Model for the calculation of the Manning roughness coefficient as a function of the height of the bottom material of the Achiguate-Guacalate river

Abstract

This article presents a proposal to estimate the Manning coefficient roughness through a mathematical model for the Achiguate-Guacalate River basin.  For this achievement, the Chezy and Manning equations were based on the aim of obtaining an expression for the coefficient of roughness as a function of the hydraulic radius "Rh" and the roughness height "K" of the particles from the bottom of the riverbed. The National Institute of Seismology, Volcanology, and Meteorology -INSIVUMEH- through its Department of Hydrology operated since 2002 the gauging stations whose data was collected and processed for the formulation of the mathematical model.  This model was validated with samples taken from the basin at three different points within it, obtaining from each of them the average diameter D50 through a granulometric analysis carried out by each of them.  With this data, a value for "n" is obtained in the selected points by applying the model. To compare results, it is analyzed with the same information with which the model is proposed, an estimation of "n" by other methods, visual and analytical. Finally, the model is compared with recent river gauging whose data are new and were not used in the creation of the model. As a result, the model   is proposed, where "K" representing the roughness of the bottom of the channel was estimated at 0.027 for sampling in Alotenango.  When applying the model for Alotenango, the equation would be  , obtaining a value for "n" of 0.073 that when compared to visual methods it is high, but is like that calculated by analytical methods.