The Application of Hydraulic and Sediment Transport Models in Fluvial Geomorphology

After publishing the famous “Fluvial Processes in Geomorphology” in the early 1960s, the work of Luna Leopold, Gordon Wolman, and John Miller became a key for opening the door to understanding rivers and streams. They first illustrated the problem to geomorphologists and geographers. Later, Chang, in his “Fluvial Processes in River Engineering”, provided a basis for engineers, showing this group of professionals how to deal with rivers and how to understand them. Since then, more informative studies have been published. Many of the authors started to combine fluvial geomorphology knowledge and river engineering needs, such as “Tools in Fluvial Geomorphology” by G. Mathias Kondolf and Hervé Piégay, or focused more on river engineering tasks, such as “Stream Restoration in Dynamic Fluvial Systems: Scientific Approaches” by Andrew Simon, Sean Bennett, and Janine Castro. Finally, Luna Leopold summarized river and stream morphologies in the beautiful “A view of the river”. It appears that we continue to explore this subject in the right direction. We better understand rivers and streams, and as engineers and fluvial geomorphologists, we can establish tools to help bring rivers alive. However, there is still a hunger for more scientific tools that we could use to further understand rivers and to support the development of healthy streams and rivers with high biodiversity in the present world, which has started to face water scarcity

A Bridge Rehabilitation Strategy Based on the Analysis of a Dataset of Bridge Inspections in Co. Cork

Ageing highway structures present a challenge throughout the developed world. The introduction of bridge management systems (BMS) allows bridge owners to assess the condition of their bridge stock and formulate bridge rehabilitation strategies under the constraints of limited budgets and resources. This research presents a decision-support system for bridge owners in the selection of the best strategy for bridge rehabilitation on a highway network. The basis of the research is an available dataset of 1,367 bridge inspection records for County Cork that has been prepared to the Eirspan BMS inspection standard and which includes bridge structure condition ratings and rehabilitation costs. There has been no previous research on a regional Irish bridge stock of this magnitude. Research objectives are the consolidation of the dataset into a usable format, the review of previous research and the formulation of a methodology for the development of a network wide bridge rehabilitation strategy model. A procedure proposed by previous research on the prioritisation of theoretical bridge rehabilitation projects on the Chilean road network has been built upon. Statistical analysis of both recent rehabilitation projects in County Cork and of a survey of experts has led to the formulation of rehabilitation project prioritisation indices. The application of these derived indices allows the forecasting and calculation of funding requirements for network wide improvements. A review of the functional life expectancies of bridges has been undertaken. A deterioration rate which predicts the annual disimprovement in condition rating of each bridge has been calculated using statistical regression analysis and provides a basis for the estimation of investment requirements for an overarching rehabilitation strategy. An economic assessment of four rehabilitation intervention strategies has been undertaken using the Net Present Worth method. A system performance method developed in this research and which uses efficiency and effectiveness indicators taken from UK, New Zealand and French practice has determined that the range of annual investment amounts equivalent to 0.27% and 1% respectively of the bridge stock replacement cost are required to achieve full bridge network rehabilitation and provide a minimum 85 year service life for all structures. A benchmarking comparison with reported international practice has confirmed the applicability of the developed methodology

Prediction and mitigation of scour and scour damage to Vermont bridges

Over 300 Vermont bridges were damaged in the 2011 Tropical Storm Irene and many experienced significant scour. Successfully mitigating bridge scour in future flooding events depends on our ability to reliably estimate scour potential, design safe and economical foundation elements accounting for scour potential, design effective scour prevention and countermeasures, and design reliable and economically feasible monitoring systems, which served as the motivation for this study. This project sought to leverage data on existing Vermont bridges and case studies of bridge scour damage, and integrate available information from stream geomorphology to aid in prediction of bridge scour vulnerability. Tropical Storm Irene’s impact on Vermont bridges was used as a case study, providing damage information on a wide range of bridges throughout the State. Multiple data sources were combined in an effort to include data, which represents the complex, interconnected processes of stream stability and bridge scour, then identify and incorporate feature that would be useful in a probabilistic model to predict bridge susceptibility to scour damage. The research also sought to identify features that could be included in inspections and into a scour rating system that are capable of assessing network-level scour vulnerability of bridges more holistically. This research also sought to review existing scour countermeasures and scour monitoring technologies available in the literature and examine efficacy of new, indirect scour countermeasures and passive scour monitoring techniques. The specific objectives of this research were to: (1) review the literature and identify methods/technologies that are adaptable to Vermont; (2) analyze Tropical Storm Irene bridge damage information and observations by collecting and geo-referencing all available bridge records and stream geomorphic assessment data into a comprehensive database for identifying features that best represent bridge scour damage; (3) conduct watershed analysis on all bridges, including creation of stream power data to assess if watershed stream power improves the prediction of bridge scour damage; and (4) investigate new scour countermeasures and monitoring technologies, and provide recommendations on implementations

Modeliranje razdiobe napetosti smicanja u prirodnim malim vodotocima metodama mekog računanja

