Climate Variability and Change—Hydrological Impacts (Proceedings of the Fifth FRIEND World
Conference held at Havana, Cuba, November 2006), IAHS Publ. 308, 2006, 99–104.
Stochastic model of flow duration curves for
selected rivers in Bangladesh
M. F. BARI1 & KH. MD. SHAFIUL
ISLAM2
1 Department of Water Resources Engineering, Bangladesh University of Engineering & Technology, Dhaka 1000, Bangladesh
2 Department of Civil Engineering,
Khulna University of Engineering & Technology, Khulna 920300, Bangladesh
Abstract To overcome the difficulty of a traditional flow duration curve (FDC)
in which the chronological sequence of occurrence of flows is masked, a
stochastic approach has been applied to obtain a calendar year FDC. Estimates
of mean flows by rank based on order statistics enable the construction of such
a FDC once the underlying frequency characteristics and distribution of the
population is known. This paper discusses the theoretical development of
a stochastic FDC and the choice of a suitable probability distribution for mean
daily discharges. The flow duration curve model is then applied to records from
four selected rivers in north-western Bangladesh. Based on visual as well as c2 and Kolmogorov-Smirnov
goodness-of-fit tests, the mixture lognormal distribution exhibited a better
fit. Expected flow duration curves were generated for each gauging station
using the chosen distribution and visually compared with observed curves. These
flow duration curves represent, respectively, the computed and observed mean
discharges by rank and showed a close agreement. Reliability of the FDC was
investigated by comparison of computed standard deviations for the chosen
distribution with those observed for all ranks, and the mixture lognormal was
found to be a flexible distribution for the highly seasonal regimes of the
selected rivers.
Key words flow duration curve;
goodness-of-fit; mean daily discharge; mixed lognormal distribution; northwest
Bangladesh; stochastic model