Showing papers on "River engineering published in 2013"

Man-induced regime shifts in small estuaries—II: a comparison of rivers

Abstract: This is Part II of two papers on man-induced regime shifts in small, narrow, and converging estuaries, with focus on the interaction between effective hydraulic drag, fine sediment import, and tidal amplification, induced by river engineering works, e.g., narrowing and deepening. Paper I describes a simple linear analytical model for the tidal movement in narrow, converging estuaries and a conceptual model on the response of tidal rivers to river engineering works. It is argued that such engineering works may set in motion a snowball effect bringing the river into an alternative steady state. Part II analyses the historic development in tidal range in four rivers, e.g., the Elbe, Ems, Loire, and Scheldt, all in northwest Europe; data are available for many decades, up to a century. We use the analytical model derived in Part I, showing that the effective hydraulic drag in the Ems and Loire has decreased considerably over time, as anticipated in Part I. We did not find evidence that the Upper Sea Scheldt is close to its tipping point towards hyperturbid conditions, but risks have been identified. In the Elbe, tidal reflections against the profound step in bed level around Hamburg seem to have affected the tidal evolution in the last decades. It is emphasized that the conceptual picture sketched in these papers is still hypothetical and needs to be validated, for instance through hind-cast modeling of the evolution of these rivers. This will not be an easy task, as historical data for a proper calibration of the models required are scarce.

Man-induced regime shifts in small estuaries—I: theory

Abstract: This is Part I of two papers on man-induced regime shifts in small, narrow, and converging estuaries, with focus on the interaction between effective hydraulic drag, fine sediment import, and tidal amplification, induced by river engineering works, e.g., narrowing and deepening. In this part, a simple linear analytical model is derived, solving the linearized shallow water equations in exponentially converging tidal rivers. Distinguishing reflecting and non-reflecting conditions, a non-dimensional dispersion equation is derived which yields the real and imaginary wave numbers as a function of the estuarine convergence number and effective hydraulic drag. The estuarine convergence number describes the major geometrical features of a tidal river, e.g., intertidal area, convergence length, and water depth. This model is used in Part II analyzing the historical development of the tide in four rivers. Part I also presents a conceptual model on the response of tidal rivers to narrowing and deepening. It is argued that, upon the loss of intertidal area, flood-dominant conditions prevail, upon which fine sediments are pumped into the river, reducing its effective hydraulic drag. Then a snowball effect may be initiated, bringing the river into a hyper-turbid state. This state is self-maintaining because of entrainment processes, and favorable from an energetic point of view, and therefore highly stable. We may refer to an alternative steady state.

The hydro-morphological index of diversity: a tool for describing habitat heterogeneity in river engineering projects

Abstract: We present a new hydro-morphological index of diversity (HMID), a tool aimed for use in river engineering projects and firstly developed at gravel-bed streams in Switzerland, but intended for a broader use. We carried out field work with extensive hydraulic and geomorphic data collection, conducted correlation analysis with hydro-morphological vari- ables, formulated the HMID, and analyzed the corre- lation between HMID and a visual habitat assessment method. The HMID is calculated by means of the coefficient of variation of the hydraulic variables flow velocity and water depth, which have been demon- strated to sufficiently represent the hydro-morpholog- ical heterogeneity of alpine gravel-bed stream reaches. Based on numerical modeling, the HMID can be calculated easily for a comparison of different alter- natives in river engineering projects and thus achieves predictive power for design decisions. HMID can be applied at a reach-related scale in engineering pro- grams involving geomorphic measures that aim at the enhancement of habitat heterogeneity of a stream. However, the application of HMID has to be inte- grated with evaluations of the long-term streambed evolvements that are considered at a catchment scale and strongly related to the sediment regime of the stream under study.

