Estimation of local extreme suspended sediment concentrations in California Rivers

Impact of the City on the Rapid Increase in the Runoff and Transport of Suspended and Dissolved Solids During Rainfall—The Example of the Silnica River (Kielce, Poland)

Urbanisation changes the water cycle and affects the parameters of transported, suspended and dissolved matter, especially in small river catchments. This paper presents the reasons why river runoff and fluvial transport rapidly increase during rainfall-induced summer floods in the stretch of the Silnica River that flows through the centre of Kielce, a city with a population of 200,000. Examples of implemented hydrotechnical solutions that aim to reduce the height of flood waves and eliminate water accumulation are also presented. The 18.05 km long Silnica River drains a catchment area of 49.4 km2. It flows through areas of varied land use, which have determined the location of five hydrometric stations (outlets) at different sub-catchments: Dabrowa(forest), Piaski (suburbia) and Jesionowa (includes a reservoir), as well as Pakosz and Bialogon (largely impervious areas in the city centre). Specific runoff, suspended and dissolved solids concentration and the specific load of these two types of fluvial transport were determined. It was found that the maximum specific runoff in the outlets of urban sub-catchments was significantly higher during floods than those of the sub-catchments upstream of the city centre; the suspended solids concentration was several times higher, and the suspended solids load was approximately 200 times higher. Recognition of the basic parameters of rainfall-induced flood waves, as well as the dynamics and size of fluvial transport at the hydrometric stations, especially at the outlets of sub-catchments with a large proportion of impervious area (approximately 30%), has become the basis for the development and implementation of modernisation projects and the construction of hydrotechnical facilities and devices in the river channel in the centre of Kielce.

Impact of Land-Use Changes on Spatiotemporal Suspended Sediment Dynamics within a Peri-Urban Catchment

Understanding sediment dynamics in peri-urban catchments constitutes a research challenge because of the spatiotemporal complexity and variability of land-uses involved. This study investigates differences in the concentration of total sediments (TSC) and suspended sediments (SSC) in the small peri-urban Mediterranean Ribeira dos Covões catchment (40% urban area) in central Portugal. Suspended sediment responses at the catchment outlet (E) and in three upstream sub-catchments, during periods of urbanization (2011–2013) and stabilizing land-use (2017–2018) are compared for storm-event datasets encompassing similar ranges of rainstorm sizes and antecedent rainfall condition. The Quinta sub-catchment, with the lowest urban area (22%) but subject to major construction activities affecting 17% of its area, led to highest TSC and SSC during urbanization (attaining 4320 mg/L and 4184 mg/L, respectively), and a median reduction of 38% and 69%, respectively, during stabilization. Espírito Santo sub-catchment, with highest urban area (49%) and minor construction activities, displayed similar median TSC in both periods (258–240 mg/L) but highest SSC reduction (76%), highlighting the impact of the anthropogenic disturbance mainly on fine-particle sediments and a good connectivity with the stream. Porto Bordalo sub-catchment, with 39% urban area and subject to the construction of a four-line road covering 1.5% of its area, showed the lowest TSC and SSC concentrations and the lowest median reductions in both periods (31% and 64%, correspondingly), mainly because of the impact of an unplanned retention basin established with soil from the construction site. Overall, median TSC and SSC reduced 14% and 59% at E, from urbanization to stabilization. Information about sediment dynamics should guide stakeholders in establishing strategies to reduce sediment loads and mitigate the impacts on urban aquatic ecosystems.

Study of biogas slurry concentrated by reverse osmosis system: characteristics, optimization, and mechanism

