scholarly journals Modelling the impact of anthropogenic modifications to river channels on the course of extreme floods. Case study: August 2002 flood, Blanice River basin, Czechia

Geografie ◽  
2008 ◽  
Vol 113 (3) ◽  
pp. 237-252
Author(s):  
Jakub Langhammer ◽  
Jan Sitař
Keyword(s):  
Negative Impact ◽  
Local Level ◽  
River Channel ◽  
Water Levels ◽  
River Channels ◽  
Extreme Floods ◽  
River Bed ◽  
Extreme Flood ◽  
Anthropogenic Modifications ◽  
The Impact

This paper presents the results of analysis of the impact of anthropogenic modifications to river channels on the course of floods by means of hydraulic modelling. The study is focused on the quantitative analysis of changes of the flow dynamics in the river bed and in the inundation zone due to river network modifications. The one-dimensional hydraulic model HEC-RAS coupled with GIS is used to simulate the effect of the river channel changes on the course of extreme flood. The analysis is made on the example of the extreme flood in August 2002 on the down course of Blanice River in Czechia. The results of the simulations proved that the common anthropogenic modifications of river channel have only a minimum impact on the overall course of extreme floods. At the local level, weirs and unsuitably dimensioned bridges have a negative impact on the course of floods. The simulations also showed a negative impact of extensive complex modifications of the river bed, performed in the lower course of Blanice River in the first half of the 20th century. However, the overall impact of common types of river channel modifications on peak flows and water levels in the culmination is negligible.

scholarly journals Aspects Concerning the Impact of Climate Aridization on Forest Ecosystems (Case Study)

2017 ◽  
Vol 11 (2) ◽  
pp. 63-75
Author(s):  
Nedealcov Maria ◽  
Donica Ala ◽  
Brașoveanu Valeriu ◽  
Grigoraș Nicolae ◽  
Deomidova Cristina
Keyword(s):  
Climate Change ◽  
Forest Ecosystems ◽  
Temporal Dynamics ◽  
Negative Impact ◽  
Local Level ◽  
Aridity Index ◽  
Climatic Conditions ◽  
Study Region ◽  
Climate Aridization ◽  
The Impact

Abstract Assessment activity and surveillance of the forests health, held at the global, regional and local level, has continuously developed, culminating in the current period with interdisciplinary and extensive scientific researches, that evaluate the effects of the main factors on forest ecosystems state, in particular, air pollution and climate change. Scientific researches have shown that among trees ecophysiological processes, forest life processes and meteorological parameters there are direct dependences, particularly in the case of trees supply with water during the growing period (May-July), with major influences for critical months (July and August), which have a decisive impact on growth, vitality and production of organic matter in forests. Dry years, from the beginning of the third millennium can lead to a decrease of mesophilic forests area (beech, sessile oak and penduculate oak), which will tend to retreat towards the center of the area (central Europe) in favor of thermophilic forests with pubescent oak. It was determined that a most significant negative impact of climate aridization will feel the forest ecosystems from Southern and central regions of country (conditioned by the mean air temperature (July-August), monthly rainfall (May-August), evapotranspiration and geographic latitude), and less - the Northern part of the country (Forestry Aridity Index calculated for 3 experimental stations revealed variations of this index between 7.8 - 8.3 - in the Central part of country, and 8.4 - 8.6 - for Southern part of country). At the same time the impact of climate change will determine the spatial and temporal dynamics of pests and pathogenic species. The phenomenon of climate aridization was expressed also through the impact of the Microsphaera alphitoides disease, intensity of “mildew” attack being based on the climatic conditions of the study region. Obtained data, for confirmation, were correlated with indications of bioindicators, present in the study region.

scholarly journals Flooding in the Mekong Delta: the impact of dyke systems on downstream hydrodynamics

2020 ◽  
Vol 24 (1) ◽  
pp. 189-212 ◽  
Author(s):  
Vo Quoc Thanh ◽  
Dano Roelvink ◽  
Mick van der Wegen ◽  
Johan Reyns ◽  
Herman Kernkamp ◽  
...  
Keyword(s):  
Mekong Delta ◽  
High Flow ◽  
Water Levels ◽  
Mekong River ◽  
Low Flow ◽  
Water Level Fluctuations ◽  
Tidal Propagation ◽  
Extreme Flood ◽  
Year 2000 ◽  
The Impact

