DESTRUCTION AND ORIGINATION, EFFECTS OF THE BOULDER COUNTY COLORADO 2013 FLOOD ON GEOLOGIC FEATURES

Boulder County was the focus of the 2013 Flood of northern Colorado. As a result of record-setting stream flooding, a wide variety of geologic features were altered or created. New bedrock outcrops were exposed by channel scouring and migration, and deposits from multiple previous floods were exposed by incision into stream banks and floodplains. Stream channels were deepened, widened, and in many locations permanently rerouted. Within the channels and on floodplains previous bedforms and deposits were altered or destroyed and new bed forms were deposited. The full stratigraphic section of Boulder County is exposed on various properties of Boulder County Parks and Open Space (BCPOS) that were extensively impacted by the 2013 Flood. Although BCPOS is actively working to mitigate flood damage, a great deal of the original destruction is still visible in the parks along the foothills and plains of Boulder County. The summer of 2014 has been spent cataloging, measuring, photographing, and obtaining GPS coordinates for mapping of some of these features in BCPOS. One finding of this research is that geologically significant features, such as Permian stromatolites newly exposed by the flooding, are subject to rapid alteration or destruction by normal stream processes. A second key finding is that the area has been affected by multiple prehistoric floods as evidenced by stacked flood deposits exposed by new stream cutting. Estimates of maximum cubic feet per second (cfs) for the 2013 Flood event as well as prehistoric flood events are being calculated from types and sizes of flood-transported clasts and bedform measurements. This study will provide BCPOS with a catalog of change in geologic features resulting from the 2013 Flood, with data on how quickly newly created or exposed features are being degraded and with evidence for repeated significant flood events along Boulder County foothills.