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A better understanding of these systems could help managers in arid regions predict when or whether runoff might reach a reservoir or how sediment could impact structures like bridges. The study helps resolve long-unanswered questions about how desert landscapes work and change. Singer fed those data, along with information on runoff for the area, into models that simulate how various flows will move sediment of various coarseness. She characterized the grain size of the channel’s sediment by measuring the dimensions of hundreds of pebbles. Study co-author Katerina Michaelides measured the topography acros 29 cross sections. The study is based on data collected from the Rambla de Nogalte, an ephemeral stream in southeastern Spain. Rivers with year-round flows have more copmlex structure like points, bars and pools. Andrews’ Department of Earth & Environmental Sciences. “You start losing water as you move downstream,” said Michael Singer, study author and lecturer at the University of St. Rain in the mountains can also trigger flows from the headwaters, but those flows diminish as the water is absorbed by the parched channel. They’re rarely as large as the whole river basin, and the smaller storms can lead to flow in one segment of the channel while it remains dry upstream. The effect is partially a result of the size of the storms that drive flows in dry channels. A new study published in the journal Geology is the first to explain what’s going on. But when the water recedes, the channel often looks like not much happened, with no sign of structures like point bars, cut banks, riffles and pools that one might expect to see if a stream with perennial flow suddenly lost its water.įor scientists who study these landscapes, that’s the “unexplained paradox”: Despite having the occasional hydraulics seemingly capable of building some complex streambed topography, desert channels tend to remain simple, smooth and straight. Stream channels in desert landscapes can lay bone-dry for weeks or months at a time before an erratic, volatile storm suddenly turns a reach into a raging torrent. The Rambla de Nogalte in Spain is an ephemeral stream with simple, straight topography.