Rain Intensity Research Articles

Dripping Rainfall Simulators for Soil Research—Performance Review

Rainfall simulators represent often-used equipment for soil research. Depending on their performance, they could be appropriate for some soil research or not. The aim of this research is to provide insight into the capabilities of existing dripping rainfall simulators (DRS) to mimic natural rainfall and the frequency of simulated rainfalls of certain characteristics, facilitate the selection of rain simulators that would best meet the needs of soil research and to reach a step closer to the standardization of rainfall simulators. DRS performance was analyzed integrally, for simulators with more than one dripper (DRS>1) and with one dripper (DRS=1). A statistical analysis was performed for the performance of the DRS, wetted area, drop size, rainfall intensity, duration and kinetic energy. The analysis showed that DRS can provide rainfall that corresponds to natural rainfall, except in terms of the drop size distribution and wetted area. However, usually there are more factors that do not correspond to natural rainfall, such as the median drop size, volume and kinetic energy. Metal and plastic tubes (MT and PT) as the most present dripper types showed a strong relation between the outer diameter (OD) and drop size, while the inner diameter (ID) relation was moderate-to-weak. However, when increasing the range of MT drippers, for diameter size, the relation significance becomes very strong for bouts ID and OD. With the increase in the ID of PT, the relation deviates from the logarithmic curve that represents all drippers together. The sizes of the drops generated by the drippers are mostly in the range between 2 and 6 mm, while the number of drops smaller than 2 mm is relatively small. The intensity and duration of the simulated rain can be successfully produced to match natural values, with the most frequently simulated short-term rainfall of a high intensity. Most simulations were conducted at a fall height of up to 2 m, and then their number gradually decreases as the height gets closer to 5 m. Most simulations (58.6%) occur in the range between 20-90% KE, then 33.0% in a range of 90-100%, with only 8.4% lower than 20% KE.

Antecedent rainfall as a critical factor for the triggering of debris flows in arid regions

Abstract. In arid regions, debris flows (DFs) are occasionally observed when heavy rainfall hits steep slopes with unconsolidated materials. Despite the related hazards, not much is yet known about the critical rainfall conditions for DF initiation in dryland areas mainly due to a lack of observations and data. In this study, we use high-resolution digital surface models and orthophotos to detect DFs on the arid slopes of the Dead Sea's northwestern margins, as well as weather radar rainfall estimates for the characterization of the triggering and non-triggering storms. We identify deposits from over 40 relatively small DFs that occurred between 2013 and 2019. We divide them into four groups based on their spatial distribution and triggering period, and we identify the most likely triggering storms based on weather radar data and additional information. We show that the DFs were likely triggered by an intense convective cell (lasting less than 45 min) which was preceded by non-negligible rainfall amounts (about 10 mm) delivered during the storm. Comparing triggering and non-triggering storms, we observed that rain intensity alone is insufficient to explain the phenomena and discuss the possibility that antecedent rainfall could represent a critical factor for the triggering of DFs on steep slopes of arid environments.

Empirical Analysis of Autonomous Vehicle's LiDAR Detection Performance Degradation for Actual Road Driving in Rain and Fog.

Light detection and ranging (LiDAR) is widely used in autonomous vehicles to obtain precise 3D information about surrounding road environments. However, under bad weather conditions, such as rain, snow, and fog, LiDAR-detection performance is reduced. This effect has hardly been verified in actual road environments. In this study, tests were conducted with different precipitation levels (10, 20, 30, and 40 mm/h) and fog visibilities (50, 100, and 150 m) on actual roads. Square test objects (60 × 60 cm2) made of retroreflective film, aluminum, steel, black sheet, and plastic, commonly used in Korean road traffic signs, were investigated. Number of point clouds (NPC) and intensity (reflection value of points) were selected as LiDAR performance indicators. These indicators decreased with deteriorating weather in order of light rain (10-20 mm/h), weak fog (<150 m), intense rain (30-40 mm/h), and thick fog (≤50 m). Retroreflective film preserved at least 74% of the NPC under clear conditions with intense rain (30-40 mm/h) and thick fog (<50 m). Aluminum and steel showed non-observation for distances of 20-30 m under these conditions. ANOVA and post hoc tests suggested that these performance reductions were statistically significant. Such empirical tests should clarify the LiDAR performance degradation.