Streambank Erosion and River Width Adjustment

Abstract: Many different methods are available to describe river channel morphology and morphological adjustments for river engineering purposes. Available approaches range from equations that predict the regime or graded morphology of equilibrium channels to mathematical models that simulate channel changes in time and space. Most mathematical models, however, neglect time-dependent channel-width adjustments and do not simulate processes of bank erosion or deposition. Although changes in channel depth caused by aggradation or degradation of the riverbed can be simulated, changes in width cannot. For prediction of the behavior of natural streams, this is a significant limitation, because channel morphology usually changes with time, and adjustment of both width and depth (in addition to changes in planform, roughness, and other variables) is the rule rather than the exception (Leopold et al. 1964; Simon and Thorne 1996). As a result, our ability to model and predict changes in river morphology and their engineering impacts is limited. This is unfortunate, because width adjustments can seriously impact floodplain dwellers, riparian ecosystems, and bridge crossings, bank protection works, and other riverside structures through bank erosion, bank accretion, or bankline abandonment of the active river channel. In this chapter, methods for assessing processes of bank erosion and river width adjustment are reviewed. Most of this chapter was originally written by the ASCE Task Committee on Hydraulics, Bank Mechanics, and Modeling of River Width Adjustment (1998a; 1998b), which was chaired by Dr. Colin R. Thorne.

Flood Protection: Highlighting an Investment Trap Between Built and Natural Capital†

Abstract: We present a simulation model developed to communicate a potential investment trap associated with using man-made river engineering to protect built infrastructure. A small system dynamics model in STELLA™ was constructed following a collaborative model-building process to increase understanding among stakeholders of the role natural capital plays in wealth creation. We set out to explore the dynamic relationship between investing tax revenue in natural capital (specifically forested headwaters and low land wetlands) rather than built capital (specifically stopbanks) for flood protection in the Manawatū watershed, New Zealand. Significant investment is currently required to maintain and enhance river engineering infrastructure and keep pace with changes in the river's geomorphology. Viewed from a systems perspective, we suggest diversion of a proportion of existing funding into restoration of forested headwaters on steep slopes and restoration of functioning wetlands on floodplains could in the longer term provide an effective approach to flood protection. Co-benefits of increased natural capital include the ecosystem services nutrient cycling, sediment capture, water purification, biodiversity, pollination, and cultural and recreational values. Overcoming an investment trap requires a longer term perspective. This simple model consisting of two feedback loops and two delays aims to contribute to an ongoing stakeholder dialogue concerning the Manawatū River watershed in New Zealand.

Discharge coefficient of a rectangular labyrinth weir

Abstract: A rectangular labyrinth weir has a very good flood release capacity as well as strong economical and structural advantages. In this study, combined analytical and experimental investigations were u...

Analysis of the Impacts of Dikes on Flood Stages in the Middle Mississippi River

Abstract: The US Army Corps of Engineers has constructed numerous river engineering structures in and along the Middle Mississippi River. River training and bank stabilization measures include pile dikes, stone dikes, bendway weirs, chevrons, and revetments. Concerns have long been voiced about the effects of these structures on flood stages. Recent debate concerning the scientific basis for these concerns has been invigorated by specific gauge analysis that appears to show a rising trend in flood stages over the past 150 years. This paper attempts to advance the debate by providing an objective review of the specific gauge analysis technique that explains how the method should be performed and the results interpreted; identifies strengths and limitations; examines the uncertainties associated with application to the Middle Mississippi River given the available data; and reassesses the conclusions that can and cannot reasonably be drawn regarding the impacts of dikes and levees on flood stages, based on spe...

Impact of dams, dam removal and dam-related river engineering structures on sediment connectivity and channel morphology of the Fugnitz and the Kaja Rivers

Abstract: In terms of changing flow and sediment regimes of rivers, dams are often regarded as the most dominant form of human impact on fluvial systems. Dams can decrease the flux of water and sediments leading to channel changes such as upstream aggradation and downstream degradation. The opposite effects occur when dams are removed. Channel degradation often requires further intervention in terms of river bed and bank protection works. The situation evolves more complex in river systems that are impacted by a series of dams due to feedback processes between the different system compartments.A number of studies have recently investigated geomorphic systems using connectivity approaches to improve the understanding of geomorphic system response to change. This paper presents a case study investigating the impact of dam construction, dam removal and dam-related river bed and bank protection measures on the sediment connectivity and channel morphology of the Fugnitz and the Kaja Rivers using a combination of DEM analyses, field surveys and landscape evolution modelling. For both river systems the results revealed low sediment connectivity accompanied by a fine river bed sediment facies in river sections upstream of active dams and of removed dams with protection measures. Contrarily, high sediment connectivity which was accompanied by a coarse river bed sediment facies was observed in river sections either located downstream of active dams or of removed dams with upstream protection. In terms of channel changes, significant channel degradation was examined at locations downstream of active dams and of removed dams. Channel bed and bank protection measures prevent erosion and channel slope recovery after dam removal. Landscape evolution modeling revealed a complex geomorphic response to dam construction and dam removal as sediment output rates and therefore geomorphic processes have been shown to act in a non-linear manner. These insights are deemed to have major implications for river management and conservation, as quality and state of riverine habitats are determined by channel morphology and river bed sediment composition.

