Sinkholes have appeared on Beijing roads after the city's most severe rainstorm in 61 years on July 21. In the twenty days following the flooding, 99 sinkholes have been reported. Among the largest was a 30 square meter wide, 3 meter deep sinkhole discovered in the Haidian District. An expert from the Chinese Academy of Geological Sciences believes there are two reasons for the appearance of such sinkholes. First, the soil layer was poorly preserved during construction. Second, the soil suffered from gradual erosion and was washed away by the floodwater. He added that the sinkholes indicate extensive structural damage to the ground that requires urgent attention.