Effects Of Rainfall Characteristics Research Articles

Effect of rainfall characteristics on the transport of trace metals in suspended particles during rainfall events

Stormwater carries significant loads of pollutants into watersheds, deteriorating water quality. The load depends on numerous factors, such as land use and rainfall characteristics. The objective was to quantify the load of metals in suspended particles and the effect of rainfall characteristics on the wash-off pollutants. A quality-quantitative approach was applied to monitor rainfall characteristics, discharge, and water quality parameters. Fourteen parameters were measured, including turbidity, dissolved oxygen (OD), temperature, total suspended solids (TSS), particle size diameter, Co, Cd, Cr, Cu, Ni, Pb, Zn, Mn, and Fe . Multivariate analyses were used to verify the correlation between parameters. The rainfall events were classified using a Euclidean clustering method according to selected rainfall characteristics. Rainfall with moderate to heavy rainfall depth (RD) and intense peaks (RImax) showed the highest loads of metals and TSS. The load of TSS carried during the rain events ranged from 1.4 to 680.2 tons. Particulate metals concentration following order Fe > Zn > Mn > Cr > Cu > Ni > Co > Pb. Emphasis to mean concentration in mg/kg of Zn (13073.7 ± 27513.5), Mn (575.8 ± 516.2), Cr (190.70 ± 84.01), Cu (88.24 ± 44.97), and Ni (45.63 ± 31.20). The RImax, RD, and maximum flow (Qmax) were the variables that most influenced metals and TSS loads in the runoff. Except for Zn, all the trace metals had a strong correlation to TSS and rainfall characteristics. The particle size of < 40 µm was predominant in 60 % of the runoff events. Knowledge of the distribution of the pollutant throughout the rainfall and the variables that may interfere is essential to improving containment strategies, such as retention at the source, and preserving the quality of aquatic systems.

Urban rainstorm and waterlogging scenario simulation based on SWMM under changing environment.

Urban rainstorm and waterlogging occurred more frequently in recent years, causing huge economic losses and serious social harms. Accurate rainstorm and waterlogging simulation is of significant value for disaster prevention and mitigation. This paper proposed a numerical model for urban rainstorm and waterlogging based on the Storm Water Management Model (SWMM) and Geographic Information System (GIS), and the model was applied in Lianhu district of Xi'an city of China. Furthermore, the effects of rainfall characteristics, pipe network implementation level and urbanization level on waterlogging were explored from the perspectives of spatial distribution of waterlogging points, drainage capacity of pipe network and surface runoff generation and confluence. The results show that: (1) with the increase of rainfall recurrence period, the peak of total water accumulating volume, the average decline rate of water accumulating volume and the number of waterlogging nodes increase; (2) optimizing the pipe diameter can shorten the average overload time of the pipe network from the entire pipe network, but for a single pipe, optimizing the pipe diameter may lead to overloading of unoptimized downstream pipeline; (3) the lower the imperviousness, the less the number of waterlogging nodes and average time of water accumulating, and (4) the west, northwest and southwest areas are relatively affected by the imperviousness, only improving the underlying surface conditions has limited influence on waterlogging in the study area. This study can provide reference for urban waterlogging prevention and reduction and pipe network reconstruction.

The response of organic carbon fractions in sediment to rainfall characteristics and slope lengths: Based on four-years on-site monitoring data

