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In rapidly urbanizing catchments, increase in stormwater runoff may cause serious erosion and frequent floods if stormwater management systems are improper and dysfunctional. Through GIS-based modelling, field investigations, resident’s questionnaire survey, and interviews with officials, the study set out to assesses the coverage and efficiency of drainage infrastructure in Mbezi River catchment basin in Dar es Salaam, Tanzania. Between 2003 and 2016, the catchment imperviousness increased by 41%, causing flood incidents, massive erosion, and numerous pollution sources. Residents strive to address stormwater hazards using terraces, hedges, and physical barriers; however, the problems persist, indicating lack of coordination and poor causality understanding between land-use changes and catchment impacts. Small-scale stormwater harvesting was exercised by 75% of the households, pointing to water supply challenges. Municipal stormwater management efforts was limited to roadside drains covering 17% of road lengths in the catchment, and 65% of those did not meet their design standards. Interviews with officials revealed a need for improved co-understanding and collaborative initiatives to bolster integrated water management. The study suggests a need to adopt a new urban stormwater management paradigm, appropriate for both residents and authorities. Without this new discourse, the urbanization led stormwater increase might jeopardize the liveability of the entire catchment.

Implementation of sustainable urban drainage systems (SUDS) as part of cities’ transition towards climate resilience encompasses unique opportunities to enhance urban nature qualities. SUDS include individual elements integrated in the urban landscape, e.g. rain gardens or wet basins, which are usually constructed with low structural heterogeneity. Structural heterogeneity of habitats is, however, associated with a high degree of biodiversity. This study explored potentials of habitat heterogeneity enhancement in SUDS using structural heterogeneity as a proxy for biodiversity potential. In an interdisciplinary workshop, landscape architects and urban ecologists designed individual SUDS elements with enhanced structural habitat heterogeneity, hereafter bio-SUDS. The redesigned SUDS elements were infiltration trench, curb extension, rain garden, swale, wet basin, and dry basin. To evaluate the bio-SUDS designs, we developed an index of habitat heterogeneity in SUDS based on registration of 45 structurally important components. The conversion from standard SUDS to bio-SUDS entailed substantial increases in structural heterogeneity ranging from 4 to 18 additional components within elements. Larger bio-SUDS elements returned higher index scores, but the relative score increases were substantial for all bio-SUDS and in the range of a factor of 2-5.5. Increased terrain differences, meandering edges, stones, gravel, boulders, deadwood, and brown roof-like vegetation were the components most often employed in the bio-SUDS designs. In conclusion, implementation of bio-SUDS has potential to increase structural habitat heterogeneity thereby providing habitat for biodiversity in urban green areas. The developed bio-SUDS index can assist in future assessments of ecological qualities in designs and real-world SUDS elements. [ABSTRACT FROM AUTHOR]

Local management of rainwater using stormwater control measures (SCMs) is gaining increased attention as a sustainable alternative and supplement to traditional sewer systems. Besides offering added utility values, many SCMs also offer a great potential for added amenity values. One way of achieving amenity value is to stage the rainwater and thus bring it to the attention of the public. We present here a methodology for creating a selection of rain events that can help bridge between engineering and landscape architecture when dealing with staging of rainwater. The methodology uses quantitative and statistical methods to select Characteristic Rain Events (CREs) for a range of frequent return periods: weekly, bi-weekly, monthly, bi-monthly, and a single rarer event occurring only every 1-10 years. The methodology for selecting CREs is flexible and can be adjusted to any climatic settings; here we show its use for Danish conditions. We illustrate with a case study how CREs can be used in combination with a simple hydrological model to visualize where, how deep and for how long water is visible in a landscape designed to manage rainwater. [ABSTRACT FROM AUTHOR]

The use of filter soil is increasing for control of quality of stormwater runoff prior to infiltration or discharge. This study aimed to gain knowledge about treatment efficacy of filter soils at field scale. Percolate samples from swale-trench systems with filter soil based on agricultural till with/without limestone were monitored for 15 and 9 rain events respectively. Further, two curb extensions with filter soil based on landfill soil were monitored for 10 and 8 events. Pollutant concentrations in percolate were compared to influent samples from the catchment area. Additionally one of the curb extensions was tested twice by adding high-dose synthetic influent containing runoff pollutants of concern. Despite generally low influent pollutant levels, phosphorus, copper, zinc, lead and some polyaromatic hydrocarbons exceeded guiding criteria for protection of groundwater and freshwater. Concentrations in the percolate were in most cases reduced, but phosphorus increased and despite reduced concentrations copper, lead and benzo(a)pyrene still exceeded guiding criteria. Pollutants from the synthetic influent were efficiently retained, except the pesticide MCPA. Filter soil based on landfill soil tended to perform better than agricultural till. No impact of limestone was observed. Overall the filter soils performed well in retaining pollutants, despite simultaneous processes of mobilization and immobilization. [ABSTRACT FROM AUTHOR]

