improved and the slope is gentle.

flood protection Japan

Google Imagery in QGIS 3

QGIS is the second most popular GIS software and the most popular free GIS. Few month ago, the latest version QGIS 3 Girona was released. It has important improvements and new features, but it also has some limitataion compared with previous versions. One important limitation is that some plugins were not updated yet. For instance the plugin for imagery services such as Google Maps is not available. In this post we present a solution for this issue.

Google Maps Layer is hosting somewhere on the Google server and sends the tab to the user who requests it. Technically it is called Tile Map Service (TMS). Therefore, we just need to find the TMS that Google uses to use the Google Maps layers. The Google Maps Layer TMS are:

  • Google Maps: https://mt1.google.com/vt/lyrs=r&x={x}&y={y}&z={z}
  • Google Satellite: http://www.google.cn/maps/vt?lyrs=s@189&gl=cn&x={x}&y={y}&z={z}
  • Google Satellite Hybrid: https://mt1.google.com/vt/lyrs=y&x={x}&y={y}&z={z}
  • Google Terrain: https://mt1.google.com/vt/lyrs=t&x={x}&y={y}&z={z}
  • Google Roads: https://mt1.google.com/vt/lyrs=h&x={x}&y={y}&z={z}

Add Google imagery to QGIS 3
To add the Google Maps map service in QGIS 3:

Go to XYZ Tiles in the Browser panel. Right-click on XYZ Tiles and create a new connection.

Enter the name, for example: Google Satellite. Copy and paste one of the Google Maps TMS listed above into the URL. Adjust the maximum zoom level (suggested to 19).

Strongest Typhoon to hit Japan: 5 numbers to understant it

Typhoon Jebi is the most powerful typhoon to hit Japan in 25 years. Last Tuesday (September 04, 2018) it slammed into the western part of the country on Tuesday, killing at least seven and injuring more than 200, disrupting transportation, heavily damaging the bridge that leads to Kansai International Airport and leading authorities to call for evacuations of areas in its path.  

As of 10 p.m. Tuesday, Jebi was traveling north-northeast over the Sea of Japan north of Niigata Prefecture at a speed of 70 kilometers per hour. Near Kansai International Airport, strong winds swept away a tanker berthed in Osaka Bay, slamming it into the sole bridge that connects the airport to the mainland and taking a large chunk out of the bridge.

There are already several posts and news about Jebi. The video from NHK shows some footages to understand the damage. In this post we summarize 5 important numbers:
  • 590. More than 590 flights cancelled
  • 57 000. More than 57000 air passengers affected
  • 2 Million. More than 2 million houses suffered power outage
  • 500. Up to 500 mm rain in one day
  • 175. Sustained winds up to 175 mph