Dam Operation Research Articles

Analysis of Water Supply Capacity of a Sand Dam

A sand dam is an old technology used to trap sand materials and store water in dry riverbeds. Besides the volume of sand stored, the water storage and supply capacity of the sand dam depends principally on material properties including hydraulic conductivity (K) and the specific yield (Sy). In this study, the water supply capacity of a sand dam, applied in South Korea with a modified scheme, was analyzed. Imported sand materials were placed in three layers, and perforated drain pipes were installed to abstract the water to a collection tank. Using a Modular Finite-Difference Groundwater Flow (MODFLOW) model, the drain pipe discharge related to aquifer properties and supply capacity of a sand dam was evaluated. Using the model, the productivity of the sand storage with several cases of inflow conditions was assessed. For the period from 9 March 2020 to 16 May 2022, the results of calculation of water supply for the installation and operation of new sand dam are as follows. Regarding the actual inflow condition, compared to the average water supply of the existing water intake source, the sand dam installation increased water supply by 61.6%, and the sand dam installation showed an effect of improving the water supply by 36.0% for the minimum water supply. The calculated water supply for the condition where the inflow was reduced by 50% showed an effect of improving water supply by over 70% on average due to the installation of the sand dam. The findings would be a benchmark for future expansions of the scheme in related places, and management and maintenance of the system.

Influence of cascade reservoir operation in the Upper Mekong River on the general hydrological regime: A combined data-driven modeling approach

Cross-border impact assessment of cascade reservoir operation on hydrological regimes is a vital prerequisite for the sustainable development and management of transboundary waters. However, assessment based on traditional hydrological modeling for transboundary rivers is limited by the availability of meteorological and hydrological data. In this study, a combined data-driven model (CV-LSTM) was built to simulate natural runoff without dam construction in the Upper Mekong River. Then, the simulated natural runoff was compared against the observation runoff influenced by dam operation to assess the impacts of reservoirs on flood and drought events. The research results are as follows: (1) CV-LSTM improved simulation performance by effectively utilizing spatial information from more extensive and diversified data, and it could overcome the limitation of classic data-driven models in that the spatial heterogeneity of input variables cannot be sufficiently considered. (2) Reservoir operation decreased the annual streamflow of the Upper Mekong River by 1.07% during the 2001–2016. In particular, with the operation of two mega reservoirs (Xiaowan and Nuozadu) after 2008, the annual streamflow decreased by 3.95%. (3) The upstream reservoirs exerted significant runoff regulative effects on the Lower Mekong during 2001–2016. Drought duration and severity significantly decreased at the Chiang Sean hydrological station, flood frequency decreased by 11%, and the mean day of flood occurrence decreased by 30%. This study developed an innovative approach, CV-LSTM, based on open-source spatial information, which could effectively analyze the cross-border impact of cascade reservoir operation. The results provide new insights into the quantitative assessment of the transboundary influence of upstream-downstream runoff change induced by cascade dams in international rivers.

Comprehensive assessment of 20 state-of-the-art multi-objective meta-heuristic algorithms for multi-reservoir system operation

