Mizukae nisoku (水替人足)
The term "mizukae nisoku (drainage laborers)" refers to those mining laborers engaged in removing the water that collects in mines and pumping it outside the mine.
The remainder of this article will focus mainly on the laborers engaged in tunnel-based drainage efforts at the Sado gold mine, which was run directly by the Edo bakufu.
The first time drainage laborers were sent to Sado gold mine was in 1777.
There was a huge influx of homeless people into Edo and its environs due to the Great Tenmei Famine and the resulting political instability, and many of the homeless committed a wide variety of serious crimes. In what was at once a preventative and punitive measure as well as an effort by the Shogun to clean up Edo, the seat of his power, the homeless who were deemed potential criminals were rounded up and sent to the Sado gold mine on Sadoga-shima Island and put to work as laborers there.
The first to propose this plan was the kanjo bugyo (commissioner of finance) Kiyomasa ISHITANI (the former Sado bugyo [commissioner of Sado]). The then-current commissioner of Sado opposed the plan, citing fears that public order would deteriorate, but proponents succeeded (not without forceful coercion) in ramming through their plan, and homeless people began to be sent to Sadoga-shima Island; thereafter, every year several dozen would be sent.
To distinguish from those who had suffered the penalty of "ento" or exile to a remote island who were called "shimanagashi" ("exiled to the island"), drainage laborers were referred to as "shimaokuri" ("sent to the island") (because the banishment to Sadoga-shima had already been abolished in 1700).
Though at first only homeless people were sent, the scope of who could be sent gradually widened, beginning in 1788 with those who had been punished with flogging or tattooing and had no personal guarantor, continuing in 1805 with those who had acted poorly at their work-houses, and finally extending to those who had shown no contrition for their crimes even after enduring exile.
One goal of the policy was to rehabilitate criminals (they earned small salaries from their labor, and those who repented of their crimes would be released. Convicts on Sadoga-shima Island, much like those at the work-houses of Tsukudajima Island, were given one type of labor to perform, and so if they showed contrition they would receive a tiny sum as savings and, after many years, would be allowed to return to their hometowns), but drainage work was extremely heavy labor, and drainage laborers were so cruelly exploited that it was said they could not survive for more than three years. Convicts on Sadoshima Island, much like those at the work-houses of Tsukudajima Island, were given one type of labor to perform, and so if they showed contrition they would receive a tiny sum as savings and, after many years, would be allowed to return to their hometowns), but drainage work was extremely heavy labor, and drainage laborers were so cruelly exploited that it was said they could not survive for more than three years. Consequently, there was a never-ending string of convicts who tried to escape, so the system failed to play its full part to isolate nor to correct these criminals.
Those who committed additional crimes while on the island were confined in mineshafts, a punishment known as "shikinai oikomi," while those who attempted to escape from the island were given a death sentence.