Continental Shelf Research 22 (2002) 1379–1395 The role of topography in small well-mixed bays, with application to the lagoon of Mururoa Pierre-Philippe Mathieu a, *, Eric Deleersnijder b , Beno # ıt Cushman-Roisin c , Jean-Marie Beckers d , Karsten Bolding e a Center for Global Atmospheric Modelling, Department of Meteorology, University of Reading, Early Gate, Reading RG6 6BB, UK b Institute of Astronomy and Geophysics G. Lema # ıtre, 2 Chemin du Cyclotron Universit ! e Catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium c Thayer School of Engineering, Dartmouth College 8000 Cummings, Hanover, NH 03755-8000–603/646-3248, USA d GeoHydrodynamics and Environment Research Laboratory (GHER), Universit ! e de Li " ege, Sart Tilman B5, B-4000 Li " ege, Belgium e Marine Environment Unit, Joint Research Center (JRC), European Commission, I 21020 Ispra (VA), Italy Received 19 July 2000; received in revised form 22 July 2001; accepted 12 September 2001 Abstract The present study aims to better understand how bathymetry and wind field interact to shape the circulation in well- mixed bays with particular emphasis on the lagoon of Mururoa. The simple model of Csanady (J. Phys. Oceanography 3 (1973) 429) is re-examined and some new analytical properties of the velocity distribution are derived. An extended version of the Csanady model, called the idealised model (IM), is then applied to the lagoon of Mururoa located in the Pacific. The circulation obtained by IM compares well with the circulation simulated by a three-dimensional hydrodynamic model. Our results show that IM provides a simple and powerful heuristic tool to gain more insight into the dominant dynamical regime of the lagoon. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Marine modelling; Topographic effect; Idealised hydrodynamic model; Lagoon dynamics; Analytical solution; Tropical pacific; Mururoa atoll lagoon 1. Introduction Wind-induced currents have been widely ac- knowledged to play a role of key importance in removing contaminants from various semi-en- closed shallow coastal bays and lagoons (Davies, 1990; Hearn et al., 1987; Hunter and Hearn, 1987; Glorioso and Davies, 1995). A good example is the semi-enclosed lagoon of Mururoa in the tropical Pacific (French Polynesia, 138155 0 W–21150 0 S), where the wind-induced circulation controls the fate of radioactive substances generated by nuclear weapon tests. The numerical simulations per- formed by Tartinville et al. (1997) showed that the residence time of radioactive tracers in the lagoon is strongly influenced by the wind-driven barotropic circulation. Namely, the circulation consists of two large gyres which tend to make water re-circulate inside the lagoon rather than to export it toward the open ocean. Given the key role of wind-driven circulation in pollution study, the present study aims at better *Corresponding author. Tel.: +44-118-987-5123; fax: +44- 118-931-8316. E-mail address: mathieu@met.rdg.ac.uk (P.-P. Mathieu). 0278-4343/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S0278-4343(02)00002-X