Past and predicted future changes in the land cover of the upper mississippi river floodplain, usa

Abstract: This study provides one historical and two alternative future contexts for evaluating land cover modifications within the Upper Mississippi River (UMR) floodplain. Given previously documented changes in land use, river engineering, restoration efforts and hydro-climatic changes within the UMR basin and floodplain, we wanted to know which of these changes are the most important determinants of current and projected future floodplain land cover. We used Geographic Information System data covering approximately 37% of the UMR floodplain (3232 km2) for ca 1890 (pre-lock and dam) and three contemporary periods (1975, 1989 and 2000) across which river restoration actions have increased and hydro-climatic changes have occurred. We further developed two 50-year future scenarios from the spatially dependent land cover transitions that occurred from 1975 to 1989 (scenario A) and from 1989 to 2000 (scenario B) using Markov models. Land cover composition of the UMR did not change significantly from 1975 to 2000, indicating that current land cover continues to reflect historical modifications that support agricultural production and commercial navigation despite some floodplain restoration efforts and variation in river discharge. Projected future land cover composition based on scenario A was not significantly different from the land cover for 1975, 1989 or 2000 but was different from the land cover of scenario B, which was also different from all other periods. Scenario B forecasts transition of some forest and marsh habitat to open water by the year 2050 for some portions of the northern river and projects that some agricultural lands will transition to open water in the southern portion of the river. Future floodplain management and restoration planning efforts in the UMR should consider the potential consequences of continued shifts in hydro-climatic conditions that may occur as a result of climate change and the potential effects on floodplain land cover. Published 2011. This article is a U.S. Government work and is in the public domain in the USA.

Shelter effect evaluation of the willow works bank protection method: a case study for Beinan River Reach 2009 Typhoon Morakot event

Abstract: Beinan River is one of the rivers with perfect ecology and full of culture values in Taiwan. It is also the habitat of many freshwater fish species. Besides, the local agricultural crops are famous for exports due to its natural environment, too. Therefore, for these reasons, the hydraulic associations set a series of ecological constructions for waterfowl and fish species around the agricultural water intake areas. For instance, the river bank protection designs the willow works and the fascine mattress by the 8th River Management Bureau for ecological function and hydraulic protection in flood season. In this study, the concept and the methodology of the fish protection habitat predicted model is revealed. Beside the simulated hydraulic models, the indoor experiments of the willow works were conducted to gain the roughness. The hydraulic methods by one- and two-dimensional are used for simulation in flood season (2009 Typhoon Morakot event) to bring up the habitat protection locations. The experimental results showed that for the Manning’s n of the willow works is between 0.1322 and 0.1333 which corresponding height to the real field is about 144–176 cm. Therefore, it provided the revetment roughness data during the shelter effect evaluation. From the velocity distribution, it proves that the vegetated revetment can reduce the flow velocity. Fulfilling previous two main steps in experiment and model calibration, the shelter effect is made good going on discussion. Most of references indicated that the vegetated revetment provided suitable and excellent habitat condition, but rare of them provided the proof in data. This study presents that the WUA is 34,939.94 m2 and PUA is 1.53% at the highest discharge of Typhoon Morakot. The whole protection concepts, simulation methods, and results can be utilized for future plan and design of river engineering.

