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Untangling the Effects of Seasonality and Post-Fire Stream Channel Erosion on the Hydrologic Response of a Burned Mountain Catchment
  • Michael Gieschen,
  • Peter Nelson
Michael Gieschen
Colorado State University

Corresponding Author:[email protected]

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Peter Nelson
Colorado State University
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Abstract

Stream channel incision and deposition are common after wildfire, and these geomorphic changes may impact runoff mechanisms and the composition of pre-event and event water in runoff. To investigate this, we monitored discharge and electrical conductivity at 6 nested sites within a 15.5 km 2 watershed in the northern Colorado Front Range that had recently burned, experienced large flooding, and well-documented and significant channel erosion and deposition. Over the study period, the watershed experienced seven precipitation events. For each hydrograph, we separate baseflow from runoff using a new method to characterize and account for the strong diurnal signal in the baseflow. Electrical conductivity is used as a tracer in a two-component end-member mixing analysis to separate the event hydrographs into event and pre-event water. Correlation coefficients were computed between key variables of the hydrologic response (such as runoff ratio, volumes of event and pre-event water) to storm and basin characteristics (including stream channel erosion/deposition, fraction of high/moderate burn severity, precipitation intensity, and antecedent precipitation). The strength and significance of correlations was found to vary seasonally. In the early season, event and pre-event volumes did not vary significantly with basin or storm characteristics. In the late season, antecedent precipitation correlated with a decrease in event runoff (R 2 = 0.34) and total runoff (R 2 = 0.40), increased precipitation intensity correlated with an increase in event runoff (R 2 = 0.48), and local erosion correlated with an increase in pre-event runoff (R 2 = 0.60) and total runoff (R 2 = 0.53). These findings indicate that seasonality and post-fire stream channel erosion influence the makeup of runoff response, most likely through their impact on the gradient of the near-stream groundwater table.
20 Jun 2022Submitted to Hydrological Processes
22 Jul 2022Submission Checks Completed
22 Jul 2022Assigned to Editor
22 Jul 2022Reviewer(s) Assigned
20 Feb 2023Review(s) Completed, Editorial Evaluation Pending
20 Feb 2023Editorial Decision: Revise Major
05 Apr 20231st Revision Received
02 May 2023Submission Checks Completed
02 May 2023Assigned to Editor
02 May 2023Reviewer(s) Assigned
02 Jun 2023Reviewer(s) Assigned
07 Jul 2023Review(s) Completed, Editorial Evaluation Pending
04 Aug 2023Editorial Decision: Accept