A modeling approach to establish environmental flow threshold in ungauged semidiurnal tidal river

A. Akter, A. H. Tanim

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

Due to shortage of flow monitoring data in ungauged semidiurnal river, ‘environmental flow’ (EF) determination based on its key component ‘minimum low flow’ is always difficult. For EF assessment this study selected a reach immediately after the Halda-Karnafuli confluence, a unique breeding ground for Indian Carp fishes of Bangladesh. As part of an ungauged tidal river, EF threshold establishment faces challenges in changing ecological paradigms with periodic change of tides and hydrologic alterations. This study describes a novel approach through modeling framework comprising hydrological, hydrodynamic and habitat simulation model. The EF establishment was conceptualized according to the hydrologic process of an ungauged semi-diurnal tidal regime in four steps. Initially, a hydrologic model coupled with a hydrodynamic model to simulate flow considering land use changes effect on streamflow, seepage loss of channel, friction dominated tidal decay as well as lack of long term flow characteristics. Secondly, to define hydraulic habitat feature, a statistical analysis on derived flow data was performed to identify ‘habitat suitability’. Thirdly, to observe the ecological habitat behavior based on the identified hydrologic alteration, hydraulic habitat features were investigated. Finally, based on the combined habitat suitability index flow alteration and ecological response relationship was established. Then, the obtained EF provides a set of low flow indices of desired regime and thus the obtained discharge against maximum Weighted Usable Area (WUA) was defined as EF threshold for the selected reach. A suitable EF regime condition was obtained within flow range 25–30.1 m3/s i.e., around 10–12% of the mean annual runoff of 245 m3/s and these findings are within researchers’ recommendation of minimum flow requirement. Additionally it was observed that tidal characteristics are dominant process in semi-diurnal regime. However, during the study period (2010–2015) the validated model with those reported observations can provide guidance for the decision support system (DSS) to maintain EF range in an ungauged tidal river.

Original languageEnglish
Pages (from-to)442-459
Number of pages18
JournalJournal of Hydrology
Volume558
DOIs
StatePublished - Mar 2018
Externally publishedYes

Funding

The research was supported by funds provided by Center for River, Harbor and Landslide Research ( CRHLSR ), Chittagong University of Engineering and Technology ( CUET ), Bangladesh. We express our gratitude to BWDB, CPA and BMD for providing bathymetric, meteorological and validation data during the study.

Keywords

  • Flow components
  • Habitat simulation
  • Tidal process
  • Ungauged rivers

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