Severe weather conditions and urban intensification are key factors affecting the response of combined sewer systems, especially during storm events. In this regard, the capacity assessment of combined sewer networks under the impact of rainfall storm events of different return periods was the focus of this work. The selected case study area was a mixed-use catchment in the city centre of Thessaloniki, Greece. The hydraulic performance of the examined sewer network was assessed using an InfoWorks ICM model. The results indicated that mitigation strategies, such as the application of nature-based solutions (NBSs) or low-impact developments (LIDs) are considered essential for controlling combined sewer overflows. A multicriteria analysis was conducted to select the most appropriate NBSs/LIDs to be located in the study area to enhance the system’s capacity. The results of this multicriteria analysis were used to propose a combined sewer overflow mitigation scenario, based on the installation of green roofs, as the most highly ranked solution in the analysis performed. Incorporating the proposed NBS/LID in the hydrologic-hydraulic model significantly increased the performance of the studied combined sewer network.

This paper focuses on deriving new approximate analytical solutions in wedge‐shaped aquifers. The proposed methodology is applicable to any type of aquifer namely, leaky, confined and unconfined, under both steady state and transient flow conditions. By applying the method of images and separating the flow field into sections using physical arguments, approximate analytical expressions are obtained for the drawdown function, which in contrast to the conventional theory, are applicable to any arbitrary wedge angle. Moreover, the solutions fully observe the boundary conditions, while they preserve the continuity of the drawdown, which can be calculated directly at any point of the flow field. Nevertheless, comparison of the results of the new approximate analytical solutions to numerical ones, has been considered necessary to check their validity. MODFLOW, a well‐known numerical tool is used to calculate the numerical results. The discrepancies between the numerical results and those of the approximate analytical solution are negligible. The main advantages of the proposed methodology are the following: (a) The model needs only finite number of terms compared to conventional analytical and numerical solutions that involve infinite series, (b) The computational load is low, so it can be easily used in conjunction with meta‐heuristic algorithms to solve groundwater resources optimization problems, (c) Stream depletion rate can be calculated rather accurately and (d) The method is applicable to related flow problems.

The study examines the impacts of climate change on the operation and capacity of the combined sewer network in the historic center of Thessaloniki, Greece. Rainfall data from three high-resolution Regional Climate Models (RCMs), namely (a) the Cosmo climate model (CCLM), (b) the regional atmospheric climate model (RACMO) and (c) the regional model (REMO), from the MED-CORDEX initiative with future estimations based on Representative Concentration Pathway (RCP) 4.5, are first corrected for bias based on existing measurements in the study area. Intensity–duration–frequency (IDF) curves are then constructed for future data using a temporal downscaling approach based on the scaling of the Generalized Extreme Value (GEV) distribution to derive the relationships between daily and sub-daily precipitation. Projected rainfall events associated with various return periods are subsequently developed and utilized as input parameters for the hydrologic–hydraulic model. The simulation results for each return period are compared with those of the current climate, and the projections from various RCMs are ranked according to their impact on the combined sewer network and overflow volumes. In the short term (2020–2060), the CCLM and REMO project a decrease in CSO volumes compared to current conditions, while the RACMO predicts an increase, highlighting uncertainties in short-term climate projections. In the long term (2060–2100), all models indicate a rise in combined sewer overflow volumes, with CCLM showing the most significant increase, suggesting escalating pressure on urban drainage systems due to more intense rainfall events. Based on these findings, it is essential to adopt mitigation strategies, such as nature-based solutions, to reduce peak flows within the network and alleviate the risk of flooding.

In this paper, we have studied ways to minimize the cost of stepwise or intermittent pumping from a system of wells under transient groundwater flow conditions. We take into account infinite confined aquifers and semi-infinite aquifers where the method of images applies Moreover, we examine optimal separation of wells in groups, in the case of alternate pumping. We have proved analytically via the method of Lagrange multipliers that, at any time, the pumping cost is minimized when the hydraulic head level drawdowns at the locations of the pumping wells are equal to each other.

This paper focuses on deriving new approximate analytical solutions in wedge-shaped aquifers. The proposed methodology is applicable to any type of aquifer namely, leaky, confined and unconfined, under both steady state and transient flow conditions. By applying the method of images and seperating the flow field into sections using physical arguements, analytical expressions are obtained for the drawdown function. In contrast to the conventional theory, the proposed solutions are applicable to arbitrary wedge angle. Comparison of the results of the derived approximate analytical solutions to numerical ones, is considered necessary to ensure its validity. MODFLOW, a well-known numerical tool is used to calculate the numerical results. The results indicate that the boundary conditions are fully observed, the drawdown is feasible to be calculated at any point of the real flow field (continuity of the drawdown function) and discrepancies compared to numerical results are considered negligible. The main advantage of the proposed procedure is that it can be easily used in conjunction with meta-heuristic algorithms to solve groundwater resources optimization problems.