Watch out for hidden hazards of buying land

When we were looking for property we consulted topographical maps prior to checking a particular piece of land in person. Understanding the elevation of a plot is important if you’re buying land near the coast or along a river. In the event of flooding or a tsunami, it’s obviously better to be located on higher ground. Older topographical maps are also helpful because they can show you the contours of the land before it was developed for residential housing.

Because of Japan’s mountainous terrain and vast tracts of farmland, housing developments are often carved out of rolling hills, with the valleys filled in using dirt taken from the hilly portions. In such cases, the filled-in portions can be unstable in the event of earthquakes and torrential rains, so knowing the original topography is useful when you talk to a realtor about land stability.

If you’re looking in a city or a more developed suburban area, it’s also helpful to consult hazard maps, which many local governments make available to residents. One of the main purposes of these maps is to tell people where to go in the case of an emergency, but they also indicate low-lying areas that are more susceptible to flooding. In a highly developed city like Tokyo, such maps are invaluable, since the original topography has been paved over. Just because these features are now covered in concrete, doesn’t mean they are not affected by natural phenomenon.

There are many hills and slopes in Bunkyo, Minato, Setagaya and other Tokyo wards that, despite being supported by retaining walls (yōheki), can still deteriorate in the event of heavy rain or major seismic activity — mudslides don’t just happen in rural areas. In many cases, these structures were built in accordance with older building standards and have not been renovated because they are on private properties. Individual ward governments are trying to get landowners to renovate their retaining walls, especially if they face public roads, but offer little in the way of incentive. Setagaya Ward, for instance, will simply steer you toward a financial institution that can set up a property improvement loan.

Consequently, even in cities it’s a good idea to understand the geological situation under the home you are interested in buying, and while hazard maps can give you an idea of these dangers, they aren’t always complete. Not surprisingly, homeowners don’t always like hazard maps, since they think the information they contain could lower property values for areas that are deemed to be higher risk. Some local governments just leave off private property and only provide information about public property, thus defeating the whole purpose of a hazard map, which is to inform residents of potential problems.

There are also different kinds of hazard maps. A naisui hazard map shows those places where storm drains may overflow in the event of a heavy downpour, while kōzui hazard maps indicate areas that can be easily flooded by nearby rivers, even when there is a levee separating the residential neighborhood from the body of water. The eastern portion of Tokyo, for instance, is veined with rivers and much of the land is actually below sea level. In the past, these areas were occasionally inundated by flash floods caused by typhoons, and while certain measures have been implemented to alleviate flooding, such as higher levee construction, it is almost impossible to prevent flooding in extraordinary circumstances, so local authorities try to promote awareness for flood preparedness and evacuation. As more and more high rises are built in low-lying areas, neighborhood associations have made arrangements for residents of houses to evacuate to nearby multistory apartment buildings in the case of flooding.

Place names can also be good indicators of the quality of the land and what might happen to it in an emergency. Shibuya means “tight valley” and Tameike was obviously built on a pond. If a place name contains the morpheme “numa,” which means “marsh,” it not only may be more susceptible to flooding, but also could liquefy in the event of an earthquake. By the same token, a place name with “dai” in it usually indicates high land. Developers, however, often change the names of areas where they are building houses in order to make it seem safer. What was once a marsh, for example, can suddenly become a “hill” (“oka”).

The unfortunate fact is that it’s difficult to completely avoid hazards in a country as disaster-prone as Japan, so it’s important to not only understand evacuation plans for your particular area, but also those measures that residents themselves can carry out to lessen the effects of a disaster.

Make sure storm sewers on your property are clear of debris. If you live along a river or in a very low-lying area, keep sandbags in storage. If you do have to evacuate during a flood, beware of falling into ditches and manholes whose covers may have been pushed away by water surges. Typhoon season is upon us.

Philip Brasor and Masako Tsubuku blog about Japanese housing at

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