Biogas slurry, also called liquid digestate, refers to the liquid part of the anaerobic digestate produced from the anaerobic digestion process, which is an environmental pollution source if it is discharged without proper treatment. To recover the nutrients in the biogas slurry, a membrane system was designed to concentrate in the work. The effects of pretreatment technology including gravity settling and ultrafiltration process were studied via analyzing the chemical oxygen demand (COD), ammonia nitrogen (NH₃ -N), total nitrogen (TN), and conductivity. Reverse osmosis was applied in the biogas slurry concentration. The performance of reverse osmosis membrane used in the concentration process was studied by analyzing the permeate and concentrate (retentate), the volume reduction factor, and the concentration factor. The suitable parameters were selected as 20.0-25.0°C for influent temperature, 0.8-1.0Mpa for operating pressure, and 6.0-8.0 for influent pH. Furthermore, the feasible concentration factor was evaluated as 4. The economic, environmental, and social benefits could be gained if (concentrated) biogas slurry was used as an alternative to chemical fertilizers. PRACTITIONER POINTS: Reverse osmosis system was established for biogas slurry concentrating. The operational factors were optimized on biogas slurry concentrating and separation. The biogas slurry separation mechanism was discussed.

Multiple Linear Regression Models for Predicting Nonpoint-Source Pollutant Discharge from a Highland Agricultural Region

Sediment runoff from dense highland field areas greatly affects the quality of downstream lakes and drinking water sources. In this study, multiple linear regression (MLR) models were built to predict diffuse pollutant discharge using the environmental parameters of a basin. Explanatory variables that influence the sediment and pollutant discharge can be identified with the model, and such research could play an important role in limiting sediment erosion in the dense highland field area. Pollutant load per event, event mean concentration (EMC), and pollutant load per area were estimated from stormwater survey data from the Lake Soyang basin. During the wet season, heavy rains cause large amounts of suspended sediment and the occurrence of such rains is increasing due to climate change. The explanatory variables used in the MLR models are the percentage of fields, subbasin area, and mean slope of subbasin as topographic parameters, and the number of preceding dry days, rainfall intensity, rainfall depth, and rainfall duration as rainfall parameters. In the MLR modeling process, four types of regression equations with and without log transformation of the explanatory and response variables were examined to identify the best performing regression model. The performance of the MLR models was evaluated using the coefficient of determination (R2), root mean square error (RMSE), coefficient of variation of the root mean square error (CV(RMSE)), the ratio of the RMSE to the standard deviation of the observed data (RSR) and the Nash–Sutcliffe model efficiency (NSE). The performance of the MLR models of pollutant load except total nitrogen (TN) was good under the condition of RSR, and satisfactory for the NSE and R2. In the EMC and load/area models, the performance for suspended solids (SS) and total phosphorus (TP) was good for the RSR, and satisfactory for the NSE and R2. The standardized coefficients for the models were analyzed to identify the influential explanatory variables in the models. In the final performance evaluation, the results of jackknife validation indicate that the MLR models are robust.

Estimating and Predicting Metal Concentration Using Online Turbidity Values and Water Quality Models in Two Rivers of the Taihu Basin, Eastern China

Turbidity (T) has been widely used to detect the occurrence of pollutants in surface water. Using data collected from January 2013 to June 2014 at eleven sites along two rivers feeding the Taihu Basin, China, the relationship between the concentration of five metals (aluminum (Al), titanium (Ti), nickel (Ni), vanadium (V), lead (Pb)) and turbidity was investigated. Metal concentration was determined using inductively coupled plasma mass spectrometry (ICP-MS). The linear regression of metal concentration and turbidity provided a good fit, with R² = 0.86–0.93 for 72 data sets collected in the industrial river and R² = 0.60–0.85 for 60 data sets collected in the cleaner river. All the regression presented good linear relationship, leading to the conclusion that the occurrence of the five metals are directly related to suspended solids, and these metal concentration could be approximated using these regression equations. Thus, the linear regression equations were applied to estimate the metal concentration using online turbidity data from January 1 to June 30 in 2014. In the prediction, the WASP 7.5.2 (Water Quality Analysis Simulation Program) model was introduced to interpret the transport and fates of total suspended solids; in addition, metal concentration downstream of the two rivers was predicted. All the relative errors between the estimated and measured metal concentration were within 30%, and those between the predicted and measured values were within 40%. The estimation and prediction process of metals’ concentration indicated that exploring the relationship between metals and turbidity values might be one effective technique for efficient estimation and prediction of metal concentration to facilitate better long-term monitoring with high temporal and spatial density.