The US Geological Survey publishes flood plain zones (for different recurrence cycles, like 10-yr. floods, 100-yr. floods) for many streams and rivers. You can usually find out if they exist for your area with a google search on USGS site and often your library or town zoning commission has copies for your area.
If the Logan River flood plain is NOT zoned by the Planning Commission as a flood plain zone restricting construction of residences, you and others should get to some planning meetings and find out why not. Public response and pressure is the best counter measure to 'developer greed' in my experience and opinion.
I recommended flood areas to be held as 'natural areas' or open-land town parks (without developments and with warning signs about flooding) -- and NO residential or high use (restaurants, theaters, etc) for flood zones. However, commercial interests often prevailed (I made many proposals that died for a lack of a second, and voted negatively alone many times). BUT, public pressure was the best response to irresponsible greed. A newspaper reporter (former student of mine in an environmental geology class) finally got front page position on the most egregious cases -- and with strong public backing, aroused by the reporting, got vociferous crowds out to some of the planning cases.
It was an interesting role -- I was appointed to the commission by a city commissioner whose earlier appointment to the post was caught taking bribes and he needed to appoint someone who would be 'clean.' Well, he got more than he bargained for -- the Planning Commission was thrust into the limelight in Las Vegas, of all places -- and change often DID take place to protect folks.
Oh, and once when all the commissioners were attending a luncheon meeting to discuss upcoming proposed zoning changes, a land developer picked up the luncheon tab. When I went to pay my bill, and found it was paid for, and the cashier would not take my money, I got her to sign a statement that I tried to pay, she couldn't accept and that the developer had paid the bill. At the public Commission meeting to discuss that developers zone change proposal, right in the middle of his presentation I interrupted him, called for our secretary, gave her an envelope and asked her to read it aloud NOW before the public meeting. It was the statement from the cashier and my $10 bill I required the secretary to give the dude right there in public.
THAT event also made the front page the next day, and no one ever tried to bribe me (or pay luncheon bills again) for as long as I served.
Long story -- sorry -- but public pressure often works on appointed or elected officials.