Optimal operation of multi-purpose multi-reservoir dams is a challenging problem for dams’ stakeholders and decision-makers. Optimization algorithms are able to present reliable solutions for such complex problems. This study compared the capability of 20 state-of-the-art robust meta-heuristic algorithms for determining the optimal operating policy of Halilrood multi-reservoir system under the three competing operational objectives of water supply, flood control, and hydropower generation. Before that, the performance of the algorithms in solving two benchmark problems (the Schaffer problem and the MMF1 problem from the CEC suite) was evaluated. Four metrics of generational distance (GD), spacing (S), spread (Δ), and maximum spread (MS) were used to compare the algorithms’ performance in solving the benchmark problems. In addition, four reservoirs performance evaluation indicators of reliability (Rel), resiliency (Res), vulnerability (Vul), and sustainability index (SI) were used to ass the algorithms’ performance in solving the real-case Halilrood problem. The results showed that although the solving capability of each algorithm depends on the nature of the problem, some algorithms were always superior in solving all three problems (2 benchmark problems and one real case). For the Schaffer benchmark problem, the MOAHA algorithm with the performance metrics of (GD = 0.00095, S = 0.58155, Δ = 0.20375, MS = 4.0002) had the best Pareto front in terms of coverage and diversity, and so it was placed at the first rank. In this problem, the MOCryStAl algorithm with (GD = 0.00141, S = 0.48395, Δ = 1.49467, MS = 3.94799) placed at the lowest rank. For the MMF1 problem, the MOMA (GD = 0.00751, S = 0.07516, Δ = 0.29519, MS = 0.99826) followed by the MOAHA (GD = 0.00833, S = 0.07660, Δ = 0.17832, MS = 1.00) had the best performance, respectively, and the MOFA algorithms was the worst. For the Halilrood real-case problem, the MOGWO algorithm (with Rel = 83.41, Res = 67.57, Vul = 22.07 and SI = 76.01) followed by the MOAHA algorithm (Rel = 84.57, Res = 64.71, Vul = 33.60, and SI = 71.41) and the MOMA algorithm (Rel = 79.82, Res = 66.67, Vul = 21.65, and SI = 74.70) obtained the best ranks in terms of reservoir's performance evaluation indicators. They could successfully minimize all three objectives of the total deficit, the flood control and electricity generation indicating the highest performance of these algorithms in the optimization problem. The Pareto front obtained by these algorithms had better distribution and was closer to the origin of coordinates compared to the other utilized algorithms. They could favorably supply the total water demand in the Halilrood basin while increasing the hydropower energy generation up to the power plant capacity at the Jiroft dam. The results of this study can be applied to the optimal operation of any other multi-reservoir system with conflict in water demands.

Evaluation of hydrological connectivity in a river floodplain system and its influence on the vegetation coverage

The river floodplain system is the basis of material and energy exchange between the river and floodplain in a region, and its connectivity is an important basis for water health evaluation and ecological protection. To clarify the effects of hydrological connectivity changes on vegetation, the graph theory method was improved based on ArcGIS and a quantitative evaluation model of river floodplain system hydrological connectivity was established. Taking the Jiahetan river floodplain system in the lower Yellow River basin as an example, the variation trend of hydrological connectivity in this region in the last 36 years and the influence of the Xiaolangdi Dam on hydrological connectivity was analyzed, and the response law of vegetation in the floodplain to the change of hydrological connectivity under different water surface ratios was obtained. The results show that because of Xiaolangdi Dam operation, the hydrological connectivity and vegetation coverage of Jiahetan increased by 28.09 % and 17.73 % on average, respectively, in the flood season. In the non-flood season, hydrological connectivity decreased by 22.91 % and vegetation coverage increased by 164.82 % on average. It is beneficial for vegetation growth to keep the hydrological connectivity value around 0.4 in the flood season and 0.3 in the non-flood season. These results provide a quantitative analysis technique for the evaluation of river floodplain hydrological connectivity, with the characteristics of a simple evaluation process and good applicability, and have important scientific significance and wide application value in providing guidance and decision-making assistance for the protection and restoration of floodplain water ecology, river system connectivity planning, and water and sediment regulation.

Identification of mixed mode damage types on rock-concrete interface under cyclic loading

The study of the mixed mode Ⅰ-Ⅱ fracture damage characteristics of the rock-concrete interface under cyclic loading is essential to grasp the operation of gravity dams under seismic loading. To reveal the mixed mode fracture damage characteristics of the rock-concrete interface under cyclic loading, a four-point shear (FPS) test for rock-concrete specimens was carried out at first. The entire fracture damage process of rock-concrete specimens was monitored in real-time by acoustic emission (AE) and digital image correlation (DIC), the widely used nondestructive monitoring techniques. The mechanical test results show that the modal angle is related to the stiffness decay of rock-concrete specimens. The quantitative identification method of tensile and shear damage based on machine learning algorithm can quantitatively identify the damage types at the interface of rock-concrete specimens. The influence of rock type and modal angle on the interface damage mechanism was quantified by the damage identification method, and the spatial and temporal evolution of tensile and shear damage with cyclic loading was determined. The spatial and temporal evolution characteristics of the damage were compared with the DIC strain contours of the corresponding stages to reveal the mechanism of the influence of the damage evolution law on the crack expansion path.

