Liliana Zaharia

Sediment Transport and River Channel Dynamics in Romania – Variability and Control Factors

Sediment transport and river channel dynamics are the result of the complex interaction between natural and human factors, at both local and regional scale. The study of sediment transport and river channel dynamics may be an important way to better know and understand the mechanisms that rule the functioning of fluvial system, allowing forecasts of its future evolution to be made and appropriate adaptation measures to be taken by society in front of the risks related to the fluvial dynamics and sediment transfer. The purpose of this chapter is to present specific aspects concerning the sediment transport and river channel dynamics in Romania and to reveal the role of various control factors. Our contribution consists mainly in regional analyses that highlight the following aspects: i) the spatial and temporal variability of suspended sediment transport; ii) the relationships between suspended sediment yield/load and some control variables (precipitation, water discharge, catchments characteristics, and human activities), and iii) the vertical and lateral dynamics of selected river channels. The chapter summarizes a part of the significant results of our previous studies and some more recent researches in the field of sediment transport and channel dynamics in Romania. It also includes new issues and approaches, based especially on case studies, which further develop the proposed topic. The analyses focus preeminently on two areas: the Carpathian’s Curvature region, and the central part of the Romanian Plain (Fig. 1A). We have chosen the first area because it has the highest sediment yield in Romania: over 20 – 25 t ha-1 yr-1, meaning more than 10 times the average sediment yield on a national scale, which is about 2 t ha-1 yr-1 (Mociorniţă & Birtu, 1997). The central part of the Romanian Plain is characterized by an intense lateral dynamics of the river channels, making it vulnerable to the risks induced by fluvial dynamics, because of the economic importance of the area and the significant density of population and settlements. The data used and the methodologies employed are mentioned in the text. This chapter is structured in four main parts concerning: i) previous researches on sediment transport and fluvial dynamics in Romania; ii) sediment transport and control variables; iii) river channel dynamics and iii) human impact on sediment transfer.

Assessment and mapping of flood potential in the Slănic catchment in Romania

Flood risk assessment is an important component of risk management. Given this context, this paper aims to identify and map areas with high potential for flash-floods and flooding occurrence, at different spatial scales (from catchment to local scale), in order to estimate the flood/flooding vulnerability. The paper is based on three main methods, which were applied in the Slănic River catchment (427 km2), located in the external curvature region of the Romanian Carpathians: (i) statistical analyses; (ii) determination and mapping of some indices to assess the flash-flood and flooding potential (FFPI and respectively FPI) and (iii) hydraulic modelling. The data used mainly include hydrological statistics (maximum monthly and annual discharges, flood-related data) and spatial data on catchment geographical characteristics (hypsometry, geology, soils, land use) obtained or derived from various sources (maps, aerial images, digital databases, field measurements) which were integrated into the GIS environment. The aforementioned methods helped to (i) highlight specificities of floods in the Slănic catchment (magnitude, frequency, flood waves characteristics); (ii) identify areas with high potential for flash-floods and flooding at the catchment spatial scale; (iii) assess the structural vulnerability in the Cernăteşti village, by simulating flood-prone areas for flood peaks with exceedance probability of 1%, 5% and 10%. The results could lead to a better knowledge and understanding of flood characteristics in the study area, in order to mitigate the flood risk through a more effective management, both at the catchment scale, as well as local scale (in the Cernăteşti village).

Mapping flood and flooding potential indices: a methodological approach to identifying areas susceptible to flood and flooding risk. Case study: the Prahova catchment (Romania)

Given that floods continue to cause yearly significant worldwide human and material damages, flood risk mitigation is a key issue and a permanent challenge in developing policies and strategies at various spatial scales. Therefore, a basic phase is elaborating hazard and flood risk maps, documents which are an essential support for flood risk management. The aim of this paper is to develop an approach that allows for the identification of flash-flood and flood-prone susceptible areas based on computing and mapping of two indices: FFPI (Flash-Flood Potential Index) and FPI (Flooding Potential Index). These indices are obtained by integrating in a GIS environment several geographical variables which control runoff (in the case of the FFPI) and favour flooding (in the case of the FPI). The methodology was applied in the upper (mountainous) and middle (hilly) catchment of the Prahova River, a densely populated and socioeconomically well-developed area which has been affected repeatedly by water-related hazards over the past decades. The resulting maps showing the spatialization of the FFPI and FPI allow for the identification of areas with high susceptibility to flash-floods and flooding. This approach can provide useful mapped information, especially for areas (generally large) where there are no flood/hazard risk maps. Moreover, the FFPI and FPI maps can constitute a preliminary step for flood risk and vulnerability assessment.

Hydroclimatic dynamics in southwestern Romania drylands over the past 50 years

The present paper examines hydroclimatic dynamics in southwestern Romania drylands, which is one of the country’s most heavily affected regions by climate change. The analysis focuses on two of the region’s representative catchments (Drincea and Desnatui), covers the past five decades (1961–2009), and is based on climate data (mean monthly and annual climatic water balance values – CWB, expressed in mm) and hydrological data (mean monthly and annual streamflow rate values – SFR, expressed in m3/s). The data were provided by five regional weather stations, i.e., by five gauging stations located within the two catchments. The analysis was conducted on three temporal scales (annual, seasonal and monthly), and used statistical methods, such as Mann–Kendall test/Sen’s slope method for trend analysis, and Spearman/Student test for the statistical association between climatic and hydrological parameters. The results indicated an overall increase in climatic water deficit, with direct effects on streamflow reduction. Statistically significant trends (climatic water deficit increase and streamflow decrease) were identified especially in spring (with maximum rate values of (−1.66 mm/yr)/(−81.3 mm/49 yrs), for the CWB, and (−0.02 m3/s/yr)/(−0.9 m3/s/49 yrs), for the SFR). In some cases (mainly in the autumn months) it was found that, while climatic water deficit has decreased, the streamflow rate has increased. Statistical correlations revealed the relationship between the considered hydroclimatic parameters, with a particularly high statistical significance in spring and summer. Weak and inverse correlations between climatic and hydrological parameters can be explained by the role of other factors controlling the streamflow, both natural (soil and lithology) and anthropogenic (wetland drainage, water body conversion, dam and reservoirs building).

