Showing papers on "River engineering published in 2017"

Proof‐of‐concept for low‐cost and non‐contact synoptic airborne river flow measurements

Abstract: This article presents an example for an image-based method to determine a small rivers’ surface velocity field, bathymetry, and its flow discharge derived thereof. While common river measurement techniques typically need to be in contact with the waterbody, at least to measure transects of water depths, the new approach is completely without direct contact to water. The scenery is recorded by an off-the-shelf action camera mounted to a low-cost quadcopter. During the analysis, image frames are orthorectified and georeferenced by an approach that combines structure from motion and multiview stereo algorithms. Particle image velocimetry based on tracer particles present in the river is utilized to compute flow velocities. Instantaneous surface flow velocity fields are used to compute the mean velocity field as well as to derive water depth estimates by turbulence metrics. The latter provide a basis to verify the bathymetry gained from the reconstructed subaqueous three-dimensional scenery. Finally, flow discharge is estimated based on the above findings. The new method will expand the scientific knowledge on river flows for diverse disciplines such as hydrology, biology, and river engineering. Due to the low cost of the measurement instrumentation being deployed, it has the potential to be applied by a broad user group.

Tracking River Flows from Space

Abstract: Satellite observations, combined with algorithms borrowed from river engineering, could fill large gaps in our knowledge of global river flows where field data are lacking.

Two-dimensional numerical modelling of sediment and chemical constituent transport within the lower reaches of the Athabasca River.

Abstract: Flows and transport of sediment and associated chemical constituents within the lower reaches of the Athabasca River between Fort McMurray and Embarrass Airport are investigated using a two-dimensional (2D) numerical model called Environmental Fluid Dynamics Code (EFDC). The river reach is characterized by complex geometry, including vegetated islands, alternating sand bars and an unpredictable thalweg. The models were setup and validated using available observed data in the region before using them to estimate the levels of cohesive sediment and a select set of chemical constituents, consisting of polycyclic aromatic hydrocarbons (PAHs) and metals, within the river system. Different flow scenarios were considered, and the results show that a large proportion of the cohesive sediment that gets deposited within the study domain originates from the main stem upstream inflow boundary, although Ells River may also contribute substantially during peak flow events. The floodplain, back channels and islands in the river system are found to be the major areas of concern for deposition of sediment and associated chemical constituents. Adsorbed chemical constituents also tend to be greater in the main channel water column, which has higher levels of total suspended sediments, compared to in the flood plain. Moreover, the levels of chemical constituents leaving the river system are found to depend very much on the corresponding river bed concentration levels, resulting in higher outflows with increases in their concentration in the bed sediment.

Flow resistance and hydraulic geometry in contrasting reaches of a bedrock channel

Abstract: Assumptions about flow resistance in bedrock channels have to be made for mechanistic modeling of river incision, paleoflood estimation, flood routing, and river engineering. Field data on bedrock flow resistance are very limited and calculations generally use standard alluvial-river assumptions such as a fixed value of Manning's n. To help inform future work we measured how depth, velocity and flow resistance vary with discharge in four short reaches of a small bedrock channel, one with an entirely rock bed and the others with 20%-70% sediment cover, and in the alluvial channel immediately upstream. As discharge and submergence increase in each of the partly or fully alluvial reaches there is a rapid increase in velocity and a strong decline in both n and the Darcy-Weisbach friction factor f. The bare-rock reach follows a similar trend from low to medium discharge but has increasing resistance at higher discharges because of the macro-roughness of its rock walls. Flow resistance at a given discharge differs considerably between reaches and is highest where the partial sediment cover is coarsest and most extensive. Apart from the effect of rough rock walls, the flow resistance trends are qualitatively consistent with logarithmic and variable-power equations and with non-dimensional hydraulic geometry, but quantitative agreement using sediment D84 as the roughness height is imperfect.

Green approaches in river engineering - supporting implementation of Green Infrastructure

Abstract: Working together with natural systems, which are powered by a diversity of life within them, provides a range of benefits to society, ranging from carbon storage, clean water and air to reduction of climate change impacts and protection against floods and other environmental hazards. This realisation has led to the concept of Green Infrastructure (GI): a network of natural and semi-natural features that intersperses and connects villages, towns and cities. Rivers are part of this green network, which has the potential to provide higher resilience and cost-effectiveness as well as more social and environmental benefits than conventional infrastructure. This document focuses on river engineering (which is concerned with river works) and therefore, we consider the river or watercourse as a natural or semi-natural corridor or infrastructure element. In this context, GI approaches are those that promote the conservation or restoration of the natural (green) character of our rivers. These approaches are fundamental to improving the water quality, morphology and ecosystems of rivers as well as contributing to an overall strategy to help people and communities adapt to the impacts of climate change.

Predicting the sequent depth ratio of a B-F hydraulic jump on a river-bed rock chute

Abstract: Rock chutes are widely used to control erosion of river beds because of their high energy loss, low environmental impact, simple construction and low cost. They typically include a negatively slope...

