Impact Of Channel Incision On Floods: A Case Study In The South-Eastern Subcarpathians (Romania)

Gabriela Ioana-Toroimac,Gabriel Minea,Gianina Neculau,Liliana Zaharia

doi:10.24057/2071-9388-2019-177

Abstract

Despite numerous researches on river channel incision, there are fewer studies on the impact of channel adjustments on floods. This paper aims to investigate channel adjustments and to analyse their impact on the frequency of floods by estimating the return period of the bankfull discharge of the Prahova River in the South-Eastern Subcarpathians (Romania). The study is based on the analysis of the maximum annual discharges and cross-section profiles of the Prahova River at Câmpina gauging station (1976–2015). To estimate the return period of the bankfull discharge, the log Pearson III distribution was used. Overall, the maximum depth and the cross-section area at the bankfull stage increased during the analysed period, indicating channel incision and lateral stability. The bankfull discharge of 1976 could be reached every year and the one of 2015 could occur almost every 5 years. Therefore, due to channel incision and increased channel capacity, overflowing the bankfull stage is a less frequent hazard on the Prahova River at Câmpina gauging station. River management appears to maintain this situation as no measure is taken to decrease channel incision.

Highlights

In the context of the European Union Water Framework Directive (EU-WFD), all water bodies affected by anthropogenic impact should be rehabilitated to a good status (European Commission 2000)
The deepest incision between two consecutive cross-section profiles of about – 1.3 m occurred in July 1988 followed a few days later by the highest aggradation of +1.3 m in relation to the second peak of the maximum annual discharges of the period 1976–2015 (Fig. 1c), indicating the new equilibrium of the hydrosystem disturbed by a flood
This paper showed that the impact of channel incision on floods is translated by an increase of the bankfull discharge and of its return period

Summary

Introduction

In the context of the European Union Water Framework Directive (EU-WFD), all water bodies affected by anthropogenic impact should be rehabilitated to a good status (European Commission 2000). Previous studies showed that efforts are made to rehabilitate incised channels (e.g., Beechie et al 2008; Stähly et al 2019). Previous studies in the South-Eastern Subcarpathians showed a decrease of the braiding activity intensity in the last century, shrinking of braided sectors until fluvial metamorphosis, a narrowing process, and an increase of woody riparian vegetation on the riverbanks of the now-abandoned active channel; in-stream vegetation was severely reduced as a result of changes in the dominant geomorphological processes, namely erosion is more intense than deposition (Ioana-Toroimac 2016). Few studies investigated the river channel incision in the South-Eastern Subcarpathians (e.g., Armaş et al 2012; Rădoane et al 2013)

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