Wanli Creek landslide lake's maximum storage capacity may be revised upward, just 7 km from Qicai Lake

(CNA) Hualien County, July 1st) The right bank of the Wanli Creek landslide lake in Hualien continues to collapse, with debris accumulating on the dam. The dam's height has increased by 6 meters from its initial state, and the maximum storage capacity may be revised upward from 4.2 million cubic meters to 5.1 million cubic meters. The lake is located just 7 kilometers in a straight line from Qicai Lake on the Nantou County border.

According to observations, as of 7:40 PM, the current storage capacity of the Wanli Creek landslide lake is approximately 2.43 million cubic meters.

The Forestry and Nature Conservation Agency's Hualien Branch Office issued a statement saying that a "Wanli Creek Landslide Lake Disaster Emergency Response Team Working Meeting" was held continuously this afternoon. The team commissioned by National Yang Ming Chiao Tung University, based on the latest aerial photography data of the landslide lake completed yesterday by the Aerial Survey and Remote Sensing Office, found that due to continuous collapse on the right bank, debris has been accumulating on the dam. The dam's height has increased by 6 meters from its initial state, and the maximum storage capacity may therefore be revised upward to 5.1 million cubic meters.

Based on the results of airborne LiDAR topographic surveys conducted by the Aerial Survey and Remote Sensing Office on June 21st, 24th, and 30th, the monitoring data of the landslide lake dam was updated. The latest data shows that the dam height is approximately 114 meters, the spillway elevation is 1086 meters, the maximum storage capacity is about 5.1 million cubic meters, and the dam volume is about 8.3 million cubic meters. Furthermore, after recalibration, the lake surface water level elevation has been revised to 1066.4 meters above sea level.

The Hualien Branch Office of the Forestry and Nature Conservation Agency explained that the aerial monitoring results today show no significant damage or abnormalities to the dam. Currently, the average daily storage capacity of the landslide lake is about 150,000 to 250,000 cubic meters. If the watershed experiences continuous rainfall exceeding 80 millimeters, leading to soil saturation, the daily storage capacity is estimated to increase to about 600,000 cubic meters.

A 3D modeling video of the Wanli Creek landslide lake and its downstream river section, created by Professor Chang Kuo-chen's team from National Central University, clearly shows the Wanli Creek winding upstream along steep mountain slopes after entering the mountains from the Lintianshan settlement, reaching the landslide lake after 28 kilometers. The Wanli Creek landslide lake is surrounded by high mountains above 2,000 meters above sea level, and is only about 7 kilometers in a straight line from Qicai Lake, which is close to the Nantou County border.

The 3D modeling images clearly show the inaccessibility of the landslide lake's location. It is currently the flood season, making it difficult for machinery and construction personnel to enter. In addition, the surrounding slopes of the dam continue to collapse. The relevant central and local government units and scholars and experts attending the meeting reconfirmed that within the short period before the landslide lake overflows, any concept of human intervention for dam area engineering treatment, whether through excavation or diversion, is currently not feasible. The urgent priority is to actively carry out various disaster prevention and mitigation preparedness measures downstream.

To further grasp the on-site situation, the Hualien Branch Office of the Forestry and Nature Conservation Agency specifically dispatched personnel from the Wanrong Work Station and invited 9 individuals, including the Eastern Region Search and Rescue Committee of the ROC Mountain Rescue Association and high-altitude support personnel with experience in investigating the Mataian Creek landslide lake, to form the "Wanli Creek Landslide Lake Task Force." With the support of a helicopter from the National Airborne Service Corps this morning, they completed a helicopter drop near Mount Da'an at an altitude of approximately 2,800 meters. They will embark on a 5-day mission to survey routes around the landslide lake, record on-site imagery, conduct geological investigations and soil sampling, and test communication signals, to provide important reference data for future disaster prevention decision-making.

The Hualien Branch Office of the Forestry and Nature Conservation Agency stated that a cross-agency response mechanism has been established between the central and local governments. The alert mechanism will continue to be adjusted based on the latest monitoring data and weather forecasts. Various disaster prevention units are also continuously reviewing preparedness measures, including inspecting dikes, bridges, roads, protective facilities, shelters, flood control supplies, and evacuation mechanisms along the Wanli Creek, to ensure that all disaster prevention and relief measures are maintained in optimal readiness to ensure the safety of downstream residents. (Editor: Huang Ming-hsi) 0701