Research Trends and Results

Estimation of the garbage volume flowing into theTokyo Bay
HINATA Hirofumi, Head (Ph. D., Engineering)
KATAOKA Tomoya, Researcher
Coastal, Marine and Disaster Prevention Department, Coastal Zone Systems Division（Key words）

Sea garbage, Ocean radar, Environment improvement ship, Inverse estimation

1. Background and purpose of the research
A floating dock has drifted down to the west coast ofAmerica, 90 or more found foreign types, it costed eighty
thousands dollars to dispose of them – Problems of thesea garbage that was come up after the Great East JapanEarthquake. Such is the environmental problem of thecrossing border type that is becoming serious mainly in
the East China Sea and Sea of Japan in our country. Ingeneral, first step to resolve the environmental problem isto recognize the actual state through the monitoring(quantification). As for the sea garbage, the most typicalmonitoring method still being used is garbage collection
by human hands, and that is the significant bottleneck toimplement the problem solution (reduction). If you wantto know the density of the dissolved oxygen (DO), justuse a DO meter. But there exists no “Sea garbage
meter” to measure the sea garbage so far.
Under such a background we are proceeding todevelop the sea garbage monitoring (quantification)technology. There are several methods such as the one tocalculate dimensions covered with drifted garbage basedon a image shot by Web camera1), another is to estimate
the sea garbage generation volume (flow-in volume)
based on the Drifting garbage collection data issued by
the national and local public agencies2 and so on. Here,
we would like to introduce the estimated result of thevolume of garbage – of reeds having the largest collection
volume when classified by type - drifted into the Tokyobay in FY2008.
2. Method
For the estimation, we have used the Drifting garbage
collection data by the Environment improvement ship
“Bay clean”(Kanto Local Management Division) andInside bay surface current speed yard measured by theOcean radar. It is possible to estimate the volume andtype of the garbage that Bay Clean has collected byreferring to the Daily Report and collected points andtime based on the ship route data. We have used theInside bay surface current speed yard by inverting it tobacktrack the garbage drifting route from the collected
point to find the flow-in source (river mouth) and flow-intime. As for the flow-in volume, we have calculated thegreen coefficient (to know the percentage of the unit
garbage flow-in volume that has arrived at the collected
point at collection time) beforehand and determine theflow-in volume by using the least square method so that it
becomes equal to the actual collection volume. It is thesame method as the Tsunami wave source inversion.

3. Application of the estimation result and outcomeThere is a distinct relation between the garbage flow involume and river water flow-in volume (Fig.). It suggeststhat it is applicable to estimate the garbage flow-in
volume from the river water flow-in volume. Flood fromthe August end to September beginning (10 days) has
produced garbage corresponding to 32% of the year totalthat has flown in. On the other hand, there found almost
no flown in garbage in a normal period that has no rain.

Fig. Estimation result of the river water (upper) andvolume of flown-in garbage
If we suppose the accumulated time of the surface
current water as some days to ten days, the density of thesea garbage shall be the order of 101 L/km2 in normal
period and around 100 times in the flood period. At thetime of the flood, the garbage shall accumulate aroundthe current rip between the plain water and seawater. On
the contrary, in normal time there is garbage of small
volume and further they are dispersed as there found no
distinct current rip. If we talk about the annual collection
volume, the point is how we can collect effectively at thetime of flood. However, another discussion shall be
required whether or not to put only the annual garbage
collection volume as the management target of theEnvironment improvement ship.
If applied the technology introduced here, it becomes
possible to estimate the garbage flow in volume anddrifting position from the current “river water” flow involume and Surface current speed yard (Ocean radar). It
becomes possible to do simulation to know how many
garbage shall be (or was) collected on what timing andwhere.
【Reference】
1)

Kataoka et al., MPB, No.64, 1829-1836, 2012.

2) KATAOKA et al, Coastal ocean research, No.49，113-126，
2012．