DSDNet: Toward single image deraining with self-paced curricular dual stimulations

A crucial challenge regarding the single image deraining task is to completely remove rain streaks while still preserving explicit image details. Due to the inherent overlapping between rain streaks and background scenes, the texture details could be inevitably lost when clearing rain away from the degraded image, making the two purposes contradictory. Existing deep learning based approaches endeavor to resolve the two issues successively in a cascaded framework or to treat them as independent tasks in a parallel structure. However, none of the models explores a proper interaction between rain distributions and hidden feature responses, which intuitively would provide more clues to facilitate the procedures of rain streak removal as well as detail restoration. In this paper, we investigate the impact of rain streak detection for single image deraining and propose a novel deep network with dual stimulations, namely, DSDNet. The proposed DSDNet utilizes a dual-stream pipeline to separately estimate rain streaks and a loss of details, and more importantly, an additional mask that indicates both location and intensity of rains is jointly predicted. In particular, the rain mask is involved in a tailored stimulation strategy that is deployed into each stream of the proposed model, serving as guidance for allowing the network to focus on rain removal and detail recovery in rain regions rather than non-rain areas. Moreover, we incorporate a self-paced semi-curriculum learning design to alleviate the learning ambiguity brought by the prediction of the rain mask and thus accelerate the training process. Extensive experiments demonstrate the proposed method outperforms the state-of-the-art methods on several benchmarks, including in both synthetic and real-world scenarios. The effectiveness of the proposed method is also validated via joint single image deraining, detection, and segmentation tasks.

Infiltration Model of Mediterranean Soil with Clay Texture

Infiltration plays an essential role in increasing the soil water content as a part of the hydrological cycle. Infiltration affects surface runoff and soil conservation. It also determines the sustainability of the groundwater system. Heavy rain intensity exceeding the infiltration capacity will result in surface runoff, and excessive surface runoff will cause soil erosion. This study aims to investigate the suitable infiltration rate model in the Mediterranean soil of clay textured with various soil conditions. Infiltration rate measurement employed a double-ring infiltrometer in soil without and with tillage. The applied infiltration rate model was an empirical model and the function of time, which includes the Kostiakov, Horton, and Philip Models. The results demonstrated that the Mediterranean soil infiltration rate with a clay texture was 0.91 cm/min and was relatively higher in the soil without tillage. The suitable infiltration rate model to be applied in soil conditions without and with tillage is the Kostiakov Model f = 0.700 t-0.25 and f = 0.682 t-0.22, respectively. The Kostiakov model is the most suitable infiltration rate model in Mediterranean textured clay, without tillage conditions, with a determination value of 0.988 and a deviation value of 0.005. Keywords: Horton model, Philip model, Infiltrometer; Kostiakov model, Tillage

Effect of Debris Flow Event on the Affected Areas in Putih River, Indonesia

Debris flow is a natural phenomenon that can cause some damage and fatalities. Debris flow from Mount Merapi frequently happens through the Putih River, so it is necessary to do research. Anticipating the occurrence of debris flows can be done with predictions to reduce the number of casualties and material losses. This research used a simulation method based on Ashida, Takashi, and Mizuyama equation that applied the Nakayasu synthetic unit hydrograph through modeling on SIMLAR V2.1 application by modifying the hyetograph pattern and the rain intensity value. The test result contained flood area, velocity, volume, flow height, and the value of degradation and aggradation that happened in each simulated pattern. The velocity value in simulation with rain intensity of 56.8 mm and one peak hyetograph is 1.36 m/s, and in simulation with rain intensity of 56.8 mm and two peak hyetograph is 1.42 m/s. It means the parameter increases by 4.4%. Based on the results, it can be concluded that the hyetograph pattern is very influential on the impact of lava floods. The increase in the hydrograph value is also directly proportional to the increase in flow velocity. The value of rain intensity and rain pattern also affects the number of areas affected by the lava flood. The increasing value of the intensity and pattern of rain is also directly proportional to the increase in the area affected by flooding.

