The area of the upper part of the River Oi is famous for its rich forests of Japanese cedors (cryptomeria), Japanese cypresses, white firs, hemlork-spruces, ete. It appears that these kinds of wood have since long been cut down by feudal lords at times.
The earliest record concerning the bringing down timber out of the area is that for the purpose of building the main toner of Sunpu (Shizuoka) Castle in the Keicho period (1590-1614) in the beginning of Tokugawa Shogunate Dynasty, and, after that, timber was continuously brought down.
It is clear that the piece of timber was brought down by the stream one by one out of the area more than seventy kilometres away from the river mouth.
It was then innevitable to ship the timber by sea to Yedo (Tokyo) where it was demanded; the timber ought to be loaded on a vessel near the mouth of the river.
However, the River Oi runs through the Akaishi mountains as high as 3000 metres, and the area is rich in rain.
These conditions create a remarkable delta at the mouth of the river, that makes the construction of a sea port most unsuitable.
The question is; How they overcame the difficulty? and From where they shipped the timber?
To answer these points, the present author looked in ancient documents and has found that in the 6th year of Genroku (1693), the famous businessman Kinokuniya-Bunzaemon built a sluice-gate, Kiya Suimon near Shimada, and that he used water-ways on the delta down till Wada Port eight kilometres north-east from the river mouth.
In later dotuments, it was found that the River Shibachi and the River Shinkawa had also been used as route to Wada Port and Fujimori Port.
Both Wada and Fujimori were the rivermouth ports safely protected from the sea by sand-dunes.
The author made field investigations in the area and found the following routes once used for the purpose:
Route A: the River Oi-Kiya sluise-a part of River Tochiyawa-the River Kiya-Wada Port. [since the Genroku period (1688-1704) till 1877]
Route B: the River Oi-Kiya Sluicc-the River shibachi-a small part of the River Tochiyama-the River Kiya-Wada Port.
Route C: the River Oi-the River Kamiizumi-Shinkawa-the River Tanaka-Fujimori port.
Route A and B are historically more interesting and their shipment was more important.
Toward the end of the 33rd year of Meiji (1900), these routes were substituted for by the railway and today what remains is their traces used as irrigation water-ways.
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