Sediment Transport Processes

Abstract: Sediment transport processes have recently gained importance in river engineering, torrent control and reservoir management due to an increasing discrepancy between a surplus of sediments in upstream and a deficit in downstream river sections (Habersack et al. 2010b). This development leads to problems in flood protection (channel change), river engineering (e.g. riverbed degradation), hydropower generation (e.g. reservoir sedimentation) and the ecological status of running waters (e.g. loss of instream structures).

Estimation of Suspended Sediment Load Using Genetic Expression Programming

Abstract: Accurate estimation of suspended sediment load carried by a natural river is important for river engineering and water resources projects. In recent years, using smart systems to increase accuracy of estimating of river sediments are common. In this study were used the Genetic Expression Programming (GEP) in order to estimate suspended sediment load in Sistan River. Root mean square error (RMSE), mean bias error (MBE) and determination coefficient (R 2 ) statistics are used for evaluating the accuracy of the models. GEP is found that scenario 3 with four function and RMSE=0, MBE=2.69×10 -4 , R2=1 in train period and RMSE=0, MBE=2.4×10 -4 and R 2 =1 in test period are superior in estimating suspended sediment load as the best accurate model. The modeling approach presented in this paper can be potentially used to reduce the frequency of costly operations for sediment measurement where hydrological data is readily available.Also estimation of suspended sediment load using other AI methods such as Particle Swarm Optimization, Tabu Search in Sistan River are suggested.

Discharge regimes, tides and morphometry in the Mahakam delta channel network

Abstract: The Mahakam delta in Indonesia constitutes a text book example of a mixed tide and fluvial dominated delta. Understanding the factors that control the division of water and sediment discharge over channels in the delta is relevant in the contexts of geology, ecology and river engineering. In the Mahakam river and its delta, the tide interacts with the river outflow. River-tide interaction exerts an influence on the discharge regimes and on the division of water and sediment at the bifurcations in the delta. Bifurcations control the dispersal of sediments that eventually govern the shape and evolution of the delta. In this thesis, spatial and temporal aspects of delta evolution are shown to be reflected in scaling relations between the geometric properties of delta channels and the discharge conveyed by the channels, which is known as downstream hydraulic geometry (HG). Downstream HG relations as established in this research, feature a transition from the landward part to the seaward part of the delta characterized by a clear break in scaling behavior. The variation of river discharge throughout the network is largely impacted by river-tide interaction, which is captured by downstream HG relations.

13.15 Hazardous Processes: Flooding

Abstract: This chapter demonstrates the value of fluvial geomorphology in flood hazard studies and identifies the links with hydrology and engineering to provide a holistic approach for flood hazard assessment. Applied flood geomorphology deals with the extension of flood records into the past from flood sediments, hydromorphological mapping of channel and floodplain landforms, and analysis and quantification of morphodynamic processes such as channel migration and sediment transport in response to individual or sequential flooding. General and specific approaches on the study of flood hazards are considered for three fluvial environments: mountain streams, alluvial fans, and alluvial rivers. Geomorphologic and stratigraphic signatures of floods are critical to understanding the linkages among climate change, environmental change, flood hydrology, and the geomorphic development of fluvial landscapes.

The study of flood hydraulics before the building of Maroon Dam by HEC-RAS, Maskingam and Muskingum - Cunge method

Abstract: Routing of rivers which flow through the important areas is from the important river engineering measures. In this research, flood routing in the Maroon River has been studied bases on hydrometric stations between Behbahan and Chamnezam. Todays, numerical computer methods are developed for the Cent and Nante equations. The HEC-RAS software and Muskingum and Muskingum - corners methods are used for this work. HEC-RAS model with solving of dynamic equations motion simulates unsteady flow in the form of onedimensional flow in open channels. After calibration and testing, the results of these methods were compared.So, the HEC-RAS model results considerably better match with the observational data.

The development of abandoned side-channels: ecological implications and future perspectives

Abstract: River–floodplain habitats have been strongly affected by damming and river regulation, which have initiated longterm trends towards terrestrialization and fragmentation. We studied the terrestrialization processes in the Donau-Auen National Park over the last 80 years by means of airborne images. The aggradation of side-arms is an ongoing process. The main parameters affecting the terrestrialization process are river bed degradation, the connectivity to the main river and the size and shape of the water bodies. As smaller water bodies silt up faster than larger ones, the process of terrestrialization speeds up. From a nature conservation point of view, inhabitants of small temporary water bodies such as amphibians and molluscs are particularly affected. First results of river engineering projects to re-connect abandoned side-channels show that the trend may be impeded. But for a sustainable solution of the problem the stop of river bed degradation is indispensable.

