Green roofs have been widely recognized as sustainable nature-based solutions to mitigate floods in urban areas, which, in the last decades, are increasing due to the combination of intense worldwide urbanization and climate change. Besides flood mitigation, green roofs provide additional benefits for the urban environment (e.g., reducing the urban heat island and ensuring energy saving for the underneath building). Moreover, green roofs facilitate the increase of urban biodiversity, attracting different species of small animals, and upgrade the city aesthetic value. Among the different types of green roofs, multilayer blue-green roofs present an additional layer to store water during rainfall events. As part of the Polder Roof field lab project, prototypes of multilayer blue-green roof developed by the Dutch company Metropolder were installed in four Italian cities: Cagliari, Palermo, Perugia, and Viterbo. The four prototypes and the experimental set up are described and the potential benefits of this innovative solution are discussed. Preliminary analyses, from December 2020 to December 2021, enable to estimate runoff reduction and thermal properties of multilayer blue-green roofs, underlying the high potential of this nature-based solution, which allows to retain most of the rainfall events and to mitigate the daily temperature variability.

@en

Indonesia strives for a renewable energy share of 23% by 2025. One option to contribute to this goal is Ocean Thermal Energy Conversion (OTEC). Despite a global theoretical potential of up to 30 TW, its economically deployable share remains unknown. This paper proposes a novel methodology, which enables to determine OTEC's economic potential for any regional scope considering technical, economic and natural variables. The methodology was tested for 100 MW_e OTEC in Indonesia on a provincial and national level. Against a regionally variable electricity tariff of 6.67–18.14 US$ct.(2018)/kWh, the national economic potential is 0–2 GW_e with a Levelized Cost of Electricity (LCOE) as low as 15.6 US$ct.(2018)/kWh. With an annual electricity production of 0–16 TWh, OTEC could provide up to 6% of Indonesia's electricity demand in 2018. The capacity factor, capital expenses and discount rate are the most sensitive variables of the LCOE on average. A nationally uniform feed-in tariff of 18 US$ct.(2018)/kWh or more could increase the economic potential significantly. The proposed methodology can be a helpful quick-scan tool for determining economically interesting OTEC sites for follow-up in-depth feasibility studies. Limitations are discussed and future research, amongst others upscaling scenarios with cost reducing effects like technological learning, is recommended.

@en

Plastic debris in water systems is a major challenge for our ecosystem, because it is extremely persistent in the environment. Apart from the importance of reducing the amount of plastic entering the ocean, clearing the rivers from debris is important for societal concerns, such as flood risks. Plastic waste accumulation at trash racks leads to a rise in upstream water level and may increase urban flood risk. Until now, most studies of riverine debris accumulation predominantly focused on organic accumulations at trash racks and bridge piers. In this study, flume experiments were used to study the behavior of plastic and mixed debris accumulations. One of the key findings from this study is that plastic debris causes a faster blockage than organic matter, as the plastic blockage contains fewer voids and therefore has a higher blockage density. In addition to the flume experiments, field measurements were performed in the Cikapundung River (Indonesia). This river is one of the tributaries of the Citarum River, which is considered one of the world’s most heavily polluted rivers. Combining the results of the flume experiments and field measurements demonstrated that a backwater rise of 1 m/h is plausible for a blocked trash rack in the Cikapundung River, illustrating the additional flood risk caused by plastic pollution. Our results emphasize the need for further quantifying riverine (plastic) debris and investigating its relation to changes in the water system behavior, including its influence on urban flood risk.

@en

Many rivers in the world carry loads of debris to the sea. Typically in urbanizing areas with limited waste collection systems, the amounts of plastic amongst the organic material can be substantial. This has an impact on e.g. water quality, clogging of the (urban) water infrastructure, and deterioration of habitats. Flood risk is increased when debris is accumulating at bridges, weirs and trash racks. Understanding the behaviour of plastics in rivers and their impact on river conveyance is important for assessing both water quality issues and flood risks. In this study samples of waste in the Citarum river basin near Bandung, Indonesia where taken using single and double trawls. The analysis showed that plastic content of those samples can amount to more than 40% of the total debris weight. Additional laboratory measurement were performed on a debris flow through a trash rack in a straight flume, to assess the effects of plastic content on debris behaviour and consequent increased energy loss in flows through a trash rack. Though limited by scale effects and simplifications in the experiment, it was concluded that the plastic content in the debris increased the rate of clogging as well as the flow resistance for a certain amount of debris. The rapidly increased resistance is considered a problem in areas with intermittent, heavy rainfall where plastics that accumulated on river banks are mobilised and flushed into the water system. The carpet formed by plastic-containing debris appears to be more coherent and to contribute more to flow resistance and a higher risk of flooding. Future research will include a wider variation of flow geometries and debris composition.@en

Several recent studies have highlighted the potential of Actively Heated Fiber Optics (AHFO) for high resolution soil moisture mapping. In AHFO, the soil moisture can be calculated from the cumulative temperature (T_cum), the maximum temperature (T_max), or the soil thermal conductivity determined from the cooling phase after heating (λ). This study investigates the performance of the T_cum, T_max and λ methods for different heating strategies, i.e., differences in the duration and input power of the applied heat pulse. The aim is to compare the three approaches and to determine which is best suited to field applications where the power supply is limited. Results show that increasing the input power of the heat pulses makes it easier to differentiate between dry and wet soil conditions, which leads to an improved accuracy. Results suggest that if the power supply is limited, the heating strength is insufficient for the λ method to yield accurate estimates. Generally, the T_cum and T_max methods have similar accuracy. If the input power is limited, increasing the heat pulse duration can improve the accuracy of the AHFO method for both of these techniques. In particular, extending the heating duration can significantly increase the sensitivity of T_cum to soil moisture. Hence, the T_cum method is recommended when the input power is limited. Finally, results also show that up to 50% of the cable temperature change during the heat pulse can be attributed to soil background temperature, i.e., soil temperature changed by the net solar radiation. A method is proposed to correct this background temperature change. Without correction, soil moisture information can be completely masked by the background temperature error.

