The international efforts and achievements have been well documented in the literature available in English such as the proceedings of the five international symposia convened by UNESCO and IAHS (UNESCO and IASH,1970;Barends et al.,1995,1998).  The international efforts and achievements have been well documented in the literature available in English such as the proceedings of the five international symposia convened by UNESCO and IAHS (UNESCO and IASH, 1970; Barends et al., 1995, 1998)