Segment 1 — The Cold Open

In June 2008, President Lee Myung-bak directed his land minister to add weirs and deepen dredging on the four major rivers rather than rely on dike reinforcement alone. The 22 trillion won project that followed created sixteen concrete structures meant to store water and reduce flood risk. Instead, the weirs produced persistent stagnation that lowered dissolved oxygen and triggered repeated algal blooms in every reservoir.

Segment 2 — The Good Intention

Lee Myung-bak had campaigned on water security and flood protection after years of drought and typhoon damage. In 2008, two months after abandoning his larger grand canal proposal amid public opposition, he turned to the four rivers as a practical alternative. Government planners initially proposed reinforcing existing dikes and limited dredging to manage peak flows. Lee believed deeper channels and controllable storage would deliver both reliable supply and safety during the monsoon season. At the time, the approach aligned with conventional engineering views that faster-moving, deeper water reduced overflow risks for downstream cities and farms. The administration treated the project as a straightforward infrastructure upgrade that would also create jobs during the global financial crisis. Planners calculated that added depth and weirs could meet both irrigation needs and peak-flow storage without requiring new land acquisition on the scale of the rejected canal.

Segment 3 — The Implementation

Between late 2008 and June 2009, Lee issued repeated design orders that raised the minimum depth on the Nakdong River from four to six meters and set a total storage target of 800 million tons. Construction crews installed sixteen large weirs and performed extensive dredging, completing the work by 2012. Early government statements highlighted reinforced banks and new water reserves as immediate gains. Some local officials reported fewer minor flood events in the first year after completion. Skeptics in environmental groups and parts of the Environment Ministry warned that the weirs would reduce flow velocity, but those concerns were set aside during the accelerated timetable. The Board of Audit and Inspection later documented that ministry staff had raised the risk of green tides yet were directed not to emphasize it. The compressed schedule meant that hydraulic modeling of the new minimum depths was completed only after the presidential directives had already fixed the storage volumes.

Segment 4 — The Unintended Consequences

Once the weirs held water at the new depths, flow on the Nakdong dropped to roughly one-tenth of its prior speed in many reaches. Lower velocity allowed nutrients to remain in place, raising biochemical oxygen demand and phytoplankton levels above the five-year average recorded before 2009. The Board of Audit and Inspection’s 2013 and 2018 reports recorded higher algae concentrations and chemical oxygen demand across all sixteen reservoirs, with visible “green latte” blooms appearing each summer. The 2014 Prime Minister’s Office panel confirmed that stagnation from the structures and dredging was the direct cause, even while noting flood protection had improved in 93.7 percent of surveyed areas. Because the weirs could not be operated to restore natural flushing without losing the storage the president had ordered, operators faced a recurring choice between water quantity and quality. Downstream communities that had expected cleaner irrigation water instead dealt with treatment costs and periodic restrictions during bloom events. The same slowed water that reduced some flood peaks also prevented the natural scouring that had once limited nutrient buildup. Over successive seasons, the ecological parks built beside the rivers required repeated interventions because the altered hydrology no longer supported the vegetation planners had assumed would thrive. The 2014 panel further observed that water leaks at six Nakdong weirs and faulty gates at twelve others compounded the difficulty of any corrective flushing, because repairs themselves demanded stable reservoir levels. Environmental groups documented fish kills and shifts in benthic invertebrate communities that had not appeared in pre-project monitoring, effects traceable to the sustained low-oxygen conditions rather than to any single typhoon.

Segment 5 — The Aftermath

Multiple audits by the Board of Audit and Inspection and the 2014 investigative commission documented the water-quality decline and structural issues at fifteen of the sixteen weirs. Successive administrations faced pressure from civic groups to open gates more frequently or remove structures, yet storage targets limited how far those measures could go. Some weirs now operate under adjusted schedules that trade a portion of the original water reserve for modest flow increases. The partial fixes have not restored pre-project oxygen levels or eliminated seasonal blooms. Public debate continues over whether further modification or full removal would be required to address the persistent eutrophication. Proposals to dismantle individual weirs have been studied, but each study must still reconcile the original 800-million-ton storage commitment with the observed oxygen deficits.

Segment 6 — The Lesson

When a single leader sets numeric targets for depth and storage without an independent review of flow consequences, the resulting structures reward volume over circulation. When an environment ministry is instructed to suppress its own risk assessments, later audits must reconstruct the original warnings from internal records rather than act on them in real time. When construction proceeds on a fixed political timetable, the completed system locks in operating rules that cannot easily adapt once monitoring data arrive. How might today’s large river or reservoir projects build an explicit test of minimum flow velocity before final design approval is granted?

Sources

• en.yna.co.kr — Audit agency: Ex-President Lee's Four Rivers Project shoddily designed
• dx.doi.org — The Four Major Rivers Restoration Project of South Korea: An Assessment of Its Process, Program, and Political Dimensions
• koreajoongangdaily.joins.com — Issues plagued four-rivers project
• koreaherald.com — Panel reveals faults in four-river project
• en.yna.co.kr — Gov't, ruling party clash over reported flaws in four-rivers project
• english.hani.co.kr — ARTICLE_URL: https://english.hani.co.kr/arti/english_edition/e_national/598190.html

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