Longbasaba and Pida lakes are two moraine-dammed lakes located at the headwaters of the Geiqu River, a tributary of the Pumqu River in the Chinese Himalayas, at an elevation of about 5700 m. The minimum distance between the two lakes is 24 m and their difference in elevation is about 76 m. Breach risks were assessed on the basis of field surveys carried out in the summers of 2004, 2005, and 2006. Empirical formulae for breaching of moraine dams and the BREACH model for earthen dam failure were employed to simulate the breach properties and hydrograph of floods at the breaching site of the dam from the two lakes. The modeling showed that an outburst flood from Longbasa-ba and Pida lakes would last for about 5.5 hours and have a peak discharge of about 3–5 × 10⁴ m³/s at about 1.8 hours after the beginning of the outburst.