Design Development and Field Application of RCC Jack Jetty and Trail Dykes for River Training

Abstract: While river training structures are important tools to provide solutions to river engineering problems, conventional structures can be expensive and can create adverse environmental impacts. There is a need to develop affordable permeable river training structures. Jack jetties have been in use in the USA for various purposes, although there was no scientific methodology to support design of the structures when used for river training works. Therefore, laboratory studies have been carried out to develop this design methodology, which was verified by field-testing. Trail dykes were also tested in a similar fashion. Both types of structures show promise for use as inexpensive river engineering works.

Emerging Methodologies for Turbulence Characterization in River Dynamics Study

Abstract: River engineering study consists of large variation in time and spatial scales. Timescale of river varies from years to second, and, similarly, the variation of spatial scales is from kilometre to millimetre. Spatial scales can be divided into river basin scale and hydraulic scale, and temporal scale can be divided into hydrological, hydraulic and turbulence. Each spatio-temporal scale has fixed contextual uses. In general, turbulence plays the most key role with respect to the influences that rivers have on their channels and beds. Turbulent flows are characterized by asymmetrical patterns, irregular behaviour and the existence of various spatio-temporal scales. To extract better turbulence events and flow structure using point velocity measurements (Eulerian approach) in river, we are proposing generalized three-dimensional octant events instead of conventional two-dimensional quadrant events. Beyond that, we characterize the transitional probability of octant event occurrence in the case of unsteady flow condition. In the field, there is the assumption of steadiness of the flow under high unsteady conditions. Basically, river discharges and all the associated processes are physically unsteady, and river channel flows are typically non-uniform. In this chapter we are mainly discussing the new emerging methodological aspects to characterize the river turbulence using state-of-the-art technology. In this chapter, some of the major issues and developments linked with river dynamics and turbulence study have also been discussed with two case studies. The case studies have been presented and discussed using experimental data and their interpretation in light of river dynamics. The study has significant importance because the turbulent motion is the natural state of river engineering problems.

Hydrological effects of the hydraulic structures constructed in the valley of the River Little Vistula in Poland from the mid-18th century to the present

Abstract: This study of the hydraulic structures constructed in the River Little Vistula (Mala Wisla) valley covers its western reach from the village of Strumien (Schwartzwasser) to the mouth of the River Przemsza. Its purpose was to assess the impact of these structures on changes in the conditions of runoff formation within the valley from the mid-18th century to the present. Historical materials (maps, sketches and plans) collected in the State Archives in Opole and Katowice were used in the study. Analyses of Austrian plane-table maps from the years 1763–1764 and 1861–1862 (1:28 800 scale) and of Prussian maps from the years 1827–1828 and 1881–1883 (1:25 000 scale) were also conducted. As a result of the study, the type and rate of hydraulic works were determined along with the techniques and methods used when constructing these structures in the 18th and 19th centuries. It was found that during the last 260 years, the main channel of the River Little Vistula moved within the meandering zone. Within the area of the Zarzecze and Mala Wisla settlements, a “new” River Vistula channel was formed during the flood in 1736, which shifted ca. 0.5–1.0 km to the south. The hydraulic structures which were constructed, mainly levees, caused water levels to rise excessively in the area during high water stages and the swollen waters often causing the levees to cave in, or to breach them. The river engineering work which was conducted also affected the formation of runoff in the valley of the River Little Vistula. It has been found that both anastomosis processes and river meandering were inhibited. In some channel reaches, temporal activation of deep erosion processes as well as channel shallowing were observed. Deep erosion reached up to 2 metres and channel shallowing up to 1 metre. These processes took place during river engineering work and the River Vistula bed took around a dozen years to stabilise following the completion of the work.

Probabilistic safety evaluation of a river bridge substructure against floods

Abstract: Many factors affect the safety of a reinforced concrete river bridge, and some of these factors might have significant uncertainty that should be evaluated. This study focuses on a system reliability analysis of a reinforced concrete bridge, which is the most common type of river bridge in Taiwan. Specifically, non-linear behaviours of core/cover concrete and steel reinforcement in the substructure of a bridge are considered. Uncertainties of stream surface elevation, water velocity, local scour depth, soil property and record-to-record variations are included in the probabilistic model. The aforementioned parameters of six river geometries are incorporated into a Hydrologic Engineering Center-river analysis system (HEC-RAS) model to assess their impacts on the bridge safety. The effect of river geometry has not been studied thoroughly. Results shown here indicate that it plays an important role. Adopting Bayesian theory to consider the record-to-record uncertainty by combining historic and HEC simulation...

