Application of the IHA methord (indicators of hydrologic alteration) to evaluate the impacts of Tri An reservoir on hydrological regime in the downstream of the Dong Nai river basin

Abstract

The Indicators of Hydrologic Alteration (IHA) based on 33 parameters in five dimensions (flow
magnitude, timing, duration, frequency and change rate) have been widely used in evaluation of
hydrologic alteration in river systems.The comparison between the “natural period” (1977-1989) and
“regulated period” is implemented by using 32 IHA parameters. The results show that Tri An reservoir
affects the downstream hydrological regime during the flood season at Bien Hoa station. Meanwhile,
the flow in the dry season is mainly influenced by tides. The hydrological regime was adjusted to be less
variation with the regulation of Tri An reservoir since 1989 to 1999. However, the water level in flood
season has been increased sharply since 2000. The surge of high water level in the flood season with the
regulation of Tri An reservoir depicts the increase of tidal water level and the influence of heavy rains
on the basin.
Keywords: Flow regime alteration, IHA (Indicators of Hydrologic Alteration).