Comparison of the “Natural” and the Present Sediment Regime of the Danube River

 Marina Babić Mladenović1, Vasiljka Kolarov1, Vanja Damjanović1 and Predrag Radosavljević2


1 Jaroslav Černi Institute for the Development of Water Resources, Jaroslava Černog 80, 11226 Pinosava, Belgrade, Serbia; This e-mail address is being protected from spambots. You need JavaScript enabled to view it

2 HPPs Djerdap Ltd., Trg Kralja Petra 1, 19320 Kladovo, Serbia

 

Abstract

This paper presents the sediment regime at the Serbian sector of the Danube River, both in natural conditions (defined as those existing prior to construction of the Iron Gate dams) and present conditions. Extensive field investigation data, obtained during implementation of the ongoing Sediment Regime and Morphological Changes Monitoring Program, conducted by the Jaroslav Černi Institute on behalf of HPPs Djerdap Ltd., form the basis for the description of changes in the Danube sediment regime that occurred following construction of the Iron Gate 1 and 2 dams. The most important parameters of sediment transport and deposition processes, including suspended sediment characteristics (grain size and concentration), morphological changes and riverbed composition, are presented in paper. The influence of large tributaries of the Danube River (the Tisa, the Sava, and the Velika Morava rivers) is also addressed.
Keywords: sediment regime, morphological changes, Danube, Serbia

 

 

Introduction

Sediment management in the Danube River Basin is gradually becoming an issue of special interest. Sediment quality and quantity were not properly addressed in the 1st Danube River Basin Management Plan 2009 due to a lack of data. A new project dealing with the Danube sediment is expected to be initiated soon, with the objective to review the current status of the Danube, including the inputs of its major tributaries, analyze pressures and impacts, assess the sediment balance and propose actions to be taken. This project may substantially contribute to the preparation of the 2nd Danube River Basin Management Plan. In this regard, the paper aims to present some facts about the natural and the present sediment regime in the Serbian part of the Danube River, and highlight changes which were initiated by the construction of the Iron Gate dams.

Water and sediment from the entire upstream portion of the Danube River Basin (570,000 km2), which is shared by 12 countries with a total population of about 80 million, concentrate at the 588 km long Serbian sector of the Danube. It is very specific because of its geomorphology and numerous and important alluvial tributaries, contributing considerably to the Danube sediment balance.

Soil erosion and sediment transport, as two important components of a river's natural process, exist in the Danube Basin as well. The effects of various human activities on these processes are considerable. Man's influence on the soil erosion process started a few millennia ago, with deforestation and increase of agricultural land use. Human influence on sediment transport in rivers began a few centuries ago, when river shortening and training works subsequently increased sediment transport capacity. On the Danube, during the 20th century, many dams and chains of hydropower plants were built in its upper reaches and tributaries, resulting in a reduction in sediment transport. Extraction of river sediment as construction material for urbanization also began. All these activities had a major influence on the natural sediment regime of the Danube River, which existed before the construction of the two large dams on the Iron Gate stretch, and which still exists upstream of the reservoir.

Presently, the Iron Gate 1 reservoir, whose volume is 3.5 km3 under average hydrologic conditions, has the most important influence on the Danube sediment regime. Its hydro-power plant operates as a run-of-river facility, providing only daily or weekly flow regulation (at low flows). The reservoir has variable length, backwater magnitude and volume, depending on the water inflow (Babić Mladenović, 2007). The hydro-power plant (HPP) operating mode addresses sediment transport and deposition phenomena: the sluice gates at the dam are fully opened and water levels reduced prior to the arrival of flood waves (at Q>11,000 m3/s), in order to allow for the passage of sediment-loaded water. Nevertheless, the sedimentation of the reservoir is considerable and has substantial environmental and water management impacts, both within its range and on downstream reaches of the Danube. The downstream Iron Gate 2 reservoir is considerably smaller. Sedimentation problems associated with this reservoir, where the water and sediment regimes are governed by the upstream reservoir, are considerably less significant.

Measurements of sediment parameters of the Danube in Serbia began in the 1960s, within the scope of preparation of technical documentation for navigation and, in particular, for the construction of the Iron Gate 1 dam. After 1974, a comprehensive research of Iron Gate 1 reservoir sedimentation was conducted by the Jaroslav Černi Institute, on behalf of HPPs Djerdap Ltd. The same scope of research was set up for the Iron Gate 2 reservoir after 1985.