Understanding sediment transport and deposition in the Liemu and Fiddien catchments

Abstract

This study aims to investigate the dynamics of suspended sediment transport and deposition in Liemu and Fiddien catchments. Situated in Rabat and Dingli, these subcatchments form part of the larger Għasel catchment and are known for being predominantly agricultural with dispersed pockets of urban fabric. To achieve the work’s aim, two methods were employed. Firstly, suspended sediment concentrations were measured at three points along the watercourse following precipitation events in order to assess how concentrations vary between sampling points, and with precipitation intensity. Secondly, deposited sediment was quantified at three sites over an area of 113.1 cm2 with the use of a sediment trap in order to obtain estimates for annual deposition rates. Values for suspended sediment concentrations ranged from 1 μgL-1 to 2746 μgL-1. This variability was explained through a combination of geomorphological properties of the areas surrounding the sampling points, and discharge. For deposited sediment, annual sedimentation rates at the chosen deposition sites ranged from 7 kgm-2 to 53 kgm-2 and once again, surrounding geomorphological features affected these values. Additionally, a sieve analysis was carried out on the collected sediment to assess size variations between suspended and deposited sediment and between different sampling points. Deposited sediment contained a larger representation of coarse sediment (>2 mm) while suspended sediment contained a larger percentage of fine sediment. While limited by a short sampling period, this study provides baseline sediment values for Maltese streams, and global IRES where such site-specific values remain scarce.