A physically based model for mesoscale SuDS - an alternative to large-scale urban drainage simulations.

This study presents a deterministic, lumped model to simulate mesoscale sustainable drainage systems (SuDS) based on a conceptualization of the stormwater control measures (SCMs) making up the system and their influence on the runoff process. The conceptualization mainly relies on parameters that are easily quantifiable based on the physical characteristics of the SCMs. Introducing a nonlinear reservoir model at the downstream end of the SuDS results in a fast model that can realistically describe the runoff process at low computational cost. Modelled hydrographs for the study area in Malmö, Sweden, matched data with regard to the overall shape of the hydrograph as well as the peak discharge and lag time. These output parameters are critical factors to be considered in the design of large systems consisting of mesoscale SuDS. The algebraic foundation of the developed model makes it suitable for large-scale applications (e.g., macroscale), where the simulation time is a decisive factor. In this respect, city-wide optimization studies for the most efficient location and implementation of SuDS are substantially accelerated due to fast and easy model setup. Moreover, the simplicity of the model facilitates more effective communication between all the actors engaged in the urban planning process, including political decision makers, urban planners, and urban water engineers.

Simulating beach and dune evolution at decadal to centennial scale under rising sea levels.

A numerical model for simulating beach-dune evolution at decadal to centennial time scales is developed. The work builds on an existing semi-empirical cross-shore model, the CS-model, to which the effect of sea level rise is added and the routines for aeolian transport and morphological dune evolution are improved. The model development is based on established conceptual models from the literature, which are translated into mathematical formulations and solved numerically. The capability of the proposed model is demonstrated through a case study at Ängelholm Beach, Sweden. The model is calibrated and validated against a seven-year long data set on morphological evolution and sediment grain-size samples. Beach and dune evolution is then simulated from 2018 to 2100 for a range of sea level rise scenarios. The model results are promising, and suggest that the model has potential to be used for long-term assessment of climate change impact on beaches and dunes.

Remotely sensed assessment of water quality levels in the Pearl River Estuary, China.

In this paper, a method of assessing water quality from satellite data is introduced. The composite pollution index (CPI) was calculated from measured chemical oxygen demand (COD) and nutrient concentration. The relationships between CPI and 240 band combinations of SeaWiFS water-leaving radiance were analyzed and the optimal band combination for estimating CPI was chosen from the 240 band combinations. An algorithm for retrieval of CPI was developed using the optimal band combination, (L(443)xL(510))/(L(412)+L(490)). The CPI was estimated from atmospherically corrected SeaWiFS data by employing the algorithm. Furthermore, the CPI value range for each water quality level was determined based on data obtained from 850 samples taken in the Pearl River Estuary. The remotely sensed CPIs were then transferred to water quality levels and appropriate maps were derived. The remotely sensed water quality level maps displayed a similar distribution of levels based on in situ investigation issued by the State Ocean Administration, China. This study demonstrates that remote sensing can play an important role in water quality assessment.

Qualitative simulation of bathymetric changes due to reservoir sedimentation: A Japanese case study.

Sediment-dynamics modeling is a useful tool for estimating a dam's lifespan and its cost-benefit analysis. Collecting real data for sediment-dynamics analysis from conventional field survey methods is both tedious and expensive. Therefore, for most rivers, the historical record of data is either missing or not very detailed. Available data and existing tools have much potential and may be used for qualitative prediction of future bathymetric change trend. This study shows that proxy approaches may be used to increase the spatiotemporal resolution of flow data, and hypothesize the river cross-sections and sediment data. Sediment-dynamics analysis of the reach of the Tenryu River upstream of Sakuma Dam in Japan was performed to predict its future bathymetric changes using a 1D numerical model (HEC-RAS). In this case study, only annually-averaged flow data and the river's longitudinal bed profile at 5-year intervals were available. Therefore, the other required data, including river cross-section and geometry and sediment inflow grain sizes, had to be hypothesized or assimilated indirectly. The model yielded a good qualitative agreement, with an R2 (coefficient of determination) of 0.8 for the observed and simulated bed profiles. A predictive simulation demonstrated that the useful life of the dam would end after the year 2035 (±5 years), which is in conformity with initial detailed estimates. The study indicates that a sediment-dynamic analysis can be performed even with a limited amount of data. However, such studies may only assess the qualitative trends of sediment dynamics.

Integrity breaches in a hollow fiber nanofilter - Effects on natural organic matter and virus-like particle removal.

Ultrafiltration and nanofiltration have become common methods to treat surface water for drinking water purposes. Common aims of a membrane step are removal of natural organic matter (NOM), softening or adding an extra microbiological or chemical barrier. In most cases, the membrane is considered a good disinfection step; commonly the viral removal is at least 4-log. To ensure a working disinfection, reliable integrity tests are required. In the present pilot study with a hollow fiber nanofilter, the membrane achieved a high NOM reduction, and the difference in parameters related to NOM quality before and after treatment proved to be useful indicators of integrity breaches. Changes in total organic carbon (TOC) concentration, UV-absorbance at 254 nm (UVA254) and fluorescence derived parameters in the permeate flow were related to leaking fibers. On average, UVA254 in the permeate was 3 times higher for a membrane with compromised fibers (0.041 cm-1) compared to an intact membrane (0.013 cm-1), while TOC was less than 2 times as high on average. Thus, this membrane had a higher reduction of UVA254 than TOC and the sensitivity for changes from leakage was higher. Therefore, it is suggested that UVA254 could be used as an indicator for membrane integrity. Additionally, there is a significant (P < 0.01) difference in fluorescence derived parameters between a leaking and an intact fiber, showing that fluorescence also has potential to be applied for online monitoring of membrane processes. During fiber failure, around 2% of the permeate flow passes through one single leaking fiber. The transport depends on the distance between the inflow and the leak, which in most cases are similar and most likely close to the middle of the fiber.

A methodology for estimating risks associated with landslides of contaminated soil into rivers.

Urban areas adjacent to surface water are exposed to soil movements such as erosion and slope failures (landslides). A landslide is a potential mechanism for mobilisation and spreading of pollutants. This mechanism is in general not included in environmental risk assessments for contaminated sites, and the consequences associated with contamination in the soil are typically not considered in landslide risk assessments. This study suggests a methodology to estimate the environmental risks associated with landslides in contaminated sites adjacent to rivers. The methodology is probabilistic and allows for datasets with large uncertainties and the use of expert judgements, providing quantitative estimates of probabilities for defined failures. The approach is illustrated by a case study along the river Göta Älv, Sweden, where failures are defined and probabilities for those failures are estimated. Failures are defined from a pollution perspective and in terms of exceeding environmental quality standards (EQSs) and acceptable contaminant loads. Models are then suggested to estimate probabilities of these failures. A landslide analysis is carried out to assess landslide probabilities based on data from a recent landslide risk classification study along the river Göta Älv. The suggested methodology is meant to be a supplement to either landslide risk assessment (LRA) or environmental risk assessment (ERA), providing quantitative estimates of the risks associated with landslide in contaminated sites. The proposed methodology can also act as a basis for communication and discussion, thereby contributing to intersectoral management solutions. From the case study it was found that the defined failures are governed primarily by the probability of a landslide occurring. The overall probabilities for failure are low; however, if a landslide occurs the probabilities of exceeding EQS are high and the probability of having at least a 10% increase in the contamination load within one year is also high.