The effect of soil erosion processes on the properties of sediment and organic carbon fractions is not well understood under complex erosion environments, such as various rainfall characteristics and transport distances, which leads to a gap in knowledge regarding the role of soil erosion in the global carbon cycle. This study investigated the impact of different rainfall characteristics (patterns and parameters) and slope lengths (5 m ∼ 20 m) on the sediment yield, particle size distribution (PSD) and properties of organic carbon fractions on China’s Loess Plateau. The results show that runoff was highest under rainfall pattern A (extreme rainfall), while the sediment concentration peaked under rainfall pattern B (heavy rainfall), with significant correlation with slope length, rainfall intensity, kinetic energy, rainfall erosivity and precipitation (p less than 0.05). Silt- and clay-sized fractions were transported as primary particles and enriched under rainfall patterns B and C with no differences between slope lengths. The enrichment ratio (ER) of sediment, effective and ultimate particles were primarily influenced by rainfall intensity-related parameters. In contrast, the aggregation ratio (AR) tended to be influenced by rainfall kinetic energy. The content and loss of organic carbon fractions correlated to rainfall parameters and slope length, although no significant difference was observed between different rainfall patterns and slope lengths. Lost organic carbon fractions were predominantly Mineral-associated organic carbon (MOC), with great enrichment under rainfall pattern C and rapid depletion as the slope length increased. Structural equation models (SEM) indicated the effect of rainfall characteristics and slope length on organic carbon loss was mainly due to the regulation of soil loss and particle size distribution of sediment in selective transport erosion processes. We highlighted the need to consider the effect of soil erosion and particle size distribution comprehensively on the carbon cycle from the perspective of organic carbon fractions to describe the potential effects of soil erosion on the carbon budget quantitatively, especially in complex environmental conditions with consideration of scale effect.

Effects of rainfall characteristics on runoff quality parameters within an industrial sector in Tennessee, USA

The relationship between rainfall characteristics and pollutant discharge has rarely been investigated in industrial sectors. To address this need, we investigated the pollutant concentrations of surface runoff and the correlation between pollutant discharge and rainfall characteristics using the self-reported stormwater quality data collected under the Tennessee Multi-Sector Permit program for two industrial facilities in West Tennessee. The variation of certain stormwater quality parameters over this period was utilized as an indicator to evaluate the effectiveness of control measures implemented at these two facilities. Furthermore, the Water Quality Index (WQI) as an indicator to assess the temporal changes in stormwater quality at industrial facilities was determined using the Weighted Sum (WSM) and Canadian Council of Ministers of the Environment (CCME) methods. The principal component analysis (PCA) and Pearson correlation coefficient were utilized to understand the correlation between runoff quality parameters, rainfall characteristics, and the sources of pollutants. The results demonstrated lower WQI indices using the WSM method compared to the CCME method. The data analysis revealed that 93.1%, 100%, 86.2%, and 48.3% of Al, Mg, Cu, and Fe experienced a concentration greater than the benchmark level, respectively. There was a significant relationship between Total suspended solids (TSS) and Al, Chemical Oxygen Demand (COD), Fe, oil and grease (O&G), and Zn concentrations. As a result, TSS could be a priority pollutant for designing various best management practices (BMPs) and low impact developments (LIDs). The result of the PCA and Pearson correlation coefficient showed that Al concentration made a significant correlation with the rainfall depth and rainfall duration. This analysis also illustrated that biochemical oxygen demand (BOD5), COD, and O&G concentrations were highly correlated with antecedent dry days (ADDs). However, pH was more related to rainfall depth and rainfall intensity. This study informs both regulatory agencies and industry stakeholders regarding the importance of evaluating self-reported stormwater quality data.

Prediction of River Pollution Under the Rainfall-Runoff Impact by Artificial Neural Network: A Case Study of Shiyan River, Shenzhen, China

Climate change and rapid urbanization have made it difficult to predict the risk of pollution in cities under different types of rainfall. In this study, a data-driven approach to quantify the effects of rainfall characteristics on river pollution was proposed and applied in a case study of Shiyan River, Shenzhen, China. The results indicate that the most important factor affecting river pollution is the dry period followed by average rainfall intensity, maximum rainfall in 10 min, total amount of rainfall, and initial runoff intensity. In addition, an artificial neural network model was developed to predict the event mean concentration (EMC) of COD in the river based on the correlations between rainfall characteristics and EMC. Compared to under light rain (&amp;lt; 10 mm/day), the predicted EMC was five times lower under heavy rain (25–49.9 mm/day) and two times lower under moderate rain (10–24.9 mm/day). By converting the EMC to chemical oxygen demand in the river, the pollution load under non-point-source runoff was estimated to be 497.6 t/year (with an accuracy of 95.98%) in Shiyan River under typical rainfall characteristics. The results of this study can be used to guide urban rainwater utilization and engineering design in Shenzhen. The findings also provide insights for predicting the risk of rainfall-runoff pollution and developing related policies in other cities.

