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Winter Storms Test Restoration Work

Submitted by July 30, 2010 2:51 pm

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During the spring of 2009, initial construction of the Watson Woods Riparian Preserve Restoration Project was completed. Planted vegetation responded well with a 95% success rate on the willow species and an 87% survival for the cottonwoods. Though precipitation in the Prescott area was lower than average, there were several small flow events that were observed through the project area in the late spring and then during the monsoon season. The flows experienced during these events approached, but did not exceed bankfull discharge (estimated to be approximately 450 – 480 cfs).

On January 21, 2010, a large flood event on Granite Creek took place. A USGS Gage (09503000) is located upstream of the project site approximately 0.5 mile. Measurements taken at the gage during the flood event show that at 11:30 am, water in the creek started to rise due to rain and snow events in the area. By 1:30 pm, the flow had risen from 28 cfs to over 1,600 cfs. And by 9:15 pm the flood had peaked at 6,200 cfs.  By running a flood frequency analysis of the peak discharges recorded at the gage, it is estimated that the flood had a recurrence interval of approximately 40 years.

The flood waters resulted in several impacts to the Preserve, the most noticeable is the off channel scouring and removal of accumulated biomass along the channel. Direct impacts to the restoration activities were most prominent in the upstream reaches and decreased going downstream. Phase II construction activities will focus on repairing and enhancing changes brought about by the flood as well as increasing the willow and cottonwood plantings.

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