From flood paths to floodways, an efficient method to map, identify and evaluate suitable floodways: A case study from Trondheim, Norway

Due to climate change and rapid urbanisation, many Norwegian cities and urban areas suffer from pluvial flooding caused by intense rainfall exceeding the capacity of the stormwater management system. This results in increased runoff rates, volumes and peak flows in the drainage network. In response to these challenges, the authors explore the potential of utilising the urban surface's ability to transport floodwater as an integral component of the stormwater infrastructure. When the capacity of the stormwater drainage system is exceeded, the overland flow paths transporting floodwater are considered a part of the stormwater management system, as floodways. The study proposes a spatial GIS method to map existing drainage lines and identify existing surface areas that function as floodways, combined with an automated process to identify which drainage lines could be implemented as stormwater management measures. Critical points are introduced to assess the floodways' potential hazards, combined with a classification method to evaluate and sort floodways. A case study from Trondheim, Norway, was used to demonstrate how drainage lines can be identified as floodways using the proposed method. The case study is also used to illustrate how a GIS-based analysis can be extended from identifying to evaluating floodways and whether GIS is sufficient for floodway evaluation. The method enables urban planners and municipalities to identify which areas of the urban surface already function as floodways during extreme events, and to prioritise measures to secure such areas and increase the city's flood resilience. The results highlight the need to assess existing areas that function as floodways, and to implement and design needed areas as floodways. GIS-based methods combined with an evaluation scheme can be an adequate tool to map and evaluate floodways in urban areas. When using GIS-based methods, however, the corresponding hazard potential, and also the uncertainty of the floodway's spatial placement, should be considered.

Lifecycle sustainability assessment for the comparison of traditional and sustainable drainage systems

Urban drainage is a topic of increasing interest due to its key role for managing water-related disasters, which are being exacerbated by the effects of Climate Change and urbanization. Since traditional drainage systems struggle to deal with the combined action of these phenomena, Sustainable Drainage Systems (SuDS) are gaining attention as an alternative to help manage these high-water management demands. In this context, this research aimed at conducting a lifecycle sustainability assessment for comparing the economic, environmental and social performance of both drainage systems. The three dimensions of sustainable development were addressed with the support of the concepts of Net Present Value (NPV), Life Cycle Assessment (LCA) and a combination of the Leopold matrix and a semi structured interview, respectively. The results of applying this approach to the case study of the Rancho Bellavista housing development (Querétaro, Mexico) showed that SuDS outperformed traditional drainage systems in environmental and social terms; however, their high maintenance costs and shorter life expectancy hindered its economic feasibility. As such, future urban plans should focus on complementary designs whereby the strengths of both drainage alternatives are combined to boost their contributions to achieving sustainable development.

Containing a sustainable urbanized environment through SuDS devices in management trains

Generating an effective and efficient sustainable drainage philosophy is imperative in alleviating the risk of flooding in a complex UK climate that is categorised by excessive rainfall. The Sustainable Drainage Systems (SuDS) approach offers a revolutionary change in using heightened flow rates and large capacities of water to our advantage, while also disguising the attenuated water into the urbanized environment. This research explores the result of integrating several SuDS devices in management trains with the sole purpose of significantly reducing overall water quantity. It will compare and contrast and prove how SuDS is more dependable than the conventional pipe-based drainage system that is characterized by its ability to remove water to the outflow quickly. Furthermore, in order to determine how a SuDS device is implemented into the natural environment, a case study was conducted at a residential area in Gibside View, Winlaton in Gateshead. The research exhibits how the newly implemented Detention basin had to be retrofitted into the already inadequate drainage system that once lived there; all in thought of alleviating the significant flooding events that were once reported to have occurred prior. As a verification method in terms of effectiveness, a questionnaire was conducted through convenient and purposive sampling at the Case Study location; data was accumulated door-to-door inside a 300 m radius of the detention basin and received about 180 valid responses. The results showed persistence of respondents who detailed flooding events prior to installing the Detention basin, who then recognised a fundamental change in the minimization of water quantity and flooding issues. The results of this research showed why Detention Basins continue to be identified as one of the most successful water reduction-based SuDS devices available for development nationwide implementation.

Suitability of Sustainable Agricultural Drainage Systems for adapting agriculture to climate change

This paper presents a comprehensive and practical method for Sustainable Agricultural Drainage Systems (SADS) design. It is aimed at studying the suitability of using surface runoff as irrigation source. The method determines the optimum amount of surface runoff to be used for irrigation considering both environmental constraints (aquifers recharge, discharge to natural water courses) and investment and operation costs. The developed method has been applied to the Spanish irrigation district "Villalar de los Comuneros Sector 1" located in Valladolid. The estimation of the optimum SADS provision was calculated for most of the major crops at the irrigation district highlighting that SADS facilities can reduce the amount of external provision of water for irrigation while maintaining the aquifer's recharge and the natural discharge to water courses. The simulations run for climate change forecasting scenarios (Representative Concentration Pathways, RCP, RCP45, RCP60, RCP85) showed that optimum SADS would reduce irrigation requirements and would increase natural fluxes (both aquifers and natural water courses) therefore improving the general water cycle in rural environments with productive agriculture.

