An Assessment of a River Hydrological Regime Alteration: A Case Study of Sungai Dungun

Abstract

Hydro-morphology of a river can be assessed using four main methods namely morphological assessment, physical habitat assessment, riparian habitat assessment and hydrological regime alteration assessment. This study focused on the fourth method where changes in flow rate are the criteria of river regime alteration. The Indicator of Hydrologic Alteration (IHA 7.0) was employed to study the pre- and post-impact of a major flood event in 2014 at Sungai Dungun as well as the other anthropogenic stress such as sand mining activities that occurred at Sungai Dungun. The daily flowrate from the monitoring site at Jerangau bridge (Station Number: 4832441) was obtained from DID (Department of Irrigation and Drainage) to assess the pre-impact flowrate (2002 – 2014) and post-impact flowrate (2015-2019). It was found that the flow duration curve decreased at the post-impact significantly compared to the pre-impact duration. The median flows dropped almost half between pre-impact and post-impact analysis. A few indicators were identified as the high range of variability approach (RVA) that defines the extent of alteration between pre- and post-analysis. The positive RVA of fall rate, high pulse duration, low pulse duration signifies the increase of frequency from pre-impact to the post-impact while negative RVA of 90-1-day minimum flows, 30-7 days maximum flows December, July and May median flow indicate the frequency of values in the category has decreased between pre- and post-analysis.