the mighty mississippi is living up to its nickname tonight, flowing higher and wider than any time in recent memory. it's been said, along with its major tributaries, by weeks of heavy rain and flooding is widespread along the entire river system. the biggest area of concern right now is memphis. the river is expected to crest there early tomorrow at 48 feet- - 14 feet above flood stage. mark strassmann is in memphis tonight. mark, hundreds of people have already been evacuated. >> reporter: and more will get out tonight katie. this street is a snapshot of why. riverside drive in downtown memphis, no longer beside the river, but in it. hour by hour through jittery memphis the mississippi is a rising threat. >> only a few feet between the river and the interstate. >> reporter: a river now three miles wide in some spots, six times its typical width. in south memphis, danny lee mitchell wades through his basement. but he's staying put-- more afraid of looters. >> we got two evacuation notices but, you know, you have to think for yourself. >> reporter: mitchell is exactly what emergency leaders don't want-- holdouts in harm's way with the river cresting within hours. in neighborhoods like this one where you can only see the roof tops, the misery is rising with the water. the mississippi will crest for as long as a week so it could be two weeks before all this water goes away. in memphis, the focus is on three bloated tributaries, so overwhelmed by the mississippi two of them are actually flowing backwards. all that water's pressuring and testing the city's flood protection system like never before. in small teams, 150 engineers walk the levees looking for soft spots and leaks. and the u.s. army corps of engineers promises its system will hold up. >> there is no potential possibility of any failures on the mississippi river levees. >> reporter: but to corps critics the levee system is a man-made disaster. >> it's deja vu all over again almost every year. >> reporter: scientists say levees stack up water behind them, spiking the river's height and power and building false confidence. more people move along the river and into the danger zone. >> we're building levees too high and we increase their heights all the time and then when something goes wrong you've got a catastrophe on your hands. >> reporter: but for the city of memphis, that system is now the last defense. >> you don't know what mother nature is going to do but you deal with it step by step. >> reporter: memphis was built on a series of bluffs, so the city does have a lot of natural protection but with the mississippi about to crest 14 feet above flood stage, people here are nervous. katie? >> couric: mark strassmann in memphis tonight. mark, thank you. meanwhile, down river, army engineers are trying to prevent flooding in new orleans. they've opened up a small section of the bonnie carrie spillway north of the city. the spillway is diverting some of the floodwater over land about six miles to lake pontchartrain. from there the water will safely flow into the gulf of mexico. now, some of that water would be welcome news in texas. that state is in the middle of an historic drought. since october, texas has had less than six inches of rain on average, that's less than half the normal amount. the driest seven-month period on record. and don teague reports that, for ranchers, a way of life is drying up as well. >> reporter: it's auction day at the west cattle barn in central texas. for 74-year-old rancher cotton deitrich, his last. deitrich is selling off his herd-- all of his cattle. because the once-fertile grasslands that fed them are gone. >> that's what it is now. it isn't what it should be. >> reporter: three quarters of texas is in extreme or exceptional drought. lubbock has had less than an inch of rain this year, houston has had just over an inch and a half in three month, about the same as the sahara desert. wildfires are scorching more than 2.3 million acres since january. to make matters worse, this is typically the texas rainy season. >> we should be seeing rainfall. if we don't get the rainfall these next few months the impacts could be devastating. >> reporter: for cotton deitrich and thousands of ranchers across texas, the only choice is to sell their herds or go broke trying to feed them. >> after a while you just laugh at it to keep from crying. >> reporter: the drought in cattle company could actually bring a short-term benefit to consumers. beef prices have been running here at record highs but with ranchers now being forced to sell off their herds, the price of beef is expected to drop. already auction prices in texas have fallen 15 cents from 80 to 65 cents per pound and could continue down through summer. but the u.s. cattle population already at a 50-year low, lower prices won't last. >> we'll be certainly looking at higher beef prices in the future just simply because fewer cows, fewer calves, less beef production so there's going to be less beef on the market for consumers to buy. >> reporter: in the meantime, cotton deitrich is already beginning his new career-- raising a more drought-tolerant herd. don teague, cbs news, west texas. >> couric: turning overseas, pakistan's prime minister angrily denied that top officials knew where osama bin