Using a multi-criteria analysis to identify rivers with hydromorphological restoration priority: Braided rivers in the south-eastern Subcarpathians (Romania)

In order to systematically plan river restoration actions at a regional scale, this paper develops a multi-criteria analysis that classifies rivers, based on their priority for hydromorphological restoration. This priority is defined by severe human pressures within the erodible corridor of the river, drastic alteration of the stream channel, and low intensity of river pattern functioning. Based on relevant indicators for three groups of features (human pressures, channel changes, and river functionality), a Hydromorphological Restoration Priority Index (HRPI) was designed. The high values (>66%) of HRPI reflect an urgent need for hydromorphological restoration while low values (<33%) reveal a less immediate necessity for restoration. The proposed methodology was applied on braided sectors of rivers crossing the south-eastern (Curvature) Subcarpathians (Romania). The values of the total HRPI ranged between 21% (Zăbrăuţ River) and almost 44% (Prahova River). According to our results, most of the analyzed sectors have a low need for hydromorphological restoration of the braided pattern, while some have a moderate necessity for restoration. Whereas the Prahova River has the highest HRPI, it should be given priority for restoration at a regional scale, which corresponds to the objectives of River Basin Management Plans for the interval beyond 2021.

Floods and Flash-Floods Related to River Channel Dynamics

Floods and flash-floods are a major factor in hydrogeomorphological river dynamics. This chapter has two main aims: (i) to analyse the characteristics of floods in Romania, based on their origin, frequency and magnitude; (ii) to present case studies on the relation between river channel dynamics and floods. In most cases, in Romania, floods occur in spring and summer (up to 3/4 of the total number of floods) and have mostly pluvial origins. Rivers from the External Curvature (Carpathians, Subcarpathians and Romanian Plain) suffered historical floods in 2005, reflected by a slight extension of the river channel (for example, Putna and Buzău watercourses). Rivers from Banat Plain also recorded floods in 2005; a high volume of water created breaches in dikes and the long stagnation of water determined morphological modifications of the floodplain. The Danube River registered historical floods in 2006; due to the morphometry of the floodplain, the river overflowed the banks and the dikes, covering the floodplain between Rast and Bistreţ towards the homonym lake. The flash-flood from Ilisua River basin in June 2006 generated some modifications in the river channel morphology due to fine materials accumulation, with a thickness of 0.2–1.5 m, and coarser ones, which created bars with heights of 0.5–1 m; materials came from landslides and bank collapse. The interactions between hydrological phenomena and morphological processes may have consequences with ephemeral character, reversible on short-term, but also on long-term, with a potential impact on the environment and on the society. This analysis underlines the applied character of hydrogeomorphology.

Overview of River-Induced Hazards in Romania: Impacts and Management

River-related hazards, mainly floods and inundations are the most widespread and frequent of all the natural damaging phenomena, causing annually significant victims and economic losses. This chapter focuses on Romania, a country with one of the highest flood risk in Europe. According to EM-DAT database, within the period 1900–2016, more than half (55%) of the total number of disasters (94 events) were induced by floods. During the mentioned period, they were responsible for 57% of the total damage costs related to the top 10 disasters in Romania. The chapter presents a synthetic overview on the river-born hazards as floods and flooding, low-waters and hydrological droughts, and other damaging phenomena (water freezing, ice jams, sediment, and channel dynamics reservoirs’ silting) with relevant examples, as well as with references to their impacts and management. Reducing the negative consequences of these hazards has become an important concern in the national water resources and related risks management policy. In this sense, two strategies are relevant: National Strategy for Drought Mitigation, Prevention and Combating Land Degradation and Desertification, on short, medium, and long term (2008), National Strategy for Flood Risk Management for medium and long term (2010), and Flood Risk Management Plans (2016).

Urbanization effects on the river systems in the Bucharest City region (Romania)

Abstract This article identifies and analyzes the effects of human pressures on the river systems, landscape, flow regime, and water quality in the Bucharest region, the largest urbanized area in Romania. The analyses focused on four streams crossing the Bucharest region, namely the Dâmboviţa, Colentina, Argeş, and Sabar rivers. Our approach relied especially on three types of information: (1) spatial data; (2) hydrological data sets; and (3) water quality data. We made a diachronic analysis of the available maps and ran classic statistical analysis of the data sets, as well as trend analysis. At the same time, we compared the flows in natural (reconstituted) and modified (current) regimes. The results showed that the stream system and its associated landscapes have considerably changed due to several engineering works (reservoirs, dams, channelization works, diversion canals, water intakes, etc.). Under these circumstances, the flow regime suffered changes that differed among the rivers. Thus, the multiannual discharges of the Argeş and Dâmboviţa rivers did not exhibit significant changes, but only mitigated the monthly discharge variability. In the case of Sabar and Colentina, a significant increase of the annual and monthly discharges was identified, due to the water transferred from the neighboring rivers. Water quality worsened, especially on the lower courses of the Dâmboviţa and Argeş rivers, degrading the states and health of the aquatic ecosystems in the study region.