Ocean Systems Engineering, Vol. 9, No. 3 (2019) 287-328 DOI: https:// doi.org/10.12989/ose.2019.9.3.287 287 Copyright © 2019 Techno-Press, Ltd. http://www.techno-press.org/?journal=ose&subpage=7 ISSN: 2093-6702 (Print), 2093-677X (Online) Multivariate design estimations under copulas constructions. Stage-1: Parametrical density constructions for defining flood marginals for the Kelantan River basin, Malaysia Shahid Latif  and Firuza Mustafa Department of Geography, University of Malaya, 50603, Kuala Lumpur, Malaysia (Received February 9, 2019, Revised July 10, 2019, Accepted July 22, 2019) Abstract. Comprehensive understanding of the flood risk assessments via frequency analysis often demands multivariate designs under the different notations of return periods. Flood is a tri-variate random consequence, which often pointing the unreliability of univariate return period and demands for the joint dependency construction by accounting its multiple intercorrelated flood vectors i.e., flood peak, volume & durations. Selecting the most parsimonious probability functions for demonstrating univariate flood marginals distributions is often a mandatory pre-processing desire before the establishment of joint dependency. Especially under copulas methodology, which often allows the practitioner to model univariate marginals separately from their joint constructions. Parametric density approximations often hypothesized that the random samples must follow some specific or predefine probability density functions, which usually defines different estimates especially in the tail of distributions. Concentrations of the upper tail often seem interesting during flood modelling also, no evidence exhibited in favours of any fixed distributions, which often characterized through the trial and error procedure based on goodness-of-fit measures. On another side, model performance evaluations and selections of best-fitted distributions often demand precise investigations via comparing the relative sample reproducing capabilities otherwise, inconsistencies might reveal uncertainty. Also, the strength & weakness of different fitness statistics usually vary and having different extent during demonstrating gaps and dispensary among fitted distributions. In this literature, selections efforts of marginal distributions of flood variables are incorporated by employing an interactive set of parametric functions for event-based (or Block annual maxima) samples over the 50-years continuously-distributed streamflow characteristics for the Kelantan River basin at Gulliemard Bridge, Malaysia. Model fitness criteria are examined based on the degree of agreements between cumulative empirical and theoretical probabilities. Both the analytical as well as graphically visual inspections are undertaken to strengthen much decisive evidence in favour of best-fitted probability density. Keywords: flood; block (annual) maxima; parametric functions; marginal distribution; goodness-of-fit 1. Introduction Basin perspective water resources operational planning, the management or either flood-related infrastructure designing often demands accurate estimations of the flow exceedance probability or Corresponding author, Ph.D. Research Scholar, E-mail: macet.shahid@gmail.com