laden was hiding. last night on "60 minutes," someone in the country must have been helping the al qaeda leader. >> we think that there had to be some sort of support network for bin laden inside of pakistan. but we don't know who or what that the support network was. we don't know whether there might have been some people inside of government, people outside of government, and that's something that we have to investigate and, more importantly, the pakistani government has to investigate. >> when you announced bin laden had been killed last sunday you said "our counterterrorism cooperation with pakistan helped lead us to bin laden in the compound where he was hiding." can you be more specific on that and how much help did pakistan actually provide in getting rid of bin laden? >> what i can say is that pakistan since 9/11 has been a strong counterterrorism partner with us. there will be times where we've had disagreements. there have been times where we wanted to push harder and for various concerns they might have hesitated. and those differences are real. and they'll continue. but the fact of the matter is that we've been able to kill more terrorists on pakistani soil than just about any place else. we could not have done that without pakistani corporation. >> couric: pakistan's prime minister said in the future any unauthorized raids within pakistan will be met with "full force." he, of course, didn't find out about the raid that killed bin laden until it was over and the american commandos were safely out of the country. here's elizabeth palmer. >> reporter: prime minister yousaf gilani faced parliament today to explain how pakistan could have missed both bin laden and the u.s. raid that killed him. >> reporter: there was an intelligence failure, he said, but no collusion with al qaeda. >> reporter: simple denials, though, aren't enough. pakistan's political opposition, like the u.s., wants to see a thorough investigation of the whole fiasco. can you describe what you think the biggest blow is to pakistan from this raid to kill bin laden? >> reporter: the u.s. didn't trust pakistan last monday when seals raided bin laden's hideout without telling the i.s.i. intelligence service. now the i.s.i. is on the defensive. the three women who used to live here, including bin laden's youngest wife, are in pakistani custody. the c.i.a. would like to question them but it took the i.s.i. a week to say yes. and then there was this: a report in the pakistani media that outed a senior c.i.a. operaive in pakistan-- apparently an attempt to blow his cover. so far there's been no reactions in the american embassy and it's far from clear who leaked this information but it's widely seen to have been an angry and humiliated i.s.i. taking revenge on the c.i.a. with the best will in the world pakistan was a prickly partner for the u.s. in fighting terrorism. last monday's raid has now torpedoed that good will and left the whole partnership in jeopardy. elizabeth palmer, cbs news, islamabad. >> couric: turning now to libya where people are fleeing the violence by sea. today united nations called on ships in the mediterranean to be on the lookout for rickety boats carrying refugees. hundreds may have died on friday when their boat sank near an island off sicily. another boat ran aground yesterday off that same island. the italian coast guard was able to rescue 400 refugees. in this country, a couple of political notes tonight. he's been contemplating it for years, now newt gingrich is doing it the former house speaker told followers on facebook and twitter he'll announce on wednesday that he's running for the republican nomination for president. and in the senate today, majority leader harry reid once an amateur boxer looked like he'd gone a few rounds. left eye black and blue, right farm a swing. but it was no fight. he slipped in the rain the other day bumping his head and dislocating his shoulder. still ahead here on the "cbs evening news," a father and daughter's years-long journey through books. from alice in wonderland to shakespeare. we'll get steve hartman's read in tonight's "assignment america." but up next, it's called chemical restraint. giving anti-psychotic drugs to nursing home patients who simply don't need them. 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i have no idea. how did that happen in three days? >> reporter: less than four weeks after entering the nursing home, william killingsworth was dead. burchard blames in part this anti-psychotic drug the nursing home inappropriately gave her father who suffered from dementia. >> he was laying in his bed unresponsive and i just looked at him and thought "what's going on?" you can look at this person and know he needs medical attention. >> reporter: anti-psychotic drugs like these were never approved for elderly patients with dementia. in fact, in 2005, the f.d.a. gave them its most severe warning, noting an increased risk of sudden death in patients with dementia. and now a new government study has found that 88% of the time medicare paid for anti-psychotic drugs in nursing homes they went to patients with dementia. the report by the health and human services inspector general also found that anti-psychotic drugs were given to nursing home residents unnecessarily over 300,000 