riverbed

[ riv-er-bed ]

/ ˈrɪv ərˌbɛd /

the channel in which a river flows or formerly flowed.

Origin of riverbed

First recorded in 1825–35; river¹ + bed

They might build one bomb and test it in a riverbed a few miles away.

The Stalled War on Terror |Richard Miniter |May 8, 2010 |DAILY BEAST
I now discovered the source of the beautiful pebbles which had so pleased me in the riverbed.

The Malay Archipelago |Alfred Russell Wallace
The worst situation seems to be in the Columbia Riverbed System.

The Thirst Quenchers |Rick Raphael
They'd let him down by a rope to find things on the bottom of the riverbed.

Slave Narratives: a Folk History of Slavery in the United States From Interviews with Former Slaves |Work Projects Administration

So rank was the vegetation that he could not fight his way through it; he was obliged to take to the riverbed.

A Voyage to Arcturus |David Lindsay
"Juan told me last night that he had found another dead calf up the riverbed, and poisoned it," said Limber.

The Long Dim Trail |Forrestine C. Hooker