Showing papers on "River engineering published in 2018"

Climatic control of Mississippi River flood hazard amplified by river engineering

Abstract: A suite of river discharge, tree-ring, sedimentary and climate data shows that the Mississippi’s flood magnitude has risen by about twenty per cent over the past half-century, largely owing to engineering works. Instrumental records of river discharge do not go far enough back in time to place recent flood activity in a longer-term context, making it difficult to understand how climate variability and human activity might have affected flooding. Now, Samuel Munoz and colleagues reconstruct the past flood frequency of the Mississippi River from a compilation of river-discharge, tree-ring, sedimentary and climate data. The results show that the magnitude of the 100-year flood has gone up by about 20 per cent over the past 500 years. Climate cycles account for most of the variability in flooding on multidecadal timescales, but engineering works account for about three-quarters of the long-term increase. Over the past century, many of the world’s major rivers have been modified for the purposes of flood mitigation, power generation and commercial navigation1. Engineering modifications to the Mississippi River system have altered the river’s sediment levels and channel morphology2, but the influence of these modifications on flood hazard is debated3,4,5. Detecting and attributing changes in river discharge is challenging because instrumental streamflow records are often too short to evaluate the range of natural hydrological variability before the establishment of flood mitigation infrastructure. Here we show that multi-decadal trends of flood hazard on the lower Mississippi River are strongly modulated by dynamical modes of climate variability, particularly the El Nino–Southern Oscillation and the Atlantic Multidecadal Oscillation, but that the artificial channelization (confinement to a straightened channel) has greatly amplified flood magnitudes over the past century. Our results, based on a multi-proxy reconstruction of flood frequency and magnitude spanning the past 500 years, reveal that the magnitude of the 100-year flood (a flood with a 1 per cent chance of being exceeded in any year) has increased by 20 per cent over those five centuries, with about 75 per cent of this increase attributed to river engineering. We conclude that the interaction of human alterations to the Mississippi River system with dynamical modes of climate variability has elevated the current flood hazard to levels that are unprecedented within the past five centuries.

Insights into bedload transport processes of a large regulated gravel-bed river

Abstract: A comprehensive monitoring program focusing on bedload transport behaviour was conducted at a large gravel-bed river. Innovative monitoring strategies were developed during five years of preconstruction observations accompanying a restoration project. A bedload basket sampler was used to perform 55 cross-sectional measurements, which cover the entire water discharge spectrum from a 200-year flood event in 2013 to a rare low flow event. The monitoring activities provide essential knowledge regarding bedload transport processes in large rivers. We have identified the initiation of motion under low flow conditions and a decrease in the rate of bedload discharge with increasing water discharge around bankfull conditions. Bedload flux strongly increases again during high flood events when the entire inundation area is flooded. No bedload hysteresis was observed. The effective discharge for bedload transport was determined to be near mean flow conditions, which is therefore at a lower flow discharge than expected. A numerical sediment transport model was able to reproduce the measured sediment transport patterns. The unique dataset enables the characterisation of bedload transport patterns in a large and regulated gravel-bed river, evaluation of modern river engineering measures on the Danube, and, as a pilot project has recently been under construction, is able to address ongoing river bed incision, unsatisfying ecological conditions for the adjacent national park and insufficient water depths for inland navigation.

Road-stream crossing an in-stream intervention to alter channel morphology of headwater streams: case study

Abstract: Basin-scale hydrological response on the geomorphology of lowland headwater streams is often neglected during the in-stream engineering works in rural India. Standard protocols to construct road-stream crossing (RSC) reveals that crossing structures at headwater streams of the Kunur River Basin in eastern India are inadequate to maintain longitudinal continuity in channel hydraulics as well as morphology. The role of crossing type (pipe, box, and small bridge) and catchment land cover are also considered for site-wise variation in channel deformation. The detailed geomorphic survey with 10 cross-sections (5 in the upstream and 5 in the downstream of crossing structure) and 1 longitudinal profile from each of the 10 sample sites were used to run one-dimensional flow modelling in Hydrologic Engineering Center’s River Analysis System, statistical analysis of channel morphometry, manning and rational methods for discharge estimation, and hydroengineering equations. Result shows that in comparison with...

