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Volume 22, issue 6 | Copyright
Hydrol. Earth Syst. Sci., 22, 3261-3273, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 12 Jun 2018

Research article | 12 Jun 2018

Impacts of changing hydrology on permanent gully growth: experimental results

Stephanie S. Day1, Karen B. Gran2, and Chris Paola3 Stephanie S. Day et al.
  • 1Department of Geosciences, North Dakota State University, Fargo, ND 58102, USA
  • 2Department of Earth and Environmental Sciences, University of Minnesota Duluth, Duluth, MN 55812, USA
  • 3Department of Earth Sciences, University of Minnesota, Minneapolis, MN 55455, USA

Abstract. Permanent gullies grow through head cut propagation in response to overland flow coupled with incision and widening in the channel bottom leading to hillslope failures. Altered hydrology can impact the rate at which permanent gullies grow by changing head cut propagation, channel incision, and channel widening rates. Using a set of small physical experiments, we tested how changing overland flow rates and flow volumes alter the total volume of erosion and resulting gully morphology. Permanent gullies were modeled as both detachment-limited and transport-limited systems, using two different substrates with varying cohesion. In both cases, the erosion rate varied linearly with water discharge, such that the volume of sediment eroded was a function not of flow rate, but of total water volume. This implies that efforts to reduce peak flow rates alone without addressing flow volumes entering gully systems may not reduce erosion. The documented response in these experiments is not typical when compared to larger preexisting channels where higher flow rates result in greater erosion through nonlinear relationships between water discharge and sediment discharge. Permanent gullies do not respond like preexisting channels because channel slope remains a free parameter and can adjust relatively quickly in response to changing flows.

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Short summary
Permanent gullies are deep steep-sided channels that erode as water falls over the upstream end. Erosion of these features is a concern where people and climate change have altered how water moves over the land. This paper analyzes a set of experiments that were used to determine how changing gully flows impact erosion. We found that while increasing the volume of water will increase erosion, changing the flow rate into gullies will not impact the total erosion, but will alter gully shape.
Permanent gullies are deep steep-sided channels that erode as water falls over the upstream end....