A Study on the Optimal Deep Learning Model for Dam Inflow Prediction

In the midst of climate change, the need for accurate predictions of dam inflow to reduce flood damage along with stable water supply from water resources is increasing. In this study, the process and method of selecting the optimal deep learning model using hydrologic data over the past 20 years to predict dam inflow were shown. The study area is Andong Dam and Imha Dam located upstream of the Nakdong River in South Korea. In order to select the optimal model for predicting the inflow of two dams, sixteen scenarios (2 × 2 × 4) are generated considering two dams, two climatic conditions, and four deep learning models. During the drought period, the RNN for Andong Dam and the LSTM for Imha Dam were selected as the optimal models for each dam, and the difference between observations was the smallest at 4% and 2%, respectively. In typhoon conditions, the GRU for Andong Dam and the RNN for Imha Dam were selected as optimal models. In the case of Typhoon Maemi, the GRU and the RNN showed a difference of 2% and 6% from the observed maximum inflow, respectively. The optimal recurrent neural network-based models selected in this study showed a closer prediction to the observed inflow than the SFM, which is currently used to predict the inflow of both dams. For the two dams, different optimal models were selected according to watershed characteristics and rainfall under drought and typhoon conditions. In addition, most of the deep learning models were more accurate than the SFM under various typhoon conditions, but the SFM showed better results under certain conditions. Therefore, for efficient dam operation and management, it is necessary to make a rational decision by comparing the inflow predictions of the SFM and deep learning models.

Evaluation of Occupational Safety in the Operation and Maintenance Activities of Dams

The accidents occurred during the operation/maintenance activities of US dams between 1984-2018 were analyzed from the OSHA database and 88 cases were selected. The objective of our study is to identify and investigate potential hazards and risk sources responsible for and affecting OHS performance in the operation/maintenance activities. Further, the factors responsible for injuries and fatalities happened during these activities are determined. It is found out that 5.2% of precaution negligence was related to the facility and wrong design and poor maintenance were the main negligence factors. The important point to be noted is that these negligence factors result in fatal accidents, albeit few. The results also show that machine safeguarding was not available or provided in most of the cases and 12.7% of those who had occupational accidents did not use appropriate PPE or did not use PPE at all.

Comprehensive Environmental Flows Assessment for Multi‐Guilds in the Riparian Habitats of the Yangtze River

AbstractThe development of new strategies for the operation of existing dams is essential for restoring ecosystems that have already been affected by the construction and current regulation of these dams. The assessment of environmental flows (EFs) is significant in guiding such strategic dam operations. However, most of the existing methods just focus on one species or guild without simultaneously considering the interactions with other aquatic organisms. This study proposes an innovative method to determine comprehensive environmental flows (CEFs) for multi‐guilds (fish, macroinvertebrates, and hygrophytes) based on the habitat simulation model. We focused on the riparian habitats in the middle reaches of the Yangtze River, coupled the biological preferences of multi‐guilds with suitable habitat factors, including velocity, depth, and substrate, and then analyzed the relationships of flow and weighted usable areas to determine the CEFs for multi‐guilds. The results showed that while the optimal CEFs could be satisfied only in Spring and Summer, the threshold CEF conditions could be met in the Jianli reach throughout the year after the impoundment of Three Gorges Dam (TGD). The results obtained by using the CEFs assessment could better satisfy the EFs for multi‐guilds than the ones developed for individual species. The CEFs could be also used to evaluate the impact of TGD on multi‐guilds’ habitats and optimize ecologically‐friendly operations in already designed dams. This study is helpful for maintaining ecosystem integrity in Yangtze River and provides a good example for use in other dams facing similar issues.

Identification of Sensitive Parameters for Deformation of Asphalt Concrete Face Rockfill Dam of Pumped Storage Power Station

