Concept: Sustainable urban drainage systems
Despite their importance in urban drainage systems, gully pot internal processes have received little scientific study. Therefore, gully pot contents were examined to gain a basic understanding of these processes and to establish the decomposition characteristics of the contents ex situ. Moisture content, organic matter content, enzyme activity and pH were measured to investigate seasonal and geographical effects, in addition to a 5-week composting trial to determine the rate and characteristics of decomposition. Little difference was observed in the content processes, especially between seasons, and the composting trial illustrated organic content decreased at an average rate of 0.1 g of organic matter per 13 g of organic matter per day. The results from this study indicate an as yet unknown initial decomposition rate. Activity monitored between gully pots also suggests they are relatively similar systems across space and time; enabling gully contents to be evaluated universally in future research.
Rainfall-Runoff Simulations to Assess the Potential of SuDS for Mitigating Flooding in Highly Urbanized Catchments
- International journal of environmental research and public health
- Published almost 4 years ago
Sustainable Urban Drainage Systems (SuDS) constitute an alternative to conventional drainage when managing stormwater in cities, reducing the impact of urbanization by decreasing the amount of runoff generated by a rainfall event. This paper shows the potential benefits of installing different types of SuDS in preventing flooding in comparison with the common urban drainage strategies consisting of sewer networks of manholes and pipes. The impact of these systems on urban water was studied using Geographic Information Systems (GIS), which are useful tools when both delineating catchments and parameterizing the elements that define a stormwater drainage system. Taking these GIS-based data as inputs, a series of rainfall-runoff simulations were run in a real catchment located in the city of Donostia (Northern Spain) using stormwater computer models, in order to compare the flow rates and depths produced by a design storm before and after installing SuDS. The proposed methodology overcomes the lack of precision found in former GIS-based stormwater approaches when dealing with the modeling of highly urbanized catchments, while the results demonstrated the usefulness of these systems in reducing the volume of water generated after a rainfall event and their ability to prevent localized flooding and surcharges along the sewer network.
Global warming increases the moisture holding capacity of the atmosphere and consequently the potential risks of extreme rainfall. Here we show that maximum hourly summer rainfall intensity has increased by about 11.2% on average, using continuous hourly gauge records for 1971-2013 from 721 weather stations in China. The corresponding event accumulated precipitation has on average increased by more than 10% aided by a small positive trend in events duration. Linear regression of the 95(th) percentile daily precipitation intensity with daily mean surface air temperature shows a negative scaling of -9.6%/K, in contrast to a positive scaling of 10.6%/K for hourly data. This is made up of a positive scaling below the summer mean temperature and a negative scaling above. Using seasonal means instead of daily means, we find a consistent scaling rate for the region of 6.7-7%/K for both daily and hourly precipitation extremes, about 10% higher than the regional Clausius-Clapeyron scaling of 6.1%/K based on a mean temperature of 24.6 °C. With up to 18% further increase in extreme precipitation under continuing global warming towards the IPCC’s 1.5 °C target, risks of flash floods will exacerbate on top of the current incapability of urban drainage systems in a rapidly urbanizing China.
Urban rivers constitute a major part of urban drainage systems, and play critical roles in connecting other surface waters in urban areas. Black-odorous urban rivers are widely found in the developing countries experiencing rapid urbanization. The mismatch between urbanization and sewage treatment is thought to be the reason of the blackening and odorization phenomenon. This phenomenon is likely a complex bio-geochemical process of which the microbial interactions with the environment are not fully understood. Here, we provide an overview over the major chemical compounds, such as iron and sulfur, and their bio-geochemical conversions during blackening and odorization of urban rivers. Scenarios explaining the formation of black-odorous urban rivers are proposed. Finally, we point out knowledge gaps in mechanism and microbial ecology that need to be addressed to better understand the development of black-odorous urban rivers.
The use of ‘Sustainable Urban Drainage Systems’ (SuDS) has become a more sustainable alternative for managing stormwater, greatly reducing the effects of soil sealing. However, the lack of monitored projects is a barrier to their implementation, as the companies which manage sewer systems cannot quantify the impact and cost-efficiency of SuDS. This paper presents a project developed in the south of Spain, in which the hydrological performance of 3 types of permeable pavements has been analyzed. The efficiencies obtained (over 70%), are higher than or similar to the efficiencies of vegetated SuDS, demonstrating the capacity of these pavements for delaying catchment area response and slow flow velocities, reducing the operating costs of sewer systems and the flood risk, while also ensuring service conditions for cities and safety for pedestrian and vehicular circulation. This pilot site has generated results which are sufficiently consistent so as to be representative, and serve as a reference for other cities with a similar climate.
- Water science and technology : a journal of the International Association on Water Pollution Research
- Published about 2 years ago
Regular and continuous monitoring of urban runoff in both quality and quantity aspects is of great importance for controlling and managing surface runoff. Due to the considerable costs of establishing new gauges, optimization of the monitoring network is essential. This research proposes an approach for site selection of new discharge stations in urban areas, based on entropy theory in conjunction with multi-objective optimization tools and numerical models. The modeling framework provides an optimal trade-off between the maximum possible information content and the minimum shared information among stations. This approach was applied to the main surface-water collection system in Tehran to determine new optimal monitoring points under the cost considerations. Experimental results on this drainage network show that the obtained cost-effective designs noticeably outperform the consulting engineers' proposal in terms of both information contents and shared information. The research also determined the highly frequent sites at the Pareto front which might be important for decision makers to give a priority for gauge installation on those locations of the network.
