American Heritage Dictionary
(4)
Century Dictionary
(2)
GNU Webster's 1913
(2)
WordNet
Elsewhere on the web
… It's the kind of rock that is used as riprap - piles of rock used for erosion control.— BYU NewsNet : Home
What the citizens gathered in protest on Saturday and the many at home who agree with them have neglected to acknowledge is that the "riprap" rock in question could be put to good use for the people of Provo.— BYU NewsNet : Home
The riprap is not done, but the National Guard returns for a couple days, he said "around Sept. 13, 14 or 15" and will do more work.— seMissourian.com Headlines
Serious fishermen go with extra long-handled nets for the riprap.
Doyle said the levee sustained minor damage, with the storm blowing riprap - the rock at the base of the levee - as much as 6 feet up the levee bank.— The Daily News - News

American Heritage Dictionary (1)
Century Dictionary (1)
Bubble size: how much this word was used in a year
Bubble height: used more or less than expected, vs. all uses evenly distributed
You can expect to see this word about once a year.