Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay
Water backflooded into the Pasco Basin because of the constriction atWallula Gap. The floodwaters could not get through a gap a mile wide.Maximum flood waters reached elevations of about 380 meters. It's fairly simpleto estimate flow through a constriction, but the picture is complicated byflooding of the gorge further downstream. When that complication is taken intoaccount, the peak flow is estimated to have been about 10 million cubic metersper second (the volume of Grand Coulee Dam every second). With a channel 2000meters wide and water 250 meters deep, that translates to a velocity of 20meters per second or 45 miles an hour. 10 million cubic meters per secondis about 50 times the flow of the Amazon River, ten times the combined flow ofall the rivers in the world and 300 times as big as thelargest historic flood along the Columbia River.
|Left and below: Looking downriver into Wallula Gap from the north.|
|Left and below: flood-scoured walls of Wallula Gap.|
|Bluffs along Wallula Gap|
|Looking upriver at the Oregon state line.|
|Looking downriver at the Oregon state line, showing the end of the gap and the much shallower gorge beyond.|
panoramic view of Wallula Gap from just south of the north entrance to thegap.
panoramic view of Wallula Gap from just north of the Oregon state line.
Created 21 November 2003, Last Update 10 June 2020