LID practices for runoff control are increasingly being used as an integrated solution in urban drainage, helping to achieve hydrological balance close to the pre-urbanized period and decrease the diffuse pollution transported to urban rivers. Regarding bioretention, there is already broad knowledge about the detention of peak flows and their treatment capacity for many pollutants. However, there are still few field studies in microdrainage scale, which analyze the actual operation of these devices and raise common problems found, especially in subtropical climate. Therefore, this study aims to show what was learnt from the field operation of a bioretention cell on a micro-drainage scale, located in an urban catchment of a Brazilian city, suggesting maintenance actions as adaptations to the pathologies found. Five rainy events were monitored during the dry season, in order to carry out a preliminary analysis for critical conditions in terms of maintenance and diffuse pollution accumulation. From the first water balance results, low storage and low infiltration capacity of the soil were found as main pathologies. They led to a great amount of runoff passing directly through the cell surface and at a high velocity, resulting in soil erosion and low water retention efficiency. To overcome these problems, some structural adaptations were made over the cell, highlighting the semi-direct injection. The maintenance and adaptations proposed were suitable to avoid the erosion process, increasing the storage and improving the water retention efficiency in bioretention. They should be considered from the very initial stages, to using sites with low permeability.
Knowledge about pollutant wash-off from urban impervious surfaces is a key feature for developing effective management strategies. Accordingly, further information is required about urban areas under semi-arid climate conditions at the sub-catchment scale. This is important for designing source control systems for pollution. In this study, a characterization of pollutant wash-off has been performed over sixteen months, at the sub-catchment scale for urban roads as impervious surfaces. The study was conducted in Valencia, Spain, a city with a Mediterranean climate. The results show high event mean concentrations for suspended solids (98mg/l), organic matter (142mgCOD/l, 25mgBOD5/l), nutrients (3.7mgTN/l, 0.4mgTP/l), and metals (0.23, 0.32, 0.62 and 0.17mg/l for Cu, Ni, Pb, and Zn, respectively). The results of the runoff characterization highlight the need to control this pollution at its source, separately from wastewater because of their different characteristics. The wash-off, defined in terms of mobilized mass (g/m(2)) fits well with both process-based and statistical models, with the runoff volume and rainfall depth being the main explanatory variables. Based on these results and using information collected from hydrographs and pollutographs, an approach for sizing sustainable urban drainage systems (SuDS), focusing on water quality and quantity variables, has been proposed. By setting a concentration-based target (TSS discharged to receiving waters <35mg/l), the results indicate that for a SuDS type detention basin (DB), an off-line configuration performs better than an on-line configuration. The resulting design criterion, expressed as SuDS volume per unit catchment area, assuming a DB type SuDS, varies between 7 and 10l/m(2).
Info-Gap robustness pathway method for transitioning of urban drainage systems under deep uncertainties
- Water science and technology : a journal of the International Association on Water Pollution Research
- Published over 2 years ago
In the urban water cycle, there are different ways of handling stormwater runoff. Traditional systems mainly rely on underground piped, sometimes named ‘gray’ infrastructure. New and so-called ‘green/blue’ ambitions aim for treating and conveying the runoff at the surface. Such concepts are mainly based on ground infiltration and temporal storage. In this work a methodology to create and compare different planning alternatives for stormwater handling on their pathways to a desired system state is presented. Investigations are made to assess the system performance and robustness when facing the deeply uncertain spatial and temporal developments in the future urban fabric, including impacts caused by climate change, urbanization and other disruptive events, like shifts in the network layout and interactions of ‘gray’ and ‘green/blue’ structures. With the Info-Gap robustness pathway method, three planning alternatives are evaluated to identify critical performance levels at different stages over time. This novel methodology is applied to a real case study problem where a city relocation process takes place during the upcoming decades. In this case study it is shown that hybrid systems including green infrastructures are more robust with respect to future uncertainties, compared to traditional network design.
In spite of the well-known green roof benefits, their widespread adoption in the management practices of urban drainage systems requires the use of adequate analytical and modelling tools. In the current study, green roof runoff modeling was accomplished by developing, testing, and jointly using a simple conceptual model and a physically based numerical simulation model utilizing HYDRUS-1D software. The use of such an approach combines the advantages of the conceptual model, namely simplicity, low computational requirements, and ability to be easily integrated in decision support tools with the capacity of the physically based simulation model to be easily transferred in conditions and locations other than those used for calibrating and validating it. The proposed approach was evaluated with an experimental dataset that included various green roof covers (either succulent plants - Sedum sediforme, or xerophytic plants - Origanum onites, or bare substrate without any vegetation) and two substrate depths (either 8 cm or 16 cm). Both the physically based and the conceptual models matched very closely the observed hydrographs. In general, the conceptual model performed better than the physically based simulation model but the overall performance of both models was sufficient in most cases as it is revealed by the Nash-Sutcliffe Efficiency index which was generally greater than 0.70. Finally, it was showcased how a physically based and a simple conceptual model can be jointly used to allow the use of the simple conceptual model for a wider set of conditions than the available experimental data and in order to support green roof design.