Hydroclimatic drivers of at‐a‐station hydraulic geometry of Brazilian rivers

Abstract

The geometry of river channels defines their discharge conveyance capacity and can alter the flood regime. While most rivers follow the Theory of Hydraulic Geometry at-a-station power laws, the spatial patterns of exponents, coefficients, and hydrological controls beyond the scale of river reaches remain poorly understood. Here, we analyze 290 Brazilian river cross-sections to test the hypothesis that the hydraulic geometry is related to basin hydroclimatic characteristics, with a significant difference between humid and dry basins. We classify the basins draining to each cross-section according to the aridity index and the baseflow index, and analyze the controls on the exponents and coefficients (i.e., parameters) of the at-a-station hydraulic geometry power-laws. Our results show that the exponents and coefficients follow a spatially coherent pattern. The exponent of the width of AGH power law is related to the aridity of the basin, being larger in drier basins with a low baseflow index. The width and velocity coefficients are strongly dependent on the basin area. Whereas the velocity coefficient decreases in large basins, the width coefficient increases in large basins, and the spatial distribution of width exponent is related to the bankfull cross-section shape. The combined analysis of hydraulic geometry and basin characteristics is a promising tool for discharge estimation in ungauged basins, flood management, and maintenance of natural rivers.