Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Desert Streams: Deceptively Simple

24.10.2014

The simple topography of dryland channels presents an interesting paradox according to scientists from UCSB’s Earth Research Institute

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.


Dryland channels exhibit very simple topography despite being shaped by volatile rainstorms. Photo Credit: Katerina Michaelides


Humid channels feature complex topography with river bars, pools or riffles. Photo Credit: Michael Singer

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

Julie Cohen | Eurek Alert!
Further information:
http://www.news.ucsb.edu/2014/014459/desert-streams-deceptively-simple

More articles from Earth Sciences:

nachricht NASA looks to solar eclipse to help understand Earth's energy system
21.07.2017 | NASA/Goddard Space Flight Center

nachricht Scientists shed light on carbon's descent into the deep Earth
19.07.2017 | European Synchrotron Radiation Facility

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

NASA looks to solar eclipse to help understand Earth's energy system

21.07.2017 | Earth Sciences

Stanford researchers develop a new type of soft, growing robot

21.07.2017 | Power and Electrical Engineering

Vortex photons from electrons in circular motion

21.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>