Regional relationships for bankfull hydraulic geometry and discharge in the southern Andes of Ecuador: An application in the estimation of geomorphological runoff thresholds

Abstract

The bankfull represents the boundary between the processes taking place in the canal and the floodplain. The geometry of the bankfull is highly correlated with the drainage area, making it possible to establish regional bankfull geometry relationships that have wide application in canal restoration, studies of river bed degradation, dimensioning of infrastructure, hydrological modeling, among others. In this study, the regional bankfull geometry relationships were determined for an Andean zone in southern Ecuador, getting coefficients comparable to those reported in literature determined in other mountainous areas of the continent. Correlation coefficients higher than 0.60 were obtained, considered statistically significant. The geomorphological runoff threshold, which represents the effective amount of rainfall needed to produce bankfull discharges, was determined using regional bankfull geometry relationships, geomorphological characteristics of the drainage basins in the study area, and the NRCS unit hydrograph. The geomorphological runoff threshold varies from 0.8 mm to 8.50 mm and is based on the concept of the unit hydrograph; therefore it presents the same application limitations and uncertainties associated with the determination of the characteristics of the basin, the bankfull and the scale of work. Future works are proposed considering more detailed scales, a greater number of observation sites and the inclusion of additional variables of the drainage area such as slope, aspect and precipitation, to improve the estimates.