Flood in Wrn Tanana Vly Wrn Yukon Vly, Alaska

Water levels rose to bankfull in Manley Hot Springs the evening of May 6th and by the morning of May 7th major flooding was observed in the community. NWS staff on a Civil Air Patrol reconnaissance flight observed a large ice jam on the Tanana River 12 miles downriver which dammed the river and backed up water into the community. The river crested around 9 am May 8th with a preliminary estimated stage of 19.50 feet, which is 6.0 feet above flood stage. This was the highest water level observed at Manley Hot Springs since the record flood of 1956 (the 1956 flood is estimated approximately 2.5 feet higher). The ice jam held for 36 hrs, releasing on the morning of May 8th and water levels began to recede through the day. Standing water remained in low lying areas of the community through the following week. Impacts to the community included many homes and structures either flooded or surrounded by water, many roads inundated with some parts of town appearing cut off and only accessible by boat, Only 6 of freeboard under the Manley Hot Springs Slough bridge, approximately 500 feet of the Elliot Highway approaching town was inundated with several feet of water, power was shut down in the community as a precaution due to the lines being buried, cellular, phone, and internet networks are down. In addition significant areas of fuel sheen on the water surface due to overturned heating fuel tanks and other sources.

An ice jam formed on the Tanana River downstream of Manley Hot Springs and caused significant flooding along the Tanana River upstream of the ice jam for approximately 15 miles. Although the temperatures preceding the ice jam were normal to below normal, the Nenana Ice Classic personnel measured an ice thickness of 30', 73% of average, on April 8th at the Tanana River at Nenana. This site is 53 miles southeast of Manley Hot Springs, but it is a reasonable indicator of basin-wide conditions. The Natural Resources Conservation Services snow water equivalent (SWE) data reported many stations with a three record snowpack in the upper Tanana River basin with an estimated basin-wide SWE more than 200% of normal. It is likely that the robust snowpack contributed to the flooding due to the large surge of water moving downriver past Manley Hot Springs.