Pumped storage power station (PSPS) is an important clean energy project that plays an important role in ensuring the economical, safe, and stable operation of power systems and alleviating the contradiction of peak load regulation. Deformation analysis of the built and under construction PSPS dam was an important process of dam design and operation, which was of great significance to ensure the safe operation of hydraulic structures in the reservoir site. Nevertheless, there were many parameters involved in the model for analyzing dam deformation, which brings a large workload to the inversion and application of model parameters. In this study, the asphalt concrete face rockfill dam (ACFRD) of a PSPS in Ningxia, China, was taken as an example, a dam deformation 3D finite element analysis model based on the Duncan–Chang E-B model was constructed, and the orthogonal test method was used. The model parameters of the main rockfill zone, secondary rockfill zone, and reservoir bottom backfill zone were taken as factors for the sensitivity analysis of horizontal displacement of dam H, vertical displacement u, and asphalt concrete face tensile strain ε. The results showed that initial bulk modulus base Kb, damage ratio Rf, and initial elastic modulus base K had a relatively higher sensitivity and had significant impacts on the calculation results, while internal friction angle φ, fraction angle reduction φ, bulk modulus index m, and elastic modulus index n had a relatively lower sensitivity, which had no significant impact on the calculation results. Therefore, when using the Duncan–Chang E-B model to analyze the deformations of a PSPS dam and asphalt concrete face, Kb, Rf, and K should be the focus. Parameters with a low sensitivity could be determined by engineering analogy so as to achieve the purpose of improving calculation efficiency under the premise of ensuring calculation accuracy. Meanwhile, these parameters should also be strictly controlled during construction. The results of this study could provide a reference for the design and safety assessment of ACFRD in PSPS.

Characterizing the Flow Regime in Brook Trout Incubation Habitats and Implications for Management in a Hydro‐Regulated River

AbstractThe operation of dams, diversions, and power generation facilities unavoidably influence the ecological function of rivers. We evaluated vertical and horizontal hydraulic gradients and subsequent water temperature changes in the hyporheic zone of a spawning area for Brook Trout Salvelinus fontinalis in a managed Lake Superior tributary in Ontario, then conducted a laboratory‐based experiment to show the impact of cold shock during incubation on the timing of larval emergence and survival. Upwelling groundwater was observed at the spawning area during the monitoring period (October 28, 2016, to January 11, 2017); hyporheic water temperatures remained above 3.7°C, whereas ambient river temperature above the substrate fell to 1.5°C until water was released from the upstream control dam. After the release event, water level increased by 0.9 m over the spawning area, and within 24 h, vertical and horizontal flow gradients were reversed in the hyporheic zone; downwelling conditions were observed for 30 h between surface and hyporheic water 1.8 m below substrate, and hyporheic water temperature decreased in unison. Hyporheic temperatures at shallow inshore sites fell below 1°C for more than 53 h. In the laboratory, applying a worst‐case scenario of dam‐induced cold shock on Brook Trout redds using historic monitoring records (i.e., <1.0°C for 40 h), we found no appreciable effect on survival and development timing of incubating Brook Trout eggs compared with a control group. Survival from fertilization to hatching was high for both treatment and control groups (>90%) and lower from fertilization to emergence (55%). Overall, our results suggest that standard winter operating procedures on a Lake Superior tributary had little impact on Brook Trout egg survival and development time to hatching and emergence; however, our findings also suggest that staged winter discharges would lessen the reversal of flow in the hyporheic zone and the magnitude of temperature changes experienced at Brook Trout redds.

Tolerance and Growth of Adult Schizothorax prenanti Exposed and Re-Exposed to Supersaturated Gas Downstream of a Dam

Total dissolved gas (TDG) is suggested to be one possible explanation for the extensive mortality of endemic fish suffered from gas bubble disease (GBD). We investigated the effects of water depth on adult Schitzothorax prenanti susceptibility to GBD in TDG supersaturated water 11.5 km downstream of Dagangshan dam in a two-year (2016–2017) live cage study. The probability of survival significantly increased at greater depth. The mortality of fish at 1–2 m was reduced to 50% of that at 0–1 m and the mortality rate for fish at 2–3 m was reduced to 25% of that at 0–1 m. Fish that survived in-situ TDG exposure in 2016 were relocated to equilibrated water and observed for 274 d to investigate sublethal effects of GBD. The surviving fish showed a substantial reduction in growth compared to the control group. During the flood discharge period in 2017, fish were re-exposed to TDG supersaturated water after a period of recovery (274 d) in equilibrated water. The mortality rate of re-exposed fish decreased to 35% compared to newly introduced fish. Our results contribute to the protection of aquatic organisms and the improvement of eco-friendly hydroelectric dam operations in the Yangtze River.

Response of riparian vegetation to short- and long-term hydrologic variation.

