Palaeoflood hydrology of the Salt river, Arizona

Geomorphic evidence along bedrock‐confined reaches of the Salt River in east‐central Arizona provides a record of the river's largest flood events. Fine‐grained flood slackwater deposits accumulated at channel margin irregularities several metres above the low‐flow channel. Discharges associated with flow events responsible for the deposits were estimated by computer flow modelling. These estimates document flood magnitudes in excess of gauged historic streamflows. Relative and radiocarbon dating suggest that a flood record in excess of 600 y is preserved in the slackwater sequences. A prominent flood scar cut into grussy hillslope soils allows the extension of the prehistoric flood record to several thousand years. A maximum discharge estimate of 4600 m³s⁻¹ affixed to the flood scar represents the largest flood event in the record, and is given a minimum recurrence interval of 1000–2000 y. The 1952 flood is the largest historic flow event experienced along the study reach and is estimated at 2900 m³s⁻¹. Two palaeoflood events preserved in the slackwater stratigraphy exceed the 1952 event, and are given recurrence intervals of 300 and 600 y. The latter flood event had an estimated discharge of 3200 m³s⁻¹. It is apparent that discharge estimates affixed to these infrequent, large‐magnitude flood events approach a maximum with decreased probabilities (large recurrence intervals). This suggests that a physical limit on discharge may exist within the Salt River drainage basin and is perhaps directly related to drainage basin size.