1. School of Engineering and Advanced Technology, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand, Environmental Fluid Mechanics Laboratory, Stanford University, Stanford, California 94305-4020, School of Civil and Environmental Engineering, Nanyang Technological University, Singapore 639798, Singapore, and Department of Chemical Engineering and Environmental Technology, Valladolid University, Paseo del Prado de la Magdalena, s/n, Valladolid, Spain