Most cities in Denmark are situated on low permeable clay rich deposits. These sediments are of glacial origin and range among the most heterogeneous, with hydraulic conductivities spanning several orders of magnitude. This heterogeneity has obvious consequences for the sizing of sustainable urban drainage systems (SuDS). We have tested methods to reveal geological heterogeneity at field scale to identify the most suitable sites for the placement of infiltration elements and to minimize their required size. We assessed the geological heterogeneity of a clay till plain in Eastern Jutland, Denmark measuring the shallow subsurface resistivity with a geoelectrical multi-electrode system. To confirm the resistivity data we conducted a spear auger mapping. The exposed sediments ranged from clay tills over sandy clay tills to sandy tills and correspond well to the geoelectrical data. To verify the value of geological information for placement of infiltration elements we carried out a number of infiltration tests on geologically different areas across the field, and we observed infiltration rates two times higher in the sandy till area than in the clay till area, thus demonstrating that the hydraulic performance of SuDS can be increased considerably and oversizing avoided if field geological heterogeneity is revealed before placing SuDS. [ABSTRACT FROM AUTHOR]

The article offers information on examining and comparing efficiency of stormwater treatment facilities (STFs) by using parameters of a minimum data set of water quality. It is said that urban stormwater impacts aquatic ecosystems and restricts the use of stormwater runoff for recreational purposes. The efficiencies of STFs are not well documented due to the highly variable runoff hydrograph. The use of the minimum data set will ensure broad spectrum testing at low costs and strengthen comparability among STFs.

The article discusses the effectiveness of twinning methodologies in building the research, development, and public policy capabilities of developing countries. A research project titled "Multipurpose Forestry in a Changing Society" financed by the Danish Development Cooperation Agency (Danida) is the focus of the article. The study linked Danish and Malaysian educational and public service institutions in efforts to foster collaboration between researchers in the two countries. The study concludes that although Malaysia's research capacity expanded as a result of the project, there was little hope of continued collaboration between the Danish and Malaysian due to a lack of common research goals. Suggestions for how to better implement twinning methodologies are offered.

Presents information on a study which compared the yield and quality of leeks that were grown either in soil amended with a mulch of compost or in soil with incorporated compost. Reasons for selecting leeks as the test crops; Physical and chemical properties of materials used in growth media; Results of compost mulching.

Studies mobilization and immobilization of phosphate (P) in loamy soils incubated under simulated reducing conditions. Factors that cause the lack of proportionality between iron(II) and P in solution; Conditions wherein the highest P concentrations were observed.

The hydraulic performance of permeable pavement (PP) systems has been well demonstrated when based on full or partial on-site infiltration, while there is only limited research on lined PP systems built to provide detention and volume reduction by evaporation only. In this study, we tested the performance of commercially available PP components when constructed as lined PP systems with un-throttled discharge to explore basic hydraulic function in a real-life-setting. Four types of PP surface products and three types of sub-base aggregates were tested in six unique combinations, built as side-by-side parking lots into an existing parking area, each stall having a size of 25 m2 and 0.5 m of depth with individual lining. Based on 12 months of monitoring precipitation and discharge from each stall, total volume reduction ranged from 3% to 37%. Analysis of up to 22 single events, representing return periods of up to two years, revealed marked detention capacities, expressed as median volume reduction of 40%, spanning 27–69% and median lag time of 1:38 h, spanning 0:39–3:16 h, across all stalls. The considerable range in hydraulic properties can be ascribed to both surface and sub-base properties. [ABSTRACT FROM AUTHOR]