@en

Tijdens het bestrijden van de gevolgen van een overstroming is het zinvol om te weten in welke richting het water stroomt en hoe laat het water een kruispunt bereikt. Deze thesis gaat over een overstromingsmodel van heel Nederland. Met dit model kan in 15 minuten het verloop van elke overstroming voor de komende 24 uur worden uitgerekend. Tot nu toe bestond een dergelijk model niet. De overstromingsmodellen die in de praktijk gebruikt worden rekenen namelijk te langzaam, waardoor alleen kaarten met het resultaat van vooraf uitgerekende theoretische scenario’s gebruikt konden worden om inzicht te verschaffen in het verloop van een overstroming. In dit onderzoek is als eerste de toegevoegde waarde van een landelijk model bij het bestrijden van een overstroming uitgewerkt. Daarna is onderzocht welke processen het model minimaal moet bevatten om een realistisch verloop van een overstroming te kunnen berekenen. Als laatste is met 3Di een eerste versie van dit model gebouwd, waarmee voor elke willekeurige plek langs de kust een doorbraak en het verloop van een overstroming snel kan worden uitgerekend. Van de verschillende crisispartners zijn vooral de waterschappen en de veiligheidsregio’s geholpen met een goede voorspelling van een overstroming. Voor de waterschappen is het berekende verloop relevant, omdat zij daarmee weten in welke richting en in welke volgorde het land overstroomt en zij met hetzelfde model snel het effect van maatregelen kunnen doorrekenen. Voor de veiligheidsregio’s is het model vooral nuttig, omdat zij daarmee weten hoe lang een bepaalde route nog gebruikt kan worden voor het aanvoeren van materiaal of het evacueren van de bevolking. Voor een model dat een realistisch verloop van een overstroming kan berekenen is een hoogtekaart nodig waarop minimaal de belangrijkste primaire dijken en boezemkaden zijn opgenomen, maar ook andere ‘objecten’ die het stromen van water beïnvloeden, zoals op het maaiveld aangelegde wegen en onder het maaiveld gelegen watergangen. Zonder deze objecten berekent het model weliswaar stroming van water, maar zijn de aankomsttijden niet realistisch. In de nu gebouwde 3Di schematisatie van Nederland is vooral aandacht besteed aan een overstroming vanuit de Noordzee, Waddenzee, IJsselmeer of Markermeer. Het rivierengebied is alleen op hoofdlijnen meegenomen. Om het model ook voor een overstroming vanuit de grote rivieren nuttig te kunnen gebruiken, wordt aanbevolen om het model daar verder uit te bouwen en te verfijnen. @en

Population growth, increasing energy demand and the depletion of fossil fuel reserves necessitate a search for sustainable alternatives for electricity generation. Hydropower could replace a large part of the contribution of gas and oil to the present energy mix. However, previous high-resolution estimates of hydropower potential have been local, and have yet to be applied on a global scale. This study is the first to formally present a detailed evaluation of the hydropower potential of each location, based on slope and discharge of each river in the world. The gross theoretical hydropower potential is approximately 52 PWh/year divided over 11.8 million locations. This 52 PWh/year is equal to 33% of the annually required energy, while the present energy production by hydropower plants is just 3% of the annually required energy. The results of this study: all potentially interesting locations for hydroelectric power plants, are available online.@en

Objective – Identifying the capacities and locations of hydropower potential is essential as the initial stage in the processes of the sustainable hydropower development. This study aims to provide a theoretical hydropower potential map of Myanmar which shows the locations and the capacities of the hydropower potential in terms of different scales and their distribution in each river basin, state, and region of Myanmar Methodology/Technique – The 3 arc sec Hydro SHED DEM and 30 min UNH-GRDC are used to simulate the discharges, heads and hydropower potential capacities using the Model Builder of ArcGIS 10.3 software. . The simulated discharges are compared with the observed recorded discharges from 13 stations of the major rivers for validation. The theoretical hydropower is estimated with the assumption of Qmin as 0.1 m3/s, Hmin as 4 m, efficiency as 85%, and Run-of-River type. The total gross theoretical hydropower potential is estimated about 82 GW with 187864 locations. Findings – The resulted capacities are classified into 5 types based on International Renewable Energy Agency standards. Among them, small hydro is the largest contributor with 45%. Concerning the river basins, and states and regions, the Upper Ayeyarwady and Kachin State are the largest contributors with 57% and 54% respectively Novelty– This study provides a comprehensive comparison of hydropower potential among states and regions, river basins in Myanmar and detailed information on a specific hydropower location. Type of Paper: Empirical@en