Flood hazard mapping requires knowledge of peak flow as well as flood wave volume and shape, usually represented as a design flood hydrograph (DFH). Statistical approaches for DFH development include nonparametric and parametric methods. The former are developed from long-term flow observations and are thus related to the physio-hydro-climatological catchment properties, but not applicable for ungauged catchments. The alternative parametric DFH can be estimated for any river cross-section, but its links with catchment characteristics are limited. The goal of this study was to introduce a novel hybrid approach for DFH estimation, where the parametric DFH is estimated from the selected properties of the nonparametric DFH (hydrograph width at the levels of 50% and 75% of the peak flow and skewness coefficient) that can be related to the catchment characteristics. The model that offers effective parameter estimation and best correspondence to the reference observation-based hydrograph was selected from among Gamma distribution, Strupczewski and Baptista candidates. The method was validated for 34 catchments of the upper Vistula River and Middle Odra water regions (Poland) based on data from the 1964–2010 period. The Baptista method was found to provide the best model for hybrid DFH construction according to the applied quality measures.

The Archer method for construction of nonparametric hydrographs was regarded as the basic one for constructing design hydrographs in gauged cross sections. The hydrographs designed using this method belong to a group of non-formalized hydrology. Unlike the commonly used formalized methods, where...

Machine learning models facilitate the search for non-linear relationships when modeling hydrological processes, but they are equally effective for automation at the data preparation stage. The tasks for which automation was analyzed consisted of estimating changes in the roughness coefficient of a mountain streambed and the extent of floods from images. The Segment Anything Model (SAM) developed in 2023 by Meta was used for this purpose. Images from many years from the Wielka Puszcza mountain stream located in the Polish Carpathians were used as the only input data. The model was not additionally trained for the described tasks. The SAM can be run in several modes, but the two most appropriate were used in this study. The first one is available in the form of a web application, while the second one is available in the form of a Jupyter notebook run in the Google Colab environment. Both methods do not require specialized knowledge and can be used by virtually any hydrologist. In the roughness estimation task, the average Intersection over Union (IoU) ranges from 0.55 for grass to 0.82 for shrubs/trees. Ultimately, it was possible to estimate the roughness coefficient of the mountain streambed between 0.027 and 0.059 based solely on image data. In the task of estimation of the flood extent, when selecting appropriate images, one can expect IoU at the level of at least 0.94, which seems to be an excellent result considering that the SAM is a general-purpose segmentation model. It can therefore be concluded that the SAM can be a useful tool for a hydrologist.

Currently, an active debate is underway among the academic community, urban planners, and policymakers regarding optimal models of urban development, given that the majority of the population now resides in cities. One concept under discussion is the 15 min city, which posits that all urban residents should be able to reach key, frequently used services within a 15 min walk or cycle. Although the literature suggests numerous potential benefits, debate persists about whether such cities would be optimal from the standpoint of sustainable development objectives and residents’ quality of life. The ongoing discussion also concerns the extent to which existing cities are capable of aligning with this concept. This is directly linked to the actual spatial distribution of individual services within the city. The literature indicates a research gap arising from a shortage of robust case studies that would enable a credible assessment of the practical implementation of this idea across diverse cities, countries, and regions. This issue pertains to Poland as well as to other countries. A desirable future scenario would involve comprehensive mapping of all cities, with respect to both the spatial distribution of specific services and related domains such as the quality and coherence of linear infrastructure. This article presents an analysis of the spatial accessibility of basic urban services in the context of implementing the 15 min city concept, using the city of Koszalin (Poland) as a case study. This city was selected due to its representative character as a medium-sized urban centre, both in terms of population and area, as well as its subregional functions within Poland’s settlement structure. Koszalin also exhibits a typical spatial and functional layout characteristic of many Polish cities. In light of growing challenges related to urbanisation, climate change, and the need to promote sustainable mobility, this study focuses on evaluating access to services such as education, healthcare, retail, public transport, and green spaces. The use of Geographic Information System (GIS) tools enabled the identification of spatial variations in service accessibility across the city. The results indicate that only 11% of Koszalin’s area fully meets the assumptions of the 15 min city concept, providing pedestrians with convenient access to all key services. At the same time, 92% of the city’s area offers access to at least one essential service within a 15 min walk. Excluding forested areas not intended for development increases these values to 14% and 100%, respectively. This highlights the extent to which methodological choices in assessing pedestrian accessibility can shape analytical outcomes and the interpretations drawn from them. Moreover, given this article’s objective and the adopted analytical procedure, the assumed pedestrian walking speed is the key parameter. Accordingly, a sensitivity analysis was conducted, comparing the reference scenario (4 km/h) with alternative variants (3 and 5 km/h). This approach demonstrates the extent to which a change in a single parameter affects estimates of urban-area coverage by access to individual services reachable on foot within 15 min. The analysis reveals limited integration of urban functions at the local scale, highlighting areas in need of planning intervention. This article proposes directions for action to improve pedestrian accessibility within the city.

Nonparametric hydrographs, constructed by the method suggested by Archer, are usually used for developing parametric design hydrographs. Flow changes in time are described by the UPO ERR Gamma complex function, which denotes a Gamma curve reformulated to have a Unit Peak at the Origin (abbreviated to UPO), supplemented by the Exponential Replacement Recession (ERR) curve. It may be observed, that this solution does not work in some areas of the upper Vistula and middle Odra catchments when the times of the rising limb of a hydrograph are higher than the times of the falling limb, i.e. when the skewness coefficient approximates 0.5 or higher values. Better results can be achieved with the function suggested by Strupczewski in 1964. It is a solution which uses two parameters of the flood hydrograph. The objective of the present paper is to assess the Strupczewski method by comparing it with a complex UPO ERR Gamma function for gauged cross-sections in the upper Vistula and middle Odra catchments. The assessment was carried out for 30 gauged cross-sections (15 in each river catchment). The parameters were optimized for width-hydrograph descriptors W75 and W50, designed by the Archer method, and for the skewness coefficient s. Optimization using only two width-hydrograph descriptors aims to test how the Strupczewski method works for cross-sections for which the values of width-hydrograph descriptors W75 and W50 are known. The assessment of both methods was carried out with reference to a nonparametric hydrograph constructed by the Archer method. The results of these assessments suggest that the Strupczewski method may be used not only for gauged cross-sections, but also for ungauged ones.

The gamma distribution functions with one shape parameter, employed to describe the parametric hydrograph, proved ineffective for the upper Vistula River and the middle Oder River water regions. It was therefore necessary to find a different function. The Pearson Type IV distribution functions proposed by Strupczewski with one and two shape parameters were analyzed for their applicability based on the data acquired from 60 water gauges, 30 of which were located on the Vistula River and the other 30 were on the Oder River. The shape parameter (parameters) and the time of rising limb were optimized based on the calculated hydrograph widths at 50% and 75% of peak flow (W50 and W75) as well as on the skewness coefficient s. The calculated parametric hydrographs were compared with the nonparametric input hydrographs with regard to the closeness of their volumes and the position of their centers of gravity. Both Pearson Type IV distribution functions proved to fit well. However, the function with two shape parameters did not yield the exact solution since the condition of the assumed objective function was met by a very large group of pairs of m and n shape parameters. It was therefore assumed that the recommended function is the Pearson Type IV distribution with one shape parameter. This function has an additional advantage of having an inflection point located between the W50 and W75, which allows to use the exponential function for the rising or recession limb that better describes either part of the hydrograph.