## Sandy Beach Changes

In order to understand the changes in the sandy and muddy beaches along the Pacific coastline from Aomori Prefecture to Chiba Prefecture (about 680 km in total length) due to the tsunami, we compared the changes in the three periods using aerial and satellite photos taken in the 1970s, before (2000s) and after the earthquake disaster. A scale of 1/10,000 was assumed for the plot accuracy and the survey range covered a width of 300-500 meters for areas with wide sandy beaches and 100 meters for areas with narrow beaches.

## Area change in from the 1970s until the earthquake

“Coastal structures” such as harbours and fishing facilities increased in all survey regions. Although the “sandy beach” area shrunk in Aomori Prefecture, the “coastal forest” area increased. In Ibaraki and Miyagi Prefectures, “sand dune vegetation area” was decreased.

## Area change before and after the earthquake

“Sand dune vegetation” and “coastal forest” were vastly reduced in all survey regions, and most were transformed through man-made developments or changed into barren lands (included under “Others”). “Sand dune vegetation” in Aomori Prefecture, “sand dune vegetation” and “coastal forest” in Miyagi Prefecture, and “coastal forest” in Chiba Prefecture were changed to “Others” by almost the same extent in terms of the area.

#### e.g. Nehama, Kamaishi City, Iwate Prefecture

## ● 1970s until before the earthquake disaster

Sand dune vegetation grew in sandbars with a width of about 50 meters while coastal forest extended towards the south. The estuary of the Unosumai River moved towards the north comparing the changes of the two periods.

Before the earthquake disaster – After the earthquake disaster

The sandbar extending from the right bank disappeared due to the tsunami. A V-shaped gulf section was formed and the shoreline receded by a maximum of about 400 meters.

Before the earthquake (February 2003)

Geographical map: 1/25,000 map of Aerial Photos: Taken by Geospatial Information Authority of Japan

Geospatial Information Authority of Japan

## Changes in the last hundred years

From the Old Edition map of the Geospatial Information Authority of Japan which was surveyed about a hundred years ago from 1903 to 1917, “old river channels,” “rivers,” “lakes and marshes,” “wetlands,” “sand dunes,” “sandy beaches” were identified and converted to GIS. As shown in the following examples, the state that the land used to be is presumed to be reflected after the earthquake.

#### e.g. Idagawaura(Minamisoma City, Fukushima Prefecture)

Before the earthquake (September 2002)

Idagawaura was once covered in water.

The land reclaimed in 1929, was used as a reclaimed paddy field.

After the earthquake $ ^{*} $ (April 2012)

Due to the impact of the tsunami, it returned to the water region and wetlands that it used to be after the earthquake.

Idagawaura, which was drained and turned into paddy-field, was still submerged even one year after the earthquake.

Geographical map: 1/25,000 map of Geospatial Information Authority of Japan

$ ^{*} $ Aerial Photos: Taken by Geospatial Information Authority of Japan

#### e.g. Torinoumi (Watari Town, Miyagi Prefecture)

1907

A series of sand dunes (orange) used to extend parallel to the coastline with the areas in-between being wetlands (yellow-green).

Before the earthquake (March 2003)

Areas which used to be sand dunes were turned into fields while areas which used to be wetlands were turned into paddy fields.

Geographical map: 1/25,000 map of Geospatial Information Authority of Japan

Although there were not big changes in the areas which used to be sand dunes after the earthquake, the ground of the areas which used to be wetlands was weakened.

Ground of inland coastal forests which used to be wetlands was lowered and submerged.

$ ^{*} $ Aerial Photos: Taken by Geospatial Information Authority of Japan