AbstractThe valley plain has the characteristics of both mountainous hills and plains, with special terrain conditions and frequent floods. In order to improve the drainage capacity of the river valley plain, this article takes the Bihu Plain in the Oujiang River Basin as an example, uses MIKE11 one-dimensional hydrodynamic software to establish a mathematical model of the river network, analyzed the flood and drainage in the river valley plain, studied the impact of Traditional Flood control mode and Flood control mode based on sponge cities concept in regional drainage, analyzes the advantages and disadvantages of different flood control strategies in practical cases, and provides solutions for regional flood control, Summarized and clarified the relationship between urban flood control and watershed flood control.
Abstract The Biforcation Structure which is located at the branching of the Moilong and Mansahang Rivers, Banggai District functions as a weir at the Moilong Free Intake and distributes water proportionally to its downstream, so that it can function as a flood control structure and at the same time supply water to the Mansahang (Toili) Weir. The flood incident on June 18, 2019 resulted in the collapse of the Biforcation structure so that it submerged seven villages in Moilong District. The restructure of the Biforcation is very much needed by the community to provide a sense of security from the destructive power of water and irrigation water supply. To prepare for the development, a research was conducted with the aim of knowing the economic feasibility of the construction of the Biforcation and the flood conrol structure. Prior to construction, a study was conducted with the aim of determining the economic feasibility of the Biforcation construction and the flood control structure. The research method used analytical methods, quantitative approaches, and conducted interviews with the relevant agencies. The data obtained are reviewed and analyzed using several assumptions of loan interest rates, and loan times. Calculation of financial analysis using the calculation of Net Present Value (NPV) and Benefit Cost Ratio (BCR). The results of the study concluded that the construction ldingof Biforcation structures and flood control structures was feasible. The results of the Net Present Value (NV) are positive at 10% and 12% interest rates. Interest 10%, benefit Cost Ratio (BCR) 6,536 (12 years), BCR 5,675 (10 years), BCR 4,633 (8 years). Interest 12%, Benefit Cost Ratio (BCR) 5,798 (12 years), Benefit Cost Ratio (BCR) 5,097 (10 years) Benefit Cost Ratio (BCR) 4,219 (8 years).
Abstract River deltas are complex aggradational systems preserving the history of their evolution in the depositional record. While coastal deltas are extensively studied, little is known about “false delta”, multi-channel systems situated at a certain distance from the sea. The term “false delta” is used here in reference to a system of bifurcating alluvial channels influenced by sea level changes, and variations in discharge and sediment delivery. These interactions resulted in the formation of a multitude of channel planforms, and a “delta-like” fluvial landscape. We present the first study that aims to determine the influence of downstream controls (sea level changes) and upstream controls (discharge and sediment delivery) on the evolution of a “false delta” multi-channel system in the postglacial areas of central Europe. Our study is based on geophysical, geological and remote sensing methods, alongside radiocarbon dating (AMS–accelerator mass spectrometry). We use the example of a “delta-like” system of palaeochannels that connected the Obra and Odra Rivers (central Europe, Poland). The “false delta” formed within an ice-marginal valley by the activity of large-scale meandering channels in the Late Glacial period. Between 13,300 and 11,200 cal. BP, a transition to an anabranching and sinuous planform was caused by the coupled effects of a lowering Baltic Sea level, an increase in flood frequency and in sediment delivery. During this period, bifurcation began conveying 30% of the flow through a former subglacial tunnel to the Warta River. The Holocene evolution of this multi-channel system was driven by the interplay of successive sea level rise and sediment delivery from the middle Obra valley, and former subglacial tunnels. The upstream controls dominated during the last 4400 cal. BP, and were enhanced by mill constructions and deforestation in the last millennium. The false delta “disappeared” in the 18th century owing to a 63% decrease in flows. Based on these findings, we propose a model describing the evolution of “false delta” river systems in postglacial areas of Europe. Three stages of evolution are identified: i) formation by high flows, ii) sustaining the flow through particular branches in conditions of dominating deposition, and iii) discontinuation of the false deltas by hydro technical works. The model can be extrapolated to other areas in postglacial Europe and North America after refinement by further field studies.
Abstract The resettlement evaluation system for the recent flood control projects in the lower Yellow River consists of many economic indicators, social indicators, resource indicators and environmental indicators. Although the design of quantitative indicators is the main one, many of them are still used in order to better reflect the evaluation objectives. Qualitative and fuzzy indicators, traditional methods and means have been difficult to be competent in the comprehensive analysis of multi-factor and multi-level in the production and living system of immigrants. Yaahp software, based on the basic research method of AHP, constructs a hierarchical structure model, and assigns weights and calculations to post-immigration evaluation indicators.
E. I. L. Silva, H. Manthrithilake, Dammika Pitigala
et al.