Hydrodynamic parameters in a flood impacted boulder block ramp: Krzczonówka mountain stream, Polish Carpathians

Abstract: Boulder block ramps are river engineering structures used to stabilise river beds. Block ramps provide a semi-natural and aesthetically pleasing solution to certain river engineering problems in mountain streams. When constructing block ramps, one can use the dissipative behaviour of large macro-roughness elements randomly placed on the river bed to enhance fish migration in an upstream direction thus, in this sense, meeting the requirements of the EU Water Framework Directive. Block ramps are often designed and constructed to replace damaged drop hydraulic structures in the channels of mountain streams. This paper investigates the resilience of a particular block ramp placed in the Krzczonowka stream (Polish Carpathians) in terms of the engineering design function and its durability against damaging. A hydrodynamic analysis of a block ramp is presented before and after a flood event that changed the configuration of the blocks. The semi-natural unstructured hydraulic structure was built on the Krzczonowka stream to protect gas pipes which are located beneath it. As a result of several floods, the boulder block chute described in this paper was damaged, and some boulders were dislodged and transported downstream. Our post-flood investigations of bathymetry and velocity revealed that even damaged boulder blocks, removed from the chute and displaced downstream of the structure, still provide significant energy dissipation of the flowing water. The novel of our paper is for the first time showing very detailed analysis of unstructured block ramp hydrodynamics parameters done in the field. Also the novel finding of our investigations shows that before and after the flood event the unstructured block ramp structure, is still fish friendly in terms of hydrodynamics.

Mathematical Modeling of Ice Dynamics as a Decision Support Tool in River Engineering

Abstract: The prediction of winter flooding is a complicated task since it is affected by many meteorological and hydraulic factors Typically, information on river ice conditions is based on historical observations, which are usually incomplete Recently, data have been supplemented by information extracted from satellite images All the above mentioned factors provide a good background of the characteristics of ice processes, but are not sufficient for a detailed analysis of river ice, which is highly dynamic and has a local extent The main aim of this paper is to show the possibility of the prediction of ice jams in a river using a mathematical model The case of the Odra River was used here Within the Lower and Middle Odra River, the most significant flood risk, in winter conditions, is posed by ice jams created when movable ice is stopped by existing obstacles such as shallow areas in the riverbed, the narrowing of the riverbed, and other obstacles caused as a result of sudden changes of the river current, backwater from sea waters, and north winds, which contribute to the creation of ice jams This in turn causes the damming of water and flooding of adjacent areas The DynaRICE model was implemented at two locations along the Odra River, previously selected as ice-prone areas Also, a thermal simulation of ice cover formation on Lake Dąbie was shown with variable discharge The results of numerical simulations showed a high risk of ice jamming on the Odra River, created within one day of ice moving downstream The prediction of the place and timing, as well as the extent, of the ice jam is impossible without the application of a robust mathematical model

Experimental Analysis of River Evolution with Riparian Vegetation

Abstract: Studying the effects of different riparian vegetation densities on river channel evolution has practical significance for predicting the river channel evolution process during flood periods and ecological river engineering via the artificial planting of vegetation. In this study, we simulated the formation and evolution processes of river channels under different riparian vegetation coverage rates in laboratory conditions. The riparian vegetation coverage rates were set as 0, 20, 40 and 80%, on unilateral and bilateral sides of a river channel bank. Given the same flow and sediment boundary conditions, experiments were carried out in a 4 × 1.5 m tank. This paper focuses on the comparative analysis of main stream stability characteristics, bend migration characteristics, river bank erosion characteristics and sediment transport intensity. The results showed that different amounts of riparian vegetation cover created different characteristics of river channel evolution and strongly impacted the stability of the banks and bed. River channel evolution under unilateral vegetation cover is often accompanied by alternate development of the main stream and branch, and the bend stability under unilateral riverbank vegetation cover is worse than under bilateral cover. For a bilateral vegetation-covered river channel, a narrow and deep regime channel more easily forms with a higher vegetation coverage rate; the curvature of the stable river bend is smaller, but the adaptation period of the flow to the river channel bed increases. Planting of riparian vegetation played a positive role in the erosion resistibility, which effectively reduced the lateral migration rate of the riverbank. The higher the vegetation coverage rate, the greater the flow shear stress needed for the same river channel migration rate. While effectively reducing lateral migration, riparian vegetation coverage increased the vertical migration and led to a trend in overall scour depth along the riverbank.

The influence of geology on the morphologic response of the Lower Mississippi River

Abstract: The Mississippi River is heavily influenced by structural and geologic controls involving regional uplifts, faults, clay plugs, outcrops of Tertiary clay, and Pleistocene gravel in its bed and tributaries. Degradation is continuing to migrate upstream on the Lower Mississippi River (LMR) and has presently moved as far upstream as the Hickman, KY, area. Left unchecked, this degradation could continue to advance on the LMR and ultimately migrate upstream into the Ohio and Middle Mississippi River systems. This degradation would not only adversely affect the stability and environmental features in the main stem of the river but also introduce headcutting into the many tributaries that enter the river in this degradational zone. Detailed studies of the exact role of these features, particularly with respect to retarding or halting long-term degradational processes along the river, have not received much attention. In this study, potential areas where geologic outcrops may influence river morphology are identified, and examples are provided that support the concept that geologic outcrops may be extremely important features that serve as temporary or permanent grade control along the river. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR. MRG&P Report No. 17 iii

