A study on siting of emergency shelters for dam failure floods considering population distribution and weather effects.

In recent years, dam failures have occurred frequently because of extreme weather, posing a significant threat to downstream residents. The establishment of emergency shelters is crucial for reducing casualties. The selection of suitable shelters depends on key information such as the number and distribution of affected people, and the effective capacity and accessibility of the shelters. However, previous studies on siting shelters did not fully consider population distribution differences at a finer scale. This limitation hinders the accuracy of estimating the number of affected people. In addition, most studies ignored the impact of extreme rainfall on the effective capacity and accessibility of shelters, leading to a low applicability of the shelter selection results. Therefore, in this study, land-use and land-cover change (LUCC) and nighttime lighting data were used to simulate population distribution and determine the number and distribution of affected people. Qualified candidate shelters were obtained based on screening criteria, and their effective capacity and accessibility information under different weather conditions were quantified. Considering factors such as population transfer efficiency, construction cost and shelter capacity constraints, a multi-objective siting model was established and solved using the non-dominated sorting genetic algorithm II (NSGA- II) to obtain the final siting scheme. The method was applied to the Dafangying Reservoir, and the results showed the following: (1) The overall mean relative error (MRE) of the population in the 35 downstream streets was 11.16 %, with good fitting accuracy. The simulation results truly reflect the population distribution. (2) Normal weather screening generated 352 qualified candidate shelters, whereas extreme rainfall weather screening generated 266 candidate shelters. (3) Based on the population distribution and weather factors, four scenarios were set up, with 63, 106, 73, and 131 shelters selected. These two factors have a significant impact on the selection of shelters and the allocation of evacuees, and should be considered in the event of a dam-failure floods.

Study on the migration characteristics of bioaerosols and optimization of ventilation patterns in a negative pressure isolation ward considering different patient postures.

Due to the serious global harm caused by the outbreak of various viral infectious diseases, how to improve indoor air quality and contain the spread of infectious bioaerosols has become a popular research subject. Negative pressure isolation ward is a key place to prevent the spread of aerosol particles. However, there is still limited knowledge available regarding airflow patterns and bioaerosol diffusion behavior in the ward, which is not conducive to reducing the risk of cross-infection between health care workers (HCWs) and patients. In addition, ventilation layout and patient posture have important effects on aerosol distribution. In this study, the spatial and temporal characteristics as well as dispersion patterns of bioaerosols under different ventilation patterns in the ward were investigated using the computational fluid dynamics (CFD) technique. It is concluded that changes in the location of droplet release source due to different body positions of the patient have a significant effect on the bioaerosol distribution. After optimizing the layout arrangements of exhaust air, the aerosol concentration in the ward with the patient in both supine and sitting positions is significantly reduced with particle removal efficiencies exceeding 95%, that is, the ventilation performance is improved. Meanwhile, the proportion of aerosol deposition on all surfaces of the ward is decreased, especially the deposition on both the patient's body and the bed is less than 1%, implying that the risk of HCWs being infected through direct contact is reduced.

Evaluation of the water pollution risk of dam and dike-break floods in the inundated area.

The inundated area of dam and dike-break floods includes various types of land and factories that release considerable amounts of pollutants into floods, causing serious water pollution and further endangering human health. Many pollution sources and factors affect the water pollution risk in inundated areas. Accurate assessment of the water pollution risk for dam and dike-break floods enables people to take measures in advance to reduce public health problems. The existing evaluation methods cannot effectively analyze the water pollution risk for dam and dike-break floods because partial or all pollution sources and influencing factors are ignored. The main factors affecting flood water quality were summarized into point source (PS), non-point source (NPS), flood depth, velocity, duration, and temperature. The water pollution risk caused by NPSs and PSs were quantified, as well as the impact of all main factors on water pollution risk. The evaluation model proposed for water pollution risk in inundated areas of dam and dike-break floods considers all pollution sources and influencing factors. The WPR was proposed to represent the water pollution risk value. The dam-break flood of Luhun Reservoir was simulated to verify the feasibility of the evaluation model. We concluded that (1) WPR varied with space and time in the inundated area and was seriously affected by PS in local areas; (2) the annual average WPR of different land use types from high to low were construction land, cropland, urban, water, rural area, woodland, and grassland. The evaluation model can be used to evaluate the water pollution risk for dam and dike-break floods at macro and micro scales. People can use this method to evaluate the impact, range, and degree of specific pollution sources or pollutants in the inundated area, thus allowing for measures to be taken in advance to reduce associated damages.