Study on Evolution of River Bed and Flood Prediction at Lanzhou Section of Yellow River

Abstract: Yellow River through Lanzhou city, so flood prevention is a very important for Lanzhou city. On the basis of the hydrologic data from 1951 to 2011 year, using river engineering model experiment, design flows and design flood hydrograph of Lanzhou section of Yellow River was simulated. On the basis of the hydrologic data from 1951 to 2011 year, evolution of river bed at Lanzhou section of Yellow River was analyzed. Sedimentation has been increasing slowly since 60 years. By the river engineering model experiments, a river-dredging plan, river width is planned 300 m, had been put forwarded. And the design flood level and water surface profile in different design flood (5600 m3/s,6500 m3/s,7920 m3/s,8350 m3/s) of Lanzhou section are gotten. It is forecast that occurrence of deluge is possible.

A first calibration of the one-dimensional model of the Nhat Le River basin

Abstract: This thesis provides a first draft of a one-dimensional model of the Nhat Le River Basin. The model is almost ready for use due to the short period of time. The model requires at least an adequate calibration before using. With this thesis a first start has been made. Eventually, with the model, the probability of water levels in the Nhat Le River (Quang Binh Province, Vietnam) can be estimated, which are needed for calculation of the embankments height along the Nhat Le River. In the beginning of the project this thesis had another research question. But at the start of the assignment the provided documents did not suffice due to missing and/or wrong drawings, wrong calculations and lack on key input. Some information should be bought and the newly presented documents never came or came too late. Although it didn’t work out as planned, a lot about the Vietnamese culture and organizational structure has been learned. The new research question was originated around the calculations of the newly proposed embankments along the Nhat Le River. The provided documents calculated the levels of the embankments with the old regulations. These calculations were based on the old Vietnamese regulations, which are not sufficient anymore. The new regulations require a one-dimensional model to estimate the highest water level in the river with different frequency floods. Due to the short period of time, the model is not yet ready for implementation. However some recommendations for optimization and further use of the model are given. The one-dimensional model is made with the computer software HEC-RAS. The Water Resources University Hanoi provided the required data, including boundary conditions and cross-sections. Data in Vietnam is not easy to obtain. It took a long time to get the proper information and support from different parties. Although, this assignment is a good first start of modelling the one-dimensional model. In order to establish the final one-dimensional model the following steps should be conducted: - More cross-sections along the Dia Giang and Kien Giang river branches in order to determine the correct slopes of the river branches; - Development of the Dia Giang and Kien Giang river branches with wider cross-sections, including floodplains and storage areas; - Calibration of the Dia Giang river branch; - Calibration of the whole Nhat Le river Branch; - Implementation of the My Trung sluice in the Kien Giang river branch; - Data of different frequency floods in the Dia Giang and Kien Giang river branch to estimate the different high water levels in the main of Nhat Le river in different scenarios; - Clearness about the positions of the newly constructed embankments.

Sea level variation from a remote river in the Gulf of Paria, Trinidad

Abstract: Short-term sea level variability is investigated by analytical methods to ascertain whether there is a link between peak tidal residuals in the Gulf of Paria (GoP), Trinidad, and peak river outflow from the Orinoco on the Venezuelan mainland. Analysis of tidal data suggests that although the Orinoco delta fronts the Atlantic ocean, significant volumes of this river runoff enter into the GoP and play a role in seasonal sea level variation on the western coastline of the southernmost Caribbean island of Trinidad. The indications from various statistical analyses including harmonic, spectral and time series analyses of tide gauge data are that mean seasonal variations in water level in the north of the GoP exhibit a positive temporal correlation between the tidal residuals and the peak river discharge associated with the Orinoco's seasonal cycle. The maximal de-tided residuals are strongly correlated with maximal values of the river runoff, as well as the discharge trend, with the residual values at initial ...