Breach blamed on ancient construction techniques

2024-07-09 13:20:13China Daily Editor : Zhao Li ECNS App Download

The Water Resources Department in Central China's Hunan province has attributed a recent dike breach at Dongting Lake to inherent weaknesses in its structure that date back to its construction centuries ago.

The breached dike, in Huarong county, is part of a network of flood storage embankments built throughout the Dongting Lake area.

Unlike traditional river levees, they are designed to create designated flood zones, alleviating the pressure on main waterways when water levels are high.

The Dongting Lake system's complexity stems from its interconnected embankments, separating the lake from the river and various sections of the lake itself. Originally built during the Three Kingdoms period (220-280), with additional structures added during the Ming and Qing dynasties (1368-1911), the embankments have limitations due to the technology of the time.

"The embankments were built on sandbars and mud flats, with some sections even crossing original river channels," an official from the department told China Central Television. "Without proper foundation construction techniques, inherent defects were introduced."

The department said several geological issues plague the embankments: sandy foundations allowing water seepage; soft foundations susceptible to landslides when water levels are high; and the poor soil quality of the embankments themselves, which leads to weaknesses and instability.

Compounding these problems was the lack of scientific analysis during initial construction. Embankment lines often followed the natural curves of sandbars, resulting in sharp bends in the river channel. Erosion during flood seasons further exacerbated these weaknesses.

Experts said methods like reverse filtration and water storage back pressure can be used to address piping — the movement of water through small channels within the embankment. However, swift action is crucial.

"If clear water emerges, the situation is manageable," the department said.

"But the presence of sand or debris indicates a more serious situation. Continued flow of sand and debris can erode the embankment's base, increasing the risk of a breach."

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