Assessment of Infiltration Swale Performance as a Low-Impact Development Technique in Tropical Coastal Environments

Operation of source control measures (SCM) in urban drainage in tropical/transitional climates are still a challenge because of higher rain volumes and more intense rains, as well as constraints from sea-level interference. In this study, the performance of a swale to control runoff was detailed and monitored in such an environment. The data on rain, runoff, and sea levels were acquired at a site located in an island in the south coast of Brazil. The results showed that even with higher rain volumes and more intense rains, the mean capture of the swale was 51.7% of the entrance runoff volume, but it depended on seasonal rain variation and interference of sea/tide level. As a result, the swale might be undersized in summer and oversized in winter. Peak flow retardation was observed in 97% of monitored events. The interference of sea/tide level was not directly correlated with infiltration volumes, but in the principal component analysis, the parameters of sea/tide level, along with the hydrological parameters of rain duration, height, and intensity, explained 60% of the variance in the data. In conclusion, the application of SCMs in tropical regions is suitable, but seasonality should be incorporated in the design. The interference of sea/tide level must be further investigated to verify how to incorporate its influence in the design.

Coevolution of Climate Change, Surface Properties, Vegetation Cover, and Drainage Network in a Loess Covered Area.

Arid and semi-arid areas are often regarded as highly sensitive to climate change. Average annual rainfall is usually regarded as the most important factor controlling soil moisture regime, water availability, and therefore various environmental variables. The present study deals with the ecology of an area located in the semi-arid area of Israel, where average annual rainfall is ~280 mm. The area is located in a loess covered area. The loess cover was deposited during a wet climatic phase. However, pedological and ecological data point to a desertification effect. Data obtained show that non-climatic factors, such as local surface properties, can exert a strong influence on the environment. In addition, the global models disregard the characteristics of the local rainfall regime, such as the distribution of rain intensities, and the duration of individual rain-showers during a rainstorm. Under the present rainfall regime about 85% of the rains are below 5 mm/hr,1, rainfall is also highly intermittent, limiting runoff generation, and infiltration depth. Under such conditions, a high evaporation rate leads to a soil salinization process.

Investigation on Variability, Broader Types and Patterns of Daily and Sub-daily Rains Using Satellite Sub-Daily Rainfall Records based in Western Indian Province

The present study was conducted during 2021 at middle Gujarat. The objectives of the study remained inclined towards the challenging task, where limited observed rainfall records (daily and sub-daily both) were utilized to project corresponding regional design hyetographs for providing the design hyetographs at similar ungauged sites in the region. This script explores suitability, appropriateness and end efficacies of blended (ground based as well as remotely sensed) precipitation data attained for a data deprived region, which was ultimately utilized to derive location specific rainfall curves adopting satellite based observed rainfall records. A set of representative type curves on rainfall (daily &amp; sub-daily) for study region were conceived, which could be potentially utilized for better rainfall-runoff modelling even under purely ungauged scenarios. Voluminous precipitation data retrieved via GPM (IMREG) satellite precipitation products was endeavoured and used to create values envelope of design curves for use in ungauged situations. 21 years of daily &amp; sub-daily rainfall records (2000–2020) were thoroughly examined and used to retrieve valid understanding towards annual, monthly, daily and even hourly based variability of rainfall across six different stations as adopted in the study. The net magnitude of dispersals in all the derived sets of mass curves/Hyetographs were worked out and suitably compared across 6 specific locations as well as their categorization in terms of storm depths, storm durations and peak rain intensities which could be of high practical importance for water resource planners other relevant research and development.