Abstract. Building high dykes is a common measure of coping with floods and plays an important role in agricultural management in the Vietnamese Mekong Delta. However, the construction of high dykes causes considerable changes in hydrodynamics of the Mekong River. This paper aims to assess the impact of the high-dyke system on water level fluctuations and tidal propagation in the Mekong River branches. We developed a coupled 1-D to 2-D unstructured grid using Delft3D Flexible Mesh software. The model domain covered the Mekong Delta extending to the East (South China Sea) and West (Gulf of Thailand) seas, while the scenarios included the presence of high dykes in the Long Xuyen Quadrangle (LXQ), the Plain of Reeds (PoR) and the Trans-Bassac regions. The model was calibrated for the year 2000 high-flow season. Results show that the inclusion of high dykes changes the percentages of seaward outflow through the different Mekong branches and slightly redistributes flow over the low-flow and high-flow seasons. The LXQ and PoR high dykes result in an increase in the daily mean water levels and a decrease in the tidal amplitudes in their adjacent river branches. Moreover, the different high-dyke systems not only have an influence on the hydrodynamics in their own branch, but also influence other branches due to the Vam Nao connecting channel. These conclusions also hold for the extreme flood scenarios of 1981 and 1991 that had larger peak flows but smaller flood volumes. Peak flood water levels in the Mekong Delta in 1981 and 1991 are comparable to the 2000 flood as peak floods decrease and elongate due to upstream flooding in Cambodia. Future studies will focus on sediment pathways and distribution as well as climate change impact assessment.

scholarly journals Exploitation of Documented Historical Floods for Achieving Better Flood Defense

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
Slobodan Kolaković ◽  
Julius Fabian ◽  
Sándor Kovács ◽  
Ljubomir Budinski ◽  
Matija Stipić
Keyword(s):  
Numerical Model ◽  
Interdisciplinary Approach ◽  
Water Levels ◽  
Flood Mitigation ◽  
Stream Network ◽  
Detention Ponds ◽  
Extreme Flood ◽  
Tisza River ◽  
Flood Elevation ◽  
The Impact

Establishing Base Flood Elevation for a stream network corresponding to a big catchment is feasible by interdisciplinary approach, involving stochastic hydrology, river hydraulics, and computer aided simulations. A numerical model calibrated by historical floods has been exploited in this study. The short presentation of the catchment of the Tisza River in this paper is followed by the overview of historical floods which hit the region in the documented period of 130 years. Several well documented historical floods provided opportunity for the calibration of the chosen numerical model. Once established, the model could be used for investigation of different extreme flood scenarios and to establish the Base Flood Elevation. The calibration has shown that the coefficient of friction in case of the Tisza River is dependent both on the actual water level and on the preceding flood events. The effect of flood plain maintenance as well as the activation of six potential detention ponds on flood mitigation has been examined. Furthermore, the expected maximum water levels have also been determined for the case if the ever observed biggest 1888 flood hit the region again. The investigated cases of flood superposition highlighted the impact of tributary Maros on flood mitigation along the Tisza River.

scholarly journals Geoinformatic assessment of extreme flood consequences - case study: Flood in August 2002 in Central Europe

Geografie ◽  
2006 ◽  
Vol 111 (1) ◽  
pp. 33-50
Author(s):  
Jakub Langhammer
Keyword(s):  
Central Europe ◽  
Environmental Changes ◽  
Retention Capacity ◽  
Protection Measures ◽  
Extreme Floods ◽  
Geostatistical Approach ◽  
Extreme Flood ◽  
Environmental Transformation ◽  
High Level ◽  
The Impact

The extreme flood events in the last decade in Central Europe served as a unique opportunity to study the impact of environmental changes on runoff process, to test the methods of their efficient assessment and to determine the applicability of the findings in effective flood protection measures. The paper presents the assessment of impact of environmental changes in landscape on the course and consequences of extreme floods. Assessment draws on selected indicators of environmental transformation related to rainfall-runoff processes, flood wave formation and transformation, and local retention capacity. The solution is based on geostatistical approach and applies to the Otava river basin located in the core zone of the extreme floods in August 2002 in Central Europe and representing area with high level of heterogeneity in terms of physicogeographic and social and economic aspects. The results of the presented research indicated evident links between physicogeographic characteristics of river basins, their anthropogenic transformation, and responses to extreme runoff situations. However the results hasn't proved the current intensity of river network shortening, riverbed transformation or floodplain and landscape modifications to be the main driving force of extremity of the flooding that occurred in August 2002 in Central Europe.

scholarly journals Analysis of floods in the upper course of the Hron River in 1930–2010

Geografie ◽  
2012 ◽  
Vol 117 (4) ◽  
pp. 415-433
Author(s):  
Andrea Blahušiaková ◽  
Milada Matoušková
Keyword(s):  
20Th Century ◽  
Frequency Analysis ◽  
Water Levels ◽  
Intense Rainfall ◽  
Extreme Floods ◽  
Extreme Flood ◽  
Extreme Flooding ◽  
Very High ◽  
Gauging Station

