Because the mountainous location is totally on the japanese Portion of the peninsula, the primary rivers tend to move westwards. Two exceptions are definitely the southward-flowing Nakdong River and Seomjin River.
Nevertheless the Sui army was lured right into a trap via the famed Koguryŏ commander Ŭlchi Mundŏk, and endured a calamitous defeat in the Salsu (Ch'ŏngch'ŏn) River. It is 토토 alleged that only two,700 with the 300,000 Sui troopers who had crossed the Yalu survived to find their way again, as well as the Sui emperor now lifted the siege of Liao-tung Fortress and withdrew his forces to China good. Yang Ti continued to send his armies from Koguryŏ but once more without the need of accomplishment, and prior to very long his war-weakened empire crumbled." ^