The coastal plains of the five northern provinces are broken by several significant streams along which most of the region’s principal population centers are located. Roughly 10 miles south of the 1954 partition line the Cua Viet empties into the southern portion of the Tonkin Gulf. Both Quang Tri City, the capital of Quang Tri Province, and Dong Ha, South Vietnam’s northernmost population center of any significance, are situated on the Cua Viet and its major tributary, the Song Cam Lo. The Song Huong (often referred to as the Perfume River), which flows past the old imperial capital of Hue, enters the sea at a point approximately half way between Da Nang and the nation’s northern boundary.[6-B] At Da Nang the Song Han (also called the Da Nang River) flows into Da Nang Harbor after its main tributary, the Song Cau Do, curves through the coastal plains immediately south and west of the city. Eighteen miles south of the Marines’ new base of operations, the Song Cau Dai empties into the South China Sea near Hoi An, the capital of Quang Nam Province. The Song Cau Dai originates about 18 miles inland at the confluence of the Song Thu Bon and the Song Vu Gia which twist seaward from the south and west respectively. Together these three estuaries constitute the most important geographic feature of the sprawling coastal plain south of Da Nang. Another major stream, the Song Tra Bong, flows on an eastward course about 32 miles south of the Song Cau Dai. Still further south is the Song Tra Khuc, a river which dominates the wide coastal plain of Quang Ngai Province in much the same fashion as does the Song Cau Dai and its tributaries in the area south of Da Nang. The provincial capital, Quang Ngai, once a major railroad center for South Vietnam, is situated several miles inland on the south bank of the Song Tra Khuc. The southernmost stream of any significance in I Corps is the Song Ve, which angles northeastward through central Quang Ngai Province. While none of these waterways is navigable far beyond its mouth by ocean-going vessels, each serves the local population as convenient local routes of communication as well as vital sources of irrigation water during the long dry seasons. [6-B] In the Vietnamese language the word “song” means stream and normally precedes the name of rivers.