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Thresholds for runoff generation in ephemeral streams with varying morphology in the Sonoran Desert in Arizona, USA




Faulconer, Joshua D., author
Kampf, Stephanie, advisor
MacDonald, Lee, committee member
Ronayne, Michael, committee member

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In ephemeral streams, infrequent surface flow can be the main source of water that sustains plants throughout long dry periods. The objectives of this research are to: (1) explore seasonality of rainfall runoff in different channel types and (2) examine how runoff thresholds vary by channel type. The study area was two watersheds with areas of 188 km² and 323 km² on the Yuma Proving Grounds (YPG) in the Sonoran Desert near Yuma, Arizona. Eight tipping bucket rain gauges were installed to measure precipitation. Runoff was measured with 18 pressure transducers in five different channel types with different channel morphologies and contributing areas ranging from 0.002 km² to 225 km². Over approximately two years there were 11 to 48 rain events at the different rain gauges. Stream types with bedrock channels and small watershed areas between 0.005 km² and 0.015 km² produced runoff when the peak 60-minute precipitation intensity (I60) exceeded 4-6 mm hr⁻¹. At these sites, 17-25 percent of the rain storms generated runoff. I60 values of 5-9 mm hr⁻¹ produced runoff in streams with contributing areas of 0.021-0.061 km² on mid-Pleistocene piedmont surfaces covered by desert pavement. At these sites, 31-36 percent of rain events produced runoff. Streams incised into bedrock with some alluvium fill produced runoff at larger I60's of 13-18 mm hr⁻¹. Contributing areas for these sites were 0.8 km² to 2.2 km², and up to 10 percent of precipitation events at these sites produced flow. Precipitation thresholds for runoff generation in streams with contributing areas >3 km² were not clearly defined due to the influences of variable precipitation in upstream tributaries and transmission losses of streamflow through channel bed alluvium. For watersheds with <3km², rain intensity thresholds increased with the log of catchment area, and as a result flow frequency tended to decrease with increasing catchment area.


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ephemeral streams
runoff seasonality
transmission losses
flow frequency
ephemeral channel types
runoff thresholds


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