times between january and june, 2007, with more than half of those drugs given in excessive dose. >> the use of anti-psychotic drugs when they're not necessary is a form of restraint. it's a form of chemical restraint. >> reporter: the department of health and human services also says it's very concerned that there are financial incentives for unnecessary drug use. in the past, those incentives have led to charges of kickbacks between nursing homes, pharmacies, and a drug company. dr. kenneth brubaker represents nursing home medical directors and agrees anti-psychotics are being used too often. he says the problem is staff turnover and training. >> often times lack of training, lack of adequate work force, whatever else it might be we tend to short cut it by going to drugs. >> i wish i would have said "what are you giving him? how much are you giving him?" >> reporter: instead, burchard sued and settled, using some of the money to create a nursing scholarship in memory of her dad. armen keteyian, cbs news, new york. >> couric: turning to the u.s. economy now, it looks like gas prices may have peaked. the energy department reported today they rose just a penny in the past week to $3.975 gallon and home prices fell another 3% in the first quarter of this year. since the bubble burst five years ago, americans have seen the value of their homes fall nearly 30%. when we come back, a new study says autism may affect nearly three times as many children as we thought. . that's good. wow. this is really good. great flavor. it's really creamy, it's really tasty. ooh, wow! jamie lee curtis! it's activia. it's delicious. i am shocked. it's hard to believe it's that good for you. it's so good. try the fabulous taste of activia today. taste it, love it, or it's free. and now discover activia dessert. in rich, indulgent flavors like blueberry cheesecake. try activia dessert today. ♪ activia no, no, no... i do not have a thing about bugs. i have a thing about bugs in our house. we used to call an exterminator. ugh... now i go ortho. home defense max. i use it once inside to kill the bugs. stops them dead. guaranteed. and outside to keep new ones from moving in. that's up to 12 months protection against bugs. and 12 months of keeping our house to ourselves. until your mother comes. right. ortho home defense max. defend what's yours. dr. scholl's custom fit orthotic center recommends the custom-fit orthotic that's best for your tired feet. foot-care scientists are behind it. you'll get all-day relief. and you could save a couple hundred bucks. for locations, see drscholls.com. thank you... ♪ ♪ ♪ ♪ introducing purina one beyond a new food for your cat or dog., >> couric: c.t. scans are a great tool for diagnosing brain injuries, but there's concern that too many children getting them, exposing their growing brains to radiation. a study out today says doctors can safely reduce the number of pediatric c.t. scans by as much as 50% by allowing each patient to be observed for a longer period of time. the study says that if the child's symptoms improve after four to six hours, a scan may not be necessary. now, another study out today suggests autism may be more prevalent than we knew. previous reports here in the u.s. estimated 1 in 110 children has traits of autism. but this new study, done in south carolina, put the rate at 1 in 38. dr. jon lapook is our medical correspondent. jon, why the figures so much higher in south korea than in the united states? >> reporter: katie, in the united states we mostly count those children who have obvious symptoms. in the korean study they screened every child school, not just those in special ed classes but those who seemed to be perfectly fine so they picked up milder cases. there was a 27 question survey that said "is the child regarded as an eccentric professor by other children?" "does the child have awkward or clumsy movements or live somewhat in the world of their own? " if the answers were yes, the child was more fully evaluated. >> couric: i know some well regarded u.s. researchers are among the authors of this south korean study. are they concluded a lot of american kids with mild awe autism going undiagnosed? >> yes, and in fact one of the authors told me need early diagnosis is crucial because early intervention can make a huge difference, even in those kids-- and this is important-- who seem to be functioning perfectly fine. >> couric: but what about parents who say "my child is functioning perfectly fine, why should have him or her tested and have a label put on them" i >> that's a common sentiment because kids with mild autism can do very well, especially a highly structured environment like in school or snort the home. down the road it may get bumpier, especially in a less structured environment, like college or work. so parents need to remember your children are best when they're most independent and you're not going to be around forever. >> couric: that's a good point. dr. jon lapook, jon, thanks so much. for more on this story, you can turn to our partner in health news webmd.com and search "autism." coming up next, parents reading to kids; kids reading to parents. steve hartman's "assignment america." steve hartman's "assignment america." 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