Chickpea Varieties and Time of Sowing Effects on Growth and Yield under North-East Monsoon Influenced in Andhra Pradesh, India

Background: In Sri Potti Sriramulu Nellore district of Andhra Pradesh, India where North-East monsoon is predominant. During this season, chickpea crop sown during October to November 1st fortnight (FN) causing total crop loss due to high intensity rains in the changing climate scenario. In this context, there is a need for identification of suitable varieties of chickpea with ideal time of sowing for Sri Potti Sriramulu Nellore district under changing climatic situations to enhance the yields of chickpea. Methods: Field experiment was carried out during rabi 2019-20 at Agricultural Research Station, Podalakur (14°22°N latitude, 79°44°E longitude and 43 m above mean sea-level), Sri Potti Sriramulu Nellore district andhra Pradesh to identify the suitable chickpea variety and optimum time of sowing. The field experiment was laid out in Split plot design with 4 varieties of chickpea (V1: Nandyala gram-49, V2: Dheera, V3: Nandyala Senaga-1 and V4: JG-11) as main plot treatments and 3 time of sowings (D1: November 2nd FN, D2: December 1st FN, D3: December 2nd FN) as sub plot treatments in three replications. Result: Nandyala Senaga-1 and Dheera have taken more number days to 50% flowering and maturity. Crop sown on November 2nd FN took significantly more days (42.8) to bear 50% flowering and maturity, while the lowest number of days per 50% flowering and maturity was taken by December 2nd FN sown crop. Chickpea variety Nandyala Gram-49 recorded the highest grain yield (1491 kg ha-1), which was statistically on par with Nandyal Senaga-1 (1465 kg ha-1). The crop sown on November 2nd FN recorded significantly the highest grain yield (1462 kg ha-1), but which was statistically on par with December 1st FN (1424 kg ha-1) sown crop.

Hydrologic performance assessment of nature-based solutions: a case study in North-eastern Italy

The consequences of climate change are exacerbated by land-use changes, which influence the rainfall-runoff relations and consequently the flood risk. Effectively, urbanization is steadily contributing to the increase of impervious areas and reducing the time-to-peak. The effect of Nature Based Solutions (NBSs) on the mitigation of these phenomena is recognized. Nevertheless, these kinds of sustainable infrastructures are still barely known and scarcely adopted in many parts of the European Countries. The LIFE BEWARE project aims to enhance hydraulic safety and spread good practices in rainwater management by promoting and facilitating the adoption of NBSs in the Altovicentino area (Northern Vicenza Province, Veneto Region, Italy). To support the dissemination activities, some full-scale NBSs have been created within the municipality areas involved in the project. The hydrological impact of the structures is continuously monitored thanks to the installation of devices measuring inlet and outlet runoff, and rainfall pattern. This study aims to analyse the monitoring data of the first two years of the built NBSs. Results show that the structures managed almost all the water runoff through processes of infiltration and retention, providing additional insights into understanding the real behaviour of NBSs exposed to the specific environmental conditions of a very rainy foothills area. In particular, mean rain intensity and rainfall duration are the variables that mostly affected the structure performance, especially for events prolonged over time (2-3 days) with mean rainfall intensity in the range of 2-3 mm/h. Therefore, the overall outcomes from this analysis resulted as being useful to improve the design of NBSs and further promote their installation in urban areas.

Studi Pengaruh Kejadian Hujan Terhadap Banjir Lahar Di Sungai Gendol Menggunakan SIMLAR

Indonesia is a country with the largest number of active volcanoes in the world and has the potential to erupt. This causes primary and secondary disasters, one of which is secondary disasters caused by lava floods during heavy rains. So disaster mitigation is needed by simulating lava floods to find out the predictions of speed, volume, height and area affected by lava floods. The simulation was carried out using SIMLAR software, carried out on Gendol River which is one of the watersheds that has the threat of lahar flooding. The test was carried out with 3 hyetograph patterns and for each pattern there were 3 simulations with different rainfall intensities, namely 162 mm, 243 mm and 324 mm. From these tests, the speed values ​​in patterns 1, 2 and 3 increased each simulation to the existing simulation. The speed value obtained by pattern 1 at 162 mm rain intensity is 2.35 m/s, at 243 mm rain intensity is 2.48 m/s, and at 324 mm rain intensity is 2.58 m/s. In addition, at high yields, volume and area also increase in each simulation due to the higher rainfall intensity. This proves that the intensity of rain is directly proportional to speed, volume, area and height. In addition, the hyetograph pattern also affects the peak hours when the maximum volume, maximum height and maximum speed are reached.

