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Rengers, Francis Kevin ¹ ; Moody, John ² ; Ebel, Brian ³

¹ University of Colorado
² USGS
³ USGS

Recently new work has begun to try to model the sediment deposition and erosion patterns that occurred in the Spring Creek Watershed following the Buffalo Creek Fire in 1996. As part of this research project, a 9 inch modified Parshall flume was built and placed in Spring Creek (near Deckers, CO) in order to better understand the current flow variations because it is believed that the creek is returning to a size and flow regime that is analogous to its pre-fire conditions. Early measurements of the water discharge in the flume have revealed surprising data, indicating a very strong diurnal shift in the water discharge. Our current hypothesis is that we are observing a sharp diurnal change in water discharge as a result of the evapotranspiration from willows that surround the riparian area.

Historic discharge data obtained for the years following the forest fire also showed a diurnal fluctuation in discharge during the summer months, however the average amplitude of the daily discharge was an order of magnitude lower in most years than it was during the summer of 2010. We hypothesize that driver behind the increased maximum and minimum discharges in Spring Creek is the riparian vegetation which has completely re-colonized the stream corridor since the Buffalo Creek fire. One strong piece of evidence is that the timing of the minimum and maximum flows has become increasing regular during the time since the willows have grown back. In summers immediately after the fire when no willows were present, the maximum and minimum flows could occur nearly any time of the day. However, now during the summer months the maximum flow rates are observed consistently in the morning, with the minimum flow rates occurring in the afternoon.

Currently several research questions are being pursued to further investigate this phenomenon. For example we are trying to determine the proportion of the change in daily discharge that is due to evapotranspiration versus loss to groundwater using a shallow groundwater well. Moreover we are still exploring the historic data in order to determine what factors set the maximum daily amplitude for the water discharge (e.g. winter snow melt that gets stored as groundwater and releases slowly or summer thunderstorms). However, our preliminary results suggest that riparian vegetation may have a 10 fold increase in the maximum and minimum daily discharges levels in a stream in the summer months.