Hydrodynamic Modelling of Floods and Estimating Socio-economic Impacts of Floods in Ugandan River Malaba Sub-catchment

River Malaba sub-catchment tends to experience dramatic flooding events, with several socio-economic impacts to the nearby communities, such as loss of lives and destructions of physical infrastructure. Analysis of spatiotemporal extents to which settlements, crops and physical infrastructures tend to be inundated are vital for predictive planning of risk-based adaptation measures. This paper presents a case study on flood risk assessment for Ugandan River Malaba sub-catchment. We applied the two-dimensional Hydraulic Engineering Center’s River Analysis System (2D HEC-RAS) for modelling of flooding extents. We considered extreme flow quantiles, lower and upper quantiles corresponding to the 95% confidence interval limits aimed at determining uncertainties in the flooding extents. Spatial extents of inundation on human settlement, land cover and infrastructure were analysed with respect to return periods of extreme flow quantiles. Finally, we estimated economic loss on infrastructure due to flooding. Results from the 2D HEC-RAS model were satisfactorily comparable with the results of observations. Amongst the land use types, cropland exhibited the highest vulnerability with at least 10,234.8 hectare (ha) susceptible to flooding event of 100-year return period (YRP). Inundated built-up land-use exhibited the highest vulnerability percentage increase (90%) between 2- and 100-YRP. In US Dollar, about US$ 33 million and US$ 39 million losses are estimated at 2- and 100-YRP, respectively, due to inundated rice gardens and these indicate a looming high risk of household food insecurity and poverty. Several infrastructure including 15 academic institutions, 12 health facilities, 32 worshiping places remain annually vulnerable to flooding. At least 6 km and 7 km of road network are also susceptible to flooding under extreme flows of return periods 2 and 100 years, respectively. Churches exhibited the highest economic losses of US$ 855,065 and US$ 1,623,832 at 2-YRP and 100-YRP, respectively. This study findings are relevant for planning the development of sustainable flood risk adaptation pathways given the established destructions within the sub-catchment due to flooding.

Assessment of a Geothermal Combined System with an Organic Rankine Cycle and Multi-effect Distillation Desalination

An analysis is reported of a geothermal-based electricity-freshwater system in which an organic Rankine cycle is integrated with a multi-effect distillation desalination unit. The system is driven by geothermal hot water extracted from the production well. Mass, energy, entropy, and exergy rate balances are written for all system components, as are energy and exergy efficiency expressions for each subsystem. The exergy destruction rate associated with the temperature and chemical disequilibrium of the freshwater and brine with the reference environment are taken into account to reveal accurate results for irreversibility sources within the desalination process. The developed thermodynamic model is simulated using thermodynamic properties of the working fluids (i.e., ammonia, seawater, distillate, and brine) at each state point. A sustainability analysis is performed that connects exergy and environmental impact concepts. That assessment expresses the extent of the contribution of the system to sustainable development and reduced environmental impact, using exergy methods. Results of the sustainability analysis indicate that, with an increase in the reference environment temperature from 20 to 35 $$^\circ{\rm C}$$ ∘ C , the exergy destruction rate decreases for the multi-effect distillation and organic Rankine cycle systems respectively from 6474 to 4217 kW and from 16,270 to 13,459 kW. Also, the corresponding sustainability index for the multi-effect distillation and organic Rankine cycle systems increases from 1.16 to 1.2 and 1.5–1.6, respectively, for the same increase in reference environment temperature.

Examining the Effectiveness of Catch Crops as a Nature-Based Solution to Mitigate Surface Soil and Water Losses as an Environmental Regional Concern

The main goal of this research was to conduct a biophysical, economic, social, and perception-based approach to foresee the solutions that could be used to mitigate the soil loss problem cost-effectively in “La Ribera del Xúquer” district (Valencia Region, Spain). To achieve these goals, a farmer perception survey was carried out, and an assessment of the biophysical impact of catch crops on soil organic matter, bulk density, steady-state infiltration rate (double-ring infiltrometer) and runoff generation, and soil erosion (rainfall simulation experiments) was carried out in 2016. For the biophysical approach, two paired plots, i.e., catch crops vs. glyphosate herbicide treatment (in advance, control plot), were selected under clementine citrus production. The results show that soil organic matter increased from 1.14 to 1.63%, and bulk density decreased from 1.47 to 1.27 g cm−3 after 10 years of treatments using catch crops. They also facilitated higher infiltration rates from 16.7 to 171 mm h−1 and a delay in runoff generation from 149 to 654 s for control and catch crop plots. Both runoff rates (from 50.6 to 3.1%) and soil erosion (from 3.9 to 0.04 Mg ha−1 h−1) were reduced once the catch crops were deployed in the field. After surveying (2018–2019), farmers stated the use of catch crops as a speck of dirt and a cause of possible loss of reputation when used. Moreover, farmers (N = 73) would accept the catch crops as an effective nature-based alternative only if a subsidy of 131.17€ ha−1 would be paid. The survey results also demonstrated that the farmers' community would see catch crop more as a benefit for the planet's health and society. Few constraints, such as ageing of the farmers’ population, lack of education and negative perception for other management factors, are the critical detrimental factors for adopting catch crops as a nature-based solution to reduce soil and water losses. There is a need for an effective agrarian extension service to change the fate of the current agriculture and achieve sustainability by adopting new management strategies in contemporary agricultural practices.