Environmental impact assessment of dam-break floods considering multiple influencing factors.

Dam-break floods cause substantial damage to the environment, and evaluating the negative impacts of dam-break floods on the environment (EI) is an important part of flood risk management. EI has been evaluated using various methods with different indices. However, the evaluation results of EI are typically one-sided or inaccurate because of diverse indices and complex influencing factors. A new method was proposed herein to calculate EI with an index system, including geomorphic changes (GC), water pollution (WP), plant biomass loss (PB), and biodiversity loss (BL). Eight factors that influence EI were sorted out, namely, erosion or deposition depth, non-point source (NPS) and point source (PS) pollution, plant biomass, species richness, plant height, and flood depth, velocity, and duration. After combining the proposed damage functions to calculate the influence of flood depth, velocity, and duration, and plant height on the environment, methods to calculate GC, WP, PB, BL, and EI were proposed. A dam-break flood scenario for Luhun Reservoir was used to verify the method. The results showed that (1) the trend in EI was similar to that in geomorphic changes in the inundated area and seriously affected by PS in local areas, (2) the average EI of woodland was the highest, while that of towns was the slowest, and (3) GC and WP contributed 93.7% of EI in the entire inundated area. This study summarized the complex impacts of dam-break floods on the environment from four aspects and proposed a method to quantify the overall impact of dam-break floods on the environment. The evaluation model could evaluate the impact of floods on the environment accurately, presenting the results on a flood inundation map. This provides a scientific basis for evaluating flood consequences and managing flood risk.

Evaluation of the impact of extreme floods on the biodiversity of terrestrial animals.

Extreme floods seriously affect the biodiversity of terrestrial animals (birds, mammals, reptiles, amphibians, and insects). The degree of impact depends on many factors, e.g., animal characteristics, natural conditions, and flood characteristics. Previous evaluation methods are not suitable for assessing the impact of floods on the biodiversity of all species in the entire submerged area, nor do they accurately reflect variability in the degree of impact. First, the influencing factors were boiled down to four: ratio of flood duration to survival time of animals in floods (D), ratio of flood depth to plant height (S), migration ability of animals (M), and temperature (T), which are represented by a coefficient I. Then, we proposed a calculation method for I based on the four factors. Third, we proposed the total and average biodiversity impact indices, namely, the TBI and ABI, respectively, indicating the overall and average impacts of floods on biodiversity in the submerged area, with the calculation method considering both the number of species and I. An extreme flood was simulated to obtain the flood parameters. In addition, we analyzed monthly changes in partial influencing factors. Finally, the impact of extreme floods on the biodiversity of terrestrial animals in the submerged area was evaluated monthly, and it was found that (1) TBI and ABI changed with space; (2) the ABI of different animals in descending order were mammals, insects, reptiles, amphibians, and birds; (3) the ABI of different land use types in descending order were cropland, orchard and shrubland, grassland, and forest and for TBI were orchard and shrubland, cropland, forest, and grassland; and (4) the TBI and ABI of different animals and land use types changed over time. The proposed method and indices are suitable for assessing the impact of floods on the biodiversity of any organism in any area.

Impact of extreme floods on plants considering various influencing factors downstream of Luhun Reservoir, China.