In this study, artificial neural networks (ANNs) and adaptive neuro-fuzzy inference system (ANFIS) were used to estimate shear stress distribution in streams. The methods were applied to the 145 field data gauged from four different sites on the Sarimsakli and Sosun streams in Turkey. The accuracy of the applied models was compared with the multiple-linear regression (MLR). The results showed that the ANNs and ANFIS models performed better than the MLR model in modeling shear stress distribution. The root mean square errors (RMSE) and mean absolute errors (MAE) of the MLR model were reduced by 47% and 50% using ANFIS model in estimating shear stress distribution in the test period, respectively. It is found that the best ANFIS model with RMSE of 3.85, MAE of 2.85 and determination coefficient (R2) of 0.921 in test period is superior to the MLR model with RMSE of 7.30, MAE of 5.75 and R2 of 0.794 in estimation of shear stress distribution, respectively.U ovoj studiji su za procjenu razdiobe napetosti smicanja u vodotocima korištene umjetne neuronske mreže (ANNs) i prilagodljivi neizraziti sustav zaključivanja (ANFIS). Metode su primijenjene na 145 nizova podataka prikupljenih na četiri različite postaje na vodotocima Sarimsakli i Sosun u Turskoj. Točnost primijenjenih modela uspoređena je s točnošću modela višestruke linearne regresije (MLR). Rezultati su pokazali da su oba modela (ANNs i ANFIS) bili bolji u modeliranju raspodjele napetosti smicanja od MLR modela. Pri korištenju ANFIS modela za procjenu raspodjele napetosti smicanja u testnom razdoblju srednje kvadratne pogreške (RMSE) i srednje apsolutne pogreške (MAE) su u odnosu na MLR model bile smanjene za 47%, odnosno 50%. Utvrđeno je da se za testno razdoblje najbolji ANFIS model, s RMSE = 3.85, MAE = 2.85 i koeficijentom određenosti R2 = 0.921, pokazao superiornim u procjeni napetosti smicanja u odnosu na MLR model, s RMSE = 7.30, MAE = 5.75 i R2 = 0.794

Soil-Water Conservation, Erosion, and Landslide

The predicted climate change is likely to cause extreme storm events and, subsequently, catastrophic disasters, including soil erosion, debris and landslide formation, loss of life, etc. In the decade from 1976, natural disasters affected less than a billion lives. These numbers have surged in the last decade alone. It is said that natural disasters have affected over 3 billion lives, killed on average 750,000 people, and cost more than 600 billion US dollars. Of these numbers, a greater proportion are due to sediment-related disasters, and these numbers are an indication of the amount of work still to be done in the field of soil erosion, conservation, and landslides. Scientists, engineers, and planners are all under immense pressure to develop and improve existing scientific tools to model erosion and landslides and, in the process, better conserve the soil. Therefore, the purpose of this Special Issue is to improve our knowledge on the processes and mechanics of soil erosion and landslides. In turn, these will be crucial in developing the right tools and models for soil and water conservation, disaster mitigation, and early warning systems

Calibrating saturated conductivity and soil cohesion in rainfall-triggered landslides in the Langhe area (1994)

In this work we have analyzed a “cold case”, i.e., the prolonged rainfall and flood event occurred in the Piedmont region (Northern Italy) in November 1994, causing several hundred of shallow landslides. The research aim is to put some focus on the possibility to calibrate soil parameters by means of the combined use of a simple hydrological model (Rosso et al. 2006) and post-event geotechnical surveys. For this purpose, a database of geometries and soil characteristics for 238 observed landslides has been used. To address the calibration of the cohesion and hydraulic conductivity parameters, the safety factor expression from the Limit Equilibrium Analysis has been targeted to assume a maximum value of 1 for all the slopes made unstable by the actual (measured) rainfall. Significant reduction of the cohesion parameter was observed after calibration, suggesting caution in the use of literature values, typically obtained on mechanically undisturbed soil sample

A gravel-sand bifurcation:a simple model and the stability of the equilibrium states

A river bifurcation, can be found in, for instance, a river delta, in braided or anabranching reaches, and in manmade side channels in restored river reaches. Depending on the partitioning of water and sediment over the bifurcating branches, the bifurcation develops toward (a) a stable state with two downstream branches or (b) a state in which the water discharge in one of the branches continues to increase at the expense of the other branch (Wang et al., 1995). This may lead to excessive deposition in the latter branch that eventually silts up. For navigation, flood safety, and river restoration purposes, it is important to assess and develop tools to predict such long-term behavior of the bifurcation. A first and highly schematized one-dimensional model describing (the development towards) the equilibrium states of two bifurcating branches was developed by Wang et al (1995). The use of a one-dimensional model implies the need for a nodal point relation that describes the partitioning of sediment over the bifurcating branches. Wang et al (1995) introduce a nodal point relation as a function of the partitioning of the water discharge. They simplify their nodal point relation to the following form: s*=q*k , where s* denotes the ratio of the sediment discharges per unit width in the bifurcating branches, q* denotes the ratio of the water discharges per unit width in the bifurcating branches, and k is a constant. The Wang et al. (1995) model is limited to conditions with unisize sediment and application of the Engelund & Hansen (1967) sediment transport relation. They assume the same constant base level for the two bifurcating branches, and constant water and sediment discharges in the upstream channel. A mathematical stability analysis is conducted to predict the stability of the equilibrium states. Depending on the exponent k they find a stable equilibrium state with two downstream branches or a stable state with one branch only (i.e. the other branch has silted up). Here we extend the Wang et al. (1995) model to conditions with gravel and sand and study the stability of the equilibrium states