• ucsantabarbara twitter avatar
    From theory to practice, this week's #GauchoCourse prepares soon-to-be professors for the real world. https://t.co/DAj0nUIwAw
    6 hours 46 min ago
  • UCSBgauchos twitter avatar
    MVB: Gauchos snap 7 match losing streak with emphatic sweep of UCSD on Friday night. RECAP >>>… https://t.co/Cee1KbeXOh
    16 hours 37 min ago
  • UCSBgauchos twitter avatar
    Women's Tennis: UC Santa Barb. 2, Oregon 5 (Final)
    19 hours 4 min ago
  • UCSBgauchos twitter avatar
    WBB: Gauchos Face First-Place UC Davis Looking to End Two-Game Skid https://t.co/wRGTYxtxDC
    20 hours 6 min ago
  • ucsantabarbara twitter avatar
    Called “tama” or “tamashii,” the belief in spirits of deceased ancestors goes back centuries. https://t.co/KUJg2oGc7k
    20 hours 31 min ago
  • UCSBgauchos twitter avatar
    Muno (2 H, 2 R), Corey (3-4, 2 R), Davis (7 IP, 2 ER, 10 K) lead @UCSB_Baseball to 7-4 win in home opener! RECAP >>… https://t.co/I32qmDSuZB
    20 hours 58 min ago
  • ArtsandLectures twitter avatar
    Fascinating! #Sapiens + #HomoDeus author #YuvalNoahHarari predicts humankind’s future: https://t.co/5P25xtpyRQ via… https://t.co/TIAzFchgfI
    21 hours 30 min ago
  • ArtsandLectures twitter avatar
    RT @AshleyyySb: Only on Twitter to continue to absorb all insight and research from @DrSidMukherjee || Stoked to attend his lecture @Artsan
    21 hours 46 min ago
  • brenucsb twitter avatar
    Does location affect how pines react to climate change? Bren PhD student Ian McCullough shares answer #BrenPhDTalks https://t.co/6zVyQetm2t
    21 hours 51 min ago
  • UCSBgauchos twitter avatar
    Softball: Fifth-Inning Dooms Gauchos in 6-4 Loss to Purdue https://t.co/XWYKVl9UPx
    21 hours 52 min ago
  • UCSB_GradPost twitter avatar
    Register for 2017 Graduate Division Commencement before May 5! https://t.co/IDP1WGLGik #UCSB #ucsbgradpost
    21 hours 59 min ago
  • brenucsb twitter avatar
    Bren PhD student Jessica Perkins' research answers: "What Makes an #LCA Study Influential?" https://t.co/HatfwVTKV4 #BrenPhDTalks
    22 hours 40 sec ago
  • brenucsb twitter avatar
    Runsheng Song shares strategies to estimate chemicals' life cycle inventories with little data #BrenPhDTalks https://t.co/gUsRney8nC #LCI
    22 hours 11 min ago
  • brenucsb twitter avatar
    #BrenPhDTalks: Bren PhD student Ying Wang looks at nanomaterial accumulation in soybeans & nitrogen-fixing bacteria https://t.co/85xiy6EmAY
    22 hours 21 min ago
  • brenucsb twitter avatar
    Bren PhD student Yuwei Qin uses US potato production to show how to model marginal production in #LCA https://t.co/jDyW0Fkzbx #BrenPhDTalks
    22 hours 31 min ago

Desert Streams: Deceptively Simple

The simple topography of dryland channels presents an interesting paradox, according to scientists from UCSB’s Earth Research Institute
Thursday, October 23, 2014 - 09:15
Santa Barbara, CA

Volatile rainstorms drive complex landscape changes in deserts, particularly in dryland channels, which are shaped by flash flooding. Paradoxically, such desert streams have surprisingly simple topography with smooth, straight and symmetrical form that until now has defied explanation.

That paradox has been resolved in newly published research conducted by Michael Singer and Katerina Michaelides, associate researchers at UC Santa Barbara’s Earth Research Institute. The pair show that simple topography in dryland channels is maintained by complex interactions among rainstorms, the stream flows these storms generate in the river channel and sediment grains present on the riverbed. Their findings appear today in the journal Geology.

Desert streams flow only during infrequent but intense rainstorms, and when they do, only parts of the channel contain water, making the flow irregular and erratic. One rainstorm may erode sediment grains in one section of the channel, while another storm moves sediment in a different area.

“Given this localized sediment movement during rainstorms, one might expect desert channels to contain mounds of sediment that undulate down the stream course reflecting the irregular flow, but they don’t,” Singer said. “The water produced in the channel only flows partially down the stream and then stops because it seeps into the riverbed, and there’s not enough water from upstream to replace it, so it just disappears.”

Because desert river channels do not feature the river bars, pools or riffles common in perennial streams, they decline in elevation downstream very smoothly. According to the researchers’ findings, feedback between two variables — complex water and sediment movements — shape such basins.

Singer and Michaelides used data collected from the Rambla de Nogalte in southeastern Spain to model these dryland channel variables. The area has a semi-arid climate with mean annual rainfall of around 14 inches, which occurs during convective rainstorms, producing large floods that recur about once a decade.

They found that dryland channel width fluctuates downstream. Their observations show that grain size (roughness) also fluctuates from sand to gravel a downstream direction.

“There’s feedback between this fluctuating width and fluctuating grain size,” Singer said. “The stream flow is generated in a discontinuous pattern along the channel. Some rainstorms produce a bit of topography in some parts of the channel. Other spatial configurations of flow generated by storms destroy that topography so the variability of the rainstorms interacting with this channel are creating and destroying the topography constantly to keep it in this simple form.”

Singer and Michaelides also produced simulations of extreme flows to determine the volume of flow necessary to reshape the channel completely. They examined the longitudinal variability of sediment flow as well as sediment storage to find the channel-shaping threshold. This threshold reshapes the entire channel and makes it smooth again. “It’s a really significant threshold that tells us the magnitude of the flood necessary to reshape the channel,” Singer said.

“Semi-arid and arid river systems are extremely important to the populations that live around them,” he concluded. “Water resources are obviously a huge limitation in the development of societies, and a lot of water is being progressively diverted for irrigation, water use and other purposes, so those can further affect the spatial patterns of where flow is in these channels and potentially impact the processes of where topography develops in the river channel. Humans can inadvertently have an impact on the shape and form of river channels like these.”

Contact Info: 

Julie Cohen
julie.cohen@ucsb.edu
(805) 893-7220

Topics: