Showing papers on "River engineering published in 2001"

Channel Restoration Design for Meandering Rivers

Abstract: : A framework for channel restoration design is presented that attempts to bridge the divide between reconnaissance level geomorphological designs at one extreme and numerical modeling of hydrodynamics, sediment transport and morphological change at the other Reestablishing equilibrium between the sediment supply and available transport capacity in the restored reach is the primary objective of the design framework A geomorphic engineering approach is presented, which recognizes that the river is ultimately the best restorer of its natural morphology and should be allowed to participate in its own recovery This is accomplished through designing an approximate channel mould, based on the broad dimensions of the river, and then allowing the river itself to develop the intricate cross-sectional detail and intra-reach morphological features to complete the recovery process Geomorphic engineering provides a practical solution by striking a balance between empirical-statistical and analytical (process-based) methods The range of techniques that comprise the design approach facilitate a realistic solution to the indeterminacy problem and confidence bands applied to typed' morphological equations provide a mechanism through which natural rivers can be used as realistic analogues for channel restoration design By accounting for natural systems variability, the design framework is an appropriate platform for generating restoration design solutions that mimic the natural channel morphologies and environmental attributes in undisturbed systems, while meeting multifunctional goals of channel stability and low maintenance commitments Rather than constructing physical habitats that constitute form without function, geomorphologically, the types and levels of physical habitat diversity that are sustainable in the restored reach are defined by the type of river, the nature of the sediment and flow regimes and the catchment context

Flood enhancement through flood control

Abstract: Flood stages for constant discharge have increased 2–4 m over the past century at numerous locations in the Mississippi River basin. However, no increases are observed on rivers such as the Meramec and the upper Missouri, which have been spared extensive river engineering projects. Flood-stage increases on the middle Mississippi River and lower Missouri River are mostly attributable to channelization.

A geomorphologist's criticism of the engineering approach to channelization of gravel-bed rivers: case study of the Raba River, Polish Carpathians.

Abstract: River engineers use sediment transport formulas to design regulated channels in which the river's ability to transport bedload would remain in equilibrium with the delivery of materials from upstream In gravel-bed rivers, a number of factors distort the simple relationship between particle size and hydraulic parameters at the threshold of sediment motion, inherent in the formulas This may lead to significant errors in predicting the bedload transport rates in such streams and hence to instability of their regulated channels The failure to recognize a nonstationary river regime may also result in unsuccessful channelization Rapid channel incision has followed channelization of the main rivers of the Polish Carpathians in the 20th century A case study of the Raba River shows that incision has resulted from the increase in stream power caused by channelization and the simultaneous reduction in sediment supply due to variations in basin management and a change in flood hydrographs Calculations of bedload transport in the river by the Meyer-Peter and Muller formula are shown to have resulted in unrealistic estimates, perhaps because the different degree of bed armoring in particular cross-sections was neglected It would have been possible to avoid improper channelization if the decreasing trend in sediment load of the Carpathian rivers had been recognized on the basis of geomorphological and sedimentological studies Allowing the rivers to increase their sinuosity, wherever possible without an erosional threat to property and infrastructure, and preventing further in-stream gravel mining are postulated in order to arrest channel incision and reestablish the conditions for water and sediment storage on the floodplains

Wave speed–discharge relationship from cross-section survey

Abstract: This paper tackles a practical problem in flood routing, the estimation of the speed of propagation of the flood wave. It is well known that this propagation speed varies with the discharge in quite a complex manner for natural rivers. The principal innovative step in this paper is the identification of a relatively simple conceptual model of river geometry to obtain two methods for generating realistic wave speeds from a standard river cross-section survey. These are verified against data from two rivers in the UK, showing good agreement with wave speeds deduced from long-term flow records. This work is expected to be of particular value in building forecasting models of ungauged or partially gauged river systems, as it removes the need for long concurrent records to estimate wave speeds.

Ecotones and hydrology: key conditions for fish in large rivers

Abstract: Fish diversity, population dynamics and production of fish depends to a large extent on the compound and often controversial effects of water level fluctuations. To balance their positive and negative effects the structural properties of the river-flood-plain systems are important. Stochasticity of flood pulses control population size. Physical disturbances apparently are of higher significance in controlling fish community structure than biological interactions (River regulation and reduction of shoreline structure enhances the negative effects of flood pulses. Short spates during early summer are apparently most destructive, while strong year classes are linked to higher water levels in spring and lower water levels in summer. Apparently the gradual decline in the population size of characteristic rheophilic species in the larger European river systems is a long-term consequence of the major river regulation schemes in the late 19th century because the buffer capacity of richly structured inshore zones have been diminished. Especially the 0+ stage of fish form excellent indicators for the diversity and function or riparian ecotones, which can be sucessfully applied in river engineering, nature conservation and landscape management.

Morphodynamics of the Mississippi River

Abstract: : The Lower Mississippi River, extending from Cairo, Illinois to the Gulf of Mexico, annually transports approximately 170 million tonnes of sediment. Historically, the quantity and calibre of sediment derived from catchment erosion have been affected by changes in land-use and management. For example, soil erosion increased during the 19th and early 20th centuries due to settlement by Europeans and this may have elevated catchment sediment supply to the Mississippi River, while more recently the supply of sediment from tributaries is known to have decreased markedly as a result of river engineering and management. Specifically, the construction of large dams as part of the Mississippi River and Tributaries (MRT Dardeau and Causey, 1990). However, a case can be made that the bed material load must have increased since the 1940s. This argument is based on analysis of morphological changes observed along the river that have led to an overall increase in slope and available stream power, coupled with the fact that bed material sizes along the river have remained almost constant.

A Hydro-Social Modeling Approach for Flash Flooding Alleviation

Abstract: Extreme floods are essentially natural hazards that occur at a relatively low frequency. Excessive precipitation is, in most cases, the main cause of catastrophic floods. However, anthropogenic factors, such as human occupation of floodways, extensive urbanization, and structural measures to mitigate floods (flood levees and walls, cutting of the river meanders, river training) have modified the natural characteristics of extreme floods [14,18]. Recent catastrophic flood events both in Europe and the USA have shown that human activities and traditional river engineering works may result in an increase in the frequency of extreme floods, of the water stage and, most importantly, of negative economic consequences such as loss of property and human life.