Increasing demand for river water now conflicts with an increasing desire to maintain riparian ecosystems. Efficiently managing river flows for riparian vegetation requires an understanding of the time scale of flow effects, but this information is limited by the absence of long-term studies of vegetation change in response to flow variation. To investigate the influence of short- and long-term flow variability and dam operation on riparian vegetation, we determined the occurrence of 107 plant species in 133 permanent plots of known inundating discharge along the Gunnison River in Colorado on five different occasions between 1990 and 2013. Individual species moved up and down the gradient of inundating discharge coincident with increases and decreases in mean annual flow, and the correlations between flow and species occurrence were strongest when flows were weighted by time before vegetation sampling with a median half-life of 1.5 years. Some tall, rhizomatous, perennial species, however, responded to flows on a longer time scale. Logistic regression of species occurrence showed a significant relation with inundation duration for 70 out of 107 species. Plot species richness and total vegetative cover decreased in association with desiccation at low inundation durations and with fluvial disturbance at high inundation durations. Within-plot similarity in species occurrence between years decreased strongly with increasing inundation duration. Moderate inundation durations were dominated by tall, rhizomatous, perennial herbs, including invasive Phalaris arundinacea (reed canary grass). Over the 23-year study period, species richness declined, and the proportion of rhizomatous perennials increased, consistent with the hypothesis that decreases in flow peaks and increases in low flows caused by flow regulation have decreased establishment opportunities for disturbance-dependent species. In summary, annual-scale changes in vegetation were strongly influenced by flow variation, and decadal-scale changes were influenced by decreases in fluvial disturbance from upstream flow regulation beginning decades prior to the onset of this study.

Effectiveness assessment of reservoir projects for flash flood control, water supply and irrigation in Wangmo Basin, China

Most flash floods in countries around the world occur in poor rural mountainous areas and typically cause more casualties and economic losses due to monitoring challenges and early warning difficulties. In mountainous regions, reservoir projects are a very effective measure for mitigating the risk of flash floods and can also be used for water supplies and irrigation, but there is a lack of research on the comprehensive benefit assessments of reservoirs. In this paper, we simulate the inundation extents of flash floods for the Wangmo Basin in China, where flash floods frequently occur, under different return periods using the HEC-HMS (HEC-Hydrologic Modelling System) model and FLO-2D model and compare the resulting housing losses with and without reservoirs. The results indicate that using dam and reservoir operations for flood control in the Wangmo River Basin decreases the flooded housing area in the county centre by approximately 12.9 %–30.2 %, which results in housing losses reductions of 19.7 %–45.7 %.These dams and reservoirs will begin to make a profit during the 38th year of operation, and the average annual net benefit reaches 101.76 million RMB in 50 years, which is equivalent to 1.43 % of the GDP of Wangmo County; the net benefits of flood control, water supply and irrigation accounted for 0.4 %, 1.0 % and 0.03 %, respectively. Priority should be given to planning and building these water conservation measures to help these poor mountainous areas. The construction of dams and reservoirs can contribute to decreasing losses in poverty and disaster-prone regions. The effectiveness evaluation framework for dams and reservoirs presented in this study can be applied to other mountainous basins for flood control and local development.

Practical steps to Global Industry Standard on Tailings Management (GISTM) compliance for operational tailings storage facilities in South Africa

The majority of the tailings dam operations in South Africa will be required to comply with the new Global Industry Standard on Tailings Management (GISTM) within the next one to three years, depending on the dam classification and the requirements of the respective investors and insurers. With up to 72 auditable requirements, the implementation of the Standard needs careful planning and prioritization. This paper focuses on the practical steps to GISTM compliance for tailings facilities in operation in South Africa. The discussions are based on current practices, South African regulations, and industry standards requirements. The possible changes in dam classifications and the associated requirements are presented.

Flood Inflow Estimation in an Ungauged Simple Serial Cascade of Reservoir System Using Sentinel-2 Multi-Spectral Imageries: A Case Study of Imjin River, South Korea

