Washway

[…] justifies a conclusion, that by the farther contraction of the descending waters over the washway, the navigation and drainage through the Wisbeach river, will be farther improved.

Source: wiktionary

[…] these frontagers were obliged to leave a washway of half-a-mile wide on the west side of the river, so as not to impede the drainage of the country; […]

Source: wiktionary

Gradually, a narrow, tree-lined stream may be converted into a broad washway of drifts of sand and gravel.

Source: wiktionary

At the edge of the washway on our left it shot out several feet into the air before falling to the jumble of boulders below.

Source: wiktionary