Effects of rainfall characteristics and contour tillage on ephemeral gully development in a field in Northeastern China

Contour tillage can be an effective measure for increasing infiltration, reducing runoff volumes and velocities, and protecting against soil erosion. However, ephemeral gullies often occur when contours are overtopped because gradients of the contoured row slopes exceed critical values, causing the runoff to collect along furrows and be transported to low-lying areas, often in natural drainages. This study aims to determine the main factors that influence ephemeral gully development on a contour tilled slope in the black soil region of northeastern China by investigating development of ephemeral gullies after each heavy rainfall during the rainy season. Cross-sectional measurements were used to obtain estimates of volumetric soil loss from the ephemeral gullies. An Unmanned Aerial Vehicle (UAV) was used to collect photogrammetric data to create DEMs with a resolution of 0.08 m for monitoring morphologic changes of the ephemeral gullies. Data was collected six times during the season. After a 24 mm rainfall event at the beginning of the rainy season, three ephemeral gullies developed on the contoured slopes, with initial rapid length extension, followed by deepening during subsequent heavy rainfall events. Gully heads formed in positions with steep slopes and large drainage areas. The volumetric soil loss from the gullies under one heavy rainfall event accounted for an estimated 29–45% of the total erosion on the field. We found that the contour ridges changed drainage patterns in the field from their natural state, effectively reducing the size of the areas that contributed runoff to the gullies. Contours were overtopped and broken when the row slopes were greater than approximately 2°. The relationship between the volumetric gully erosion (ESL) and estimated surface runoff volume (VQ) was: ESL = 0.707 *VQ0.598 (R2 = 0.84). The critical relationship between gully runoff volume (VQ) and critical slope gradient (S) for ephemeral gully heads and deep gullies was SEG = 0.043 *VQ0.232 and SDG = 0.078 *VQ−0.050. This study provides a reference for the prediction and prevention of gully erosion on contoured tillage areas.

Effect of rainfall characteristics on the sewer sediment, hydrograph, and pollutant discharge of combined sewer overflow

Significant management needs raised in urban sewer system to facilitate urban resilience to rainstorm. The work investigated the effects of temporal evolution of rainfall on hydrograph and pollutant discharge of CSO over an intensive observation period of 12 months, with special attention to differences in temporal scale for supporting management decision making. The characteristics of rainfall in different temporal scales helped overflow-risk identification and assessment. Prolonged dry seasons over 112 days in the CSO monitored year 2018 increased the sediment buildup in the pipes. The built sediment was mostly flushed out to overflow (and the treatment facility) by initial rainfall during 47 h. Following CSO hydraulics and pollutant discharge follows initial peak patterns which responded to rainfall patterns. Results of Redundancy analysis and network analysis showed that the combined effects of rainfall, urbanization, and sediments as “CSO troika” are the driving forces for CSO pollutants in the long-term. The improved characterization of CSO events and the associated pollutants has refined our understanding of how overflow hydrograph and pollutant discharge responds to rainfall temporally, which methodology supported decision making in the combining source/process control with terminal management for facilizing urban resilience.

Throughfall and its spatial heterogeneity in a black locust (Robinia pseudoacacia) plantation in the semi-arid loess region, China

Throughfall in a forest ecosystem has potential hydrological impacts in the semi-arid loess region of China due to continuous human intervention. However, in black locust forests in this region, throughfall and its spatial heterogeneity and controlling factors remain unclear. We examined throughfall, its spatial variability and the effects of rainfall characteristics and vegetation structure on throughfall in a black locust stand experiment. Of the 489.72 mm cumulative gross rainfall during 20 sampled events, the average of throughfall for all trees, interception loss (IL) and stemflow (SF) were 380.93 mm (77.71%), 98.48 mm (20.19%) and 10.30 mm (2.10%), respectively. For a single tree, measured throughfall percentage decreased from upper to bottom in the canopy vertical layer, and the horizontal distribution increased with distance from the trunk. A correlation analysis between throughfall and rainfall characteristics, indicated that rainfall amount had a greater effect on throughfall than rainfall intensity and duration. Throughfall generally occurred following rainfall events of more than 0.76 mm for black locust. Throughfall percentage initially increased weakly, and then decreased with increasing rainfall intensity, while it initially increased, and then remained constant with increasing rainfall duration. Throughfall percentage decreased with increasing leaf area index (LAI) during differently-sized rainfall events, whereas throughfall variations were different in differently-sized rainfall events. Throughfall is affected by tree height, diameter at breast height (DBH), canopy width and canopy openness to some degree, while the effects were higher in larger storms than in smaller storms. Our study highlights the need to consider the effects of throughfall on hydrological processes, particularly for forest management in semiarid regions.