Extreme floods caused by dike or dam breaks have led to substantial damage to various types of vegetation, including forests, orchards, grass, and crops. Many factors affect the impacts of extreme floods on plants, e.g., flood parameters, plant characteristics and natural factors. However, these factors have never been systematically analyzed or considered when evaluating the impacts of extreme floods on plants. Firstly, we summarized the main influencing factors and simplified them into six categories: temperature, geomorphic change, plant age, flood velocity, ratio of the flood depth to the plant height, and ratio of the flood duration to the plant waterlogging tolerance time. Secondly, we proposed the two indices of unit risk biomass (URB) and total risk biomass (TRB) to represent the impacts of floods on plants regionally and over the entire inundated area, respectively. In addition, the calculation methods of URB and TRB considering plant biomass and the comprehensive influence coefficient (I) were put forward. To calculate I, we considered the six influencing factors with different weights according to their importance and varying conditions. The flood parameters and geomorphic changes caused by a simulated dam-break flood of Luhun Reservoir in China were then calculated. Furthermore, we divided a year into six time periods according to the species and growth characteristics of the plants in the inundated area. Then we evaluated the impacts of the dam-break flood on the plants during each period. The results showed that: (a) the URB varied with space in the inundated area; (b) because of the large inundation area of crops, the TRB was far greater than that of forests and orchards and affected the TRB of the whole inundated area; and (c) both the URB and TRB changed with time with the changes in crop species, crop parameters and temperature.

Impact evaluation of geomorphic changes caused by extreme floods on inundation area considering geomorphic variations and land use types.

Extreme floods caused by dam breaches, dike breaches, and rainstorms cause significant erosion and deposition in the flooded area. Furthermore, geomorphic changes have various impacts on different land use types, which is an important aspect extreme flood outcomes. The impact type and degree depend on geomorphic variations and land characteristics. However, neither the amount of geomorphic variations nor its impact on the inundation area have been fully understood. Firstly, we propose the use of a numerical simulation method to calculate erosion and deposition depths of the whole inundation area caused by extreme floods. Secondly, combined with the characteristics of erosion, deposition, and land use types, the impact type of geomorphic changes on different land use types were divided into positive, negative, and negligible impacts, and the impact degree was expressed by two indices of impact grade and impact score. In addition, the calculation methods of the two indices were put forward. Then, we propose a method for evaluating the impacts of geomorphic changes on the whole inundation area from five aspects of mesh, land use type, overall erosion region, overall deposition region, and overall inundation area. Combined with the simulation of the flood process caused by dam breach of Luhun Reservoir in China, this method was verified, and the results showed that: (a) geomorphic changes had a negative impact on 94.7% of the inundation area, and only part of the water bodies were positively affected and the towns were not affected, accounting for 2.1% and 3.2% respectively; (b) the negative impact degree of each land use type in descending order was grassland, town, cropland, forest, shrubland and water body; and (c) the area of deposition was larger than that of erosion, whereas the severity of negative impact was opposite.

Economic risk criteria for dams considering the relative level of economy and industrial economic contribution.

When a dam breaks, huge floods will be generated that may inundate urban areas, enterprises, farmlands, and infrastructure and cause giant economic losses. Economic risk criteria are a kind of basis for determining dam risk levels and to decide whether risk control measures should be taken or not. However, compared to loss-of-life risk criteria, much fewer economic risk criteria for dams have been proposed and implemented for two main reasons: (a) The ability of most areas to endure economic losses caused by dam breach changes over time because of the constant development of their economic levels; and (b) Economic development levels in an area are distinct from the levels in other areas, resulting in significant differences in the ability of different areas to endure economic losses caused by a dam breach. Therefore, an equivalent economic scale (EES) that indicates the relative economic level of an area to the whole country in a given period of time is a preferred measure. It was shown in this paper that EES has much more stable values than do ordinary economic measures; therefore, it was taken as the basic index for establishing economic risk criteria. Furthermore, due to the distinct economic loss rates of different industries, the index of industrial economic contribution (IEC) was introduced to determine the correction coefficient to modify the ESS to reflect the potential economic loss of the area to be evaluated. This is the first research that pays careful attention to the change of ability to endure economic losses, in which the established economic risk criteria are applicable over a relatively long time and for different areas based on the consideration of the relative level of the economy and the industrial economic contribution.