this is the cbs evening news with russ mitchell. mitchell: good evening. for army engineers hoping to keep ahead of the rising mississippi, it is the most drastic step yet. this afternoon they opened the first of the floodgates of the morganza spillway, up stream from baton rouge and new orlea orleans. potentially flooding thousands of square miles of countryside. dean reynolds is in organza with the very latest. reporter: good evening, russ. officials told us this afternoon everyone in the area the water will take 24 hours to reach has already departed and as you can see behind me, with good reason. only one of the 125 gates on this 4,000-foot-long spillway was opened, a cautious first step to give everyone and everything a chance to flee. we ll open one bay today. we ll open one or two tomorrow. and then we ll open gates based upon the river conditions as they exist. reporter: the mississippi is cresting now near helena, arkansas, over 250 miles north of the morga
mitchell: and good evening, floodwaters are rising tonight and so are anxieties up and down the mississippi valley with memphis most immediately at risk. take a look. this is the mississippi and its tributaries in normal times. these are the waters this evening. and these are the counties facing flood warnings. the waters are expected to crest in just two days in memphis which is where randall pingston is standing by live. good evening. reporter: good evening, russ the u.s. army corps engineers flood control system cost billions of dollars and decades to build. as an engorged mississippi river moves south that system faces its biggest test yet. from the sky the mayor of memphis sees his city under attack by the mississippi river and its tributaries. notice how close this is getting to the interstate highway, that s another concern. reporter: the rising waters are creating havoc on the roads. a section of u.s. 351, a major north south artery was shut down yesterday. th