The Imjin River is a representative transboundary river in the Korean Peninsula, originating from North Korea and flowing into South Korea. Upstream of Imjin River, on the North Korean side, is the Hwanggang Dam, with a 350 million m3 of storage capacity, which is in operation for power generation and water supply. The sharing of the operation information of Hwanggang Dam has been limited due to political and military tension. South Korea has constructed the Gunnam Flood Control Reservoir downstream of the Imjin River to prevent potential flood damage due to the urgent and unilateral release from the Hwanggang Dam. However, it is difficult to manage the flood of the Imjin River basin under the situation of limited shared real-time information on the Hwanggang Dam operation. In this study, a hydrological analysis system was established to estimate the inflow and release of the Hwanggang Dam by building a lumped hydrological model and an Auto ROM (Reservoir Operation Method)-based reservoir operation algorithm. To estimate the inflow of the Gunnam Flood Control Reservoir, the water level of the Hwanggang Dam was calculated using the Sentinel-2 multi-spectral images, and the hydrological analysis system was calibrated. The evaluation index of the water level of the ungauged Hwanggang Dam derived from January 2017 to August 2020 using the hydrological analysis system was shown to have a coefficient of determination of 0.76 and an RMSE of 3.97 m. In the case of the flood event in August 2020, the coefficient of determination of the flood inflow in the Gunnam Flood Control Zone was calculated to be 0.86.

Abundance and Migration Success of Overshoot Steelhead in the Upper Columbia River

AbstractSummer steelhead Oncorhynchus mykiss may enter freshwater almost a year before spawning and potentially make long migrations (>1,000 km) to interior headwater habitats. However, in response to suboptimal freshwater habitat conditions (e.g., warmer water temperatures), adult summer steelhead may exhibit complex behaviors during upstream migration in the Columbia River basin. Steelhead may migrate upstream of their natal tributary (hereafter, referred to as “overshoot”) and spend days to several months before subsequently migrating downstream (hereafter, referred to as “fallback”) to their natal tributary to spawn. An expansion of an existing Bayesian patch occupancy model, derived from observations of adult steelhead that were PIT‐tagged to estimate population‐specific abundance upstream of the tagging location, incorporated downstream detection locations to estimate the abundance of overshoot fallbacks. Overshoot steelhead abundance at the tagging location was estimated based on the relationship between the number of known overshoot fallbacks (i.e., the number of steelhead that overshot and successfully migrated downstream to their natal tributary) and their model‐estimated abundance. During the study period (2010–2017), the annual mean proportion of overshoot steelhead that successfully migrated downstream of the tagging location (Priest Rapids Dam) was 0.59 (SD = 0.14). The number of dams encountered by overshoot steelhead during their downstream migration was negatively correlated with their downstream migration success probability. Improved downstream passage survival for adult steelhead will increase the abundance of affected populations while reducing potential genetic introgression of upstream populations (i.e., strays). This is the first study to estimate the abundance of overshoot and fallback steelhead, providing the data necessary for scientists to estimate potential conservation benefits of improved downstream survival. For example, surface flow passage routes (e.g., sluiceways and temporary spillway weirs) are very effective in guiding and passing adult steelhead downstream of Columbia River hydroelectric projects and data from this assessment show that changes in dam operations throughout the downstream migration period may maximize conservation benefits.

Pharmaceuticals and personal care products (PPCPs) in water, sediment and freshwater mollusks of the Dongting Lake downstream the Three Gorges Dam.

Pharmaceuticals and personal care products (PPCPs) are a group of emerging anthropogenic pollutants. Here we investigated the occurrence and concentrations of 35 typical PPCPs in water, sediment, and freshwater mollusks (Hyriopsis cumingii, Unio douglasiae, Sinanodonta woodiana, Lamprotula leai and Corbicula fluminea) of the Dongting Lake downstream of the Three Gorges Dam. As results, 33 PPCPs were detected in water and sediment of the lake. Ketoprofen (not detected (ND)-292.8ng/L, mean 91.1ng/L) and roxithromycin (13.7-141.9ng/L, mean 30.4ng/L) were the primary PPCPs measured in lake water, while ibuprofen (ND-105.0ng/g, mean 30.0ng/g) and ketoprofen (ND-142.9ng/g, mean 27.6ng/g) were dominant in the sediment. Distinct seasonal difference in PPCP compositions was observed in both water and sediment of the Dongting Lake, potentially associated with the water-level fluctuations driven by the Three Gorges Dam operations. Ketoprofen and ibuprofen were also frequently detected in the soft tissues of freshwater mollusks, with concentrations of 42.5-1206.6 and 44.9-992.7ng/g, respectively. Significant species-specific accumulation characteristics of PPCPs in mollusks were observed, with the highest total contents being reported for Corbicula fluminea (3.18±1.13μg/g). Moreover, gonads of mollusks were identified as the target organ to accumulate these compounds. Correlation analysis further revealed the strong associations of PPCP concentrations in mollusks with those in water and sediment, suggesting the importance of controlling dissolved and sedimentary bioavailability of PPCPs for ecological risk management in this freshwater lake ecosystems.