Local authorities face a great challenge in translating officially announced sustainability commitments into everyday management practices. With the objective of developing a tool for supporting such goal-to-practice translation processes, three primary tool criteria were formulated, and used to develop a guide on how to apply the tool. Subsequently, the tool was applied and evaluated in an interactive study involving the local authority of a Danish municipality. The first toolcriterion concerns the organisation of the translation process. It states that in order to obtain a clear understanding of the unique local conditions, the tool shall be able to act as a bridge between different disciplines, and allow for direct collaboration between expertswith context-independent knowledge and local administrators with context-dependent knowledge. The second criterion concerns the identification of sustainable management strategies. It states that the tool shall secure a thorough two-sided analysis of society's claims on one side, and on the other side the ability of available resources to meet these claims in a sustainable way. The third criterion concerns thedistribution of the results of the analysing phase. It states that in order to support dialogue and decision making across professional and societal boundaries, the identified claims and resources as well as the associated obstacles shall be presented in simple and preferably visual overviews. In testing the tool we focused on the ability of the municipality's urban green structure (the resource) to contributeto sustainable management of organic waste, surface runoff and biodiversity (the claims). Based on the outcome of the test, and an interview survey with the participating local administrators, it is concluded that the tool criteria are sound. This is despite the fact that the test of the tool was not applied in full accordance with the tool guidelines. It is anticipated that the application of this tool can increa [ABSTRACT FROM AUTHOR]

Control of P from sewage outlets has not led to expected improvementof Danish freshwater quality, calling the diffuse P losses especially from drained agricultural land into question. We studied some mechanisms for P loss from the fertilized topsoil from selected catchmentsthat have been monitored for P losses: (i) losses due to desorption of P from A horizons enriched throughout the last decades by fertilization, (ii) losses of P associated with temporarily reducing conditions imposed on A horizons, and (iii) losses associated with application of fresh cattle manure to the soil surface or by mixing into the soil matrix. The effluent concentrations of P from 15 intact topsoil samples were 10 to 40 times lower than what could be expected from batch studies, presumably due to nonhomogeneous now conditions. Addition of solid cattle feces by incorporation or directly on the surface had markedly differing effects on P leaching. While incorporation did result in a 10- to 20-fold increase in effluent P concentration, surface application resulted in a further 10- to 20-fold higher effluent concentration of molybdate-reactive P. These results indicate that while desorption from the soil matrix is likely to be much less than expected from batch chemical considerations, special attention should be given to drained pastures, where the important P source may not be the soil matrix per se, but fecal remnants on the surface, that may be transported directly to the drains through macropores.Furthermore, reductive dissolution of Fe associated P may be of someimportance. [ABSTRACT FROM AUTHOR]

Summary: Stormwater infiltration measures such as soakaways are expected to be part of future urban drainage systems. However, few studies exist on the effect of extensive stormwater infiltration through soakaways on the overall urban water system, including sewers and groundwater, at city catchment scale. In particular such estimates have not been made in real urban settings with multiple physical and structural constraints. This paper presents a methodology for conducting such an analysis, and provides quantitative estimates of the effects on the urban water flows. Using an interdisciplinary, three-step approach that employed GIS analyses and physically distributed, dynamic pipe flow modelling in an iterative manner, this study estimates the impact of infiltration on combined sewage overflows (CSOs) in a 3km2 urban catchment in Copenhagen. The first step was the creation of a baseline scenario. The second step led to a potential infiltration scenario where 65% of the total impervious area was connected to soakaways, and resulted in an estimated reduction in annual sewage overflow volume of 68%. This scenario was then further developed in the third step by adding groundwater constraints, which formed a more realistic scenario where only 8% of the impervious area was connected to soakaways and the reduction in CSO volume was 24%. The potential and realistic scenarios were modelled both with hydraulic coupling between soakaway and sewer, and as fully disconnected. Results show that infiltration is constrained mainly by the quality of the stormwater runoff from roads and limited land availability in the potential infiltration scenario, and by low-permeable soils and a problematically high groundwater level in the realistic infiltration scenario. The hydraulically coupled model gives higher CSO volume than the fully disconnected model for the potential infiltration scenario, whereas no difference is seen between these two models in the realistic infiltration scenario. The effect of infiltration on combined sewer overflows is thus expected to be limited in the case study area. General conclusions are that groundwater constraints are important to consider when evaluating the potential of infiltration-based stormwater management, and that it is important to include the hydraulic coupling between soakaways and sewers in models if soakaways are expected to give overflow to the sewers. [Copyright &y& Elsevier]