Dry riverbed (4)
I believe the answer is:
wadi
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">dry riverbed</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for wadi that I've seen before include "Seasonal water course (in Arabic-speaking lands)" , "dry course" , "North African gully, dry except in the rainy season" , "Rocky watercourse in N Africa" , "(Usually) dry desert riverbed" .)