Rainfall thresholds for flow generation in desert ephemeral streams. Such beds are given various names according to regional differences, such as wadi or oued in North Africa and Saudi Arabia and dry wash or arroyo in the southwestern United States. We recommend using mean rainfall intensity over the drainage area for threshold analysis because this reduces apparent scale dependence in thresholds caused by incomplete rainfall information. The beds of ephemeral streams are commonly almost flat in cross section and are dry most of the time. The choice of rain data strongly influenced threshold values single rain gauges were only adequate for threshold prediction in <1‐km 2 watersheds, and incomplete rainfall data led to increases in thresholds with drainage area. Higher runoff thresholds and lower flow frequencies in small semiarid watersheds likely relate to greater ground cover and soil development compared to the desert pavement and bedrock surfaces in hyperarid sites.
In the desert ephemeral streams how to#
Watershed mean 60‐min intensity thresholds ranged from 3–13 mm/hr in hyperarid watersheds and 7–16 mm/hr in semiarid watersheds. As ADEQ contemplates how to continue to protect the water quality of rivers, streams, and wetlands in the wake of the new federal rule, the inclusion of. At both locations flow frequency decreased with drainage area, but the decrease was steeper in hyperarid watersheds. However, even in wet regions, temporary streams at the head of river networks can account for >50 of the total stream network.
Although hyperarid sites had fewer flow events, their flow frequency (fraction of rain events causing flow) was higher than in semiarid sites for small (<1 km 2) watersheds. In many parts of the world, such as the desert southwest, temporary streams may comprise a majority of the river network, >80 in some areas.Streams flowed an average of 0–5 times per year in hyperarid watersheds and 3–11 times per year in semiarid watersheds. At both sites rainfall and streamflow were monitored in watersheds ranging from 10 −3 to 10 2 km 2. In the Mediterranean region, ephemeral streams exhibit certain climatic, geomorphological and anthropic characteristics which condition the hydro. The study sites are in southern Arizona, USA one is hyperarid and the other is semiarid.
This paper quantifies thresholds in ephemeral streams and evaluates how they are affected by rainfall and watershed properties. Rainfall thresholds for streamflow generation are commonly mentioned in the literature, but studies rarely include methods for quantifying and comparing thresholds.
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