A three week period where it had rained on all but three days had left the soil around Toowoomba very wet . When a line of storms hit the city on 10 January , the heavy rain rapidly ran off down gullies and streets . A three week period where it had rained on all but three days had left the soil around Toowoomba saturated and when a line of storms hit the city on 10 January , the resulting torrential rain rapidly ran off down gullies and streets .