Wildfire-Induced Changes in Flood Risk in Recreational Canyoning Areas: Lessons from the 2017 Jerte Canyons Disaster

Few studies identify potential hazards affecting canyoning. This activity has an increasing number of practitioners, and hence, a greater number of people are affected by potential natural hazards. Mountain rivers are located in places subject to several hydrological hazards; the risks are mostly connected with floods produced by intense storms or dam operation, but changes in hydrological factors may alter the usual basin behavior given even moderate or less severe storms. Data about flood events and the peak discharge of the 2017 flood in the two studied canyons were collected by means of a quick field survey of water levels after the flood, hydrological modeling, and soil analysis. The present research shows the dramatic consequences of a two-year return period storm affecting a guided group of canyoneers. A previous wildfire changed the soil, leading to hydrophobic conditions and increasing the flood effects. Peak discharge increased from 2 m3 s−1 in normal conditions to 12 m3 s−1 under a hydrophobic regime related to wildfire occurrence; moreover, a reduction in the time of concentration also occurred, pointing to a more powerful and dangerous flood event. In this paper, some hydrological recommendations are highlighted that will be helpful in recreational canyoning management, leading to safer practice.

A Hybrid Model of Ensemble Empirical Mode Decomposition and Sparrow Search Algorithm-Based Long Short-Term Memory Neural Networks for Monthly Runoff Forecasting

Monthly runoff forecasting plays a vital role in reservoir ecological operation, which can reduce the negative impact of dam construction and operation on the river ecosystem. Numerous studies have been conducted to improve monthly runoff forecast accuracy, of which machine learning methods have been paid much attention due to their unique advantages. In this study, a conjunction model, EEMD-SSA-LSTM for short, which comprises ensemble empirical mode decomposition (EEMD) and sparrow search algorithm (SSA)–based long short-term neural networks (LSTM), has been proposed to improve monthly runoff forecasting. The EEMD-SSA-LSTM model is mainly carried out in three steps. First, the original time series data is decomposed into several sub-sequences. Second, each sub-sequence is simulated by LSTM, of which the hyperparameters are optimized by SSA. Finally, the simulated results for each sub-sequence are summarized as the final results. The data obtained from two reservoirs located in China are used to validate the proposed model performance. Meanwhile, four commonly used statistical evaluation indexes are utilized to evaluate model performance. The results demonstrate that compared to several benchmark models, the proposed model can yield satisfactory forecast results and can be conducive to improving monthly runoff forecast accuracy.

Conjunctive Operation of Sand Dam and Groundwater Well for Reliable Water Supply during Drought Conditions

Some mountainous regions without water service facilities are among the areas most vulnerable to drought. In these locations, it is particularly essential to establish practical alternatives to cope with the increase in the intensity and duration of droughts caused by climate change. This study proposes a methodology for the conjunctive use of a sand dam and groundwater well under various drought conditions. The method has been applied to a small mountainous area in South Korea. Owing to the scarcity of observational data, it is crucial to properly estimate the hydrological components necessary for judging the feasibility and reliability of conjunctive operations. The step-by-step procedures for performing the tasks are presented in this study. For the inflow of the sand dam, which is a portion of the basin runoff, two different approaches were employed and compared: the Kajiyama formula and a simple two-parameter monthly water balance model (TPM). Water budget analysis allowed for the determination of whether the current and increased water demand could be met under various drought conditions. Preliminary analysis revealed that a sand dam alone could not reliably meet the demand for 10-year or more severe drought conditions. Various water allocation scenarios between surface water (i.e., sand dam) and groundwater were tested. Conjunctive use of a sand dam and groundwater well turned out to increase the reliability of the water supply. As water demand increases and droughts become more severe, the role of groundwater increases. With appropriate resource allocation, 100% water supply reliability could be achieved, even for one year-lasting 50-year drought. We demonstrated how a system could be flexibly operated to meet the target demands monthly, given the system reliability level.