The effects of rainfall characteristics and land use and cover change on runoff in the Yellow River basin, China

Abstract The changes of runoff in the middle reaches of the Yellow River basin of China have received considerable attention owing to their sharply decline during recent decades. In this paper, the impacts of rainfall characteristics and land use and cover change on water yields in the Jingle sub-basin of the middle reaches of the Yellow River basin were investigated using a combination of statistical analysis and hydrological simulations. The Levenberg Marquardt and Analysis of Variance methods were used to construct multivariate, nonlinear, model equations between runoff coefficient and rainfall intensity and vegetation coverage. The land use changes from 1971 to 2017 were ascertained using transition matrix analysis. The impact of land use on water yields was estimated using the M-EIES hydrological model. The results show that the runoff during flood season (July to September) decreased significantly after 2000, whereas slightly decreasing trend was detected for precipitation. Furthermore, there were increase in short, intense, rainfall events after 2000 and this rainfall events were more conducive to flood generation. The “Grain for Green” project was carried out in 1999, and the land use in the middle reaches of the Yellow River improved significantly, which make the vegetation coverage (Vc ) of the Jingle sub-basin increased by 13%. When Vc approaches 48%, the runoff coefficient decreased to the lowest, and the vegetation conditions have the greatest effect on reducing runoff. Both land use and climate can change the water yield in the basin, but for areas where land use has significantly improved, the impact of land use change on water yield plays a dominant role. The results acquired in this study provide a useful reference for water resources planning and soil and water conservation in the erodible areas of the middle reaches of the Yellow River basin.

Analysis of total suspended solid content based on rain characteristics in the Ciliwung River basin

Total suspended solid (TSS) is one of the parameters that determines whether or not a body of water is polluted. One factor that influences the amount of TSS content is the characteristic of rainfall in an area. Purpose of this study was to determine the relationship between the effect of rainfall characteristics and TSS content in Ciliwung River. Multiple regression analysis was used for analytical method. Results of multiple regression analysis showed that the correlation coefficient (adjusted R2) for the factors of rainfall, discharge and sediment show a low correlation to changes the content of TSS in Ciliwung River. The value of each correlation coefficient in the upstream, middle, and downstream of Ciliwung River are 0.21, 0.31, and 0.09 respectively. According to the F test, rainfall, discharge and sediment were significantly affect TSS content in the upstream and middle stream. Based on t test, it is known that only rainfall affect TSS content in the upstream and midlle stream.

Stormwater Quality Benefits of Permeable Pavement Systems with Deep Aggregate Layers

Green infrastructure (GI) stormwater control measures (SCMs), such as permeable pavement systems, are common practices used for controlling stormwater runoff. In this paper, two permeable pavement strips were studied to quantify their water quality performance. The quality monitoring was coupled with comprehensive rainfall analysis to investigate the effects of common rainfall characteristics on the quality performance of the systems. The pavements utilized deep aggregate layers to promote higher infiltration, and were installed in parking lanes of an urban neighborhood. Water quality samples were collected from upgradient stormwater runoff and from stormwater captured by the permeable pavements. In addition to total suspended solids (TSS), nutrients, and dissolved metals, this research also investigated bacterial contamination (Escherichia coli, E. coli). The results indicated that the two permeable pavement systems significantly reduced concentrations of TSS, E. coli, total phosphorus, and ammonia. The average reductions of TSS and E. coli between the two systems were 47% and 69%, respectively. It was also observed that pollutant loadings in the stormwater runoff, as well as pollutant reductions, were affected by the intensity of sampled rainfall events. Thus, it is suggested to consider the effects of rainfall characteristics when reporting the water quality benefits of stormwater GIs.