Impact of Rain Intensity on Interstate Traffic Speeds Using Connected Vehicle Data

With the emergence of connected vehicle data and high-resolution weather data, there is an opportunity to develop models with high spatial-temporal fidelity to characterize the impact of weather on interstate traffic speeds. In this study, 275,422 trip records from 41,234 unique journeys on 42 rainy days in 2021 and 2022 were obtained. These trip records are categorized as no rain, slight rain, moderate rain, heavy rain, and very heavy rain periods using the precipitation rate from NOAA High-Resolution Rapid-Refresh (HRRR) data. It was observed that average speeds decreased by approximately 8.4% during conditions classified as very heavy rain compared to no rain. Similarly, the interquartile range of traffic speeds increased from 8.34 mph to 12.24 mph as the rain intensity increased. This study also developed a disaggregate approach using logit models to characterize the relationship between weather-related variables (precipitation rate, visibility, temperature, wind, and day or night) and interstate speed reductions. Estimation results reveal that the odds ratio of reducing speed is 5.8% higher for drivers if the precipitation rate is increased by 1 mm/h. The headwind was found to have a positive significant impact of only up to a 10% speed reduction, and speed reduction is greater during nighttime conditions compared to daytime conditions by a factor of 1.68. The additional explanatory variables shed light on drivers’ speed selection in adverse weather environments, providing more information than the single precipitation intensity measure. Results from this study will be particularly helpful for agencies and automobile manufacturers to provide advance warnings to drivers and establish thresholds for autonomous vehicle control.

Evaluation of a Modular Filter Concept to Reduce Microplastics and Other Solids from Urban Stormwater Runoff

This paper describes an innovative Decentralized Technical Sustainable Drainage System (SuDS) concept, which is based on technical devices, such as sieves, sedimentation barriers, floating barriers and a magnetic module, which addresses, mainly, the fine matter. The SuDS is designed as a retrofit system so that no costly and time-consuming conversion measures are necessary. Due to the possibility of free configurability of individual modules in the three levels, road, gully and drain, a novel solution approach is presented, which is not available on the market, for a reduction in solids in general and microplastics in particular. The retention performance of selected modules and their combinations is demonstrated by means of bench tests according to the test procedure of the German Institute for Construction Engineering (DIBt) for the evaluation of decentralized treatment systems. Four different rain intensities, from light to medium up to heavy rain, are charged to the filter modules. Collected and fractionated road-deposited sediment (RDS) was selected as the test substance (10 kg). Additional tests with tyre powder, PE pellets, cigarette butts and candy wrappers helped to make clear the filter process of the particulate matter. The retention performance was determined by the mass balance between the defined dosage and at the outlet. For this purpose, the total volume flow of the effluent was passed over a stainless-steel sieve with a diameter of 600 mm and a mesh size of 20 µm. For the test substance, RDS retention rates up to 97% were measured. Very fine matter, particularly, was technically challenging to obtain; &lt;63 µm up to 66% could be retained by the filter modules. Modules in the road space, such as porous asphalt or additional retention spaces, in the area of the curb as well as direct infiltration in the road drainage shaft are theoretically described and discussed. The outlook also addresses the potential of an intelligent network to reduce the input of pollution from urban stormwater runoff.