Towards urban resilience through Sustainable Drainage Systems: A multi-objective optimisation problem

The necessity of incorporating a resilience-informed approach into urban planning and its decision-making is felt now more than any time previously, particularly in low and middle income countries. In order to achieve a successful transition to sustainable, resilient and cost-effective cities, there is a growing attention given to more effective integration of nature-based solutions, such as Sustainable Drainage Systems (SuDS), with other urban components. The experience of SuDS integration with urban planning, in developed cities, has proven to be an effective strategy with a wide range of advantages and lower costs. The effective design and implementation of SuDS requires a multi-objective approach by which all four pillars of SuDS design (i.e., water quality, water quantity, amenity and biodiversity) are considered in connection to other urban, social, and economic aspects and constraints. This study develops a resilience-driven multi-objective optimisation model aiming to provide a Pareto-front of optimised solutions for effective incorporation of SuDS into (peri)urban planning, applied to a case study in Brazil. This model adopts the SuDS's two pillars of water quality and water quantity as the optimisation objectives with its level of spatial distribution as decision variables. Also, an improved quality of life index (iQoL) is developed to re-evaluate the optimal engineering solutions to encompass the amenity and biodiversity pillars of SuDS. Rain barrels, green roofs, bio-retention tanks, vegetation grass swales and permeable pavements are the suitable SuDS options identified in this study. The findings show that the most resilient solutions are costly but this does not guarantee higher iQoL values. Bio-retention tanks and grass swales play effective roles in promotion of water quality resilience but this comes with considerable increase in costs. Permeable pavements and green roofs are effective strategies when flood resilience is a priority. Rain barrel is a preferred solution due to the dominance of residential areas in the study area and the lower cost of this option.

Stormwater harvesting from landscaped areas: effect of herbicide application on water quality and usage

The suitability of stormwater harvested from pervious pavement system (PPS) structures for reuse purposes was investigated in conditions where glyphosate-containing herbicides (GCH) are applied as part of PPS maintenance procedure. The experiment was based on the four-layered design previously described as detailed in CIRIA C582. Results indicated that the highest sodium absorption ratio (SAR) of 1.6 recorded in this study, was less than that at which loss of permeability begins to occur as well as deterioration of matrix structure. Furthermore, the maximum electrical conductivity (ECw) of 2990 μS cm(-1), recorded for 7200 mg L(-1) concentration (GCH) was slightly below the unstable classification range at which salinity problems related to water quality occur such that salts accumulate in the root zone to the extent that crop yields are adversely affected. However, GCH concentration of 720 mg L(-1) was within 'permissible' range while that of 72 mg L(-1) was within 'excellent' range. Current study raises some environmental concerns owing to the overall impact that GCH at concentrations above 72 mg L(-1) exerts on the net performance of the organic decomposers, heavy metal and hydrocarbon release from the system and thus, should be further investigated. However, effluent from all the test models including those dosed with high GCH concentration of 7200 mg L(-1) do not pose any threat in terms of infiltration or deterioration associated with salinity although, there are indications that high dosage of the herbicide could lead to an elevated electrical conductivity of the recycled water. Graphical abstract Impact of herbicide on irrigation water quality.

Systemic solutions for multi-benefit water and environmental management

The environmental and financial costs of inputs to, and unintended consequences arising from narrow consideration of outputs from, water and environmental management technologies highlight the need for low-input solutions that optimise outcomes across multiple ecosystem services. Case studies examining the inputs and outputs associated with several ecosystem-based water and environmental management technologies reveal a range from those that differ little from conventional electro-mechanical engineering techniques through methods, such as integrated constructed wetlands (ICWs), designed explicitly as low-input systems optimising ecosystem service outcomes. All techniques present opportunities for further optimisation of outputs, and hence for greater cumulative public value. We define 'systemic solutions' as "…low-input technologies using natural processes to optimise benefits across the spectrum of ecosystem services and their beneficiaries". They contribute to sustainable development by averting unintended negative impacts and optimising benefits to all ecosystem service beneficiaries, increasing net economic value. Legacy legislation addressing issues in a fragmented way, associated 'ring-fenced' budgets and established management assumptions represent obstacles to implementing 'systemic solutions'. However, flexible implementation of legacy regulations recognising their primary purpose, rather than slavish adherence to detailed sub-clauses, may achieve greater overall public benefit through optimisation of outcomes across ecosystem services. Systemic solutions are not a panacea if applied merely as 'downstream' fixes, but are part of, and a means to accelerate, broader culture change towards more sustainable practice. This necessarily entails connecting a wider network of interests in the formulation and design of mutually-beneficial systemic solutions, including for example spatial planners, engineers, regulators, managers, farming and other businesses, and researchers working on ways to quantify and optimise delivery of ecosystem services.