An individual-based model (IBM) to simulate the movement of a single fish through a vertical slot fishway has been developed. The turbulent water flow in the fishway was first obtained using CFD-software. Trajectories of live fish measured by Rodrigues et al. (2011) were superimposed on several different parameters characterising the flow, such as the turbulent kinetic energy (TKE). The correlations between these hydrodynamic parameters and the measured trajectories were examined and TKE was identified as the single most important stimulus. To mimic positive rheotaxis, the mean velocity was adopted as a secondary agent. The new Lagrangian IBM-model was combined with the Eulerian CFD-model to an Eulerian-Lagrangian Agent Method. This ELAM approach was used to compute the trajectory of a virtual fish. The simulated trajectories were in good agreement with their measured counterparts in the same fishway. Both the preferred direct route and the alternative longer route through an active pool were faithfully reproduced.

Various methods have been proposed to define the rainfall thresholds for the landslide prediction. Once the appropriate threshold is determined, it remains the same regardless of the antecedent soil moisture conditions. However, given the important role of the antecedent soil moisture in the initiation of landslides, it is considered if the rainfall threshold level varies according to the antecedent soil moisture conditions, the prediction performance will be improved. Therefore, in this study we propose a probabilistic threshold to integrate antecedent soil moisture conditions with rainfall thresholds. In order to take into account the conditions with landslides and without landslides, the Bayesian analysis is applied to estimate the landslide occurrence probability given the various combinations of two factors: the antecedent soil moisture and the severity of the recent rainfall event. These combinations are then divided into conditions that are likely to trigger landslides and those unlikely to trigger landslides by comparing their probabilities with a critical value. In this way, the probabilistic threshold is determined. Here the soil moisture is estimated using the distributed hydrological model, and the severity of the rainfall event is characterized by the cumulated event rainfall-rainfall duration (ED) thresholds with different exceedance probabilities. The proposed approach was applied to a sub-region of the Emilia-Romagna region in northern Italy. The results show that the probabilistic threshold has a better prediction performance than the ED rainfall threshold, especially in terms of reducing false alarms. This study provides an effective approach to improve the prediction capability of the ED rainfall threshold, benefiting its application in the landslide prediction.

Three Gorges Reservoir (TGR) is one of the largest man-made lakes in the world. Since the impoundment in 2003, however, algal blooms have been often observed in the tributary embayments. To control the algal blooms, a thorough understanding of the hydrodynamics (e.g., flow regime, velocity gradient, and velocity magnitude and direction) in the tributary embayments is particularly important. Using a calibrated three-dimensional hydrodynamic model, we carried out a hydrodynamic analysis of a typical tributary embayment (i.e., Xiangxi Bay) with emphasis on the longitudinal patterns. The results show distinct longitudinal gradients of hydrodynamics in the study area, which can be generally characterized as four zones: riverine, intermediate, lacustrine, and mainstream influenced zones. Compared with the typical longitudinal zonation for a pure reservoir, there is an additional mainstream influenced zone near the mouth due to the strong effects of TGR mainstream. The blooms are prone to occur in the intermediate and lacustrine zones; however, the hydrodynamic conditions of riverine and mainstream influence zones are not propitious for the formation of algal blooms. This finding helps to diagnose the sensitive areas for algal bloom occurrence.

