Flash Flood in Guam, July 30, 1999

Flash flooding event in Merizo. Heavy rain from a nearly stationary thunderstorm caused flash flooding across a small section along the southern tip of Guam. Nexrad radar indicated that thethunderstorm was mainly offshore, with heavy rain occurring in the affected area for approximately50 minutes from about 1740 to 1830. 3 hour precipitation estimates from the Nexrad radar indicate a peak of 4 inches in the region. Rain fell in the Merizo area in a small strip along an near the coast from Achang Bay, the Manell River eastward to the Sumay River. Water flowing down the Manell River, which is located northeast of Achang Bay, normally flows down the river then into a drainage culvert which empties out into Achang Bay. Slabs of cement in the newly renovated 16 foot culvert made passage too narrow for the tons of bamboo and foliage debris that was washed down the Manell River with the flood water. The debris formed a dam which then allowed the flood water to stream onto people#s land and into houses. 50 people and 13 homes wereaffected by the flooding. The flood water was 3 to 4 feet in certain places at certain times. The flood water also washed out a 15 foot section of the gravel topped road and collapsed part of the drainage culvert. Through all of this no one was injured.