methodology for the estimation of the maximum volume extraction of river materials

Abstract

Sand and gravel mining on rivers causes erosion or incision of the river bed, upstream erosion in tributaries, damage to different structures (bridges, water intakes, dykes, bank protection works, houses and roads), and, it alters the river equilibrium, affecting the fluvial ecosystem. In order to minimize the negative effects a methodology is proposed for estimating the maximum annual extraction volumes, based on the annual sediment transport of the river, in other terms, on the natural replenishment rate. Initially it is important to carry out an integral study of the river to understand the fluvial dynamics, including the different aspects (hydrology, hydraulics, sediment transport.) with emphasis on the geomorphologic processes and the identification of other aspects (dams, intakes, protection works.) that could be affecting it. The possible areas of aggradation should be estimated, this is, the areas that are potentially exploitable, and the morphological changes due to the mining activities should be estimated. The proposed methodology also requires a periodic monitoring of the bed load and of the variation of the river bed levels, the updating of the annual sediment loads duration curve and the forecasts of the river discharges for a given year.