Christian Chreties

Analysis of the recent evolution of the sand spit at the Solís Chico river mouth

ABSTRACT Solari, S., Chreties, Ch., López, G., Teixeira, L., 2014. Analysis of the recent evolution of the sand spit at the Solís Chico river mouth. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 616–620, ISSN 0749-0208. The Solís Chico river, located on the southern Uruguayan coast, flows into the Río de la Plata estuary. The seaside resorts La Floresta and Parque del Plata are located on the estuary. In recent years the river mouth has migrated westward, away from the river axis, forming a sand spit that hinders the recreational use of Parque del Plata beach. In turn, at La Floresta there is a beach nourishment project whose main objective is to mitigate the erosion of the beach and the adjoining cliffs. This work aims to identify the causes of the recent migration of the river mouth and to analyze the possibility of using the sand spit as a borrow area for the beach nourishment. The river sediment supply to the coast for the period 1900–2010 was estimated, along with the long-shore and cross-shore sediment transport produced by sea waves. Furthermore, the plan-view stability of the river was studied in order to determine if the long-term evolution of the river is affecting the migration of the mouth. It was found that the migration of the mouth is mainly due to an extraordinarily high river sediment supply in 2002, combined with an increase in the net westward potential long-shore transport rate since the late 90s, and that the meander dynamics of the river are not affecting the evolution of the mouth. Additionally, the most likely area of natural breaching of the sand spit was identified, recommending its use as a borrow area for nearby beach nourishment.

Pile Group Protection with Riprap Mattress

New experimental data on plan dimensions for riprap mattresses used in pile group protection against edge failure are analyzed. The influence of flow conditions and the distance between piles in plan dimensions of riprap mattresses are addressed. An alternative methodology for the experimental study of edge failure in pile groups is proposed and verified, significantly reducing the duration of tests (from several days to a few hours) and yielding similar results. For the pile group configuration tested, a design expression for minimum riprap width is obtained. The influence of the distance between the piles on the width of riprap dimensions is shown to be small, and the proposed expression compares well with some of the expressions for single piers found in the literature.

Riprap Sizing for Pile Groups

This work presents results on riprap sizing for pile group protection against local scour. Shear failure mechanism is addressed, avoiding edge, bed-form undermining, and winnowing modes. The influences of the flow conditions and the distance between the piles are analyzed. As a result of a laboratory experimental campaign, and within a detailed dimensional analysis framework, the writers propose expressions for riprap block size to resist shear failure. The influence of the distance between the piles on the block size is shown to be small, and the proposed expressions compare well to some of the literature expressions for single piers.