Late-Holocene stream dynamics on the middle Gila River, Pinal County, Arizona

Abstract

An archival-stratigraphic investigation of the middle Gila River provides insights into late-Holocene channel behavior and flood-plain formation. Historical records detail changes in channel patterns that correlate with changing frequency of large floods, but channel sensitivity is also affected by factors such as flood seasonality, changes in sediment load, human disturbances, and internal thresholds. Because the frequency of large floods is the dominant factor in channel changes, radiocarbon-dated flood deposits in late-Holocene alluvial terraces allow for a reconstruction of prehistoric channel behavior. A period of reduced large flood frequency and channel stability 4,000-1,000 years BP separates periods of increased large flood frequency and channel instability 5,000-4,000 and 1,000-0 years BP. Transformations between braided and single channel morphologies affect the conveyance of floods and change the spatial characteristics of flood hazards. These channel dynamics are also important in analyzing changes in Hohokam-Pima irrigation technology and settlement patterns.