Urban environment

Learning from river-side management in Japan: Rapid assessment using satellite images

As the previous article in this webpage, the reservation of precious waterside areas along river-side in Tokyo are under good condition (light green color along river side). The improvement and development of minor rivers to protect Tokyo from suffered serious damage from floods due to typhoon strikes are also well prepared and maintained in Japan.

The buffer zone along main river are vary, between 100 to 200 m (see Figure 1). These buffer zones are utilized as open green space for urban inhabitants in dry season. Baseball field, jogging tracks, and small parks are some of the urban green space available here. While in the rainy season or when the runoff relatively higher due to typhoon strikes, the buffer zone along river-side will work to protect the inhabitant from being submerged. River diversion in smaller channel is typical common management in Japan`s urbanized area.

Buffer zones along river-side in Tokyo.  Image acquisition of Landsat 8 OLI was May 2013
Figure 1. Buffer zones along river-side in Tokyo.
Image acquisition of Landsat 7 ETM+ was 4 May 2013. Color composite of bands 754 with image Gram-Schmidt enhancement technique to acquired 15 m resolution.

In contrary, in Great Megapolitan Jakarta, river-side environments are in bad condition. From the rapid assessment  using remotely-sensed image we can see that there is no buffer zone available (see Figure 2). Uncontrolled development can be seen from the density of man-made objects along river-side.

There is no buffer zone
Figure 2. Satellite image of Jakarta.
Image acquisition of Landsat 8 OLI was 25 August 2013. Color composite of bands 754 with image Gram-Schmidt enhancement technique to acquired 15 m resolution.

Furthermore, if we compare the topography condition between two great megapolitan area, we could understand that there is quite similar characteristics between Jakarta and Tokyo as shown in the following figures.

Comparing topography
Comparing topography of Jakarta and Tokyo. We draw line across Jakarta and Tokyo to show the cross-section of topography condition form north to southern part of the cities.
Source: Google Earth, elevation profile fuction

Tokyo`s elevation profile along 64.5 km is lower than Jakarta`s elevation profile, but there was no huge-wide floods event during the last two decades in Tokyo Megapolitan Area since the better management in buffer zone always done regularly.

Water will flow from the higher elevation to lower elevation, we need to manage many variables (including; land use land cover in the upper streams and down streams, physical condition, and  socio-environment condition) in order to overcome the flood. One of the solution of floods in Great Megapolitan Jakarta is management along river-side. It will not be achieved in short-term project, however it could begin now!

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