Analysis of Vsat Gyro performance based on the power level of the antenna receiver on the Pelni ship

The satellite communication system that is used for ship communication in Indonesian waters is expected to transmit real time data at any time under any conditions. However, currently, the Vsat Gyrsoscope antenna that is installed on the Pelni ship still uses the Ku band frequency. This frequency band is very susceptible to rain attenuation. Vsat Gyro will automatically search for satellites that cover it. Only when it is raining and the ship is moving towards the port, is there a decrease in the receiving power level. SNR and power and C/N will drop. Therefore, it is necessary to do an analysis to overcome this problem so that it is not disconnected during the transmission. This study conducted an analytical study to validate the analytical predictions of phasing the vsat power signal level on the pelni ship to maintain communication during sea operations, which are included in TKT 3 (three). The tools used in the measurement are vsat modem, PRTG application, laptop, RJ 45 cable, and Spectrum Analyzer. By optimizing the calculation of the margin link budget, the calculation of Qos and the parameters vsat Eb/No, C/N and SNR when adjusted to the operating conditions of the ship with high rain intensity so that communication can continue to run even when the worst conditions can be maintained properly.Â

A data-driven physics-informed stochastic framework for hurricane-induced risk estimation of transmission tower-line systems under a changing climate

Hurricanes are one of the most devastating natural hazards which result in significant damage to civil infrastructure. The transmission tower-line system is specifically highly vulnerable to hurricane effects. Recent studies have indicated that the collapse of the transmission tower-line system during hurricane events is mainly due to the joint occurrence of wind and rain. Therefore, it is important to assess the failure probabilities of these structures under wind and rain-induced loads. With climate change, those probabilities are expected to significantly change where the brunt of the damage and economic losses would be disproportionately borne by coastal communities. This study proposes a hybrid risk-responsive, data-driven and physics-informed framework which evaluates the hurricane-induced damage to transmission lines in vulnerable regions and communities under several climate scenarios. The framework is founded upon an advanced physics informed hurricane simulation model followed by a Gaussian kernel density technique to efficiently estimate the intensity measures and quantify the associated uncertainties accurately. The generated hazard intensities are coupled with fragility surfaces expressed in terms of wind speed and rain intensity. Then, the failure probabilities are obtained for the transmission tower-line system under the joint excitation and future climate scenario. The framework is applied to several coastal cities along the US east coast. It is shown that, due to the involved system nonlinearity, the obtained failure probabilities change drastically with the future climate scenario. In addition, rainfall-induced loads which significantly impact the failure probabilities of the transmission tower-line systems are not only function of the selected sites, but also depend on the considered limit state and climate scenario. Therefore, their consideration is important for the structural design and estimation of the system performance.

Hydrometeorological characterization and estimation of landfill leachate generation in the Eastern Amazon/Brazil.

The complex physical-chemical and microbiological composition of leachate in sanitary landfills sets the adequate treatment for different waste types. However, before the final disposal of wastes in receptor waterbodies, it is essential to use specific methods to quantitatively prevent internal flows to find proper treatments. The aim of the present research is to use hydrological models to estimate monthly leachate flow generation in Macapá's Municipal Sanitary Landfill (ASMM), Amapá State, Brazil. Disregarding the temporal trend bias, the average (0.45 m3s-1), minimum (0.07 m3s-1) and maximum (0.72 m3s-1) flows were estimated based on hydrological models in the literature (Rmax = 99%, p<0.05). The results estimated from different hydrological gauges pointed towards significant spatial variations in final discharge. Thus, estimated flows worked as reference to calculate the loads of coproducts and nutrients concerning different operational stages in ASMM. Therefore, rain intensity estimates have pointed out precipitation variability, and it has significantly affected leachate flow. In conclusion, there would be a proportional increase in leachate flow during extreme maximum precipitation events; overflow would be the effect of such flows and it would assumingly have impact on its surrounding areas. It is also possible estimating some degree of rainfall impact over ASMM's infrastructure in the long term (>10 years), since it could influence its lifespan.