The main focus of this research is concentrated on the flood analyses in the upper course of the Hron River in the period 1930–2010. The study includes an evaluation of the flood seasonality, frequency and extremity in two periods 1930–1991 and 1992–2009. The year 2010 has been added because of a very high amount of precipitation between May–September 2010 which caused extreme flooding. The most extreme flood in the 20th century occurred in October 1974. At the gauging station Banská Bystrica, discharge values reached 560 m3.s−1 which corresponds to the 100-year flood. In the last decade, extreme floods occurred in years 2002 and 2010. The main reason for the flooding was an intense rainfall and local storms with high amount of precipitation. The frequency analysis (in equally long periods 1950–1979 and 1980–2009) proved that there is a higher frequency of floods since 1980 (17 in the period 1950–1979 and 27 between 1980–2009). Higher water levels during floods were reached in the period 1950–1979. The summer floods dominate in both observed periods, but winter floods also occurred very often (7 floods in the period 1950–1979 and 12 in 1980–2009). This is due to the hollow relief of the upper course of the Hron River.

scholarly journals Zones of Contention: A Comparative Analysis of the Impact of Two Regimes of Enrolment Regulations in New Zealand

2021 ◽  
Author(s):  
◽  
Timothy James Stubbs
Keyword(s):  
New Zealand ◽  
Qualitative Data ◽  
Negative Impact ◽  
Local Level ◽  
Ethnically Diverse ◽  
Geographic Area ◽  
Regulatory Regime ◽  
Ministry Of Education ◽  
Lower Decile ◽  
The Impact

<p>A number of New Zealand studies have identified a relationship between enrolment regulations and school enrolments, in particular drawing attention to the negative impact that the abandonment of ‘home zones’ in 1991 have had on many lower decile and ethnically diverse schools. The progress of a group of secondary schools within a geographic area in New Zealand from before the introduction of Tomorrow’s Schools in 1989 up to 2009 is tracked using quantitative data from the Ministry of Education, New Zealand Qualifications Authority and Statistics New Zealand combined with qualitative data from interviews with those who were principals during the period. This mixed-methods approach shows that both enrolment numbers and academic achievement in three of the four schools fell and then rose almost simultaneously with the removal in 1991 and then reinstatement in 2000 of geographic home zones. The ethnic and socioeconomic polarisation that resulted from the earlier change, however, has not reversed. The quantitative and qualitative data together provide clear evidence that geographic home zones provide a level of stability and security in the provision of education at a local level that is not matched by the alternative regulatory regime that operated in the 1990s.</p>

scholarly journals The Impact of Embankments on the Geomorphic and Ecological Evolution of the Deltaic Landscape of the Indo-Bangladesh Sundarbans

2020 ◽  
Author(s):  
Subhamita Chaudhuri ◽  
Punarbasu Chaudhuri ◽  
Raktima Ghosh
Keyword(s):  
18Th Century ◽  
High Water ◽  
Water Levels ◽  
Tidal Range ◽  
Mangrove Forests ◽  
Fish Ponds ◽  
Ecological Evolution ◽  
Late 18Th Century ◽  
Anthropogenic Modifications ◽  
The Impact

The deltaic landscape of the Ganga-Brahmaputra delta has evolved through a complex interplay of geomorphic processes and tidal dynamics coupled with the anthropogenic modifications brought over in course of the reclamation of the islands since the late 18th century. The reclamation process was characterized by clearing lands for paddy farms and fish ponds by building a mesh of earthen embankments along creek banks to restrict saltwater intrusion. The length of the embankments in the Indian Sundarbans alone is 3638 km (World Bank, 2014) which altered the tidal inundation regimes, sediment accretion and geomorphic character of the deltaic inlets. The mean annual sedimentation rate (2.3 cm y−1) in the central Ganga-Brahmaputra delta is over two times higher than sedimentation within the natural intertidal setting of the Sundarbans (Rogers et al., 2017). The tidal range has also increased inland due to polder construc¬tion, with high water levels within the polder zone increasing as much as 1.7 cm y−1 (Pethick and Orford, 2013). Embankments have impacted on the biodiversity and physiological adaptations of mangroves within the sphere of tidal ingression, habitat fragmentation and seedling establishment. The chapter attempts to reappraise the impact of dykes on the geomorphology of the deltaic landscape and on the functionalities of mangrove forests.

scholarly journals Zones of Contention: A Comparative Analysis of the Impact of Two Regimes of Enrolment Regulations in New Zealand

2021 ◽  
Author(s):  
◽  
Timothy James Stubbs
Keyword(s):  
New Zealand ◽  
Qualitative Data ◽  
Negative Impact ◽  
Local Level ◽  
Ethnically Diverse ◽  
Geographic Area ◽  
Regulatory Regime ◽  
Ministry Of Education ◽  
Lower Decile ◽  
The Impact

