Water backflooded into the Pasco Basin because of the constriction at Wallula Gap. The floodwaters could not get through a gap a mile wide. Maximum flood waters reached elevations of about 380 meters. It's fairly simple to estimate flow through a constriction, but the picture is complicated by flooding of the gorge further downstream. When that complication is taken into account, the peak flow is estimated to have been about 10 million cubic meters per second (the volume of Grand Coulee Dam every second). With a channel 2000 meters wide and water 250 meters deep, that translates to a velocity of 20 meters per second or 45 miles an hour. 10 million cubic meters per second is about 50 times the flow of the Amazon River, ten times the combined flow of all the rivers in the world and 300 times as big as the largest 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 the gap.
Panoramic view of Wallula Gap from just north of the Oregon state line.
Created 21 November 2003, Last Update 01 July 2012
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