Hydraulic Losses in River Meanders

Energy losses along a channel reach occur from friction along the channel boundaries and bed surface and channel irregularities, obstructions, vegetation, channel meandering, and many other parameters of lesser importance. Conventional application of hydraulic computations between two cross sections requires that these losses be represented by the application of a resistance or roughness coefficient. These coefficients are determined empirically. Although much research has been expended developing relations for resistance due to grain size, bed form, and vegetation, relatively little research has focused on the influence of channel meanders. This shortcoming has implications in stream restoration practice for urban channels because many designs include sinuous channels in areas where flooding impacts must be assessed. This technical note discusses and analyzes several methods to estimate the hydraulic loss induced by river meanders (hereafter referred to as meander losses). These methods may be used to adjust the channel Manning's roughness coefficient used in hydraulic calculations and in numerical models such as HEC-RAS, HEC-2 and HEC-6. A method is recommended, with conditions, and topics of further study are suggested in this technical note.