Rainfall partitioning into throughfall, stemflow and interception loss by maize canopy on the semi-arid Loess Plateau of China

Rainfall or sprinkler irrigation water partitioning by the crop canopy is an important way of affecting the effective use of water by maize. To investigate the rainfall partitioning by maize canopy at different growth stages as well as its influencing factors on the water-limited Loess Plateau of China, the gross rainfall, throughfall and stemflow were measured during the growing seasons of 2015 and 2016. The effects of rainfall characteristics (gross rainfall and rainfall intensity) and canopy structure (leaf area index) on rainfall partitioning were further evaluated, based on which multiple regression models were developed to predict the partitioned rainfall components. Results showed that the measured throughfall, stemflow and derived interception loss accounted for 65.2%, 22.3% and 12.5% of cumulative gross rainfall during the whole growing season of maize, respectively. Specifically, the relative throughfall declined from 83.2% at the seedling stage to 52.2% at the tasseling stage, and then increased to 58.6% at the maturity stage. The relative stemflow and interception loss increased from 13.6% and 3.1% at the seedling stage to 30.6% and 17.3% at the tasseling stage, and then declined to 25.0% and 16.5% at the maturity stage, respectively. Smaller rainfall events contributed to a lower percentage of throughfall and stemflow but higher percentage of canopy interception loss. The percentages of stemflow and throughfall showed an increased tendency with increasing gross rainfall and rainfall intensity, while the increasing leaf area index resulted in a decrease in the relative throughfall but an increase in relative stemflow and interception loss. Generally, the amount of throughfall, stemflow and canopy interception loss can be predicted reasonably well using the developed multiple linear regression models, but the proportions of partitioned rainfall components generally had a relatively lower accuracy using the developed nonlinear models, especially for relative stemflow. This study can help to determine more precise irrigation schedule by the water balance method and give implications for the operation of sprinkler irrigation systems for higher irrigation water use efficiency.

Demonstrating Effect of Rainfall Characteristics on Wheat Yield: Case of Sinana District, South Eastern Ethiopia

Demonstrating Effects of Current and Projected Rainfall Characteristics on Wheat yield has been investigated in Sinana district for the period 1995-2016. Data on rainfall and crop yield for the period 1995-2016 were obtained from National Meteorological Agency and Sinana District Agricultural Offices, respectively. Following data quality checking, rainfall data (current and future), correlation and regression studies were analyzed using Statistical software like Instat V3.36 and SPSS V20. Downscaling the output of CSIRO-Mk3.6.0 GCM model (daily rainfall data) for RCP8.5 emission scenario using a web based software tool (Marksim GCM) for the period 2020-2049 were used to determine seasonal total rainfall and ascertain its impact on yield. This study used mean, coefficient of variation, correlation and regression analysis to ascertain the relation, cause and effect relationship between rainfall characteristics and wheat yields. The results indicated that the mean onset date of the main rainy season (JJAS) for Robe and Sinana station was June 30 and July 3. Furthermore, the results of Pearson Correlation Coefficients indicated that kiremt rainfall total (JJAS) had moderate positive relationship (r = 0.499) with wheat yield in the study area. It was also observed that nearly fifty percent of total variance of crop yield is explained jointly by kiremt rainfall total and rainy day (R2 value was 47.9%). The result of projected wheat yield indicated that there will be a slight decrease in wheat yield (qt/ha) after 2030 years due to the impact of expected weakening of kiremt rainfall total. Taking in to account the above findings, it could be suggested that the farmers’ community will be encouraged encouraged to utilize timely climate information issued from National Meteorological Agency of Ethiopia (NMA) and other centers for farm level decision to enhance their crop production.

