Implications of a specific storm event for understanding adjustment of urban dryland channels

Abstract

AbstractDryland stream channels adjusting to urbanization are difficult to study without some indication of the extent and frequency of specific hydrological events. Investigations of changing channels in Fountain Hills, Arizona, urbanized since 1970, can benefit from knowledge gained from a storm event of over 55 mm rainfall in January 2016, equivalent to ~25% of annual precipitation. Morphological flow capacity was reached with this rainfall event, which had a recurrence interval of 1.4 years for a 24‐h period and 3.6 years for a 3‐day duration. This storm is typical of events that occur in less than half the years of record, occurring between zero and three times each year in the 26 years of record available. Analysis of this event assists in the calibration of measured cross‐sections, providing a useful benchmark for space‐time substitution in dryland environments where flow is ephemeral. Correspondence of the recurrence interval of the storm to somewhat frequent ‘bankfull’ channel‐forming events, despite signs of flashiness, suggests a tight coupling between rainfall and runoff and a tempered response to urbanization effects in Fountain Hills—achievable through decades of proactive planning and adaptive wash management in a master‐planned community.