Flooding in Big Thompson River, Colorado, tributaries: Controls on channel erosion and estimates of recurrence interval

Abstract

Channel erosion in tributaries of Colorado's Big Thompson River was studied following the 1976 flash flood. In two catchments, no measurable erosion occurred. Erosion in other catchments was intense (maximum observed sediment yield = 308 m3·ha−1). Relationships between “total” storm precipitation ( P t ) and sediment yield give values for the maximum potential sediment yield at a given storm magnitude. Sediment mobilization begins when P t = 140 to 150 mm or when short-term rainfall intensity = 140 to 170 mm·h−1. Qualitative and quantitative evidence suggests that a large, rare event is needed to modify the Big Thompson tributaries geomorphically. Catchment denudation values are used to estimate the recurrence interval of the 1976 event; the results suggest the possibility that previously estimated recurrence intervals may be too long by factors of 1.6 to 8.