Environmental flow describes the stream flow (quantity and regime) required to sustain upstream and downstream habitats, riparian vegetation, human livelihoods and wildlife. When natural rivers or tributaries are held back by weirs, anicuts, barrages or dams, for a variety of purposes such as diversion for irrigation, hydropower generation or flood control often the downstream flow requirement is ignored or neglected. Although there is no universally accepted definition, convention or law on environmental flow, it has been now recognized that environmental flow is essential for sustainability of riparian ecosystem and their services, which are essential for our own existence, livelihoods and many more. This paper looks at physical structures constructed across rivers and tributaries in Sri Lanka since ancient times to date (including mini-hydro power stations) with a view to understand whether simple ancient wisdoms are more appropriate than modern structures for nature conservation. There are tangible evidence to defend that the ancient anicuts known as “amuna” surged sufficient water in tributaries and rivers, to sustain the environment than modern engineering works which has created dead river beds immediately downstream in many streams and rivers. DOI: http://dx.doi.org/10.4038/sljas.v19i0.7447 Sri Lanka J. Aquat. Sci. 19 (2014): 3-14
AbstractUncertainty is a key factor to be taken into account in river flood forecasting. Every forecast is subject to several sources of uncertainty. Knowledge on the relative importance of the different sources would be useful to determine the most effective improvement actions to reduce the uncertainty. In this paper, three key uncertainty sources are studied for hydrological flood forecasting in the Belgian case study of the Rivierbeek: model uncertainty, forecasted rainfall uncertainty and uncertainty in the initial conditions. A non‐parametric data‐based approach is used to quantify the total uncertainty in the forecasts. By resimulating in the model historical forecasts with optimal initial conditions and observed rainfall, the uncertainty generated by each of the key sources could be identified. In order to reduce the model uncertainty, which was primarily identified as the most important source of uncertainty, a step‐wise physically based calibration technique was suggested. After recalibration of the model with this technique, a significant reduction of the contribution of the model uncertainty to the total forecast uncertainty could be achieved. Further improvement of the initial conditions, identified as the second most important uncertainty source for short lead times, could be obtained by applying data assimilation. Both uncertainty reduction techniques combined led to a reduction of the total forecast uncertainty with 30% to 40%.
The transport of sediment by flowing water commands great interest in connection with the control of floods, land reclamation, and the construction of harbours and coast protection works. A distinction can be drawn between littoral drift in rivers and in the sea. The sediment transportation in rivers has been investigated by several authors, e.g. Shields, Meyer Peter, Kalinske, and Einstein, see (16) pp„ 769-83*+. Einstein's latest theories have given reliable results in practice (9). As pointed out by Einstein (7), there cannot be much difference, physically, between transportation of sediment in rivers and longshore drift at sea shores, apart from the littoral zone with its extremely complex conditions. In the attempt to understand the complex problem of sea shores the practice so far has been to split them up into several reaches and investigate them separately. This work has given a number of results of practical interest in connection with littoral drift and coastal protection technology, see (2), (3), (5)» (6), (11), (13), and (16). According to Einstein, Johnson and Chien (8) there exist two types of sediment load, one that bears a certain relationship with the discharge (bed-material load), and the other which does not (wash load). The result of flume study indicates that the transport rate of wash load, just as that of the bed-material load, can be calculated according to the Einstein bed-load function (9), if the instantaneous bed composition is known. On the other hand, the bedmaterial load is equally available'in the entire bed, but only the surface bed layer contains any significant amount of wash-load material. Any change of flow or of sediment supply may immediately change the composition of the wash-load material in the bed. The bed composition as determined from the instantaneous condition of the channel has no lasting significance so far as the wash load is concerned, and this makes the prediction of the wash-load rate from.the bed-load function impossible. The following deals with a mode of bed-load transportation which, as far as can be seen, takes place in large "waves" or humps. Introductorily are mentioned investigations made in the United States on migrating sand bars and sand waves in rivers, and investigations in Holland on migrating sand bars on the bottom of the sea. The major part of the paper deal with migrating sand humps along the North Sea coast of the peninsula of Jutland, Denmark, see Fig. 3.
E. Wendland, Eduardo Mario Mendiondo, Regina Mambelli Barros
Since 2002, the Municipality of São Carlos, SP, Brazil (PMSC) has developed a Master Plan, thereby establishing guidelines for flood prevention and control. However, the present scenario shows expensive, on-site antiflood works in São Carlos. Due to the absence of previous watershed planning, the area around the Municipal Market (MMSC) is continuously threatened by overspill flood events in the floodplain of Gregorio River. The purpose of this work is to provide information to support decision-making in the Master Plan using structural and nonstructural measures, such as flood zoning of risk-prone RBRH — Revista Brasileira de Recursos Hídricos Volume 12 n.2 Abr/Jun 2007, 05-17 17 areas. Critical flood events that produced inundation at MMSC were identified by interviewing people living in these urban risk-areas. Those critical events were simulated using integrated rainfall-runoff transformation and wave routing with the IPHS-1 concentrated model and the distributed model, HIDRORAS, whose results were compared. Input data were calibrated from monitored flood events. Uncertainties inherent to each model were identified. Results depict initial yardsticks for flood mapping to be included in the Master Plan agenda. Structural flood control measures consisting of a retention basin without excavation and non-structural measures such as increased infiltration area, were investigated. It was concluded that for urban watersheds like the Gregório basin, changes in the flow patterns due to urban streets are better represented by the distributed model, HIDRORAS. However, a number of uncertainties still remain for this model, such as the influence of saturated hydraulic conductivity of the soil. Key-words: Floods, urban drainage, flood-prone areas.