Review on Artificial Bending Cutoff and Regulation of Distorted River Bends

Abstract: The distorted river bends often occurs in the lower reaches of the Yellow River, which poses a great threat to the life and property safety of the people in the beach area. It also brings many difficulties to the safe operation and defense of flood discharge and river regulation projects. Scholars at home and abroad have done a lot of research on the abnormal river regime, and have achieved good results by adopting artificial bending and straightening or river engineering regulation measures to control the distorted river bends. After the artificial cutting of Donglu reached the goal of lowering the Tongguan elevation, but the reasonable cutting ratio, cutting section and other conditions should be chosen to achieve successful cutting and good results. In the future, the occurrence mechanism and evolution rule of abnormal river regime should be discussed deeply, and predictive research should be carried out to eliminate or mitigate the harm of abnormal river regime.

Morphological Changes in the Lower Reach of Megech River, Lake Tana Basin, Ethiopia

Abstract: This study examined and identify, map the plan-form changes and to evaluate, investigate and explore the effect and impact or influence of drivers/catchment process induces for the plan-form changes along a 44.43-km stretch of Lower Reach of Megech River, Lake Tana Ethiopia, for the last 30 years by using secondary climate data, catchment characteristics, field observation, key informant interview and Satellite images of the year 1984, 1995, 2000, 2006, 2009 and 2014. For data preparation and analysis, Image analysis software (ERDAS 2014), Arc GIS and Terrain analysis tools were used. Lower reach of Megech River has undergone major plan-form changes for the past 30 years. At a distance about 19.3 km from the Lake, the river abounded the old channel course and shifted from west to east and developed new channel which directly drains to Lake Tana. The sinuosity of Megech River shows an overall increase of 8.2% for the 30-year study period. Generally, the plan form alteration of Megech River at different reach is due to natural and artificial influences. Hence, appropriate river engineering works should be practiced so as to minimize the negative aspects of channel bank retreats.

Protecting River Environment through Proper Management of Material Mining by Matrix Method (Case Study of A'la River in Iran)

Abstract: Regarding the importance of rivers, appropriate management of aggregate mining is of great significance. Mining of river materials has a direct impact on environmental conditions of the river. Today, aggregate mining management represents a crucial topic in river engineering. Often selected based on the pattern of the considered river, matrix method provides a suitable approach to improve the river aggregate mining management. The present research aims at presenting the application of the matrix method in river material mining location evaluation. Given the capabilities of the matrix method for determining potential of mine area and aggregate mining method, this method can be seen as a suitable solution for reducing negative environmental impacts of river material mining. A'la River is one of the most important rivers streaming in Khouzestan Province (Iran), with its sediment load and mining potential being of critical importance. In this research, the reach of A'la River at the intersection of Rood-Zard River and Rahmhormoz diversion dam was studied for aggregate mining and application of matrix method. The main purpose of this work is to study the application of matrix method to A'la River. The results indicate braided pattern of the river and appropriateness of the matrix method. Available volume of aggregate for mining within the mentioned reach of A'la River was estimated as 50,000 m 3 , and scraping method at a maximum depth of 1 m was proposed for mining of the aggregates.

The challenge of restoring dynamics by river engineering: where to find the truth about river flow - in the computer, in the lab or in the field?

Abstract: Rivers are probably the most complex features which we can be found in the environment. They have been and are still the driving force for shaping landscapes and biotopes on our planet. The behavior of river systems is a result of the complex interaction between flow, sediments, morphology and habitats. “Nature is not to be trifled with, she is always true, always earnest, always severe; she is always right, and the faults and errors are always those of man.” (Goethe) Hydraulic engineers responsible for the planning of river training and restoration works as well as scientists doing river research should bear well in mind this quotation from Goethe. Reliable and sustainable protection against floods can only be assured by hydraulic structures that preserve the natural character of a watercourse during flood events which is often difficult to identify. Accordingly, modern river engineering must take a river's natural forces and behavior into account. For example, attempts to straighten a meander that has developed naturally may be dangerous: in extreme flood conditions, if not earlier, the apparently tamed river will recall and reoccupy the space to which it is entitled [1]. “The world is like a river, running along in its bed, this way and that, forming sand bars by chance and then being forced by these to take a different course. Whereas this all proceeds smoothly and easily and gradually, the river engineers have great difficulties when they seek to counteract this natural behavior.” (Goethe)