This study developed an IBM (individual-based model) to model fish movement trajectories integrating hydraulic stimulus variables (turbulent kinetic energy (TKE), velocity (V) and strain rate (SR)) to which fish responded, and the rules for individual fish movement. The fish movement trajectories of the target fish, silver carp (Hypophthalmichthys molitrix), were applied to model fish trajectories in a 1% vertical slot fishway at a discharge of 13.5 L/s. Agreement between measured and simulated trajectories implied the plausibility of the movement rules, which illustrated that the fish movement trajectories model has the preliminary ability to track individual fish trajectories for this fishway.2 of 16 etc.). However, these models do not incorporate individual fish movement behavior with hydraulic parameters. The main challenge in modeling fish movement is linking these parameters. The hydraulic information of the fishway is regarded as a stimulus, which is the Eulerian framework, while the response of a fish to a stimulus is an individual-based framework, which can add individuals' behavior and track their movement. One advantage of the individual-based framework is its relevance to internal states, such as environmental conditions or individual heterogeneity [17][18][19][20]. Therefore, an individual-based model (IBM) approach can be applied to model fish movement trajectories in the fishway. Goodwin et al. (2006) [21] developed a model called ELAM (Eulerian-Lagrangian-agent method) using an IBM approach to model fish movement paths at a hydropower dam forebay. Later, Gao et al. (2016) [12] established an Eulerian-Lagrange fish movement model of a fishway. However, the model only considered turbulent kinetic energy (TKE) as a hydraulic stimulus factor. Validation and calibration of a model principally depends on experimental data. Therefore, it is important to consider a more refined model.Before using the IBM approach, one theory was based on the assumption that the response of fish in the experimental fishway was the same [12]. That means the physiological indices were constant, even then the physiological indices may change after a response has been made. If so, the above assumption implied that a fish swam with similar/ average velocity in all the pools in the model.Black carp (Mylopharyngodon piceus), grass carp (Ctenopharyngodon idella), silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis), herein called Asian carps, are the most commercially important freshwater fish species in China, especially in the Yangtze River basin. Asian carps are typical potamodromous fish and have typical migratory activities in spawning and nursery periods [8]. Most research has focused on the swimming performance of carps [8], and little is known about how the fish respond to hydraulic stimulus variables in fishways. The commonly used hydraulic parameters include flow velocity and turbulence [22,23]. It has been well recognized that the slots of fishways change the spatial distribution of th...

Water and mass exchange between rivers and lakes are key processes that maintain the health of the ecology of river-lake systems. Alteration to river-lake interactions have great impacts on water and mass balances. Naturally connected to the middle Yangtze River are the Poyang Lake and Dongting Lake, which are the largest and the second largest freshwater lakes in China. The operation of the Three Gorges Dam (TGD) in the upper Yangtze River was found to have substantial impacts on the middle Yangtze river-lake system. In the past decade, unusual seasonal dryness was evident in the two lakes. Considerable deviations in lake water quality and wetland ecosystem were also detected. In order to explore and distinguish the causal factors influencing the river-lake system, the Ministry of Sciences and Technology (China) launched a research project in 2012, the National Basic Research Program of China (973 Program) (2012CB417000). This article provides an overview of advances in this research, including the evolution of the river-lake interactions, the impacts of the TGD, and the influences on lake hydrology, water quality, and ecosystem. The 20 papers in this issue deliver part of the research outcomes of this project.

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Water release operation is crucial for water quality in large reservoirs such as Three Gorges Reservoir (TGR), because it determines the hydrodynamics and hence the self-purification capability. As algal blooms were often observed in some tributary bays of TGR during the release periods, high frequency field observations were carried out in a typical eutrophic tributary bay (Xiangxi River) from February 9 to May 10, 2009. In this paper we assess the hydrodynamic behaviour, density stratification, and trophic status in this bay, respectively using a series of observations for flow, physical, chemical and biological parameters . Then, we analyze the effects of reservoir release operations on algal blooms using correlation analysis method. An empirical prognosis is concluded for the likelihood of algal bloom occurrence as a function of daily fluctuation of water level (DFWL) and water temperature. Our results indicate that during the release period, the algal bloom occurrences are closely tied to the DFWL in that if the ratio of DFWL to total water depth ranges from 10×10 4 to 0, the possibility of algal blooms may reach up to 70%, and if the ratio is less than 10×10 4 , then that risk can be significantly reduced to less than 10%. This paper finally suggests that a wave-type water release operation should be beneficial in reducing bloom frequencies in the tributary water bodies, which is helpful for TGR water quality management, especially for the water release operation optimization.Three Gorges Reservoir, Xiangxi River, water release operation, algal bloom, water quality, wave-type operation