Effect of Rainfall Characteristics on Runoff and Water Erosion for Different Land Uses in a Tropical Semiarid Region

Rainfall intensity, duration, frequency and magnitude influence both runoff generation and sediment yield. In this study, 176 rainfall events over a five-year period were classified into four regimes based on rainfall depth, duration and 30-minute maximum intensity, using hierarchical cluster analysis in the semiarid region of Brazil. Rainfall Regimes were grouped from higher to lower rainfall depth, longer to shorter duration, and higher to lower I30. Rainfall regime impact on surface runoff and sediment yield was studied in three watersheds under different land use - native tropical dry forest, thinned tropical dry forest, and slash and burn followed by grass cultivation. Thinning of native dry tropical forest reduced surface runoff and sediment yield due to the protective effect of the well-developed herbaceous layer. Runoff generation in the three watersheds showed strong dependence on antecedent soil moisture and the type of rain. Rainfall depth was the major factor for highest sediment yields.

Stemflow of a xerophytic shrub (Salix psammophila) in northern China: Implication for beneficial branch architecture to produce stemflow

Summary Stemflow is an important mechanism to replenish soil water for xerophytic shrubs in water-stressed ecosystems, whereas the biotic influences of leaf and branch on shrub stemflow were not completely investigated. In this study, the stemflow of 98 branches with various basal diameter under 42 rainfall events was measured for Salix psammophila in northern China during the rainy seasons of 2014 and 2015. The effects of rainfall characteristics, and plant traits of leaf and branch on stemflow were detected. Stemflow productivity (branch stemflow production of unit biomass) was proposed to determine the beneficial branch architecture for efficient stemflow production. The developed allometric equations by expressing the plant traits as a power function of branch basal diameter could satisfactorily estimate the leaf traits and biomass. There were significant differences of branch stemflow between different basal diameter and precipitation classes. The average shrub stemflow depth and percentage was 0.77 mm (0.004–3.32 mm) and 5.54% (0.70–7.92%), respectively. The precipitation amount and leaf fresh biomass were identified as the most influential rainfall characteristic and plant trait of stemflow, respectively. The stemflow production increased linearly with precipitation amount, and stemflow percentage increased with precipitation amount to approach the asymptotic value of 7.61%. The threshold precipitation amount of 2.1 mm was required to initiate shrub stemflow. The stemflow productivity decreased with basal diameter of branches and increased with precipitation amount. Allocating aboveground biomass to grow new branches and develop small ones was an energy-conserving strategy to ensure stemflow production. The branch architecture with more small branches, higher leaf biomass, and larger branch angle was more efficient for stemflow production.

Effects of Rainfall Characteristics on the Stability of Tropical Residual Soil Slope

Global climate change has a significant impact on rainfall characteristics, sea water level and groundwater table. Changes in rainfall characteristics may affect stability of slopes and have severe impacts on sustainable urban living. Information on the intensity, frequency and duration of rainfall is often required by geotechnical engineers for performing slope stability analyses. Many seepage analyses are commonly performed using the most extreme rainfall possible which is uneconomical in designing a slope repair or slope failure preventive measure. In this study, the historical rainfall data were analyzed and investigated to understand the characteristics of rainfall in Singapore. The frequency distribution method was used to estimate future rainfall characteristics in Singapore. New intensity-duration-frequency (IDF) curves for rainfall in Singapore were developed for six different durations (10, 20, 30 min and 1, 2 and 24 h) and six frequencies (2, 5, 10, 25, 50 and 100 years). The new IDF curves were used in the seepage and slope stability analyses to determine the variation of factor of safety of residual soil slopes under different rainfall intensities in Singapore.

The response of soil water and deep percolation under Caragana microphylla to rainfall in the Horqin Sand Land, northern China

