Spatial variability of small‐basin paleoflood magnitudes for a southeastern Arizona mountain range

Abstract

Paleohydrological procedures were used to analyze spatial variations in flood magnitude in drainage basins of the Santa Catalina Mountains (maximum elevation 2791 m), southeastern Arizona. Paleoflood reconstructions in eight watersheds, ranging from 10 to 110 km2, were obtained for the largest floods in stable canyon reaches, yielding discharges ranging from 50 to 270 m3 s−1. Although there is a high correlation between drainage area and flood magnitude, it is also clear that basins located in the southern half of the Santa Catalina Mountains have larger unit discharges (peak discharge divided by drainage area) and that these values decrease toward the northern part of the range. This spatial pattern is probably the result of local hydroclimatological conditions whereby the largest floods are associated with the northward influx of moist, tropical, and subtropical air. For this atmospheric circulation the northern part of the range experiences a rain shadow effect that decreases the unit discharges generated in those basins. The unusually high unit discharge for one of the south facing basins is explained by its basin morphometry. Inverse problem solutions using a rainfall‐runoff model demonstrate that both this basin and another with a comparable drainage area but a much lower estimated peak paleoflood discharge can have their peak flood outputs produced by the same storm intensity. The results demonstrate the potential of paleoflood data collection for understanding spatial variability in small basin flood hydrology.