Characteristics of Ephemeral Hydrographs in the Southwestern United States.

A collection of archived hydrographs for 28 ephemeral streams provided a unique opportunity to quantify hydrograph characteristics for channels of the arid/semiarid Southwestern United States. Recurrence of flow and volume calculated using annual maxima converge with those of the complete series by 7 years, suggesting that records of annual maxima are sufficient for estimates of extreme event recurrence. The relationship between peak discharge and volume for a flow event cannot be tightly constrained without consideration of event duration. As a result, volumes , for recurrence intervals , cannot be estimated from corresponding peaks . Instead, volume recurrence should be estimated based on the joint distribution of peak discharge and duration. Although the density governing event duration in these semiarid study regions decays as a power law with time, the authors could not identify a probability density that provides a good fit to volume magnitude. Deterministic relationships exist between peak discharge and volume for an event of a given magnitude for the Las Vegas, Nevada; Phoenix, Arizona; and Albuquerque, New Mexico regions. [ABSTRACT FROM AUTHOR]