In the semi-arid Horqin Sandy Land of northern China, Caragana microphylla, a leguminous shrub, is the dominant plant species widely used in re-vegetation efforts aimed at stabilization of mobile sandy lands. However, the effect of rainfall characteristics on soil water dynamics and deep percolation in C. microphylla shrublands are not well understood. The objective of this study was to examine the responses of volumetric water content (VWC) and deep percolation under the root zone of C. microphylla to different rainfall characteristics.An underground chamber with 23 concrete basins (200×200×230cm3) was constructed to conduct this experiment during the growing seasons from 2010 to 2013. For this study, three of the basins were filled with sandy soil taken from the C. microphylla shrublands near to the station (about 200m) and one C. microphylla shrub was transplanted into each basin in 2009. The corresponding hourly rainfall data were obtained from an automated meteorological station. VWC was recorded hourly using MiniTrase Soil Moisture Monitoring System at 0–20, 20–40, 40–60, 60–80, 80–100, 100–120, 120–140, and 140–160cm soil depths. Deep percolating water was collected in the underground chamber and measured daily.Our results showed that rainfall amount, intensity, duration, and the duration of the dry interval were significantly correlated with VWC in different soil layers. The amount of deep percolation was significantly correlated with rainfall amounts and rainfall duration, but not with rainfall intensity and the duration of the dry interval. Average deep percolation in C. microphylla shrublands was 97.5, 114.3, 66.8, and 15.1mm in 2010, 2011, 2012, and 2013, respectively, and accounted for 62.79%, 49.41%, 27.96%, and 7.36% of rainfall during the growing season. The coefficient of deep percolation was significantly negatively associated with annual mean shrub cover and canopy size, but not with annual mean height of C. microphylla.Our results suggested that re-vegetation with C. microphylla in this region is likely to result in a reduction in potential groundwater recharge and decrease of soil water content relations with an increase in age of the shrub.

Effects of rainfall characteristics on corrosion indices in Korean river basins

Corrosion indices have been widely used to assess water quality in countries such as the USA, Japan, France, and The Netherlands since Langelier first introduced this concept in 1936. The most commonly used corrosion indices are the Langelier saturation index (LSI), the Ryznar stability index (RSI), and the aggressiveness index (AI). Here, the changes in LSI, RSI, and AI due to corrosion factors such as pH, Ca hardness, and alkalinity were characterized according to the rainfall during the rainy season at four river basins in Korea. The results of a sensitivity analysis of corrosion indices with varying corrosion factors showed that pH had the greatest effect with a value of 0.1, which indicates that pH affects corrosion more than any other corrosion factor. By comparing the monthly pattern of corrosion factors at each river, it was found that pH and alkalinity decreased during the rainy season, whereas Ca hardness showed only subtle changes across the year. In addition, when comparing the relationship between the corrosion factors and corrosion indices at each river basin in the rainy season, LSI, RSI, and AI all showed strong corrosiveness with values of −2.97, 12.80, and 9.26, respectively, in the Nakdong River basin.

Effect of rainfall characteristics on removal efficiency evaluation in vegetative filter strips

The efficiency of a facility to remove non-point source pollution is likely to fluctuate according to conditions such as facility type and rainfall events; therefore, it is required to use a proper method to estimate removal efficiency. This study was conducted to estimate the efficiency of a facility with vegetative filter strips to remove pollutants by using methods previously used for the estimation of removal efficiency and compensate for weaknesses of the known methods. Other ways were presented to estimate an efficiency by which rainfall events were classified according to meteorological condition and amount of rainfall. Rainfall of frequency and summation of load as rainfall of frequency, where the frequencies per rainfall class were considered in efficiency ratio and summation of loads, respectively, seemed to have higher removal efficiencies than those estimated with the previous methods. Although it rained at the basin site, often in small quantity (below 10 mm), the rainfall events of below 10 mm were less frequent, during the monitored rainfall events, which accordingly resulted in low removal efficiencies. However, if the frequencies per rainfall class were considered, overall removal efficiencies of VFS might be increased because the removal efficiencies of the rainfall class under 10 mm was higher than other rainfall classes. Therefore, it is desirable to take into account such factors as effects of rainfall when it comes to measuring the removal efficiency of a non-point source pollutant of a factor, because those facilities are likely to be influenced by meteorological conditions including rainfall characteristics.

Runoff and water erosion on road side-slopes: Effects of rainfall characteristics and slope length

To investigate the effects of rainfall and slope length on water erosion on road side-slopes, runoff and soil loss are measured from natural runoff plots along the Qinghai-Tibet highway near Tuotuo River. Rainfall erosivity used in the revised universal soil loss equation is a good predictor for runoff and soil loss from road side-slopes. Runoff depth, sediment concentration and soil loss decreases as slope length increases.