Analysis of the effect of short dikes on flow hydraulics and sedimentation in Karun River within urban boundaries of Ahwaz

Abstract: Identification, analysis and prediction of the erosion and sedimentation or the increase and decrease in river bed level are among the most complex and yet up-to-date topics of deposit hydraulics and river engineering. If cross structures in rivers and canals are also to be considered the complexity of flow pattern and deposit transfer increases. In this research using the one-dimensional mathematical model HEC-RAS 4.1 the effect of short dikes on flow hydraulic and the trend of sedimentation and erosion in the Karun River were simulated and analyzed within the boundaries of Ahwaz City. The area introduced into the model started from the Ghir dike to Khoramshahr. Moreover, the Mollathani, Farsiat and Ahwaz hydrometric stations were used as the upper limit, lower limit and calibration limit of the model, respectively. The flow was assumed to be quasi-unsteady and based on the existing knowledge of different methods and experiences with the methods in other studies the Toffaleti method was used to solve the deposit equations. The model was prepared and applied in the following four states: without dike and with dikes 0.7, 1.2 and 1.7 m above the average level in the desired areas. Finally, results of the model applied with and without short dikes revealed that the short dikes and dikes 1.2 m above the average floor level of modeled areas were significantly ineffective under hydraulic conditions and morphological changes. Moreover, the majority of changes in the river bed and all the morphological changes, in general, were the result of other factors. Dikes with heights of 1.7 m above the average floor level significantly caused sedimentation in the upstream and affected the hydraulics of flow.

Geomorphology and Hydrology of 2014 Kelantan Flood

Abstract: The December 2014 Kelantan floods were the worst on records in terms of depth and extent of inundation as well as damages to properties and infrastructure. Therefore, a comprehensive and integrated flood monitoring, forecasting, and warning methods are needed to allow planning of responses to potential future floods by the government and related environmental agencies. The Kelantan state has been affected by floods every year in modern times. Meteorological and hydrological records have shown that the Kelantan River often overflows during the NE monsoon season. This preliminary due to heavy rainfall, causing an almost annual recurrence of floods to the state between the end of November till March (DID 2014/2015). Excessive land use changes such as deforestation (i.e. logging and clearing for agriculture) and increased precipitation intensity and frequency are the possible causes for this change. However, little research has been conducted to understand and quantify how these factors contribute to changes in the magnitude and frequency of flooding in the area. This research will attempt to integrate geomorphological, hydrological and meteorological data and evaluate their impact on the recurrence of the annual flood in Kelantan. The main objective of this research project is to study all factors that contribute to the flooding events in Kelantan and propose a strategy to minimize the impact of future flooding events. The methodology planned to achieve the specific objectives for this research comprises of: (i) analysis of satellite imagery and remote sensing images to map general geomorphology of Kelantan; (ii) analysis of medium-term climatic data (temperature and rainfall data) to evaluate the impact of hydrology on the flooding events. From the Digital Elevation Model (DEM) map, the geomorphology of Kelantan can be clearly seen where at the southern part of Kelantan (Gua Musang and Kuala Krai area) is more hilly and highly elevated, and toward northern parts of Kelantan which cover area Kota Bharu, Pasir Puteh, Tumpat, Bachok, Pasir Mas, Tanah Merah, the elevation more gentle since it near to coastal region area. This lowland geomorphology allows becoming an escape route for the water and later transported to the nearby delta before escaping to the sea which is the main basin. The fluvial geomorphology at the Kelantan Delta area is meandering since it located at downstream area. More than that, the urbanization aggressively increases at floodplain area and also forces the flooding to occur. Meanwhile the data could also identify the water flow from rivers in southern upstream highland region (Lebir River and Galas River) to Kelantan Delta area. The existence of bottle necks in southern parts of Kelantan area such as Dabong, Manek Urai, and Kuala Krai can be identified under the image whereby the river flows through a narrow or obstructed section from catchment area. It could assist to decelerate the water flow to Kelantan River in the event of flood and long duration rainfall. However, river-bottle neck will accelerate the rise of flood level in southern upstream highland area. The Kelantan River Basin experiences the northeast (NE) monsoon climate which is responsible for the heavy rains that hits the east coast of the Peninsular Malaysia, such as the state of Kelantan, Terengganu, and Pahang, and frequently cause overflow of riverbank flooding. The flooding that occurred in 2014/2015 was caused by heavy rains brought by the northeast monsoon winds blown from November to March. Floods in 2014 showed the total rainfall in rural areas is more dense (>60 mm) than the coastal areas (DID 2014/2015). Heavy rain began to fall in the Gunung Gagau on December 16, 2014, in which a total of 6648.0 mm in the coastal areas have been covered by 6 new stations in Kota Bharu, Tumpat, Pasir Mas, Machang, Bachok, and Pasir Puteh while in rural areas of 7373.0 mm, which also includes 6 stations, namely Dabong, Jeli, Gua Musang, Laloh, Aring and Gunung Gagau for the month of December. Continuous heavy rains until early January as recorded stations involved. Based on the preliminary geomorphological and hydrological analysis, DEM and satellite data, future development plan of residential areas, reforestation and plantation, town planning, and river engineering projects for Kelantan state should incorporate the details of the studies. Several flood management strategies are proposed here. In the southern upstream areas, desilting of the river system needs to be carried out. The deforestation projects should be stopped in the areas which forms large rainfall catchment areas. The logging activities should be limited to non-catchment, intermediate, and lowland areas. In the lowland, Kelantan delta areas, urbanization and river engineering projects need to be re-evaluated. Construction of large monsoon drains may help to distribute the floodwaters more efficiently.