Erosion Hazard Levels in Padang Batung Sub-district, Hulu Sungai Selatan Regency, South Kalimantan Province, Indonesia

Erosion is a form of damage to the soil caused by changes in land function on certain plains without management. The Padang Batung Sub-district area experienced land damage which was characterized by the distribution of critical land area reaching half of the area. The purpose of this study is to analyze the level of erosion hazards that occur in Padang Batung Sub-district. This study used a terrain unit map as the basis for the sample analysis unit. The number of samples in this study was 20 samples using the purposive random sampling method. The data analysis used is in the form of the Universal Soil Loss Equation (USLE) equation which can predict the level of erosion hazard through several parameters in the study area. The results showed that the erosion hazard level in Padang Batung Sub-district was dominated by severe criteria with an affected area of 74 km2 with an average erosion rate of 345.27 tons/ha/yr. One of the dominating factors causing the high erosion in Padang Batung Sub-district to be included in the medium and high classification is rain intensity, high erodibility, unstable topography and land cover vegetation.

Pollutant characteristics and size distribution of trace elements during stormwater runoff events

Priority trace elements As, Cu, Cr, Ni, Pb, and Zn are largely present in urban stormwaters and should be controlled due to their impact on water bodies. As it has been observed that there are numerous limitations in the purification performance of roadway stormwater runoff treatment systems, the particulate size distribution of trace elements was studied extensively to assess the colloidal fractions present in stormwater runoff of a high-traffic roadway site (100 000 vehicles/day). Besides the evaluation of the total Event Mean Concentrations (EMCs) and dissolved concentrations, a complete fractionation scheme of low settling phase of runoff water (<30 µm) was applied to a series of rain events, considering 8 µm and 5 kDa, as relevant cut-offs between particulate/colloidal elements, and colloidal/truly dissolved elements. The intra-event size distribution was also considered to assess the first-flush effect and the variation of the physical speciation. The high-level traffic associated with climatic conditions (rainfall depth) are responsible for very high EMCs for Zn and Cu, together with a significant exceedance of the European environmental water standards (<0.45 µm concentrations). Ni, Cr and Pb are mainly present as particulate and colloidal metals. Therefore, considering a more complete size distribution is relevant for these elements. For As, Cu and Zn, the conventional fractionation at 0.45 µm seems to be sufficient to evaluate the highly mobile fraction. The results also indicate that, while the main particulate load may be collected within the early volumes of the rainfall events (about 30%), the variability of rain intensity during long events induces changes in particulate and colloidal metals in the runoff. The treatment of runoff must then be considered as a whole in view of the variability of trace metal size distribution. This suggests that urban stormwater runoff treatment systems which employ only the settleable fraction are not sufficient to limit the chemical and ecological risks to receiving water bodies.

Increasing areas of aquaculture ponds and reservoirs reshape runoff coefficients: evidence from a subtropical catchment, China.

Detention pond is a key storm water management measure employed both to attenuate surface runoff and to regulate depression storage, yet the effects of aquaculture ponds and reservoirs on runoff coefficient are not well quantified in a subtropical humid monsoon climate zone, China. Here, a set of six subcatchments ranging in size from 0.7 hm2 to 10,000 hm2 were evaluated over the 2011-2015 period. (i) The annual average runoff coefficient differed with different subcatchments due to the spatial heterogeneity of landscape patterns, while the event-based runoff coefficient under the same catchment showed a decreasing trend with increasing rainfall intensity. (ii) The annual average and event-based runoff coefficients initially increased and then decreased with an increase in the area ratio of aquaculture ponds and reservoirs. The critical area ratio of aquaculture ponds and reservoirs for the maximum runoff coefficient in annual, light, and moderate rainfall intensity was about 4%; but this value would be transferred forward to the position of < 4% under the intensity of heavy rain, rainstorms, and heavy rainstorms. (iii) All runoff coefficients decreased with increasing forestland but increased with increasing paddy fields, and the decreasing rate was greater than the increasing rate. The trends of runoff coefficient for the annual and event-based rainfall are opposite between river development coefficient and watershed shape coefficient. The results provide underlying insights for decision-makers in aquaculture land-use planning and the sustainable utilization of water resources in the upstream and downstream systems of a catchment.