<p>A number of New Zealand studies have identified a relationship between enrolment regulations and school enrolments, in particular drawing attention to the negative impact that the abandonment of ‘home zones’ in 1991 have had on many lower decile and ethnically diverse schools. The progress of a group of secondary schools within a geographic area in New Zealand from before the introduction of Tomorrow’s Schools in 1989 up to 2009 is tracked using quantitative data from the Ministry of Education, New Zealand Qualifications Authority and Statistics New Zealand combined with qualitative data from interviews with those who were principals during the period. This mixed-methods approach shows that both enrolment numbers and academic achievement in three of the four schools fell and then rose almost simultaneously with the removal in 1991 and then reinstatement in 2000 of geographic home zones. The ethnic and socioeconomic polarisation that resulted from the earlier change, however, has not reversed. The quantitative and qualitative data together provide clear evidence that geographic home zones provide a level of stability and security in the provision of education at a local level that is not matched by the alternative regulatory regime that operated in the 1990s.</p>

scholarly journals Environmental assessment of the estimated dredging volumes on the Ob River

2021 ◽  
Vol 937 (2) ◽  
pp. 022042
Author(s):  
Y Bik ◽  
M Buchelnikov ◽  
V Kofeeva
Keyword(s):  
Damage Assessment ◽  
Large Scale ◽  
Negative Impact ◽  
Large River ◽  
Assessment Method ◽  
River Channel ◽  
Environmental Load ◽  
Novosibirsk Reservoir ◽  
Advantages And Disadvantages ◽  
The Impact

Abstract The object of the study is the impact of dredging in the Ob riverbed on individual components of the environment, in particular, ichthyofauna. The volumes of transit and capital dredging in the river channel on the crossing sections that are difficult for navigation have been determined and substantiated. To calculate the damage, a method to determine the loss of ichthyofauna was used, taking into account the death of benthic and planktonic organisms in turbidity plumes and on the bottom areas subjected to development by dredgers and buried under dumped fills. It has been established that the greatest losses of ichthyomass will occur in the sections of the Upper Ob (up to the Novosibirsk reservoir) and the Middle Ob (up to the mouth of the Tom River), which is explained by the presence of numerous crossovers that impede navigation and require constant dredging. In the Lower Ob, the negative impact on benthos, plankton and ichthyofauna will be insignificant due to the small number of small crossovers. The volumes of dredging in the fairway required to maintain guaranteed depths and dimensions have a certain environmental load, the level of which is not critical for the ecosystems of a large river. However, when creating large-scale capital bypass channels, it can increase sharply in certain years. By reducing the load, a stable shipping lane can be created and the frequency of dredging operations at each of the crossover sections can be reduced. The advantages and disadvantages of the used damage assessment method are noted.

scholarly journals Assessment of the impact of the Odra river water levels on groundwater levels in Rzeczyca region

2012 ◽  
Vol 34 (2) ◽  
pp. 3-17 ◽  
Author(s):  
Mieczysław Chalfen ◽  
Beata Głuchowska ◽  
Leszek Pływaczyk
Keyword(s):  
River Channel ◽  
Groundwater Table ◽  
Water Levels ◽  
Primary Role ◽  
Flood Wave ◽  
Wave Impact ◽  
Groundwater Levels ◽  
Odra River ◽  
The Impact ◽  
Flood Waves

Abstract Groundwater table levels in a river valley depend, among other factors, on meteorological and hydrogeological conditions, land use and water levels in watercourses. The primary role of a watercourse is to collect surface and groundwater, and it becomes an infiltrating watercourse at high water levels. Changes in groundwater levels and the range of these changes depend chiefly on the shape, height and duration of the flood wave in the river channel. The assessment of flood wave impact on groundwater was based on long-term measurements of groundwater levels in the Odra valley and observations of water levels in the river channel. Simulations were performed with the use of in-house software FIZ (Filtracja i Zanieczyszczenia; Filtration and Contamination), designed for modelling unsteady water flows within a fully saturated zone. A two-dimensional model with two spatial variables was employed. The process of groundwater flow through a porous medium, non-homogeneous in terms of water permeability, was described with Boussinesq equation. The equation was solved with the use of finite element method. The model was applied to assess groundwater level fluctuations in the Odra valley in the context of actual flood waves on the river. Variations in groundwater table in the valley were analysed in relation to selected actual flood water levels in the Odra in 2001-2003 and 2010. The period from 2001 to 2003 was used to verify the model. A satisfactory agreement between the calculated and the measured values was obtained. Based on simulation calculations, it was proved that flood waves observed in 2010 caused a rise in groundwater table levels in a belt of approximately 1000 metres from the watercourses. It was calculated that at the end of hydrological year 2009/2010, the highest growths, of up to 0.80 m, were observed on piezometers located close to the Odra river channel. The passage of several flood waves on the Odra caused an increase of subsurface retention by 3.0% compared to the initial state.

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