What controls the coarse sediment yield to a Mediterranean delta? The case of the Llobregat River (NE Iberian Peninsula)

Juan P Martín-Vide,Arnau Prats-Puntí,Carles Ferrer-Boix

doi:10.5194/nhess-20-3315-2020

Juan P Martín-Vide, Arnau Prats-Puntí + Show 1 more

Open Access

https://doi.org/10.5194/nhess-20-3315-2020

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Abstract

Abstract. The human pressure upon an alluvial river in the Mediterranean region has changed its riverine and deltaic landscapes. The river has been channelized in the last 70 years while the delta has been retreating for more than a century (a set of data unknown, so far). The paper concentrates on the fluvial component, trying to connect it to the delta evolution. Is the channelization responsible for the delta retreat? We develop a method to compute the actual bed load transport with real information of the past river morphology. The paper compares the computation with very limited measurements, among which are bulk volumes of trapped material at a modern, deep river mouth. The decrease in sediment availability in the last 30 km of the channelized river is deemed responsible for the decrease in the sediment yield to the delta. Moreover, power development and flood frequency should be responsible for a baseline delta retreat during the 20th century. The sediment trapping efficiency of dams is less important than the flow regulation by dams, in the annual sediment yield. Therefore, it is more effective to dismantle channelization than to pass sediment at dams, to provide sand to the beaches.

Highlights

Introduction and objectiveThe framework for this research is the human pressure upon an alluvial river in the Mediterranean region
Our method is to examine one by one the causes of change of river sediment yield, of bed load
Our objective is to ascertain to which extent the river sediment yield is important to the delta evolution, as the distribution of beach retreat in Fig. 3 suggests

Summary

Introduction

Introduction and objectiveThe framework for this research is the human pressure upon an alluvial river in the Mediterranean region. The practice of channelizing a river generally involves increasing channel capacity and so an erosional response is to be feared, this is not always the case (Simon and Rinaldi, 2006). It involves narrowing of the flood channel by taking a large part of the floodplains for urban uses. This floodplain width reduction (encroachment or contraction) implies a perturbation of the equilibrium (a degradation), as demonstrated analytically and experimentally by Vanoni (1975), yet this is only one of the several causes of the degradation of a river bed (Galay, 1983)

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